ML20149K468
| ML20149K468 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-018-01 | |
| Download: ML20149K468 (5) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 245/85-018 Rev. 1 Event
Description:
LOOP from Hurricane Gloria and Isolation Condenser Trip Date of Event: September 27, 1985 Plant: Millstone 1 EVENT DESCRIPTION Sequence On September 27, 1985, at 1334 h while in the shutdown mode (486"F, 600 psig), a loss of normal power occurred, causing various isolations and system initiations. The loss of normal power was caused by hurri-cane Gloria. The reactor water cleanup system isolated, and the standby gas treatment initiated, as designed, as a result of the loss of normal power. While placing the isolation condenser in service in anticipation of loss of normal power, the condensate return valve (IC-3) was throt-tled remotely and the isolation condenser isolated on a high steam!
condensate flow signal (Group 4). This isolation was not related to the loss of normal power. The Group 4 isolation was reset, and IC-3 was then manually throttled. operations personnel followed the operator ac-tions delineated in procedures for "Loss of All Station AC Power." The isolation condenser was placed in service and used to maintain the re-actor in hot shutdown.
Corrective Action Initiation of the Group 4 isolation of the isolation condenser system was investigated.
Plant/Event Data Systems Involved:
Electrical and isolation condenser Components and Failure Modes Involved:
Off site power lines and isolation condenser -failed during operation (also, see the LER)
Component Unavailability Duration: NA Plant Operating Mode: 0% (hot shutdown)
Discovery Method: Operational event Reactor Age: 14.9 years Plant Type: -BWR Event Identifier: 245/85-018 E-4 1
Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP 0.10 Base case nonrecovery (0.34) x probability of occurring at power (0.30)
Branches Impacted and Branch Nonrecovery Estimate Isolation 0.04 0.04 for reset of isolation and manual condensers valve throttling FWCI 1.0 Recovery likelihood under LOOP conditions adjusted to reflected dependence on gas turbines for power (note that the FWC1 branch is represented by the HPCI branch in the model)
PlantModels Utilized BWR plant Class B Event Identifier: 245/85-018 E-4 2
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 245/85-018 Rev 1 Event
Description:
LOOP from Hurricane Gloria and Isolation Condenser Trip Event Date: 9/27/85 Plant: millstone 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 1.020E-0I1 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV LOOP 3.7B5E-05 Total 3.7B5E-05 CD LOOP 3.027E-05 Total 3.027E-05 ATWS LOOP 2.132E-06 Total 2.132E-06 DOMINANT SEQUENCES End State: CV Conditional Probability: 3.778E-05 222 LOOP -EMERG.POWER SCRAM -SLC.OR.RODS HPCI -SRV.ADS -LPCS -SDC End State: CD Conditional Probability: 1.276E-05 213 LOOP -EMERG.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM SRV.CLOSE HPCI SRV.ADS End State: ATWS Conditional Probability: 2.071E-06 236 LOOP -EMERG.POWER SCRAM SLC. OR. RODS
'Event Identifier: 245/85-018 Rev I E-4 3
SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prob Non-Recovtt 207 LOOP -EMERG.POWER -SCRAM SRV.CHALLILOOP.-SCRAM.-SRV.CLOSE is ED 2 7B8E -06 1.490E-04 OL.COND HPCI CRD SRV.ADS 213 LOOP -EMERB.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM SRV.CLOSE HP CD 1.276E-05 I 1.708E-02 CI SRV.ADS 220 LOOP -EMERG.POWER -SCRAM -SRV.CHALLILOOP.-SCRAM ISOL.COND HP CD 6.565E-06 1.490E-04 CI CRD SRV.ADS 222 LOOP -EMERS.POWER SCRAM -SLC.OR.RODS HPCI -SRV.ADS -LPCS -SD CV 3.778E-05 I 9.400E-02 C
235 LOOP -EMER6.POWER SCRAM -SLC.OR.RODS HPCI SRV.ADS ED 1.843E -06 1.640E-02 236 LOOP -EMERG.POWER SCRAM SLC.OR.RODS ATWS 2.071E-06 I 2.224E-02 238 LOOP EMERG.POWER -SCRAM SRV.CHALLILOOP.-SCRAM -SRV.CLOSE is CD 1.762E-06 2.081 E-03 OL.COND HPCI 240 LOOP EMERB.POWER -SCRAM SRV.CHALL/LOOP.-SCRAM SRV.CLOSE HP CD 4.001IE-07 5.202E-02 CI 242 LOOP EMERG.POWER -SCRAM -SRV.CHALL/LOOP.-SCRAM ISOL.COND HP CD 4.149E-06 2.081E-03 CI I dominant sequence for end state Itnon-recovery credit for edited case Not e:
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:bwrbtree.cmp DATA: b:millprob.cep No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.142E-03 1.000OE+00 LOOP 1.305E-05 1.305E-05 3.400E-01 ) 1.020E-01 Branch Model: INITOR Initiator Freq: 1.305SE-05 LOCA 3.250E-06 3.400E-01 SCRAM 4.100E-04 1.000E+00 SLC. OR. RODS 1.000E-02 1.000E+00 4.OOOE-02 PCSI TRANS 1.700E-01 1.000E+00 PCS/LOCA 1.000E+00 1.000E+00 SRV. CHALL/TRANS. -SCRAM 3.000E-01 1.000E+00 BRY. CHALLITRANS. SCRAN 1.000E+00 1.000E+00 Event Identifier: 245/85-018 Rev 1 E-44
SRV. CHALL/LDOP. -SCRAM 3.OOOE-01 1.OOOE+OO SRV. CHALL/LOOP.SCRAM 1.OOOE+00 1.OOOE+OO SRV. CLOSE 9.OOOE-03 1.OOOE+OO EMERS. PWER 2.8e50E-03 5.IOOE-01 FWIPCS. TRANS 2.900E-01 3. 400E-01 FWIPCS. LOCA 1.O00E-03 3.400E-01 HPCI 1.0OOE-01 > 1.OOQE+OO 5.700E-01 > I.OOOE+00 Branch Model: 1.OF.1 Train I Cond Prob: 1.OOOE-O1 > I.OOOE+OO ISOL.COND 1.O0OE-02 > 1.OOOE+00 1.00OE+00 > 4.OOOE-02 Branch Model: 1.0F.1 Train I Cond Prob: i.OOOE-02 > 1.0OOE+00 CRD I.OOOE-02 I.0OOE+00 4.OOOE-02 SR?. ADS 6.700E-03 1.ODOE+00 4.OOOE -02 COND/FN. PCS 1.OOOE+OO 3. 400E-01 LPCS 2.OOOE-03 3.400E-01 LPCI 1.OOOE-03 3.400E-01 FIREWTR. OR. DTHER/LPCS. LPCI/TRA 1.OOOE+00 1.000E+00 FIRENTR. OR.DTHERILPCS. LPCI/LDO I.OOOE+00 1.OOOE+00 FIRENTR. OR. DTHER/LPCS. LPCI /LOC 1.0OOE+00 1.OOOE+OO SDC 2.89BE-03 3. 400E-01 LPCI (CC) 1.OOOE-03 3. 400E-01 LPCI (CC) ILPCI l.OOOE+0O 1.OOOE+00 C.I.AND.V/LPCI 1.OOOE+00 3.400E-01 III forced JD HARRIS 10-03-1986 10:09:17 Event Identifier: 245185-018 Rey I E-4 5