ML20149K472
| ML20149K472 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-021-00 | |
| Download: ML20149K472 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 220/85-021 Event
Description:
LOFW Plus Loss of One FWCI Train and One ADS Valve Date of Event: November 1, 1985 Plant: Nine Mile Point 1 EVENT DESCRIPTION Sequence During normal operation at 98% power on November 1, 1985, the No. 12 feedwater flow control valve malfunctioned, causing a 95-in.-high reactor water level condition that tripped the turbine and subsequently caused the reactor to scram. The event was caused by a problem with the instrument air system. Instrument air pressure dropped substantially, causing the feedwater flow control valve lockup circuits to activate as designed. The No. 12 feedwater flow control valve did not lock in position upon loss of air, however, because the valve's positioner malfunctioned, causing the valve to drift open. HPCI was initiated upon turbine trip but was unable to be manually reset because contacts on the emergency trip (limit) switch failed to change state as designed. To control reactor water level, ,the No. 12 feedwater pump was locked out and restarted several *times but then failed to restart. The No. 11 feedwater pump remained operable.
With turbine and turbine stop valve closure, a high reactor pressure spike caused five of the six solenoid actuated electromatic relief valves (ERV) to open. All six ERVs should have automatically opened. A subsequent investigation revealed that ERV 113 had failed to open because of a failure of its solenoid actuator assembly. The remainder of the scram recovery was normal.
Corrective Action Repairs were made to all components.
Plant/Event Data Systems Involved:
HPCI, ADS, instrument air, and main feedwater Components and Failure Modes Involved:
HPCI (FWCI) - fails on demand (1 train) 1 ADS valve - fails on demand Event Identifier: 220/85-021 E-2 6
Component Unavailability Duration: NA Plant Operating Mode: 1 (98% power)
Discovery Method: Operational event Reactor Age: 16.1 years Plant Type: BWR Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 No recovery Branches Impacted and Branch Nonrecovery Estimate ADS Base case Not considered degraded FWCI Base case One of two trains failed MFW 1.0 Isolated on high reactor water level PCs 1.0 Unavailable on initial MFW isolation Plant Models Utilized BWR plant Class A Event Identifier: 220/85-021 E-2 7
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 220185i-021 Event
Description:
LOFW Plus Loss of One FWCI Train and One ADS Valve Event Date: 11/1/85 Plant: Nine Mile Point 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OOOE+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 7.249E-06 Total 7.249E-06 CV TRANS 6.315SE-05 Total 6.315SE-05 ATWS TRANS I2.034 E-05 Total 2.034E-05 DOMINANT SEQUENCES End State: CD Conditional Probability: 3.843E-06 108 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM -SRV.CLOSE ISOL.COND FW/PCS.TRANS FWCI/FW.TRANS CRD SRV. ADS End State: CV Conditional Probability: 4.154E-05 127 TRANS SCRAM -SLC.OR.ROOS PCS/TRANS FW/PCS.TRANS FWCI/FW.TRANS -SRV.ADS -CONO/FW.PCS -SDC End State: ATWS Conditional Probability: 2.034E-05 Event Identifier: 220/85-021 E-28
141 TRANS SCRAM SLC.OR.RODS0 SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-Recov**
108 TRANS -SCRAM PCSITRANS SRV.CHALL/TRANS.-SCRAM -SRV.CLOSE IS ED 3.B43E-t'6 t 1.241E-02 OL.COND FW/PCS.TRANS FWCJ/FW.TRANS CRD SRV.ADS 115 TRANS -SCRAM PCSS/TRANS SRV.CHALL!TRANS.-SCRAM SRV.CLOSE FW CO 2.840E-07 5.6~93E-02
/PCS.LOCA FWCi/FW.LOCA SRV.ADS 127 TRANS SCRAM -SLC.OR.RDDS PCS/TRANS FW/PCS.TRANS FWCI/FW.TR CV 4.154E-05 I 2.063E-01 ANS -SRV.ADS -CONDIFW.PCS -SDC 131 TRANS SCRAM -SLC.OR.RODS PCS/TRANS FWIPCS.TRANS FWCI/FW.TR CV 2.1I3BE-05 1.06,,E-01 ANS -SRV.ADS COND/FW.PCS -LPCS -SDC 140 TRANS SCRAM -SLCL.OR.RODS PCS/TRANS FW1'PCS.TRANS FWCI/FW.TR CD 3.076E-06 5.4b5E-021 ANS SRV.ADS 141 TRANS SCRAM SLC.OR.RODS ATWS 24.0334E-05 t 2.181E-01 I dominant sequence for end state Itnon-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: A:bwratree. cmp DATA; A:nineprob.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch system Non-Recov Opr Fail TRANS 1. 142E-03 1.000OE+00 LOOP 1.305E-05 3.400E-01 LOCA 3.250E-06 3.400E-01 SCRAM 4.IOOE-04 1.000OE+00 SLC. OR. RODS 1.OOOE-02 I.OOOE+00 4.OOOE-02 PCSITRANS 1.000E+00 Branch Model: l.8F.1 Train 1 Cond Prob: 1.700E-O1 > 1.OOOE+00 PCS/LOCA 1.O00E+00 1.000OE+00J SRV.CHALL/TRANS. -SCRAM 1.OO0E+00 I.OOOE+00 SRV. CHALL/TRANS. SCRAM 1.000E+00 1.00OOE+00 SAY. CHALL/LOOP. -SCRAM 1.000E+00 1.000OE+00 SAY. CHALL/LOOP. SCRAM 1.000E+00 SRV. CLOSE 1.80OE-02 1.000OE+00 EMER6. POWER 2i..850E-03 5.100OE-01 Event Identifier: 220/B5-021 E-29
FW/PCS. TRANS 1.000E+00 1.OOOE+00 FWIPCS. LOCA I.000'E+00 1.OOOE+00 lSOL.COND 1.OOOE-02 1.OOOE+00 FWCi/FW. TRANSU 2.900E-01 > 5.OOOE-01 .3.
400E-01 Branch Model: I.OF.1 Train I Cond Prob: 2.900E-01 > 5.OOOE-0I FWC I LOOP 1.000OE+00 1.OOOE+00
.FWC.I/FW.LOC.A 1.OOOE-033 3.400E-0I CR0 1.000E-02 1.0(00E+00 4. OOOE-02 SRY. ADS 6.700E-03 1.000E+00 4. OOOE-02 CONDIFW. PCS 1.OOOE+00 3.400E-01 LPCS 2.OOOE-03 3.400E-01 FIRE WTR. OR. OTHER/LPCS. TRANS I.000OE+00 1.GOOE+00 FIRE WTUR.ORTHER/LPICS. LOOP L.OOAE+00 1.OOOE+00 FIRE WTR. OR.OTHERiLPCS. LOCA I.OOOE+00 1.O+0 SOC 1.089E-02 3.400E-01 CC/SOC 1.000E-03 3.406E-01 CSL AND. V 1.OOOE+00 3.400E-01 It$ forced Austin OB-12-1986 13:531:21 Event Identifier: 220/85-021 E-30