ML20149K497
| ML20149K497 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-021-00 | |
| Download: ML20149K497 (5) | |
Text
B-6 7 Accident Sequence Precursor Program Event Analysis LER No: 255/88-021 Event
Description:
Potential loss of service water pumps Date of Event: November 4, 1988 Plant: Palisades Summnary Spurious service water pump trips led to the discovery of incorrectly set relays that could have resulted in a loss of service water during high heat load situations. The conditional probability associated with the event is estimated to be 2.7 x 10-5. The relative significance of this event compared with other potential events at Palisades is shown below.
-LER 255/88-021 1E-8 I1E-7 IE-6 IE-5 I1E-4 IE-3 IE-2 TpLOOP] L EP Unaai1 Trip w/1 AFW AFW Unavail Train Unavail (360 hrs)
Event Description From Feb. 5, 1987, through Nov. 9, 1988, several spurious service water pump trips occurred. The cause of these trips was that the original relay settings did not account for the motor service factor rating.
These low settings allowed the time overcurrent (TOC) relays to pick up and prevented the high drop out (HDO) relays from dropping out, which resulted in the pump trips. Under these conditions a pump trip could occur shortly after starting or it may occur several days after starting if the HDO relay never resets. No spurious service water pump trips occurred prior to Feb. 5, 1987. Prior to late 1986, the service water pump impellers were improperly filed. In late 1986, the service water pump impellers were properly filed and installed. Prior to the proper filing of the impellers, it was determined that service water pumps were
B-68 not pumping sufficient flow. This resulted in the pumps requiring lower currents prior to late 1986.
Event-Related Design Information Three half-capacity motor-driven pumps draw screened and intermittently chlorinated Lake Michigan water and supply component cooling water heat exchangers and emergency diesel generators with service water. Service water is also provided to the (1) containment air coolers, (2) engi-neered safeguards room coolers, (3) instrument air compressors, (4) con-tainment fire hose reel station, and (5) control room air-conditioning components. The component cooling water system provides cooling for (1) high-pressure injection, (2) low-pressure injection, (3) containment spray, and (4) various radwaste and fuel-building systems.
ASP Modeling Assumptions and Approach This event has been conservatively modeled as a potential loss of emergency power, high-pressure injection, low-pressure injection, and feed and bleed capability during time periods when each service water pump would be operating in high heat load situations. This has been assumed to exist when the D~s are operating and sump recirculation cooling is being utilized. Because the diesels start on an SI signal, these situations involve all cases in which CSR is utilized. (Note that service water pump trips were not observed in conjunction with DG test-ing.)
Analysis Results The conditional probability of severe core damage estimated for this event is 2.7 x 1O-5. Two sequences are dominant:
- 1. A LOOP with the same mitigating system failures (this sequence is highlighted on the following event tree).
- 2. A trip with unrecoverable loss of secondary-side cooling, successful bleed and feed (which is expected to initiate SI), and failure of containment cooling due to service water pump trip.
B- 69 LOOP RTALOOP EP AWI SR\'
IPORV/ SRV I PORV SEAL EP REC HP PI OR SEQ END I(LONG) HI OPEN CS NO STATE ICHALL RESEAT LOCA I I OK OK 41 CO 42 CO OK OK 56 CO 43 CO 44 Go 45 CO OK 46 CO 47 CO 48 CO OK 49 CO 50 CO OK 51 CO 52 CO 53 CO OK 54 CO 55 CO 40 ATWS Dominant Core Damage Sequence for LER 255/88-021
B-70 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event identifier: 255/88-021 Event
Description:
Potential loss of service water pumps Event Date: 11/04/88 Plant: Palisades UNAVAILABILITY, DURATION= 6130 NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 6. 7E-01 LOOP 5. 3E-02 LOCA 6. 3E-03 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 1. lE-OB LOOP 1. 6E-05 LOCA 1. 4E-07 Total 2. 7E-05 ATWS TRANS B. BE+B0 LOOP B. BE-400 LOCA 0 .BE+00 Total B. BE+BB SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER) 55 Sequence End State Prob N Rec 56 loop -rt/loop -emorg.power afw -hpi(f/b) -hpr/-hpi -porv.open CO I. 6E-05 1. 4E-Bl CSR 19 trans -rt afw miw -hpi(f/b) -hpr/-hpi -porv.open CSR CD 1.1E0 8 .BE-02
-non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State P rob N Recet 19 trans -rt afw mfw -hpi(f/b) -hpr/-hpi -porv.open CSR CD 1. 1E-05 8. 8E-02 56 loop -rr/loop -emerg.power afw -hpi(f/b) -hpr/-hpi -porv.open CD 1. 6E-05 1.4E-01 CSR
-* 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\pwrgseal.cmp BRANCH MODEL: c:\asp\sealmod\palis.sll PROBABILITY FILE: c:\asp\sealmod\pwr_bsll.pro No Recovery Limit BRANCH FREQUENCIEE/PROBABILITIES Branch System Non-Recov Opr Fail t rans l.lt-04 l.BE+BB Event Identifier: 255/88-021
B-7 1 loop 1. GE-OS 5.3E-01 boca 2.46E-0 6 4. 36-01 rt 2. 8E-0 4 1.26-01 rt/ loop 0.0E+ 0 0 1.06+00 exnerg .power 2. 9E-03 8.06-01 a fw 1. 3E-03 2. 66-01 afw/emerg .power 5.0OE-02 3. 46-01 mfw 2.OE-0l 3.gE-0l porv.or.srv.chall 4 .0E-02 1.06+00 porv.or.srv. reseat 2 . OE-02 1.16-02 porv.or.srv.reseat/emerg.power 2 . OE-02 1.06+00 seal. loca 4 .6E-02 1.06+00 ep.rec(sl) 5. 7E-01 1 .06+00 ep. rec 1.6E-01 1.06+00 hpi 1 .0E-03 8.46-01 hpi (f/b) 1.06E-03 8.46-01 1.06E-02 porv .open 1 .0E-02 1. 0 +00 4.06-04 hpr/-hpi 1. 5E-04 1.06+00 1. 0 -0 3 CSR 2.06-03 > 1.06+00 3.46-01 > 1.06+00 Branch Model: 1.06.2 Train 1 Cond Prob: 2.06-02 > Unavailable Train 2 Cond Prob: 1.06-01 > Unavailable
- branch model file
- forced Minarick 11-14-198 9 13: 44 :0 0 Event Identifier: 255/88-021