ML20149K486
| ML20149K486 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-007-00 | |
| Download: ML20149K486 (5) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 269/85-007 Event
Description:
LOFW and Stuck-Open Relief Valves Date of Event: April 25, 1985 Plant: Oconee 1 EVENT DESCRIPTION Sequence On April 25, 1985, at 0533 h, Oconee 1 tripped from 94% full power when both MNW pumps tripped on high discharge pressure. The trip occurred because of a chain of events that began at 0448 h with alarms actuating on five separate static inverters. In actual fact, there was only a consecutive failure of one static inverter and a related static transfer switch. Most of the Unit 1 control room statalarm panelboards and chart recorders were disabled when the 1KX static transfer failed to occur, incorrectly indicating that four other inverters had failed. A loss of power occurred to the MFW pump turbine controls. When power was restored, feedwater flow oscillations developed because of integrated control system action, and the feedwater pumps tripped shortly thereafter. A reactor trip followed the feedwater pump trip.
Main steam relief valves (MSRVs) lifted to reduce secondary side pressure. MSRVs failed to reseat until main steam pressure was reduced to '900 psig in loop A and 835 psig in loop B. Emergency feedwater pumps actuated and maintained adequate steam generator loads.
Corrective Action The immediate corrective actions ensured that the unit was stabilized at hot* shutdown conditions. The problem was investigated, and the failed components were identified and repaired.
Plant/Event Data Systems Involved:
MFW, 1KX auxiliary power system, main steam relief Components and Failure Modes Involved:
MFW pumps - tripped on high discharge pressure caused by inverter failure MSRVs - failed to close on demand (LMS-4, 1MS-8, and LMS-lO)
Event Identifier: 269/85-007 E-9 1
Component Unavailability Duration: NA Plant Operating Mode: 94% power Discovery Method: Operational event Reactor Age: 12.0 years Plant Type: PWR Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate MFW 0.12 Failure was recoverable from the control room but was not a routine action because of the flow oscillations and confusion from the control power failures Secondary-side 0.12 MSRVs were reseated from the control release termi- room after main steam pressure wag nated reduced from the control room, a non-routine action Secondary-side 0.12 Same rationale as above release terminated; given MEW success Plant Models Utilized PWR plant Class D Event Identifier: 269/85-007 E-9 2
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 269/85-007 Event
Description:
LOFW and Stuck Open Relief Valves Event Date: 4/25/85 Plant: Oconee I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS I.O00E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 2.094E-05 Total 2.094E-05 CD TRANS 2.098E-0b Total 2.O9BE-06 AIMS TRANS 3.OQOE-OS Total 3.OOOE-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 1.722E-05 109 TRANS -RT -AFN -PORV.-OR.SRV.CHALL SS.RELEAS.TERM HPI End State: CD Conditional Probability: 1.075E-06 103 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HPR/-HPI -SS.DEPRESS LPR/-HPI.HPR End State: ATOS Conditional Probability: 3.ODOE-0S 128 TRANS RT Event Identifier: 269/85-007 E-9 3
SEQUENCE CONDITIONAL PROBABIL ITIES Sequence End State Seq. Prob Non-Recov**
101 TRANS -RT -AFN PORV.OR.SRV.CHALL -PORV.OR.SRV.RESEAT SS.RELE CV 1.496E-06 6.240E-02 AS.TERM HP!
102 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HP! HP CV 5.293E-07 2.964E-03 RI-HP! -SS.DEPRESS -LPRI-HPI.HPR 103 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HP! HP CD 1.075E-06 f 2.764E-03 RI-HP! -SS.DEPRESS LPRI-HPI.HPR 104 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.DR.SRV.RESEAT -HPI HP CD 5.989E-08 2.964E-03 RI-HPI SS.DEPRESS 109 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI CV 1.722E-05 6.240E-02 122 TRANS -RT AFW tIFW -HPI(FIB) HPR/-HPI -SS.DEPRESS -COND/MNF CV 8.397E-07 1.217E-03 123 TRANS -RI AFW MFW -HPI(FIB) HPRi-HPI -SS.DEPRESS COND/MFW CD 4.326E-07 6.269E-04 124 TRANS -RI AFW MFW -HPI(FIB) HPRI-HPI SS.DEPRESS CD 4.751E-00 1.844E-03 125 TRANS -RI AFW MFW HPI(FIB) -SS.DEPRESS -CONDIMFW CV 8.441E-07 8.?20E -04 126 TRANS -RT AFW MFW HP!(FIB) -SS.DEPRESS CONDIMFW CD 4.34BE-07 4.595SE-04 127 TRANS -RT AFW MFW HPI(FIB) SS.DEPRESS CD 4.776E-08 1.351E-03 128 TRANS RT ATUS 3.OOOE-05 1.200E- 01
- dominant sequence for end state If non-recovery credit for edited case Note:
Conditional probability values are differential values which reflect the added risk due to failures associated with an event.
Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
MODEL: b:pwrdtree.cop DATA: b:oconprob.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch system Non-Recov Opr Fail TRANS 1.030E-03 1.OOOE+00 LOOP 2.2B0E-05 3.400E-01 LOCA 4.170E-06 3.400E-01 RI 2.500E-04 1.200E-01 RI/LOOP 0.OOOE+00 1.OOOE+00 EMERG. POWER 1.OOOE-03 1.OOOE+00 AFW 1.020E-03 2.700E-01 AFW/EMER6. POWER 5.OOOE-02 3.400E-01 MFW 2.OOOE-01 > l.0OOE+00 3.400E-01 ) 1.200E-01 Branch Model: 1.OF.1 Train 1 Cond Prob: 2.OOOE-01 ) Failed Event Identifier: 269/85-007 E-9 4
PORY. OR. SRV. CHALL 8.OOOE-02 I.OOOE+00 PORV. OR. SRV. RESEAT 1.O0OE-02 5.OOOE-02 PORV. OR. SRV. RESEAT /EfIERS. POWER 1.OOOE-02 5.OOOE-02 SS. RELEAS. TERM 1.500E-02 > 1.OOOE+00 3.400E-01 > 1.200E-01 Branch Model: 1.OF.1 Train 1 Cond Prob: 1.500E-02 >Failed