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Presentation prepared by Vladimir KUZNETSOV (NENP)

Coordinated Research Project “Development of Advanced Methodologies for Substantiation of Passive System Performance for Advanced Reactors” (Proposal for P&B 2008-2011). Presentation prepared by Vladimir KUZNETSOV (NENP). CONTENT 1. Introduction 2. Background

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Presentation prepared by Vladimir KUZNETSOV (NENP)

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  1. Coordinated Research Project “Development of Advanced Methodologies for Substantiation of Passive System Performance for Advanced Reactors” (Proposal for P&B 2008-2011) Presentation prepared by Vladimir KUZNETSOV (NENP) NC RCM4, VIC, IAEA, 10-13 September 2007

  2. CONTENT 1. Introduction 2. Background 3. Generic approach to reliability assessment of passive systems 4. Methodologies for reliability assessment of passive safety systems (IAEA TM 12-16 June 2006) - Status - Common points and differences -`Alternative approaches? - Approaches to integrate PS reliability into PSA - Complementarity and options for cooperation 5. General incentives to develop a common approach to reliability assessment of passive safety systems 6. Proposal for a CRP “Development of Advanced Methodologies for Substantiation of Passive System Performance for Advanced Reactors” (P&B 2008-2011) 7. Conclusion – Expected outcomes NC RCM4, VIC, IAEA, 10-13 September 2007

  3. Introduction • There are rising expectations regarding the future role of nuclear power • Many advanced reactor designs, both evolutionary and innovative, are under development in Member States, see, e.g.: • IAEA-TECDOC-1391; IAEA-TECDOC-1485; IAEA-TECDOC-1536, etc. • Many advanced reactor designs rely strongly on passive safety design options: inherent and passive safety features and passive safety systems NC RCM4, VIC, IAEA, 10-13 September 2007

  4. Background (1) • Passive systems should, by definition, be able to carry out their mission with minimum or no reliance on external sources of energy and should operate only on the basis of fundamental natural physical laws, such as gravity. • Some operating reactors, and even more recently certified and newly build reactors incorporate passive (safety) systems (AP600, AP1000, VVER-1000, KLT-40S, etc.) • Deterministic approach to validation and licensing (certification) of reactors with passive (safety) systems established in several Member States: • Separate effect tests • Development of models and codes • Integral tests • Validation and certification of codes • Conservatism applied in validation NC RCM4, VIC, IAEA, 10-13 September 2007

  5. Background (1) • Passive systems may play a significant role to reduce the conditional probabilities of occurrence of severe accident scenarios following extreme external events, which could jeopardise operator initiated and plant protection system initiated interventions. • To evaluate these conditional probabilities, it is important to have an assessment of reliability of passive systems. • It may be stipulated that a passive system may fail to fulfil its mission because of a consequence of the following two failures: • Component failure: Classical failure of a component or components (passive or active) of the passive system; • Phenomenological failure: Deviation from expected behaviour due to physical phenomena, e.g., related to thermal hydraulics or due to different boundary or initial conditions. • The reliability of components of a passive system can be evaluated by means of well-proven classical methods. NC RCM4, VIC, IAEA, 10-13 September 2007

  6. Background (2) • However, aspects like lack of data on some phenomena, missing operating experience over the wide range of conditions, and the smaller driving forces make the reliability evaluation of passive system phenomena a challenging one. • For evaluating the failure probability of passive systems, the methodology may move from the classical methods used for Probabilistic Risk Analysis (PRA) and consider, in addition to real components (valves, pumps, instrumentation, etc), virtual components, that represent the natural mechanism upon which the system operation is based (natural circulation, gravity, internal stored energy, etc.). • The contribution of real components can be easily assessed by resorting to the reliability databases available, whereas for evaluating the virtual component contribution (process condition related) it is necessary to develop a procedure that allows such assessment despite the lack of failure data. NC RCM4, VIC, IAEA, 10-13 September 2007

  7. Background (2) NC RCM4, VIC, IAEA, 10-13 September 2007

  8. IAEA Technical Meeting 12-16 June 2006 (RMPS – EU with CEA France as a leader) NC RCM4, VIC, IAEA, 10-13 September 2007

  9. IAEA Technical Meeting 12-16 June 2006 (APSRA, BARC India) NC RCM4, VIC, IAEA, 10-13 September 2007

  10. IAEA Technical Meeting 12-16 June 2006 (APSRA) NC RCM4, VIC, IAEA, 10-13 September 2007

  11. IAEA Technical Meeting 12-16 June 2006 (Failure response surface, an APSRA example) NC RCM4, VIC, IAEA, 10-13 September 2007

  12. IAEA Technical Meeting 12-16 June 2006 (several different models under development) • Common points / differences in approaches • Common points of RMPS and APSRA: • The use of the “functional failure” concept; • The fact that there are two elements that may contribute to a failure of the expected performance: failure of the components in a system, and failure of a physical process • Differences (example): • RMPS - it has no meaning to define an inherent reliability for a thermal-hydraulic (Category B) passive system. - Even if, at the moment of a thermal-hydraulic passive system start-up, the initial and boundary conditions are beyond the design conditions, it is still possible that a safe state could be reached; and - In the case where, at the moment of a start-up, the initial and boundary conditions are within the design conditions, it is still possible that a safe state could not be reached, because passive phenomena could be very complex. • BARC (India) thinks the opposite. NC RCM4, VIC, IAEA, 10-13 September 2007

  13. IAEA Technical Meeting June 2006 (several different models under development 2) • Complementarity of approaches/ Options for Cooperation • APSRA incorporates an important effort on qualification of the model and use of the available experimental data. These aspects have not been studied in RMPS, given the context of this project • APSRA includes in the PSA model the failure of those components, which cause a deviation of the key parameters resulting in a system failure, but does not take into account the fact that the probability of failure of a physical process could be different from unity. • RMPS proposes to take into account in the PSA model the failure of a physical process. It is possible to treat such data (best estimate code plus uncertainty approach is suitable for this purpose). • In fact, two different philosophies or approaches have been used in RMPS and APSRA, and the two developed methodologies are, therefore, different. At the same time, certain parts of the APSRA and the RMPS could be merged in order to obtain a more complete methodology. NC RCM4, VIC, IAEA, 10-13 September 2007

  14. Assessment of passive system performance (Alternative Approaches? - Example) NC RCM4, VIC, IAEA, 10-13 September 2007

  15. Assessment of passive system performance (Alternative Approaches - Example) NC RCM4, VIC, IAEA, 10-13 September 2007

  16. Assessment of passive system performance (Alternative Approaches? - Example) NC RCM4, VIC, IAEA, 10-13 September 2007

  17. How to treat passive systems in PSA?Borrow from seismic (external event) PSA Methodology?A suggestion from ESS/NSNI (2005) NC RCM4, VIC, IAEA, 10-13 September 2007

  18. System Analysis • Event Tree/Fault Tree (PSA):CDF • Seismic Plant Fragilities (Margin approach) : HCLPFPlant • Compare with Review Level Earthquake NC RCM4, VIC, IAEA, 10-13 September 2007

  19. Seismic Hazard Analysis • Frequency (or probability) of exceedance of a given ground motion measure x Where, fM,R(m,r) : joint density probability function of magnitude M; Vi: mean annual rate of occurrence of earthquake NC RCM4, VIC, IAEA, 10-13 September 2007

  20. Fragility Analysis • The conditional probability of SSC failure for given level of seismic parameters • Family of fragility curves reflecting uncertainty in the parameter values and in the models NC RCM4, VIC, IAEA, 10-13 September 2007

  21. Fragility Analysis NC RCM4, VIC, IAEA, 10-13 September 2007

  22. Methodologies for reliability assessment of passive (safety) systems • Necessary R&D for passive systems could be made more effective via applying a consensus approach to reliability assessment • The degree of conservatism applied in deterministic validation of passive (safety) systems could be reduced (?) • Risk-informed approach in the design, qualification, and licensing of advanced NPPs (?) with passive systems could help secure a high safety level at a reasonable plant cost • The methodologies are still at an early stage of development • Member States have an intention to cooperate to move toward a more consensus approach NC RCM4, VIC, IAEA, 10-13 September 2007

  23. Coordinated research project “Development of Advanced Methodologies for Substantiation of Passive System Performance for Advanced Reactors” (2008-2011) In coordination with INPRO, TWG-LWR, TWG-HWR,TWG-FR&ADS, NS/SAS, NS/ESS, International Probabilistic Safety Assessment Review Team (IPSART) Overall Objective: To identify a consistent approach to substantiation of passive system performance, which would merge both the deterministic and the probabilistic aspects in a time saving and cost-effective way, and will help to overcome important open issues, which have arisen in recent years. NC RCM4, VIC, IAEA, 10-13 September 2007

  24. Specific Research objectives: • To identify the application goals and common requirements for a technology-neutral methodology of reliability assessment of passive systems for advanced NPPs • To work out a consensus set of definitions relevant to reliability assessment of the passive systems and their treatment in PSA • To identify a set of common benchmark problems to compare and validate methodologies for reliability assessment of passive systems • To perform trial applications of various approaches to reliability assessment of selected benchmark problems, with evaluation of uncertainties (based on already available results for some approaches?) • To perform comparative analysis of the results; and work out suggestions for a consensus analysis-and-test based approach; • To identify a possible consensus approach and identify directions for further elaboration of IAEA Safety Standards NC RCM4, VIC, IAEA, 10-13 September 2007

  25. Organizations that confirmed their interest to participate: • Research Centre Cadarache of the CEA of France (CEA/DEN/DER/SESI/LCFR) • Bhabha Atomic Research Centre (BARC) of India • The University of Rome “La Sapienza” (Italy) • The ENEA (Italy) • The Massachusetts Institute of Technology (USA) • EDO “Gidropress”(Russian Federation) • Instituto de Engenharia Nuclear/CNEN (Brazil) The list is still open! NC RCM4, VIC, IAEA, 10-13 September 2007

  26. Schedule of works: NC RCM4, VIC, IAEA, 10-13 September 2007

  27. Conclusion - Expected outcomes: • Increased capability of Member States to achieve progress in the development of a common technology-neutral and risk-informed approach to substantiation and reliability assessment of passive system performance; • Directions for further elaboration of IAEA Safety Standards NC RCM4, VIC, IAEA, 10-13 September 2007

  28. THANK YOU! E-mail: v.v.kuznetsov@iaea.org Publications planned for 2007-2008: • NE Series Report “Review of Passive Safety Design Options for SMRs” (2007) • NE Series Report “Approaches to Assess SMR Competitiveness” (2008) • NE Series Report “Status of Validation and Testing of Passive Systems for Advanced Reactors” (2008) NC RCM4, VIC, IAEA, 10-13 September 2007

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