ML20147A472
| ML20147A472 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter Office of Nuclear Regulatory Research |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-029-00 | |
| Download: ML20147A472 (6) | |
Text
B.25-1 B.25 LER No. 324/82-029 Event
Description:
Scram with RHRSW System Degradations Date of Event:
February 3, 1982 Plant:
Brunswick 2 B.25.1 Summary Brunswick Unit 2 was operating at approximately 73% power when an unsuccessful attempt was made to start "A" residual heat removal (RHR) service water (SW) pump. At the same time that A RHRSW pump was inoperable, the emergency power supply for RHRSW pump B was out of service for maintenance. A scram occurred the same day that the RHRSW system degradations were detected. The conditional core damage probability estimated for the event is 3.4 x I0".
B.25.2 Event Description On February 3, 1982, Brunswick 2 personnel were investigating a signal regarding A RHRSW pump when they unsuccessfully attempted to start the pump. They determined that an RHRSW loop I low-suction header pressure lockout signal had been generated by a failed pressure switch, rendering loop I inoperable. At the same time, the No. 4 emergency diesel generator (EDG) was out of service due to maintenance. As a result, RHRSW pump 1 B did not have an emergency power supply, and RHRSW loop II was declared inoperable.
A high main steamline radiation indication resulted in a scram on the same date.
B.25.3 Additional Event-Related Information None.
B.25.4 Modeling Assumptions It was assumed that the RHRSW failure existed at the time of the scram, which occurred on the same day.
This event was modeled as a transient with one loop of RHRSW inoperable. Failure of the RHRSW train II low suction pressure switch prevented automatic or manual start of the train 1I RHRSW pumps. The RHRSW pumps at Brunswick maintain a positive pressure differential between the tube and shell side of the RHR heat exchangers, which prevents primary coolant leakage into the service water (SW) system. Adequate decay heat removal can be provided using the SW pumps once one valve (F068A/B) in each train is locally opened. An operator error probability of 0.01 was estimated for this action in the Brunswick individual plant examination (IPE). Because of the unavailability of RHRSW train II, one train of RHR was modeled as failed in all modes except low-pressure coolant injection (LPCI). Although the specific failure discovered was apparently not present in the other train at the same time, other common cause modes remained and could have affected LER No. 324/82-029
B.25-2 system performance. A common cause failure probability of 0.1 was assumed for train I and, as this value dominates the component failure probabilities in the system, the probability of RHR failure was set to 0.1 in the model.
The licensee event report indicates that a high main steamline radiation signal was received during the event.
It was assumed that this signal caused an automatic isolation of the main steam isolation valves, resulting in power conversion system (PCS) and main feedwater unavailabilities (PCS was assumed to be recoverable in the long term). The probability of RHR nonrecovery was revised to 0.01 to reflect the potential failure of the operators to open F068A and B. For sequences involving potential RHR or PCS recovery, the nonrecovery estimate was revised to 0.01 x 0.17 [PCS long-term nonrecovery given main steam isolation valve (MSIV) closure (see Appendix A)], or 1.7E-4.
B.25.5 Analysis Results The conditional core damage probability estimated for this event is 3.4 x 10-'. The dominant core damage sequence, highlighted on the event tree in Figure B.25. 1, involves the observed scram, failure of the power conversion system, main feedwater success, and RHR failure.
LER No. 324/82-029
U) z Z5-a2 '
C.)
z 0
0.
C-a U.)
a:
U.)
B.25-3 0---0---000-----------------
0---0 --------
Figure B.25.1 Dominant core damage sequence for LER 324/82-029 LER No. 324/82-029
B.25-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
324/82-029 Event
Description:
Scram and RHRSW degradations Event Date:
February 3. 1982 Plant:
Brunswick 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OE+O0 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER) 3.4E-05 3.4E-05 Sequence End State Prob 103 105 403 trans -rx.shutdown PCS srv.ftc.<2 -MFW RHR.AND.PCS.NREC trans -rx.shutdown PCS srv.ftc.<2 MFW -hpci RHR.AND.PCS.NREC trans rx.shutdown -rpt -slcs PCS -ads.inhibit -hpci RHR(SPCOO L)
CD CD CO CD CD 1.8E-05 9.OE-06 3.3E-06 N Rec**
1.1E-04 5.7E-05 9.9E-02 121 trans -rx.shutdown PCS srv.ftc.2 -hpci -cond RHR 414 trans rx.shutdown rpt
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER) 8.5E-07 6,6E-03 6.7E-07 1.0E-01 Sequence End State Prob 103 105 121 403 trans -rx.shutdown PCS srv.ftc.<2 -MFW RHR.AND.PCS.NREC trans -rx.shutdown PCS srv.ftc.<2 MFW -hpci RHR.AND.PCS.NREC trans -rx.shutdown PCS srv.ftc.2 -hpci -cond RHR trans rx.shutdown -rpt -slcs PCS -ads.inhibit -hpci RHR(SPCOO L)
CD CD CD CD CD 1.8E-05 9.0E-06 8.5E-07 3.3E-06 N Rec**
1.IE-04 5.7E-05 6.6E-03 9.9E-02 414 trans rx.shutdown rpt 6.7E-07 1.0E-01
- non-recovery credit for edited case LER No. 324/82-029
B.25-5 SEQUENCE MODEL:
BRANCH MODEL:
PROBABILITY FILE:
c:\\asp\\1982-83\\bwrc8283.cmp c:\\asp\\1982-83\\bruns2.82 c:\\asp\\1982-83\\bwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans loop loca rx.shutdown PCS Branch Model:
I.OF.1 Train 1 Cond Prob:
srv.ftc,<2 srv.ftc,2 srv.ftc,>2 MFW Branch Model:
1.OF.1 Train 1 Cond Prob:
hpci rcic srv.ads crd(inj) cond 1pcs Ipci rhrsw(inj)
RHR Branch Model:
1.OF.4+opr Train I Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
RHR.AND.PCS.NREC Branch Model:
1.OF.4+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
RHR/-LPCI Branch Model:
1.OF.l+opr Train 1 Cond Prob:
rhr/Ipci RHR(SPCOOL)
Branch Model:
1.OF.4+ser+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
1.1E-03 1.6E-05 3.3E-06 3.5E-04 1.7E-01 > 1.OE+O0 1.7E-01 > 1.OE+O0 1.OE+O0 1.3E-03 2.2E-04 4.6E-01 > 1.OE+O0 4.6E-01 > 1.OE+O0 2.9E-02 6.OE-02 3.7E-03 1.OE-02 1.OE+O0 2.OE-03 1.1E-03 2.OE-02 1.5E-04 > 1.0E-01 **
1.OE-02 1.0E-01 3.OE-01 5.OE-01 1.5E-04 > 1.0E-01 **
1.OE-02 1.0E-01 3.OE-01 5.OE-01 O.OE+O0 > 1.0E-01 **
O.OE+O0 1.0E+O0 2.1E-03 > i.0E-01 **
- 1.
OE+00 3.6E-01
- 6.
7E-01 1.DE-Ol
- 1.
OE+0O
- 1.
OE+00
- 1.
OE+00
- 1.
OE+00 3.4E-01 7.OE-01 7.OE-01 7.OE-01 1.OE+O0 3.4E-01 1.OE+O0 1.OE+O0 1.OE+O0 1.6E-02 > 1.OE-02 8.3E-03 > 1.7E-04 1.OE+O0 > 1.OE-02 1.OE+O0 1.OE+O0 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-02 1.DE-01
.3.OE -01
- 5.
OE-01 LER No. 324/82-029
B.25-6 Serial Component Prob:
RHR(SPCOOL)/-LPCI Branch Model:
1.OF.l+ser+opr Train 1 Cond Prob:
Serial Component Prob:
ep ep.rec rpt slcs ads.inhibit man.depress 2.OE-03 2.OE-03 > 1.OE-01 **
O.OE+O0 2.OE-03 2.9E-03 1.6E-01 1.9E-02 2.OE-03 O.OE+O0 3.7E-03
- 1.
OE+0O
- 8.
7E -01
- 1.
OE+OO
- 1.
OE+OO
- 1.
OE-+0O
- 1.
OE+OO
- 1.
OE+0O 1.OE-03 1.OE-02 1.OE-02
- 1.
OE-02 branch model file
- forced I
I LER No. 324/82-029