oecd_l2psa_szb/mla/dmj/02039.ppt oecd/nea international workshop on l2 psa and sam, 29 th -31 st...

OECD_L2PSA_SZB/mla/dmj/02039.ppt

OECD/NEA International Workshop on L2 PSA and SAM, 29th-31st March 2004, Koln

Approach in the PSR for Sizewell B LPSA

M Ang, E Grindon, K Peers (NNC)

N E Buttery (Sizewell B, BE)

P Lightfoot (BE)


Contents

• Development of Sizewell B PSA

• POSR Level 2 PSA approach

• Approach to PSR

• Conclusions


Development of Sizewell B PSA

• PSA has been used in early days to:

• Confirm adequacy of final design

• Identify further design refinements

• PSA’s carried out at various stages in process

• L1: internal initiators at power (1982)

• L3: internal initiators at power (for public enquiry, 1982)

• L3: all faults at all power levels (for POSR, 1992)

• LPSA based on POSR model with revised L1

• LPSA formed part of PSR (submitted to NII Dec 2003)

• IAEA IPSART on LPSA for Risk Informed Management (Jan 2004)


Key Features of SZB Level 2 PSA (1)

• Core damage PDSs (14)

• faults at power (10)

• faults at shutdown (4)

• quantification via CET• Reactor building bypass PDSs (7)

• SG (4)

• interfacing systems (3)

• MAAP analysis• CET

• 20 nodes

• mainly phenomenological issues

• conservative approach, no claim on SAM -> RPV failure is assumed

• SAM actions treated in sensitivity studies based on expanded CET (22 nodes) to support ALARP reviews


Key features of SZB Level 2 PSA (2)

• CET quantification

• Probabilistic containment structural integrity model, leakage

pathways by gross failure/enhanced leakage/DB leakage

• SA and ST analyses provided by MAAP3.0B

• Supporting analysis for key sequences by other codes (e.g.

SCDAP/RELAP5, CORCON, VICTORIA, CONTAIN - CORDE)

• expert reviews on SA and ST issues

• FCI addressed by expert group

• UK and international R&D programmes

• NUREG-1150 and other PSAs

• 2 stage radiological categorisation process

• Structured sensitivity analyses (code and CET) -> statistical uncertainty analysis was judged inappropriate


Issue quantification approach in CET

Discrete

Probability

DET Monte Carlo CET Sensitivity Study

Creep rupture failure of RCS

X X

In-vessel steam explosion

X X

H2 burn

HPME

DCH

X

X

XX

X

Ex-vessel steam explosion

X

CCI X X

Source Term Issues

X

AM Issues X


Containment Failure Modes

Early3%

Late

22%

Basemat20%Bypass

12%

Intact

43%


Use of Level 2 PSA in SAM application

• Use of fire suppression system

• reduce likelihood of basemat failure

• ex-vessel cooling uncertain

• Other SOI 8.8 measures (e.g. depressurisation) reinforces likely outcome

• Level 2 PSA results an input to ALARP reviews

• Provided justification for not installing FV


Level 2 PSA activities post licensing PSA study

• Maintained a watching brief on international studies on SA phenomenological issues (e.g. USNRC issue resolution studies, OECD reviews, MACE, RASPLAV) and L2 PSA development (IAEA, OECD)

• Implementation of MAAP4 and analysis provided for key sequences

• Re-assessment of shutdown sequences, assessment of accident progression and ST behaviour from air entrainment phenomenon

• Participation in a number of EU FW programmes, e.g.

• H2 combustion: H2DDT

• ST issues: STU, OPTSAM, IC, ASTERISM

• SAM issues (e.g. core cooling recovery, IVR strategy): OPTSAM, SAMEM

• containment leakage: CONT-LEAK, CESA

• L2 PSA methodology: SAMEM, BEEJT

Participation allowed access to cluster information

• Feasibility of WOG SAMG implementation


PSR of Level 2 PSA

• Undertaken as part of PSR (chapter on ‘Safety Analysis Based Review of PSA and HF - Development and Issues)

• Process proceeded in 2 stages: (i) significant issue review and (ii) detailed review

• Significant issue review

• no ‘significant’ issues identified

• further L2 PSA quantification not necessary

• identified scope and issues for detailed review

• Issues for detailed review

• SA phenomenological issues treated in CET

• other key issues not treated in CET, including SAM issues

• ST issues

• status of MAAP code, models and validation

• SAM issues • SAMG development and implications

• Instrumentation survivability in SA conditions

• Review based on information derived from listed activities following POSR


Example of review: In-vessel fuel coolant interaction

• POSR assessment

• SERG-1 and Theofanous’ ROAAM analysis

• UK study based on ROAAM methodology, 6 x 10-4 - 4 x 10-4 calculated for pressure ranges

• PSR assessment

• SERG-2 study (1996)

• OECD study (1999), including a review of KROTOS experiments

• Theofanous’ study (1995)

• POSR results in accordance with more recent studies


Example of review: ST issues

• Review considered:

• status of key issues (group 1)

• status of key issues not explicitly covered in MAAP analysis

(group 2)

• implications for POSR results

• Review of Group 1 issues based on STU project results. 13 issues included: e.g. aerosol behaviour in containment, iodine chemistry, Te chemistry, late revaporisation and others

• More detailed review of Group 2 issues: speciation of releases, iodine behaviour in containment, containment leakage, SAM actions on fp behaviour

• POSR approach remains a conservative interpretation of fp behaviour


Results of review

• SA phenomenological issues

• recent research evidence in concurrence withassumptions/conclusions derived in POSR

• no single issue has been identified which would contradict POSR conclusions derived from a conservative L2 PSA

• ST issues

• assumptions affecting fp behaviour remain bounding and in some cases remain conservative interpretation of current data

• MAAP status

• future analysis to be based on MAAP4

• impact of re-analysis of POSR model based on MAAP4 is unlikely to provide a major impact on the overall L2 PSA results

Overall, the conclusions derived from a conservative L2 PSA model are judged to remain valid. The model remains valid for licensing application


Where do we go from here?

Future direction of the L2 PSA will depend on:

• SZB NPP’s requirement on LPSA for RI applications

• Outcome of NII review of PSR

• Outcome of IAEA IPSART results


© 2004 Published in the United Kingdom by British Energy Generation Ltd and the National Nuclear Corporation. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording, without the written permission of the copyright holder, application for which should be addressed to the publisher. Such written permission must also be obtained before any part of this publication is stored in a retrieval system of any nature.Requests for copies of this document should be referred to Barnwood Document Centre, Location 12, BEGL, Barnett Way, Barnwood, Gloucester GL4 3RS (Tel: 01452-652791). LIMITATION OF LIABILITY - Whilst British Energy Generation Limited ("BEGL") and the National Nuclear Corporation ("NNC") believe that the information given in this document is correct at the date of publication they do not guarantee that this is so, nor that the information is suitable for any particular purpose. Readers/users must therefore satisfy themselves as to the suitability of the information for the purpose for which they require it and must make all checks they deem necessary to verify the accuracy thereof. BEGL and NNC shall not be liable for any loss or damage arising from any use to which the information is put.

oecd_l2psa_szb/mla/dmj/02039.ppt oecd/nea international workshop on l2 psa and sam, 29 th -31 st...

Documents