ML20149K475
| ML20149K475 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-019-00 | |
| Download: ML20149K475 (6) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 338/84-019 Event
Description:
Trip and One AFW Train Fails Date of Event: November 14, 1984 Plant: North Anna 1 EVENT DESCRIPTION
-Sequence At 0640 h a vital bus inverter failure caused Unit 1 to trip from 100% power. The inverter was supplying power to the 125-V ac vital bus I-III. The inverter failure caused this bus and its associated equip-ment to become deenergized. Loss of power to the relay that senses "C" RCP breaker position caused the reactor trip on loss of RCS flow coin-cident with reactor power >30%. The "C" RCP never stopped running dur-ing this event.
Vital bus 1-III was deenergized for <2 min. The inverter had damr-aged SCRs and a blown fuse which prevented it from being reenergized.
The bus was subsequently powered from its backup regulating transformer. All equipment power from vital bus 1-III responded as expected during loss and restoration of the bus. The most significant equipment response involved "B" SG. The "B" main feed valve (FCV-1488) and "B" feed bypass valve (FCV-1489) both failed closed. "B" wide-range SG level indication (LI-1487) failed low. The AFW pump (1-FW-P-3B) that supplies "B" SG failed to autostart and was manually started by the con--
trol room operator. These actions caused "B" SG level to drop below the narrow range indication while no-wide range level indication was avail-able. Level was restored to "B" SG within a few minutes.
Loss of vital bus 1-III also deenergized all four water boxes' vacuum breakers, which caused all circulating water pumps to trip. This has been assumed to have resulted in an LOFW.
Vital bus 1-III also supplies power to many containment isolation trip valves, including CC to the RCPs. other significant equipment powered from the 1-III vital bus included 1 power range detector (N43),
26 incore thermocouples, SSPS channel III inputs, SSPS train B output relays, train B RV-level instrumentation, radiation monitor cabinet 1-2, and other equipment.
Event Identifier: 338/84-019 D-169
One of the blowdown-containment isolation trip valves did not close automatically and would not close manually during this event. A solenoid-operated valve for this trip valve would not change position.
Maintenance personnel agitated the solenoid valve, and the trip valve was subsequently cycled satisfactorily. Blowdown containment isolation trip valves are cycled every three months during a periodic test to verify valve-stroke time.
The source range excore detectors had to be manually reinstated because one intermediate-range detector was undercompensated. This detector had its compensation voltage adjusted before the reactor was taken critical.
The unit was placed in mode 2 on November 17, 1984, and returned to 100% power on November 19, 1984.
Corrective Action Repairs were made.
Plant/Event Data Systems Involved:
AFW, electrical Components and Failure Modes Involved:
AFW pump - failed on demand Component Unavailability Duration: NA Plant Operating Mode: 1 (100% power)
Discovery Method: Operational event Reactor Age: 6.6 years Plant Type: PWR Comments None Event Identifier: 338/84-019 D- 170
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Not recoverable Branches Impacted and Branch Nonrecovery Estimate AFW Base case one train unavailable MFW 0.34 Assumed recoverable locally at the equipment Plant Models Utilized PWR plant Class A Event Identifier: 338/84-019 D- 171
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 338/84-019 Event
Description:
Trip and One AFW Train Fails Event Date: 11/14/84 Plant: North Anna 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CV TRANS i.IE-05 Total 2.1E-05 CD TRANS 1.OE-05 Total 1.OE-05 ATWS TRANS 3.OE-05 Total 3.OE-05 DOMINANT SEOLENCES End State: CV Conditional Probability: 5.9E-06 112 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI End State: CD Conditional Probability: 2.4E-06 135 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS COND/MFW End State: ATWS Conditional Probability: 3.OE-05 Event Identifier: 338/84-019 D-172
137 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 2.4E-07 1.8E-01 AS.TERN HPI 102 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI -HP CV 5.OE-07 1.7E-02 RI-HP! CSR -SS.DEPRESS -LPR/-HPI 103 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI -HP CD I.OE-06 1.7E-02 RI-HPI CSR -SS.DEPRESS LPR/-HPI 105 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HP! HP CV 5.3E-07 2.8E-02 R/-HP! -SS.DEPRESS -LPR/-HPI 106 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HP! HP CD 1.1E-06 2.8E-02 RI-HPI -SS.DEPRESS LPR/-HPI 112 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HP! CV 5.9E-06 * .8E-01 125 TRANS -RT AFW MFW -HP! (F/B) -HPRI-HPI -CSR PORV.OPEN -SS.DE CV 9.9E-07 6.OE-02 PRESS -CONDIMFW 126 TRANS -RT AFW MFW -HP! (FIB) -HPRI-HPI -CSR PORV.OPEN -SS.DE CD 5.IE-07 3.1E-02 PRESS COND/MFW 128 TRANS -RT AFW MFW -HPI(F/B) -HPRI-HPI CSR -SS.DEPRESS -COND CV 4.2E-06 2.1E-02 IMFW 129 TRANS -RT AFW MFW -HP! (F/B) -HPR/-HPI CSR -SS.DEPRESS COND CD 2.2E-06 1.1E-02
/MFW 130 TRANS -RT AEW MFW -HP! (FIB) -HPRI-HPI CSR SS.DEPRESS CD 2.4E-07 3.1E-02 131 TRANS -RT AFW MFW -HPI(F/B) HPR/-HPI -SS.DEPRESS -COND/MFW CV 4.5E-06 3.4E-02 132 TRANS -RT AFW MFW -HP! (F/B) HPR/-HPI -SS.DEPRESS COND/MFW CD 2.3E-06 1.7E-02 133 TRANS -RT AFW MFW -HPI(F/B) HPR/-HPI SS.DEPRESS CD 2.5E-07 5.1E-02 134 TRANS -RT AFW MFWHPI(F/B) -SS.DEPRESS -COND/MFW CV 4.6E-06 3.2E-02 135 TRANS -RT AFW MFWHPI(F/B) -SS.OEPRESS COND/MFW CO 2.4E-06
- 1.2E-01
- dominant sequence for end state
RT 2.5E-04 I1.2E-01I RT/LOOP 0.OE+00 I.OE+00 EP 2.9E-03 .5.1E-01 AFW 1.OE-03 )1.9E-03 2.7E-01 Branch Model: 1.GF.3+ser Train I Cond Prob: 2.OE-02 Train 2 Cond Prob: 1.0E-01 > Unavailable Train 3 Cond Prob: 5.GE-02 Serial Com~ponent Prob: 9.2E-04 AFW/EP 5.0E-02 3.4E-01 MFW 1.9E-01 > 1.0E+00 3.4E-01 Branch Model: 1.OF.1 Train I Cond Prob: I.9E-01 > Unavailable PORV.GR.SRV.CI4ALL 4.OE-02 I.OE+00 PORV .OR.SRV .RESEAT 2.0E-02 5.OE-02 65 .RELEAS .TERM 1.5E-02 3A.E-01 66 .RELEiS .TERM/-MFW 1.5E-02 3.4E-01 SS .DEPRESS 3.6E-0P2 I.0E+00 COND/MFW 1.0OE+00 3A.E-01 HPI 2.3E-03 J52E-01 HPI (F/B) 2.3E-03 5.21-01 4.GE-02 PORY .OPEN 1.OE-02 1.OE+00 HPR/-HPI 3.OE-03 5.6E-01 4.OE-02 CSR 3.OE-03 3A.E-01 4 .0E-021 LPI/HPI 1.0OE-03 3.4E-01 LPR/-HPI 6.7E-01 1.OE+00 LPR/HPI 2.OE-03 I.OE+00
- forced Minarick 04-12-1987 10:2.5:50 Event Identifier: 338/84-019 D- 17 4