French practices and experiences in PSA review

1. French practices and experiences in PSA review

2. Summary • Introduction • Initial applications • Today applications • Periodic safety review • Complementary domain • Operating events analysis • Other Applications French practices and experiences in PSA review - 2014

3. Introduction Beginnings of the PSA in France • Partial probabilistic studies were carried out by EDF and IRSN since the 1970s • Two global level 1, internal events PSAs were completed in 1990 (for the 900 MWe plants by IRSN and 1300 MWe plants by EDF) • This allowed the development of the PSA techniques and tools and demonstrated the impact of using the probabilistic analysis on the nuclear safety related activities • Historically the first PSA applications had the objective of reducing the risk related to dominant contributions French practices and experiences in PSA review - 2014

4. Introduction PSA Developments In France • An important PSA development program is still in progress at IRSN and at EDF • The developments aim to improve PSA quality and to extend their scope, in order to increase the field of applications • EDF objective is to establish reference PSAs for each plant series • IRSN objective is to obtain independent insights, precious for evaluating and completing EDF studies • These two independent developments, which could be considered as a particularly deep external review, highly contribute to the quality of the studies French practices and experiences in PSA review - 2014

5. Specifics of the French context Nuclear Power Plants • 58 in operation • Built by the same manufacturer (formerly Framatome, today AREVA) • Operated by the same utility (Electricite de France) • 80% of French electricity, standardized in only 3 PWR series (900MWe, I300MWe and 1400MWe) • EPR under construction Real advantages in terms of experience feedback French practices and experiences in PSA review - 2014

6. Introduction PSA Developments In France - EDF • EDF presented updated PSA for each periodically safety review, starting with second decennial visit (VD) of 900 MWe plants: • VD2 900: PSA1/REP900 • VD2 1300: PSA1/REP1300 • VD3 900: PSA1/REP900 and PSA2/REP 900 • VD1 N4: PSA1 N4 • VD3 1300: PSA1 REP1300, PSA internal flooding REP1300, PSA Fire REP1300 and PSA2 REP1300 • EPR: PSA1, PSA2, internal fire PSA, internal flooding PSA, external events Note: PSA1 = Internal events Level 1 PSA PSA2 = Internal events Level 2 PSA French practices and experiences in PSA review - 2014

7. Introduction PSA Developments In France - IRSN • Under development • PSA1/N4 • PSA1/EPR • Reactor • Fuel Pool • PSA Earthquake/REP900 • PSA2/EPR • In the future • PSA internal flooding • PSA “climatic events” • Ageing • Finalized – Periodically updated • PSA1/REP900 • PSA Fire/REP90O • PSA1/REP1300 • PSA1/CP0 • PSA Fire/REP1300 • PSA2/REP900 • PSA2/REP1300 French practices and experiences in PSA review - 2014

8. Initial Applications • The first PSAs results analysis led to several important modifications in plant operation and design: • Heterogeneous dilutions • Loss of reactor heat removal during mid-loop operation • Reactor vessel fragile rupture risk, mainly by inadvertent isolation of the rector heat removal system • Safety Injection design modification (for Small LOCA) • Automatic isolation of the letdown line of the chemical and volume control system French practices and experiences in PSA review - 2014

9. Today applications • Periodic safety review • Complementary domain • Operating events analysis • Other Applications French practices and experiences in PSA review - 2014

10. PSA Application to Periodic Safety Reviews • For plants in operation PSA became an important part of the periodic safety reviews (PSR) • PSR general principles: • In the first step, the PSR procedure aims to demonstrate the conformity of the “reference plant situation” with the “safety reference system” • The “safety reference system” consists of all the safety rules, criteria and specifications applicable to a reactor type resulting from the safety analysis report • The “reference plant situation” consists of the state of the installation and its operating conditions • In the second step, the “safety reference system” is assessed • Analysis of national or international operating experience • The provisions adopted on the most recent reactors French practices and experiences in PSA review - 2014

11. PSA Application to PSR • Assess the core damage frequency and its change • Analysis of the changes in system characteristics (equipment reliability, for example) and in operating practices • Identification of the main contributions to the core damage frequency highlights any weak points for which design and operation changes can be studied, or even judged necessary • They can be ranked so as to prioritize the work • The most important verification of EDF PSAs by IRSN takes place during the PSR • other partial verifications are also performed for any current PSA application French practices and experiences in PSA review - 2014

12. PSA Application to PSR • EDF update its PSA models before the PSR in order to take into account the latest operating experience, data and knowledge • A single PSA is developed and used by EDF (at least for level 1 PSA and internal initiating events) for a whole series of plants • The EDF PSAs are verified by IRSN: • plant safety level and need for further plant improvements (design or operation) • PSA use for complementary domain definition • PSA representativeness for other applications • PSA model improvements • At the end of the PSR EDF updates its PSA models in order to take into account the issues and conclusion of the verification process • the updated PSA will be used by EDF until the next PSR French practices and experiences in PSA review - 2014

13. PSA Application to PSR • EDF PSAs are developed following the French PSA basic safety rule which indicates the acceptable development methods and PSA applications • only Level 1 PSA “internal events” for reactor is covered by PSA basic safety rule • EDF uses in-house guidelines for other PSAs (Level 2, internal hazards, fuel pool..) • the guidelines are developed mainly following international state of the art • IRSN PSA do not strictly follow the PSA basic safety rule requirements • IRSN PSAs are only tools to verify EDF “reference” PSAs, then more flexibility is allowed (focus on some issues, limited scope, sensitivity models…) • IRSN verification of EDF PSA • conformity with PSA basic safety rule • coherence of the methods with international status of the art French practices and experiences in PSA review - 2014

14. PSA Application to PSR • Procedure • EDF do not send to IRSN the PSA models, but only the associated documentation • EDF PSA models are however available for detailed verification at EDF offices • Technical questionnaires are developed by IRSN • EDF answers and other topics are discussed during technical meetings • IRSN assessment is discuss with EDF before finalizing • Intensive use of IRSN PSA models • results comparison • confirmatory studies • aspects not treated by EDF • sensitivity studies for important aspects (assumptions, data, HRA…) French practices and experiences in PSA review - 2014

15. PSA Application to PSR • Contents of EDF PSAs verification by IRSN • PSA scope (completeness, coherence with the specific uses…) • Initiating events (definition, data, operating experience, new knowledge) • Accident sequences (model, supporting studies…) • Systems models • Human reliability • Data (mainly the updating based on operating experience) • The PSA verification involve specialist from many domains: • PSA, thermohydraulic, reactor physics, data, human reliability, internal hazards, external hazards, systems design (mechanical, electrical, I&C)… • also specialists in charge with the reactors operation overseeingmay be involved: • TechSpecs, Tests, Maintenance • Operating experience French practices and experiences in PSA review - 2014

16. Second 900 MWe PSR • The second 900 MWe PSR (first use of PSA in Periodic Safety Review), the main following backfits were required by the Safety Authority: • Functional redundancy of AFWS for all modes of operation (by MFWS or RHRS) • Improvement of the ventilation system • Diversification of the reactor scram function • Modifications which could mitigate the Common Cause Failure of safety switch boards (improvement of SG feedwater and of RCP seals injection functions) French practices and experiences in PSA review - 2014

17. Second 1300 MWe PSR • PSA was used with a more formal method • The EDF reference PSA model was used according to a new, more systematic methodology: • The risk is no longer distributed in accident families, but in functional sequences, which are characterized by the ultimate measure (equipment or operator action) preventing the core degradation French practices and experiences in PSA review - 2014

18. Second 1300 MWe PSR • Method: • Functional sequences : • group together elementary sequences (> 10-8) with similar functional characteristics • same mitigation feature can be applied to the functional sequences • Assess the risk contribution associated with the functional sequences • Provision decision if • the functional accident sequence is a new one which was not identified before • the functional accident sequence has an importance at least of 10% • the current functional accident sequences frequency is higher with factor of more than 2 over the previous one French practices and experiences in PSA review - 2014

19. Second 1300 MWe PSR • The main findings of this review were: • follow-up of the control rods reliability • modifications which could mitigate the consequences of 6.6 kV switchboards common cause failure (improvement of RCP seals injection functions) • similar with the 900 MWe plants design modification French practices and experiences in PSA review - 2014

20. Third 900 MWe PSR • In 2005 the third 900 MWe PSR was carried out, and the use of PSA was increasing with the introduction of PSA level 2 and of Fire PSA • For the level 1 PSA and the level 2 PSA, the discussions were based on the EDF reference PSA • IRSN used also its own studies for the analysis • For the Fire PSA, the only study was carried out by IRSN • the IRSN Fire PSA was then the basis of the discussion French practices and experiences in PSA review - 2014

21. Third 900 MWe PSR • The findings of level 1 PSA • The main PSA level 1 insights were already taken into account during previous safety reviews • Additional issues: • ISLOCA design modification • rupture of the main pumps thermal barrier scenario • Additional studies for heterogeneous dilution (MCP leak-off lines heat exchanger internal leak) • Containment Spray System testing procedure improvement • The Fire PSA identified two sensitive rooms (containing electrical equipment), and EDF is studying the possibility of improving the situation • On the other hand, the Fire PSA underlined the positive effect of the recent EDF fire action plan French practices and experiences in PSA review - 2014

22. example for VD3 900 French practices and experiences in PSA review - 2014

23. PSA Application to PSR • The first N4 PSR was carried out in 2009 • The PSA allowed identifying several important safety issues: • the safety significance of the bypass LOCA • the impact of the failure of the ventilation systems • the importance of the reactor vessel cold rupture protection • The third PSR of 1300 MWe will be completed this year • Important using of the PSA for internal events and of the internal flooding and fire PSAs • EDF feasibility study for external events PSAs • Seismic PSA exercise developed by EDF French practices and experiences in PSA review - 2014

24. Complementary Domain • Identification of the important plant features (components or human actions) considered in the PSA, but not included in the initial deterministic safety demonstration • “complementary domain” = Risk Reduction Categories (RRC) = beyond design basis • Several “complementary domain” applications were already done by EDF and verified by IRSN • 900 MWe (2003 and 2008) • 1300 MWe (2005, 2007 and 2013) • N4 (2009) • EPR (only the method; the application is under way ) French practices and experiences in PSA review - 2014

25. Complementary Domain • Identification of the potential RRC-A features • Identification of the sequences not covered by the PCCs • Checking for the efficiency of the features • Checking for global probabilistic target meeting French practices and experiences in PSA review - 2014

26. Complementary Domain • Identification of the potential RRC-A features • Specific non-F1 systems (Gas turbine, SBO diesel, LLS, AFWS Tank water supply circuits…) • Specific functions (feed and bleed, manual cooldown,…) • Identification of the sequences not covered by the PCCs • Definition of a reference plant state -> PSA level 1 without feature • Identification of functional sequences: • criteria : Pcore melt > Probabilistic target • groupment of core melt sequences : • common functional characteristics • the same feature can reduce the risk • sequences will be also identified on Probability of releases to the environment (e.g. SGTR+SLB) but criteria are not yet fixed (PSA level 2) French practices and experiences in PSA review - 2014

27. Complementary Domain PSA level without feature Pcore meltfunctional sequence < Probabilistic target depending on consequences Pcore meltfunctional sequence > Probabilistic targetdepending on consequences RRC-A Feature not needed RRC-A Feature needed • equipment • operator action French practices and experiences in PSA review - 2014

28. Complementary Domain • Checking for the efficiency of the features • Thermal-hydraulic analysis rules : • dominant physical parameters cover at 95 % • no Single Failure • acceptance criteria = PCC4 criteria • Modeling in the PSA level 1 • Evaluation of CMF of functional sequence with RRC-A feature • The RRC-A features • Included in the Technical Specifications • Surveillance Requirements are defined/verified French practices and experiences in PSA review - 2014

29. Probabilistic analysis of operating events • Objectives: • Prioritization of events according to the conditional probability of core damage and the assessment of the pertinence of the corrective actions • Enrichment of the safety culture of the plant operator (dissemination of the lessons of PSAs based on analysis of events that have occurred on the sites) • PSA improvement (comparison of models with the course of actual events) French practices and experiences in PSA review - 2014

30. Probabilistic analysis of operating events • The probabilistic analysis of operating events which occur in the plants is on going, by EDF for all events, and by IRSN for some representative examples • An operating event is considered as a Precursor when the conditional CMF due to this event is higher than 10-6 /r*y • For the most important events (conditional CMF higher than 10-4/r*y), in a short term, corrective measures have to be defined French practices and experiences in PSA review - 2014

31. Other Applications for Plants in Operation • Technical specification definition (especially for new reactors) • Technical specification exceptions • Cost/benefit evaluations • Use of PSA in the context of the plant life extension assessment • … French practices and experiences in PSA review - 2014

32. Conclusion • Despite a limited regulatory framework and careful positions, PSA was widely used in France for improving the safety of plants • A large variety of PSA applications are today performed: • Safety Review • Complementary domain • Operating events analysis • Technical Specifications • Cost Benefits • … French practices and experiences in PSA review - 2014