ML20161A160
| ML20161A160 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1986-039-00 | |
| Download: ML20161A160 (5) | |
Text
PRECURSOR DESCRIPTIONSHEET LER No.: 250/86-039 Event
Description:
Trip occurs with stuck-open PORV Date of Event: December 27, 1986 Plant: Turkey Point 3 EVENT DESCRIPTION Sequence Unit 3 was tripped manually following a loss of turbine governor oil system pressure and a subsequent rapid electrical load decrease from 730 to 0 MW(e). No automatic control rod insertion occurred. The reac-tor control operator, noting that the coolant temperature was increasing above the reference temperature, placed the rods under manual control, and initiated rod insertion. Concurrently, a second reactor control operator attempted to raise the oil pressure, unsuccessfully. At this time (-24 s into the transient) it became clear that the unit could not be recovered, and the unit was tripped manually. During the transient, a PORV opened but then would not fully close, necessitating closure of the associated block valve. The unit was stabilized in <5 min. The most probable cause of the drop in oil pressure was the clearing of blockage of the governor impeller orifice, resulting in the auxiliary governor dumping control oil. The control rods failed to insert auto-matically because of two cold solder joints in the final variable gain summator of the power mismatch circuit. The cause of the PORV failure to close was under investigation. The PORV, turbine governor impeller, and associated components were inspected; and no problems were found.
The cold solder joints were repaired. The control, lube, and seal oil piping were to be cleaned.
Corrective Action The PORV block valve was closed.
Plant/Event Data Systems Involved:
Pressurizer relief Components and Failure Modes Involved:
PORV - failed to open in operation Component Unavailability Duration: NA Plant Operating Mode: 1 (100% power)
Discovery Method: operational event Reactor Age: 14.1 years Plant Type: PWR Event Identifier: 250/86-039 D-31
Comments Manual control rod insertion occurred before any trip signal actua-tions.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 No recovery Branches Impacted and Branch Nonrecovery Estimate PORV/SRV reseat Base case Recoverable from the control room by closing the block valve Plant Models Utilized Plant Class E Event Identifier: 250/86-039 D-3 2 i
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 250/86-039 Event
Description:
Trip and Stuck Open PORY Event Date: 12/27/B6 Plant: Turkey Point 3 INITIATIN6 EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CV TRANS 6.5E-04 Total 6.5E-04 CD TRANS 1.4E-03 Total 1.4E-03 ATWS TRANS 3.4E-05 Total 3,4E-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 6.4E-04 102 TRANS -RT -AFN PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HPR/-HPI -SS.DEPRESS -LPR/-HP I. HPR End State: CD Conditional Probability: 1.3E-03 103 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRY.RESEAT -HPI HPR/-HPI -SS.DEPRESS LPR/-HP I.HPR Event Identifier: 250/86-039 D-33
End State: ATWS Conditional Probability: 3 4E-05 125 TRANS RT SEQUENCE COND1TIONAL PROBABILITIES Sequence End State Prob N Reca' 102 TRANS -RT -AFW PORV.ORSRV.CHALL PORV.OR.SRV.RESEAT -HPI HP CV 6.4E-04
- 5. OE-02 R/-HPI -SS.DEPRESS -LPR/-HPI.HPR 103 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP CD 1.3E-03
- 5.OE-021 R/-HP] -SSDEPRESS LPR/-HPI.HPR 104 TRANS -RT -AFW PORV.OR.SRV.CHALL PORVOR.SRY.RESEAT -HPI HP CD 7.2E-05 5.OE-02 R/-HP! SS.OEPRESS 128 TRANS RT ATWS 3.4E-05 # 1.2E-01
- dominant sequence for end state 4* non-recovery credit for edited case SEQUENCE MODEL: c: \asp\newmodel\pwrbtreecmp BRANCH MODEL: c:\asp\newmodel\turkey.txt PROBABILITY FILE: c:\asp\newmodel\pwr~b.pro No Recovery Limit BRANCH FREQUENCIESIPROBABILITIES Branch System Non-Recov Opr Fail TRANS 4,BE-04 i.OE+0O LOOP 4.6E-06 3.9E-01 LOCA 2,4E-06 4.3E-01 RT 2.BE-04 1.2E-01 RT/LOOP 01OE+0 I.OE+00 ENERV.POWER 2.9E-03 8.OE-01 AFW 1.5E-03 2.7E-01 AFW/ENERB.POWER 1.5E-03 2.7E-01 NFW 1.9E-01 3.4E-01 PORV.OR.SRV.CHALL 4.OE-02 ) I.OE+O0 cc I.OE+00 Branch Models I.OF.,
Train i Cond Prob3 4.OE-02 PORY.OR.SRV.RESEAT 2.OE-02 > I.OE+00, 5.OE702 Branch Modeli I,OF.,
Train I Cond Prob: 2.OE-02 ) Failed PORV.OR.SRV.RESEAT/EMERS.POWER 2.OE-02 1.OE+00 SS.RELEAS.TERM 1.5E-02 3.4E-01 SS.RELEAS.TERNI-MFW 1.5E-02 3.4E-01 HPI 3.OE-04 B.4E-01 HPI(F/D) 3,0E-04 8.4E-01 4.OE-02 Event Identifierl 250/86-039 D-34
HPR/-HPI 1.5E-04 1.OE+00 4.0E-02 PORY.OPEN I.OE-02 1.OE+00 SS.DEPRESS 3.E-02 I.OE+0O COND/RFW 1.OE+00 3.E-01 LPI/HPI 1.5E-04 M.E-01 LPR/-HPI.HPR 6.E-01 1.OE+00 LPR/HPI 1.SE-04 1.OE+00
- branch model file
- forced Austin 09-11-1967 11:16:50 Event Identifier: 250/16-039 D-35