ML20149K392
| ML20149K392 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-017-00 | |
| Download: ML20149K392 (4) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 409/85-017 Event
Description:
Loss of Offsite Power Date of Event: October 22, 1985 Plant: LaCrosse EVENT DESCRIPTION Sequence LaCrosse experienced a loss-of-load transient from 98% power when the 69-ky tie line breaker 2NB11, which ties the plant to the grid, opened during maintenance activities. The plant scrammed due to high flux. A LOOP was also experienced because the reserve transformer is also sup-plied through 2NB11. Both emergency DGs started and supplied essential loads. Recirculation pump 1A discharge valve failed to fully close.
This valve is required to close before restart of the recirculation pump but does not affect the transient.
The breaker opened when an electrical test and maintenance technician who was winterizing the breaker air receiver bumped the emergency trip lever. Offsite power was restored 1 h later when the breaker was closed. Because the receiver had been depressurized for winterization, power had to be supplied to the receiver compressor before the breaker could be reclosed. The compressor's power supply was deenergized because of the event.
Corrective Action Power was restored 1 h later. EPS supplied power in the interim. The normal power supply to the breaker compressor will be changed to a supply unaffected by the breaker opening. The emergency trip lever was removed to prevent reoccurrence of this incident. Alternative measures are being considered for permanent corrective action.
Plant/Event Data Systems Involved:
Electrical, reactor coolant circulation Components and Failure Modes Involved:
Breaker - trips were off Component Unavailability Duration: NA Plant Operating Mode: 1 (98% power)
Discovery Method: Operational event Reactor Age: 18.2 years Plant Type: BWR Event Identifier: 409/85-017 E-273
Comments The adjacent coal plant, Genoa 3, also tripped because it is also supplied power from this line.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP 0.34 The offsite power was recoverable from the switchyard Branches Impacted and Branch Nonrecovery Estimate None Plant Models Utilized BWR unique model for LaCrosse Event Identifier: 409/85-017 E-274
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 409/85-017 Event
Description:
Loss of Offsite Power Event Date: 10/22/85 Plant, LaCrosse INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 3.400E-01 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 2.052E-05 Total 2.052E-05 cv LOOP 0.OOOE+00 Total 0.OO0E+0O AIWS LOOP 7.768E-06 Total 7.76BE-06 DOM INANT SEQUENCES End State: CD Conditional Probability: B.484E-06 205 LOOP -EMERG.POWER -SCRAM HPCS HPSN End State: ATWS Conditional Probability: 6.870E-06 206 LOOP -EMERG.POWER SCRAM -HPCS SLC.OR.RODS SEQUENCE CONDITIONAL PROBABILITIES Event Identifier: 409/85-017 E-275
Sequence SeueceEnd State Seq. Prob Non-Recovif 202 LOOP -EMERG.POWER -SCRAM HPCS -HPSW -SRV.CLOSE SHUTDOWN.COND CD 2.00O6E-06 73.400E-01 ENSER MANUAL. DEPRESS 204 LOOP -EMERS.POWER -SCRAM HPCS -HPSW SRV.CLOSE MANUAL.DEPRES CD 2.026E-06 3.400E-01 S
205 LOOP -EMERG.POWER -SCRAM HPCS HPSW CD 8.484E-06
- 3.400E-0 I 206 LOOP -EMERS.PGWER SCRAM -HPCS SLC.OR.RODS ATWS 6.870E-06 # 7. 414E-02 207 LOOP -EMERG.POWER SCRAM HPCS AIWS 6. 960E-07 3.400E-01 209 LOOP EMERG.POWER -SCRAM -HPSW -SRV.CLOSE SHUTDOWN.CONDENSER CD 5.839E-07 1.734E-01 MANUAL. DEPRESS 2410 LOOP EMERG.PDWER -SCRAM -HPSW SRV.CLOSE CD 4.915E-06 1.734E-01 211 LOOP EMERS.POWER -SCRAM HPSW CD 2.470E-06 1.734E-01 Idominant sequence for end state 1*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:lactree.cmp DATA: b:lacprob.cmp No Recovery Limit BRANCH FREQUENCIESIPROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.142E-073 1.000E+00 LOOP 1.305E-05 3.400E-01 LOCA 3.250E-06 3.400E-01 SCRAM 4.IOOE-04 1.0OO0E+00 SLC.OR.RODS 1.OOOE-02 1.OOOE+00 4.OOOE-02 EMERG. POWER 2.50E-03 5.100E-01 FW 1.O0OE-01 3.400E-01 HPSW 5.OOOE-03 1.000E+00 SHUTDOWN. CONDENSER 1.OOOE-02 1.O0OE+00 HPCS 5.OOOE-03 1.0OOOE+00 LPCS 1.000E-03 1.OOOE+00 SRV. CLOSE 1.OOOE -02 1.OOOE+00 DH 1.OOOE-02 1.OOOE+00 MANUAL. DEPRESS L 200E-01 1.000E+00 f#I forced Austin Event Identifier: 409/85-017 E-2 76