ML20161A174
| ML20161A174 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1987-015-01, LER 1987-016-01 | |
| Download: ML20161A174 (4) | |
Text
B-190 PRECURSOR DESCRIPTION SHEET LER No.: Special Reports 482/87-015 Ri and -016 Ri Event
Description:
Unavailability of DGs within a 9-d period Date of Event: 12/11/87 Plant: Wolf Creek 1 EVENT DESCRIPTION Sequence On 12/11/87, with the plant shut down for refueling and DC A in the tenth hour of its yearly 24-h run, a fitting in its lube oil line cracked and caused excessive oil leakage. The DG was forced to be shut down. During subsequent maintenance, a problem with the mechanical governor was also corrected; a pin had sheared on the speed setting shaft. The governor was replaced but failed after 20 min testing. A second governor was installed and also failed after 20 min of testing.
It was decided to rebuild the original governor, following which DG A passed its hot 24 h on 12/18/88. The governors had failed from exces-sive shaft loading.
On 12/19/88, DG B failed its operability test when it could not be synchronized to the bus. The cause of the failure was a result of the potential transformer fuse knives not inserting fully into the fuse tabs. This result caused an unstable voltage output. The circuit closing linkage was adjusted to provide sufficient force to insert the knives.
The DG was returned to service on 12/22/88.
Corrective Action Repairs were made.
Plant/Event Data Systems Involved:
Emergency power Components and Failure Modes Involved:
DGs fail in test Component Unavailability Duration: 360 h (assumed)
Plant Operating Mode: 6 (0%)
Discovery Method: Testing Reactor Age: 2.6 y Plant Type: PWR Comments It has been assumed that these failures could have occurred at power.
Event Identifier: 482/SR87-015, 016(RI)
B-191 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 short-term recovery appears possible Plant Models Utilized PWR plant Class B Event Identifier: 482/SR87-015, 016(Rl)
B-192 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 482/87-015 Ri (special report)
Event
Description:
Unavailability of DGs within a nine day period Event Date: 12/11/87 Plant: Wolf Creek 1 UNAVAILABILITY, DURATION= 360 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 6.5E-04 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 1.2E-04 Total 1.2E-04 CV LOOP 2.7E-06 Total 2.7E-06 ATWS LOOP O.OE+00 Total O.OE+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
217 loop -rt/loop EMERG.POWER ep.rec CD I.IE-04 6.6E-02 216 loop -rt/loop EMERG.POWER -ep.rec afw/emerg.power CD 9.1E-06 1.1E-01 215 loop -rt/loop EMERG.POWER -ep.rec -afw/emerg.power -porv.or.srv CV 2.6E-06 1.1E-01
.chall ss.releas.term 213 loop -rt/loop EMERG.POWER -ep.rec -afw/emerg.power porv.or.srv CV 1.1E-07 I.IE-01
.chall -porv.or.srv.reseat/emerg.power ss.releas.term
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
213 loop -rt/loop EMERG.POWER -ep.rec -afw/emerg.power porv.or.srv CV 1.1E-07 1.1E-01
.chall -porv.or.srv.reseat/emerg.power ss.releas.term 215 loop -rt/loop EMERG.POWER -ep.rec -afw/emerg.power -porv.or.srv CV 2.6E-06 l.IE-01
.chall ss.releas.term 216 loop -rt/loop EMERG.POWER -ep.rec afw/emerg.power CD 9.1E-06 1.1E-01 217 loop -rt/loop EMERG.POWER ep.rec CD 1.1E-04 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\pwr_bnew.cmp BRANCH MODEL: c:\asp\newmodel\wolf.new PROBABILITY FILE: c:\asp\newmodel\pwrbnew.pro Event Identifier: 482/87-015 RI (special report)
B-193 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 loca 2.4E-06 4.3E-01 rt 2.8E-04 1.2E-01 rt/loop 0.OE+00 1.OE+00 EMERG.POWER 2.9E-03 > 1.OE+00 B.OE-01 > 1.0E+00 Branch Model: l.OF.2 Train 1 Cond Prob: 5.OE-02 > Failed Train 2 Cond Prob: 5.7E-02 > Failed ep.rec 1.0E+00 1.7E-01 afw 3.8E-04 2.6E-01 afw/emerg.power 5.OE-02 3.4E-01 mfw 2.OE-01 3.4E-01 porv.or.srv.chall 4.OE-02 1.OE+00 porv.or.srv.reseat 2.OE-02 l.lE-02 porv.or.srv.reseat/emerg.power 2.OE-02 1.0E+00 ss.releas.term 1.5E-02 3.4E-01 hpi 1.OE-03 8.4E-01 hpi(f/b) 1.OE-03 8.4E-01 1.OE-02 hpr/-hpi 1.5E-04 1.0E+00 1.OE-03 porv.open 1.OE-02 1.0E+00 4.OE-04 ss.depress 3.6E-02 1.OE+00 cond/mfw 1.OE+00 3.4E-01 1.OE-02 lpi/hpi 1.5E-04 3.4E-01 lpr/-hpi.hpr 6.7E-01 1.OE+00 lpr/hpi 1.5E-04 1.OE+00
- branch model file
- forced Minarick 05-16-1989 06:54:15 Event Identifier: 482/87-015 RI (special report)