ML20147A502
| ML20147A502 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter Office of Nuclear Regulatory Research |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-018-00 | |
| Download: ML20147A502 (5) | |
Text
B-286 Accident Sequence Precursor Program Event Analysis LER No: 397/88-018 Event
Description:
Both emergency diesel generators unavailable Date of Event: May 22, 1988 Plant: Washington Nuclear Plant, Unit 2 Sunmmary While at 0% power, an emergency diesel generator was discovered unavail-able while the other was out for maintenance. Based on event specifics, this could have occurred at power. The conditional probability of core damage has been calculated at 5.6 x 10-6. The relative significance of this event compared with other potential events at WNPS 2 is shown below.
LER 397/88-018 IE- IE7IE- 1:-5I-4 IE3IE-Trip TripLOOP L EP(360Unavail hrs)
HPCI/RCIC Unavail (360 hrs) Trip with HPCI Unavail Event Description While at 0% power, the control room operator noted that the green status light for the division two emergency diesel generator start circuit was not energized. Investigation revealed that a two-position transfer switch was in a midposition between the " Normal" and "Emergency" posi-tion, which would probably prevent the diesel generator from starting on demand. Since the switch was located at waist height and 6 in. from the edge of the control panel, it was postulated that the switch may have been inadvertently bumped into this middle position by an equipment operator. Coincident with the unavailability of the division two emer-gency diesel generator, the division one diesel generator was out of service for modification. Corrective action was taken to determine if protective barriers should be installed to prevent recurrence of this incident.
B-287 Event-Related Plant Design Information The emergency power system on WNPS 2 utilizes two diesel generators that supply power to two safety-related divisions. A third diesel generator powers the high-pressure core spray pumps.
ASP Modeling Assumptions and Approach The event has been modeled as a 10-h emergency power system unavail-ability. The likelihood of nonrecovery was estimated to be 0.34 (local recovery).
Analysis Results The conditional probability of core damage is estimated to be 5.6 . 10-6. The dominant core damage sequence (highlighted in the following event tree) is associated with a loss of offsite power occurring during the 10-h vulnerability (p = 8.6 x 0-5), failure to recover emergency power (p =.34), and failure to recover electric power in the long term (p =0.17).
B3-288 LOOIUP H-C RV PCI RHER RHR EW GO P SHUT REC SyGEC OR RC R RP (E (R4FQ (SOC (OP OR 40 END COMA (105) CHAL "Pps ADS MODE) MRCOE) OER NO STATE OK
- ,1 GORED E
- 4. CORE DAMAGE OK 49 GORE DAMAGE OK 4 GOREDAMAGE OR OR S1 CORE DAMAGE OR OR 53 coREDAMAGE 54 CORE DAMAGE OR S. COGREDAMAGE G4OR DAMAGE OR OR DAMAGE MACOE COR o DAMAGE OK DAMAGE MACOE OR OK COREDAMAGE
- 2 54 CORE DAMAGE OR 62 COe DAMAGE OREDAMAGE G3 0A CoREDAMAGE OK OR DAMAGE 00 OREDAMAGE G0 OK OREDAMAGE G9 OK OK al COReDAMAGE
.2 COREDAMAE 93 COGRE DAMAGE 97 RAlWS Dominant Core Damage Sequence for LER 397/88-018
B-289 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 397/88-018 Event
Description:
Unavailability of emergency power Event Date: 05/22/88 Plant: MNPSS 2 UNAVAILABILITY, DURATION= 10 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 8 . SE-I5 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 5. SE-IS6 Total 5.IOE-06 ATNS LOOP 5.EE-l7 Total 5.6E-17 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rectk 83 loop EMERG.POWER -rx.shutdown/ep ep.rec CD 5.IOE-06 1 BE-01 97 loop EMERG.POMER rx.shutdown ATWS 8. 8E10l I 8 E-Il 98 loop -EMERG.POWER rx.shutdown AIMS 8.8E-10 3. 5E-01
-non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
98 loop -EMERO.PONER rx.shutdown ATWS 8.8E-10 3. 5E-Il 83 loop EMERG.POWER -rx.shutdown/ep ep.rec CD 5. SE-IS 1.8E-Il 97 loop ENERG.POWER rx.shutdown AIMS 8. 8E-I0 1. SE-Il
- non-recovery credit for edited case Note: For unavailabilities, conditional probability values are differential values which reflect the added risk due to failures associated with an event. Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
SEQUENCE MODEL: c:\asp\sealmod\bwrcseal.cmp BRANCH MODEL: c:\asp\sealmod\wnp2.sll PROBABILITY FILE: c:\asp\sealmod\bwr_csll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch. System Non-Rocov Opt Fail trans 4 .SE-04 l.IE-t-I loop 1.6E-05 5.IE-01 loca 3.3E-06 5.IE-Il rx.shutdown 3.IE-05 l.IE+II rx.shutdown/ep 3.5E-04 l.IE+I0 pcs/trans 1.7E-01 l.IE+II srv.chall/trans .-scram l.IE+II l.IE+II Event Identifier: 397/88-018
B-290 srv.chall/loop.-scram 1 .06+00 1 .OE+00 srv.close 5. 9E-02 1. 06.00 EMERO .POWER 2.9E-03 > 1.06-tOO 8.OE-01 > 3.4E-01 Branch Model: 1.OF.2 Train 1 Cond Prob: 5.06-02 > Unavailable Train 2 Cond Prob: 5.76-02 > Unavailable ep. rec 1.7E-01 1. OE+/-00 fw/pcs .trans 4. 6E-01 3.4E-01 fw/pcs.boca 1.06+00 3 .4E-01 hpc i 2 .0E-02 3.4E-01 rcic 6.0OE-02 7 .OE-01 o rd 1. OE-02 1. OE+00 1. 0 -02 srv .ads 3. 76-03 7.1E-01 1.06-02 lpos 2 .0E-02 3.4ZE-01 lpci (rhr)/lpon 6. OE-04 7.1lE-01 rhr (sdc) 2 .3E-02 3.4E6-01 1.06-03 rhr (sdc) /-lpci 2 . OE-02 3.4E-01 1.06-03 rhr (sdo) Ilpci 1. OE+00 1 .06+00 1.06E-0 3 rhr(spcool) /rhr(sdc) 2 . OE-0 3 3. 4E-01 rhr (spcooi) /-lpci .rhr (sdo) 2 .0E-03 3.4E-01 rhr(spoool) /lpci.rhr(sdc) 9. 3E-02 1.06+/-00 rhrsw 2 . OE-02 3.4E-01 2.06E-03
- branch model file
- forced Minarick 11-13-19899 13:31:53 Event Identifier: 397/88-018