ML20149K394
| ML20149K394 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-093-00, LER 1982-094-00 | |
| Download: ML20149K394 (5) | |
Text
B.46-1 B.46 LER No. 373/82-093, 373/82-094 Event
Description:
Scram and Multiple Failures Date of Event: August 21, 1982 Plant: LaSalle 1 B.46.1 Summary A controlled shutdown of LaSalle was initiated from an unspecified power level, due to an inadequate condensate inventory. During the course of the shutdown, the condensate inventory shortage became acute, forcing operators to scram the unit. In addition to the condensate and feedwater systems, the control rod drive (CRD) hydraulic system and the reactor core isolation cooling (RCIC) system were compromised or unavailable after the scram. In addition, a gross failure of the IA recirculation pump seal was experienced.
The conditional core damage probability estimated for this event is 1.1 x 10'.
B.46.2 Event Description At approximately 0300, a controlled shutdown was initiated because insufficient water inventory was available for normal plant operation. Later, numerous condensate system alarms were received. Because of concern about condensate pump cavitation and about the adequacy of the CRD condensate supply, the unit was manually scrammed at 0536.
At an unspecified time on the same date, the RCIC system was inspected and it was discovered that the RCIC turbine was leaking oil from its sight glass and that the oil level could not be maintained in the turbine.
Accordingly, RCIC was declared inoperable.
Initially after the scram, reactor makeup was supplied by the CRD system, but high CRD suction and discharge filter differential pressures developed and the CRD pump was tripped at 0745. Loss of CRD purge flow to the recirc pump seals meant that the seals were cooled only by the reactor building closed cooling water (RBCCW) system. Seal temperature on recirc pump IB rose to 150'F and stabilized; however seal temperature on recirc pump IA continued to rise. By 0828, 1A recirc pump seal temperature reached 175 'F and the pump was tripped. Subsequently, the seal temperature rose to 235 0 F. At that time, around 0910, a drywell entry was made and the RBCCW flow to the seal was found to be low. The operations foreman increased flow from below 13 gpm to about 25 gpm over a period of about 1 minute and seal temperature dropped abruptly to about 100OF. The resulting thermal stress completely fractured both the number 1 and number 2 (backup) seals, and water and steam began blowing out directly to the drywell around the seal assembly. The flow rate increased over time, eventually reaching about 27 gpm, based on one indication which was averaged over a two-hour period.
Around 1000, operators attempted to close the recirc pump suction and discharge valves, but were unable to fully close the suction valve. Recirc pump 1A seal temperature continued rising, exceeding 300°F. Around LER No. 373/82-093, 373/82-094
B.46-2 1225, an operator entered the drywell again and manually closed the recirc pump suction valve, stopping the leak.
B.46.3 Additional Event-Related Information None.
B.46.4 Modeling Assumptions This event was modeled as a scram with condensate, feedwater, CRD, and RCIC inoperable. Condensate and feedwater were assumed failed, due to the inadequate condensate inventory. The CRD and RCIC systems were assumed failed due to the equipment failures previously described.
B.46.5 Analysis Results The conditional core damage probability estimated for this event is 1.1 x 10',. The dominant core damage sequence, highlighted on the event tree in Figure B.46.I, involves the observed scram, failure of the power conversion system, feedwater failure, HPCI and RCIC failure, and failure of automatic depressurization (ADS) and CRD injection.
LER No. 373/82-093, 373/82-094
B.46-3 d.
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Figure B.46.1 Dominant core damage sequence for LER 373/82-093, 373/82-094 LER No. 373/82-093, 373/82-094
B.46-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 373/82-093 Event
Description:
Scram and multiple failures Event Date: August 21. 1982 Plant: LaSalle 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OE+O0 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 1.1E-04 Total 1.IE-04 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
119 trans -rx.shutdown PCS srv.ftc.<2 MFW hpci RCIC srv.ads C CD 8.5E-05 2.4E-01 RD(INJ) 105 trans -rx.shutdown PCS srv.ftc.<2 MFW-hpci rhr.and.pcs.nrec CD 1.8E-05 8.3E-03
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
105 trans -rx.shutdown PCS srv.ftc.<2 MFW-hpci rhr.and.pcs.nrec CD 1.8E-05 8.3E-03 119 trans -rx.shutdown PCS srv.ftc.<2 MFW hpci RCIC srv.ads C CD 8.5E-05 2.4E-01 RD(INJ)
- non-recovery credit for edited case SEQUENCE MODEL: d:\asp\models\bwrc8283.cmp BRANCH MODEL: d:\asp\models\lasallel.82 PROBABILITY FILE: d:\asp\models\bwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail LER No. 373/82-093, 373/82-094
B.46-5 trans 1.5E-03 1.OE+00 loop 1.6E-05 5.3E-01 1oca 3.3E -06 6.7E- 01 rx.shutdown 3.5E- 04 iCOE-0l PCs 1.7E-01 > 1.OE+00 1.OE+00 Branch Model: I.OF.1 Train 1 Cond Prob: 1.7E-01 > 1.OE+00 srv.ftc.<2 1.OE+00 1.OE+00 srv.ftc.2 1.3E-03 1.OE+00 srv.ftc.>2 2.2E-04 1.OE+00 MFW 2.9E-01 > 1.DE÷00 J.4E-01 > .OE+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 2.9E-01 > 1.OE+00 hpci 2.DE-02 3.4E-01 RCIC 6.OE-02 > 1.OE+00 7.OE-01 > 1.OE+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 6.OE-02 > 1.OE+00 srv.ads 3.7E-03 7.OE-01 1.OE -02 CRD(INJ) 1.OE-02 > 1.OE+00 1.OE+00 1.OE-02 Branch Model: 1.OF.l+opr Train I Cond Prob: 1.OE-02 > 1.OE+00 cond 1.0E+00 iCE-0l 1.CE-03 1pcs 2.OE-02 1.OE+00 1pci 6.JE-04 1.OE+00 rhrsw(inj) 2.OE-02 1.0E--00 1.OE-02 rhr 1.OE-03 1.6E-02 1.OE-05 rhr.and.pcsnrec 1.OE-03 8.3E-03 iCE-05 rhr/-lpci 0.OE+00 1.OE+00 1.OE-05 rhr/lpci 1.OE+00 1.OE+00 iCE-OS rhr(spcool) 2.OE-03 1.OE+00 1.OE-03 rhr(spcool)/-lpci 1.OE-03 1.OE+00 i.OE-03 ep 2.9E-03 8.7E-01 ep.rec 1.7E-01 1.OE+00 rpt 1.9E-02 1.OE+00 slcs 2.OE-03 1.OE+00 1.OE-02 ads.inhibit 0.OE+00 1.OE+00 1.OE-02 man.depress 3.7E-03 1.OE+00 1.OE-02
- branch model file
- forced LER No. 373/82-093, 373/82-094