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Risk Assessment of NPP Level1 PSA

Risk Assessment of NPP Level1 PSA. 2011 6.10 JNES-VARANS Review Meeting. Contents. 1. Overview of PSA 2. Level1 PSA Methodology - Initiating Events - Event Tree Analysis - Fault Tree Analysis - Quantification of Plant Risks. 1. Overview of PSA - What is PSA? -.

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Risk Assessment of NPP Level1 PSA

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  1. Risk Assessment of NPPLevel1 PSA 2011 6.10 JNES-VARANS Review Meeting

  2. Contents 1. Overview of PSA 2. Level1 PSA Methodology - Initiating Events - Event Tree Analysis - Fault Tree Analysis - Quantification of Plant Risks

  3. 1. Overview of PSA - What is PSA? - • PSA is “Probabilistic Safety Assessment”. • PSA is a comprehensive approach to evaluatethe safety of NPPs quantitatively with probabilistic methods. • PSA indentifies accident sequences and quantifies plant risks (CDF, CFF, etc). • PSA models plant design, plant procedures and human performance. CFF : containment failure frequency NPPs : Nuclear Power Plants CDF : core damage frequency

  4. 1. Overview of PSA - What is Benefit? - • Weak and Strong feature of safety designs • Comparison with various safety designs quantitatively • Effective upgrade of safety designs • Optimization of safety designs • Effective plant operation PSA can provide “Risk Profile” of NPPs and “Importance Factor” (Influence of each Safety Function to plant risks).

  5. 1. Overview of PSA - Levels of PSA - Level 1 Level 2 Level 3 FP Release and Exposure Internal Event Core Damage Sequence Containment Failure Sequence Risk to Public Source Term CDF CFF External Event Reliability and Phenomenon Analysis - Mitigation System - Physical Phenomena Reliability Analysis - Safety Systems - Human Performance Core Damage Containment Failure CDF: Core Damage Frequency Source term means a kind, amount, timing, period and energy of discharged FPs CFF: Containment Failure Frequency FP : Fission Product

  6. 1. Overview of PSA - Deterministic Approach - Braking the bike Got a flat tire The handle is stuck （Unusual event） （Single failure） Prevent any accidents even if one function fails at unusual events. (Deterministic approach is based onSingle Failure Criterion.) Prevent the crash 1 The safety of the bike is confirmed.

  7. 1. Overview of PSA - Probabilistic Approach - The brake doesn’t work The handle is stuck Got a flat tire 10-2 / demand 10-1 / demand 10-2 / year Crash! Multiple failures with a probability would cause an accident. The frequency of the crash is 10-5 / year

  8. 1. Overview of PSA-Deterministic vs Probabilistic-

  9. 1. Overview of PSA - Historical Background - U.S. ・1972-75: WASH-1400 report ・1979: TMI-accident → Recognition of usefulness of PRA ・1995: Final policy statement of usage PRA methods in nuclear regulatory activities. Japan ・1992:Nuclear Safety Commission indicated to implement PSA for all NPPs to study Accident Management. ・PSA is conducted in PSR for all NPPs per 10 years. PRA: Probabilistic Risk Assessment PSR: Periodic Safety Review

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