ML20156A118
| ML20156A118 | |
| 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 1985-058-00 | |
| Download: ML20156A118 (4) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 528/85-058 Event
Description:
Loss of Offsite Power Due to Multiplexer Failure Date of Event: October 3, 1985 Plant: Palo Verde 1 EVENT DESCRIPTION Sequence At 1644 h, Unit 1 was at 52% power when a reactor trip occurred because of flow-projected, low departure from nucleate boiling ratio on all four core protection calculators. This was due to a LOOP that caused the speed of the RCP to decrease.
The LOOP was caused by switchyard breakers opening because of an apparent malfunction in the plant multiplexer (PMUX). Because of the LOOP, both emergency diesel generators (DGs) started and loaded, and the Engineered Safety Features system actuated.
The non-safety-grade steam turbine bypass system did not generate a quick open signal because of the LOOP. The LOOP resulted in a false low RCS average temperature input, which blocked the open permissive. Three SG MSRVs opened to relieve steam. The atmospheric steam dump valves were also opened. The RCPs could not be restarted because of operator failure to reset their lockout signal.
Power was restored in 25 min (1709 h). The "B" DG was unloaded too fast by error; alarms sounded, and it shut down. The DG was reset.
Corrective Action To prevent recurrence of the reactor trip, the switchyard breakers that were affected by the apparent PMUX failure were hardwired, bypassing the PMIJX.
Plant/Event Data Systems Involved:
Switchyard breakers, DGs, RCPs, and turbine bypass Components and Failure Modes Involved:
Multiplexer - failed in operation DG - experienced problems during unloading Turbine bypass valves - failed to open on demand RCPs - failed to reset on demand Event Identifier: 528/85-058 E-316
Component Unavailability Duration: NA Plant Operating Mode: 1 (52% power)
Discovery Method: Operational event Reactor Age: 0.4 year Plant Type: PWR Comments See LER 528/85-076 on October 7, 1985, for a similar event MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP 0.12 Failure was recoverable within 30 min but was not routine Branches Impacted and Branch Nonrecovery Estimate None Plant Models Utilized PWR plant Class G Event Identifier: 528/85-058 E-317
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 528/85-05B Event
Description:
Loss of Offsite Power Due to Multiplexer Failure Event Date: 1013185 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 2.6J6E-07 Total 2.616bE-07 CD LOOP 3.360E-05 Total 3.360E-05 AINS LOOP 0.OOOE+00 Total 0.000E+00 DOMINANT SEQUENCES End State: CV Conditional Probability: I.62BE-07 211 LOOP -RT/LOOP EMERG.POWER -AFW/EMERG.POWER -PORV.OR.SRV.CHALL SS.RELEAS.TERM End State: CD Conditional Probability: 3.171E-05 207 LOOP -RT/LODP -EMERB.POWER AFW -HPI(F/B) PORV.OPEN SEQUENCE CONDITIONAL PROBABILITIES Event Identifier: 528/85-058 E-3 18
Sequence SeueceEnd State Seq. Prob Non-Recov*$
204 LOOP -RT/LOOP -EMERG.POWER -AFW -PORV.OR.SRYV.CHALL SS.RELEAS. Cv 9.351E-08 2.122E-02 TERM HPI 207 LOOP -RT/LOOP -EMERG.POWER AFW -HPI(F/B) PORV.OPEN CD 3.171E-05 I 3.11 OE-02 208 LOOP -RT/LOOP -EHERG.POWER AFW HPI(F/B) CD 1.326E -06 1.351IE-03 211 LOOP -RT/LOOP EMERS.POWER -AFW/EMERG.POWER -PORV.OR.SRY.CHALL Cv 1.62BE-07 I 2.057E-02 SS.RELEAS. TERN t dominant sequence for end state tl 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:pwrgtree.cMP DATA: b:paloprob.cMP No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.030E-03 1.000E+00 LOOP 2.280E-05 ) 2.2B0E-05 3.400E-01 ) 1.200E-01 Branch Model; INITOR Initiator Freq: 2.280E-05 LOCA 2.560OE-02 3.400E-01 RT 2.500E-04 1.200E-01 RT/ LOOP 0.OO0E+00 1.OOOE+00 ENERB. POWER 5.415SE-04 5.IOOE-01 AFW 1.020E-03 2.700E-01 AFW/EMERB. POWER 5.OOOE-02 3.400E-01 MFW 2.000E-0 1 3.400E-01 PORY. OR.BRY. CHALL 2.OOOE-02 1.00OE+00 PORV. OR. SRV. RESEAT I.OOOE-02 1.200E-01 PORY. OR. SRV. RESEAT/EMERG.POWER 1.OOOE-02 1.200E-01
- 59. RELEAS. TERN 1.5OOE-02 31.400E-01 SS.RELEAS. TERM/-MFW 1.500E-02 3.400E-01 SS. DEPRESS 3.600E-02 1.OOOE+00 COND/MFW 1.OOOE+00 3.400E-01 HPI 3.OOOE-04 5.200E-01 HP! (F/B) 3.OOOE-04 5.200E-01 4.OOOE-02 PORY. OPEN 1.OOOE+00 1.OO00E+00 HPR/-HPI 1.OOOE-03 1.OOOE+00 CSR 2.OOOE-03 3.400E-01
$1* forced Event Identifier: 528/05-058 E-319