ML20156A197
| ML20156A197 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1987-022-00 | |
| Download: ML20156A197 (3) | |
Text
B-52 PRECURSOR DESCRIPTION SHEET LER No.:
312/87-022 Event
Description:
Emergency power system is unavailable Date of Event:
7/29/87 Plant:
Rancho Seco EVENT DESCRIPTION Sequence During routine testing of DG A,
leakage of cooling water was detected.
The DG was removed from service to replace the cooling water
- pump, which had a leaking shaft seal.
The seal retainer spring had failed.
DC B was undergoing testing following modifications and was not available for service.
Both DGs were unavailable for 19 h.
Corrective Action The pump was replaced.
Plant/Event Data Systems Involved:
Emergency power Components and Failure Modes Involved:
Pumps are unavailable Component Unavailability Duration:
19 h Plant Operating Mode:
5 (0%)
Discovery Method:
Testing Reactor Age:
13.0 y Plant Type:
PWR Comments It has been assumed for analysis purposes that this event could have occurred at power.
MODELING CONSIDERATION AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Postulated LOOP Base case nonrecovery Branches Impacted and Branch Nonrecovery Estimate EPS 1.0 No recovery Plant Models Utilized PWR plant Class D Event Identifier:
312/87-022
B-53 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
312/81-022 Event
Description:
Emergency power system is unavailable Event Date:
07/29/87 Plant:
Rancho Seco UNAVAILABILITY, DURATION= 19 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 3.4E-05 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 6.3E-06 Total 6.3E-06 CV LOOP 1.4E-07 Total 1.4E-07 ATWS LOOP O.OE+00 Total O.OE+O0 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
217 loop -rt/loop EMERG.POWER ep.rec CD 5.8E-06 6.6E-02 216 loop -rt/loop EMERG.POWER -ep.rec afw/emerg.power CD 4.SE-07 1.1E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
216 loop -rt/loop EMERG.POWER -ep.rec afw/emerg.power CD 4.BE-07 I.1E-01 217 loop -rt/loop EMERG.POWER ep.rec CD 5.BE-06 6.6E-02
- 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\\newmodel\\pwrtdnew.cmp BRANCH MODEL:
c:\\asp\\newmodel\\rancho.new PROBABILITY FILE:
c:\\asp\\newmodel\\pwrbnew.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 4.8E-04 1.0E+00 loop 4.6E-06 3.9E-01 Event Identifier:
312/87-022
B-54 loca rt rt/loop EMERG.POWER Branch Model:
l.OF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
ep.rec afw afw/emerg.power mfw porv.or.srv.chall porv.or.srv.reseat porv.or.srv.reseat/emerg.power ss.releas.term hpi hpi(f/b) hpr/-hpi ss.depress cond/mfw lpi/hpi lpr/-hpi.hpr lpr/hpi 2.4E-06
- 2. 8E-04
- 0. OE+0O 2.9E-03 > 1.OE+00 5.OE-02 > Failed 5.7E-02 > Unavailable 1.OE+00 1.3E-03 5.OE-02 2.OE-0O 8.OE-02 1.OE-02 1.OE-02 1.5E-02 3.OE-04 3.OE-04 1.5E-04 3.6E-02 1.OE+00 1.5E-04 6.7E-01 1.5E-04 4.3E-01 1.2E-01 I.OE+00 8.OE-01 > I.OE+00 1.7E-01 2.6E-01 3.4E-01 3.4E-01 1.OE+00 I.1E-02 1.OE+00 3.4E-01 8.4E-01 8.4E-01 1.OE+00 1.OE+00 3.4E-01 3.4E-01 1.OE+O0 1.OE+00 1.OE-02 1.OE-03 1.OE-02 branch model file
- forced Minarick 05-16-1989 06:51:55 Event Identifier:
312/87-022