conseil scientifique et technique du service de physique...

Conseil Scientifique et Technique du

Service de Physique Nucléaire

December 16, 2002

CEA/Saclay, DSM/DAPNIA/SPhN,

Orme des Merisiers, Building 703

Contents

Contents 1

Agenda 3

List of members 5

Introduction 7

Status Report MINI-INCA 9

Status Report GELINA 19

Status Report nTOF - CERN 27

Status Report Spallation studies 33

Letter of Intent SPALLADIN 41

Proposal Photofission experiments at SAPHIR 55

Proposal Update MEGAPIE 63

Proposal TRADE 73

Status Report Modeling Transmutation Systems 81

Proposal High Temperature Reactors 93

Conseil Scientifique et Technique duService de Physique Nucléaire

December 16, 2002CEA/Saclay, DSM/DAPNIA/SPhN,Orme des Merisiers, Building 703

Agenda

Public Session (building 703, room 135)

Monday, December 16 9:00 – 9:20 Introduction Nicolas Alamanos (15 + 5') 9:20 – 9:40 Status report of the MINI-INCA project Alain Letourneau (15' + 5') 9:40 – 10:00 Status report GELINA Eric Berthoumieux (15' + 5')10:00 – 10:20 Status report nTOF - CERN Frank Gunsing (15' + 5')

10:20 – 10:40 Break

10:40 – 11:10 Status report Spallation studies Sylvie Leray (25' + !!5')11:10 – 11:30 Spalladin (Letter of Intent) Jean-Eric Ducret (15' + !!5')11:30 – 12:00 Photofission experiments at SAPHIR

(proposal) Henri Safa (15' + !!5')12:00 – 12:20 Megapie (proposal update) Frédéric Marie (15' + !!5')

12:20 – 14:00 Break

14:00 – 14:20 The TRADE project (proposal) Samuel Andriamonje (15' + 5')14:20 – 14:40 Status report on Modeling of

Transmutation Systems, Neutron andRNB Production Danas Ridikas (15' + 5')

14:40 – 15:00 Basic nuclear physics for high Henri Safa (15' + 5')temperature reactors (proposal)

Closed Session (building 703, room 125)

Monday, December 1615:00 – 18:00 Closed Session

Unknown

3


Members

Membres de droit:

Nicolas Alamanos Michel SpiroChef du SPhN Chef du DAPNIA

CEA/Saclay CEA/Saclay

DSM/DAPNIA/SPhN DSM/DAPNIA

F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette

France France

Membres élus:

Michel Garçon (chairman) Frank Gunsing (secretary) Wolfram KortenCEA/Saclay CEA/Saclay CEA/Saclay

DSM/DAPNIA/SPhN DSM/DAPNIA/SPhN DSM/DAPNIA/SPhN

F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette

France France France

Fabienne Kunne Danas RidikasCEA/Saclay CEA/Saclay

DSM/DAPNIA/SPhN DSM/DAPNIA/SPhN

F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette

France France

Membres nommés:

Wolfgang Bauer Alex Brown Piet van DuppenNSCL NSCL Inst. Kern- en Stralingsfysica

Michigan State University Michigan State University Department Natuurkunde en

East Lansing, MI 48824-1321 East Lansing, MI 48824-1321 Sterrenkunde

USA USA University of Leuven

Celestijnenlaan 200 D

B - 3001 Leuven

Belgium

Dietrich von Harrach Marek Lewitowicz Yuri OganessianInstitut für Kernphysik GANIL Flerov Lab. of Nuclear Reactions

Joh. Gutenberg Universität BP 55027 JINR

J. J. Becher Weg 45 F-14076 Caen Cédex 141980 Dubna, Moscow region

D-55099 Mainz France Russia

Germany

Invités permanents:

Françoise Auger Jean-Paul Blaizot Paul Bonche Adj. au Chef du SPhN Chef du SPhT CEA/Saclay

CEA/Saclay CEA/Saclay DSM/SPhT

DSM/DAPNIA/SPhN DSM / SPhT F-91191 Gif-sur-Yvette

F-91191 Gif-sur-Yvette F-91191 Gif-sur-Yvette France

France France

Daniel Guerreau Yves TerrienDirecteur Adjoint Assistant du Directeur

IN2P3 CEA/Saclay

3, Rue Michel-Ange DSM/DIR

F-75781 Paris Cédex 16 F-91191 Gif-sur-Yvette

France France

Pascal Debu Pierre-Olivier Lagage François DamoyChef du SACM Chef du SAP Chef du SDA

CEA/Saclay CEA/Saclay CEA/Saclay

DSM/DAPNIA/SACM DSM/DAPNIA/SACM DSM/DAPNIA/SDA



Philippe Rebourgeard Pierre-Yves Chaffard Bruno MansouliéChef du SEDI Chef du SIS Chef du SPP

CEA/Saclay CEA/Saclay CEA/Saclay

DSM/DAPNIA/SEDI DSM/DAPNIA/SIS DSM/DAPNIA/SPP




December 16, 2002

CEA/Saclay, DSM/DAPNIA/SPhN,

Orme des Merisiers, Building 703

Introduction

The present Conseil Scientifique et Technique du Service (CSTS) is intended to examine the

activities of SPhN related to the transmutation of nuclear waste. This theme is one of the four

main topics of research of SPhN together with the study of the structure of the nucleon,

nuclear phase transitions, and nuclear structure.

The transmutation activities have for long been concentrated on the exploration of the relevant

nucleon-nucleus reactions, for a large part experimentally but also with an important

contribution of model development and simulations. The experiments are focussed on the

efficient neutron production by means of proton induced spallation reactions and on neutron-

nucleus interactions. A dozen of energy decades going from the meV region up to the GeV

region are covered by these activities, each of them being addressed by its own particular

physics context and experimental difficulties, and experiments being performed at the

appropriate facilities.

Among these activities are the study of spallation reactions, with experiments at the now

decommissioned facility SATURNE, and more newly at GSI, (see also the letter of intent on

SPALLADIN). These experiments, corresponding to high incident proton energies of the

order of 1 GeV, are accompanied by a substantial effort on reaction modelling. In these

energy regions reaction cross sections can be measured only partially and serve to develop

and fine-tune reliable models.

Also the neutron-nucleus reaction measurements are part of these activities. Integral

measurements in the thermal meV region are being performed at ILL within the Mini-Inca

project. Although integral measurements loose the energy dependence of the reaction cross

section (which at thermal energies can often be reconstructed when the energy distribution of

the flux is known), they can be performed with a very high neutron flux and therefore a very

low amount of material, giving access to isotopes difficult to obtain or handle, and for this

reason impossible to measure at a neutron time-of-flight installation.

Energy dependent neutron-induced cross sections are being studied by SPhN at the neutron

time-of-flight facility GELINA and more recently at CERN-nTOF. Since the reaction cross

sections for incident neutrons from thermal up to the keV region are dependent on the

properties of individual nuclear states of the compound nucleus at excitation energies of

several MeV, nuclear models cannot predict the cross sections and only measurements can

supply this information.

In addition to these activities, which could be qualified as core activities of the nuclear

physics division SPhN, the participating physicists have been involved or invited to be

involved in related activities, appealing to the complementary skills and competences unified

in SPhN.

A project has started to modelize photonuclear reactions. As an example a subcritical nuclear

reactor, coupled to an external neutron source driven by an electron beam, was modelled in

detail. This so-called beta compensated reactor is proposed as a more economic alternative for

a proton-based accelerator system.

The project MEGAPIE concerns a high power lead-bismuth spallation source. Neutron flux

measurements of this installation, initially not foreseen by the project committee, could be

performed with DAPNIA-developed micro fission chambers in order to confirm flux

simulations. In addition these chambers can be used to measure integral cross sections from

incineration rates for a number of actinides in the MEGAPIE flux.

The project TRADE consists of a subcritical reactor coupled to a proton beam. SPhN and

SEDI could participate in the development and instrumentation of neutron flux measurements

for different reactor configurations, using gamma-ray spectroscopy, micro-fission chambers

and possibly a MicroMegas-based device.

Also the development of a helium-cooled high temperature reactor, a possible candidate for

future nuclear power plant, could benefit from a contribution of SPhN, notably on simulation-

based calculations and on the study of the high temperature behaviour and high burn-up of the

fuel particles.

Finally, a promising technique with photofission experiments at the SAPHIR facility, initiated

by SPhN, would allow improve the sensitivity of the actinide detection level in nuclear waste

barrels.

It seems necessary to reflect on the way how the existing and newly proposed activities on

one side, and the currently available personnel and budget on the other side, can reach a

satisfactory balance. The CSTS has been asked for recommendations in this respect. The

overview of transmutation related activities at SPhN will be the sole subject of this CSTS

session and should contribute a helpful step towards defining a long-term strategy in this

domain.

Frank Gunsing,

Secretary of the CSTS.

Conseil Scientifique et Technique du SPhN

RESEARCH PROPOSAL

Title: The Mini-INCA project : The search of the optimal conditions for Minor

Actinide transmutation in high intensity neutron fluxes

Experiment carried out at: ILL Grenoble

Spokes person(s): F. Marie

Contact person at SPhN: F. Marie

Experimental team at SPhN: M. Fadil, A. Letourneau, D. Ridikas

List of DAPNIA divisions and number of people involved:

SIS(2)

List of the laboratories and/or universities in the collaboration and number of people involved:

ILL Grenoble - CEA/DAM/SPN Bruyeres-le-Chatel - Los Alamos National Laboratory (USA)

Lawrence Berkeley Laboratory (USA) - GEEL/IRMM (Belgium)

SCHEDULE

Possible starting date of the project and preparation time [months]: 2003 – 36 months

Total beam time requested:

Expected data analysis duration [months]:

REQUESTED BUDGET

Total investment costs for the collaboration:

Share of the total investment costs for SPhN:

Investment/year for SPhN: 80 kEuro

Total travel budget for SPhN:

Travel budget/year for SPhN: 35 kEuro

If already evaluated by another Scientific Committee:

If approved Allocated beam time: Possible starting date:

If Conditionally Approved, Differed or Rejected please provide detailed information:

PROPOSITION AU CONSEIL SCIENTIFIQUE ET TECHNIQUE

Service de Physique Nucléaire, CEA/Saclay,16 et 17 décembre 2002

The Mini-INCA Project: The search of the optimal

conditions for Minor Actinide transmutation in high

intensity neutron fluxes

F. Marie, M. Fadil, A. Letourneau, D. Ridikas, C. Veyssiere

CEA/Saclay, DSM/DAPNIA, 91191 Gif-sur-Yvette, France

Introduction

The Mini-INCA project at the CEA/DSM is a project whose objectives are defined in the

framework of the French law of December 30th

1990 about nuclear waste management.

This project has been initiated in 1997 at the SPhN, to determine the optimal conditions

for the transmutation of minor actinides in high intensity neutron fluxes. To achieve this

goal, integral measurements of neutron capture and fission cross sections, branching ratio

and incineration potential are performed at the High Flux Reactor of the Institute Laue-

Langevin at Grenoble [6,7,8], together with simulations of the neutronic performances of

new generation critical and sub critical systems, dedicated to the transmutation of nuclear

waste [1,2,3,4] or high intensity neutron sources [18].

The experimental studies have been focalized to the isotopes of interest [5], whether they

are found to contribute for a major part in the mass inventory of the core of future

transmutation systems at the equilibrium, or their evaluated nuclear parameters, tabulated

in the different nuclear data libraries [9,10,11] are not precisely known or insufficiently

consistent. All these measurements answer to the high priority needs for nuclear data

requested by French industry applications [12].

The very high intensity neutron flux (up to 2.1015

n/s/cm2) available at the HFR at ILL

offers a unique possibility to study short lived and low cross section isotopes, such as 242gs

Am, 244

Am , 238

Np or 242

Pu, that couldn’t be studied properly elsewhere, and to

investigate the behavior of minor actinides under realistic irradiation conditions,

anticipating the very high neutron fluxes needed for nuclear waste transmutation.

Finally, one of the advantages of the high flux intensity available with the Mini-INCA

setup is to allow to irradiate small sample masses (typically <100 mg), which do not

perturb locally the neutron flux, leading to fast and reliable analysis.

Experimental Method

In order to measure these parameters, the Mini-INCA project has developed innovative

experimental solutions at the HFR of ILL (see Fig 1), which are giving access to nuclear

data from pure thermal to variable epithermal neutron spectra :

¶ The first solution consists in activation experiments where the samples are

irradiated in the H9 channel. The neutron flux available in the H9 channel is a



98% thermal flux with an intensity of 6.1014

n/s/cm2. After irradiation (up to 50

days), the samples are automatically transported to a measurement chamber (see

Fig 2), where alpha and gamma spectroscopy are performed. The main advantage

of this facility is to allow an analysis in a very short time after the irradiation,

giving access to short lived isotopes. The samples can also be re-irradiated,

providing both capture and absorption cross sections.

¶ The second solution has been to instrument the vertical channel V4, giving access

from thermal to epithermal neutron fluxes with an intensity up to 1.8 1015

n/s/cm2

.

In this channel we have developed [13,14,15] new kind of fission micro chambers

that allow to determine minor actinide incineration potential and fission rates in

very high neutron fluxes. The V4 channel is also available for various kind of

activation experiments, where irradiated samples can be analyzed by mass

spectrometry or gamma spectroscopy in the Mini-INCA chamber. The V4

channel is also an ideal device for production of short-lived isotopes (147

Pm, 155

Eu

and 171

Tm) or low production rate isomers (177m

Lu).

Lohengrin : mass

spectrometer

fission chambers

thermalised fl x u

beam tube H9

Spectroscopy : alpha

and gamma

variable flux

inclined tube V4

Figure 1: Schematic view of the ILL reactor core and Mini-INCA experimental setup.



Figure 2: Picture of the Mini-INCA vacuum chamber coupled to the H9 target

exchanger.

Experimental results so far

Several experiments have been already performed in the H9 channel and results reported

to previous CSTS cessions in 2000 and 2001:

¶ The measurement of

242gsAm capture cross section and

241Am capture branching

ratio[6] leading to the conclusion of a possible transmutation of 241

Am in high

thermal neutron fluxes.

¶ The measurements of 243

Am and 242

Pu capture cross sections realized in the frame

of a PhD thesis [8], where cross sections have been found to be respectively 11%

and 40% higher than the evaluated data.

In 2002 we have also performed irradiation on 237

Np, to extract 237

Np capture and 238

Np

absorption and capture cross sections. The data are currently under analysis.

In the frame of studying the optimal conditions of transmutation systems and particularly

those which are based on Pb-Bi spallation targets, we have investigated the problematic

of 210

Po formation by measuring the capture branching ratio of 209

Bi to the 210gs

Bi and 210m

Bi states. The results of the experiment performed at ILL based on a prompt capture

gamma spectroscopy method, show that the probability of formation of the 210

Po is 30%

lower than what was evaluated before [16,17].

One of the noticeable results from Mini-INCA project concerns the new type of fission

micro chambers we have developed, in collaboration with CEA/DEN/DED/SCCD/SMN,

and irradiated in December 2001 during 20 days in the V4 channel. Using 235

U deposit

chambers, we have measured a neutron flux of 1.75 1015

n/s/cm2

with a relative

uncertainty of 4%. It was the first time fission chambers were providing an absolute



measurement of the neutron flux, two orders of magnitude above their conventional

operating conditions. The expertise we have gain on this topics of research has led us to

propose to operate fission micro chambers for the measurement of the neutron flux in the

liquid Pb-Bi MEGAPIE spallation target at PSI [19,20].

In 2002, a new concept of double body fission chambers has been developed to determine

transmutation and incineration potential of minor actinides. Two isotopes are being

irradiated (241

Am and 237

Np) at ILL and the results will be part of a PhD thesis to be

finished in the beginning of 2003.

Finally, we have took benefit of the very intense flux available in the V4 channel to

collaborate, with CEA/DAM/SPN in the production of isomeric 177m

Lu target in the

framework of the search of the super-elastic scattering, and with Los Alamos National

Laboratory for the production of short lived isotopes (147

Pm, 155

Eu and 171

Tm) of interest

for stellar nucleo-synthesis thematic.

Proposed experiments

In the following years, we propose to wider the field of investigation to all the isotopes of

interest. After the measurement of 241,242,243

Am and 242

Pu capture cross sections, we will

measure capture and fission cross sections together with transmutation and incineration

potentials, and focalize first to the isotopes of Cm (A=242 to 246), 249

Bk and Cf (A=250

to 252), 241,243

Pu and 238,239

Np, which are created along the 241

Am transmutation chain,

and whose role are dominant in the composition of the core of transmutation systems at

the equilibrium. Most of these isotopes have poor experimental data and there nuclear

parameters need to be precisely studied in order to provide predictable calculations of the

neutron performances of innovative systems. As an example, in table 1 are presented the

isotopes for whom the cross section discrepancies observed between different evaluated

data bases are the most significant.

Isotopes Dscth

(%) Dsfth

(%) Dscres

(%) Dsfres

(%) 249

Bk 55 - 70 100 250

Cf 10 - 25 100 243

Cm 15 43 30 12 238

Np 120 2 100 3 251

Cf <1 7 2 43 Table 1: Biggest relative differences between evaluated capture and fission cross

section at thermal and resonance neutron energies, compared to JEF2.2 values

The measurements will be performed with the techniques described above and the

impacts of these new measurements on the transmutation efficiency of different scenario

(critical or sub-critical reactors) with various types of fuels (molten salt, TRISO) will be

calculated.

Together with minor actinides, we will measure other isotopes of interest for new fuel

cycles, such as 233

Pa capture cross section which is important for the 232

Th/233

U cycle,



and also elements related to the problematic of transmutation. In this spirit, we propose to

wider the study of 209

Bi capture branching ratio performed this year at thermal neutron

energy, to the resonance region and fast energy neutron spectra. This experiment will be

performed in collaboration with IRMM Geel and will definitely answer on the

problematic of 210

Po formation in future spallation targets.

The extraordinary neutronic performances available with the Mini-INCA experimental

set-up at ILL lead us to continue our fruitful collaboration with CEA/DAM and Los

Alamos Laboratory for the production of short lived isotopes. We also consider strongly

this unique opportunity to test and to measure, in a short time, the resistance of structural

materials and the behaviour of new types of fuel elements (for ex : PuOx TRISO coated

particles of HTR), under epithermal neutron fluxes. Therefore, in this spirit, we will

collaborate with Framatom and Nuclear Institute of Lituania for the irradiation of

graphite from nuclear power plants.

Budget and manpower

To balance the departure of two students, one CEA staff and one PostDoc by the end of

2002, the realisation of the Mini-INCA program in the 3 next years requires, at least, the

arrival of one permanent position and 1 PhD student in 2003. The total amount of

men.year working on this project will be (1+0.5+0.5+1PhD)

The budget for 2003 is 80 kEuro (nat 30/90) for irradiation shuttles, targets, fission

chambers and mass spectrometry analysis.

The budget for mission is 35 kEuro.

Conclusions

The Mini-INCA set-up at ILL is now fully operational. In the past few years, outstanding

results, such as 241

Am, 242gs

Am and 242

Pu capture cross sections, have been already

obtained, and new types of detectors have been developed (fission micro chambers), that

allow to determine the transmutation and incineration potentials of minor actinides in

high neutron fluxes. The technical solutions developed for the Mini-INCA project at ILL

allow to obtain fast and reliable results and there remarkable performances have led us to

export them to other nuclear installations with different neutron spectra (ex: Fission

chambers for MEGAPIE). Moreover, the unique flux conditions available with the Mini-

INCA experimental set-up represent a great opportunity for the scientific community to

improve the knowledge of nuclear parameters for isotopes which most often couldn’t be

studied properly elsewhere. The experimental program we propose to carry on will take

benefit of these powerful tools to study optimal conditions for the transmutation of the

nuclear waste, together with radiation damages in structural materials, under realistic

high intensity neutron fluxes.



References

[1] D. Ridikas, G. Fioni, P. Goberis, O. Deruelle, M. Fadil, F. Marie, Modelling of

Critical and Sub-critical GT-MHRs for Waste Disposal and Proliferation-Resistant Fuel Cycles. Proceedings of the 6th OECD/NEA Information Exchange Meeting on

Actinide and Fission Product Partitioning and Transmutation, 11-13 December

2000, Madrid, Spain.

[2] D. Ridikas, L. Bletzacker, O. Deruelle, M. Fadil, G. Fioni, A. Letourneau, F. Marie,

R. Plukiene, Comparative Analysis of the ENDF, JEF and JENDL Data Libraries by

Modelling High Temperature Reactors (GT-MHR) and Plutonium Based Fuel Cycles. Proc. the Int. Conference on Nuclear Data for Science and Technology,

ND2001, Oct. 7-12, 2001, Tsukuba, Ibaraki, Japan, in press.

[3] R. Plukienne, D. Ridikas, Modelling of HTRs with Monte Carlo : from homogeneous

to an exact heterogeneous core with microparticules, DAPNIA/SPhN-02-242,

CEA/Saclay (2002), submitted to Annals of Nuclear Energy.

[4] P. Goberis, Modelling of innovative critical reactor with thermalized neutron fluxes

in the frame of the Mini-INCA project , DAPNIA/SPhN-00-68, CEA/Saclay (2000)

[5] F. Marie, O. Deruelle, M. Fadil, G. Fioni, Ph. Leconte, J. Martino, D. Ridikas,

H. Faust, Mesures Intégrales des sections efficaces de capture et fission d’actinides

DAPNIA/SPhN-00-50, CEA/Saclay (2000).

[6] G. Fioni, M. Cribier, F. Marie, M. Aubert, S. Ayrault, T. Bolognese, J.-M. Cavedon,

F. Chartier, O. Deruelle, F. Doneddu, H. Faust, A. Gaudry, F. Gunsing, Ph. Leconte,

F. Lelievre, J. Martino, R. Oliver, A. Pluquet, M.Spiro, S. Veyssière

Incineration of 241

Am induced by thermal neutrons

Nuclear Physics A 693 (2001) 546-564.

[7] F. Marie, M. Cribier, O. Deruelle, H. Faust, G. Fioni, Ph. Leconte, J. Martino, S.

Röttger, C. Veyssière, g- spectroscopy experiments relevant for nuclear waste

transmutation. American Institute of Physics Conference Series 529, (2000) 416-423

[8] O. Déruelle, F. Marie, I. Almahamid, M. Fadil, H. Faust, G. Fioni, A. Letourneau,

P. Mutti, R. Plukienne, D. Ridikas, Measurement of neutron capture cross sections

relevant for nuclear waste transmutation by alpha and gamma spectroscopy Proceedings of the 11th Int. Internaltional Symposium on Capture Gamma-Ray

Spectroscopy and Related Topics, 2-6 september 2002, Prague, Czech Republic, in

press.

[9] ENDF/B-VI "The US evaluated nuclear data file for neutron reactions",

IAEA-NDS-100 Rev. 6 (1995).

[10] JEF-2.2 "The evaluated neutron nuclear data of the NEA data bank",

IAEA-NDS-120 Rev. 3 (1996).

[11] JENDL-3.2 "The Japanese Evaluated Nuclear Data Library",

IAEA-NDS-110 Rev. 5 (1994).

[12] Besoins prioritaires en donnes nucleaires pour les applications industrielles Francaise, CEA/DEN/CAD/DER SPRC, DO 75, 2002.

[13] M. Fadil, Ch. Blandin, S. Christophe, O, Deruelle, G. Fioni, F. Marie, C. Mounier,

D. Ridikas, J.P. Trapp, Development of fission micro-chambers for nuclear waste

incineration studies. Nuclear Instruments and Methods A 476 (2002) 313-317.



[14] M. Fadil, O. Deruelle, G. Fioni, F. Marie, D. Ridikas, Ch. Blandin, J. P. Trapp

Chambres à fission à géométrie cylindrique : formulations mathématiques et modélisation. DAPNIA/SPhN-00-56, CEA/Saclay (2000).

[15] M. Fadil, O. Deruelle, G. Fioni, F. Marie, D. Ridikas, Ch. Blandin, J. P. Trapp

Chambres à fission à géométrie cylindrique : étude de conception

DAPNIA/SPhN-00-65, CEA/Saclay (2000).

[16] A. Letourneau , E. Berthoumieux, O. Déruelle, M. Fadil, H. Faust, G. Fioni,

F. Gunsing , F. Marie, L. Perrot, D. Ridikas, H. Boerner, H. Faust, P. Mutti,

G. Simpson, P. Schillebeecks, Thermal Neutron Capture Branching Ratio using a

Gamma-Ray Technique. Proceedings of the 11th Int. Internaltional Symposium on

Capture Gamma-Ray Spectroscopy and Related Topics, 2-6 september 2002, Prague,

Czech Republic, in press.

[17] D. Pankratov, S. Ignatiev, D. Ridikas, A. Letourneau, Estimation of 210

Po losses from solid

209Bi target irradiated in a thermal neutron flux. Accepted for publication

in Annals of Nuclear Energy (2002).

[18] D. Ridikas, H. Safa, M.L. Giarci, Conceptual study of neutron irradiator driven

by electron accelerator. DAPNIA/SPhN-02-244, CEA/Saclay (2002),

Proceedings of 7th Information Exchange Meeting on Actinide and Fission Product

P&T (NEA/OECD), Jeju, Korea, 14-16 October, 2002.

[19] M. Fadil, D. Ridikas, O. Deruelle, G. Fioni, M.L. Giacri, A. Letourneau, F. Marie,

C. Blandin, S. Breaud « Feasibility study of new microscopic fission chambers

dedicated for ADS ». DAPNIA-02-243 (2002), Proceedings of 7th Information

Exchange Meeting on Actinide and Fission Product P&T (NEA/OECD), Jeju,

Korea, 14-16 October, 2002.

[20] F. Marie, M. Fadil, G. Fioni, S. Leray, A. Letourneau, D. Ridikas, H. Safa,

C. Blandin, F. Groeschel, E. Lehmann, “Measurement of the neutron flux at

MEGAPIE”. Proposition au Conseil Scientifique et Technique du DAPNIA/SPhN,

3-4 juin 2002.


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Title: Status Report of the project nTOF at CERNDate of the first CSTS presentation: June 1999

Experiment carried out at: CERN

Spokes person(s): Noulis Pavlopoulos

Contact person at SPhN: Frank Gunsing

Experimental team at SPhN: Gaëlle Aerts (CFR), Samuel Andriamonje (détaché CNRS),

Eric Berthoumieux (CEA staff), Frank Gunsing (CEA staff),

Julien Pancin (BDI), Luc Perrot (postdoc)

List of DAPNIA divisions and number of people involved: SPhN, SEDI


nTOF Collaboration (about 150 physicists from 40 institutes)

SCHEDULE

Starting date of the experiment [including preparation]: April 2000

Total beam time allocated:

Total beam time used:

Data analysis duration:

Final results foreseen for: 2005

BUDGET Total Already Used


Share of the total investment costs for SPhN: 100 k€ for 2003Total travel budget for SPhN:

Please include in the report references to any published document on the present experiment.

Status Report of the project nTOF at CERN

SPhN nTOF group

IntroductionThe interest in high resolution neutron capture cross section data has gained much in-terest in recent years due to the development of new activities related to nuclear energy,like the transmutation of nuclear waste, the thorium-based nuclear fuel cycle and accel-erator driven systems (ADS). These new applications have triggered a renewed interestin neutron-nucleus reactions in particular for isotopes and energy regions of isotopesessential for the development and efficiently optimized design of the above mentionedconcepts. Indeed many of the relevant isotopes have received less attention in the pastand at present the existing measured data are still insufficient, incomplete or sometimeseven lacking.

A new neutron time-of-flight facility has recently been constructed and has becomeavailable at CERN. The high instantaneous neutron flux, high resolution and low back-ground make this facility well suited for high quality neutron cross section measure-ments. The scientific programme of the nTOF collaboration include the measurementsof neutron capture, fission and (n,xn) reaction cross sections for nuclear technology, nu-clear astrophysics and fundamental nuclear physics. SPhN has been strongly involvedin the project based on an initial idea by Rubbia et al. [1] already since the early devel-opment phase. The project is supported by the European Commission’s 5th FrameworkProgramme under contract number FIKW-CT-2000-00107.

The nTOF project has been approved by the CERN Research Board in April 1999as experiment PS213. After several delays due to different causes of organizational andtechnical order, the facility at CERN has become fully operational in May 2002 whenthe scientific programme has started.

The CERN-nTOF facilityA detailed description of the facility can be found in the technical design report [2].Neutrons are created by spallation reactions induced by a pulsed, 6 ns wide, 20 GeV/cproton beam with up to 7 � 10

12 protons per pulse, impinging on a 80x80x60 cm3

lead target. A 5 cm water slab surrounding the lead target serves as a coolant and atthe same time as a moderator of the initially fast neutron spectrum, providing a wideenergy spectrum from 1 eV to about 250 MeV. A vacuum neutron guide leads to theexperimental area with the capture sample position at about 185 m from the lead target.Two collimators are present in the neutron beam, one with a diameter of 13.5 cm placedat 135 m from the lead target and one at 180 m with a diameter of 2 cm for the capture

(MeV)nE10

-610

-510

-410

-310

-210

-11

cou

nts

/bin

per

7e1

2 p

pp

(50

bp

d)

10-3

10-2

10-1

1

May 2001November 2001May 2002

Figure 1: Comparison of the background during different phases of the commis-sioning.

measurements. This collimation results in a Gaussian-shape beam profile at the sampleposition which has been measured [3, 4]. At a distance of 120 m a 1.5 T sweepingmagnet is placed in order to remove charged particles from the beam. A previouslyobserved background due to negative muon capture has been drastically reduced bymeans of a 3 m thick iron shielding located after the sweeping magnet [5, 6].

The background level has been measured with C6D6-based gamma-ray detectorsand 20 mm diameter and 6.35 mm thick carbon disk in the neutron beam. Since thecapture cross section of C is very low, the observed count rate is due to background fromsample scattered neutrons and photons and ambient background. The improvement ofthe background is shown in figure 1 where the level is shown as a function of equivalentneutron energy for three periods: after the first commissioning in May 2001, after thebackground measurement campaign with additional shielding in November 2001, andwith the final shielding at the start of the scientific programme in May 2002.

An in-beam neutron flux monitor, located a few meters upstream of the sample posi-tion, consists of a 6Li deposit on a mylar foil and 4 off-beam silicon detectors measuringthe particles from the 6Li(n,�)T reaction. Two C6D6-based gamma-ray detectors havebeen used for the capture measurements, viewing the capture samples from the sides.The samples are positioned in a vacuum carbon fiber remotely controlled sample ex-changer.

The data acquisition system uses flash ADCs with a sampling rate of up to 1 GHz forrecording the detector signals during nearly 20 ms for off-line analysis. This generates ahigh data rate but ensures zero deadtime and a replay of the events in the entire neutronenergy range.

In order to appreciate the flux characteristics of the neutron source we comparethe neutron flux of the CERN-nTOF facility at the position of the experimental area at

103

104

10-1 101 103 105 107 109

nTOF - CERN @ 185 m (4/16.8 Hz)

GELINA @ 30 m (800 Hz)

dn

/dln

E (

n /

cm2 /

s)

En (eV)

10-4

10-2

100

102

104

10-1 101 103 105 107 109

nTOF - CERN @ 185 m (7x1012 p)GELINA @ 30 m

dn

/dT

(n

/ cm

2 / µ

s / p

uls

e)

En (eV)

Figure 2: The neutron flux of GELINA at 30 m compared with preliminary fluxdata from CERN-nTOF at 185 m. The left panel shows the time-averaged flux for the given repetition rates. The right panel shows theinstantaneous flux for a single pulse.

185 m to that of the 30 m measurement station of the GELINA neutron time-of-flightfacility in Geel. From the left panel of figure 2 it can be seen that the time-averagedneutron flux for the usual repetition rates is comparable for both installations. Howeverthe right panel shows that the instantaneous neutron flux for a single pulse is three ordersof magnitude higher. This very high instantaneous neutron flux makes the nTOF facilityparticularly suitable for measurements with a low signal to background ratio, like forradioactive or low-mass samples.

Experiments performed in 2002For the year 2002 neutron capture measurements with C6D6 detectors have been per-formed for the isotopes 56Fe, 197Au, 151Sm, 204;206;207;208Pb, 209Bi and 232Th. They havebeen completed by fission measurements on 234U and 232Th relative to 235U and 238U.

Although SPhN has been actively participating in preparing, performing and ana-lyzing all experiments and the capture experiments in particular, the measurement of232Th(n, ), since it is under the responsibility of SPhN, receives our special attention.A preliminary spectrum of this measurement in the energy range from 1 eV to 100 keVis shown in figure 3. A first estimation of the ambient background, constant per unittime-of-flight and mainly due to the radioactivity of the sample, and the backgrounddue to scattered photons are also shown in the figure.

It should be noted that one PhD student of SPhN working on nTOF has continuouslybeen present at CERN during one year. In addition, a postdoc of SPhN has been invitedby the nTOF collaboration for one month at CERN for the development of analysisprocedures.

100

101

102

103

100 101 102 103 104 105

232Th(n,γ)scattered photon backgroundradioactivity background

dn

/d(l

nE

)co

un

ts p

er b

un

ch

neutron energy (eV)

100

101

102

103

0 50 100 150 200

dn

/d(l

nE

)co

un

ts p

er b

un

ch

neutron energy (eV)

Figure 3: The first raw data from the measurement of the 232Th(n, ) cross section,together with a first rough estimate of the background due to radioactiv-ity and due to scattered photons. The reaction rates correspond to countsper eV multiplied by the neutron energy, for a single bunch of 7 � 10

12

protons.

OutlookFor the year 2003 the experimental programme will be more focussed on fission mea-surements. A capture measurement of 236U under the responsibility of SPhN is alsoforeseen. A to be developed 4� BaF2 capture detector, allowing the measurement oflow-mass and fissile samples, is planned to be operational for the year 2004, as foreseenin the programme of the FP5 contract.

References[1] C. Rubbia et al., CERN/LHC/98-02, CERN (1998)

[2] S. Andriamonje et al. , CERN/INTC/2000-004, CERN (2000)

[3] J. Pancin et al. , submitted for publication

[4] The n TOF Collaboration, CERN/INTC 2001-021, CERN (2001)

[5] A. Ferrari, C. Rubbia and V. Vlachoudis, CERN/SL-EET/2001-036, CERN (2001)

[6] The n TOF Collaboration, CERN/INTC 2001-038, CERN (2001)



Title: Spallation studies

Date of the first CSTS presentation:

Experiment carried out at: GSI

Spokes person(s):

Contact person at SPhN: S. Leray

Experimental team at SPhN: A.Boudard, J.C. David, J.E. Ducret, C. Volant, L.Donadille, B. Fernandez,

C. Villagrasa



GSI, IN2P3, Santiago Univ., Munich Univ. for the experiments, Liege

Univ., GSI for modelisation.

SCHEDULE

Starting date of the experiment [including preparation]:




Final results foreseen for:

BUDGET Total Already Used





SPALLATION STUDIES

Status report

November 2002

1. General motivations

Spallation reactions play an important role in accelerator-driven systems (ADS), in particular in thespallation module. They govern the number of neutrons produced in the spallation target, theemission of energetic neutrons (important for shielding problems) as well as gas production anddamages in the window and target. The radioactivity of the target is essentially due to the spallationresidues, the volatile ones being of particular concern. Also the production of some undesirableelements may lead to structural changes in alloys used for the window or to corrosion problems inliquid metal targets.

It is therefore of particular importance to be able to predict all these quantities with a sufficientaccuracy, or at least to assess the accuracy that can be reached. This can be done only if one has aprecise knowledge of the elementary spallation mechanism and nuclear models are developed whichcan calculate cross-sections and characteristics of all the reaction products. These models should thenbe directly implemented into the high-energy transport codes that are used to design spallationsources or ADS, since above 150-200 MeV (contrary to what is done below) the use of evaluated datalibraries is not possible because of the too large number of open channels. Actually, high-energyreactions are modeled as a two step mechanism: a fast stage governed by nucleon-nucleon collisions,the Intra-Nuclear Cascade (INC) leading to an excited residue, followed by a de-excitation stage ofparticle evaporation or, for heavy nuclei, fission.

The goals of our group are precisely:ÿ to achieve a complete understanding of spallation reactions through experiments covering a

wide range of channels,ÿ to develop high-energy nuclear models, which will be confronted to the experimental data,

and, once validated on a wide set of data, will be implemented into high-energy transportcodes

ÿ to assess the impact of the new tools on quantities relevant for ADS design and theuncertainties on the simulated quantities.

All this work is also being done in the framework of the European FP5 project HINDAS (High andIntermediate energy Nuclear Data for Accelerator-driven Systems).

2. Experimental data measurements

After the measurements at SATURNE [1] of neutron energy spectra on both thin and thick targets,we are now interested in residue measurements.

We participate (in collaboration with GSI, CNRS, Santiago University) to the inverse kinematicsexperiments at the fragment separator (FRS) of GSI Darmstadt, which aims at isotopically identifyingall the residues produced in spallation reaction and measuring their production rate and velocity. Upto now several systems have been investigated, our group being in particular involved in the analysisof the Pb+p at 1 GeV [2], of the fission residue production in Pb+p at 500 MeV/a (thesis ofB.Fernandez in progress) and of Fe+p at 300, 500, 750, 1000 and 1500 MeV/A (thesis of C.Villagrasain progress). A new experiment concerning an intermediate mass system (Xe+p) at different energiesis presently being carried out. An example of the data obtained at 500 MeV/A is shown on figure 1where the mean value of the N/Z ratio for each isobar is plotted and compared to results obtained forsimilar systems at different energies. This shows that the fission fragments are more neutron-rich as

the excitation energy in the systems after the cascade stage gets lower due to a lesser neutronevaporation prior to fission.

Figure 1. Mean value of the N/Z ratio for isotopes of a given mass for different systems measured at GSI , Pb+pat 500 1000 MeV/A (B.Fernandez preliminary results) and 1000 MeV/A [2], pb+d at 1000 MeV/A [3] and Pb+p at

600 MeV/A measured at ISOLDE [4] (solid curve between dashed-dotted curves showing the uncertainty region).The dashed curve represents the valley of stability.

The main conclusion obtained from the comparisons of the data measured at SATURNE and at GSIwith models (and confirmed by other experiments done, for instance, by the NESSI collaboration [5])was that the models most widely used in the high-energy transport codes for applications, i.e. thecombination of the Bertini INC [6] with the Dresner evaporation-fission [7] models show seriousdeficiencies. In particular Bertini leads to an overestimation of the excitation energy at the end of thecascade stage and Dresner is unable to correctly predict isotopic and fission distributions. On the otherhand, better predictions have been obtained if the Liege INC (INCL) [8] and the GSI ABLAevaporation-fission [9] models are used.

The second experimental program in which the group is involved is the SPALADIN experiment inpreparation at GSI. It aims at measuring, using the inverse kinematics, simultaneously the heavyresidues, identified in mass and charge, and the evaporated particles, neutrons and charged ones. Themotivation for this experiment is to reach a deeper understanding of the reaction mechanism byreconstructing as far as possible the system before the de-excitation stage. This should allow thedisentangling of the INC and de-excitation stages, which, as shown in the following, is often difficultwith inclusive data, and should lead to stronger constraints on the models. The experiment will bedone for Fe+p system at 1 GeV/A, for which (see below) the recently developed models do not workso well without our clear understanding of the reasons why. Because of the limitations of the ALADINdipole and of the charged particle tracking detectors, study of heavier systems would require thedevelopment of a new magnet and new detectors. Details of the SPALADIN experimental setup,status of the experiment and foreseen developments can be found in the letter of intent we havesubmitted to the CSTS.

3. Model development

Although the INCL intra-nuclear cascade model gave encouraging results, especially when coupled t othe ABLA evaporation-fission models, it was still suffering from severe deficiencies, due in particularto the fact that the diffuseness of the nuclear surface was not taken into account. We have developed,in collaboration with J.Cugnon from Liège University, a new version of this model, called INCL4[10], in which a smooth nuclear surface has been introduced. The shape of the matter density is now

described with a two-parameter Fermi model, the parameters being obtained from electron scatteringdata. Other improvements have also been made which mainly concern:

- the treatment of the Pauli blocking which has been improved so that negative excitationenergy cannot happen;

- the collisions between spectator nucleons which are now forbidden, but spectators are stillmoving in the nuclear potential;

- the intrinsic angular momentum of the residual nuclei which is now calculated from angularmomentum conservation (this is important for the evaporation-fission stage);

- the pion emission which has been reduced by increasing absorption in order to get closer t opion experimental data.

This model has been compared to the whole bulk of available data and has been found to give anoverall good agreement without changing any parameter. Examples are shown in figure 2. It canbe seen that neutron production double-differential cross-sections are very well reproduced (right) andthat the mass and isotopic distributions of heavy and fission residues are correctly predicted (left). Adiscrepancy still remains for light evaporation residues. However, in this region it is not possible t odetermine whether this has to be ascribed to the INC stage (too low excitation energy) or to theevaporation model (too much evaporation for a given excitation energy).

Figure 2. Left: Charge and, for a few elements, isotopic distributions obtained with the INCL4-ABLA model andthe previous version INCL3 compared to the data measured at GSI for Pb+H2 at 1 GeV/A [2]. Right: Double-

differential cross-sections measured at SATURNE for p+Pb at 1200 MeV [1] and calculated with INCL4-ABLA.

We have implemented the INCL4 and ABLA models into the LAHET3 code system [11] provided byR.Prael from Los Alamos. This makes it possible now to make thick target calculations and estimatequantities relevant for applications. An agreement has been signed with the MCNPX [12] (the newcode merging LAHET and MCNP, which is becoming the most widely used code for ADS design) teamin Los Alamos to include of our models as possible options besides Bertini-Dresner and other models.The INCL4-ABLA models have also been delivered to FZJ Julich (partner in HINDAS) forimplementation into the HERMES software package. A request for the models has recently been sentby one of the authors of GEANT4.

4. Applications

Having high-energy transport codes that now contain models that have been shown to much betterreproduce experimental data than those usually used, it is possible to assess the impact on quantities

relevant for applications. Calculations using LAHET3 with different models have been done of theactivity of cylindrical Pb [13] and Pb-Bi spallation targets (1m long, 10 cm diameter) irradiatedduring one year by a 1mA, 1 GeV proton beam. Figure 3 (right) shows, in the case of natural Pb, theactivity (total and of main contributors) due to the spallation products. Actually, activity due to asurrounding thermal neutron flux (supposed to be of the order of 3.1014 n/cm2/s) was also estimated

and found always smaller (except for the Pb-Bi target around a few months after irradiation when thecontribution of 210Po can be of the same order of magnitude). It can be seen that the total activity is

due to a lot of different isotopes and that the main contributors are nuclei close to the targetconstituents. In fact, results differing by less than 30% are found if INCL4-ABLA is replaced byBertini-Dresner. This is not surprising since in the region of the main contributing isotopes themodels give similar results. On the other hand, concentration of impurities produced by the spallationreactions is much more sensitive to the choice of the models. Results of INCL4-ABLA and Bertini-Dresner calculations are displayed on figure 3 (left). Differences of the order of a factor 3 are foundfor fission fragments and up to 30 for lanthanide elements. Since we have shown that INCL4-ABLAreproduces much better than Bertini-Dresner the experimental elementary production rate in theregion of fission, it can be said that someone who uses transport codes with the default options, whichgenerally correspond to Bertini-Dresner, can underestimate the production of volatile elements as Kr,I and Xe by a factor 3.

Figure 3. Right: Activity (total and of main contributors) of a lead spallation target irradiated by 1 GeV, 1 mAproton beam during one year as a function of time during the irradiation and decay, calculated using INCL4-ABLA

model implemented into LAHET3. Left: Concentration of impurities produced by the spallation reactions in thesame target calculated with LAHET3 using INCL4-ABLA and Bertini-Dresner, and ratio of the two calculations.

The Fe + p experimental data measured at GSI can directly be used to estimate the beam inducedradiation damages on an ADS iron window. Isotopic cross sections allow calculating theconcentrations of impurities that can be responsible for problems of corrosion or alloy cohesion. Thefragment recoil velocities can be used to estimate atomic displacements (DPA) that lead t oembrittlement of the window. Estimations of impurity concentrations have already been done usingprevious data [14] but the new GSI measurements will permit more precise evaluations extending tomuch lighter elements and the calculation of DPA.

5. Future

The data collected within the HINDAS project have already allowed the developing of new high-energy nuclear models that give encouraging results, in particular for heavy systems. However, thereremains a large place for improvement in domains that have clearly been identified. Figure 4 givesexamples of observables that are not very well predicted by the INCL4-ABLA model: isotopicdistributions for light systems (right) and energy spectra of alpha particles (left). For the latter, twoproblems are identified: the lack of high-energy alpha production in the INC stage and, at lowerenergy, the wrong behavior of the evaporation models.

Figure 4. Right: Comparison of the isotopic distributions measured at GSI for the Fe+p reaction at 1 GeV/A(C.Villagrasa preliminary results) with calculations done with the INCL4-ABLA. Left: Energy spectrum of alphaparticles measured by the NESSI collaboration compared with calculations done with INCL4-ABLA (solid curve)

and INCL4-Dresner (dashed curve).

In the future, we plan to continue to simultaneously work on experiments, model developments andapplications. This work will be done in the framework of the new project to be proposed to theEuropean FP6 program concerning nuclear data relevant for transmutation, in the definition of whichour group is strongly involved.

ÿ ExperimentsThe priority of the group is obviously the SPALADIN project and its extension allowing the study ofheavier systems, since coincidence experiments are considered as the only way to further progress inthe understanding of spallation physics. However, we also plan to measure total fission cross-sectionsat different energies with the FRS at GSI with a higher precision than the one we can have from theisotopic measurements (because of the low transmission of fission fragments in the FRS). We alsoforesee to collect experimental data with SPALADIN (isotopic cross-sections, neutron, light chargedparticle production) on very light (A< 30) targets for which only few data exist and the conventional

models do not work.

ÿ Model developmentsWe still work on the improvement of INCL4. For instance, we have already began to implement thepossibility of forming composite light charged particles in order to better reproduce the shape of theenergy spectra, as the one shown in figure 4 (left), and because this is important for predicting gas

production. Simultaneously, we also want to study more precisely the de-excitation stage and work onthe improvement of evaporation models and the testing of models specific of light nuclei (as Fermi-breakup), these elements (as Al, O, …) being major components of structure materials.

ÿ ApplicationsAfter activity calculations, the radiotoxicity of spallation targets will be studied. This could lead t odifferent conclusion concerning the sensitivity of the results to the models. We are also interested inparticipating to the analysis of measurement of spallation products in Pb and Pb-Bi rods irradiated inthe SINQ target at PSI in conjunction with the MEGAPIE project.

References

[1] X. Ledoux et al., Phys. Rev. Lett. 82 (1999) 4412; S.Leray et al., Phys. Rev. C 65 (2002)044621.[2] Wlazlo et al., PRL 84 (2000) 5736, Enqvist et al., NP A686 (2001) 481.[3] Enqvist et al., NP A703 (2002) 435.[4] E.Hagebo and T.Lund, J. Inorg. Nucl Chem. 37 (1975).[5] Enke et al., Nucl. Phys.A657 (1999) 317; D.filges et al., Eur. Phys. J. A11 (2001) 467.[6] H. W. Bertini, Phys. Rev. 131, 1801 (1963).[7] L. Dresner, Oak Ridge report ORNL-TM-196, 1962.[8] J. Cugnon, Nucl. Phys. A462 (1987) 751; J. Cugnon, C. Volant and S. Vuillier, Nucl. Phys. A620(1997) 475.[9] A. R. Junghans, M. de Jong, H. G. Clerc, A. V. Ignatyuk, G. A. Kudyaev and K.-H. Schmidt, Nucl.Phys. A629 (1998) 635.[10] A.Boudard et al., Phys. Rev C66 (2002) 044615.[11] R. E. Prael and H. Liechtenstein, report LA-UR-89-3014, Los Alamos National Laboratory,1989 and R.E.Prael private communication.[12] H.G. Hughes et al., MCNPX-The LAHET/MCNP Code Merger, X-Division Research NoteXTM-RN(U)07-012, Report LA-UR-97-4891 Los Alamos National Laboratory (1997).[13] L.Donadille et al., Journal of Nuclear Science and Technology, Suppl. 2 (August 2002) p 1194.[14] C.Villagrasa et al., J. Phys. IV France 12 (2002) Pr8-63.


LETTER OF INTENT

Title: The next step in exclusive spallation measurements : toward heavy elements

Experiment carried out at: GSI-Darmstadt, Germany

Spokes person(s): J.E. Ducret

Contact person at SPhN: J.E. Ducret

Experimental team at SPhN: A. Boudard, J.C. David, L. Donadille, J.E. Ducret, S. Leray,

C. Villagrasa & C. Volant

List of DAPNIA divisions and number of people involved: SEDI, SPhN (+ SACM for the

dipole magnet design)

List of the laboratories and/or universities in the collaboration and number of people involved: DAPNIA,

GSI.

SCHEDULE

Estimated total duration of the proposed experiment: not evaluated yet

Possible starting date of the experiment:

Expected duration of the data analysis:

ESTIMATED BUDGET

Total investment costs for the collaboration: not yet defined. Money asked to the European

Union inside the 6th F.P.

Share of the total investment cost for SPhN: not yet defined.

Total Travel Budget for SPhN: within travel expenses of the spallation group.

Letter of intent

The next step in exclusive spallation

measurements: toward heavy elements

By A. Boudard 1, M. Combet 2, J.C. David 1, L. Donadille 1, J.E. Ducret 1,

S. Leray 1, C. Villagrasa 1 & C. Volant 1

1 S.Ph.N., 2 S.E.D.I.

1/ The SPALADIN experiment

The SPALADIN experiment aims at measuring, as exclusively as possible, the

final states of the spallation reaction 56Fe + p in reverse kinematics. This

experiment was approved both by the C.S.T.S. of the S.Ph.N. and the

experimental advisory committee of G.S.I. in 2000. The principle of the

experiment is to take advantage of the Lorentz boost provided by reverse

kinematics and the mass asymmetry of the initial state of the reaction to

measure, event by event and in a relatively small solid angle, the coincidence

between 1) the heavy residue of the reaction, 2) the light particles (essentially

neutrons, protons, deuterons and alphas) evaporated by the compound nucleus

formed at the end of the fast cascade phase of the reaction.

The reverse kinematics presents two advantages for the measurement:

- It concentrates the light evaporation products, which have a very low

energy in the center of mass frame, and the heavy residues essentially at

zero degree with respect to the beam direction and with approximately the

beam velocity,

- It filters out the light particles emitted during the cascade phase of the

reaction since those are emitted preferentially in the proton direction, in

the center of mass frame and, thus, in the direction opposite to that of

the heavy nucleus. Due to the Lorentz boost, the particles emitted during

the intra-nuclear cascade have, in the laboratory frame, a small energy

and are emitted at quite large angles with respect to the beam direction.

The charged particles are then washed out of the detectors by the dipole

field of the magnet and the neutrons have a very little probability to be

inside the solid angle of the neutron detector. Thus the light particles

detected in our experiment are essentially evaporated particles.

The fully exclusive detection of the final state of the reaction event by event is

aiming at reconstructing the mass, the charge and the excitation energy of the

compound nucleus resulting from the intra-nuclear cascade. Such a

reconstruction will provide a test for the models of intra-nuclear cascade.

Furthermore, once this reconstruction is performed, it will be possible to study,

for a given range of compound nuclei (in mass, charge and excitation energy,

depending on the resolution achieved in the experiment), the different

evaporation channels and to quantify their branching ratios.

This experiment is quite challenging since we need to have many different

detectors work together: heavy fragments charge identification ionization

chambers, a ring imaging Cerenkov (RICH) to provide velocity determination for

the heavy residues, high resolution position detectors for the reconstruction of

the magnetic rigidity of the heavy residues, an efficient neutron detector (LAND),

which is currently working in G.S.I., and multi-wire proportional chambers

(MWPCs) and scintillator arrays for the light charged particle spectrometry and

identification. On an event-by-event basis, these detectors will have to provide:

- Mass and charge identification of the heavy residues of the reaction,

- Neutrons multiplicities and neutron center of mass energies for the events

with small neutron multiplicities,

- Mass and charge identification of the light charged particles with their

momentum and vertex angle reconstruction.

All theses quantities are needed in order to reconstruct the compound nucleus

between the intra-nuclear cascade and the evaporation.

Since the approval of the experiment we have been working on setting up the

experiment, creating the data acquisition program using GSI/MBS environment

and libraries as well as developing the data analysis program, based on the

GO4/ROOT environment of G.S.I. and C.E.R.N. and building and testing the

dedicated high resolution position detectors in DAPNIA/SEDI. We took data in

2001 and 2002 with the aim of:

- Testing the data acquisition and the data analysis in full scale and realistic

beam conditions,

- Calibrating the RICH with radiator geometries and materials not used so

far,

- Measuring the level of noise in the MWPCs as well as their in-beam

behavior (the ion beam actually goes through the MWPCs in our setup).

In our last run (July 2002) with a 58Ni beam, we had in coincidence:

- Two ionization chambers for the ion charge identification,

- The RICH detector,

- One high resolution position detector, called drift chamber (we will have to

use three of them in the physics experiment setup),

- MWPCs in the foreseen experimental configuration,

- Scintillator arrays for light charged particle identification.

This setup is relatively close to the experimental setup to be installed for the

physics run, which can be seen on the figure below. In this figure, ALADIN is the

large acceptance dipole magnet we will use for the physics run. The typical scale

of the experiment in the distance between the target and the ALADIN time of

flight (ToF) wall: around 7-8 m. The analysis of the data of this run is underway.

Some results will be shown during the presentation in front of the C.S.T.S. of the

S.Ph.N. The installation of the experiment and the physics run are planned for

the second half of 2003.

Our goal of these exclusive measurements of spallation reactions is not restricted

to 56Fe. Our final aim is to perform this kind of exclusive measurements on heavy

nuclei such as 208Pb or possibly 238U. As argued in the SPALADIN proposal

presented to the C.S.T.S., models, which reproduce well data on one nucleus

may not be good at reproducing data on the other, as can be seen on the heavy

residues measurements performed at SATURNE (L.N.S.) for 56Fe and G.S.I. for208Pb (see the SPALADIN proposal for more details). Since, for the spallation

program of our group related to the accelerator driven systems studies, it is

much more important to have a good predictability of models for lead, which will

be the main material of the spallation target, it will be necessary to have data on208Pb.

For these measurements, we already know that the performances of our present

setup for the iron experiment are not sufficient. There are two reasons for this:

- The combination of the bending power of the magnet ALADIN and the

resolution of the drift chambers does not provide enough A/Z resolution

for heavy fragments in the region A ~ 150-200.

- The average multiplicity of 208Pb spallation events combined with the

average number of hits of the d-rays generated by the passage of the

heavy residues through the matter in front of the wire chambers (air and

magnet vacuum windows) is far too high to allow a good tracking

efficiency in the MWPCs set-up we will use for the 56Fe run, as we could

prove it with Monte-Carlo simulations.

Thus, to perform a measurement with 208Pb, we will have to think about another

set-up. Our involvement in the R.H.I.B. (RHIB) project does give us an

opportunity for this.

2/ The R.H.I.B. project

Since some years now, G.S.I. is working on a project for the future development

of the laboratory. This study has been compiled in a conceptual design report,

which can be found at the Web address: http://www.gsi.de/Gsi-Future/cdr. Our

group has been involved in the nuclear physics part of this project, which was

called R3B and was funded by the European Union in the 5th framework program.

R3B stands for Reactions studies with Relativistic Radioactive Beams. The

achievements of R3B are summarized at the following Web address: http://www-

land.gsi.de/r3b/documents.html. In R3B , our group was involved in the

conceptual design of a large acceptance dipole magnet, which was mainly

performed by the DAPNIA/SACM, and in the definition of the general features of

the experiments to be performed with this new magnet. We also contributed to

the Monte-Carlo simulation part of R3B.

The RHIB project is the continuation of R3B. RHIB stands for Reactions with High

Intensity Beams of exotic nuclei. It is so far an expression of interest and will be

the subject of a proposal within the I3NS initiative in the 6th framework program

(I3NS means Integrated Infrastructure Initiative in Nuclear Structure). This

expression of interest is given in appendix, in a preliminary version.

The physics case of RHIB is described in details in the G.S.I. future conceptual

design report. It will cover the field of reactions and nuclear structure studies

with nuclear beams far from stability, which goes beyond nuclear physics with,

for example, measurements of cross-sections of reactions of astrophysical

interest. Some important differences with projects such as SPIRAL or EURISOL

have to be underlined:

- The energy domain is different: 300-1000 A.MeV as compared to a

maximum value of 10-25 A.MeV. The physics study is related to the

projectile rather than to the target nucleus with limited initial state

interactions linked to the very fast scattering time.

- This allows reactions to be studied with, as in the case of SPALADIN, a

strong forward focusing.

- The method of exotic nuclei production is the fragmentation/fission of the

projectile, not of the target nucleus. This allows a powerful separation of

the desired exotic isotope from the other produced species.

- The problem of the ionic charge states is largely avoided at these energies,

- The large velocities provide short time of flight even for heavy exotic

nuclei, giving thus access to short lived isotopes.

RHIB is thus very complementary with the above quoted projects.

As R3B, the RHIB project is divided into different sub-projects:

- Coupling of the super-conducting fragment separator to the experimental

setup,

- Feasibility study of the large-acceptance super-conducting dipole,

- Detector and electronics developments,

- Reaction theory (this comes in addition to the R3B work, which focused on

experimental aspects),

- Pilot experiments,

- Simulations.

3/ The involvement of the Saclay spallation group in R.H.I.B.

In the expression of interest given in appendix, our group is involved in two sub-

projects: detector developments and pilot experiments. On the one hand, a

spallation measurement is foreseen as a pilot experiment on the new large

acceptance dipole. On the other hand, SPALADIN is also considered as a pilot

experiment for kinematically complete reaction measurements in reverse

kinematics.

We also wish to contribute to this RHIB project with detector developments by:

- Proving in-beam the in-lab measured good performances of our high

resolution detectors, designing such detectors with a large active area and

providing them with multi-hit capabilities in order to use them in fission

experiments for magnetic rigidity determination,

- Designing a multi-track detector for light charged particles to be used

inside or at the exit of the new large acceptance dipole. What is considered

so far is either to use and improve an existing TPC (MUSIC III) or to

design a new one. This is just the beginning of the study and the phase-

space to be considered for such a detector is a priori wide open. For

example, it may be also feasible and less expensive to work with high-

resolution tracking chambers inside the magnet gap and at the exit and

add in between a rather elementary TPC whose purpose will be only to

make the links between the hits inside the magnet and at the exit and

provide Ú dldxdE )/( information for the particle identification. In this case,

the parameters of the TPC are only governed by the density of tracks and

not by the spectrometry resolutions (angles and momenta). Such a device

could also be used for fragmentation experiments.

4/ Conclusions

We wish to continue our experimental program on exclusive measurements of

spallation reactions. To that end, we need to get involved in the RHIB project.

With respect to this project with one of his goal being to setup exclusive

measurements of various nuclear reactions, SPALADIN is already, for our

collaboration and us, a pilot experiment. In fact, on the experimental point of

view, a success of SPALADIN will prove the feasibility of the determination of the

complete kinematics of spallation reactions. The generic tools we are actually

using for SPALADIN, will be used for RHIB: the data acquisition environment, the

GO4/ROOT based data analysis and the GEANT-4 simulation we are going to

install soon to describe our experimental setup. The technical developments we

will do for our experiment inside RHIB will be usable for other experimental

programs of this project, like actinide fission or fragmentation experiments.

Furthermore, getting involved in RHIB will give us the possibility to explore the

large physics potential of such a facility. For these reasons, we need an official

approval for our involvement in RHIB.

Appendix

"Reactions with High-Intensity Beams of exotic nuclei (RHIB)"

Expression of Interest for a Proposal to be incorporated in the

Integrated Infrastructure Initiative in Nuclear Structure (I3NS)

within the Sixth Framework Programme of the European Commission

October 8, 2002

In view of the proposed new international accelerator facility at GSI and with regard to

the successful completion of the R3B proposal within the 5th Framework Program of the

EC, we submit this Expression of Interest, which forms the basis for a future detailed

proposal within the planned I3NS initiative in the 6th Framework Program. The aim is to

pursue the most important developments that have emerged from R3B and to define

additional R&D objectives of key importance to improve the quality and to take full

advantage for experiments with exotic nuclei at the present GSI accelerator facility and

the proposed future GSI facility.

Within the 5th Framework Program, the EC has supported the R3B proposal devoted to

improve substantially the research opportunities with secondary beams of exotic nuclei at

the existing GSI accelerator facility. Design studies for i) an advanced experimental setup

for reaction studies with rare isotope beams, and ii) an improved scheme for the

production of secondary beams separated in-flight were delivered. Reports summarizing

the achievements are available at http://www-land.gsi.de/r3b/documents.html .

Meanwhile, GSI has prepared a Conceptual Design Report on its future international

facility and presented this concept to the worldwide research community. A number of

national and international committees have evaluated the GSI project; their statements

are encouraging and in support of the GSI project. Production of high-intensity beams of

exotic nuclei and related experimental instrumentation form one major research field

addressed with the GSI future project. Intense R&D is required in this context, a

substantial part of which will be covered by this RHIB proposal.

Objectives and physics background

The physics motivation is described extensively in the 'Conceptual Design Report' for the

future GSI project (see http://www-aix.gsi.de/GSI-Future/project/eng/index.php ). RHIB

will cover experimental reaction studies with exotic nuclei far off stability. Nuclear

structure and dynamics, astrophysical aspects, and technical applications are concerned.

The objectives of the RHIB project are to define the demands for and to develop a

versatile experimental setup, which can accomplish all the different requirements of the

various reaction experiments with high-energy radioactive beams. This includes in

particular pilot experiments in case of new experimental methods/reactions and test

experiments as part of the detector development. In the past decade several types of

reactions were explored demonstrating the potential of high-energy radioactive beams to

study the structure of exotic nuclei. In conjunction with the development of reaction

theory a quantitative analysis of reaction studies in terms of nuclear structure became

possible for some reactions. The objective of RHIB is to advance experimental conditions

for reaction studies in a two-fold way: Improvements of the experimental conditions in

terms of beam intensity, resolution, efficiency, rate-capability etc; but also to make

accessible new experimental methods not developed so far, using essentially the same

experimental setup. This requires a versatile setup including new detection systems but

also the development of experimental concepts and the corresponding reaction theory. A

few reaction types will be discussed below.

Knockout reactions and quasi-free scattering

Experiments have shown that valuable information can be gained from high-energy

reactions even with beams of very low intensity. Examples are knockout reactions, which

have emerged as a standard tool for extracting spectroscopic factors for high-energy

projectiles with intensities down to one ion/sec. First experiments with a liquid hydrogen

target (a R3B development) have indicated that a kinematically complete measurement

including the target recoil can yield additional information on the reaction mechanism

enhancing the potential of such reactions significantly: the study of cluster knockout

reactions such as (p,pa) seems feasible as well as knockout reactions from deeply bound

states. Alpha knockout reactions, for example, potentially shed light on clustering in

nuclei, but also can become an important reaction to study very neutron-rich nuclei even

beyond the drip line, e.g. 7H in a 11Li(p,pa)7H reaction or the four-neutron system

through the 8He(p,pa)4n reaction. In order to explore the full potential of quasi-free

scattering experiments in inverse kinematics, new detector systems determining the

momentum vectors of the proton recoils as well as the corresponding reaction theory has

to be developed. Both aspects are part of the RHIB proposal (see subprojects 3 and 4).

In addition, pilot experiments have to be performed (subproject 5). Up to now

experiments at the present LAND/ALADIN facility were often limited to relatively low

beam energies of about 200 to 250 MeV/u. The reason for this is the limited bending

power of the dipole magnet presently in use. From the reaction theory point of view,

higher beam energies would be beneficial, but also experimental reasons: The neutron

detection efficiency of LAND reaches a value above 90% for neutron energies above 400

MeV, while below the efficiency drops rapidly and also the absolute value of the efficiency

becomes less accurate. In addition, the small bending angle also gives rise to background

since the beam is dumped close to the neutron detector LAND. A new bending magnet

with a much higher field integral is essential to overcome such limitations. An innovative

design of such an device was elaborated within the R3B project. A feasibility study

including tests of the superconductor, the quench-protection system, and the

construction of a small prototype is the aim of subproject 2 of RHIB.

So far, knockout reactions have been studied only for light nuclei. The extension to

heavier neutron-rich nuclei requires an efficient transport of fission fragments to the

experimental area (see subproject 1) and better resolution to identify the fragment mass

after the reaction (high field-integral dipole, tracking detectors, see subprojects 2 and 3).

Coulomb breakup

Coulomb breakup is a complementary reaction mechanism to study the single-particle

structure of exotic nuclei. The fact that electromagnetic excitation at high beam energies

gives quantitative access to matrix elements via semi-classical calculations makes this

reaction especially suited for the determination of reaction rates of astrophysical

importance. Both, (g,n) and (g,p) (and the inverse) rates can be determined. In this

context the low-energy part of the cross section distribution is often of special interest,

which requires a precise measurement of the differential cross section ds/dErel at very

low relative energy Erel between fragment and proton (neutron). Such demands imply the

need for developments of high-resolution tracking systems (see subproject 3) in

conjunction with a large-acceptance spectrometer (subproject 2) and a precise time-of-

flight measurement for all outgoing particles including neutrons. Subproject 2 aims for a

resolution better than 50 ps. In case of (g,p) reactions the detectors need in addition

multi-hit capability. The challenge here is the dynamical range needed to detect both the

heavy fragment and the (minimum ionizing) proton. Finally, the extraction of

astrophysical S factors and of spectroscopic factors from the differential cross sections

rely on a quantitative description of the process provided by proper reaction theory (see

subproject 4).

Giant resonances and dipole strength

Beside the (g,n) and (g,p) threshold strength discussed above, electromagnetic excitation

using high-energy beams allows to measure the dipole strength up to relatively high

excitation energies (~25 MeV) including the giant resonances. A first experiment was

performed with the present setup to deduce the dipole strength function for neutron-rich

oxygen isotopes. The GDR region (25 MeV for such light nuclei), however, could hardly

be reached because the cross section drops rapidly for higher excitation energies due to

the adiabatic cutoff. Higher beam energies would be needed in order to reach higher

excitation energies, which requires again a higher field-integral of the bending magnet

(subproject 2). The extension of such studies to heavier nuclei is presently hampered by

two facts: i) The transport efficiency of fission fragments is rather low due to the

relatively low energies. The higher field integral of the R3B dipole is necessary to make

use of higher beam energies and thus improve transport efficiency (by a factor of 5 e.g.

for 132Sn at the present GSI facility). ii) A much better resolution for tracking the

fragment through the magnetic field is required in order to identify the fragment mass.

The development of high-resolution position-sensitive detectors is the aim of subproject

3. The beam-energy and scattering-angle dependence of electromagnetically induced

dipole and quadrupole excitations are rather different. So far, electromagnetic excitations

of the giant quadrupole resonance in heavy ion collisions were not explored. Such studies

require precise measurements of the scattering angle and thus high-resolution position

measurements (see subproject 3), and the use of thin targets, which in turn require

higher beam intensities. Pilot experiments have to be performed to study the feasibility

of extracting the quadrupole strength function of exotic nuclei (subproject 5).

Charge-exchange reactions

Charge-exchange reactions such as (p,n) are potentially well suited to excite isobaric

analog resonances, Gamov-Teller transitions and spin-dipole resonances in inverse

kinematics. So far, these reactions were not yet explored with radioactive beams in a

kinematically complete measurement. Spin-dipole resonance excitations were studied in

target excitations using stable beams and targets. From the measured cross sections the

evolution of the neutron-skin thickness in (stable) tin isotopes was extracted. This

method seems to be quite attractive to obtain neutron-skin thicknesses of radioactive

short-lived nuclei. The experiments in inverse kinematics have very similar requirements

as the giant-resonance measurements discussed above as far as the detection of heavy

fragment and projectile-like neutrons is concerned. The challenge here is the detection of

the slow neutrons from the liquid-hydrogen target in the (p,n) reaction. Pilot experiments

have to be performed and analyzed in order to explore the potential of such reactions,

and a new concept for a neutron-detection system may have to be developed if

necessary (see subproject 5).

Fission, Multifragmentation, Spallation

First-generation experiments performed at GSI have proven that the use of secondary

beams opens exciting new prospects for studies of nuclear fission. The RHIB setup is

potentially useful to study fission of short-lived nuclei through a kinematically complete

measurement of all decay products, including the two fission fragments, neutrons as well

as gamma-rays. The additional demands for the setup concern the multi-hit capability of

the tracking detectors (subproject 3) and the resolution needed for velocity and

momentum measurements of the fragments. Similar demands arise from

multifragmentation experiments and from the studies of spallation reactions in complete

kinematics. Such studies are of particular importance also for applications like nuclear-

waste transmutation scenarios or accelerator-driven fission reactors. The challenging

requirement for such an experiment is the coincident measurement of heavy fragments,

protons in a wide angular range, other light charged particles, neutrons, as well as

gamma rays. Advanced detection systems have to be developed to enable a

reconstruction of the tracks of all charged particles through the magnetic field in order to

identify them and deduce their momenta. Subproject 3 aims for the design of such a

detection scheme. This includes prototype construction and testing, as well as the

accomplishment of a pilot experiment (subproject 5).

In summary, the main objective of this RHIB proposal is to identify and, in part, realize

optimal conditions for the production of intense exotic nuclear beams and for studying

them in reactions at intermediate to high energies. The development of a versatile

experimental setup including innovative developments of a super-conducting large-

acceptance magnet and advanced detection schemes, the development of new

experimental methods and corresponding reaction theory are the main subjects of the

proposal. The results should promote the development of an upgraded research facility

according to the needs of the European research community.

Proposed subprojects

1) Coupling of the Super-conducting Fragment Separator (Super-FRS) to the RHIB setup

Within R3B, the ion-optical layout of the proposed Super-FRS has been elaborated. The

next steps are

• the ion-optical and technical layout of the coupling between Super-FRS and the

experimental setup for reaction studies, which assures in particular high

transmission for fission fragments;

• design of degrader stations to separate the fragments;

• the development of diagnostic detectors allowing coupled operation of Super-FRS

and the RHIB setup, in particular position-sensitive detectors with high-rate

capability and excellent time resolution (e.g. diamond detectors).

2) Feasibility study of the large-acceptance dipole magnet

The corresponding sub-project within R3B delivered a technical design report for the

magnet. In view of the novel design of this super-conducting dipole including large

acceptance for fragments and neutrons/protons (~+/- 100 mr), active shielding

technology, large field integral of 5 Tm etc., extensive studies and tests have to be

performed before the full-scale magnet can be constructed:

• Tests of the superconductor, final design of the cable;

• Construction of a prototype magnet including auxiliary devices (e.g. the quench

protection system) in order to demonstrate the technical feasibility of the

innovative features of the device;

• Final design of the dipole magnet (the construction of the full-size magnet is not

subject of this proposal).

3) Detector development for reaction experiments

The RHIB project includes several developments of advanced detector systems beyond

those foreseen in R3B, in particular:

• High-resolution tracking detectors for heavy ions and/or protons (e.g. Si strip

detectors); particular problems are high rate capability, multi-hit capability,

dynamical range (in case of coincident detection of minimum-ionizing protons and

heavy fragments), DE resolution, fast and economical readout electronics;

• Large-area high-resolution detectors for heavy ions and/or light charged particles

behind the magnet (e.g. multi-wire drift chambers); detection of light charged

particles and fragments in one detector with multi-hit capability and sufficient

dynamical range, or separate detectors if necessary;

• Development of a compact proton detection system for target recoil protons and

knockout protons adapted for the use in conjunction with the liquid hydrogen

target and surrounding gamma ray detectors (e.g. Si-strip detectors);

• Fast-timing TOF wall and neutron detector aiming at improvements of one order

in magnitude for the time-of-flight resolution for fragments, protons, and

neutrons.

The detector developments include highly integrated electronics and readout schemes as

an integral part of each of the respective subprojects.

4) Reaction theory

The study of reactions of high-energy radioactive beams have become a major tool for

investigating the properties of short-lived nuclei only due to the concurrent development

of high-energy radioactive beams and new experimental concepts in conjunction with the

development of corresponding reaction theory. Developments of reaction theory is

subject of RHIB in order to provide a quantitative description of Coulomb breakup at high

energies, which is of particular importance to extract astrophysical S factors and

spectroscopic factors from measured cross sections. Theoretical developments are in

particular foreseen in conjunction with the exploration of quasi-elastic scattering

experiments. The coincident measurement of all particles in a AP(p,px)A-xP type of

reactions opens new perspectives to study cluster knockout, unbound states, but also the

measurement of spectral functions seems feasible. The corresponding reaction theory has

to be elaborated.

5) Pilot experiments

One aspect of RHIB is the exploration of new experimental methods. First kinematically

complete measurements of fission and spallation will be carried out. Pilot experiments

are foreseen in order to explore the prospects of new experimental methods like charge-

exchange reactions or quasi-free scattering in inverse kinematics.

6) Simulations and detector-test experiments

Extensive simulations of new experimental setups are an integral part of their

development. The corresponding tools are either available in general-purpose packages

(GEANT3, GEANT4) or have been developed for these packages. They now have to be

applied to simulate future experiments, including present and new detectors. Whenever

possible, test experiments at existing facilities should verify the validity of the

simulations.

Working plan, deliverables and role of participants

(to be done)

Financial support requested from EC

The total budget estimated for the project outlined above amounts to about 10 M€.

Excluding costs for the construction of the full-size magnet, which is not subject of this

JRP, the costs amount to about 6.5 M€. These costs include (within a 5-year period) the

test program and prototype for the large-acceptance magnet (0.75 M€), costs of

prototype detectors and electronics (0.7 M€), and manpower for subprojects 1, 3, 4, 5

and 6 (70 person-years, 5 M€ including travel and overheads). Financial support from the

EC is requested for 50% of the manpower estimated for all projects (about 2.8 M€) plus

equipment to develop prototype detectors and electronics (0.25 M€) and the prototype

magnet (0.2 M€). This adds up to a total of 3.25 M€ over a 5-year period for the project.

Participating institutions

GSI, Darmstadt, Germany

Justus-Liebig-Universit t, Giessen, Germany

Technische Universit t M nchen, Germany

Jagellonian University, Cracow, Poland

DAPNIA/SACM, SPhN, C.E.A Saclay, France

GANIL, Caen, France

Institut de Physique Nucleaire, Orsay, France

University of Surrey, Guildford, U.K.

University of Liverpool, U.K.

Universidad de Santiago de Compostela, Spain

CSIC Madrid, Spain

Chalmers University of Technology, Goeteborg, Sweden

Aarhus University, Denmark


RESEARCH PROPOSAL

Title: PHOTOFISSION EXPERIMENTS AT SAPHIRExperiment carried out at: CEA SACLAY

Spokes person(s): Henri SAFA

Contact person at SPhN:

Experimental team at SPhN:

List of DAPNIA divisions and number of people involved: SPhN, SDA, SACM, SIS, SEDI


DEN / DPA, DRT / DIMRI

SCHEDULE

Possible starting date of the project and preparation time [months]: 01 / 01 / 03

Total beam time requested: 75


REQUESTED BUDGET


Share of the total investment costs for SPhN: 170 k€

Investment/year for SPhN: 70 k€


Travel budget/year for SPhN:




PHOTOFISSION EXPERIMENTS AT SAPHIR

H. Safa,CEA Saclay, DSM/DAPNIA/SPhN

91191, Gif-sur-Yvette, France

Abstract :

The aim of the proposal is to perform basic photofission experiments at theSAPHIR facility located in the main center of CEA Saclay. The experimental resultswould be compared to calculation made using a Monte-Carlo code (MCNP) enhancedwith photonuclear capability. These experiments could offer ways to improve thesensitivity of the actinide detection level using photofission. The final goal is a full-scale demonstration of the lowest possible mass detection embedded inside a realnuclear waste barrel.

1. IntroductionThe photofission process is known since long time, based on the excitation of the

Giant Dipolar Resonance (GDR) of elements using gamma rays. High-energy photons mayinduce enough nuclear excitation to provoke particle emission (most likely neutrons,eventually charged particles like p or α) or even lead to fission for actinides. Even though theelectromagnetic process suffer from the (1/137) factor compared to the strong nuclear force,the enhancement due to the GDR in the 10 to 20 MeV energy range makes its cross-sectionincreased to a fraction of a barn (typically 100 to 500 mbarns). That puts the photonuclearprocess at almost the same level than other reactions in a most remarkable and interestingphenomenon.

At that point, although the photofission process has extensively been studied in the70's, few indications are available on the way the process is actually occurring. How does thenucleus excited at the resonance loose its excitation? For example, the intensity spectrum ofthe fission products is not known at all and consequently the amount of delayed neutrons withtime following the fission. This information is of prime importance for our experiments aswill be shown later on.

Concerning the photonuclear reactions, the elementary cross sections of (γ,n), (γ,2n)and (γ,f) reactions have been measured for a few but important nuclei (like 238U). But thefraction of neutrons emitted from each reaction is not yet determined. It is important to get theratio of neutrons coming from fission, relative to the total neutrons emitted. At the same time,the importance of the angular distribution of these neutrons is totally unknown. That is quitecrucial for the simulations. It must be emphasized that the present calculation is assuming a

perfectly isotropic angular emission. From the physics point of view, which might be true forthe fission neutrons but it is very unlikely it is also the case for the direct photonuclearreactions.

Finally, in the photofission process, an actinide cannot be identified by its emittedfission neutrons. It has been established though that a possible identification could be doneusing the delayed gammas. But this technique appears to be quite cumbersome and difficult toapply. Are there other ways to check which nucleus is hit using its photonuclear byproducts?An answer to that question could bring up additional techniques helping the problem of non-destructive detection of nuclear matter embedded in a waste barrel.

2. Preliminary ExperimentThe SAPHIR accelerator is an electron machine located at the main area of the

CEA/Saclay. Electrons are accelerated to an energy from 10 to 35 MeV, in pulses of roughly2.5 µs and with a repetition rate varying between 6.25 Hz and 400 Hz.

In order to experimentally evaluate the (γ,f) process in 238U, a first experiment hasbeen set up in 2001 where the beam is first selected in energy and then sent to a pure uraniumtarget (a small thick cylinder of 20 mm length and 7 mm diameter. Two kinds of detectorshave been used. First the "standard" Helium3 neutron detector to study the delayed neutrons.That will give some information on the fission rate. Then a fission detector to measure theneutrons produced during the pulse. These prompt neutrons are a signature of the sum of allnuclear interaction mainly (γ,n) (γ,2n) and (γ,f). Combining the two results give the branchingratio between the two processes for a thick target and for a given energy. The experimentalsetup may equally give the angular dependence for each process. The experimentalmeasurement can also be compared with the theoretical predictions.

Because the electron energy distribution coming out from the SAPHIR accelerator isvery wide, it is not quite well suited to make energy dependence measurements. But thephotofission process is really a threshold process as regard to electron energy with almost noproduction below some 15 MeV. And the production rate rises very steeply in the range 20 to40 MeV. So it is quite important to work with almost monoenergetic electrons. In that sense, aspecific transport line has been built and installed at the SAPHIR facility. Preliminary resultsare very encouraging and have already been discussed in an earlier CSTS report [1].

3. Photofission Experiments

3. 1 - Basic Experiment

The basic experimental set-up testing a nuclear waste barrel is shown in Figure 1. Theaccelerated electrons are converted to gamma by bremsstrahlung on a tungsten converter(typically 2 mm thick) then the gamma beam spreads on the test barrel. Seven neutrondetectors are positioned all around the barrel, covering angles from (-135°) to (+135°). Basedon a helium 3 EURYSIS type, their sensitivity is as high as 150 counts/s per unit flux(n/cm2.s) with an active length of 1 m. The basic nuclear reaction is the n + He3 → H + T,liberating an energy of 765 keV and ionizing the gas detector. The corresponding chargeinduced is then collected through an amplifier chain and the pulse is detected in a countingchannel. If the flux rate is not too high, each neutron will generate a pulse that can beaccounted for. These detectors are basically used for delayed neutron measurements.

BARREL

Accelerator

Converter

Detector

Figure 1 – Overall layout of the non-destructive photofission active probe.

3. 2 - Noise Limitation

Following a photofission reaction between a gamma ray and an embedded actinideinside a nuclear waste barrel, fission products are produced. Some of these will releasedelayed neutrons, which have to travel all along the concrete surrounding the nuclear wastebefore having any chance to hit a detector.

It can be shown that a linear relation maybe found between the detected counts and theactinide mass probe m

[ ] [ ] [ ]Agd

scounts ImeAS µα−=/

Where d is the distance separating the actinide from the barrel surface and I theaccelerator average current.

Using a Monte-Carlo neutron transport code (MCNP4), the exponential decrease ofthe neutron created inside the barrel can be estimated to be of the order of α = 17.26 m-1 for aconcrete with a density of 2.4 g/cm2.

The coefficient A can be calibrated using a known mass of actinide. It has been doneusing a 282.734 g of uranium 238 placed at the center of a concrete barrel (density 2.4, outerdiameter 1.08 m). The barrel has been irradiated at a frequency of 25 Hz with electronshaving 15 MeV of mean energy. The counting rate on the detectors placed at a distance of30 cm from the barrel was on average S = 0.120 counts/s [2].

The coefficient A may then be deduced as

A = 0.54 (counts/s)/(g.µA)

The noise on the detectors has been evaluated to be B = 0.25 counts/s. The mass limitsensitivity is therefore given by the relation

IAeB

Md

limit

α=

This limit has been estimated to be around 10 g for 30 MeV electrons.

3. 3 - How to improve the (Signal/Noise) ratio?

Our proposal is to study the basics of photofission in order to find ways to improve the(S/N) ratio for waste management purpose. Because the actual mass detection limit is wayover the desired one to allow proper characterization of the waste, several techniques have tobe implemented and tested to check whether a gain in (S/N) ratio may result.

A non-exhaustive list of these possible improvements is given here:

• ShieldingNoise is coming either from the surrounding walls or from the concrete barrelitself. A good shielding may reduce the noise (and consequently increase the(S/N) ratio). Irradiation of the walls by the gamma rays should be avoided (whichcould be done using a lead shielding).

• Direct IrradiationDirect irradiation of the barrel may be a good solution to avoid gamma spreadingall over the surroundings. Moreover, electrons will convert inside the concretewith a better penetration up to the actinide. A specific additional vacuum line isrequired with focusing and rastering magnets.

• Time measurementsA delayed time is needed to properly measure the delayed neutron signal due tothe high noise following an electron pulse (gamma flash). It is not yet clear howdoes the (S/N) ratio vary with time, both signal and noise decreasing withdifferent constant times.

• Energy studyThere are some annoying nuclear reactions like

( ) nOONpO 16171718 +→→γ *,

That generates neutrons long after the electron pulse (decay time 4.16 s). Butthese have an energy threshold (that particular one is at 15.9 MeV). Therefore the(S/N) ratio should also be energy dependent.

• DetectorsBy modifying the absorber (cadmium) and moderator (polyethylene) thickness,the energy at which a neutron is detected can be moved. An optimization shouldbe made to check what is the best energy giving an optimal (S/N) ratio. Also,prompt neutron detectors maybe installed and operated.

• Fake BarrelIn order to better subtract all unknown physics (or estimated with a great deal oferror margin), an irradiation of a fake barrel containing no actinides can give aground level signal and a reference noise figure.

All these proposed techniques maybe tried separately to check their importance on the(S/N) ratio. It is important to point out that they could also be implemented all together ifnecessary to achieve the best performance on a final test.

4. Cost and ScheduleThe overall cost of the present experimental program has been estimated to amount to

170 k€ not including the cost of the SAPHIR beam. The program is running over a three-yearperiod (2003 – 2005), ending with a full demonstration experiment on an actual waste barrelwith all the included improvements.

The required manpower for the SPhN is 6 man-year.

1 "Conseil Scientifique et Technique du SPhN", 3 & 4 June 20022 L. Roux, DIMRI/LIST/SIAR, "Interrogation Photonique- Principaux ordres de grandeurs", 2001


RESEARCH PROPOSAL

Title: Measurements of the neutron fluxes in the liquid Pb-Bi spallation target at

MEGAPIE

Experiment carried out at: PSI (Villigen – Switzerland)

Spokes person(s): F. Marie

Contact person at SPhN: F. Marie

Experimental team at SPhN: M. Fadil, A. Letourneau, D. Ridikas


SIS(6)


CEA/Cadarache/DEN/DER/SPEX/LPE

PSI Villigen

SCHEDULE

Possible starting date of the project and preparation time [months]: 2003 – 36 months


Expected data analysis duration [months]: 12

REQUESTED BUDGET

Total investment costs for the collaboration: 235*1.1=260 kEuro

Share of the total investment costs for SPhN: 140 kEuro

Investment/year for SPhN:

Total travel budget for SPhN: 70 kEuro

Travel budget/year for SPhN: 23 kEuro

If already evaluated by another Scientific Committee: MEGAPIE collaboration 29/10/02





Measurements of neutron fluxes in the liquid Pb-Bi

spallation target at MEGAPIE

F. Marie, M. Fadil, A. Letourneau, D. Ridikas, J.C. Toussain

CEA/Saclay, DSM/DAPNIA, 91191 Gif-sur-Yvette, France C. Blandin

CEA/Cadarache, DEN/Cadarache/DER/SPEX/LPE, St Paul-les-Durance, France F. Groeschel, E. Lehmann

PSI, Villigen, Switzerland

Introduction

The present proposal describes the project to implement micro fission chambers [4] as

neutron detectors inside the liquid Pb-Bi spallation target, to measure online, thermal,

epithermal and fast components of the neutron flux during the operation of the

MEGAPIE experiment at PSI. This document provides complementary informations to

the first proposal of Measurement of the neutron flux at MEGAPIE which has been

presented at the previous CSTS in June 2002 [1]. Following its recommendations and

remarks, physicists and engineers involved in the project have worked during the last

months to define more precisely the technical constraints, observables and the

geometry/positioning of the detectors. Thus, a feasibility study of new microscopic

fission chambers dedicated to ADS [2] has definitely convinced us of the possibility to

implement such detectors inside the MEGAPIE target, and has showed all the interest of

these detectors for an online measurement of the thermal, epithermal and fast components

of the neutron flux. Finally, a detailed study of the technical solutions, detector geometry,

mechanic, budget and manpower of the project, has been realized in the frame of the

DAPNIA Resource Evaluation Comity [3].

In this present document, we would like to provide answers to the questions that were

pointed out at the last CSTS :

¶ Detector geometry and layout

¶ Gamma and proton background calculations

¶ Measurement of fast components of the flux

¶ Temperature and electronic tests

¶ Budget and manpower

Apart the points mentioned above, the body of the proposal remains identical to the one

of June 2002. Thus, for any information about the physics motivations, PSI experimental

context, thermal and epithermal flux measurement preliminary studies, please refer to the

previous CSTS proposal [1].



Additional studies added to the original CSTS proposal

Detector Geometry and Layout

The implantation of the neutron detectors has been carefully studied (see Fig 1), in

particularly with respect to the geometrical constraints of place, airtight passage, pressure

and thermo mechanical properties. The proposed layout consists of a cylindrical container

which will be inserted in the lower part of the central rod of the target. In order to be able

to measure, at the same position, both signal and background, the inner diameter of the

central rod has been enlarged from 10 mm to 13 mm. 8 micro fission chambers (F=4.7

mm) will be disposed in the container. The container will be filled with He gas for

thermo conductivity reasons. The positions of the neutron detectors within the container

and the nature of the active deposits have been determined to allow simultaneous

measurements of thermal, epithermal, and fast components of the flux at different

distances from the target window :

¶ 32 cm : two 300 mm Gadolinium filtered (235

U and no deposit) fission chambers

to measure the epithermal component of the flux and the background. After few

days of irradiation, this chamber will be sensible only to thermal neutrons at low

position.

¶ 39 cm : 242

Pu and 241

Am (Gadolimium filtered or not) deposit fission chambers

to measure fast components of the flux and to probe the incineration potential

and transmutation of minor actinides in a realistic spallation neutron source.

¶ 46 cm : Flux monitors for offline measurement of fast components of the flux.

Gamma spectroscopy will be performed after irradiation and cooling time.

¶ 47 cm : 235

U deposit fission chambers for thermal component of the flux and

background at middle position.

¶ 77 cm : 235

U and no deposit fission chambers to measure thermal flux at high

position.

The masses of the deposits will vary from 20 mg to 40 mg for 235

U except for minor

actinides for which they will be 200 mg.

The 8 chambers will be connected to 15 m long mineral Thermocoax cables (F=1 mm).

An airtight passage (F=16 mm) isolates the fission chambers from the rest of the central

rod.

Two thermocouples will be also placed at low and high positions to monitor the

temperature of the neutron detectors.

The container will be inserted in the target via a 4.5 m long steel pole of handling, which

will remain in place as shielding during the irradiation of the target.



Fig 1: Drawing of the set-up of irradiation of the fission chambers

Gamma and proton backgrounds

Proton and gamma background, including Bremsstrahlung and radiative capture

processes, have been calculated with MCNPX code and compared to the neutron flux for

various positions of the detectors (5 to 32cm ) from the target entrance (see Fig2).

Fig 2: Gamma (green) and Proton (red) fluxes compared to neutron spectrum (blue) at

various distances from the PB-Bi target entrance ranging from 5 to 32 cm.



These results show a ratio, between the neutron flux and proton or gamma fluxes, of

respectively 17 and 1850 at a distance of 32 cm from the target entrance. Taking into

account these numbers, the impact of the protons in the fission chambers should be

negligible. Concerning the gamma flux, these predictions have been compared to the

same simulations made for ILL which show a ratio of at least Fn/Fg=3 for Fn=7. 1013

n/s/cm2. Thus, from our experience of ILL background currents, we can estimate that the

signal over background ratio should be larger than 1 within the MEGAPIE experimental

conditions. In addition, the background will be corrected properly with the “no deposit”

reference chambers.

Measurement of the fast component of the flux

We have studied the possibility to irradiate minor actinide deposit fission chambers in

order to measure the fast component of the flux. As shown in Fig 3, some minor actinides

have larger fission cross sections at high neutron energies than at thermal neutron energy.

For these reasons we have estimated [2] the corresponding currents (see Fig 4) for three

deposits : 241

Am, 237

Np and 242

Pu . The currents would be ranging from 400 nA to 20

mA. To balance potential impurities of thermally fissile isotopes, a Gadolinium filter

could be placed around these chambers.

Another complementary offline method to measure the fast component of the flux

consists in the irradiation of flux monitors which present an energy thresholds for some

specific reactions (n,p n,2n etc…). After several months of cooling time after the

irradiation, the monitors will be extracted from the MEGAPIE target and analysed by

gamma spectroscopy. Table 1 presents possible isotopes with different energy thresholds

and dedicated half-lives.

Fig 3: 242Pu (plain) and 237Np (dash) fission cross sections



Fig 4 : Current estimations during irradiation of micro fission chambers with different

minor actinide deposit at 32 cm from the target window.

Table 1 : Possible flux monitors candidates for offline fast spectrum determination.

Reaction Half –life [d] Gamma lines [KeV] Energy treshold [MeV] 54Fe(n,p)54Mn 312.1 840 2.2 58Ni(n,p)58Co 70.8 510 & 810 1.3

59Co(n,2n)58Co 70.8 510 & 810 10.3 93Nb(n,n’)93mNb 5953.6 19 & 17 0.03

Temperature and electronic tests

The main technical constraints of the project, that slightly differ from the experience

encountered at ILL, are temperature and low current measurement. The temperature of

the fission chambers during measurements will be 350–450 oC, with variations of 100

oC

in a few seconds every 20 min approximately. Moreover, after the insertion of the

detectors in the central rod, the temperature will rise up to 600 oC for a few hours. These

unconventional running conditions require specific mechanical studies to design detectors

that will stand such unprecedented high temperature level. The studies will be performed

by Photonis and CEA/DEN/DER/SPEX and the temperature modelization would be

taken in charge by DAPNIA. 235

U deposit chamber prototypes will be irradiated in 2003

at ILL, after heating cycles in 700 oC oven and mechanical and electrical inspection, in

order to verify the temperature resistance of these new chambers. In principle, according

to the manufacturers, there would be no difficulty to built detectors that fit such criteria.

On the other hand, these high temperatures should not be a problem concerning the

running point of the detectors, as an increase of the polarisation of the fission chambers

by 100 V will allow to recover the original conditions (calibration) encountered at ILL.

The other point that requires dedicated studies is the new high precision acquisition

system that will allow to measure currents from 100 nA to 100 mA with a relative

uncertainty of 1%. This high precision electronic will measure sequentially (every sec)

the current in the 8 detectors, keeping their polarization (+/- 250V) stable. Several



systems are presently under study [2] and one (over 8) module will be tested at ILL in

2003. From what we know about electrical environment at MEGAPIE and providing

additional precautions with ground shielding of the apparatus and cables, the expected

electromagnetic noise (direct and induced) should be overcome.

Budget, manpower and planning

The detailed budget of this project and the technical resources needed have been

evaluated [3], without any margin, and are presented in Table 2. The investment cost

(235 kEuro) would be financed for one half by the MEGAPIE project, providing the

complementary financing is found (DSM) in 2004 for the rest of the project.

Furthermore, a financing support of 15 kEuro has been requested in 2003 in the frame of

GEDEON, covering temperature (2 fission chambers) and new electronic (1 module)

tests.

Table 2: Total budget of the project

Fissions chambers

8+2 detectors

Masses analysis

Temperature tests

Transport

56 kEuro

30 kEuro

5 kEuro

2 kEuro

93 kEuro

Electronic and Acquisition

8 precision modules (nA)

Electronic cards, Acquisition

Cables, connectors

40 kEuro

24 kEuro

13 kEuro

77 kEuro

Mechanic

Detector disposal

Assembling

Gadolinium filters

Flux monitors

Cables, thermocouples

Radiative shielding

Transport

34 kEuro

10 kEuro

10 kEuro

5 kEuro

2 kEuro

2 kEuro

2 kEuro

65 kEuro

Minimum investment budget 235 kEuro

ILL irradiations, calibrations and man power from

Cadarache

40 kEuro

Missions (supported by DAPNIA) 70 kEuro

Man power (supported by DAPNIA)

Engineers :

Technicians :

Physicists :

279 men.days

108 men.days

1400 men.days

The manpower required for the realization of this project is one additional CEA staff or

PostDoc and one PhD (2003-2006). In these conditions the total amount of SPhN people

involved in the realization phase would be (1+1+0.5=2.5).

The planning of realization will be :



¶ end 2002: DAPNIA resources evaluation comity

¶ mid 2003: realization of 235

U deposit chambers

¶ end 2003: temperature and electronic tests

¶ beginning 2004 : realization of minor actinides chambers and mechanic

¶ mid 2004 : final assembly of the chambers

¶ end 2004 : insertion in the central rod at PSI and tests

¶ 2005 : irradiation of MEGAPIE target – flux measurements

¶ 2006 : flux monitor spectroscopy

Conclusions

Since the previous presentation of this proposal at the CSTS, background, electronic

temperature constraints and detector layout have been studied in detail, confirming that

the original proposition of measuring online, thermal, epithermal and fast components of

the flux with a precision better than 10%, was achievable. However, the unconventional

running conditions at MEGAPIE (temperature and low signals) oblige us to perform

several studies and tests in 2003 to verify the ability of the detectors to stand high

temperature and to check the new high sensibility acquisition system. This proposal has

been recently accepted by the MEGAPIE collaboration and our requirements concerning

the geometry and the insertion of the detectors have been fully taken into account in the

MEGAPIE target global design performed by SUBATECH/Nantes.

This project will allow to determine the neutronic performances of the first liquid Pb-Bi

spallation target whose results will define the next generation targets for the future ADS.

In addition, the time and space monitoring of the neutron flux, for a wide range of

energy, will provide the scientific community with experimental results in realistic

irradiation conditions for the validation of both generation and transport neutron codes.

Moreover, without any additional constraint, this project will offer a unique opportunity

to measure the incineration potential and the transmutation efficiency of minor actinides

in a realistic spallation neutron flux.

References

[1] F. Marie, M. Fadil, G. Fioni, S. Leray, D. Ridikas, H. Safa, C. Blandin, F. Groeschel,

E. Lehmann, “Measurement of the neutron flux at MEGAPIE”.

Proposition au Conseil Scientifique et Technique du DAPNIA/SPhN, 3-4 juin 2002.

[2] M. Fadil, D. Ridikas, O. Deruelle, G. Fioni, M.L. Giacri, A. Letourneau, F. Marie,

C. Blandin, S. Breaud « Feasibility study of new microscopic fission chambers

dedicated for ADS ». DAPNIA-02-243 (2002), Proceedings of 7th Information

Exchange Meeting on Actinide and Fission Product P&T (NEA/OECD),

Jeju, Korea, 14-16 October, 2002.

[3] J.C. Toussain, Evaluation des Ressources du projet de mesure du flux de neutrons

par des micro chambres a fission dans MEGAPIE, Rapport DAPNIA, nov 2002

[4] M. Fadil, Ch. Blandin, S. Christophe, O, Deruelle, G. Fioni, F. Marie, C. Mounier,

D. Ridikas, J.P. Trapp, Development of fission micro-chambers for nuclear waste

incineration studies. Nuclear Instruments and Methods A 476 (2002) 313-317


RESEARCH PROPOSAL

Title: TRADE Project (TRiga Accelerator Driven Experiment)

Experiment carried out at: ENEA-Casaccia Italy

Spokes person(s): C. Rubbia

Contact person at SPhN: S. Andriamonje

Experimental team at SPhN: S. Andriamonje, A. Delbart (SEDI), E. Ferrer (SEDI),

Y. Giomataris (SEDI), J. Pancin

List of DAPNIA divisions and number of people involved: SPhN (2), SEDI (3)

List of the laboratories and/or universities in the collaboration and number of people

involved: ANSALDO (2), CEA-DEN (6), DOE-USA (4), CERN (4), ENEA (18),

FZK (3), PSI (3)

SCHEDULEPossible starting date of the project and preparation time [months]: November 2002 [24]


Expected data analysis duration [months]: 72

REQUESTED BUDGETTotal investment costs for the collaboration: 60 M

Share of the total investment costs for SPhN: include in the CEA contribution

to the project (10 M for the duration of the project (5 years))

Investment/year for SPhN:

Total travel budget for SPhN: 90 k

Travel budget/year for SPhN: 15 k


If approved Allocated beam time: Possible starting date: November 2002


EXPERIMENTAL MEASUREMENTS ON THE TRADE PROJECT(TRIGA ACCELERATOR DRIVEN EXPERIMENT)

CEA-ENEA-CERN collaboration

The TRADE [1] project, which is part of the European Roadmap [2] towards the development of Accelerator DrivenSystems (ADS), foresees the coupling of a 110 MeV, 2 mA proton cyclotron with the core of a 1 MW TRIGA researchreactor. The aim of this proposal concerns the experimental measurement and instrumentation programme for theproposed project. That concerns in particular, the measurement of the neutron flux for different configurations of thereactor and the development of different techniques such as a micro fission chamber, a gamma ray spectroscopyassociated with “fast rabbit” system and a new neutron detector based on the Micromegas technology. After a summarydescription of the TRADE project and the actual status of the project, we describe briefly the experimental programme andthe technical instrumentation to be used for the different measurements.

I - SUMMARY DESCRIPTION AND ACTUALSTATUS OF THE TRADE PROJECT

In the European Roadmap towards the experimentaldemonstration of ADS (Accelerator Driven System) [2],several experiments are indicated which should allowvalidating the separated components of an ADS. This is thecase for the accelerator (IPHI, TRASCO), the target (e.g. theMEGAPIE experiments), the sub-critical core (the FEAT[3], TARC [4,5] and MUSE [6] experiments).The project named TRADE (TRiga Accelerator DrivenExperiment) is based on the coupling of a 110 MeV, 2 mAproton cyclotron with a 1 MW reactor of type TRIGA,operating at the ENEA Casaccia Centre (Italy). The reactorcore will be modified in order to run the experiment atdifferent levels of sub-criticality to explore the transitionfrom an “external source” dominated regime to onedominated by core thermal-feedbacks. Moreover, anessential modification will consist of inserting at the centerof the core a tungsten target for the production of spallationneutrons.The TRADE experiment is based on an original idea ofCarlo Rubbia, presented at CEA in October 2000.A first feasibility report was produced on June 2001 by anENEA (and partners: Ansaldo, CERN) and CEA WorkingGroup and delivered to the ENEA/CEA management on July2001.A Final Feasibility Report was prepared by the WorkingGroup on March 2002 and delivered to the ENEA/CEAmanagement on April 2002. The results of these new studiesconfirm the general conclusions of the 2001 report as far asfeasibility, and provide further credibility to a realisticimplementation of the experiment in the time horizon of2006-2008.The TRADE Final Feasibility Report was endorsed by theENEA/CEA management in its meeting of May 7, 2002.An external presentation – at international level - of theresults of the feasibility study was given in Rome, on June 7,2002.

After the 7 June meeting, the following main eventsoccurred:- Contact persons to define a common basis for an

international collaboration and further develop thevarious technical aspects of the project have beendesignated by the following 14 organizations: AAA(France), AIMA (France), ANSALDO (Italy), CEA(France), CIEMAT (Spain), CNRS (France), DOE(USA), ENEA (Italy), FZK (Germany), IBA (Belgium),JAERI (Japan), JRC (Germany), PSI (Switzerland),SCK.CEN (Belgium).

- Waiting for the formalisation of the internationalcollaboration on TRADE, all interested partners haveexpressed their feedback and comments to the workperformed by the Working Group within the feasibilitystudy. This temporary situation will evolve in time,when the different organisations will have expressedformally their commitments. At that point a distinctionit will be obviously made between organisationsfounding the project and those to be founded by theproject.

- The designated contact persons + experts in the differentfields have decided to meet periodically, on a two-month basis. The first three general progress meetingshave been held on July 23, in Paris, on September 4, inKarlsruhe and on October 23, in Rome. The nextgeneral progress meeting will be held on December 4, inParis.

- The TRADE Working Group, along with some expertsof the potential partners, has continued its activities anda progress report and some technical draft documentshave been prepared and presented at the aforementionedgeneral progress meetings.

- On June 7, 2002 an Expression of Interest – TRADE-PLUS – has been submitted to EC, in the frame of the 6th European Framework Program.

- A Memorandum of Understanding (MOU) among“founding” partners - ENEA, CEA, DOE and FZK – isprepared and under signature of the top management ofthe involved organizations.

II - EXPERIMENTS

The experiments of relevance to ADS development to becarried out in TRIGA concern:• The dynamic regime: the possibility to operate at somehundred kW of power and at different sub-criticality levels(0.90 ÷ 0.99) will allow to validate experimentally thedynamic system behaviour vs. the neutron importance of theexternal source and to obtain important information on theoptimal sub-criticality level both for a demonstrator and, byextrapolation, a transmuter.• Sub-criticality measurements at significant power.• Correlation between reactor power and proton current. Thiscorrelation can be studied at different sub-criticality andpower levels.• Reactivity control by different means and possibly byneutron source importance variation, keeping the protoncurrent constant. In principle, this can be obtained changingthe neutron diffusion properties of the buffer medium aroundthe spallation source (e.g. using different materials in theempty innermost fuel ring close to the target).• Start up and shut down procedures, including suitabletechniques and instrumentation.The TRIGA experiments will benefit from the extensiveexperimental techniques development performed in the zero-power MUSE experimental program. Most of theexperimental techniques will be directly applicable, inparticular in the domain of reactivity level measurement andmonitoring. Even if the TRIGA experiments are made in athermal neutron system, the frequency behaviour of thesystem transfer function is similar to its behaviour in a fastsystem. This fact makes of the TRIGA experiment a crucialprecursor of any future ADS larger size experiment. Thepossible different steps can be summarise in table 1.

Table 1 : Different steps of ADS project

Configuration Source Kinetics Powereffect

Time

MUSE DD/DT Fast No � 2003TRIGA DD/DT Thermal No 2003

�2006TRIGA Spallation Thermal No 2007TRIGA Spallation Thermal Yes 2007

ADS Spallation Fast Yes

As we can see from table 1, we approach the validation tothe ADS by not changing more than one parameter from oneconfiguration to the next.

III - MEASUREMENT CAMPAIGN

The detail of the experimental campaign is described inTRADE Final Feasibility Report – March, 2002. Threephases are proposed: In phase I (divided in two parts: phaseIA and phase IB), we will perform reference and ancillaryexperiments before the accelerator is installed. This phasecould be done partially in the second half of 2002 (phase IA)and, more widely, in the year 2003, and would require about

8 months of reactor operations. Phase II is performed afterall is installed, and is essentially the startup phase ofTRADE. This entails characterization of the spallationsource as well as rebuilding the core to its referenceconfiguration of phase I. For phase II, we envision 6 monthsof operations before we can begin the major experimentalcampaign of phase III. Phase III will then require two tothree years to complete, based on MUSE experience [6].

III.1 Phase IA: Reference subcritical core configurationfor TRADE (4 months)

As in the MUSE program, the first step will be themeasurements taken at a reference configuration which is atcritical or just subcritical. This reference must be reasonablyclose to the first subcritical configuration envisaged with theaccelerator. In addition, even though the accelerator has notbeen installed at this point, there should be somematerials/structures in the core that simulate the beam tubeand target.The approach to criticality in this configuration is performedin the standard way with the aid of the Am-Be startup source(which is normally placed in the periphery of the core, butfor this experiment it will be placed in the center in order toassess the source importance).

III.2 Phase IB: Experiments with DD and DT source(4 months)

The next step is to perform experiments with a DD and DTsource before the spallation source is assembled. This willprovide a much smoother transition from MUSE to TRADE.We will obtain source importance for Am-Be, Cf, DD, DT,and spallation neutrons in the same configuration. Becauseof the great uncertainties in cross-sections above 20 MeV,this step is almost essential to understanding the results wewill see at the higher energies.

III.3 Phase II: Start-up (6 months)

Concerning the start-up, the first shot of the acceleratorshould be produced when the core is exclusively loaded withinstrumented dummy elements (steel or depleted uranium-ZrH). This phase should be dedicated to the characterizationof the target spallation neutron source + residual spallationneutron source linked to beam losses along the beam pipe,etc.. The information provided by the ancillary experiencescan be precious in this phase, allowing having somereference points during the gradual loading of the core. Eachsuccessive configuration, in a reactivity scale, should bedriven by the spallation source at very low power(continuous mode) and signals from multiple in-core and ex-core detectors should be recorded and analyzed beforeproceeding to the next loading configuration. The earliermeasurements in Phase IA (reference) must be revisited atthis point.

III.4 Phase III: TRADE Experiments(2 to 3 years)

The future operation of an ADS at reference power (eg, 100MWth) requires an experimental program to validate theability to calculate parameters important to safety (e.g., βeff,fission rates) and the ability to monitor operating parameters(e.g., power to current relations, levels of sub-criticality,effects of feedback). The requirements for validation ofsafety and operational parameters lead to the types ofexperiments that must be performed:• Source importance• Flux distributions and reactor parameters• Reactivity measurements• Proton current/power relations• Power operation (startup and shutdown)

The experiments in a TRIGA reactor described here aredesigned to bridge the gap from MUSE to an operatingADS. At the same time, methods developed in the MUSEprogram will be validated in the TRADE experiments, thusdemonstrating a sort of `generic validation’ of methodsdeveloped in a fast system applied to a thermal system.

IV - INSTRUMENTATIONS

Most of the experiments are axed on the measurement of theneutron flux. In this issue we propose to use three types ofinstrumentation, which are already used in MUSE [6],TARC [4,5] and n_TOF [7]: - the micro-fission chamberdeveloped by the Cadarache DEN group [8,9], - Gamma rayspectroscopy associated with “fast rabbit” system incollaboration with the CERN group - and the new neutrondetector based on Micromegas technology developed by ourDAPNIA group in collaboration with the Cadarache DENgroup.

IV.1 Sub-Miniature Fission Chamber (SMFC)

Miniature fission chambers are the most widely used in-coreneutron detectors, in power and research reactors. Thisdetector is basically an ionisation chamber, one electrode ofwhich is coated with fissile material. The CEA/Cadarachehas been developing the miniature fission chamberstechnology for more than 40 years and the latestdevelopments are focusing on a new ∅1.5 mm fissionchamber (see Figure 1), the so-called "Sub-MiniatureFission Chamber (SMFC)". Compared to the classical 3 mmor 4.7 mm diameter fission chambers coated with 235U -usually used for mobile instrumentation in French PWRs -, atechnological gap was bridged with this small detector [8].The new SMFC technology is mainly characterised by theuse of a special nickel and alumina gas-tight feedthrough(external diameter of 1.3 mm) between the chamber bodyand the mineral cable [9] in order to contain the filling gas(argon) on the level of the sensitive part. The gas pressuremust be well controlled to have a constant neutron

sensitivity because the SMFC operates in current mode. Thedetail of the description and the results of different tests canbe found in reference [8].

Figure 1: Schematic views of the 1.5 mm cylindricalfission chamber [8]

IV.2 Measurement of high-energy neutron: Gammaray spectroscopy associated with “fast rabbit”system.

IV.2.1 Brief description of the “fast rabbit” technique

As we mentioned before, in the TRADE project, severalexperiments are planned for the validation of the safety andoperational parameters. One of them is the determination ofthe neutron flux distribution in the core. Spectral informationas a function of distance from the source is needed to studythe behaviour of different buffers and to be able to assesspotential materials damage.Unfortunately the neutron spectra can not be obtained usingonly one type of detector. To cover all the range of energy ofthe neutron produced, several detection techniques will beused. We propose to use two techniques: the first one isbased on gamma ray spectroscopy with GeHP detector andthe second one is the use of the new Micromegas detectordescribed in the next paragraph.In the gamma ray spectroscopy method, the neutron flux isdeduced from the intensity of the typical gamma ray emittedby the radioactive nucleus formed after neutron capture. Thehigh resolution of GeHP detector permits to distinguishwithout any ambiguity the typical gamma ray. As wellknown this type of detector is very sensitive to neutrondamage. The GeHP detector must be placed outside of thereactor environment. A pneumatic system named “fastrabbit” can be used [10] (see Figure 2). The sample isplaced in an appropriate shuttle. The shuttle is thentransferred by a pneumatic system from the irradiation portinside the core to a measurement port and inversely.

IV.2.2 Proposed measurements

The proposed system is dedicated to the measurement of theformed radioactive nucleus having a short lifetime.Close to the spallation target where fast neutrons areproduced, it is very interesting to measure the neutron fluxas a function of energy (especially 16N and 17N activation in

water). For that, the reactions 12C(n,2n)11C (threshold of22 MeV) and 12C(n,3n)10C (threshold of 34.5 MeV) can beused. The lifetime of the formed nucleus 11C and 10C are tooshort (20 mn and 19 s respectively), leading to a very shorttime for the transfer of the shuttle between the irradiationport and the measurement port.An example of the gamma spectra obtained with the specialcarbon shuttle is shown in Figure 3. The neutron flux arededuced from the number of counts under the 511 keV (the

result of the e+e– annihilation, following the + decay of11C) and 718 keV (10C) lines.

Figure 2: Schematic Layout of the "Fast Rabbit" system: a)View of the irradiation port; b) View of the gamma raydetection station where Vi (I = 1 to 6) = electrovalves, DRand DM optical detectors, PR and PM pressure gauges (Rfor Irradiation port and M for Measurement port) and SAcompressed air reservoirs c) Schematic view of the shuttle.

Figure 3: Gamma-ray spectrum from the irradiated special12C shuttle.

IV.3 Measurement of neutron spectra: the Piccolo-Micromegas

IV.3.1 Introduction

From recent results [11,12], it has been demonstrated that aMicromegas detector is excellent for neutronic studies at avery large energy range from thermal up to 100 MeV. Thedetector can be used not only for a neutron beam profiler but

also for neutron flux measurement for research withneutrons. An example is shown for the determination of thecharacteristic and performance of the CERN n_TOF facility[7]. For this experiment, an appropriate neutron/chargedparticle converter has been used (see Figure 4):(i) 6Li(n,α) for the neutron having an energy up to 1 MeV,(ii) H(n,n')H and 4He(n,n')4He for higher energy neutron.We propose to extend this method for the measurement ofneutron flux in-core environment. A fissionable elementsuch as 235U, 238U, 232Th or other can be used forneutron/charged particle converter.

The aim of this proposal is the new development of adetector used in particle physics for the use in reactorenvironment where the conditions are very different: thepresence of very high background of neutron and gammaand the operation in high temperature. One of the mainqualities needed for that detector is his high resistance to theradiation. Several experiments show that the Micromegasdetector meets with this requirement.In opposite of the usual Micromegas detector used in particlephysics experiment we propose to develop a compact andvery small detector (3 cm x 3 cm x 3cm) [13].

IV.3.2 Brief description of MICROMEGAS

The general description of the principle of Micromegas(MICRO-MEsh-GAseous Structure) technology can befound in references [14] and [15]. We describe here thetypical aspect of the proposed Micromegas detector for in-core measurement in reactor.An example of Micromegas neutron detector used in n_TOFexperiment [12] is reported in Figure 4. As shown in thisfigure, the amplification occurs between the mesh plane andthe microstrip plane. A small gap, of about 100 µm, betweenthe anode and cathode plane is kept by precise insulatingspacers. The device operates as a two-stage parallel plateavalanche chamber.

Figure 4: The principle of Micromegas for neutron detectorused in n_TOF experiment [12]

Ionization electrons, created by the energy deposition of anincident charged particle in the conversion gap, drift and canbe transferred through the cathode micromesh; they areamplified in the small gap, between anode and cathode,under the action of the electric field, which is high in thisregion. The electron cloud is finally collected by the anodemicrostrips, while the positive ions are drifting in theopposite direction and are collected on the micromesh.

A schematic representation of the proposed detector isshown in Figure 5 . The detailed description of the detectorcan be found in reference [13].

Figure 5: Schematic view of the Piccolo-Micromegasdetector for neutron spectrum measurement.

IV.3.3 - Construction and test of the detector

In TRADE project the estimated power is 1 MWatt, theexperimental condition is different compared with particleand nuclear physics experiments. We are in presence of thevery high background of neutron and in particular a gamma.A special study and test of the material that will be used forthe detector constituent (cell, cabling, etc) must beperformed. The experiences of the DEN Cadarache physicistare necessary to perform in good conditions the detector. Wenote that this future measurement is the extension of theMUSE programme [6].Usually a flowing gas is used in Micromegas, in the presentcase it is not convenient to have a long gas tube for this task.A test of the detector placed in sealed box filled byappropriate mixed gas and in operational pressure is needed.The possibility to use a flowing gas with a very small andspecial bottle of the pre-mixed gas will be envisaged. Thismethod is already used in space experiment, permitting acompensation of the possible micro leaks of the detector boxand gas renewal if it is necessary.The construction of the drift electrode equipped by 6Li or10B, 235U and other fissile elements will be performed withthe DEN Cadarache collaboration. The experience acquiredfor the development of Cadarache ionisation chamber [8]will be relevant for the design and construction of theproposed special Micromegas detector.The combination of both type of detector such as a ionisationfission chamber actually used in MUSE [6] experiment andthe new proposed Micromegas permit to obtain in goodconditions the neutronic parameters needed in TRADEproject. A large part of the neutron spectra can be obtained.Examples of the first preliminary results from the n_TOFexperiment are shown in Figure 6. In this figure is reportedthe time converted to equivalent neutron energy of therelative flux seen by Micromegas detector, for the resultobtained from the 4He + (3.8%)iC4H10 and Ar + (2%)iC4H10

respectively.

Figure 6 shows clearly the 1/v response at lower energiesand the resonance at 250 keV characteristic of the 6Liconverter. At higher energy (several MeV) there is a largebump as a consequence of the increase of neutron fluence inthis energy (spallation peak) and also the increase of detectorefficiency provided by the detection of recoil nuclei from thefilling gas. Several deeps are observed in the energiescorresponding to the different elastic resonances of the 16O.This is the result of the dispersion of neutron of thoseenergies from the main beam by the oxygen present in thewater used for cooling of the spallation lead target. The shift,observed in the figure between the two plots, is the result ofthe presence of the elastic resonance of the 4He(n,n')4Hereaction.The use of the pre-mixed gas of 4He + iC4H10 or otherquencher combined with the four neutron/charged particlementioned before allows to obtain a large part of the neutronspectra of the TRADE project.One of the advantages of Micromegas is the possibility tomeasure simultaneously neutron, alpha and fission. Inaddition, at low neutron flux it is possible to count one byone the incident particle using a low noise preamplifier. Atvery high counting rate (~ 1 GHz) only a continuous currentmeasurement can be used.

Figure 6: Relative flux (counts rate) of the n_TOF neutronbeam seen by Micromegas detector as a function of theneutron energy.

V CONCLUSION

After pioneering works on ADS such as FEAT, TARC andMUSE we propose to perform a pilot experiment, whichwould be the first example of ADS component coupling “atreal size”. ENEA-CEA collaboration has elaborated afeasibility study of the project; the experimental campaign isextended to international collaboration.Inside this collaboration our proposal consists on thetransposition of the different techniques already used in thepreliminary study of the ADS project to TRADE. Inaddition, we propose to develop a new generation of neutrondetectors able to measure directly the fast neutron spectrum.

REFERENCES

[1] The TRADE Working group, “TRiga AcceleratorDriven Experiment (TRADE)” Feasibility Report.ENEA Report, March 2002.

[2] The European Technical Working Group on ADS,“A European Roadmap for Developing AcceleratorDriven System (ADS) for Nuclear WasteIncineration”, April 2001.

[3] S. Andriamonje et al , “Experimental determinationof the energy generated in nuclear cascades by ahigh energy beam”, Phys. Lett. B 348 (1995) 697.

[4] H. Arnould et al, “Experimental Verification ofNeutron Phenomenology in Lead andTransmutation by Adiabatic Resonance Crossing inAccelerator Driven System” Phys. Lett. B 458(1999) 167.

[5] A. Abanades et al, “Experimental verification ofneutron phenomenology in lead and transmutationby adiabatic resonance crossing in acceleratordriven systems A summary of the TARC project atCERN”, Nucl. Instr. & Meth. A 463 (2001) 586.

[6] M. Salvatores et al., “MUSE-1: a first experiment at MASURCA to validate the physics of sub-critical

multiplying systems relevant to ADS” – 2nd ADTTConference, Kalmar, Sweden, June 1996.

[7] C. Rubbia et al., “A High Resolution SpallationDriven Facility at the CERN--PS to MeasureNeutron Cross Sections in the Interval from 1 eVto250 MeV”, CERN/LHC/98-02 (EET) (1998) and“a Relative Performance Assessment”,CERN/LHC/98-02 (EET)-Add. 1, Geneva, 15 June1998.

[8] G. Bignan and J.C. Guyard (1994), “Sub-miniatureFission Chamber with Tight Feedthrough”, PatentCEA N°94-14293.

[9] O. Poujade and A. Lebrun (1999), “Modeling of theSaturation Current of a Fission Chamber takinginto Account the Distortion of Electric Field due toSpace Charge Effects”, Nucl. Instr. & Meth, A443,673-682.

[10] TRADE Experimental Working group (CEA,ENEA, CERN) “The “Fast Rabbit” system for highenergy neutron measurement in the TRADEproject” October 2002.

[11] S. Andriamonje et al, “Experimental studies of aMICROMEGAS neutron detector”, Nucl. Instrum.Methods A 481 (2002) 36-45.

[12] S. Andriamonje et al, “The Micromegas neutrondetector for CERN n_TOF” to be published,Nucl. Phys. B, Proceedings of the InternationalConference on Advanced Technology andParticle Physics, Como-Italy (2001).

[13] S. Andriamonje et al “Micromegas detector for in-core measurements” TRADE working group reportApril 2002.

[14] Y. Giomataris et al., “A high-granularity positionsensitive gaseous detector for high particle-fluxenvironments”, Nucl. Instr. & Meth. A376 (1996)29.

[15] G. Charpak et al., “First beam test results withmicromegas, a high rate, high resolution detector”,CERN LHC/97-08(EET), DAPNIA-97-05.



Title: Modeling of transmutation systems, neutron and RNB production

Date of the first CSTS presentation: 07 June 2001

Experiment carried out at: DAPNIA/SPhN

Spokes person(s): Danas RIDIKAS

Contact person at SPhN: Danas RIDIKAS

Experimental team at SPhN: Pavel BOKOV, Marie-Laure GIACRI, Danas RIDIKAS

List of DAPNIA divisions and number of people involved: SPhN; 1 permanent +

1 PhD student started on 1 October 2002 + 1PhD student started on 2 December 2002)


CEA/DEN: 2, KFKI Budapest (Hungary): 2 , Physics Institute (Vilnius, Lithuania): 3, LANL (USA): 2,

KAERI (Korea): 1.

SCHEDULE

Starting date of the experiment [including preparation]: the project continues




Final results foreseen for:

BUDGET 2003 Total Already Used

Total investment costs for the collaboration: 22kEuros 0

Share of the total investment costs for SPhN: 0 0Total travel budget for SPhN*: 10kEuros 0* Normally included/requested within the Mini-Project.


Status Report on Modeling of Nuclear Systems by D. Ridikas, CSTS of DAPNIA/SPhN, 16 December 2002.

Modeling of Transmutation Systems, Neutron and RNB Production(Status Report for the period of Oct. 2001 – Oct. 2002)

Danas RIDIKAS

E-mail: [email protected]

CEA Saclay, DSM/DAPNIA/SPhN, F-91191 Gif-sur-Yvette Cedex, France

In the frame of the Mini-Inca project - integral measurements relevant to nuclear wastetransmutation systems -- neutron beams delivered by the High Flux Reactor (HFR) of the

Institut Laue-Langevin (ILL) in Grenoble are used. Complex computer code systems wereimplemented to simulate

(initially)• Neutron fluxes inside the experimental Mini-Inca tubes, and

(afterwards and presently)• Innovative critical and sub-critical nuclear systems;

• Neutron sources based on spallation and photonuclear reactions;• Radioactive nuclear beam production scenarios.

A number of projects being either completed, or in progress, or planned in the near future will

be given.

Introduction

So far, there was no quantitative and consistent study of the neutron fluxes accessible for

Mini-Inca in the newly installed V4 channel in the HFR of ILL Grenoble. In this context westarted our modeling activities in 2000 by performing a number of detailed calculations of the

fuel evolution and the corresponding comparison (time- and spatial-dependence) of theneutron fluxes both in the reactor active core and experimental channels. Our investigations

showed that neutron fluxes in the experimental channels V4 and H9 are not changed (both inabsolute value and energy spectra) due to the burn-up of the fuel element or move of the

control rod. This result simplifies most of the irradiation experiments (and data analysis inparticular), which employ the above experimental channels. Recent flux measurements

performed in V4 with microscopic fission chambers agree well with our model predictions.

As long as the transmutation of nuclear waste is concerned, initially we decided to look forinnovative nuclear systems, being critical or sub-critical, characterized by neutron fluxes

(thermal-epithermal) similar to ones presently available for the Mini-Inca installation. A HighTemperature Reactor (HTR), where neutrons are efficiently moderated by graphite, was our

starting point for this type of investigations. Later on, our studies have been extended also tothe systems characterized by fast neutrons.

Section 1 presents a brief summary of our simulations related to the modeling of the HTR,

namely a gas turbine-modular helium reactor (GT-MHR). By now system's performance as afunction of either different data libraries used (ENDF, JEF, JENDL) or different geometry

description (homogeneous versus single-heterogeneous and double-heterogeneous) has beeninvestigated in detail within a Monte Carlo approach.


Section 2 is also dedicated to the problematic of transmutation. In this case, a molten salt sub-

critical transmutation blanket, driven by a fusion device (external neutron source), is modeled.We have finished a series of optimization calculations, where the system was characterized as

a function of different treatment of fission products, different TRU feeding options andvariable moderation of the neutron flux.

Section 3 reports on our progress made on modeling of the photonuclear reactions, namely

(g,n), (g,2n) and (g,fiss), and their potential applications for the neutron and RNB production

as well as for the transmutation of nuclear waste. Benchmarking of the new code system and

photonuclear data library was completed and some preliminary complex system simulationshave been started (RNB production target based on photo-fission, neutron irradiator driven by

electron accelerator, nuclear waste transmutation in high photon and neutron fluxes, bothcreated by electron beams).

Section 4 introduces our new initiative, where (in cooperation with CEA/DEN) a

deterministic safety analysis procedure in the case of advanced nuclear systems for nuclearwaste incineration, will be developed. A co-financed PhD thesis work on this subject will start

in Dec. 2002.

In a close cooperation with DAPNIA/SDA we intend to participate in a new project related tothe characterization of concrete and graphite originating from the accelerator installations

and/or nuclear reactors to be shutdown. This initiative is briefly presented in Section 5.

Within the Mini-Inca project, two theoretical investigations related to the European MegaPieinitiative have been completed (see Section 6). These include: a) a detailed feasibility study

on the use of microscopic fission chambers dedicated to the neutron flux and incineration ratemeasurements in the MegaPie target; b) estimations of Po-210 formation and losses from the

solid Bi-209 target irradiated in the thermal neutron flux in the HFR of ILL Grenoble.

Finally, Section 7 briefly summarizes our activities on the modeling of the RNB productiontechniques. Here our participation and contribution to the SPIRAL-2 (GANIL) and EURISOL

(EU) projects is underlined.

We note separately that each Section provides only a brief summary of the latest results, whilea more detailed description of the corresponding investigations can be found in the References

provided separately.

1. Modelling of HTRs with Monte Carlo: from homogeneous to an exact heterogeneous

core with micro-particles (project continues; possibility for a future project)

PhD thesis work, Oct. 2000 - Oct. 2003, Vytautas Magnus University and Physics Institute (LT)

Financed by NATO, Physics Institute (LT), DRI&MAE, DSM/DAPNIA/SPhN

Other interested parties: General Atomics, Framatome, CEA/DEN-SERMA, Physics Institute (LT)

[1] D. Ridikas et al., “Comparative Analysis of the ENDF, JEF and JENDL Data Libraries by Modeling High

Temperature Reactors (GT-MHR) and Plutonium Based Fuel Cycles”, Journal of Nuclear Science and

Technology, S2 08/02 (2002) 1167.

[2] D. Ridikas, R. Plukiene, “Modeling of HTRs: from Homogeneous to Heterogeneous Geometry with Monte

Carlo”, Proceedings of ANS RPD Topical Meeting PHYSOR2002, October 7-10, 2002, Seoul, Korea; in print.

[3] R. Plukiene and D. Ridikas, “Modeling of HTRs with Monte Carlo: from a Homogeneous to an Exact

Heterogeneous Core with Micro-Particles”, submitted for publication to Annals of Nuclear Energy; also

available as internal report DAPNIA-02-242, CEA Saclay, September 2002.


Gas-cooled reactor technologies (e.g. GT-MHR) seem to offer significant advantages inaccomplishing the transmutation of plutonium isotopes and nearly total destruction of

239Pu in

particular. GT-MHR uses a variable in time neutron spectrum, operates at high temperatureand employs ceramic-coated fuel. It utilizes natural erbium as a non-fertile burn-able poison

with the capture cross section having a resonance at a neutron energy such that ensures astrong negative temperature coefficient of reactivity. The lack of interaction of neutrons with

coolant (helium gas) makes sure that temperature feedback is the only significant contributorto the power coefficient. As a matter of fact, no additional plutonium is produced since no238

U is used. A gas-cooled high temperature reactor or a separate irradiation zone in the centerof GT-MHR assembly, coupled to an accelerator, could also provide a fast neutron

environment due to the same reason - the helium coolant is essentially transparent to neutronsand does not change neutron energies. Since other actinides with an exception of plutonium

are more inclined to fission in a fast neutron energy spectrum, one could consider anadditional fast stage, following a thermal stage, in order to eliminate the remaining actinides.

Recently, we investigated two different aspects related to the above system: a) performance of

HTR depending on the data libraries used [1], and b) performance of HTR depending on thegeometry description [2,3].

In the 1st study we performed detailed simulations in order to compare different sets of data

libraries in terms of keff eigen-values, the length of the fuel cycle, neutron characteristics andthe evolution of fuel composition in particular. In all cases the same Monteburns code system

was used making our results dependent only on the evaluated data tables. We showed that ingeneral the performance of GT-MHR is not considerably influenced by the choice of the data

libraries employed. Nevertheless, a number of major differences among ENDF, JENDL andJEF data files were identified and quantified in terms of the averaged one-group cross sections

both for military (MPu) and civil (CPu) plutonium based fuel cycles. This study was intendedto provide the first guidelines for experimental programs, where the measurements of fission

and capture cross-sections were planned.

The main goal of our 2nd

study was to compare the performance parameters of the GT-MHRcore in the once-through cycle as a function of different geometry representation, i.e.

homogeneous (HTR1), single-heterogeneous (HTR2) and double heterogeneous (HTR2),including micro-particles, within Monte Carlo approach. We have shown that it is very

important to model the reactor geometry as precise as possible in order to characterizeproperly the performance of the system (e.g., keff, its behavior with time, the length of the fuel

cycle, burn-up, etc.). In brief, a significant difference was found in keff values between HTR1,HTR2 and HTR3 both at the beginning of the fuel cycle as well as in its evolution as a

function of burn-up. keff of HTR2 and HTR3 starts at higher values and it decreasesconstantly. Contrary, keff of HTR1 begins at much lower value, increases to its maximum and

later decreases. In addition, HTR3 fuel cycle ends much faster compared to the other twocases. A different behavior of keff is explained by different modeling of burn-able poison(homogeneous versus heterogeneous distribution) and also by an enhanced self-shielding

effect in micro particles (single-heterogeneous versus double-heterogeneous geometry).Consequently, the burn-up of erbium and changes in isotopic fuel composition (e.g.,

240Pu and

241Pu) is rather different during the fuel cycle.

We note separately that the system was modeled exactly in 3D without any approximations.Therefore, our study could serve as a reference calculation for other complementary and


independent investigations (e.g., deterministic approach), and the physicists from CEA/DEN-

SERMA have already expressed their interest in a potential cooperation.

2. Modeling of fusion-fission hybrid system for nuclear waste incineration (project

continues)

PhD thesis work, Oct. 2000 - Oct. 2003, Vytautas Magnus University and Physics Institute (LT)

Financed by NATO, Physics Institute (LT), DRI&MAE, DSM/DAPNIA/SPhN

Other interested parties: TSI Research (US), Physics Institute (LT)

[1] R. Plukiene, D. Ridikas and E.T. Cheng, "Fusion-fission Hybrid System for the Transmutation of TRU",

Proceedings of the XIX International Autumn School on New Perspectives with Nuclear Radioactivity, 8-13 Oct.

2001, Lisbon, Portugal; also available as internal report DAPNIA-02-04, CEA Saclay, March 2002.

[2] D. Ridikas, R. Plukiene and E.T. Cheng, "Fusion-fission Hybrid System for the Transmutation of Minor

Actinides", Proceedings of the International Workshop on Fast Neutron Physics, 5-7 Sep. 2002, Dresden,

Germany; DAPNIA report is in preparation.

An intensive neutron source is needed for the transmutation process of nuclear waste. Aplasma based fusion device is naturally a candidate neutron source. We analyzed a typical

molten salt (flibe) blanket, driven by a plasma based fusion device, dedicated to burn eitherTRU or MAs extracted from the LWR spent fuel. Performance parameters such as kscr, burn-

up, fluxes and equilibrium conditions were quantified to assess the characteristics of a flibebased transmutation plant. It seems that nearly 1.1 metric tons of spent fuel TRU can be

burned annually with an output of 3GWth fission power. Detailed burn-up calculations showthat equilibrium conditions of the fuel concentration in the flibe transmutation blanket could

be achieved, provided that fission products were removed at least in part and fresh spent fuelTRU was added during burn-up on-line.

A negative result of this investigation was that a considerable amount of Cm isotopes was

accumulated at the end of the fuel cycle. For this reason we had to optimize the systemtowards its better performance. In our new scenario the fusion-fission hybrid system starts

with a typical TRU vector but is replenished only by MAs originating from the used fuel. Cmaccumulation now is controlled thanks to the thermal component of the neutron flux. In

addition, nearly 1.1 metric tones of pure MAs are incinerated annually in this particularscenario. Our future study will concentrate on the sensibility investigations of the system as

above (dominated by minor actinides in the fuel load) due to the different data libraries used,namely ENDF, JENDL, JEF.

3. Electron Driven Systems: from material irradiation to nuclear waste incineration

(future project)

PhD thesis work, Oct. 2002 - Oct. 2005 (Caen University), CFR fellowship, financed by DSM/DAPNIA

Other interested parties: CEA/DEN, KFKI (Hungary), KAERI (South Korea), LANL (US)

[1] P. Vertes, D. Ridikas, “Some Test Calculations with the IAEA Photonuclear Data Library”, Journal of

Nuclear Science and Technology, S2 08/02 (2002) 1049.

[2] D. Ridikas, P. Vertes, "Code and Data Benchmarking with the New IAEA Photonuclear Data Library",

Proceedings of the 12th Biennial Topical Meeting of the Radiation Protection and Shielding Division (RPSD) of

the American Nuclear Society (ANS), Santa Fe, New Mexico, USA, 14-18 Apr. 2002.

[3] D. Ridikas, H. Safa and M.-L. Giacri, “Conceptual study of neutron irradiator driven by electron accelerator”,

Proceedings of the 7th Information Exchange Meeting on Actinide and Fission Product P&T (NEA/OECD),

Jeju, Korea, 14-16 Oct., 2002.

[4] D. Ridikas, S. Benomard, M.-L. Giacri, “Incineration of Nuclear Waste in High Intensity Photon Fluxes”,

DAPNIA report in preparation.


[5] D. Ridikas, H. Safa and B. Bernardin, “A prototype beta compensated reactor (BCR) driven by electron

accelerator”, Proceedings of ANS RPD Topical Meeting PHYSOR2002, Oct. 7-10, Seoul, Korea.

Recently, a world-wide interest in photonuclear processes is experienced, what is motivated

by a number of different applications such as shielding problems of medical or fundamentalresearch accelerators, the need of new cost effective neutron sources, transmutation of nuclear

waste either directly by photons or by neutrons created from photonuclear reactions,radioactive nuclear beam factories based on photo-fission, etc. We have started our activity in

this domain by code and data benchmarking calculations [1, 2].

Encouraged by the above results, we proposed a new study (PhD thesis work) based onelectron driven systems (EDS). Within this project three major aspects will be investigated:

a) Spallation neutron sources, though very effective in neutron production, are large,

expensive and presently would involve certain difficulties in their operation (e.g., high-energyhigh-intensity proton beam trips). Contrary, an electron driver, although much less effective in

neutron production, is rather cheap and compact machine that, at the same time, might bringadvantages in terms of reliability. Here we would like to investigate the use of an external

neutron source (irradiator) driven by an electron accelerator. A schematic layout and design ofa compact neutron irradiator has already been proposed with its neutronics being analyzed and

discussed [3]. The system (preliminary) is based on a spherical geometry in which an electronbeam interacts with the target-envelope. Neutrons are produced in the natural or enriched

uranium by photonuclear reactions. The system is well sub-critical (keff < 0.8) and uraniumenrichment is below 20%. Neutron balance is optimized in terms of different geometry and

material configurations. Our preliminary calculations show that variable (up to 10% thermaland/or up to 30% with energies higher than 1 MeV) neutron fluxes of a few 10

14 n*s

-1*cm

-2

could be obtained for different irradiation purposes. An electron machine of ~8 MW powerand 100 MeV incident energy should be sufficient to produce external neutrons to drive the

system. Further optimization studies will continue.

b) With a recent progress made in high intensity electron accelerators a nuclear wasteincineration in high gamma fluxes are worthwhile being reexamined. In this context a new

calculation code for material evolution in photon environment will be developed in a closecooperation with the LANL (US). A photonuclear data library and corresponding routines will

be incorporated into the CINDER'90 evolution code, and therefore material and/or nuclearfuel evolution in a multi-particle flux (neutrons, protons and gammas) will be possible for the

first time.

Our preliminary analysis on nuclear waste incineration with gammas [4] shows that some ofthe long-lived fission fragments (e.g., Zr) or actinides (e.g., Np) can be efficiently incinerated

in the gamma fluxes of the order of 1017

-1018

g*cm-2

*s-1

. For comparison, we note that similar

incineration speed could be reached also in the neutron fluxes of the order of

1015

-1016

n*cm-2

*s-1

.

c) Present critical nuclear reactors would not be able to burn all long-lived nuclear wasteproduced and accumulated during last 40 years. Indeed, it would be extremely dangerous to

operate standard PWR reactors with a high content of actinides in the fuel due to a very smallnumber of delayed neutrons. Therefore, dedicated Accelerator Driven Systems (ADS) have

been envisaged for nuclear waste transmutation. Coupling an external nuclear source(typically high energy protons producing neutrons by spallation) to a sub-critical assembly


enables to run safely the system even without any delayed neutrons. But until now, ADS have

been facing a number of difficulties. The accelerator part by itself is a very long (300 to 500meters) and quite expensive (150 to 300 MEuros) item with extremely stringent requirements

(less than one trip a month). Very high beam power is required if the nuclear assembly has tooperate in a well under-critical regime (keff = 0.90 to 0.95). In addition, the nuclear part would

demand long and extensive fuel development for fabrication and processing.

Recently we have proposed an unusual system eliminating most of the problems encounteredin conventional ADS [5]. The accelerator is an electron machine, and neutrons are produced

in a uranium carbide target by photonuclear rather than spallation process. Under operation,the nuclear assembly is slightly under-critical with an effective multiplication factor of keff =

0.995 to 0.997. On the other hand, there is a dynamic feedback between the neutron fluxmeasured and the intensity of the external source of neutrons to simulate the existence of

delayed neutrons. The delayed neutrons, which are not created in sufficient quantity in a fueldominated by minor actinides, are supplemented by delayed neutrons coming from the

external source in order to guarantee the controllability of the system and its safety. So, thewhole system (under-critical core plus external source having a suitable feedback) has the

behavior of a critical system and control rods are used to control it like a traditional reactor.This kind of system is called Beta Compensated Reactor (BCR) after the fraction beta of

delayed neutrons. A schematic layout and design of a small demonstrator (50 MWth) wasproposed based on a high temperature reactor core using standard particle fuel with its

neutronics being analyzed and discussed. We note separately in this connection that anelectron driven sub-critical facility IBR-30 with a multiplication factor of 200 (or keff ~ 0.995)

have been operating successfully for nearly 30 years as a pulsed neutron source for nuclearmeasurements at JINR Dubna in Russia.

Further optimization studies on the three aspects as above will be carried as a function of

different geometry and material configurations including some safety and radioprotectioninvestigations in particular. A direct and quantitative comparison with other innovative

systems based on spallation processes will be established and quantified in detail.

4. Deterministic Safety Study of Advanced Nuclear Systems Dedicated for Nuclear

Waste Incineration (future project)

PhD thesis work, Dec. 2002 - Dec. 2005 (University of Grenoble), CTBU fellowship, financed by DSM & DEN

Interested parties: CEA/DEN, CNRS/IN2P3

[1] I. Slessarev, P. Bokov, “Deterministic Safety Study of Advanced Molten Salt Nuclear Systems for

Perspective Nuclear Power”, Technical Note Note NT02-407 (2002), CEA Cadarache, DEN/DER/SPRC/LEDC.

Current problems of Nuclear Energy such as long-lived nuclear waste, simplification of fuelcycles as well as their protection against weapon proliferation, safety enhancement, and

expansion of fuel reserves gave birth to numerous of innovative concepts. In principle, manyof these problems could be solved if more neutrons were available per fission taking place in

a core. This neutron surplus would allow to use natural fuels such as U and Th, simplifyand/or eliminate the necessity of irradiated fuel reprocessing, expand fuel reserves and

improve resistance to proliferation. As a matter of fact, most of the safety enhancements alsocan be realized with the help of supplementary neutrons: a) either directly for well sub-critical

systems, say, keff ~ 0.95 or b) indirectly for slightly sub-critical systems, say, keff ~ 0.99 ifthese neutrons are delayed with respect to prompt fission neutrons. Taking into account that

the fraction of delayed neutrons in a critical reactor, and particularly in incinerators, is very


limited, some supplementary delayed neutrons might be sufficient to enhance system's safety

radically.

Production of supplementary neutrons can be realized in "hybrid" systems where fission offuel takes place in a sub-critical core simultaneously with supplementary external neutrons

produced via spallation, thermo-nuclear fusion or photonuclear reactions. It is clear that asuitable sub-criticality should be chosen in order to improve safety but, at the same time, not

to worsen economics and simplicity of the system. What is this optimal and still safe sub-criticality level, how does it depend on the character of the system itself (e.g., fast neutrons

versus thermal, solid fuel versus molten, cooling by gas versus liquid, etc.)? In this context adeterministic safety analysis procedure will be developed with two major aspects: the choice

of initial level of sub-criticality and study of multiple unprotected transients with realistic feedback effects. A direct comparison among different sub-critical systems including critical

reactors will be established. A particular emphasis will be given to characterize the safety ofslightly sub-critical systems, for example Beta Compensated Reactor (BCR) as introduced in

the previous Section.

5. Simulations and experiments related to the characterization of the concrete and

graphite originating from the accelerator installations and/or nuclear reactors to be

shutdown (future project)

Scientific visitor for 1 year (PhD student) in 2003; financed by DRI and DSM/DAPNIA/SPhN

PostDoc 2003-2004; financed by DAPNIA/SDA and DAPNIA/SPhN (to be confirmed)

Other interested parties: DAPNIA/SDA, DEN, EDF, Framatome, Physics Institute (LT)

A typical procedure related to the closure of nuclear installation (particle accelerators, nuclearreactors, etc.) definitely requires a good characterization of irradiated materials both due to

the radioprotection and economical reasons. In this costly operation both experimental andtheoretical approaches should be combined. In a close collaboration with DAPNIA/SDA and

Physics Institute of Lithuania we plan to initiate a new project related to the classification ofconcrete (shielding material) and graphite (moderating material) originating from the nuclear

installations.

DAPNIA/SPhN will contribute to the modeling and theoretical predictions of radio-activitiesin the realistic conditions. The results will be compared to the experimental data from

dedicated experiments performed by DAPNIA/SDA, Physics Institute (LT), and probably byDAPNIA/SPhN. After the theoretical approach is validated, the rest of the classification of

irradiated materials will be based on the calculations.

6. Theoretical work related to the MegaPie Project within Mini-Inca (project continues)

Other interested parties: CEA/DEN, PSI (Switzerland), MegaPie collaboration, IPPE Obninsk (Russia)

Financed by DAPNIA/SPhN, DRI&MAE

[1] M. Fadil, D. Ridikas et al., "Feasibility study of new microscopic fission chambers dedicated for ADS",

Proceedings of 7th Information Exchange Meeting on Actinide and Fission Product P&T (NEA/OECD), Jeju,

Korea, 14-16 October, 2002; also available as internal report DAPNIA-02-243, CEA Saclay, Sep. 2002.

[2] D. Pankratov, S. Ignatiev, D. Ridikas and A. Letourneau, "Estimation of Po-210 losses from solid Bi-209

target irradiated in a thermal neutron flux", accepted for publication by Annals of Nuclear Energy; also available

as internal report DAPNIA-02-241, CEA Saclay, Sep. 2002.


Within the Mini-Inca project (DAPNIA/SPhN), two theoretical investigations were initiated

and completed:

a) A detailed theoretical feasibility study, related to the neutron flux and incineration ratemeasurements in the MegaPie target has been performed. We showed that in principle with

the newly developed mFCs, adopted accordingly for the particular MegaPie target conditions,

both thermal and fast components of the neutron flux could be determined experimentally

including their time- and space-variations on-line. These measurements should bring a muchbetter understanding of the macroscopic and, in some sense, microscopic processes involved

in high power spallation targets and will provide highly requested quantitative data to testsimulations codes, both for neutron generation and transport in realistic geometries. We also

pointed out that this feasibility study can be easily generalized for other ADS projects, whereneutron fluxes of the order of 10

14-10

15 n*cm

-2*s

-1 are expected.

b) A brief summary of Po formation processes and release mechanisms from polonium-

contained media was investigated. Quantitative estimations of Po-210 losses from the solidBi-209 target irradiated in the thermal neutron flux were given as an example. We showed

that not more than 1% of the created Po could be lost in the most penalizing scenario. Thisresult is extremely important for the neutron capture cross section measurements, where alpha

activity of Po-210 is an observable (see the Mini-Inca project presented at this CSTS). Inaddition, a similar approach on Po formation and release estimates could be easily applicable

for other applications such as ADS for nuclear waste transmutation, neutron spallationsources, RNB production targets, etc., where either solid or molten metals containing Po or

other volatile substances are present.

7. Simulations related to the production of RNB (project terminated)

PostDoc of 6 months in 2002; financed by EURISOL and DSM/DAPNIA/SPhN

Other interested parties: IPN Orsay, GANIL, EURISOL

[1] D. Ridikas, "Production of neutron-rich fragments for SPIRAL-2: neutrons or photons? ", Proceedings of the

International workshop on drip-line nuclei HALO'02, Goteborg, Sweden, 13-15 June 2002.

[2] A. Plukis and D. Ridikas, "Characterization of Energy Deposition and Outgoing Particles for W, Hg and UCx

targets of EURISOL", to be published within EURISOL final report (2002); available as internal report

DAPNIA-02-265, CEA Saclay, Oct. 2002.

Two interlinked projects dealing with the RNB production scenarios kept us busy, namely

a) investigations related to the future options to produce intense neutron-rich beams atGANIL [1], and

b) characterization of energy deposition in direct- and converter-targets typical for theEURISOL project [2].

In the 1st study, as requested by “Conseil Scientifique du GANIL”, we investigated in detail

the production of neutron-rich fission fragments via photo-fission. An innovative productiontarget design was proposed with detailed estimates of expected fission rates and possible

intensities of the secondary beams. The study also included heat deposition calculations,radioprotection issues and cost evaluations. A part of this work was included in the final

report on “SPIRAL II : Preliminary Design Study”, Nov. 2001, GANIL R 01 04.

The 2nd

study was performed in the frame of the EURISOL project, where we presented thecalculations of 1 GeV proton beam interacting with different targets. Natural tungsten,

mercury and UCx were considered as target materials. Total energy deposition was estimated


including its spatial distributions all over the target. In addition, outgoing particle (neutron,

proton and photon) energy spectra and angular distributions were provided.

Conclusions

In this report I have outlined a number of different investigations related to the modeling of

complex nuclear systems as critical and sub-critical nuclear systems, future RNB factories andneutron production facilities. A sophisticated code systems have been employed to simulate

realistic 3-D geometries with a possibility to transport charged particles (p, d, e, ...) as well asneutrons and gammas with Monte Carlo techniques including time-dependent evolution of

nuclear fuels and/or irradiation/production targets.

I believe that I have shown that there is a possibility to link the understanding of fundamentalphysics, being either experimental or theoretical, to a variety of exciting applications. I also

hope that the above activities will be supported and encouraged to continue, and evenstrengthened in the future.

Budget and manpower

The total amount of man power working on this project will be (1 permanent + 2PhD).

1 scientific visitor (PhD student) will join us in 2003 for 1 year (fully financed by DRI).

DAPNIA/SDA most probably will finance 1 PostDoc for the period of 2 years (2003-2004).

We would need another PostDoc for the period of 2 years if one thinks that modelling of HTR

and cooperation on this subject with CEA/DEN-SERMA is worthwhile continuing. The HTRproject proposed by H. Safa et al. (if supported) eventually might be a solution in this

particular case.

The budget for 2003 is ~22 kEuro (financed by DAPNIA/SDA) for the purchase and

technical support of a new computer cluster (4-6 bi-processor units) based on PC/LINUX OSto be operational at DAPNIA/SPhN shortly.

The budget for missions is ~10 kEuro, and normally is previewed/requested by the Mini-

Inca project.


RESEARCH PROPOSAL

Title: BASIC NUCLEAR PHYSICS FOR HIGH TEMPERATURE REACTORSExperiment carried out at:

Spokes person(s): Henri SAFA

Contact person at SPhN:

Experimental team at SPhN:



DEN / DDIN / SF, DEN / DM2S, DEN / DEC

SCHEDULE

Possible starting date of the project and preparation time [months]: 01 / 01 / 03



REQUESTED BUDGET


Share of the total investment costs for SPhN: 240 k€

Investment/year for SPhN: 90 k€


Travel budget/year for SPhN:




BASIC NUCLEAR PHYSICS FOR HIGHTEMPERATURE REACTORS

H. Safa,CEA Saclay, DSM/DAPNIA/SPhN

91191, Gif-sur-Yvette, France

Abstract :

A possible next generation of future nuclear power plants is looking at the useof high temperature reactors (HTR) cooled by helium. An important R&D effort havebeen initiated by the CEA in order to cover all the important aspects needed for thiskind of reactor in France. Thanks to previous experience from fundamental nuclearstudies, the SPhN have acquired skills which fall right on the spot of many hot topicsrequired for the development of these future foreseen systems. That ranges fromtheoretical calculations (using the Monte-Carlo neutron transport code MCNP) to themore practical development of fuel particles containing uranium compounds (oxideand/or carbide) and their behavior at high temperature.

1. IntroductionHigh Temperature Reactors (HTR) offer many advantages over present Pressurized

Water Reactors (PWR) technology. Due to the possible high temperature use, the overallefficiency is significantly higher (thermal to electrical). Consequently, the use of nuclear fuelis more efficient and leads to less spent fuel and waste for a given electrical energy produced.Also, a definite advantage is the so-called "intrinsic safety" because, contrary to the PWR, anaccident like a loss of coolant would not end up in a catastrophic scenario, melting the core.

In a HTR, the fuel is composed of tiny spherical particles (less than 1 mm in diameter)containing a ceramic (oxide or carbide) and coated with different protective layers. Apartfrom the silicon carbide barrier, all other layers are based on graphite. Consequently, due tothe high carbon content in its core, the average neutron spectrum of a HTR is highlythermalized. Before trying to move towards a harder spectrum (which would be desirablefrom the neutronics point of view), it is quite important to master all the technology requiredfor that type of reactor (fuel fabrication, irradiation, waste management). CEA is giving astrong push for this generic R&D towards the next generation of future systems.

There are basically two domains in which the SPhN is able to efficiently contribute tothis R&D. First, from the theoretical side with the use of neutron transport codes to answerspecific questions like the impact of some important parameters on the whole system. Second,on the experimental part, taking advantage of irradiation techniques and know-how in the useof uranium carbide and oxide at very high temperatures (2000°C) [1].

2. Simulation ProgramThis part would be a joint effort of the SPhN in collaboration with the DM2S/SERMA

(simulation group of the Direction de l'Energie Nucléaire - DEN). The standard code used inreactor simulation is a determinist code able to calculate any core parameter as the neutronicsflux, deposited power, keff, isotopic vectors etc… This type of code is based on solvingcoupled equations in which each reactor element is submitted to a neutronics flux with a givenspectrum. These equations (diffusion, generation, absorption and losses) are solved using aself-consistent method by iteration. A quite interesting alternative is the use of a statisticalcode based on Monte-Carlo generating events. Each neutron is tracked step by step in a givengeometry, and each time an interaction occurs, all the particles generated will be equallyfollowed. In that way, each individual cross-section is used with no approximation.Unfortunately, for statistical reasons, this method requires a large number of events in order toget high precision results. One should notice that the two approaches are rathercomplementary. In that sense, in most cases, they are both required. That is even moreimportant when new systems with almost no past available experience are to be calculated.While the determinist code is very useful to give precise and detailed calculation like the localpower profile, the Monte Carlo code can be used for a fast and global approach used forgeneric work. As an example, the influence of a given parameter, like the size of the fuelparticle, can be immediately evaluated, even though the local precision is quite poor. Anotherexample is the study of the possibility of using HTR for burning nuclear waste. Some fuelparticles containing minor actinides may be used, heavily impacting the overall parameters ofthe core. In that sense, the global change in the core can be given as a function of the actinideloading and transmutation performance evaluated (burn-up, cycle). This kind of study havealready started at SPhN and a full geometry description of a GT-MHR is already available [2].

A joint program has been identified in between the SERMA and the SPhNhighlighting the most important actions for which both parties agreed. Three major items havebeen considered to be of primary need :

1) The dynamic (time) evolution of the reactor core. It is quite important toevaluate not only the core parameters at a given time, but also to predict howthe system will evolve. An evolution code is here required coupled to theneutronics code. One has to be quite careful in this coupling scheme, ascalculation errors may propagate, leading sometimes to a non physicaldivergence.

2) A complete comparison between a determinist and a statistical code can bedone on the very same geometry and using the same nuclear database.

3) To establish a statistical model of a bundle of particles enabling a macroscopicview of the system. Because there is a very large number of particles in thecore (above 10 billion !), it is not possible to run the codes with each elementalparticle taken into account. A more realistic approach would be to try to findsome homogenization technique allowing to simulate the fuel at an upper levelscale, with all the microscopic evaluated issues included (self-shielding forinstance).

The general aim of that work would be to try to evaluate what are the ultimate limitsof application for each type of code and at which precision each simulation should have to beconsidered. This basic approach should help any following simulation development orimprovement in the near future.

3. Experimental Program

Complementary to the simulation program, the SPhN can also help the Départementd'Etudes du Combustible (DEC) in the experimental R&D work on the HTR fueldevelopment. The important point here is to qualify a particle behavior under irradiation athigh temperature, including the most extreme temperatures that might be reached in case ofaccident, like a loss of coolant. These temperatures maybe as high as 1600°C. In any case, inorder to guarantee the intrinsic safety of that kind of reactor, the particle itself should maintainits integrity at even higher temperatures for safety margins. Also the behavior of all fissionproducts produced and their possible diffusion through the different protective layers have tobe fully studied and demonstrated on actual fuel particles. Damage under irradiation andstructural change due to the use of high temperatures may greatly influence the physicalproperties of the layers and eventually lead to particle deterioration. Therefore, it is of primaryimportance to try to give the most precise evaluation of all the elements produced duringirradiation (transuranian, fission products, activation of structural material). These evaluatedamounts may also be experimentally checked for some of the elements by different analysistechniques following irradiation.

The experimental program can be divided in three steps. The first one would deal withparticles containing only structural elements with the different protective layers on. Irradiationcan be done inside a research reactor having a dedicated channel at a given temperature. Afterirradiation, the particle can be first characterized by spectroscopy (gamma rays, identifyingthe most important radioactive elements generated). Following, after some proper coolingtime, element analysis (chemical) and/or structural analysis will complete the picture. Thesecond step will focus on real particle fuel containing basically uranium. Finally, the thirdirradiation batch may deal with more exotic particles, evolving from the standard uraniumtype. These improvements may as well be on the fuel side (for example, using minor actinidesceramics) or on the outer layers modifications (for example, using a less effective moderatorthan graphite to achieve a harder spectrum). The final aim of that experimental program is tooffer and to open future possibilities for more advanced characterization of next generation offuel particle. Of course, these can only be done in close collaboration with the fabricationtechniques (CEA Cadarache), and with the full support of the simulation team (see above).

4. Cost and ScheduleThe cost of the overall program has been estimated to amount to 240 k€. The program

has been assumed to run over three fiscal years (2003 to 2005).The required manpower for the SPhN is 9 man-year.

1 "Photofission target for SPIRAL II", APS, June 20022 R. Plukiene & D. Ridikas, "Modelling of HTRs with Monte Carlo …", DAPNIA-02-242, September 2002

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