ML20147A491
| ML20147A491 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter Office of Nuclear Reactor Regulation |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1986-006-00 | |
| Download: ML20147A491 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 318/86-006 Event
Description:
Trip occurs, and one atmospheric dump valve fails to close Date of Event: September 5, 1986 Plant: Calvert Cliffs 2 EVENT DESCRIPTION Sequence While the reactor was at 100% power, a surge capacitor in the 21A RCP failed and shorted to ground. The RCP tripped off, which led to an automatic reactor trip on low flow.
The cooldown rate was faster than expected because an atmospheric steam dump valve was stuck open. It was closed manually after 22 min.
Corrective Action The solenoid valve associated with the atmospheric dump valve was found to be leaking high-pressure air by its seats. The solenoid valve materials were replaced.
Plant/Event Data Systems Involved:
RCS and atmospheric steam dump Components and Failure Modes Involved:
RCP - failed in operation Atmospheric steam dump valve - failed to close on demand Component Unavailability Duration: NA Plant Operating Mode: 1 (100% power)
Discovery Method: Operational event Reactor Age: 9.8 years Plant Type: PWR Comments None Event Identifier: 318/86-006 D-96
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate SS release 1.0 Atmospheric dump valve failed to close terminated from control room and is not closed locally for 22 min Plant Models Utilized PWR plant Class G Event Identifier: 318/86-006 D-97
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 318/86-006 Event
Description:
Trip and One ASD Valve Fails to Close Event Date: 9/5/86 Plantl Calvert Cliffs 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS l.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 2.5SE-04 Total 2.5E-04 CD TRANS l.BE-O6 Total 1.SE-06 ATWS TRANS 3.4E-05 Total 3.4E-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 2.4E-04 104 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI End State: CD Conditional Probability: 1.6E-06 102 TRANS -RI -AFW PORV.DR.SRV.CHALL PDRV.OR.SRV.RESEAT -HPI HPR/-HPI End State: ATWS Conditional Probability: 3,.4E-05 Event Identifier: 318/86-006 D-98
121 TRANS RT SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prob N Rec**
101 TRANS -RT -AFW PORV.OR.SRV.CHALL -PORV.OR.SRV.RESEAT SS.RELE CV 1.0E-05 8.4E-01 ASTERM HPI 102 TRANS -RT -AFW PORV.OR.SRVCHALL PDRV.OR.SRV.RESEAT -HPI HP CD I.bE-06
- 8.4E-01 116 TRANS -RT AFN MFW -HPiF/B) HPR/-HPI -SS.DEPRESS COND/MFW CD 8.5SE-08 3. OE-02 119 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS CONDIMFW CD 8.9E-08 2.5E-02 121 TRANS RT ATWS 3.4E-05 4 1.2E-01
- dominant sequence for end state
- non-recovery credit for'edited case SEQUENCE MODEL: c:\asp\newaodel\pwrqtree.cmp BRANCH MODEL: c:\asp\newmodel\caIvert.txt PROBABILITY FILE: c:\asp\newmodel\pwr~b.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 4. BE-04 1.OE+00 LOOP 4.6E-06 3.9E-01 LOCA 2.4E-06 4.3E-01 RT 2.8E-04 1.2E-01 RT/LOOP O.OE00 1.0E+400 EMERS.POWER 5.4E-04 B.OE-01 AFW 3.BE-04 2.6E-01 AFW/EMERB.POWER 5.0E-02 3.4E-01 MFW 2,OE-01 3.4E-01 PORV.OR.SRV. CHALL 4. 0E-02 J,0E+00 PORV.OR.SRV.RESEAT 2.0E-02 S.OE-02 PORV.OR.SRV.RESEAT/EMERG.POWER 2. OE-02 1.OE+00 SS.RELEAS.TERM 1.5E-02 > 1.0E+00 3.4E-01 > 1.0E+00 Branch Model: I.OF.1 Train I Cond Prob: 1.5E-02 > Failed SS.RELEAS.TERM/-MFW -1.5E-02 3.4E-01 89.DEPRESS 3.6E-02 1.OE+00 COND/MFW 1.0E+00 3.4E-01 HPI 3.OE-04 B.4E-01 HPI(F/B) 3.OE-04 B.4E-01 4.OE-02 PORV.OPEN I.OE-02 1.OE+00 Event Identifier: 318/86-006 D-99
NPR/-HPI 115E-04 1.0E400 CSR 2.OE-03 M.E-01
- branch mode! file ef forced Austin 09-11-1987 12032337 Event Identifiers 318/16-006 D-100