ML20149K407
| ML20149K407 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-004-00 | |
| Download: ML20149K407 (5) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 369/85-004 Event
Description:
Reactor Trip With Stuck-Open SG Relief Valve Date of Event: January 28, 1985 Plant: McGuire 1 EVENT DESCRIPTION Sequence A reactor trip occurred on lo-b SC level when MFW pump tripped on a false low-suction pressure signal. Following the pump trip, a turbine runback did not occur on demand because of a control system failure, resulting in a drop in the SC levels. A manual turbine runback was attempted, unsuccessfully. Low SG level occurred within 1 min, causing RPS trip. AEW automatically initiated.
The SC "B" PORV opened because of instrument drift, remained open for ~-4 min, and caused excessive cooldown and loss of SC inventory. Th e SC PORV was fully isolated by the operators (closing the block valve) about 2 min after it had closed by itself.
The discharge check valve on the' turbine-driven AFW pump failed to close as the pump was secured after following the reactor trip. SG backf low occurred but was stopped when the SC isolation valve was closed. This isolation valve later failed to open' on demand during realignment of the system. The valve was manually opened. Two charging pumps were used to recover vessel level.
Corrective Action The MFW suction pressure transmitter was repaired and recalibrated.
During the 1985 refueling outage, the instrumentation will be modified so that a recurrence of such a single-component failure will initiate a multiple logic trip. The main steam pressure transmitters that activate the SC PORVs will be placed on an active preventative maintenance schedule to help detect calibration drift. Actions are being reviewed to correct the AFW check valve problem and to eliminate the diode failures that caused the turbine-runback failure.
Plant/Event Data Systems Involved:
MFW, AEW, turbine control (feedback), and SC PORVs Event Identifier: 369/85-004 E-237
Components and Failure Modes Involved:
MFW - one pump failed in operation Turbine runback - failed (electronic component failure)
AFW check valve - failed on demand AFW isolation valve - fails to open on demand, rendering turbine-driven AFW pump inoperable Component Unavailability Duration: NA Plant Operating Mode: 100% power Discovery Method: During operation Reactor Age: 3.47 years Plant Type: PWR Comments See LER 370/84-025 for similar check valve failure event.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Non recoverable Branches Impacted and Branch Nonrecovery Estimate MFW 0.34 Manual recovery difficult but possible locally at equipment Secondary-side 0.12 Valve was capable of closing by itself release or of being isolated terminated Secondary-side 0.12 Same recovery rationale as above release terminated; given MFW success Plant Models Utilized PWR plant Class F Event Identifier: 369/85-004 E-238
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 369/B5-004 Event
Description:
Reactor Trip With Stuck Open SG Relief Valve Event Date: 1128/85 Plant: Mc~uire I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OOOE+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 6.8B55E-05 Total 6.855E-05 CD TRANS 4.755E-06 Total 4.755E-06 ATWS TRANS 3.OOOE-05 Total 3.OOOE-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 5.989E-05 109 TRANS -RI -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI End State: CD Conditional Probability: 1.6 11E-06 103 TRANS -RI -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HPR/-HPI -SS.DEPRESS LPR/-HPI.HPR End State: ATWS Conditional Probability: 3.OOOE-05 128 TRANS RT Event Identifier: 369/85-004 E-2 39
SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-Recovil 101 TRANS -RT -AFW PORV.OR.SRV.CHALL -PORV.GR.SRY.RESEAt SS.RELE Cv 2.491E-06 6.231E-02 AS.TERM HP!
103 TRANS -RT -AFN PORV.OR.SRV.CHALL PORY.OR.SRV.RESEAT -HPI HP CD 1.611E-"i
- 2.964E-03 RI-HP! -SS.DEPRESS LPRI-HPI.HPR 104 TRANS -RT -AFN PDRV.OR.SRY.CHALL PORY.OR.SRV.RESEAT -HPI HP CD 8.981E-08 2.?64E-03 RI-HPI SS.DEPRESS 109 TRANS -RT -AFW -PORV.OR.SRY.CHALL SS.RELEAS.TERM HPI CV 5.989E-05
- 6.240E-02 120 TRANS -RT AFW MFW -HP! (FIB) -HPRI-HPI PORV.OPEN -SS.DEPRESS CD 2.822E-07 2.874E-02 CONDIMFW 122 TRANS -RI AFW MFW -HPI(FIB) HPRI-HPI -SS.DEPRESS -'CONDIMFN Cv 2.37GE-06 3.447E-03 123) TRANS -RT AFW MFW -HPI(FIB) HPRI-HPI -SS.DEPRESS CONDINFW CD 1.225E-06 1.776E-03 124 TRANS -RI AFW MFW -HPI(FIB) HPRI-HPI SS.DEPRESS CD 1.346E-07 5.223E-03 125 TRANS -RT AFW MFW HPI(FIB) -SS.DEPRESS -CONDINFW CV 2.4 12E-06 2.766E-03 126 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS COND/MFW CD 1.243E-06 1.425E-03 127 TRANS -RI AFW MFW HPI(FIB) SS.DEPRESS CD 1.365E-07 4.192E-03 128 TRANS RT 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 in risk compared to a similar period without the existing failures.
MODEL: b:pwrbtree.cmfp DATA: b: mcgurpro. cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.030E-03 1.O0OE+00 LOOP 2.280E-05 3.400E-01 LOCA 4.170E-06 3.400E-01 RT 2.500E-04 1.200E-01 RT/LOOP 0.OOOE+00 1.OOOE+00 EME RB.POWER 2.850E-03 5.100E-01 AFW 1.020E-03 2.700E-01 AFW/EMERG. POWER 5.OOOE-02 3.400E-01 MFW 2.OOOE-01 > 1.00OE+00 3.400E-01 Branch Model: 1.OF.1 Train I Cond Prob: 2.OOOE-01 > Failed Event Identifier: 369/85-004 E-240
PORY. DR. SRV.CHALL 4.OOOE-02 1.OOOE+OO PORY. UR.SRV.RESEAT 31.
OOOE-02 5.OOOE-02 PORV. OR.SRV.RESEAT/EMERG.POWER 3.OOOE-02 5.000OE-02 SS. RELEAa. TERN 1.500E-02 > 1.000E+00 3.400E-01 ) 1.200E-01 Branch Model: 1.0F.1 Train 1 Cond Prob: 1.500E-02 > Failed SS. RELEAS.TERM/-MFW 1.500E-02 > 1.000E+00 3.400E-01 > 1.200E-01 Branch Model: 1.0F.1 Train 1 Cond Prob: 1.500E-02 'fFailed HPI 1.000E-03 5.200E-01 HPI (FIB) 1.000E-03 5.200E-01 4.000E-02 HPRI-HPI 3.000E-03 5.600E-01 4.OOOE-02 POR V.OPEN 1.000E-02 1.000E+00 S8. DEPRESS 3.600E -02 1.000E+00 COND/MFW 1.OOOE+00 3.400E-01 LPI/HPI 1.OOOE-07) 3.400E-01 LPRI-HPI.HPR 6.700E-01 1.OO0E+00 LPR/HPI 1.OOOE-03 1.OOOE+00 if* forced Austin 08 1986 06: 27: 53 Event Identifier: 369/B5-004 E-2 41