ML20149K473
| ML20149K473 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-036-00 | |
| Download: ML20149K473 (5) | |
Text
B-305 Accident Sequence Precursor Program Event Analysis LER No: 410/88-036 Ri Event
Description:
Both diesel generators unavailable for 42 h Date of Event: July 21, 1988 Plant: Nine Mile Point 2 Sunmmary While at 100% power, both diesel generators were inoperable for about 42 h. Due to equipment failure, one diesel was not recognized as being unavailable, while the second diesel was taken out of service for test and maintenance. The first diesel was inoperable due to a failed con-tact in a remote shutdown panel, which disabled the opening circuit in its associated cooling water valve control logic. The conditional probability of core damage for this event is estimated to be 1.1 x 0-5.
The relative significance of the event compared with other potential events at Nine Mile Point 2 is shown below.
-_LER 410/88-036 RI ILI I I I Trip_] IL EP Unavail TripLOOP (360 hrs)
HPCI/RCIC Unavail (360 hrs) Trip with HPCI Unavail Event Description On July 21, during a surveillance test of the Division II diesel generator service water valve, a contact on the remote shutdown panel transfer switch failed to return to its normal position. This disabled the opening circuit in the valve's control logic. Since operator indi-cation appeared normal, unavailability of the valve was not detected and the diesel was not recognized as being inoperable. The Division I diesel was taken out of service for 42 h (between July 25 and July 26) for the purpose of performing instrument calibrations. The failed ser-vice water valve was discovered on July 28, during the monthly opera-tional surveillance test for the Division II diesel.
B-306 Event-Related Plant Design Information Two diesel generators are provided on Nine Mile Point 2 to supply the redundant safety-related buses. A third diesel generator provides power to the high-pressure core spray pump. This DC was available during the event.
ASP Modeling Assumptions and Approach This event has been modeled as a 42-h unavailability of emergency power with a probability of diesel nonrecovery within 30 min assigned p(nonrecovery) =0.34. This estimate is based on the assumption that the inoperability of the cooling water valve for the Division II DG could be detected, the DG tripped prior to damage, the valve locally opened, and the DG restarted if required.
Analysis Results The core damage frequency for this event is estimated to be 1.1 x 10-5.
The dominant sequence for this event (highlighted on the following event tree) involves a postulated loss of offsite f ower during the 42-h emergency power unavailability (p = 1.6 x 10- ), failure to recover emergency power (p =0.34), and failure to recover AC power prior to battery depletion (p 0.21). This estimate is considered conservative, since the HPCS diesel was operable, and it is possible that power could have been provided to the Division I or II battery chargers from this diesel ge~nerator.
B-307
.0 LOOP ORT IPTI 01 014 RU SHU DOOOP RETS LONG SAM OR RG PS O P O E Z40- N
... t, IO TOREDAMAGE OK 0O CORE DAMAGE SD OREDAMAGE 0:
I9 CORE DAUSGE OK 43 CORE DAMAGE 00 OK 14 CORE DAMAG OK TOEDAMAGE CO 00 SO OREDAMAGE S0 TORTDAMAE 09 49 TOREDAMGE OREDAMAE CS OK 01 TOR DAMAGE 0K TORE DAMAGE
- 1 03 OREDAMAGE TORE DAMAE s4 00 EM OiS TOREDAM.E I. TOREDAMAGE OREDAMAGE CO TOIRT DAMAGE O COREDAMAGE 00 COREDAMAGE U OREDAMAGE OREDAMAGE C3 07 COREMW0 Dominant Core DamageSectience for LER410/88-036 RI
B-308 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 410/88-036 Event
Description:
Both emergency diesel generators unavailable for 42 hours4.861111e-4 days <br />0.0117 hours <br />6.944444e-5 weeks <br />1.5981e-5 months <br />.
Event Date: 07/21/88 Plant: Nine Mile Point 2 UNAVAILABILITY, DURATIDN= 42 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 1. 6E-04 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/initiator Probability CD LOOP 1.1E-05 Total l.1E-0S AIMS LOOP I4.4E-16 Total (4.4E-16 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER) t Sequence End State Prob N Rec-83 loop EMENG.POWER -rx.shutdown/ep ep.rec CO l.lE-05 8.2E-02 97 loop EMERG.POMER rx.shutdown ATMS 1.EE-09 8.2E-02 98 loop -EMERO.POWER rx.shutdown ATMO 1.6E-09 ) 1.EE-0l
-- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
98 loop -EMERG.POMER rx.shutdown ATWS l.6E-09 1 .6E-01 83 loop EMERG.POMER -rx.shutdown/ep ep.rec CD l.lE-05 8.2E-02 97 loop EMERD.POMER rx.shutdown ATWS 1.6E-09 8.2E-02
--non-recovery credit for edited case Note: For unavailabilities, conditional probability values are differential values which reflect the added risk duEý to failures associated with an event. Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
SEQUENCE MODEL: a: \sealmod\bwrcseal .cmp BRANCB MODEL: a:\sealmod\ninemi2.sll PROBABILITY FILE: a:\sealmod\bwr_csll.pro No Recovery Limit BRANCB FREQUENCIES/PROBABILITIES Branch System Non-Recov Opt Fail trans 1. IE-03 1. GE-I-G loop 1. 6E-05 2.4E-01 1 oca 3. 3E-0 6 5.OE-01 rx.shutdown 3.GOE-05 1. GEtOG rx .shutdown/eD 3. 5E-04 1. GE+00S pcs/t tans 1. 7E-01 1. GE-GO srv.chall/trans .-scram 1.OE+00 1. GE-i-G Event Identifier: 410/88-036
B- 309 srv.chall/loop.-scram l.OE+00 1.06+00 srv close 5. 9E-02 1.06+00 EMERG. POWER 2.9E-03 > 1.06+00 8.06-01 > 3.4E-01 Branch Model: 1.OF.2 Train 1 Cond Prob: 5.OE-02 > Unavailable Train 2 Cond Prob: 5.7E-02 > Failed ep. rec 2.1E-01 1 .06+00 fw/pcs .trans 2 .9E-0 1 3.4E-01 fw/pcs .loca 4.06-02 3.46-01 hpc i 2 . OE-02 3.4E-01 robc 6. OE-02 7.06-01 o rd 1 .0E-02 1 .06+00 1.0E-02 s rv .ads 3. 7E-03 7.1E-01 1.0E-02 Ipos 2.O0 -02 3.46-01 Ipol (rhr) /lpcs 6. 0OE-04 7.1E-01 rhr (sdc) 2.36-02 3.4E-01 1 .06-03 rhr (sdc)/ I-poi 2.06E-02 3. 4E-01 1. 0 -03 rhr (sdc) /lpci 1. 0 +00 1 .06+00 1.06E-0 3 rhr(spcooJ2 /rhr(sdc) 6. 7E6-03 1 .06+00 rhr(spcool) /-lpci.rhr(sdc) 2.06E-03 1 .06+00 rhr(spcool) /lpci.rhr(sdc) 9.36-02 1.06+00 rhrsw 2 .0E-02 3 .4E-01 2 .06-03
- branch model file
- forced tMinarlck 11-12-1989 15:23:06 Event Identifier: 410/88-036