ML112560288
| ML112560288 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 09/23/2011 |
| From: | NRC/RES/DRA |
| To: | |
| DeMoss Gary RES/DRA 301-251-7584 | |
| References | |
| IR-10-005 | |
| Download: ML112560288 (8) | |
Text
1 Final Precursor Analysis Accident Sequence Precursor Program - Office of Nuclear Regulatory Research H. B. Robinson Reactor Trip with a Loss of Main Feedwater and Pressurizer Power-Operated Relief Valve Opening on Demand Event Date: 9/9/2010 LER: 261/10-007 IRs: 50-261/10-05 CCDP = 3x10-6 EVENT
SUMMARY
Brief Event Description. At 1437 on September 9, 2010, with H. B. Robinson Steam Electric Plant, Unit 2, in Mode 1 at approximately 100% power, an automatic reactor trip occurred. The reactor trip signal was based on the over-temperature/differential temperature (OTT) reactor protection function. Due to the plant transient condition, the steam generator power operated relief valves (PORVs) opened and one pressurizer PORV cycled momentarily in response to pressure changes in the steam generators and pressurizer. The auxiliary feedwater system automatically actuated, as expected and provided feedwater to the steam generators. The main steam safety valves did not open during the event. Additional information is provided in References 1 and 2.
Key Event Details. The following details are important to the modeling of this event analysis:
The reactor tripped and main feedwater (MFW) was lost due to the load rejection.
A pressurizer PORV opened after the reactor trip and successfully closed after the demand.
ANALYSIS RESULTS Conditional Core Damage Probability. The conditional core damage probability (CCDP) for this event is 3.0x10-6.
The Accident Sequence Precursor (ASP) Program acceptance threshold is a CCDP of 1x10-6 or the CCDP equivalent of an uncomplicated reactor trip with a non-recoverable loss of secondary plant systems (e.g., feedwater and condensate), whichever is greater. This CCDP equivalent for H. B. Robinson is 2.7x10-6.
Dominant Sequence. The dominant accident sequence, Loss of Main Feedwater (LOMFW)
Sequence 13-16 (CCDP = 1.6x10-6) contributes 55% of the total internal events CCDP.
Additional sequences that contribute greater than 1% of the total internal events CCDP are provided in Appendix A.
The dominant sequence is shown graphically in Figure B-1 in Appendix B. The events and important component failures in LOMFW Sequence 13-16 are:
Loss of MFW transient occurs, Reactor trip fails, and
Reactor pressure increases above the reactor pressure vessel design pressure (the vessel fails).
SAPHIRE 8 Report. The SAPHIRE 8 Worksheets (Appendix A) provide the following:
Modified basic events and initiating event frequencies, including base and change case probabilities/frequencies.
Dominant sequences (including CCDPs).
Sequence logic for all dominant sequences.
Fault tree definitions.
Sequence cutsets.
Definitions and probabilities for key basic events MODELING ASSUMPTIONS Analysis Type. The Revision 8.16 of the Robinson Standardized Plant Analysis Risk (SPAR)
Model created in September 2010 was used for this event analysis. This event was modeled as a loss of feedwater transient initiating event.
Analysis Rules. The ASP program uses Significance Determination Process results for degraded conditions when available. However, the ASP Program performs independent initiating event analysis when an initiator occurs.
Key Modeling Assumptions. The following modeling assumptions and associated basic event modifications were required for this event analysis:
The initiating event was modeled as loss of main feedwater. The auxiliary feedwater system started automatically, when the main feed water was lost, due to a full load reject.
- The frequency of IE-LOMFW (Initiating Event-loss of feedwater) was set to 1.0; all other initiating events frequencies were set to zero.
The following basic event was modified due to the opening of a pressurizer PORV after the OTT reactor protection function initiated the reactor trip.
- The probability of basic event PPR-SRV-CO-TRANS (PORVs/SRVs open during transient) was set to TRUE.
The non-recoverability probability for basic event HPR-XHE-XM-RECIRC (Operators fail to initiate high-pressure recirculation) was set to 5x10-3. This value was calculated using the SPAR-H Method (Reference 3).
- This human failure event contains both diagnosis and action activities. Since operators would have enough time to perform the action, the nominal action human error probability of 1x10-3 was applied.
- The following performance shaping factors (PSF) were adjusted. All other PSFs were determined to be nominal (i.e., x1).
PSF for Diagnosis Multiplier Notes Time Available 0.1 Several hours exist for operators to initiate recirculation given a failure of RCS depressurization or shutdown cooling. Therefore, Extra Time (i.e., x0.1) was selected.
Stress 2
The PSF for diagnosis stress is assigned a value of High Stress (i.e., x2) due to the initiation of the event and multiple failures experienced during the postulated sequences.
Complexity 2
The PSF for diagnosis complexity is assigned a value of Moderately Complex (i.e., x2) due to the long procedure (41 pages) used to align recirculation and initiate sump recirculation.
Diagnosis HEP 4E-3 Action HEP 1E-3 Adjusted Total HEP 5E-3 REFERENCES
- 1. Progress Energy, "LER 261/10-007-Reactor Trip Due to a Degraded Connection on a Circuit Board in the Electro-Hydraulic Control Cabinet, dated January 17, 2011.
- 2. U.S. Nuclear Regulatory Commission, H. B. Robinson Steam Electric Plant - NRC Integrated Inspection Report 05000261/2010005, dated January 28, 2011.
- 3. Idaho National Laboratory, NUREG/CR-6883: The SPAR-H Human Reliability Analysis Method, dated August 2005.
LER 261/10-007 A-1 Appendix A: SAPHIRE 8 Worksheets Summary of Conditional Event Changes Event Description Cond. Value Nominal Value HPR-XHE-XM-RECIRC OPERATOR FAILS TO INITIATE HPR CL RECIRC 5.000E-3 2.000E-3 IE-LOMFW LOSS OF MAIN FEEDWATERa 1.000E+0 1.000E-1 PPR-SRV-CO-TRAN PORVs/SRVs OPEN DURING TRANSIENT True 4.000E-2
- a.
All other initiating event frequencies set to zero.
Dominant Sequence Results Only items contributing at least 1.0% to the total CCDP are displayed.
E V E N T T R E E S E Q U E N C E CCDP
% C O N T R I B U T I O N D E S C R I P T I O N LOMFW 13-16 1.627E-6 54.5%
RPS, RCSPRESS LOMFW 12 8.023E-7 26.9%
/RPS, AFW, FAB LOMFW 05 2.914E-7 9.8%
/RPS, /AFW, PORV, /HPI, /SSC, RHR, HPR LOMFW 11 1.083E-7 3.6%
/RPS, AFW, /FAB, SSCR, HPR LOMFW 13-07 1.045E-7 3.5%
RPS, /RCSPRESS, /MFW, BORATION Total 3.406E-6 100.0%
Referenced Fault Trees Fault Tree Description AFW AUXILIARY FEEDWATER AVAILABLE BORATION EMERGENCY BORATION FAB FEED AND BLEED HPR HPR PRESSURE RECIRC PORV PORV/SRVs ARE CLOSED RCSPRESS RCS PRESSURE LIMITED RHR RESIDUAL HEAT REMOVAL RPS REACTOR TRIP SSCR SECONDARY SIDE COOLING RECOVERED Cutset Report - LOMFW 13-16 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L%
C U T S E T 1.627E-6 100 Displaying 62 of 62 Cutsets.
1 2.093E-7 12.87 IE-LOMFW,PPR-MOV-FC-535,RPS-BME-CF-RTBAB 2
2.093E-7 12.87 IE-LOMFW,PPR-MOV-FC-536,RPS-BME-CF-RTBAB 3
1.746E-7 10.73 IE-LOMFW,PPR-MOV-FC-535,/RPS-CCP-TM-CHA,RPS-TXX-CF-6OF8,RPS-XHE-XE-NSGNL 4
1.746E-7 10.73 IE-LOMFW,PPR-MOV-FC-536,/RPS-CCP-TM-CHA,RPS-TXX-CF-6OF8,RPS-XHE-XE-NSGNL 5
1.573E-7 9.67 IE-LOMFW,PPR-MOV-FC-535,RPS-ROD-CF-RCCAS 6
1.573E-7 9.67 IE-LOMFW,PPR-MOV-FC-536,RPS-ROD-CF-RCCAS 7
1.184E-7 7.28 IE-LOMFW,PPR-MOV-FC-535,/RPS-CCP-TM-CHA,RPS-CCX-CF-6OF8,RPS-XHE-XE-NSGNL 8
1.184E-7 7.28 IE-LOMFW,PPR-MOV-FC-536,/RPS-CCP-TM-CHA,RPS-CCX-CF-6OF8,RPS-XHE-XE-NSGNL 9
2.254E-8 1.39 IE-LOMFW,RCS-PHN-MODPOOR,RPS-BME-CF-RTBAB 10 1.881E-8 1.16 IE-LOMFW,RCS-PHN-MODPOOR,/RPS-CCP-TM-CHA,RPS-TXX-CF-6OF8,RPS-XHE-XE-NSGNL
LER 261/10-007 A-2 CCDP T O T A L%
C U T S E T 11 1.694E-8 1.04 IE-LOMFW,RCS-PHN-MODPOOR,RPS-ROD-CF-RCCAS Cutset Report - LOMFW 12 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L%
C U T S E T 8.023E-7 100 Displaying 1278 of 1278 Cutsets.
1 1.860E-7 23.19 IE-LOMFW,AFW-FCV-CF-REG,HPI-XHE-XM-FB 2
6.512E-8 8.12 IE-LOMFW,AFW-FCV-CF-REG,PPR-SRV-CC-455C 3
6.512E-8 8.12 IE-LOMFW,AFW-FCV-CF-REG,PPR-SRV-CC-456 4
2.533E-8 3.16 IE-LOMFW,AFW-FAN-CF-FR7AB,AFW-TDP-FS-SDP,HPI-XHE-XM-FB 5
1.809E-8 2.26 IE-LOMFW,AFW-FAN-CF-FR7AB,AFW-TDP-TM-SDP,HPI-XHE-XM-FB 6
1.739E-8 2.17 IE-LOMFW,AFW-FAN-CF-FS7AB,AFW-TDP-FS-SDP,HPI-XHE-XM-FB 7
1.484E-8 1.85 IE-LOMFW,AFW-FAN-CF-FR7AB,AFW-TDP-FR-SDP,HPI-XHE-XM-FB 8
1.242E-8 1.55 IE-LOMFW,AFW-FAN-CF-FS7AB,AFW-TDP-TM-SDP,HPI-XHE-XM-FB 9
1.155E-8 1.44 IE-LOMFW,AFW-MDP-CF-FSAB,AFW-TDP-FS-SDP,HPI-XHE-XM-FB 10 1.019E-8 1.27 IE-LOMFW,AFW-FAN-CF-FS7AB,AFW-TDP-FR-SDP,HPI-XHE-XM-FB 11 8.865E-9 1.1 IE-LOMFW,AFW-FAN-CF-FR7AB,AFW-TDP-FS-SDP,PPR-SRV-CC-455C 12 8.865E-9 1.1 IE-LOMFW,AFW-FAN-CF-FR7AB,AFW-TDP-FS-SDP,PPR-SRV-CC-456 13 8.250E-9 1.03 IE-LOMFW,AFW-MDP-CF-FSAB,AFW-TDP-TM-SDP,HPI-XHE-XM-FB Cutset Report - LOMFW 05 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L%
C U T S E T 2.914E-7 100 Displaying 341 of 341 Cutsets.
1 8.450E-8 29 IE-LOMFW,HPR-XHE-XM-RECIRC,PPR-MOV-FC-535,PPR-MOV-FC-536,PPR-SRV-OO-551C 2
8.450E-8 29 IE-LOMFW,HPR-XHE-XM-RECIRC,PPR-MOV-FC-535,PPR-MOV-FC-536,PPR-SRV-OO-551A 3
8.450E-8 29 IE-LOMFW,HPR-XHE-XM-RECIRC,PPR-MOV-FC-535,PPR-MOV-FC-536,PPR-SRV-OO-551B 4
4.350E-9 1.49 IE-LOMFW,HPR-XHE-XM-RECIRC,/PPR-MOV-FC-536,PPR-MOV-OO-536,PPR-SRV-OO-455C 5
4.350E-9 1.49 IE-LOMFW,HPR-XHE-XM-RECIRC,/PPR-MOV-FC-536,PPR-SRV-OO-455C,PPR-XHE-XM-BLK 6
4.350E-9 1.49 IE-LOMFW,HPR-XHE-XM-RECIRC,/PPR-MOV-FC-535,PPR-MOV-OO-535,PPR-SRV-OO-456 7
4.350E-9 1.49 IE-LOMFW,HPR-XHE-XM-RECIRC,/PPR-MOV-FC-535,PPR-SRV-OO-456,PPR-XHE-XM-BLK Cutset Report - LOMFW 11 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L%
C U T S E T 1.083E-7 100 Displaying 269 of 269 Cutsets.
1 4.651E-8 42.95 IE-LOMFW,AFW-FCV-CF-REG,HPR-XHE-XM-RECIRC 2
6.332E-9 5.85 IE-LOMFW,AFW-FAN-CF-FR7AB,AFW-TDP-FS-SDP,HPR-XHE-XM-RECIRC 3
4.523E-9 4.18 IE-LOMFW,AFW-FAN-CF-FR7AB,AFW-TDP-TM-SDP,HPR-XHE-XM-RECIRC 4
4.347E-9 4.01 IE-LOMFW,AFW-FAN-CF-FS7AB,AFW-TDP-FS-SDP,HPR-XHE-XM-RECIRC 5
3.710E-9 3.43 IE-LOMFW,AFW-FAN-CF-FR7AB,AFW-TDP-FR-SDP,HPR-XHE-XM-RECIRC 6
3.105E-9 2.87 IE-LOMFW,AFW-FAN-CF-FS7AB,AFW-TDP-TM-SDP,HPR-XHE-XM-RECIRC 7
2.888E-9 2.67 IE-LOMFW,AFW-MDP-CF-FSAB,AFW-TDP-FS-SDP,HPR-XHE-XM-RECIRC
LER 261/10-007 A-3 CCDP T O T A L%
C U T S E T 8
2.547E-9 2.35 IE-LOMFW,AFW-FAN-CF-FS7AB,AFW-TDP-FR-SDP,HPR-XHE-XM-RECIRC 9
2.062E-9 1.9 IE-LOMFW,AFW-MDP-CF-FSAB,AFW-TDP-TM-SDP,HPR-XHE-XM-RECIRC 10 1.739E-9 1.61 IE-LOMFW,AFW-FCV-CF-142425,AFW-TDP-FS-SDP,HPR-XHE-XM-RECIRC 11 1.692E-9 1.56 IE-LOMFW,AFW-MDP-CF-FSAB,AFW-TDP-FR-SDP,HPR-XHE-XM-RECIRC 12 1.536E-9 1.42 IE-LOMFW,AFW-MOV-CF-1416ABC,HPR-XHE-XM-RECIRC 13 1.242E-9 1.15 IE-LOMFW,AFW-FCV-CF-142425,AFW-TDP-TM-SDP,HPR-XHE-XM-RECIRC 14 1.086E-9 1
IE-LOMFW,AFW-FAN-CF-FR7AB,AFW-FCV-CC-6416,HPR-XHE-XM-RECIRC Cutset Report - LOMFW 13-07 Only items contributing at least 1% to the total are displayed.
CCDP T O T A L%
C U T S E T 1.045E-7 100 Displaying 11 of 11 Cutsets.
1 3.220E-8 30.81 IE-LOMFW,CVC-XHE-XM-BOR,RPS-BME-CF-RTBAB 2
2.687E-8 25.7 IE-LOMFW,CVC-XHE-XM-BOR,/RPS-CCP-TM-CHA,RPS-TXX-CF-6OF8,RPS-XHE-XE-NSGNL 3
2.420E-8 23.15 IE-LOMFW,CVC-XHE-XM-BOR,RPS-ROD-CF-RCCAS 4
1.821E-8 17.42 IE-LOMFW,CVC-XHE-XM-BOR,/RPS-CCP-TM-CHA,RPS-CCX-CF-6OF8,RPS-XHE-XE-NSGNL 5
2.080E-9 1.99 IE-LOMFW,CVC-XHE-XM-BOR,RPS-UVL-CF-UVDAB,RPS-XHE-XE-SIGNL Referenced Events Event Description Probability AFW-FAN-CF-FR7AB CCF OF AFW HVAC HVH-7A&B TO RUN 1.809E-4 AFW-FAN-CF-FS7AB CCF OF AFW HVAC HVH-7A&B TO START 1.242E-4 AFW-FCV-CC-6416 FAILURE OF AFW SDP DISCHARGE PATH HYDRAULIC VALVE 6416 1.200E-3 AFW-FCV-CF-142425 CCF OF AFW MDPS FCVs 1424 & 1425 4.968E-5 AFW-FCV-CF-REG CCF OF AFW FEED REG VALVES 9.302E-6 AFW-MDP-CF-FSAB CCF OF AFW MOTOR DRIVEN PUMPS TO START 8.250E-5 AFW-MOV-CF-1416ABC CCF OF STEAM GENERATOR INLET MOVs 3.072E-7 AFW-TDP-FR-SDP AFW TURBINE DRIVEN PUMP FAILS TO RUN 4.102E-3 AFW-TDP-FS-SDP AFW TURBINE DRIVEN PUMP FAILS TO START 7.000E-3 AFW-TDP-TM-SDP AFW TDP UNAVAILABLE DUE TO TEST AND MAINTENANCE 5.000E-3 CVC-XHE-XM-BOR OPERATOR FAILS TO INITIATE EMERGENCY BORATION 2.000E-2 HPI-XHE-XM-FB OPERATOR FAILS TO INITIATE FEED AND BLEED COOLING 2.000E-2 HPR-XHE-XM-RECIRC OPERATOR FAILS TO INITIATE HPR CL RECIRC 5.000E-3 IE-LOMFW LOSS OF MAIN FEEDWATER 1.000E+0 PPR-MOV-FC-535 BLOCK VALVE RC-535 FOR PORV PCV-456 CLOSED 1.300E-1 PPR-MOV-FC-536 BLOCK VALVE RC-536 FOR PORV PCV-455C CLOSED 1.300E-1 PPR-MOV-OO-535 BLOCK VALVE RC-535 FOR PORV PCV-456 FAILS TO CLOSE 1.000E-3 PPR-MOV-OO-536 BLOCK VALVE RC-536 FOR PORV PCV-455C FAILS TO CLOSE 1.000E-3 PPR-SRV-CC-455C PORV PCV-455C FAILS TO OPEN ON DEMAND 7.000E-3 PPR-SRV-CC-456 PORV PCV-456 FAILS TO OPEN ON DEMAND 7.000E-3 PPR-SRV-OO-455C PORV PCV-455C FAILS TO RECLOSE AFTER OPENING 1.000E-3 PPR-SRV-OO-456 PORV PCV-456 FAILS TO RECLOSE AFTER OPENING 1.000E-3 PPR-SRV-OO-551A FAILURE OF SRV RC-551A TO RECLOSE 1.000E-3 PPR-SRV-OO-551B FAILURE OF SRV RC-551B TO RECLOSE 1.000E-3 PPR-SRV-OO-551C FAILURE OF SRV RC-551C TO RECLOSE 1.000E-3 PPR-XHE-XM-BLK OPERATOR FAILS TO CLOSE BLOCK VALVE 1.000E-3
LER 261/10-007 A-4 Event Description Probability RCS-PHN-MODPOOR MODERATOR TEMP COEFFICIENT NOT ENOUGH NEGATIVE 1.400E-2 RPS-BME-CF-RTBAB CCF OF RTB-A AND RTB-B (MECHANICAL) 1.610E-6 RPS-CCX-CF-6OF8 CCF 6 ANALOG PROCESS LOGIC MODULES IN 3 OF 4 CHANNELS 1.830E-6 RPS-ROD-CF-RCCAS CCF 10 OR MORE RCCAS FAIL TO DROP 1.210E-6 RPS-TXX-CF-6OF8 CCF 6 BISTABLES IN 3 OF 4 CHANNELS 2.700E-6 RPS-UVL-CF-UVDAB CCF UV DRIVERS TRAINS A AND B (2 0F 2) 1.040E-5 RPS-XHE-XE-NSGNL OPERATOR FAILS TO RESPOND WITH NO RPS SIGNAL PRESENT 5.000E-1 RPS-XHE-XE-SIGNL OPERATOR FAILS TO RESPOND WITH RPS SIGNAL PRESENT 1.000E-2
LER 261/10-007 B-1 Appendix B: Key Event Tree Figure B-1. H. B. Robinson LOMFW event tree.
IE-LOMFW LOSS OF MAIN FEEDWATER RPS REACTOR TRIP FTF-LOOP-RECOVERY AFW AUXILIARY FEEDWATER AVAILABLE PORV PORV/SRVs ARE CLOSED FTF-LOSC LOSC LOSS OF SEAL COOLING HPI HIGH PRESSURE INJECTION FAB FEED AND BLEED SSCR SECONDARY SIDE COOLING RECOVERED SSC COOLDOWN (PRIMARY &
SECONDARY)
RHR RESIDUAL HEAT REMOVAL HPR HPR PRESSURE RECIRC End State (Phase - CD) 1 OK 2
LOSC 3
OK 4
OK 5
CD 6
OK 7
CD 8
CD 9
OK 10 OK 11 CD 12 CD 13 ATWS