ML20112F316
| ML20112F316 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 04/16/2002 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| References | |
| LER 2002-002-01 | |
| Download: ML20112F316 (31) | |
Text
Final Precursor Analysis Accident Sequence Precursor Program --- Office of Nuclear Regulatory Research July 14, 2004 Braidwood Station Inoperable PORV Bleed Path due to Leaking Accumulator Check Valves Unit 1 Event Date: 4/16/2002 LER: 456/02-002-01 CDP = 4x10-6 456-2002-002-01 Condition Summary Description. On April 16, 2002, the licensee found that Braidwood Station, Unit 1 was operating with pressurizer power-operated valve (PORV) instrument air (IA) accumulator check valves (85A and 86A for train A and 85B and 86B for train B) in a failed condition due to leakage.
These four check valves would have been incapable of maintaining pressurizer PORV IA accumulator pressure during a loss of IA supply to the containment building. The inspection by Region III Office (References 1 and 2) noted that both the pressurizer PORVs may have been inoperable for several operating cycles, including the operating cycle (March 2000 to September 2001). The licensee determined (Reference 3) that prior to September 2001, Unit 1 was operating with inoperable pressurizer PORV bleed path for any plant trips. Transients, loss of offsite power (LOOP) event, loss of instrument air event, and other transients could have demanded the operators to open PORVs for bleed path.
Cause. The cause of the Unit 1 check valve failures was the incorrect link bushing gap that resulted in disc o-ring interference with the valve seat.
Condition duration. The condition duration for the primary event is estimated to be one year (10/1/2000 thru 9/30/2001). During this period, the PORVs were found to be inoperable (fail-to open mode) due to IA accumulator check valve leakage.
Recovery opportunity. During LOOP events (single unit LOOP event or dual unit LOOP event),
the service air compressor that provides air to pressurizer PORV accumulators at Unit 1 would be lost. However, Unit 1 service air compressor may be powered by local manual operator actions from the Unit 2 emergency bus and its emergency diesel generator. Except for dual LOOP events, air supply could be recovered for all LOOP events (severe-weather LOOP events, grid-related LOOP events, and plant-centered LOOP events). For dual LOOP events, recovery of at least one diesel generator is needed to power the service air compressor.
Other related conditions or events. A review of LERs submitted by the licensee for the period between 9/30/2000 and 9/30/2001 indicated that none of the LERs were applicable for evaluation of overlapping conditions. A review of the Region III-issued Green SDP findings and unresolved issues of the inspection findings for the same period was also conducted in identifying potential overlapping conditions. It was found that none of the SDP findings were applicable for evaluation of potential overlapping conditions for the above one year period.
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LER 456/02-002-01 Analysis Results
! Importance1 The risk significance of inoperable PORVs due to check valve leakage for one year condition duration was determined by subtracting the nominal core damage probability from the conditional core damage probability:
Conditional core damage probability (CCDP) = 3.3E-5 Nominal core damage probability (CDP) = 2.9E-5 Importance (CDP = CCDP - CDP) = 4.4E-6 The estimated importance (CCDP-CDP) for the operational condition was 4.4E-6.
! Dominant Sequence Loss of offsite power involving successful operation of at least one emergency diesel generator, Sequence 21; importance = 4.0E-6. The events and important component failures in this sequence are as follows:
- loss of offsite power initiating event,
- successful reactor trip at Unit 1,
- failure of the AFW system,
- PORVs were inoperable for bleed function due to leaking accumulator check valves, and
- failure of operator recovery of PORVs.
Potential paths for dominant Sequence 21 is shown in Figure 1.
! Results Tables
- Table 1 provides the conditional probabilities for the two dominant sequences.
- Table 2a provides the event tree sequence logic for the dominant sequences listed in Table 1a.
- Table 2b provides the definitions of event tree sequence logic elements listed in Table 2a.
- Tables 3a and 3b provide the conditional (CCDP) cut sets for the two dominant sequences.
- Table 4 provides the definitions and probabilities for basic events for dominant sequences, including the added basic events to the Braidwood model and condition-affected basis events.
- Table 5 provides importance estimates due to operating condition, including uncertainty estimates.
1 Since this condition did not involve an actual initiating event, the parameter of interest is the measure of the incremental change between the conditional probability for the period in which the condition existed and the nominal probability for the same period but with the condition nonexistent and plant equipment available. This incremental change or importance is determined by subtracting the CDP from the CCDP. This measure is used to assess the risk significance of hardware unavailabilities especially for those operating conditions where the nominal CDP is high with respect to the incremental change of the conditional probability caused by the hardware unavailability.
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- Table 6 provides human recovery failure probability estimates for LOOP initiating event.
S Table 7 provides human recovery failure probability estimates for non-LOOP initiating events.
S Table 8 lists initiating event-specific recovery events, fractional frequency events, and associated HOUSE events.
Modeling Assumptions
! Assessment Summary Assessment type. This event was modeled as an at-power condition assessment with the PORVs inoperable due to accumulator check valves that were leaking for a one-year period (8760 hours0.101 days <br />2.433 hours <br />0.0145 weeks <br />0.00333 months <br />).
Model use. The Revision 3 Standardized Plant Analysis Risk (SPAR) model for Braidwood (Version 3.02, dated September 2003) was used for this assessment (Reference 4).
Event response and recovery modeling. Given an initiating event at power and the failure of the AFW system, the PORVs may be challenged in establishing bleed path. To open PORVs, additional air supply is required due to leaking PORV accumulator check valves. If instrument air supply would be lost due to an initiating event (e.g., single unit PC LOOP, dual unit PC LOOP, severe weather-related LOOP, grid-related LOOP, and loss of instrument air), the air supply could be provided thru the Service air compressors.
However, service air compressors need AC power and require manual starting. So, recovery of inoperable PORVs to establish bleed function would require recovery of service air compressors, recovery of AC power, and starting the compressors from the control room. For LOOP events, AC power could be recovered from the other Unit (Unit 2). For transients (IE-TRAN), steam generator tube rupture events (IE-SGTR), and other support system loss initiators (IE-LDCA, IE-LOESW, AND IE-CCW), recovery of air supply system may be performed by starting the instrument air compressors after resetting the containment isolation signal from the control room.
! Model Updates The Revision 3 Standardized Plant Analysis Risk (SPAR) model for Braidwood (Version 3.02, dated September 2003) was further modified to reflect a few system modeling changes: These changes were: (1) a boolean flag to indicate that air leak occurred in the accumulator check valves, (2) the air supply recovery to two PORVs, and (3) recovery of the required instrument air supply for non-LOOP initiators and the required station air supply for LOOP initiators.
The model updates include:
- a. Frequency values for four LOOP types and loss of instrument air were updated based on recent operating experience and estimates for recent critical years experience for PWRs and BWRs (1987 - 2001). The following updated frequency estimates for four loss of offsite power (LOOP) types are noted:
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- b. Frequency of dual unit plant-centered LOOP (IE-DPCLOOP)- A frequency of 6.279E-3 per critical year (7.16781E-07per critical hour) was estimated based on three operating events during the period 1987 - 2001 for multi-unit sites (417.2 critical years based on 534.9 calendar years for multi-unit sites and an average criticality factor of 0.78). Identification of the above three operating events were documented in References 5 and 6.
- c. Frequency of severe weather-induced LOOP (IE-SWLOOP)- A frequency of 4.448E-3 per site critical year (5.07763E-07 per critical hour) was estimated based on five operating events during the period 1987 - 2001 (1015 site critical years). Identification of the above five operating events were documented in References 5 and 6.
- d. Frequency of grid-related LOOP (IE-GPLOOP)- A frequency of 9.852E-4 per site critical year (1.12466E-07 per critical hour) was estimated based on one grid-related operating events (referred to as grid-instability event) during the period 1987 - 2001 (1015 site critical years). Identification of the above one operating events were documented in References 5 and 6.
- e. Frequency of single unit plant-centered LOOP (IE-SPCLOOP)- A frequency of 3.158E-2 per critical year (3.605E-06 per critical hour) was estimated based on 25 operating events for PWRs and BWRs during the period 1987 - 1996 (791.7 critical years). Identification of the above 25 operating events were documented in Table C-1 of NUREG/CR-5496 and estimate of critical years at power operations was documented in Table C-5 of NUREG/CR-5496.
- f. Based on the frequency estimates for the four LOOP types, estimates for fractions of the each LOOP type (frequency of a LOOP type divided by the total LOOP frequency) were calculated and documented in Table 8. These fraction estimates along with the LOOP type-specific recovery probabilities for the air supply was used in quantifying the air supply recovery probabilities to the PORVs (Figure 3).
- g. Frequency of loss of instrument air (IE-LOIA). A frequency of 2.046E-2 per critical year (2.336E-06 per critical hour) was estimated based on six operating events during the period 1987 - 2001 at PWRs (624 critical years). Identification of the above six operating events were documented in Table 4.2 of Reference 6.
Based on the frequency estimate for LOIA, estimate for frequency fraction of the LOIA to TRAN (frequency of LOIA divided by the Transient frequency) was calculated and documented in Table 8. This fraction estimate along with the LOIA-specific recovery probability for the air supply was used in quantifying the air supply recovery probability to the PORVs for the LOIA initiator (Figure 3).
- h. Air supply recovery to two PORVs. A new AND gate (IA-PORV12-LK = air supply fails to PORVs 1 & 2- IE specific) was modeled to represent air supply support dependency failure contribution. This gate was modeled at the train level (BLEED-PORV1 and BLEED-PORV2) of the BLEED1-PORVS gate (AND) of the BLEED1 fault tree (Figures 3B, 3C, and 3D). BLEED1 fault tree was connected to the FAB fault tree (feed and bleed cooling- Figure 3A).
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- i. IA-PORV12-LK (AND gate). One OR gate (IA-PORV12) to model failures of the air supply based on initiators and one basic event to model the on/off event of an air leak in the PORV accumulator were added (Figure 3E).
- j. IA-PORV12 (OR gate). Six AND gates were added to represent the failure probability contribution due to six initiators. These six initiators were: 1. Single unit plant-centered LOOP, 2. dual unit plant-centered LOOP, 3. Severe weather LOOP, 4. Grid-related LOOP, 5. Loss of instrument air, and 6. Other five scenarios (LOCCW, LDCA, LOESW, SGTR, and TRAN). To each of these six gates, an initiator-specific air supply recovery event (in 30-minutes) and a HOUSE event to indicate the onset of the initiating event (one at a time) were added. To the four AND gates involving four LOOP types, a basic event (PPR-SP-FR, PPR-DP-FR, PPR-SW-FR, PPR-GP-FR) was added to represent the LOOP type frequency fraction for each of the four LOOP types. Also, a basic event (PPR-IA-FR) was added to the AND gate for the loss of instrument air initiator to represent the LOIA frequency fraction. The IA-PORV12 fault tree is shown in Figures 3F, 3G, 3H, and 3I.
- k. The basic event, PPR-IA-FR (Frequency fraction of loss of instrument air over transients = 1.7E-2) was also added to the Main Feed Water (MFW) fault tree to reflect the failure portion that corresponds to the loss of instrument air initiator-induced failure contribution to the MFW system failure probability. This is shown in Figure 4.
This modified version of the Revision 3.02 SPAR Braidwood model was used as part of the condition analyses of the operating condition.
! Basic Event Probability Changes Table 4 documents the basic events that were added to the original plant model (Revision 3.02) and the basic events that were modified to reflect the operating condition being analyzed. The bases for these changes are as follows:
Conditional assessment probability changes. As part of the conditional analyses, probabilities for the following basic events were changed:
- a. PPR-XHE-DP-REC30, PPR-XHE-SW-REC30, PPR-XHE-GP-REC30. These basic events were set to 0.5 per demand for dual unit LOOP events (PPR-DP-FR), severe weather LOOP events (PPR-SW-FR), and grid-related LOOP events (PPR-GP-FR). Basis for this failure probability was estimated based on fail-to-recover probability for at least one diesel generator within 30 minutes (Reference 4). One diesel generator would be needed to power the service air compressor which would provide makeup air supply to PORV1 and/or PORV2.
- b. PPR-XHE-SP-REC30. This basic event was set to 0.1 per demand for single unit LOOP events (PPR-SP-FR). Basis for this failure probability was estimated based on ASP human reliability estimation method (Reference 7). Probability derivation-related details are provided in Tables 6A and 6B.
- c. PPR-XHE-IA-REC30. Fail to recover instrument air for PORV1 and/or PORV2 within 30 minutes - This basic event was set to 0.1 per demand for loss of 5
LER 456/02-002-01 instrument air (LOIA) events (PPR-IA-FR). Basis for this failure probability was based on operating experience information for the time dependent recovery of LOIA events which was documented in Table 4-8 of Reference 6.
- d. PPR-XHE-TR-REC30. Fail to recover instrument air for PORV1 and/or PORV2 within 30 minutes - This basic event was set to 0.04 per demand for transients and other support system loss initiators (IE-LDCA, IE-LOESW, IE-LOCCW, IE-SGTR). Probability derivation-related details are provided in Tables 7A and 7B.
- e. HE-NOTSPRAY (Normal spray system). This basic event was set to FALSE to reflect the fact that a probability credit was not given to the system.
- f. PPR-PRV-CKV-LK (both PORVs check valve leaked- flag). This flag was set to TRUE to initiate the leak event (operating condition) and associated recoveries.
! Uncertainty Analysis Uncertainty analysis of the operating condition along with parameters was performed using the SAPHIRE code. Default distribution types for applicable initiating events (e.g.
loss of offsite power, transients) and basic events for components were documented in the Revision 3.02 SPAR model for Braidwood. These uncertainty values and uncertainty values for condition-affected basic events were used in estimating mean condition-CDP values and mean condition-CCDP values. Other statistical values such as point values, median values, 5% values, and 95% values were also estimated for CDP and CCDP analysis cases. Estimated statistical values for the operating condition are shown in Table 5.
References
- 1. USNRC, Region III, BRAIDWOOD STATION, UNITS 1 AND 2, NRC INSPECTION REPORT 50-456/02-03 (DRP) and 50-457/02-03 (DRP) Dated June 25, 2002. ADAMS Accession Number ML021760800
- 2. USNRC Office of Enforcement, FINAL SIGNIFICANCE DETERMINATION FOR A WHITE FINDING AND NOTICE OF VIOLATION (NRC INSPECTION REPORT NO. 50-456/02-03; 50-457/02-03) (BRAIDWOOD STATION, UNIT 1) - EA-02-118 dated July 23, 2002. ADAMS Accession Number ML022040424
- 3. Exelon Nuclear, LER 456-2002-002-01, Failure of Pressurizer PORV Instrument Air Accumulator Isolation Check Valves Caused by Improper Maintenance Procedures dated September 27, 2002. ADAMS Accession Number ML022770579
- 4. Robert F. Buell, et al., Standardized Plant Analysis Risk (SPAR) Model for Braidwood Units 1 and 2 (ASP PWR B) by Idaho National Engineering and Environmental Laboratory, September 2003.
- 5. C. L. Atwood, et al., Evaluation of Loss of Offsite Power Events at Nuclear Power Plants: 1980-1996, NUREG/CR-5496", U.S. Nuclear Regulatory Commission, November 1998.
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- 6. Memorandum from P. Baranowsky of RES to J. Zwolinski of NRR, TRANSMITTAL OF PRELIMINARY ASP ANALYSIS OF NOVEMBER 2001 OPERATIONAL CONDITION AT POINT BEACH 1 AND 2, dated February 25, 2003.
- 7. J. C. Buyers, et. Al., Revision of the 1994 HRA Methodology (Draft), INEEL/EXT 0041, Idaho National Engineering and Environmental Laboratory, January 1999.
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LER 456/02-002-01 Table 1. Conditional probabilities (point values) for the dominant sequences Conditional core Core damage probability Event tree Sequence damage probability (CDP) Importance name no. (CCDP) (CCDP - CDP)2 LOOP 21 4.5E-6 4.2E-7 4.0E-6 LDCA 10 1.8E-6 1.6E-6 2.3E-7 1
Total (all sequences) 3.3E-5 2.9E-5 4.4E-6 Notes:
- 2. Importance is calculated using the total CCDP and total CDP from all sequences of all applicable event trees. Sequence level importance measures are not additive.
Table 2a. Event tree sequence logic for dominant sequences Event tree name Sequence Logic No. (/ denotes success; see Table 2b for top event names)
LOOP 21 (/RT-L) * (/EP) * (AFW) * (FAB-L)
LDCA 10 (/RT) * (AFW) * (FAB)
Table 2b. Definitions of fault trees used in event tree logic listed in Table 2a AFW NO OR INSUFFICIENT AFW FLOW EP EMERGENCY POWER IS UNAVAILABLE RT-L REACTOR FAILS TO TRIP DURING LOOP RT REACTOR TRIP FAB FEED AND BLEED COOLING FAILS FAB-L FEED AND BLEED COOLING FAILS (LOOP)
MFW FAILURE OF THE MAIN FEEDWATER SYSTEM DURING TRANSIENT 8
LER 456/02-002-01 Table 3a. CCDP cut sets for LOOP Sequence 21.
CCDP Percent Minimal cut sets1 contribution Event Tree: LOOP, Sequence 21 1.402E-7 3.2 AFW-DDP-FR-1B
- AFW-XHE-XL-EDPFR
- EPS-DGN-TM-1A
- PPR-XHE-SP-REC30
- PPR-SP-FR
- ACP-XHE-XA-XTIEA 1.402E-7 3.1 AFW-DDP-FR-1B
- AFW-XHE-XL-EDPFR
- EPS-DGN-TM-1A
- PPR-XHE-DP-REC30
- PPR-DP-FR
- ACP-XHE-XA-XTIEA 4.000E-6 Total2 Table 3b. CCDP cut sets for LDCA Sequence 10.
CCDP Percent Minimal cut sets1 contribution Event Tree: LDCA, Sequence 10 5.957E-7 33.7 AFW-DDP-FR-1B
- AFW-XHE-XL-EDPFR
- HPI-XHE-XM-FB 2.453E-7 13.6 AFW-DDP-FS-1B
- AFW-XHE-XL-EDPFS
- HPI-XHE-XM-FB 2.300E-7 Total2
- 1. See Table 4 for definitions and probabilities for the basic events.
- 2. Total CCDP includes all cut sets (including those not shown in this table).
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LER 456/02-002-01 Table 4. Definitions and probabilities for added-basic events and condition-affected basis events.
Basic event name Description Added to Probability Modified Note Base to reflect model condition PPR-DP-FR RATIO OF DUAL UNIT LOOP FREQUENCY TO TOTAL LOOP FREQUENCY YES 1.378E-001 YES 1 PPR-GP-FR RATIO OF GRID-RELATED LOOP FREQUENCY TO TOTAL LOOP FREQUENCY YES 2.163E-002 YES 1 PPR-SP-FR RATIO OF SINGLE UNIT LOOP FREQUENCY TO TOTAL LOOP FREQUENCY YES 6.933E-001 YES 1 PPR-SW-FR RATIO OF SEVERE WEATHER LOOP FREQUENCY TO TOTAL LOOP FREQUENCY YES 9.765E-002 YES 1 PPR-IA-FR RATIO OF LOIA FREQUENCY TO TRAN FREQUENCY YES 1.668E-002 YES 1 PPR-XHE-DP-REC30 FAIL TO RECOVER AIR IN 30 MIN.
- DPCLOOP YES 5.000E-001 YES 1 PPR-XHE-GP-REC30 FAIL TO RECOVER AIR 30 MIN.
- GRLOOP YES 5.000E-001 YES 1 PPR-XHE-SP-REC30 FAIL TO RECOVER AIR IN 30 MIN.
- SPCLOOP YES 1.000E-001 YES 1 PPR-XHE-SW-REC30 FAIL TO RECOVER AIR IN 30 MIN.
- SWLOOP YES 5.000E-001 YES 1 PPR-XHE-TR-REC30 FAIL TO RECOVER AIR IN 30 MIN.
- TRAN YES 4.000E-003 YES 1 PPR-XHE-IA-REC30 FAIL TO RECOVER AIR IN 30 MIN.
- LOIA YES 4.000E-002 YES 1 PPR-PRV-CKV-LK BOTH PRESSURIZER PORV CKVS LEAK YES FALSE YES 2 HE-NORSPRAYHOUSE EVENT- NO CREDIT GIVEN NO 1.000E-001 YES 3 AFW-DDP-FR-1B AFW DIESEL DRIVEN PUMP 1B FAILS TO RUN NO 1.900E-2 NO AFW-DDP-FS-1B AFW DIESEL DRIVEN PUMP 1B FAILS TO START NO 2.300E-2 NO AFW-XHE-XL-EDPFR OPERATOR FAILS TO RECOVER AFW DDP 1B (FAIL TO RUN) NO 7.500E-1 NO AFW-XHE-XL-EDPFS OPERATOR FAILS TO RECOVER AFW DDP 1B (FAIL TO START) NO 2.500E-1 NO EPS-DGN-TM-1A DG 1A UNAVAILABLE DUE TO TEST AND MAINTENANCE NO 3.100E-2 NO ACP-XHE-XA-XTIEA OPERATOR FAILS TO CROSS-CONNECT ALT POWER TO DIVISION A NO 1.000E-1 NO 10
LER 456/02-002-01 Table 4. Definitions and probabilities for added-basic events and condition-affected basis events (cont).
Basic event name Description Added to Probability Modified Note Base to reflect model condition HPI-XHE-XM-FB OPERATOR FAILS TO INITIATE FEED AND BLEED COOLING NO 2.000E-2 NO LOSP HOUSE EVENT: LOSS OF OFFSITE POWER HAS OCCURED NO FALSE NO 4 TRAN HOUSE EVENT: TRANSIENT INITIATOR HAS OCCURED NO FALSE NO 4 SGTR HOUSE EVENT: STEAM GENERATOR TUBE RUPTURE HAS OCCURED NO FALSE NO 4 LODC HOUSE EVENT: LOSS OF DC BUS 111 HAS OCCURED NO FALSE NO 4 LOESW HOUSE EVENT: LOSS OF ESSENTIAL SERVICE WATER HAS OCCURED NO FALSE NO 4 LOCCW HOUSE EVENT: LOSS OF COMPONENT COOLING WATER HAS OCCURED NO FALSE NO 4 Notes:
- 1. Basic events were affected by the operating condition through the use of the initiating event-specific HOUSE gate.
- 2. PPR-PRV-CKV-LK was set to TRUE to reflect the operating condition.
- 3. Normal spray was not taken credit. Therefore, HE-NORSPRAY was set to FALSE.
- 4. House events were invoked automatically during quantification of sequences initiated by an initiating event (Table 8).
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LER 456/02-002-01 Table 5. Uncertainty estimates for the operating condition.
Plant: Braidwood Station, Unit 1 LER ID : 456-2002-002-01 Inspection Report ID: 50/456/02-03 SDP: EA-02-118 Analysis type = Monte Carlo Samples = 3000; Seeds = 97453 Initiating event (IE) Risk measure Point estimate mean estimate 5% estimate 50% estimate 95% estimate All internal events CCDP (one hour) 3.806E-09 6.102E-09 1.031E-09 3.346E-09 1.719E-08 All internal events CDP (one hour) 3.304E-09 4.961E-09 9.302E-10 2.897E-09 1.303E-08 All internal events CCDP (8760 hours0.101 days <br />2.433 hours <br />0.0145 weeks <br />0.00333 months <br />) 3.334E-05 5.345E-05 9.032E-06 2.931E-05 1.506E-04 All internal events CDP (8760 hours0.101 days <br />2.433 hours <br />0.0145 weeks <br />0.00333 months <br />) 2.894E-05 4.346E-05 8.149E-06 2.538E-05 1.141E-04 All internal events Importance (8760 hours0.101 days <br />2.433 hours <br />0.0145 weeks <br />0.00333 months <br />) 4.398E-06 9.995E-06 8.830E-07 3.933E-06 3.644E-05 Note:
CCDP = conditional core damage probability CDP = core damage probability 12
LER 456/02-002-01 Table 6a. ASP HRA Work Sheet for Recovery event PPR-XHE-SP-REC30 for LOOP event tree.
Does the task contain significant amount of diagnosis? YES___ NO X Diagnostic failure probability estimate Performance Multiplier Shaping PSF Basis for non-nominal PSF levels Factors (PSF) Levels U
- 1. Available Inadequate 1.0a Time Barely adequate < 20 m 10 Nominal . 30 m 1 Extra > 60 m 0.1 Expansive > 24 h 0.01
- 2. Stress Extreme 5 High 2 Nominal 1
- 3. Complexity Highly 5 Moderately 2 Nominal 1
- 4. Experience/ Low 10 Training Nominal 1 High 0.5
- 5. Procedures Not available 50 Available, but poor 5 Nominal 1 Diagnostic/symptom 0.5 oriented
- 6. Ergonomics Missing/Misleading 50 Poor 10 Nominal 1 Good 0.5
- 7. Fitness for Unfit 1.0a Duty Degraded Fitness 5 Nominal 1
- 8. Work Poor 2 Processes Nominal 1 Good 0.8 Combined PSFs = 1 (1)x(2)x(3)x(4)x(5)x(6)x(7)x(8)
Nominal Failure Probability 1.0E-2 Adjusted Probability = Total x Nominal NA
- a. Task failure probability is 1.0 regardless of other PSFs.
NA = not applicable.
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LER 456/02-002-01 Table 6b. ASP HRA Work Sheet for Recovery event PPR-XHE-SP-REC30 for LOOP event tree (cont).
Action failure probability estimate Performance Multiplierb]
Shaping PSF Basis for non-nominal PSF levels Factors (PSF) Levels U
- 1. Available Inadequate 1.0a Time Time available . time 10 X Note 1 required Nominal 1 Available > 50x time 0.01 required
- 2. Stress Extreme 5 High 2X Note 2 Nominal 1
- 3. Complexity Highly 5X Note 3 Moderately 2 Nominal 1
- 4. Experience/ Low 3 Training Nominal 1 High 0.5
- 5. Procedures Not available 50 Available, but poor 5 Nominal 1
- 6. Ergonomics Missing/Misleading 50 Poor 10 Nominal 1 Good 0.5
- 7. Fitness for Unfit 1.0a Duty Degraded Fitness 5 Nominal 1
- 8. Work Poor 2 Processes Nominal 1 Good 0.8 Combined PSFs = 100 (1)x(2)x(3)x(4)x(5)x(6)x(7)x(8)
Nominal Failure Probability 1.0E-3 Adjusted Probability = Total x Nominal 0.1
- a. Task failure probability is 1.0 regardless of other PSFs.
Combined failure probability = Diagnosis failure Probability + Action failure Probability = 0 + 0.1 = 0.1 Is this basic event assigned to first task in a sequence of Event Trees SPCLOOP, DPCLOOP, GRLOOP, SWLOOP-?
YES X NO____
(No means that there exists dependence between tasks which should be evaluated furher.)
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LER 456/02-002-01 Note 1: 30 minutes would be available to recover power from unit 2 to station air compressor of unit 1. The same time would be required to perform the recovery action. Recovery action would involve resetting containment isolation signals, closing of breakers locally, and starting the station air compressors to provide makeup air supply to inoperable PORVs..
Note 2: a level of high stress would exist. For dominant sequences, both trains of the AFW pumps would be inoperable, and the instrument air compressors would be tripped due to LOOP event.
Note 3: This recovery action is a non-routine recovery action for the anticipated LOOP event. The recovery action is performed for mitigating inoperable PORVs due to leaked air accumulator check valves. It would be very difficult to perform the recovery action locally during a LOOP event.
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LER 456/02-002-01 Table 7a. ASP HRA Work Sheet for Recovery event PPR-XHE-TR-REC30 for non-LOOP event trees.
Does the task contain significant amount of diagnosis? YES___ NO X Diagnostic failure probability estimate Performance Multiplier Shaping PSF Basis for non-nominal PSF levels Factors (PSF) Levels U
- 1. Available Inadequate 1.0a Time Barely adequate < 20 m 10 Nominal . 30 m 1 Extra > 60 m 0.1 Expansive > 24 h 0.01
- 2. Stress Extreme 5 High 2 Nominal 1
- 3. Complexity Highly 5 Moderately 2 Nominal 1
- 4. Experience/ Low 10 Training Nominal 1 High 0.5
- 5. Procedures Not available 50 Available, but poor 5 Nominal 1 Diagnostic/symptom 0.5 oriented
- 6. Ergonomics Missing/Misleading 50 Poor 10 Nominal 1 Good 0.5
- 7. Fitness for Unfit 1.0a Duty Degraded Fitness 5 Nominal 1
- 8. Work Poor 2 Processes Nominal 1 Good 0.8 Combined PSFs = 1 (1)x(2)x(3)x(4)x(5)x(6)x(7)x(8)
Nominal Failure Probability 1.0E-2 Adjusted Probability = Total x Nominal NA
- a. Task failure probability is 1.0 regardless of other PSFs.
NA = not applicable.
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LER 456/02-002-01 Table 7b. ASP HRA Work Sheet for Recovery event PPR-XHE-TR-REC30 for non-LOOP event trees (cont).
Action failure probability estimate Performance Multiplierb]
Shaping PSF Basis for non-nominal PSF levels Factors (PSF) Levels U
- 1. Available Inadequate 1.0a Time Time available . time 10 X Note 1 required Nominal 1 Available > 50x time 0.01 required
- 2. Stress Extreme 5 High 2X Note 2 Nominal 1
- 3. Complexity Highly 5 Moderately 2X Note 3 Nominal 1
- 4. Experience/ Low 3 Training Nominal 1 High 0.5
- 5. Procedures Not available 50 Available, but poor 5 Nominal 1
- 6. Ergonomics Missing/Misleading 50 Poor 10 Nominal 1 Good 0.5
- 7. Fitness for Unfit 1.0a Duty Degraded Fitness 5 Nominal 1
- 8. Work Poor 2 Processes Nominal 1 Good 0.8 Combined PSFs = 40 (1)x(2)x(3)x(4)x(5)x(6)x(7)x(8)
Nominal Failure Probability 1.0E-3 Adjusted Probability = Total x Nominal 0.04
- a. Task failure probability is 1.0 regardless of other PSFs.
Combined failure probability = Diagnosis failure Probability + Action failure Probability = 0 + 0.04 = 0.04 Is this basic event assigned to first task in a sequence of non-LOOP event Trees? YES X NO____
(No means that there exists dependence between tasks which should be evaluated furher.)
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LER 456/02-002-01 Note 1: 30 minutes would be available to provide air to the PORVs after two AFW pumps would be lost and the failure to recover one of the two main feedwater pumps to steam generators. The same time would be required to perform the recovery action.
Recovery action would involve resetting many containment isolation signals, and starting the compressor from the control room to provide makeup air supply to inoperable PORVs.
Note 2: a level of stress higher than the nominal level would exist for those sequences of event trees in which both trains of the AFW pumps would be inoperable, and the instrument air compressors would be tripped due to the above initiating events.
Note 3: This recovery action is somewhat difficult to perform since many containment isolation signals would have to be reset prior to starting the compressor to provide makeup air to the PORVs.
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LER 456/02-002-01 Table 8. List of Initiating event-specific recovery events for operating condition, fractional frequency events, and HOUSE events.
Initiating event HOUSE Recovery event for Fractional frequency Estimate for event6 operating condition6 event for initiating fractional event6 frequency event Single unit loss of offsite LOSP PPR-XHE-SP-REC30 PPR-SP-FR Note 1 power (SPCLOOP)
Dual unit loss of offsite LOSP PPR-XHE-DP-REC30 PPR-DP-FR Note 2 power (DPCLOOP)
Grid-related loss of offsite LOSP PPR-XHE-GR-REC30 PPR-GP-FR Note 3 power (GPLOOP)
Severe weather loss of LOSP PPR-XHE-SW-REC30 PPR-SW-FR Note 4 offsite power (SWLOOP)
Loss of instrument air TRAN PPR-XHE-IA-REC30 PPR-IA-FR Note 5 (LOIA)
Transients TRAN PPR-XHE-TR-REC30 NOT APPLICABLE NOT APPLICABLE (TRAN)
Steam generator tube SGTR PPR-XHE-TR-REC30 NOT APPLICABLE NOT APPLICABLE rupture (SGTR)
Loss of DC bus 1A LODC PPR-XHE-TR-REC30 NOT APPLICABLE NOT APPLICABLE (LDCA)
Loss of essential service LOESW PPR-XHE-TR-REC30 NOT APPLICABLE NOT APPLICABLE water (LOESW)
Loss of component LOCCW PPR-XHE-TR-REC30 NOT APPLICABLE NOT APPLICABLE cooling water (LOCCW)
Note:
- 1. PPR-SP-FR - A fractional estimate of 6.933E-001 was calculated based on a value of 3.605E-6 per hour for frequency of SPCLOOP and a value of 5.250E-006 per hour for frequency of total LOOP event.
2 PPR-DP-FR - A fractional estimate of 1.378E-001 was calculated based on a value of 7.168E-7 per hour for frequency of DPCLOOP and a value of 5.250E-006 per hour for frequency of total LOOP event.
3 PPR-GP-FR - A fractional estimate of 2.163E-002 was calculated based on a value of 1.125E-7 per hour for frequency of GRLOOP and a value of 5.250E-006 per hour for frequency of total LOOP event.
4 PPR-SW-FR - A fractional estimate of 9.765E-002 was calculated based on a value of 5.078E-7 per hour for frequency of SWLOOP and a value of 5.250E-006 per hour for frequency of total LOOP event.
5 PPR-IA-FR - A fractional estimate of 1.668E-2 was calculated based on a value of 2.336E-6 per hour for frequency of LOIA for PWRs and a value of 1.400E-4 per hour for frequency of all transients.
6 Basic event description is documented in Table 4.
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LER 456/02-002-01 L O SS O F R E AC T O R EM E RG EN C Y A U XI L IA R Y PO RV s R C P S E AL S O FFS I TE F &B H IG H O F F S IT E RCS R ES ID U A L LOW HI G H O F F S IT E TR I P PO W E R FE E D W A TE R AR E S U R VI VE PO W E R C O O L IN G P RE S SU R E PO W ER R EC C O OLD OW N H EA T P R ES S U RE PR E SS U R E PO W E R S YS T E M C L O SE D LOO P R EC O VE R Y ( L O O P) IN J E CT IO N IN 6 H R S R EM O VA L R E C IR C U L AT IO N RE C IR C U L A T IO N IE -L O OP R T -L EP AF W P O RV S R CPSL O P -2H F A B -L HP I OP -6 H C O O LD OW N RHR LP R HP R # E N D -S T A TE 1 O K 2 O K 3 O K 4 O K 5 CD 6 O K 7 CD 8 CD 9 O K HP R - L 10 CD H P I- L 11 CD 12 O K 13 CD 14 O K HP R - L 15 CD H PI -L 16 CD 17 O K 18 CD 19 O K H PR - L 20 CD 21 CD 22 T SBO 23 CD Figure 1. Braidwood 1 - Loss Of Offsite Power Event Tree Showing Dominant Sequence LOOP-21.
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LER 456/02-002-01 LO S S O F RE A C T O R A U X ILI A R Y PO R Vs F &B HI G H R CS R E S ID U A L HIG H DC B US 11 1 TR IP FE E D W A T E R AR E CO O LIN G P R E S S UR E C O O LD O W N H EAT P R E S S UR E CL O S E D IN J E C T IO N R EMO VAL RE C IRC IE - L D C A RT AF W PO R VS F AB H PI C O O LD O W N RHR H PR # E N D -S T A T E FR E QU E N C Y 1 OK 2 OK 3 OK 4 CD 5 OK 6 CD 7 CD 8 OK 9 CD 10 CD 11 CD Figure 2. Braidwood 1 - Loss of DC Bus A Event Tree Showing Dominant Sequence LDCA 10.
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LER 456/02-002-01 F EED AND BLEED C O O LIN G F A ILS FAB F A ILU R E T O P R O V ID E B L E E D P O R T IO N N O O R IN S U F F IC I E N T O F FE E D A N D B LE E D F LO W FR O M TH E C O O LIN G HP I SYST EM B L E ED 1 HPI Figure 3a. Braidwood 1 - Fault tree for Feed and Bleed Cooling.
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LER 456/02-002-01 F A I L U R E T O P R O V ID E BL EE D P O R T IO N O F F EE D A N D BL EE D C O O L IN G B LE ED 1 O PE R AT O R F AILS F AIL U R E O F P O R V S T O I N IT IA T E F E E D T O O PE N A N D B L E E D C O O L IN G H P I- X H E -X M -F B B L E E D 1 -P O R V S P O R V 1 F A IL U R E S P O R V 2 F AILU R E S
( R C -4 5 5 A ) (R C -4 5 6 )
B L E E D -P O R V 1 B L E E D -P O R V 2 Figure 3b. Braidwood 1 - Fault tree for Bleed Portion of Feed and Bleed Cooling.
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LER 456/02-002-01 P O R V 1 F A IL U R E S
( R C -4 5 5 A )
B L E E D -P O R V 1 P OR V 1 BL OC K D IVISIO N 1 A P O R V 1 F A IL S V A L VE F A ILS IN D C P O W E R F A ILS T O O PE N O N D EM A N D C L O S E D P O S IT I O N B LE E D - P O R V 1- BL K 1 D I V -A -D C -L T P P R -S R V - C C -P R V 1 P O R V 1 B LO C K P O R V 1 BLO C K VA LV E F A ILU R E S VA LV E IS C LO SE D D U R IN G F U L L PO W ER B L E E D -P O R V 1 -B L K 2 P P R -M O V - F C -B L K 1 A IR S U PP LY F A ILS T O P O R V S 1 & 2 - IE SP EC IF IC D I V I S IO N 1 A P OR V 1 BL OC K A C P O W E R FA I L S V AL VE F A ILS T O O PE N I A -P O R V 1 2 -L K D I V -A -A C P P R - M O V -C C -B L K 1 Figure 3c. Braidwood 1 - Fault tree for PORV1 Failures.
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LER 456/02-002-01 P O R V 2 FA IL U R E S
( R C -4 5 6 )
BLE E D-P O RV 2 P O RV 2 B L O CK P O R V 2 F A IL S D IV I S ION 1 B V A L V E F A IL S IN T O O PEN O N D EMAN D D C P O W E R FA I L S C L O S E D P O S IT IO N B LE E D -P O R V 2 -B L K 1 D IV -B -D C -L T P P R - S R V - C C -P R V 2 P O R V 2 B LO C K P O RV 2 B LO C K V A L V E FA IL U R E S V A L V E IS C L O S E D D URI NG F ULL P O W E R B L E E D - P O R V2 - B L K2 P P R - M O V- F C -B L K 2 A IR S U P P L Y F A IL S T O P O R V S 1 & 2 - IE S P E C IFIC D IV IS IO N 1 B P O RV 2 B L O CK A C P O W E R F A IL S V A L V E FA IL S TO O PEN IA - P O R V 1 2 - LK D IV - B -A C P PR - M O V - C C -B L K 2 Figure 3d. Braidwood 1 - Fault tree for PORV 2 Failures.
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LER 456/02-002-01 A IR S U P P L Y F A IL S T O P O R V S 1 & 2 - IE S P E C IF IC IA -P O R V 1 2 -L K A IR S U P P L Y R E C O V E R Y O C -B O T H F A IL S T O P O R V S 1 & 2 - IE P R E S S U R IZ E R P O R V S P E C IF IC CKV S LE AK ED IA -P O R V 1 2 P P R -P R V -C K V -L K Figure 3e. Braidwood 1 - Fault tree for Air Supply Fails to PORVs 1 & 2.
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LER 456/02-002-01 AIR SU P PL Y R EC O VE R Y F AILS T O PO R V S 1& 2- IE SP EC IF IC IA- P O R V 12 D U AL U N IT PC L O O P M O R E B AS IC E VE N T S IN S T R U M EN T A IR G R ID -R E LAT ED F OR IA- PO R V1 2 L OO P G A TE R EC -D PC LO O P IA- P O R V 12 -1 R E C -LO IA R E C -G R LO O P F R AC T IO N OF F AIL T O R EC O VE R F AIL T O R EC O VE R F R AC T IO N O F D P C LO O P O VE R AI R IN 30 M IN .- AIR IN 30 M IN .- G R LO OP O VE R LO OP L OO P D P C LO OP G R LO O P 1 .4 E- 1 5 .0 E- 1 5.0E - 1 2.2E - 2 P P R -D P -F R P P R -X H E - D P -R E C 30 P P R -X H E - G P -R E C 30 P PR -G P -F R H O U S E EV EN T : H O U S E EV EN T :
LO SS O F O F F S IT E LO SS O F OF F S IT E PO W ER H A S O C C U R ED PO W ER H AS OC C U R E D F A LS E F A LS E LO S P LO S P Figure 3f. Braidwood 1 - Fault Tree for Air Supply Recovery Fails to PORVs 1 & 2.
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LER 456/02-002-01 M O R E B AS IC E VE N T S F O R I A- PO R V1 2 GA T E IA- P O R V 12 -1 S IN G L E U N I T O T H ER F O U R I E s S EV ER E W E AT H E R PC L O O P L OO P R EC -S P C L O O P R E C -O T H E R 4 R E C -S W LO O P F R AC T IO N O F F AI L T O R EC O VE R F AIL T O R EC O VE R F R AC T IO N O F S PC L O O P O VE R AIR I N 30 M IN .- AIR IN 30 M IN . - S W L O O P O VE R L O O P L OO P S PC L O O P S W LO O P 6 .9 E- 1 1 .0 E- 1 5.0E - 1 9.8E - 2 P P R -S P -F R P P R -X H E - SP - R E C 3 0 P P R -X H E - SW -R E C 30 P PR -S W -F R H O U S E EV EN T : H O U S E EV EN T :
LO SS O F O F F S IT E LO SS O F O F F S IT E PO W ER H A S O C C U R ED PO W ER H AS O C C U R E D F A LS E F A LS E LO S P LO S P Figure 3g. Braidwood 1 - Fault Tree for Air Supply Recovery Fails to PORVs 1 & 2 (cont).
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LER 456/02-002-01 IN S T R U M E N T A I R R E C - L O IA F R A C T IO N O F F A IL T O R E C O V E R H OU SE EVEN T:
L O IA O V E R T R A N A I R I N 3 0 M I N .- T R A N S IE N T IN IT IA T O R L O IA HA S O C CU R E D P P R - IA - F R P P R - X H E - IA - R E C 3 0 TRAN Figure 3h. Braidwood 1 - Fault Tree for Instrument Air.
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LER 456/02-002-01 O T H ER F O U R IE s RE C-O THER4 F AIL T O R E C O VE R F IR E O T H ER F O U R AI R IN 30 M IN .- IE S - O N E A T A TRA N T IM E 4.0E -3 P PR-X HE-T R-RE C30 RE C-FO UR-IE S H O U SE E VE N T : H O U S E EV E N T : H O U S E E VE N T : H O U SE EV E N T :
L O S S O F C C W H AS LO SS O F D C BU S LO SS O F E SW H A S S G T R H AS O C C U R E D O CCURE D 1 11 H A S O C C U R E D O CCURE D FALS E F A LSE FAL SE FA LS E LO CCW LO DC LO ES W S GTR Figure 3i. Braidwood 1 - Fault Tree for Other Four IEs.
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LER 456/02-002-01 F A ILU R E O F T H E M AIN F EE D W A T ER S YST EM D U R IN G T R A N S M FW B OT H U N IT 1 M AIN F EE D W A T ER O PE R AT O R F AILS F R A C T IO N OF SA T s O O S F OR S YS T EM U N A VA IL AB LE T O R ES T O R E M F W L OIA O VE R T R AN T& M G IVE N IN IT IAT O R F L OW 1 .0 E- 2 2.0E - 1 1 .0 E -2 1.7E - 2 AC P -T R M -FC - 2S A TS M F W - S YS -U N AV A IL M FW -X H E -E RR O R P P R- IA- FR F AILU R E OF D IV ISION 1 A D IVIS IO N 1B M O T OR - D R IV EN M F W D C P OW E R F A IL S D C PO W E R F AILS P U M P S T O IN J EC T D IV- A -D C- LT D IV - B- DC -L T M F W -P U M PS Figure 4. Braidwood 1 - Fault Tree for Main Feedwater During Transients.
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