safety objectives for generation iii npp applied to epr design options presentation 26 – 29...

SAFETY OBJECTIVES FOR GENERATION III NPP APPLIED TO EPR DESIGN OPTIONSPRESENTATION

26 – 29 September 2010, Nesebar, Bulgaria

WATTELLE Emmanuel

IRSN, France

Safety objectives for Generation III NPP applied to EPR design options

BgNS conference, 26-29 September 2010

SUMMARYSUMMARY

Context

General safety approach

Technical/regulatory safety approach : Technical guidelines

Illustrations :Safety demonstrationSafety function : confinementDefense in depth : severe accident



CONTEXTCONTEXT

Nuclear energy renaissance worldwide : increases in energy demand in spite of the efforts for a more economic and effective use possibility of global climate changes

But context has changed since Generation II nuclear reactors (late 60’s) :

Increase in public awareness about radiological consequencesImprovement of international standards of safety :INSAG 3 (1988) INSAG 12 (1999) “safety principles for nuclear power plants”

WENRA reference levels for reactor safety (2008)



FRENCH GENERAL SAFETY APPROACHFRENCH GENERAL SAFETY APPROACH

Need for a significant improvement of the safety levelsignificant improvement of the safety level of future plants at the design stage, compared to the safety level of existing plants

Choice of an evolutionary approachevolutionary approach, taking into account:

the large operating experience on PWR plantsthe results of in-depth studies performed on these plants, in particular the probabilistic safety assessmentsthe results of research and development activities, notably on severe accidents

Innovative featuresInnovative features to be considered.



EPR EVOLUTIONARY DESIGN

Framatome N4 Siemens KONVOI

PWRExperience feedback

Evolutionary design



FRENCH TECHNICAL/REGULATORY SAFETY FRENCH TECHNICAL/REGULATORY SAFETY APPROACHAPPROACH

TECHNICAL GUIDELINESTECHNICAL GUIDELINES (FOR THE DESIGN AND CONSTRUCTION OF THE NEXT GENERATION OF NUCLEAR POWER PLANTS WITH PRESSURIZED WATER REACTORS) :

Sum up safety principles and objectives :General approachSafety functionsPrevention and control of accident (including severe accident)…

Have been :Assessed by IRSN/GRSAdopted by French/German experts plenary meetings held in 2000Addressed to French utility by Nuclear safety authority in France

Are consistentAre consistent with last internationalinternational safety requirements



TECHNICAL GUIDELINES : SAFETY OBJECTIVESTECHNICAL GUIDELINES : SAFETY OBJECTIVES

Reduction of :the number of significant incidents hence to limiting the possibilities of accident situations developing from such eventsthe global core melt frequency : less that 10-5 per plant operating year, uncertainties and all types of failures and hazards being all types of failures and hazards being taken into accounttaken into account

Significant reduction of potential radioactive releases due to all conceivable accidents :

without core melt : no necessity of protective measuresno necessity of protective measures for people living in the vicinity of the damaged plant (no evacuation, no sheltering)with core melt :

have to be practically eliminatedpractically eliminated in case they would lead to large early releases. This objective applies notably to high high pressure core melt sequencespressure core melt sequences

low pressure core meltlow pressure core melt sequences have to be dealt with so that the associated maximum conceivable releases would necessitate only very limited protective measuresvery limited protective measures in area and in time for the public

Objectives widening further than safety :reduction of individual and collective doses for the workersreduction of quantities and activities of radioactive wastes



TECHNICAL GUIDELINES : REINFORCEMENT OF TECHNICAL GUIDELINES : REINFORCEMENT OF DEFENCE IN DEPTH PRINCIPLEDEFENCE IN DEPTH PRINCIPLE

General :Reinforcement of all levelsuse of diversifieddiversified meansSpecial attention to be given to shutdown statesshutdown states

Level 1/Prevention of abnormal operation and failure : “quality of design, manufacturing, construction and operation is essential”

Level 2/Control of abnormal operation and failure to avoid escalation to accident conditions : reduction of the frequency of initiating event

Level 3/Control of accidental conditions to limit radiological releases and to avoid core melt should take into account both :

Design basis accidents : single initiating eventBeyond design basis accidents : Multiple failuresMultiple failures

Level 4/control of core melt accident (severe accident) core melt accident (severe accident) : severe accident is postulated at the design stage

Level 5 not directly applicable to NPP (off-site emergency response in case of significative releases)



TECHNICAL GUIDELINES : SAFETY DEMONSTRATIONTECHNICAL GUIDELINES : SAFETY DEMONSTRATION

Achieved in a deterministicdeterministic way

Supplemented by probabilisticprobabilistic methods

Appropriate research and development work are necessary

Analyzes :single initiating eventsmultiple failure situationsinternal and external hazards

Possible links between internal and external hazards and single initiating events have also to be considered



EPR DESIGN OPTIONS – 3 EXAMPLESEPR DESIGN OPTIONS – 3 EXAMPLES

3 ways to illustrate3 ways to illustrate

Safety demonstration : deterministic, probabilistic

Safety function : confinement

DiD Level : level 4 - severe accident



Safety demonstration illustrationSafety demonstration illustration

Safety injection system deterministic approach (1/2)Safety injection system deterministic approach (1/2)

How many trains needed :

•1 train lost due to the breaklost due to the break

•1 train failed (single failure criterionsingle failure criterion)

•1 train in maintenancemaintenance

1 train available1 train available designeddesigned

to cope with accidentsto cope with accidents

Physical and spatial separation

M

M

M

M

M

M

M

M

M

M

M

M

M M

M

M

M



Safety demonstration illustrationSafety demonstration illustrationSafety injection system deterministic approach Safety injection system deterministic approach

(2/2)(2/2)

Internal hazard(fire, explosion,missile, flooding)one division lost

External hazard(airplane crash)division 1 or 4 lost

airplane protection



Safety demonstration illustrationSafety demonstration illustrationSafety injection system probabilistic insights (1/3)Safety injection system probabilistic insights (1/3)

Common cause failure : heavy weight in probabilistic demonstration

More than 4 similarsimilar trains : not lead to important improvment

DiversifiedDiversified means are very important

2 examples :

• Electrical supply

• Cooling system of low pressure injection motor



SBO 1

690V3~

Div. 1 Div. 4

MainDiesel 1

10kV3~

SBO 2

690V3~

MainDiesel 4

10kV3~

Div. 2

MainDiesel 2

Div. 3

MainDiesel 3

Addition of two diversified diesels generators to face common failure of the four existing

main diesels





• Low pressure injection motor need to be cooled

• Component cooling water system is backed up by main emergency diesel generators

Motors cooled by :Component cooling water systemAnd, if necessary : chilled water system



Safety function illustrationSafety function illustrationConfinement (1/5)Confinement (1/5)

• Main challenge Significant reductionreduction of potential radioactive releasesreleases due to all conceivable accidentsconceivable accidents

simple presentation of the main principles

ContainmentContainment Building

Objectives can be achieved through the use of a double wall containment concept including:

inner wall in pre-stressed concrete and metallicmetallic linerouter wall in reinforced concrete, airplane protection annulus between them maintained at a sub-atmosphericsub-atmospheric pressure :

to collect all possible leaks through the inner wall to filter them before release to the environment via the

stack




ContainmentContainment Building

Inner wall with metallicmetallic liner low leak rate

outer wall – airplaneairplane protection

Venting system :

•Filtration

•Subatmospheric pressure

Annulus at sub-atmosphéricsub-atmosphéric pressure

avoid direct leak due to leaktightness of building




ContainmentContainment building : only one part of confinement function Possible leaks due to penetrationspenetrations

Through peripheral buildings

Direct to atmosphere




Penetrations only between RB and

PB

Leaktightness criterion



Safety function illustrationSafety function illustrationConfinement and severe accident (5/5)Confinement and severe accident (5/5)

• Accident sequences (core melt) involving containment containment bypassingbypassing have to be practically eliminatedpractically eliminated

• The residual heat after a severe accident must be removed from the containment building without venting device

• The design pressure and design temperature of the containment building must allow a grace period of 12 hours without containment heat removal device without containment heat removal device actuationactuation

• The containment building must also withstand the global deflagration or fast local deflagration of global deflagration or fast local deflagration of hydrogenhydrogen that may be generated during severe accident situations

• The penetrationpenetration of the basemat of the containment building by a corium must be avoidedavoided (core-catcher)



DiD level illustrationDiD level illustrationSevere accident (1/6)Severe accident (1/6)

Mitigation of severe accident has to be addressed in the design

Accident situations with core melt which would lead to large early releases have to be practically eliminatedpractically eliminated :

Accident sequences involving containment by-passcontainment by-pass :Confinement design principlesSpecific technical solution for hatch closing within 2

hoursReactivity accidentReactivity accident resulting from fast introduction of cold and deborated waterHigh pressure core meltHigh pressure core melt situations :

Dedicated valves for severe accident depressurizationGlobal hydrogen detonations and steam explosions threatening the containment integrity :

passive autocatalytic recombinersDry corium spreading room




Core-catcherCore-catcher

Reactor pitReactor pit : Collect the corium in dry cavity (no risk of steam explosion)Transfer the corium :

initiated by the passive melting of a « gate » (a steel grid covered by concrete) under the effect of the corium

to the spreading room through a transfer channel protected by zirconia layer

Spreading roomSpreading room : Composed of steel cooling plates covered with a layer of sacrificial concrete. The steel cooling plates have cooling channels at their bottomCorium spreading melting - by the corium - of passive fusible wires opening of spring-loaded valve the water from the In-containment Refueling Water Storage Tank (IRWST) flows through the cooling channels (cooling the bottom of the spreading room) to finally spread over the corium and flood its surface

The evaporated water condenses in the containment building and returns to the IRWST




Core-catcher : First stage (0 -12 hours, when CHRS is not Core-catcher : First stage (0 -12 hours, when CHRS is not actuated) - Passive cooling of the core catcher from actuated) - Passive cooling of the core catcher from

the IRWSTthe IRWST




Core-catcher : Second stage (after 12 hours, CHRS Core-catcher : Second stage (after 12 hours, CHRS actuated) actuated)

Active cooling of the core catcher (1 file)Active cooling of the core catcher (1 file)and containment spray (1 or 2 files)and containment spray (1 or 2 files)



Thank you

Благодаря

safety objectives for generation iii npp applied to epr design options presentation 26 – 29...

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