ML20161A163
| ML20161A163 | |
| 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 1985-019-00, LER 1985-021-00 | |
| Download: ML20161A163 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 250/85-019, 021 Event
Description:
Multiple AFW Train Failures Following LOFW from Hot Standby Date of Event: July 22-24, 1985 Plant: Turkey Point 3 EVENT DESCRIPTION Sequence Three events occurred in close sequence. While in hot standby and recovering from a prior reactor trip, a MFW bypass valve failed to open. The trip had occurred because of a lightning strike that caused a spurious signal. A low SG level resulted in AFW autostart. AFW trains A and C failed on demand because of governor problems. Train B oscillated near its trip set point but did not actually fail. Train A was restarted in 5 min.
During the subsequent recovery, a MFW bypass valve failed to close, resulting in a high SG level and a trip of the only operating MFW pump. AFW autostarted, but train B's flow control valve failed open.
Later, during restart, two ANW train flow control valves failed to open during testing. The valves all failed because of moisture in the instrument air lines.
Corrective Action Repairs were made. The plant remained shut down until repairs were com-pleted.
Plant/Event Data Systems Involved:
ANW and MFW Components and Failure Modes Involved:
MFW bypass valves - failed on demand AFW` pumps and flow control valves -failed on demand and in operation Event Identifier: 250/85-019, 021 E-5 1
Component Unavailability Duration: NA Plant Operating Mode: 3 (0% power)
Discovery Method: Operational event Reactor Age: 12.6 years Plant Type: PWR Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 No recovery assumed Branches Impacted and Branch Nonrecovery Estimate AFW Base case Two of three trains failed MFW Base case Failed Plant Models Utilized PWR plant Class E Event Identifier: 250/85-019, 021 E-52
CONDITIONAL CORE DAMAGE CALCULATIONS LER Number: 250/85-019,021 Event
Description:
Multiple AFW Train Failures Following LDFW Event Date: 6/22/85 Plant- Turkey Point 3 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.000E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS 1.566E-03 Total 1.566E-03 CD TRANS 8.956E-04 Total 8.956E-04 ATWS TRANS 3.OOOE-05 Total 3.OOOE-05 DOMINANT SEQUENCES End State: CV Conditional Probability: 7.035E-04 125 TRANS -RT AFN MFW HP.I(F/B) -SS.DEPRESS -COND/MFW End State: CD Conditional Probability: 3.624E-04 126 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS COND/MFW End State: ATWS Conditional Probability- 3.OOOE-05 128 TRANS RT Event Identifier: 250/85-019,021 E-5 3
SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Seq. Prab Non-Recovit 119 TRANS -RI AFW IIFW -HPI(F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS CV 1.612E-04 5.579E-02
-COND/MFW 120 TRANS -RI AFW MFW -HPI (F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS ED 8.303E-05 2.874E-02 COND/MFW 122 TRANS -RI AFW MFW -HPI (F/B) HPR/-HPI -SS.DEPRESS -CONDIMFW CV 6.998E -04 3.448E-03 123 TRANS -RI AFW MFW -HPI (F/B) HPR/-HPI -SS.DEPRESS COND/MFW CD 3.605E-04 1.776E-03 124 TRANS -RI AFW IIFW-HPI (F/B) HPR/-HPI 95. DEPRESS CD 3.960E -05 5.224E-03 125 TRANS -RI AFW MFW HPI(F/B) -SS. DEPRESS -COND/IIFW Cv 7.035E-04 I 2.527E-03 126 TRANS -RI AFN MFW HPI(F/B) -SS. DEPRESS CONDINFW CD 3.624E-04 I 1.302E-03 127 TRANS -RI AFW MFW HPI(F/B) SS. DEPRESS Cd 3.980E-05 3.829E-03 128 TRANS RI AIWS 3.OOOE-05 I 1.200E-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 in risk compared to a similar period without the existing failures.
MODEL: b:pwrbtree.4cop DATA: b:turkprob.iEMP No Recovery Limit BRANCH FREgUENCIES/PROBABILIIIES Branch system Non-Recov Opr Fail TRANS 1.030E-03 1.000E+00 LOOP 2.280E-05 3.400E-01 LOCA 4.170E-06 3.400E-01 RI 2.500E-04 1.200E-01 RI/LOOP 0.OOOE+00 1.O00E+00 EMERG. POWER 2.B50E-03 5.100OE-01 AFW 1.500E-03 > 3.OOOE-01 2.700E-01 Branch Model: 1.0F.3 Train 1 Cond Prob: 5.000E-02 > Failed Train 2 Cond Prob: l.000E-01 > Failed Train 3 Cond Prob: 3.000E-01 AFW/EMERG. POWER 1.500E-03 > 3.000E-01 2.700QE-01 Branch Model: 1.OF.3 Train 1 Cond Prob: 5.OOOE-02 ) Failed Train 2 Cond Prob: 1.OOOE-01 > Failed Train 3 Cond Prob: 3.OOOE-01 Event Identifier: 250/85-019,021 E-54
MFW 1.900E-01 > i.OO0E+00 3.400E-01 Branch Model: 1.OF.1 Train 1 Cond Prob: 1.900E-01 > 1.OO0E+00 PGRY.QR. SRV. CHALL 4.OOOE-02 1.OOOE+00 PORV.OR. SRV. RESEAT 2.000E-02 5.000E-02 PIJRV. OR. SRV. RESEAT/EMERS. POWER 2.O0OE-02 5.OOOE-02
- 55. RELEAS. TERM 1.500E-02 3.400E-01 SS.RELEAS. TERN/-MFW 1.500E -02 3.400E-01 HP I 3.000E-04 5.200E-01 HPI (F/B) 3.OOOE-04 5.200E-01 4.OOOE-02 HPR/-HPI 3.OOOE-03 5.600EC-01 4.OOOE-02 PORY. PEN 1.00OE-02 1.000E+00 SS. DEPRESS 3.600E-02 1.000E+00 COND/MFW 1.000E+00 3.400E-01 IPI /HPI 1.OOOE-03 3.400E-01 LPR/-HPI .HPR 6.700E-01 1.000E+00 LPR/HPI 1.OOOE-03 1.OOOE+00 It$ forced Ad harris 10-03-1986 13:32:01 Event Identifier: 250/85-019,021 E-55