ML20149K330
| ML20149K330 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1989-007-00 | |
| Download: ML20149K330 (5) | |
Text
B-270 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No:
Event
Description:
Date:
Plant:
348/89-007 Motor-driven AFW pumps fail to start under manual control November 12, 19 89 Farley 1 Su mma ry Operators experienced difficulties in manually restarting the motor-driven auxiliary feedwater (AFW) pumps during recovery from a trip and safety injection. During investigation of these difficulties it was discovered that, because of a wiring error, the motor-driven AFW pumps would not restart once they had automatically initiated and then been secured unless the auto-initiation signal was cleared. The conditional core damage probability estimated for this event is 1. 1 x 10-6. The relative significance of this event compared with other postulated events at Farley is shown below.
_LER 348/89-007 1E-7 1E_6/
I L rip W + 11 L360 h EP L
pMTR AFW L6OLOOP L.precursor cutoff Event Description The motor-driven AFW pumps initially functioned as designed following a trip and safety injection at Farley 1. Some time after the trip, they were secured by the operator so that steam generator blowdown could be established. Subsequent efforts to manually restart the motor-driven AFW pumps were initially unsuccessful. After about 10 min of investigation, it was discovered that placing the motor-driven AFW pump autostart defeat switches in "defeat" would permit restart of the motor-driven AFW pumps. They were then operated as needed.
The pumps' failure to start was caused by a wiring error. A designer had assumed that
B-271 switchgear wiring for Unit 1 was identical to Unit 2 and developed a design change for Unit 1 on that basis.
During the utility's analysis of the event, it was initially believed that the problem was restricted to a wiring error associated with the "autodefeat" switches.
It was subsequently discovered that, once the pumps had automatically initiated and been secured, they could not be manually restarted until the autostart signal was removed.
Additional Event-Related Information The motor-driven AFW pumps at Farley 1 receive automatic start signals when both steam generator feedpumps are tripped. These autostart signals may be blocked by means of "autodefeat" switches. Since these switches were apparently providing the automatic start signals to the motor-driven AFW pumps during the event, placing them in "defeat" removed the signals from the pumps. It was then possible for the operator to manually start the motor-driven AFW pumps. Had the autostart signal been applied fr-om some other source, it would have been necessary to remove that signal to restart the pumps.
ASP Modeling Assumptions and Approach The event has been modeled as a reactor trip with main feedwater isolation and degraded AFW. The probability of failure for the degraded AFW system was estimated by assuming the turbine-driven pump was not impacted by the event (failure probability =
0.05), and that 10% of the time the AFW pumps will be tripped and restarted following a trip. If they are tripped, the probability of successful restart was assumed to be 0. 12 (non-proceduralized in-control room action). This results in an increase in AFW system probability of p(turbine-driven pump) x p(AFW pumps tripped during trip recovery) x p(operator fails to restart motor-driven pumps) = 0.05 x 0. 1 x 0. 12 = 6.0 x 10O4 Analysis Results The core damage probability estimated for the event is 1.1 x 10-6. The dominant sequence associated with the event (highlighted on the following event tree), involves failure of AFW, failure to recover main feedwater, and failure of feed and bleed.
B-272 AFW M1 1 PORV/
OV PIIHR PR ITRANS T
SI~A W
IRV SRV OP PR ENR I I I
ICHAL RESEAT OPEN SEQ END NO STATE OK OK 11 C
12 C
OK OK OK 13 cD 14 CD OK OK 15 00 (1) 16 CD 17 0D 1s ATWS (1) OK for Class D Domidnant core damage sequence for LER 348/89-007
B8-273 CONDITIONAL CORE DAMAGE Event Identifier:
348/89-007 Event
Description:
Motor-driven ATM pumps fail to Event Date:
11/12/89 Plant:
Farley 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator PROBABILITY CALCULATIONS restart following trip
- 1. OE+00 Probability CD TRANS Total ATWS 1.1E-06 1.1E-06 3.4E-05
- 3. 4E-05 TRANS Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence 15 trans -rt AFN mfw, -bpi (f/b) -hpr/-hpi porv.open 17 trans -rt AFN mfw hpi(f/b) 16 trans -rt APH mfw -bpi(f/b) hpr/-hpi 18 trans rt non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence 15 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open 16 trans -rt ArM mfw -bpi(f/b) hpr/-hpi 17 trans -rt AFM mfw hpi(f/b) 18 trans rt non-recovery credit for edited case SEQUENCE MODEL:
c: \\asp\\19B9\\pwrbseal.cmp BRANCH MODEL:
c:\\asp\\19B9\\farleyl.sll PROBABILITY FILE:
c:\\asp\\1989\\pwrý_bsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System trans 2.5E-04 loop 1.6E-05 loca 2.4E-06 rt 2.8E-04 rt/loop 0.OE+00 emerg.power 2.9E-03 AFW 3.8E-04 >5.4E-03
- Branch Model:
1.OF.3+ser Train 1 Cond Prob:
2.OE-02 End State CD CD CD ATWS End State CD CD CD ATWS Non-Recov 1.OE+00 5.3E-01 4.3SE-01 1.2E-01 l.OE+00 8.05-01 2.6E-01.> 1.3E-01 Prob
- 5. IE-07
- 5. 1E-07 5.7E-08 3.4E-05 Prob 5.1E-07 5.7E-08 5.1E-07 3.4E-05 N Rec**
9.15-03
- 7. 6E-03
- 9. 15-03 1.2E-01 N Rec**
9.15-03
- 9. 1E-03
- 7. 6E-03 1.2E-01 Opr Fail Event Identifier:
348/89-007
B-274 Train 2 Cond Prob:*
1.OE-Ol Train 3 Cond Prob:
5.OE-02 Serial Component Prob:
2.8E-04 afw/emerg.power 5.OE-02 3.4E-01 mfw l.OE+OO 7.OE-02 l.0E-03 porv.or.srv.chail 4.OE-02 l.OE+OO porv.or.srv.reseat 2.OE-02 1.1E-02 porv.or.srv. reseat/emerg.power
- 2. OE-02
- 1. OE+OO seal.loca 2.7E-01 l.OE+OO ep.rec(sl) 5.7E-01 l.OE+OO ep..rec 7.OE-02 l.OE+OO hpi 3.OE-04 8.4E-Ol hpi(f/b) 3.OE-04 9.4E-Ol l.OE-02 hpr/-hpi 1.5E-04 l.OE+OO l.OE-03 porv.open l.OE-02 l.OE+OO 4.OE-04
- branch model file
- forced Minarick 06-12-1990 17:57:28 Event Identifier: 348/89-007