ML20147A473
| ML20147A473 | |
| 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 1982-123-00 | |
| Download: ML20147A473 (6) | |
Text
B.26-1 B.26 LER No. 324/82-123 Event
Description:
Scram with Emergency Bus E-3 De-energized Date of Event:
October 10, 1982 Plant:
Brunswick 2 B.26.1 Summary Brunswick Unit I was operating at approximately 17% power during an attempted controlled shutdown when operators experienced difficulty in transferring bus 2D from the unit auxiliary transformer (UAT) to the startup auxiliary transformer (SAT). When the UAT breaker was opened, the output breakers from both the SAT and the number 3 emergency diesel generator (EDG) failed to close, resulting in scram and loss of power to bus E-3. The conditional core damage probability estimated for the event is 1.2 x 10'.
B.26.2 Event Description On October 10, 1982, operators were performing a controlled shutdown of Brunswick Unit 2 when they attempted to transfer electrical bus 2D from the UAT to the SAT. When the UAT breaker opened, the feeder breaker from the SAT failed to close in. Subsequent troubleshooting determined that the breaker charging spring motor shaft had broken, and the breaker was not charged. When the SAT feeder breaker failed to close in on the bus, EDG 3 should have started and powered the bus, but it failed to do so and buses 2D and E-3 were de-energized. An investigation of that failure determined that inappropriately calibrated relays were simultaneously providing open and close signals to the EDG output breaker. As a result, the EDG output breaker was prevented from closing.
B.26.3 Additional Event-Related Information De-energization of bus E-3 caused a scram and main steam isolation valve (MSIV) isolation. In addition, the 2A core spray and residual heat removal (RHR) pumps were rendered inoperable by the loss of their normal and emergency power supplies.
B.26.4 Modeling Assumptions This event was modeled as a scram and MSIV isolation with core spray pump 2A and RHR pump 2A inoperable. With MSIVs isolated, the power conversion and feedwater systems were initially unavailable.
Because of the multiple failures required to render the 2A core spray and RHR pumps inoperable, the potential for common cause failure of other pumps was assumed to be small. The nonrecovery probability for the power conversion system (PCS) was revised to 0.017 to reflect the MSIV closure (see Appendix A). Combining this value with the estimated long-term RHR nonrecovery probability of 0.016 results in a combined nonrecovery probability for RHR and PCS of 2.7E-4.
LER No. 324/82-123
B.26-2 B.26.5 Analysis Results The conditional core damage probability estimated for this event is 1.2 x 10'. The dominant core damage sequence, highlighted on the event tree in Figure B.26. 1, involves the observed scram, failure of the power conversion system, main feedwater success, and failure of RHR.
LER No. 324/82-123
wQ)O a:
as az E) 0 0 cc2z LU crz C-.
B.26-3 OOUOUOUOUOUOQOU.UOUQOQ000Q QU0UU0U00Uv0U0U0OUOOUUC Figure B.26.1 Dominant core damage sequence for LER 324/82-123 LER No. 324/82-123
B.26-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
Event
Description:
Event Date:
Plant:
324/82-123 Scram with emergency bus E-3 deenergized October 10.
1982 Brunswick 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator CD TRANS Total SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER) 1.0E+O0 Probability 1.2E-05 1.2E-05 Sequence End State Prob 103 105 414 413 412 138 trans trans trans trans trans trans
-rx.shutdown PCS srv.ftc.<2 -MFW RHR.AND.PCS.NREC
-rx.shutdown PCS srv.ftc.<2 MFW -hpci RHR.AND.PCS.NREC rx.shutdown rpt rx.shutdown -rpt slcs rx.shutdown -rpt -slcs PCS ads.inhibit
-rx.shutdown PCS srv.ftc.2 hpci srv.ads CD CD CD CD CD CD 6.6E-06 3.4E-06 6.7E-07
- 4. 1E-07 3.4E-07 3.3E-07 N Rec**
1.8E-04 9.1E-05 I.OE-OI I.OE-OI I.OE-OI 4.9E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob 103 trans -rx.shutdown PCS srv.ftc.<2 -MFW RHR.AND.PCS.NREC 105 trans -rx.shutdown PCS srv.ftc.<2 MFW -hpci RHR.AND.PCS.NREC 138 trans -rx.shutdown PCS srv.ftc.2 hpci srv.ads 412 trans rx.shutdown -rpt -slcs PCS ads.inhibit 413 trans rx.shutdown -rpt slcs 414 trans rx.shutdown rpt CD CD CD CD CD CD 6.6E-06 3.4E-06 3.3E-07 3.4E-07
- 4. 1E-07 6.7E-07 N Rec**
1.8E-04
- 9. 1E-05 4.9E-01 1.OE-O1 I OE-OI I.OE-01
- non-recovery credit for edited case LER No. 324/82-123
B.26-5 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:
1.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 LPCS Branch Model:
1.OF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
LPCI Branch Model:
1.OF.4+ser Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Train 4 Cond Prob:
Serial Component Prob:
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/-Ipci 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 > 2.OE-02 2.OE-02 1.OE-01 > 1.OE+O0 1.1E-03 > 1.3E-03 1.OE-02 1.OE-01 3.OE-01 5.OE-01 > 1.OE+O0 1.OE-03 2.OE-02 1.5E-04 > 3.OE-04 1.OE-02 1.0E-01 3.0E-01 5.OE-01 > 1.0E+O0 1.5E404 > 3.OE-04 1.OE-02 1.0E-01 3.OE-01 5.OE-01 > 1.OE+O0 O.OE+O0
- 1. OE+00 3.6E-01 6.7E-01 1.0E-01 1.OE+O0 1.OE+0O 1.OE+0O 1.0E+O0 3.4E-01 7.OE-01 7.OE-01 7.OE-01 1.OE+0O 3.4E-01 1.OE+O0 1.OE+0O 1.OE+O0 1.6E-02 8.3E-03 > 2.7E-04 1.OE+O0 1.OE-02
- 1.
OE-02
- 1.
OE-03 1.OE-02 1.OE-05
- 1.
OE-05 1.OE-05 LER No. 324/82-123
B.26-6 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:
Serial Component Prob:
rhr(spcool)/-Ipci ep ep.rec rpt slcs ads.inhibit man.depress 1.OE+O0 2.1E-03 > 2.3E-03 1.OE-02 1.OE-O1 3.OE-01 5.OE-01 > 1.OE+O0 2.OE-03 2.OE-03 2.9E-03 1.6E-01 1.9E-02 2.OE-03 O.OE+O0 3.7E-03
- 1.
OE+OO
- 1.
OE+OO
- 1. OE+OO
- 8. 7E-O01
- 1. OE+0O
- 1. OE+OO
- 1. OE+OO
- 1. OE+OO
- 1. OE+00 1.OE-05 1.OE-03 1.OE-03 1.OE-02 1.OE-02 1.CE-02 branch model file
- forced LER No. 324/82-123