ML20147A532
| ML20147A532 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 3987-011 | |
| Download: ML20147A532 (7) | |
Text
B-91 PRECURSOR DESCRIPTION SHEET LER No.: 346/87-011 Event
Description:
Trip with 13.8-kV power failure, service water pump inoperability, and decay heat train failure Date of Event: 9/6/87 Plant: Davis-Besse 1 EVENT DESCRIPTION Sequence While at 100% power at 1139, on September 6, 1987, a main feedwater flow transmitter failed causing a low flow indication in Loop 2. As a result, the ICS increased feedwater flow, which resulted in a power increase to 103%. The situation was aggravated when an operator adjusted the axial power shaping rods in lieu of the normally control-ling Croup 7 rods. At 1140, the reactor tripped on high flux and the main steam safety valves lifted. All valves except one reseated. At 1142 power to 13.8-kV Bus A was lost when breaker HX01A failed to auto-transfer on demand. The power failure caused the loss of. two reactor coolant pumps, two circulating water pumps, and a failure to automati-cally isolate steam flow to the moisture separator reheater No. 1 second-stage reheat.
Emergency diesel generator 1 started as required on loss of bus Cl; however, service water pump 1 did not auto restart when power was restored. During this time the pressurizer level reached a low level of 15.47 in. At 1147 service water pump 1 was manually started. At 1321, an operator inadvertently tripped RCP 2-1. Within 1 min, this pump was restarted. After power was restored on Bus A (1343 h), operators con-tinued recovery by restarting the motor-driven feed pump and the two failed reactor coolant pumps. Normal recovery continued until 1510 when a turbine bypass valve failed to open due to an improper valve travel stop adjustment. This caused a steam and feedwater rupture control system (SFRCS) actuation, which started both auxiliary feed pumps. The steam generators wereallowed to reach a level of 60 in. each before the auxiliary feed pumps were secured. During continued cool down the next morning (0500 h), operators failed in two successive attempts to put decay heat loop 2 in service, resulting in pressurizer level drops.
Failure of the decay heat removal system was later attributed to 50 ft 3 nitrogen void in the low-pressure injection system discharge piping inside containment.
Event Identifier: 346/87-011
B-92 Corrective Action Failed components in the service water pump, valve SPl3A3, the feedwater flow transmitter, and the 345-kV switchyard main disconnect transfer breaker were repaired/replaced. A vent valve was installed to provide a constant bleed-off of system water and nitrogen to prevent a recurrence of the void in the DHR/LPI piping.
Plant/Event Data Systems Involved 13.8-kV AC power Service water Main feedwater Low-pressure injection Components and Failure Modes Involved:
Breaker HX11A - failed to auto-transfer on demand Service water pump 1 - failed to auto-restart on demand Turbine bypass valve SP13A3 - fails open Low pressure injection - train unavailable due to nitrogen void Component Unavailability Duration: N/A Plant Operating Mode: 1 (100% power)
Discovery Method: Operational event Reactor Age: 10.1 y Plant Type: PWR Comments To address the potential for recovery of the faulted DG, the calcu-lation was performed in two steps:
- 1. core damage likelihood was calculated given the diesel was failed, and
- 2. core damage likelihood was calculated given the diesel was recovered.
These two estimates were combined considering the likelihood of failing to recover the diesel: p (core damage) = p (core damage DG faulted)
- p (DG recovered).
For the first calculation, feed and bleed, LPI, HPR, and LPR were assumed faulted and not recoverable. One train of HPI was assumed unavailable, and secondary-side release was assumed not terminated (because of the stuck-open relief valve and TBV). Feed and bleed was assumed unavailable because both makeup pumps must operate for success-ful feed and bleed on Davis-Besse (along with opening of the PORV).
LPI, LPR and HPR were assumed failed because of the nitrogen in DHR loop 2 plus the assumed faulted DC. For the second calculation, secondary-side release was assumed failed and LPI and LPR were assumed degraded (because of the nitrogen bubble).
Event Identifier: 346-87-011
B-93 Using a nonrecovery likelihood of 0.12 for failing to recover the DG results in an overall estimate for the event of: p(core damage) =
4.3 x 10-5
- 0.12 + 7.6 x 10-7 * (I-0.12) = 5.8 x 10-6.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 No recovery assumed possible Branches Impacted and Branch Nonrecovery Estimate See comments Plant Models Utilized PWR plant Class B Event Identifier: 346/87-011
B-94 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 346/87-011 Event
Description:
Trip with Unavailable Essential Bus (Bus Faulted)
Event Date: 09/06/87 Plant: Davis-Besse INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OE+O0 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 4.3E-05 Total 4.3E-05 CV TRANS 2.9E-03 Total 2. 9E-03 ATWS TRANS 3.4E-05 Total 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
126 trans -rt afw mfw HPI(F/B) -ss.depress cond/mfw CD 3.1E-05 3. 1E-02 103 trans -rt -afw porv.or.srv.chall porv.or.srv.reseat -HPI HPR/ CD 8. 4E-O6 1. 1E-02
-HPI -ss.depress LPR/-HPI.HPR 127 trans -rt afw mfw HPI(F/B) ss.depress CD 3. 4E-06 9.2E-02 109 trans -rt -afw -porv.or.srv.chall SS.RELEAS.TERM HPI CV 2. 6E-03 2. 9E-01 101 trans -rt -afw porv.or.srv.chall -porv.or.srv.reseat SS.RELEAS CV 2. 3E-04 2.9E-01
.TERM HPI 128 trans rt ATWS 3.4E-05 1.2E-O0
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
101 trans -rt -afw porv.or.srv.chall -porv.or.srv.reseat SS.RELEAS CV 2. 3E-04 2.9E-01
.TERM HPI 103 trans -rt -afw porv.or.srv.chall porv.or.srv.reseat -HPI HPR/ CO 8. 4E-06 1.IE-02
-HPI -ss.depress LPR/-HPI.HPR 109 trans -rt -afw -porv.or.srv.chall SS.RELEAS.TERM HPI CV 2.6E-03 2.9E-01 126 trans -rt afw mfw HPI(F/B) -ss.depress cond/mfw CD 3.1E-05 3. 1E-02 127 trans -rt afw mfw HFI(F/B) ss.depress CD 3. 4E-06 9.2E-02 128 trans rt ATWS 3.4E-05 1.2E-01
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\newmodel\pwrbnew.cmp BRANCH MODEL: c:\asp\newmodel\davis.new PROBABILITY FILE: c:\asp\newmodel\pwr_bnew.pro Event Identifier: 346/87-011
B-95 No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trana 4.8E-04 1.0E+00 loop 4.68-06 3.9E-01 loca 2.4E-06 4.3E-01 rt 2.8E-04 1.2E-01 rt/loop 0.O0+00 1.OE+00 emerg power 2.9E-03 8.0E-01 ep.rec 1.08+00 1.78-01 afw 5.0E-03 2.7E-01 afw/emerg .power 5.0E-03 2.7E-01 mfw 2.o0-01 3.4E-01 porv.or.arv.chall 8.0E-02 1.OE+00 porv.or.arv.reseat 1.0E-02 1.1E-02 porv.or.arv.reseat/emerg.power 1.0E-02 1.0E+00 SS.RELEAS.TERM 1.5E-02 > 1.0E+00 3.4E-01 Branch Model: 1.OF.1 Train I Cond Prob: 1.5E-02 > Failed HPI 1.0E-03 > 1.0E-02 8.4E-01 Branch Model: l.OF.2 Train 1 Cond Prob: I.0E-02 Train 2 Cond Prob: I.0E-01 > Unavailable NPI(F/B) 1.0E-03 > 1.0E+00 8.4E-01 > 1.0E+00 1.0E-02 Branch Model: l.OF.2+opr Train 1 Cond Prob: 1.0E-02 > Unavailable Train 2 Cond Prob: 1.0E-01 > Unavailable HPR/-HPI 1.5E-04 > 1.O0+00 1.O+00 1.0E-03 Branch Model: 1.OF.2+opr Train I Cond Prob: 1.o0-02 > Failed Train 2 Cond Prob: 1.5E-02 > Unavailable porv.open 1.OE-02 I.OE+00 4.0E-04 as.depress 3.6E-02 1.08+00 cond/mfw 1.08+00 3.4E-01 1.OE-02 LPI/HPI 1.5E-04 > 1.0E+00 3.4E-01 > 1.0E+00 Branch Model: l.OF.2 Train I Cond Prob: 1.OE-02 > Failed Train 2 Cond Prob: 1.5E-02 > Unavailable LPR/-HPI.HPR 6.7E-01 > 1.0E+00 1.0E+00 Branch Model: 1.OF.l Train 1 Cond Prob: 6.7E-01 > Failed LPR/NPI 1.5E-04 > 1.0E+00 1.0E+00 Branch Model: l.OF.2 Train 1 Cond Prob: 1.0E-02"> Failed Train 2 Cond Prob: 1.5E-02 > Unavailable
- branch model file
- forced Minarick 05-16-1989 06:53:28 Event Identifier: 346/87-011
B-96 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 346/87-011 Event
Description:
Trip with Unavailable Essential Bus (Bus Operable)
Event Date: 09/06/87 Plant: Davis-Besse INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 7.6E-07 Total 7.6E-07 CV TRANS 2.9E-04 Total 2. 9E-04 ATWS TRANS 3.4E-05 Total 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
126 trans -rt afw mfw hpi(f/b) -ss.depress cond/mfw CD 3. 3E-07 2.6E-02 120 trans -rt afw mfw -hpi(f/b) -hpr/-hpi porv.open -ss.depress CD 3.1E-07 3.1E-02 cond/mfw 127 trans -rt afw mfw hpi(f/b) ss.depress CD 3.7E-08 7.7E-02 121 trans -rt afw mfw -hpi(f/b) -hpr/-hpi porv.open ss.depress CD 3.5E-08 9.2E-02 123 trans -rt afw mfw -hpi(f/b) hpr/-hpi -ss.depress cond/mfw CD 3.5E-08 3.1E-02 109 trans -rt -afw -porv.or.srv.chall SS.RELEAS.TERM hpi CV 2.6E-04 2.9E-01 101 trans -rt -afw porv.or.srv.chall -porv.or.srv.reseat SS.RELEAS CV 2.3E-05 2.9E-01
.TERM hpi 128 trans rt ATWS 3.4E-05 1.2E-O1
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
101 trans -rt -afw porv.or.srv.chall -porv.or.srv.reseat SS.RELEAS CV 2.3E-05 2.9E-01
.TERM hpi 109 trans -rt -afw -porv.or.srv.chall SS.RELEAS.TERM hpi CV 2.6E-04 2.9E-01 120 trans -rt afw mfw -hpi(f/b) -hpr/-hpi porv.open -ss.depress CD 3.1E-07 3.1E-02 cond/mfw 121 trans -rt afw mfw -hpi(f/b) -hpr/-hpi porv.open ss.depress CD 3. SE-08 9.2E-02 123 trans -rt afw mfw -hpi(f/b) hpr/-hpi -ss.depress cond/mfw CD 3.5E-08 3.1E-02 126 trans -rt afw mfw hpi(f/b) -ss.depress cond/mfw CD 3. 3E-07 2.6E-02 127 trans -rt afw mfw hpi(f/b) ss.depress CD 3.7E-08 7.7E-02 128 trans rt ATWS 3.4E-05 1.2E-01
- non-recovery credit for edited case Event Identifier: 346/87-011
3-97 SEQUENCE MODEL: c:\asp\newmodel\pwr_bnew.cmp BRANCH MODEL: c:\asp\newmodel\davis.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.OE+O0 loop 4.6E-06 3.9E-01 loca 2.4E-06 4.3E-01 rt 2.BE-04 1.2E-OI rt/loop O.OE+O0 1.OE+O0 emerg.power 2.9E-03 B.OE-01 ep.rec 1.OE+00 1.7E-01 afw 5.OE-03 2.7E-01 afw/emerg.power 5.OE-03 2.7E-01 mfw 2.OE-OI 3.4E-01 porv.or.srv.chall 8.0E-02 1.OE+00 porv.or.srv.reseat l.OE-02 i.1E-02 porv.or.srv.reseat/emerg.power 1.OE-02 1.OE+00 SS.RELEAS.TERM 1.5E-02 > I.OE+00 3.4E-01 Branch Model: I.OF.I Train 1 Cond Prob: 1.5E-02 > Failed hpi 1.OE-03 8.4E-01 hpi(f/b) I.OE-03 8.4E-01 1.OE-02 hpr/-hpi 1.5E-04 1.OE+O0 1.OE-03 porv.open I.OE-02 1.OE+O0 4 .OE-04 ss.depress 3.6E-02 1.OE+00 cond/mfw 1.OE+O0 3.4E-01 1.OE-02 LPI/HPI 1.5E-04 > 1.5E-02 3.4E-01 Branch Model: l.OF.2 Train 1 Cond Prob: 1.OE-02 > Failed Train 2 Cond Prob: 1.5E-02 lpr/-hpi.hpr 6.7E-01 1.OE+00 LPR/HPI 1.5E-04 > 1.5E-02 I.OE+O0 Branch Model: 1.OF.2 Train 1 Cond Prob: 1.OE-02 > Failed Train 2 Cond Prob: 1.5E-02 branch model file
- forced Minarick 05-16-1989 06:53:30 Event Identifier: 346/87-011