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 1 E-8 I1E-7 I E-6 I E-5 I1E-4 I E-3 I E-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 I IPORV/
PORV I LOOP RTALOOP EP AW SR\\'
OR I
I I ICHALL RESEAT LOCA I(LONG)
HI OPEN CS SEQ END NO STATE 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 LOOP LOCA SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator
- 6. 7E-01
- 5. 3E-02
- 1. lE-OB
- 1. 6E-05
- 1. 4E-07
- 2. 7E-05 B. BE+B0 B. BE-400 0.BE+00 B. BE+BB TRANS LOOP LOCA Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence 56 loop -rt/loop -emorg.power afw -hpi(f/b) -hpr/-hpi -porv.open CSR 19 trans -rt afw miw -hpi(f/b) -hpr/-hpi -porv.open CSR End State CO CD Prob I. 6E-05 1.1E0 N Rec 5 5
- 1. 4E-Bl 8.BE-02
-non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State 19 trans -rt afw mfw -hpi(f/b) -hpr/-hpi -porv.open CSR CD 56 loop -rr/loop -emerg.power afw -hpi(f/b) -hpr/-hpi -porv.open CD CSR
-* non-recovery credit for edited case Note:
For unavailabilities, conditional probability values are differential values added risk due to failures associated with an event.
Parenthetical values indicate 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 t rans l.lt-04 l.BE+BB P rob
- 1. 1E-05
- 1. 6E-05 N Recet 8. 8E-02 1.4E-01 which reflect the a reduction in risk Opr Fail Event Identifier: 255/88-021
B-7 1 l oop boca rt rt/ loop exnerg.power a fw afw/emerg.power mfw porv.or.srv.chall porv.or.srv. reseat porv.or.srv.reseat/emerg.power seal. loca ep.rec(sl) ep. rec hpi hpi (f/b) porv.open hpr/-hpi CSR Branch Model:
1.06.2 Train 1 Cond Prob:
Train 2 Cond Prob:
- 1. G E-OS 2.46E-0 6
- 2. 8E-0 4
- 0. 0E+ 0 0
- 2. 9E-03
- 1. 3E-03 5.0 OE-02 2.OE-0l 4.0E-02 2. OE-02 2. OE-02 4.6E-02
- 5. 7E-01
- 1. 6E-01 1.0E-03 1.06E-03 1.0E-02
- 1. 5E-04 2.06-03 > 1.06+00 2.06-02 > Unavailable 1.06-01 > Unavailable
- 5. 3E-01
- 4. 36-01 1.26-01 1.06+00 8.06-01
- 2. 66-01
- 3. 46-01 3.gE-0l 1.06+00 1.16-02 1.06+00 1.06+00 1.06+00 1.06+00 8.46-01 8.46-01
- 1. 0 +00 1.06+00 3.46-01 > 1.06+00 1.06E-02 4.06-04
- 1. 0 -0 3
- branch model file
- forced Minarick 11-14-198 9 13: 44 :0 0 Event Identifier: 255/88-021