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INITIATING EVENTS IDENTIFICATION AND SELECTION

IAEA.PNRA.05.05. Stetkar

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INITIATING EVENTS IDENTIFICATION AND SELECTION

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    1. IAEA.PNRA.05.05 Stetkar & Associates 1 INITIATING EVENTS IDENTIFICATION AND SELECTION by John W. Stetkar Presented to National Training Course on Probabilistic Safety Assessment Islamabad, Pakistan May 2 - 6, 2005 IAEA Project C7-PAK/9/028-001

    2. IAEA.PNRA.05.05 Stetkar & Associates 2 DEFINITION "An initiating event is an event that creates a disturbance in the plant and has a potential to lead to core damage, depending on the successful operation of the various mitigating systems of the plant." (IAEA Safety Series No. 50-P-4)

    3. IAEA.PNRA.05.05 Stetkar & Associates 3 INITIATING EVENT CONSIDERATIONS SCOPE OF PSA FUNCTIONAL IMPACTS DEPENDENT IMPACTS

    4. IAEA.PNRA.05.05 Stetkar & Associates 4 SCOPE OF PSA PLANT OPERATING MODE FULL POWER LOW POWER SHUTDOWN SCOPE OF ANALYSES INTERNAL EVENTS INTERNAL HAZARDS EXTERNAL EVENTS SCOPE OF PSA MODELS CORE DAMAGE (LEVEL 1) CONTAINMENT RELEASES (LEVEL 2)

    5. IAEA.PNRA.05.05 Stetkar & Associates 5 FUNCTIONAL IMPACTS CORE PROTECTION FUNCTIONS (LEVEL 1 PSA) CORE SUBCRITICALITY CORE HEAT REMOVAL COOLANT INVENTORY CONTROL CONTAINMENT PROTECTION FUNCTIONS (LEVEL 2 PSA) CONTAINMENT HEAT REMOVAL FISSION PRODUCT CONTROL CONTAINMENT ISOLATION

    6. IAEA.PNRA.05.05 Stetkar & Associates 6 DEPENDENT IMPACTS PLANT THERMAL / HYDRAULIC RESPONSE EVENT SEQUENCE PROGRESSION CORE DAMAGE MITIGATION SUCCESS CRITERIA EVENT TIMING FRONTLINE SYSTEMS SUPPORT SYSTEMS OPERATOR ACTIONS

    7. IAEA.PNRA.05.05 Stetkar & Associates 7 INITIATING EVENT SELECTION METHODS DEDUCTIVE ANALYSIS REFERENCE TO PREVIOUS PSAs ENGINEERING EVALUATION OPERATIONAL EXPERIENCE

    8. IAEA.PNRA.05.05 Stetkar & Associates 8 DEDUCTIVE ANALYSIS

    9. IAEA.PNRA.05.05 Stetkar & Associates 9 DEDUCTIVE ANALYSIS METHODS MASTER LOGIC DIAGRAM "TOP-DOWN" EXAMINATION OF BASIC FUNCTIONS DEMONSTRATE COMPLETENESS IN EARLY PSAs HEAT BALANCE FAULT TREE EXAMINATION OF PLANT ENERGY TRANSFERS EQUAL FOCUS ON LOCAs AND TRANSIENTS ACCOUNTS FOR DECREASE AND INCREASE IMPACTS ADAPTED FOR PLANT-SPECIFIC FEATURES

    10. IAEA.PNRA.05.05 Stetkar & Associates 10 TYPICAL PWR MASTER LOGIC DIAGRAM

    11. IAEA.PNRA.05.05 Stetkar & Associates 11 TYPICAL PWR HEAT TRANSPORT PATHS

    12. IAEA.PNRA.05.05 Stetkar & Associates 12 TYPICAL PWR HEAT BALANCE FAULT TREE TOP LEVEL LOGIC

    13. IAEA.PNRA.05.05 Stetkar & Associates 13 TYPICAL PWR HEAT BALANCE FAULT TREE INCREASE / DECREASE IN CORE HEAT GENERATION

    14. IAEA.PNRA.05.05 Stetkar & Associates 14 TYPICAL PWR HEAT BALANCE FAULT TREE INCREASE / DECREASE IN HEAT REMOVAL FROM CORE

    15. IAEA.PNRA.05.05 Stetkar & Associates 15 TYPICAL PWR HEAT BALANCE FAULT TREE INCREASE / DECREASE IN RCS HEAT TRANSFER TO SCS

    16. IAEA.PNRA.05.05 Stetkar & Associates 16 TYPICAL PWR HEAT BALANCE FAULT TREE INCREASE / DECREASE IN SCS HEAT REMOVAL FROM RCS

    17. IAEA.PNRA.05.05 Stetkar & Associates 17 TYPICAL PWR HEAT BALANCE FAULT TREE INCREASE / DECREASE IN SCS ENERGY TRANSFER

    18. IAEA.PNRA.05.05 Stetkar & Associates 18 TYPICAL PWR HEAT BALANCE FAULT TREE INCREASE / DECREASE IN ELECTRICAL OUTPUT

    19. IAEA.PNRA.05.05 Stetkar & Associates 19 TYPICAL PWR HEAT BALANCE FAULT TREE INCREASE / DECREASE IN THERMAL OUTPUT

    20. IAEA.PNRA.05.05 Stetkar & Associates 20 REFERENCES TO PREVIOUS PSAs

    21. IAEA.PNRA.05.05 Stetkar & Associates 21 REFERENCE TO PREVIOUS PSAs INTERNATIONAL PSA EXPERIENCE IS MATURE REFERENCE SOURCES IAEA U.S. NRC, INTERNATIONAL REGULATORY BODIES REACTOR OWNERS' GROUPS UTILITY-SPONSORED PLANT-SPECIFIC PSAs COMPLETENESS IN GENERIC INITIATING EVENTS USE REFERENCES FROM MID-1990's TO PRESENT

    22. IAEA.PNRA.05.05 Stetkar & Associates 22 REFERENCE TO PREVIOUS PSAs *** CAUTIONS *** CLEAR DEFINITION OF INITIATING EVENT AVOID SUMMARY LISTS AND TABULATIONS AVOID DIRECT USE OF PRE-DEFINED INITIATING EVENT GROUPS AVOID DIRECT USE OF LOCA DEFINITIONS, SIZES, AND LOCATIONS – REQUIRES PLANT-SPECIFIC ANALYSIS AVOID DIRECT USE OF SUPPORT SYSTEM INITIATING EVENTS – REQUIRES PLANT-SPECIFIC ANALYSIS

    23. IAEA.PNRA.05.05 Stetkar & Associates 23 ENGINEERING EVALUATION

    24. IAEA.PNRA.05.05 Stetkar & Associates 24 PLANT-SPECIFIC INITIATING EVENTS LOCA SIZES / LOCATIONS / SUCCESS CRITERIA "LARGE" / "SMALL" MEDIUM LOCAs SMALL LOCA "VERY SMALL" LOCA INTERFACING SYSTEM LOCAs SIZE LOCATION SYSTEM / FUNCTIONAL IMPACTS SUCCESS CRITERIA LEVEL 2 PSA IMPACTS

    25. IAEA.PNRA.05.05 Stetkar & Associates 25 PLANT-SPECIFIC INITIATING EVENTS FRONTLINE SYSTEMS PRIMARY COOLANT MAKEUP / LETDOWN MAIN CONDENSER / CONDENSATE / FEEDWATER STEAM RELIEF (SAFETY VALVES, RELIEF VALVES, TURBINE BYPASS) SUPPORT SYSTEMS ALWAYS REQUIRE PLANT-SPECIFIC ANALYSIS INITIATING EVENT FREQUENCY PSA IMPACTS

    26. IAEA.PNRA.05.05 Stetkar & Associates 26 SUPPORT SYSTEM INITIATING EVENTS GENERIC DATA NOT DIRECTLY RELEVANT GENERIC EXPERIENCE USEFUL FOR "SANITY CHECK" DEVELOP PLANT-SPECIFIC MODELS ACCOUNT FOR OPERATOR ACTIONS

    27. IAEA.PNRA.05.05 Stetkar & Associates 27 SUPPORT SYSTEM INITIATING EVENTS OFFSITE / ONSITE AC POWER DC POWER COOLING WATER SYSTEMS INSTRUMENT / CONTROL AIR SYSTEMS VENTILATION / ROOM COOLING "PARTIAL" SYSTEM FAILURES OPERATOR ACTIONS / RECOVERY

    28. IAEA.PNRA.05.05 Stetkar & Associates 28 ONSITE ELECTRIC POWER FAILURES IMPACTS ON PLANT RESPONSE "SAFETY-RELATED" BUSES "NON-SAFETY" BUSES IMPACTS ON ELECTRIC POWER RECOVERY POWER SUPPLY TO BUS TRANSFORMER FAILURE BUSWORK FAILURE

    29. IAEA.PNRA.05.05 Stetkar & Associates 29 "PARTIAL" SYSTEM FAILURES ONE AC BUS ONE DC BUS OFFSITE POWER TRANSFORMERS ONE TRAIN OF COOLING WATER ONE TRAIN OF VENTILATION

    30. IAEA.PNRA.05.05 Stetkar & Associates 30 "PARTIAL" SYSTEM FAILURES HIGHER FREQUENCY THAN TOTAL FAILURE CONDITIONAL CORE DAMAGE FREQUENCY MAY BE HIGH ACCOUNT FOR NON-SYMMETRIC PLANT DESIGN ACCOUNT FOR OPERATING / STANDBY ALIGNMENTS

    31. IAEA.PNRA.05.05 Stetkar & Associates 31 FAILURE MODES AND EFFECTS ANALYSIS (FMEA) SYSTEMATIC EXAMINATION OF EQUIPMENT FAILURE MODES AC / DC ELECTRICAL BUSES TRANSFORMERS OPERATING EQUIPMENT (PUMPS, FANS, CHILLERS, COMPRESSORS, ETC.) VALVES (SPURIOUS OPENING / CLOSURE) INSTRUMENTATION / CONTROL LOOPS IMPACTS ON PLANT OPERATION TURBINE TRIP REACTOR TRIP RUNBACK CHALLENGE FORCED MANUAL SHUTDOWN

    32. IAEA.PNRA.05.05 Stetkar & Associates 32 FAILURE MODES AND EFFECTS ANALYSIS (FMEA) IMPACTS ON PSA MODELS FAILED SYSTEMS / EQUIPMENT SUCCESS CRITERIA RECOVERY ANALYSES OPERATOR ACTION DEPENDENCIES

    33. IAEA.PNRA.05.05 Stetkar & Associates 33 EXAMPLE FMEA RESULTS

    34. IAEA.PNRA.05.05 Stetkar & Associates 34 OPERATOR ACTION DEPENDENCIES MUST ACCOUNT FOR DEPENDENCIES WITH OPERATOR ACTIONS IN INITIATING EVENT MODELS QUANTIFY SEPARATE INITIATING EVENTS INITIATING EVENT CAUSED BY ONLY HARDWARE FAILURES NO PRECEDING ERROR DEPENDENCE INITIATING EVENT CAUSED BY COMBINATION OF HARDWARE FAILURES AND OPERATOR ERRORS DEPENDENCE ON PRECEDING ERRORS DIFFERENT POST-INITIATOR ERROR RATES

    35. IAEA.PNRA.05.05 Stetkar & Associates 35 OPERATIONAL EXPERIENCE

    36. IAEA.PNRA.05.05 Stetkar & Associates 36 OPERATIONAL EXPERIENCE INDUSTRY EVENT SUMMARIES REACTOR OWNERS' GROUPS PLANT-SPECIFIC EXPERIENCE

    37. IAEA.PNRA.05.05 Stetkar & Associates 37 PRECURSOR EVENTS CONDITIONS THAT REQUIRE RAPID AUTOMATIC OR MANUAL POWER REDUCTION (MORE THAN ~ 30% POWER) AUTOMATIC / MANUAL PLANT RUNBACK REACTOR POWER REDUCTION TURBINE-GENERATOR POWER REDUCTION FEEDWATER REDUCTION STEAM RELIEF

    38. IAEA.PNRA.05.05 Stetkar & Associates 38 PLANT RUNBACK MODELS PLANT-SPECIFIC MODEL FOR INITIATING EVENT FREQUENCY AND IMPACTS SUCCESSFUL RUNBACK PLANT STABILIZED AT REDUCED POWER NO PSA INITIATING EVENT RUNBACK FAILURE PLANT TRIP PSA INITIATING EVENT MAY BE GROUPED WITH OTHER SIMILAR INITIATORS

    39. IAEA.PNRA.05.05 Stetkar & Associates 39 PLANT RUNBACK MODELS / DATA AVOID DETAILED MODELS FOR RUNBACK LOGIC / SIGNALS / CIRCUITS DERIVE FAILURE RATES FROM OBSERVED EXPERIENCE RELIABILITY OF RUNBACK FUNCTION ACTUAL EXPERIENCE USUALLY WORSE THAN MODEL PREDICTIONS CATEGORIES OF RUNBACK CHALLENGES

    40. IAEA.PNRA.05.05 Stetkar & Associates 40 MANUAL SHUTDOWN MANUAL TRIP ALWAYS AN INITIATING EVENT FORCED MANUAL SHUTDOWN EQUIPMENT FAILURES REACTOR COOLANT LEAKS STEAM / FEEDWATER LEAKS OTHER PLANT-SPECIFIC CONDITIONS NOT INCLUDED AS INITIATING EVENT IN EARLY PSAs MANY INTERNATIONAL PSAs NOW INCLUDE FOR COMPLETENESS

    41. IAEA.PNRA.05.05 Stetkar & Associates 41 MANUAL SHUTDOWN (continued) NO CLEAR OR CONSISTENT DECISION CRITERIA CONSIDERATIONS EXTENT OF EQUIPMENT FAILURES FUNCTIONAL SUCCESS CRITERIA OPTION TO REMAIN AT POWER TIMING / RATE OF SHUTDOWN DIFFICULT TO EXPLICITLY ACCOUNT FOR PARTIALLY DEGRADED SYSTEMS / EQUIPMENT IN PSA MODELS INTERFACE WITH SHUTDOWN PSA MODELS

    42. IAEA.PNRA.05.05 Stetkar & Associates 42 “INTERNAL” / “EXTERNAL” INITIATING EVENTS LOSS OF ONSITE ELECTRICAL BUSES / TRANSFORMERS LOSS OF OFFSITE POWER INTERNAL FIRES INTERNAL FLOODS PIPE BREAKS / STEAM RELEASES RIVER / LAKE FLOODING DAM FAILURES LOSS OF VENTILATION / ROOM COOLING

    43. IAEA.PNRA.05.05 Stetkar & Associates 43 “INTERNAL” / “EXTERNAL” INITIATING EVENTS HIGH WINDS / TORNADOES TOXIC GAS RELEASES INDUSTRIAL / TRANSPORTATION ACCIDENTS EARTHQUAKES AIRCRAFT CRASHES TURBINE MISSILES COOLING WATER INTAKE PLUGGING SABOTAGE / TERRORISM

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