safety of fusion power reactor concepts in the view of the ... · introduction to grs first iaea...

Safety of Fusion Power Reactor Concepts in the

View of the German Nuclear Fission Regulation

J. Herba, C. Pistnerb, J. Raederc, A. Wellerc, R. Wolfc,

L. V. Boccaccinid, D. Carlonid, X. Z. Jind , R. Stieglitzd

aGesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH, bÖko-Institut e.V. (Institute for Applied Ecology),

cMax-Planck-Institut für Plasmaphysik, dKarlsruhe Institute of Technology (KIT)

5th May, 2016 First IAEA Technical Meeting (TM) on the Safety, Design and Technology of Fusion Power Plants 1

Introduction to GRS

First IAEA Technical Meeting (TM) on the Safety, Design and Technology of Fusion Power Plants 2

GRS is the central Technical Safety Organisation (TSO) and a major research

institution in the field of nuclear safety in Germany

Development, validation, and application of computer codes for the simulation of

thermal hydraulics, reactor physics, fuel behaviour, fission product chemistry, and

structural mechanics

Scientific staff >300

Work Related to Fusion

Simulation of severe accidents (MELCOR)

Provide software for containment simulations (ASTEC, COCOSYS)

Review of safety concept

Provide system code ATHLET for thermal hydraulic analysis in fusion

5th May, 2016

German Safety Requirements for Nuclear Power Plants (SiAnf)


IAEA SAFETY STANDARDS

GUIDES

REQUIREMENTS

FUNDAMENTALS

Consti-

tution

Atomic Energy

Act

Ordinances

General administrative

provisions

Safety Requirements for NPPs

(SiAnf)

BMU publications

RSK guidelines, RSK and SSK recommendations

KTA safety standards

Technical specifications for components and systems

Organisation and operating manuals

German Safety Requirements for Nuclear Power Plants (SiAnf)


0 Fundamental principles

1 Organisational requirements

2 Technical safety concept

2.1 Defence-in-depth concept

2.2 Concept of the multi-level confinement of the radioactive

inventory (barrier concept)

2.3 Fundamental safety functions

2.4 Protection concept against internal and external hazards

as well as against very rare human-induced external

hazards

2.5 Radiological safety objectives

3 Technical requirements

3.1 General requirements

3.2 Requirements for the reactor core and the shutdown

systems

3.3 Requirements for the equipment for fuel cooling in the

reactor core

3.4 Requirements for the reactor coolant pressure boundary

and the pressure-retaining walls of components of the

external systems

3.5 Requirements for structures

3.6 Requirements for the containment system

3.7 Requirements for instrumentation and control

3.8 Requirements for control rooms

3.9 Requirements for the electrical energy supply

3.10 Requirements for the handling and storage of the fuel

assemblies

3.11 Requirements for radiation protection

4 Postulated operating conditions and events

4.1 Operating conditions, anticipated operational occurrences

and accidents

4.2 Internal and external hazards and very rare human-induced

external hazards

4.3 Events involving the multiple failure of safety equipment

4.4 Accidents involving severe fuel assembly damages

5 Requirements for the safety demonstration

6 Requirements for the operating rules

7 Requirements for the documentation

SiAnf were developed with German NPPs (PWR/BWR) in mind

They implement the concept of defense in depth

Their principles can – to some extend – also be applied to fusion power plants (FPP)

Concept of defense in depth (SiAnf)


Level of

DiD Description Objectives

1 Normal operation prevent the onset of anticipated operational occurrences and accidents

prevent events with multiple failure of safety installations

2 Abnormal operation

control any on setting anticipated operational occurrences,

prevent the onset of accidents

prevent events involving the multiple failure of safety installations

3 Accidents

control accidents

prevent the onset of events involving the multiple failure of safety

installations

4a Very rare events control the effects of very rare events

4b

Events with multiple

failure of safety

installations

in the case of events involving the multiple failure of safety installations

prevent severe core damage (preventive accident management

measures)

4c Accidents involving

severe core damage

in the case of an accident involving severe core damage limit the release

of radioactive materials into the environment as far as possible (mitigating

accident management measures)

5 Mitigation of radiological consequences of significant releases of

radioactive material

Additionally: external events and very rare human induced external hazards

Concept of defense in depth (WENRA)


Most recent international developments of defense in depth concepts tighten

requirements for very rare events/accidents with multiple failures

Levels of

DiD

Associated plant

condition categories

Objective Essential means Radiological

consequences

Level 1 Normal operation Prevention of abnormal

operation and failures

Conservative design and high quality

in construction and operation, control

of main plant parameters inside

defined limits

Regulatory

operating limits for

discharge

Level 2 Anticipated operational

occurrences

Control of abnormal

operation and failures

Control and limiting systems and

other surveillance features

Level 3 DiD Level 3.a

Postulated single initiating

events

Control of accident to limit

radiological releases and

prevent escalation to core

melt conditions

Reactor protection system, safety

systems, accident procedures

No off-site

radiological impact

or only minor

radiological impact

DiD Level 3.b

Postulated multiple failure

events

Additional safety features, accident

procedures

Level 4 Postulated core melt

accidents

(short and long term)

Control of accidents with

core melt to limit off-site

releases

Complementary safety features4 to

mitigate core melt,

Management of accidents with core

melt (severe accidents)

Limited protective

measures in area

and time

Level 5 - Mitigation of radiological

consequences of significant

releases of radioactive

material

Off-site emergency response

Intervention levels

Off site

radiological impact

necessitating

protective

measures

Concept of defense in depth (FPP)


Level of DiD Description

1 Prevention of deviations from normal operation and system failures

2 Control of deviations from normal operation and detection of failures

3 Control of accidents within the design basis

4 Control of severe conditions

5 Mitigation of radiological consequences of significant releases of radioactive

materials

PPCS based on INSAG-10

Fundamental safety functions (SiAnf)


The fundamental safety functions are:

reactivity control

fuel cooling

confinement of the radioactive materials

to implement the fundamental safety objective

to protect people and the environment from harmful effects of ionizing radiation

Reactivity control


SiAnf (NPP)

Fuel contains by far the largest part of

the radioactive inventory

Chain reaction

Danger of re-criticality

Fusion power plants

Activated structures, dust, and (depending

on plant design) corrosion products

contains significant part of radioactive

inventory

Fuel (Tritium)

Impurities by plasma – wall interaction or

leaks result in inherent shut down of

fusion reaction

Oversupply of fuel leads to shut down

No chain reaction

No re-criticality

Shut down is one of six supporting safety

functions in DEMO for the fundamental

safety function “confinement”

Reactivity control: Applicability of SiAnf


Control of reactivity is fulfilled inherently

Requirements for ability to shut down facility under any circumstances fulfilled by:

• active systems

• Inherently

Shut down ability as fundamental safety function

Re-criticality not possible (SiAnf cannot be applied)

Barriers NPP


SiAnf

Three barriers:

fuel cladding

reactor coolant pressure boundary

containment

Additionally

active systems (e. g. maintaining low

pressure in containment)

reactor building (protection against

external hazards)

Barriers FPP


Three barriers in two confinement

systems:

vacuum vessel (VV) & primary heat

transport system (PHTS)

VV pressure suppression system

(VVPSS), expansion volume

tokamak building

Barrier concept in FPP is based on safety

functions of systems

Active systems

HVAC, detritiation system, emergency

cooling

Inventories

coolants

Source terms (tritium, dust, activated

corrosion products (ACP), activation

products, neutron sputtering products, …)

Barriers: Applicability of SiAnf


Nevertheless, barrier concept in FPP along the lines of fission regulation

Same goal: One or more barriers have to remain intact (depending on level of DiD)

Due to differences in inventory and potential propagation paths different

implementations

Levels of defense in depth and independence (in SiAnf/NPPs)


Concept of defense in depth

Measures and installations on different level of DiD shall be independent of each

other

Failures in one level of DiD shall not interfere with higher levels of DiD

Examples of layered measures/installations

Control of reactivity: volume control system/control rod drives, power limitation

system, SCRAM system, emergency boration system, inherent negative reactivity

feedback by power increase

Secondary feeding: operational feed water system, emergency feed water system,

mobile (fire) pumps

Assign postulated (initiating) event to level of DiD

Identify measures and installations necessary to control postulated event

Assign measures and installations to level of DiD of postulated event

Levels of defense and independence (in FPPs)


Concept of defense in depth

in principle, measures and installations can be assigned to levels of DiD

Example: Power control

fuel supply (DiD levels 1, 2)

fusion plasma shutdown system (DiD level 3)

inherent termination of fusion (DiD level 3/DiD level 4)

Other examples: emergency power supply, cooling, fast magnet discharging

Currently exemplary, no systematic assignment of safety functions to LoD

possible yet due to current level of detail of plant designs

Assign postulated (initiating) event to level of DiD

Level of defense 4 (NPP)


Extend the original safety concept of NPP due to experiences derived from accidents

and PSA results

(therefore “beyond design basis” for older NPPs)

Is integral part of SiAnf

DiD level 4a: very rare events (e. g. ATWS)

DiD level 4b: events with multiple failures of safety installations

(e. g. station blackout)

DiD level 4c: accidents involving severe core damage

Examples for measures and installations in NPPs:

primary/secondary bleed and feed

pressure relief of containment (venting)

H2 recombiners

diverse ultimate heat sink

Level of defense 4 (FPP) - Applicability of SiAnf


Comparable events are part of safety concept

Different physics

different event sequences

plasma control (power excursion, not FPP)

decay heat removal by passive means

(has to be confirmed for specific plant design)

possibly hydrogen production/explosion (H2O as coolant, in-box & in-vessel

LOCAs)

possible dust explosions (amplified by H2)

Pressure confinement / pressure relief system

Adaption of regulation required

External events and very rare human induced external hazards


… are integral part of SiAnf

Fundamental safety functions have to be fulfilled in these cases

Where not covered in detail in the safety concepts of FPPs

Only external hazards/energies can endanger the containment of the radioactive

inventory (PPCS)

External hazards shall be considered in safety analyses

Depending on the design of a FPP the fundamental safety functions “shut down” and

“cooling” might be fulfilled by inherent properties and/or passive means

For a FPP the assumed loads will be comparable to that of a NPP

based on the site

especially important for the assumed loads on the reactor building (2nd confinement

system)

SiAnf applicable

First fusion power plant and operational experience


NPP: about 13.000 reactor years of operational experience

SiAnf demand

the evaluation of the operational experience

the use of proven technologies and qualified materials

the use of validated calculation methods for the safety demonstration

FPP: Several aspects are beyond current operational experience

magnetic fields/coils

tritium self-sufficiency

fuel cycle aspects (to be tested at ITER)

material properties (due to high neutron fluences and temperature gradients)

Radioactive source terms

Adaption of regulation required

Cooling of residual heat (1/2)


In NPP active systems are necessary to remove residual heat to prevent core melt

In a FPP

the residual heat of activated structures has same order of magnitude as in a NPP

(about 1 % of the thermal power 1 h after shut down)

power density significantly lower

Cooling of residual heat (2/2)


Also in a FPP

it has to be shown that decay heat potentially does not endanger the integrity of the

first wall

emergency cooling systems planned for DiD level 3

ability for passive heat removal is planned to be shown

“bounding event” analyses have shown that residual heat can be removed

passively (assuming the failure of all active systems) [PPCS]

SiAnf can be applied correspondingly

if residual heat removal by passive means can be demonstrated successfully,

requirements for active systems might be reduced

“Leak-before-break concept”


Required for NPP for certain parts of pressure boundary

(fast opening leak can result in pressure waves in the coolant resulting in the

destruction of the reactor core geometry => cool ability cannot be proven anymore)

LBB is considered in DEMO

Relevant if fluids with high pressure and enthalpy are used as coolant

Has to be considered in the design of the plant (e. g. requirements for verifiability,

material selection, embrittlement due to neutron fluence)

Depending on plant design (coolant) SiAnf might be applicable

Fusion specific extensions


Due the differences in physics between FPP and NPP:

operational conditions and system functions in FPP without equivalents in (German)

NPPs

vacuum vessel

superconducting magnets

temperatures (of the first wall)

high energy neutron flux (14 MeV => 100 – 150 dpa)

liquid metal coolant

fusion source terms

Special regulatory requirements have to be developed

Conclusions


Comparison of the safety concept of FPP concepts with German nuclear regulation:

Both are based on the concept of defense in depth

SiAnf fundamental safety functions can be applied to FPPs:

• control of reactivity/shut down ability: fulfilled inherently

• cooling: (for the PPCS plant models) analyses have shown that passive heat

removal is sufficient to ensure integrity of barriers

• containment of radioactive inventory: based on passive and active systems

(e. g. HVAC, detritiation systems)

Currently it is not possible to assign all measures and installations to distinct level of

defense in depth and show independence between levels due to limited detail of plant

designs

External events and very rare human induced external hazards shall be covered

Fusion specific operational conditions and safety functions will need extensions of

regulatory requirements

With respect to on-going ITER construction and DEMO development, safety

requirements to the likely regulatory regime for the FPP licensing will be elaborated

and complemented.

Main References


German Safety Requirements for Nuclear Power Plants (SiAnf):

http://regelwerk.grs.de/sites/default/files/cc/dokumente/dokumente/2015-09-

11_safety%20requirements%20for%20NPPs%2003-03-2015.pdf

EFDA, A Conceptual Study of Commercial Fusion Power Plants 2005

(GRS 389) Review of the safety concept for fusion reactor concepts and

transferability of the nuclear fission regulation to potential fusion power plants

(and references given there)

http://www.grs.de/publikation/grs-389

http://regelwerk.grs.de/sites/default/files/cc/dokumente/dokumente/2015-09-11_safety requirements for NPPs 03-03-2015.pdf












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