ML20147A531
| ML20147A531 | |
| 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 1985-013-00 | |
| Download: ML20147A531 (6) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 346/85-013 Event
Description:
LOFW and AFW Failure Date of Event: June 9; 1985 Plant: Davis-Besse 1 EVENT DESCRIPTION Sequence While operating at 90% of full power, the No. 1 MFW pump turbine tripped on overspeed because of a control failure. An automatic plant runback was initiated because the No. 2 pump did not have adequate capacity for the existing reactor power, but the reactor still tripped on high RCS pressure 30 s later. The pump was under manual control because of ICS control problems. Within 8 s of the reactor trip, a spurious Steam and Feedwater Rupture Control System (SFRCS) full trip occurred, closing both MSIVs, resulting in isolation of steam to the No. 2 MFW pump tur-bine. This spurious trip resulted in only a partial actuation of the SFRCS components because only the MSIVs closed. With MFW unavailable, steam generator water levels decreased to the low SC level trip set point of the SFRCS, and SFRCS Channel 1 initiated the No. 1 AFW pump.
To align the No. 2 AFW pump, a control room operator attempted to manually initiate the SFRCS but incorrectly initiated SFRCS on low steam pressure instead of low SG level. He also actuated it for both S~s, resulting in isolation .of ANW to both SGs. Independently of the SG isolation, both AFW pumps tripped on overspeed. The SFRCS was manually reset, but the AFW isolation valves failed to open on demand automati-cally or from the control room.
RCS temperature and pressure increased because of the loss of heat transfer. The pressurizer PORV actuated three times and did not reseat at the proper RCS pressure after the third actuation. The control room operator closed the PORV block valve but did not realize the PORV had remained open. Operators placed the startup feed pump in operation, locally opened the AFW isolation valves, and restored both ANW to service. The quench tank contained the discharges from the PORV.
The RCS cooldown had lowered RCS pressure to 1720 psig. The operators manually initiated the No. 1 HPI pump in piggyback mode to restore pressure. Adequate subcooled margin was available throughout the tran-sient. Several other equipment malfunctions that did not affect the physical response of the plant occurred. Two source range nuclear instrumentation channels were inoperable (emergency boration was suc-cessfully initiated manually, as a result). The display units for the SPDS, including SC level, were inoperable in the control room at the Event Identifier: 346/85-013 E-211
time of the trip. Twenty-three minutes into the transient, the suction of the No. 1 AEW pump automatically transferred from the CST, to the SW system. The operator manually realigned the pump suction back to the CST. One main turbine bypass valve was discovered failed closed.
Corrective Action Additional information on the event is provided in the two-volume "Davis-Besse Course of Action" submittals. See LER pp. 8 and 18-20.
Plant/Event Data Systems Involved:
SFRCS, MFW, main steam isolation, AFW, and PORV Components and Failure Modes Involved:
SFRCS - design failure and operator actuation error ANW pumps - failed on demand AFW isolation valves - failed to open on demand PORV - failed to close on demand One MFW pump - made unavailable because of spurious SFRCS actuation Other MFW pump - failed on demand Component Unavailability Duration: NA Plant Operating Mode: 90% power Discovery Method: Operational event Reactor Age: 7.8 years Plant Type: PWR Comments The plant has been shut down since this event. See LER pp. 8 and 9 for previous failures related to this event.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Event Identifier: 346/85-013 E-212
Branches Impacted and Branch Nonrecovery Estimate MFW and AFW 0.34 The probability of failing to restore either MFW or AFW was combined and
.estimated at 0.34. Dif ficult manual action locally at the AFW pumps, as well as use of the startup feed pump, would have restored feedwater to the SGs. (Note that the combined nonre-covery estimate is modeled by assuming no recovery on the AFW branch and carrying the 0.34 on the MFW branch.)
PORV challenged 1.0 The PORV was challenged in the transient PORV reseats 0.005 0.1 x 0.05 0.1 reflects the in-creased probability that the PORV would fail to reseat at design pres-sure given the failures during the event; 0.05 reflects the probability of failure to close the PORV block valve - 0.04 for the operator action plus 0.01 for the equipment component Bleed and feed See calcu- Branch tailoring was done to reflect lations the bleed-and-feed procedure imple-mented implemented during the event and to reflect the use of LPI as a suction source for HPR HPR See calcu- Branch tailoring was done to reflect lat ions the bleed-and-feed procedure imple-mented during the event and to reflect the use of LPI as a suction source for HPR LPR See calcu- Branch tailoring was done to reflect lations the bleed-and-feed procedure imple-mented during the event and to reflect the use of LPI as a suction source for HPR Plant Models Utilized PWR plant Class B Event Identifier: 346/85-013 E-2 13
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 346/85-013 Event
Description:
LOFW and AFW Failure Event Date: 6/9/85 Plant: Davisg-Besse INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OOOE+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probabil ity CV TRANS 1.956E-02 Total 1.956E-02 CD TRANS 1.131'E-02 Total 1.132E-02 ATNS TRANS 3.OOOE-05 Total 3.OOOE -05 DOMINANT SEQUENCES End State: CV Conditional Probability: 9.085E-03 125 TRANS -RT AFW MFW HPI(FIB) -SS. DEPRESS -COND/MFW End State: CD Conditional Probability: 4.6B0E-03 126 TRANS -RT AFW MFW HPI(FIB) -SS. DEPRESS COND/MFW End State: ATNS Conditional Probability: 3.OOOE-05 128 TRANS RT Event Identifier: 346/85-013 E-2 14
SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-Recov**
119 TRANS -RI AFW MFW -HPI(F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS CY 1.987E-03) 2.066E-01
-CONDIMFW 120 TRANS -RI AFW MFW -HPI(FIB) -HPR/-HPI PORV.OPEN -SS.DEPRESS CD 1.024E-07) 1.064E-01 COND/MFW 122 TRANS -RI AFW MFW -HPI(F/B) HPR/-HPI -SS.DEPRESS -COND/MFW CV 8.488E-03 1.325E-02 123 TRANS -RI AFW MFW -HPI(F/B) HPR/-HPI -SS.DEPRESS COND/MFW CD 4.373E-03 6.825E-03 124 TRANS -RI AFW MFW -HPI(FIB) HPRI-HPI SS.DEPRESS CD 4.603E-04 2.007E-02 125 TRANS -RI AFW MFW HPI(F/B) -SS.DEPRESS -COND/MFW CV 9.085E-01)
- 7.148E-03 127 TRANS -RT AFW MFW HPI(F/B) SS.DEPRESS CD 5. 140E-04 2.102E-02 128 TRANS RI ATWS 3.OOOE-05
- 1.200E-01 Idominant sequence for end state 1*non-recovery credit for edited case Note:
Conditional probability values are differential values which reflect the added risk due to observed failures.
Parenthetical values indicate a reduction inrisk compared to a similar period without the existing failures.
DATA: b-davispro.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.030E-03 1.000OE+00 LOOP 2.280E-05 3.400E-01 LOCA 4.170E-06 3.400E-01 RI 2.500OE-04 1.200E-01 RI/LOOP 0.OOOE+00 1.OOOE+00 EMERG. POWER 2.B50E-03 5.1IOOE-0lI AFW 5.000E-03) > l.000E+00 2.700E-01 > 1.000E+00 Branch Model: 1.OF.2 Train 1 Cond Prob: 5.OOOE-02 > Failed Train 2 Cond Prob: 1.OOOE-01 ) Failed AFW/EMERG. POWER 5.OOOE-03 > 1.OOOE+00 2.700E-01 > 1.OOOE+00 Branch Model: l.OF.2 Train I Cond Prob: 5.OOOE-02 > Failed Train 2 Cond Prob: 1.000E-01 > Failed MFW 2.OOOE-01 > l.OOOE+00 3.400E-01 Branch Model: l.OF.1 Event Identifier: 346/85-013 E-2 15
Train 1 Cond Prob: 2.OOOE-01 > Failed PORV. OR.SRV. CHALL 8,OOOE-02 > 1.00OE+00 1.OOOE+00 Branch Model: 1.OF.1 Train I Cond Prob: B.OOOE-O2 ) 1.000E+00 PORY. OR.SRV.RESEAT 1.000E-02 > l.000E-01 5.OOOE-02 Branch Model: 1.0F.1 Train 1 Cond Prob: l.0OOE-024 > 1.OOOE-01 PORY. OR. SRV. RESEAT/EMERG.POWER 1.OOOE-02 '/1.00OE-01 5.OOOE-02 Branch Model: 1.0F.1 Train 1 Cond Prob: 1.00OE-02 > l.0OOE-01 S5. RELEAS. TERM 1.500OE-02 3.400E-01 S9. RELEAS. TERM/-MFW 1.500OE-02 3.400E-01 HPI 1.OOOE-03 5.200E-01 HPI (FIB) 1.OOOE-03 > 4.OOOE-03 5.200E-01 4.OOOE-02 Branch Model: I.OF.2+opr Train 1 Cond Prob: 1.0Q0E-02 > 4.OOOE-02 Train 2 Cond Prob: 1.OOOE-01 HPRI-HPI 3.OOOE-03 ) 1.0OOE-03 5.600E-01 > 1.000E+00 4.OOOE-02 Branch Model: l.IJF.2+opr Train 1 Cond Prob: 3.OOOE-02 > 1.OOOE-022 Train 2 Cond Prob: 1.000E-01 PORV. OPEN 1.OOOE-024 1.OOOE+00 SS. DEPRESS 3.600E-02 1.OOOE+00 CON D/MFW 1.OOOE+00 3.400E-01 LPI/HPI 1.000E-03 3.400E-01 LPR/-HPI.HPR 6.700E-01 ) 1.OOOE+00 1.000E+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 6.700E-01 > l.000E+00 LPR/HP I 1.O6OE -03 1.OOOE+00
- 4 forced Austin 08-13-1986 05: 23- 03 Event Identifier: 346/B5-013 E-216