ML20156A119
| ML20156A119 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-076-00 | |
| Download: ML20156A119 (4) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 528/85-076 Event
Description:
Loss of Offsite Power While Troubleshooting Multiplexer Date of Event: October 7, 1985 Plant: Palo Verde 1 EVENT DESCRIPTION Sequence At 1958 h, Unit 1 was in Mode 3, with the RCS pressure at ~-2250 psia and temperature of -.565 0 F, when a LOOP caused a reactor trip. The part length and shutdown control element assemblies had been withdrawn in preparation for startup. The RPS sensed a low RCS flow based on SG differential pressure and tripped.
The RCPs speed decreased as a result of the LOOP. The plant protection system sensed low RCS flow, measured by SG differential pressure, and initiated a reactor trip. The LOOP occurred while troubleshooting was being conducted on the plant multiplexer (PMUX). A false signal had been generated. Because of the LOOP, both emergency diesel generators started and loaded, and the Engineered Safety Features system actuated.
Of fsite power was restored by 2011 h, and one RCP restarted by 2042 h.
Corrective Action To prevent recurrence of the reactor trip, the switchyard breakers that were affected by the apparent PMUX failure have been hardwired, effectively bypassing the PMUX breaker control.
Plant/Event Data System Involved:
Switchyard multiplexer and breakers Components and Failure Modes Involved:
Multiplexer - gave false signal in operation Component Unavailability Duration: NA Plant Operating Mode: 0% power (startup)
Discovery Method: Operational event Reactor Age: 0.5 year Plant Type: PWR Comments See also LER 528/85-058 on October 3, 1985 Event Identifier: 528/85-076 E-320
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP 0.12 Nonroutine recovery within required time Branches Impacted and Branch Nonrecovery Estimate None Plant Mo'dels Utilized BWR plant Class G Event Ide ntifier: 528/85-076 E-321
CONDITIONAL CORE DAMIAGE CALCULATIONS LER Number: 528/85-076 Event
Description:
Loss of Offsite Power While Troubleshooting Multiplexer Event Date: 1017/85 Plant: Palo Verde I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 1.200E-01 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV LOOP I4.616E-07 Total 2.6 16E-07 CD LOOP 3.360E-05 Total 3.360OE-05 AIWS LOOP 0.OOOE+00 Total 0.OOOE+00 DOMINANT SEQLUENCES End State: CV Conditional Probability: 1.628E-07 211 LOOP -RT/LOOP EMERG.POWER -AFWIEJIERG.POWER -PORV.OR.SRV.CHALL SS.RELEAS.TERM End State: CD Conditional Probability: 3.171E-05 207 LOOP -RT/LOOP -EMERG.POWER AFW -HPI(F/B) PORV.OPEN SEQUENCE CONDITIONAL PROBABILITIES Event Identifier: 528/85-076 E-322
Sequence SeueceEnd State Seq. Prob Non-Recov*t 204 LOOP -RT/LOOP -EMERG.POWER -AFW -PORV.OR.SRY.CRALL SS.RELEAS. Cv 9.351E-OB 2.122E-02 TERM HPI 207 LOOP -RT/LOOP -ENERG.POWER AFN -HPIfF/B) PORV.OPEN CD 3.171E-05 t 3.11 OE-02 208 LOOP -RT/LOOP -EMERG.POWER AFW HPI1F/B) CD 1.326E-06 1.351E-03 211 LOOP -RT/LOOP EMERS.POWER -AFW/ENERG.POWER -PORV.OR.SRV.CHALL CV 1.62SE-07 t 2.057E-02 SS.RELEAS. TERN I dominant sequence for end state tt 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:pwrgtree.cmp DATA: b:paloprob.cmp No Recovery Limit BRANCH FREQUENCIESIPROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.030E-03 1.900OE+00 LOOP 2.2B0E-05 > 2.280E-05 3.400E-01 > 1.200E-01 Branch Model: INITOR Initiator Freq: 2.280E-05 LOCA 2.560E-02 3.400E-01 RT 2.500E-04 1.200E-01 RT/ LOOP 0.000E+00 1.000OE+00 ENERG. POWER 5.415E-04 5.IOOE-01 AFW 1.020E-03 2.700E-01 AFN/ENERS. POWER 5.OOOE-02 3.400E-01 NFW 2.000E-01 3.400E-01 PORV.OR.SRV. CHALL 2.OOOE-02 1.OOOE+00 PORY.OR. SRV. RESEAT 1.000E-02 1.200E-0 I PORY.OR.BRY. RESEAT/EMERG.PO HER 1.000E-02 1.200E-01 SS.RELEAS. TERN 1.500E-02 3.400E-01 SS. RELEAS. TERN/-MFW 1.500E-02 3.400E-01 SS. DEPRESS 3.600OE-02 1.000E+00 COND/ HF 1.000OE+00 3.400E-01 HPI 3.000E-04 5.200E-01 HP! (F/B) 3.OOOE-04 5.200E-01 4.00E -02 PORY. OPEN 1.000E+00 1.000E+00 HPR/-HPI 1.OOOE-03 l.000E+00 CSR 2.OOOE-03 3.400E-01 111 forced Event Identifier: 528/85-076 E-323