ML20149K353
| ML20149K353 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-090-00 | |
| Download: ML20149K353 (5) | |
Text
B.23-1 B.23 LER No. 321/83-090, Rev. 1, -093 Event
Description:
Manual Scram with HPCI and RCIC Unavailable Date of Event:
August 25, 1983 Plant:
Hatch 1 B.23.1 Summary On August 24, 1983, the high-pressure coolant injection (HPCI) pump was manually tripped during surveillance testing following receipt of a low oil pressure alarm. Operators attempted to run HPCI a second time, and the same problems were encountered. On August 25, 1983, the reactor core isolation cooling system (RCIC) tripped on low bearing oil pressure, and a low flow alarm for the B RCIC area cooler was received in the control room. The unit was brought to cold shutdown because of the concurrent HPCI and RCIC unavailabilities. The conditional core damage probability estimated for the event is 1.3 x 10-5.
B.23.2 Event Description On August 24, 1983, a HPCI turbine bearing oil pressure low alarm was received in the control room when HPCI was started for its pump operability test. HPCI was manually tripped. The plant operators attempted to run HPCI a second time, and the same problems were encountered.
On August 25, 1983, RCIC tripped on low bearing oil pressure during the performance of the RCIC pump operability test. Also during the test, a low flow alarm for the B RCIC area cooler was received in the control room. Later on August 25, 1983, while washing down the cooling coils for the B RCIC area cooler, water drenched the RCIC turbine exhaust high-pressure switches, causing a turbine trip and an alarm in the control room. As a result of the combined HPCI and RCIC unavailabilities, the unit was brought to cold shutdown.
The shutdown was initiated by a manual scram.
The cause of the HPCI turbine bearing oil pressure low alarm was attributed to the HPCI turbine thrust bearing oil supply valve being closed and providing insufficient oil supply to the bearing. Also, the HPCI turbine governor end radial bearing oil supply valve was found to be open too much (providing oil at 30 psig when it should have been 10 to 12 psig). The valves were repositioned, and the oil pressure on the HPCI turbine was adjusted.
A visual inspection of the HPCI turbine overspeed trip ball and tappet assembly revealed a broken ball, thus making the HPCI turbine overspeed trip nonfunctional. It is believed that this damage occurred when the HPCI turbine was started on August 24, 1983, and ran erratically. The HPCI turbine overspeed trip ball and tappet assembly was replaced. HPCI was tested and returned to operability on August 29, 1983.
LER No. 321/83-090, Rev. 1, -093
B.23-2 The cause of the RCIC low bearing oil pressure alarm and trip was attributed to setpoint drift of the RCIC low bearing oil pressure switch. The cause of the RCIC B area cooler low flow alarm was a sensing element (pitot tube) partially stopped up with dust. The oil pressure switch was recalibrated and the pitot tube was cleaned and blown out. The water-drenched RCIC turbine exhaust switches were dried out and their calibration was checked.
B.23.3 Additional Event-Related Information The HPCI and RCIC systems are the primary source of reactor pressure vessel (RPV) makeup in the event of a loss of feedwater.
B.23.4 Modeling Assumptions This event is modeled as a reactor trip with both RCIC and HPCI unavailable. Neither HPCI nor RCIC was deemed repairable, and a nonrecovery probability of 1.0 was assigned to each of them.
B.23.5 Analysis Results The conditional core damage probability estimated for this event is 1.3 x 10-5. The dominant core damage sequence, highlighted on the event tree in Figure B.23.1, involves the observed transient, failure of the power conversion system, failure of feedwater, HPCI failure, RCIC failure, failure of the safety relief valves (SRVs) to reduce pressure, and failure of the control rod drive system to provide RPV makeup.
LER No. 321/83-090, Rev. 1, -093
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Figure B.23.1 Dominant core damage sequence for LER 321/83-090 LER No. 321/83-090, Rev. 1, -093
B.23-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
321/83-090 Event
Description:
Manual scram with HPCI and RCIC unavailable Event Date:
August 25. 1983 Plant:
Hatch 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 1.0E+O0 Probability CD TRANS Total 1.3E-05 1.3E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence 119 trans -rx.shutdown pcs srv.ftc.<2 mfw HPC rd(inj) 138 trans -rx.shutdown pcs srv.ftc.2 HPCI srv 103 trans -rx.shutdown pcs srv.ftc.<2 -mfw rhr 414 trans rx.shutdown rpt 413 trans rx.shutdown -rpt slcs 109 trans -rx.shutdown pcs srv.ftc.<2 mfw HPC ond rhr
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence 103 trans -rx.shutdown pcs srv.ftc.<2 -mfw rhr 109 trans -rx.shutdown pcs srv.ftc.<2 mfw HPC ond rhr 119 trans -rx.shutdown pcs srv.ftc.<2 mfw HPC rd(inj) 138 trans -rx.shutdown pcs srv.ftc.2 HPCI srv 413 trans rx.shutdown -rpt slcs 414 trans rx.shutdown rpt
- non-recovery credit for edited case I
RCIC srv.ads c
.ads
.and.pcs.nrec I
RCIC -srv.ads -c
.and.pcs.nrec I RCIC -srv.ads -c I
RCIC srv.ads c
.ads End State CD CD CD CD CD CD End State CD CD CD CD CD CD Prob 6.6E-06 2.8E-06 1.6E-06 6.7E-07 4.1E-07 2.1E-07 Prob 1.6E-06 2.1E-07 6.6E-06 2.8E-06 4.1E-07 6.7E-07 N Rec**
2.4E-01 7.OE-01 7.3E-03 1.0E-01 1.0E-01 3.6E-03 N Rec**
7.3E-03 3.6E-03 2.4E-01 7.0E-01 I.OE-01 IOE-01 LER No. 321/83-090
B.23-5 SEQUENCE MODEL:
BRANCH MODEL:
PROBABILITY FILE:
d:\\asp\\models\\bwrc8283.cmp d:\\asp\\models\\hatchl.82 d:\\asp\\models\\bwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans loop loca rx. shutdown pcs srv.ftc.<2 srv.ftc.2 srv. ftc.>2 mfw HPCI Branch Model:
I.OF.1 Train I Cond Prob:
RCIC Branch Model:
1.OF.1 Train 1 Cond Prob:
srv.ads crd(inj) cond Ipcs Ipci rhrsw(inj) rhr rhr. and. pcs. nrec rhr/-Ipci rhr/lpci rhr(spcool) rhr(spcool )/-Ipci ep ep. rec rpt slcs ads.inhibit man.depress branch model file
- forced 1.6E-03 1.6E-05 3.3E-06 3.5E-04 1.7E-01 1.OE+00 1.3E-03 2.2E-04 4.6E-01 2.9E-02 > 1.OE+O0 2.9E-02 > I.OE+O0 6.OE-02 > 1.OE+O0 6.0E-02 > 1.OE+O0 3.7E-03 I.OE-02 1.OE+00 2.OE-03 1.1E-03 2.OE-02 1.5E-04 1.5E-04 O.OE+O0 I.0E+O0 2.1E-03 2.OE-03 2.9E-03 1.6E-01 1.9E-02 2.OE-03 O.OE+O0 3.7E-03 1.0 E+O0 3.6E-01 6.7E-01 I1,E-01 1.OE+0O 1.OE+00 1.OE+0O 1.OE+O0 3.4E-01 7.OE-01 > 1.OE+O0 7.OE-01 > 1.OE+O0 7.OE-01 1.0E+00 3.4E-01 1.OE+O0 1.OE+O0 I.OE+O0 1.6E-02 B.3E-03 I.OE+00 1.0E+O0 1.OE+O0 1.OE+O0 8.7E-01 l.0E+O0 1.0E+O0 1.OE+O0 1.OE+00 1.OE+00 1.OE-02 1.OE-02 1.OE-03 1.OE-02 1.OE-05 1.OE-05 1.OE-05 1.OE-05 1.OE-03 1.OE-03 1.OE-02
- 1.
OE-02 1.OE-02 LER No. 321/83-090