ML20147A530
| ML20147A530 | |
| 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 1985-002-00 | |
| Download: ML20147A530 (5) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 346/85-002 Event
Description:
Reactor Trip, Loss of Feedwater, and AFW Train Failure Date of Event: January 15, 1985 Plant: Davis-Besse 1 EVENT DESCRIPTION Sequence During zero power physics testing with the reactor in a critical condition, it was discovered that the Integrated Control System (ICS) was not controlling SC I level at the desired set point. The MFW valves were placed in manual control to allow adjustments in the ICS low-level limit control. SC 1 level continued to decrease to the low level set point of the Steam and Feedwater Rupture Control System (SFRCS), which initiated a reactor trip and MEW isolation.
AFW initiated; however, the No. 1 AEW pump became unavailable when the pump suction transferred to the SW system 30 s after the SFRCS actuation, and the operator subsequently isolated the SW supply. The transfer had occurred because of the low suction pressure switch actuated isolating the condensate storage tank, which also caused isolation of steam to the No. 1 AFW pump turbine. The No. 2 AFW pump operated properly and maintained proper levels in S02 throughout the event. The pressure switch is located upstream of the two AFW pumps and downstream of the condensate storage tank strainer.
Corrective Action See LER, p. 3.
Plant/Event Data Systems Involved ICS, SFRCS, AEW, and MEW Components and Failure Modes Involved:
AFW pump - failed to deliver flow on demand One ICS function level control in SC I - failed on demand Component Unavailability Duration: NA Plant Operating Mobde: Startup mode (0% power)
Discovery Method: During startup testing Reactor Age: 7.43 years Plant Type: PWR Event Identifier: 346/85-002 E-206
-Comments:
The reactor had been shut down in a refueling outage for over four months.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate One AFW train Base case MFW Base case Recovery would require reset of the SFRCS-trip, a nonroutine but possible action under the circumstances of the transilent Bleed and feed, See calcu- Branch tailoring was done to reflect HPR, and LPR lations the bleed-and-feed procedures in effect and the use of LPI as a suction source for HPR Plant Models Utilized PWR plant Class B Event Identifier: 346/85-002 E-207
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 346/85-002 Event
Description:
Reactor Trip, LOFW, and AFW Train Failure Event Date: 1/15/85 Plant: Davi s-Besse INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OOOE+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 5.SOBE-04 Total 5.30BE-04 CD TRANS 3.036E-04 Total 3.036E-04 AIMS TRANS 3.OOOE-05 Total 3.OOOE-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 2.453E-04 125 TRANS -RT AFW MFW HPI(FIB) -SS.DEPRESS -COND/MFW End State: CD Conditional Probability: 1.264E-04 126 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS COND/MFW End State: ATNS Conditional Probability: 3.OOOE-05 128 TRANS RT Event Identifier: 346/85-002 E-208
SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-Recov**
119 TRANS -RT AFW MFW -HPI(F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS Cv 5.366E-05 5.57BE-01'
-CONDINFW 120 TRANS -RT AFN MFW -HPI(F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS CD 2.764E-05 2.874E-02 COND/ HF 122 TRANS -RT AFW MFW -HPI(F/B) HPRI-HPI -SS.DEPRESS -CDND/MFN Cv 2.292E-04 3.577E-03 123 TRANS -RT AFW MFW -HPI(F/B) HPRI-HPI -SS.DEPRESS COND/MFW CD 1.IBIE-04 1.84")E-03 124 TRANS -RT AFN MFW -HPI(F/B) HPR/-HPI SS.DEPRESS CD 1.297E-05 5.420E-03 125 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS -COND/MFW Cv 2.453E-04 # 3.746E-03 126 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS CDND/MFW CD 1.264E-04
- 1.9301-03 127 TRANS -RT AFW MFW HPI(F/B) SS.DEPRESS CD 1.38BE-05 5.676E-03 128 TRANS RT ATWS 3.OOOE-05
- 1.200E-0 I fdhainant sequence for end state 4I 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.
MODEL: b:pwrbtree.cmp DATA- b-davispro.cmp No Recovery Limit BRANCH FREGUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.030E-03 1.000E+00 LOOP 2.2BOE-05 3.400E-01 LOCA 4.170E-06 3.400E-01 RT 2.500OE-04 1.200E-01 RT/LOOP 0.OOOE+00 1.000E+00 EMERG. POWER 2.850E-03 5.100E-01 AFN 5.000E-03 ) 1.O0OE-01 2.700E-01 Branch Model: 1.OF.2
.Train I Cond Prob: 5.000E-02 > Failed Train 2 Cood Prob: 1.OOOE-01 AFW/ENERG.POWER 5.000E-03 2.700E-01 MFW 2.OOOE-01 ) 1.OOOE+00 3.400E-01 Branch Model: 1.DF.I Train 1 Cond Prob: 2.000E-0l > Failed PORV. OR. SRV. CHALL 8.000E-02 1.000E+00 PURY. DR. SRV. RESEAT 1.000OE-02 5.OOOE-02 Event Identifier: 346185-002 E-209
PORV. OR. SRV. RESEAT/EMERG. PGWER 1.00OE-02 5.OOOE-02 SS. RELEAS. TERM 1.500E-02 3.400E-01 SS. RELEAS. TERM/-MFW 1.500OE-02 3.400E-01 HPI 1.OOOE-03 5.200E-01 HPI (F/B) 1.0OOOE-03 >4.OOOE-03 5.200E-01 4.QOOE-02 Branch Model: 1.OF.2+opr Train I Cond Prob: 1.0OOE-02 >4.OOOE-02 Train 2 Cond Prob: 1.OO0E-01 HPR/-HPI 3.OOOE-03 >1.OOOE-03 5J.600E-O1 > 1.OOOE+00 4.OOOE-02 Branch Model: l.OF.2+apr Train 1 Cond Prob: 3.000E-02 > .OO0E-024 Train 2 Cond Prob: 1.OOQE-01 PGRV. OPEN 1.OOOE-022 1.DOQOE+00 SSB.DEPRESS 3.600E-02 1.OOOE+00 COND/MFW 1.OOOE+00 3.400E-01 LPI/HPI 1.QOOE-03 3.400E-01 LPR/-HPI .HPR 6.700E-01 > 1.OO0E+00 1.OOOE+OO Branch Model: l.0F.1 Train I Cond Prob: 6.700E-01 ) 1.OOOE+00 LPR/HPI 1.000E-03 1.000E +00
- forced Austin OB-13-1986 05:-58: 26 Event Identifier: 346/B5-002 E-210