ML20156A225
| ML20156A225 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-183-00 | |
| Download: ML20156A225 (6) | |
Text
B.32-1 B.32 LER Nos. 327/83-183 and -186 Event
Description:
Unavailability of One Emergency Diesel Generator and the Turbine-Driven Auxiliary Feedwater Pump Date of Event:
December 2, 1983 Plant:
Sequoyah 1 B.32.1 Summary Emergency diesel generator (EDG) IA-A tripped due to high crankcase pressure during surveillance testing.
The diesel suffered extensive damage which was determined to be due to incorrect assembly. Ten days earlier, stroke testing of the turbine-driven auxiliary feedwater (TDAFW) pump revealed that the steam supply valve was inoperable because of a failed Limitorque operator-geared limit switch. The estimated increase in core damage probability, or importance, over the duration of the event is 3.1 x 10'-.
The base-case core damage probability (CDP) over the duration of the event is 1.6 x 10-6, resulting in an estimated conditional core damage probability (CCDP) of 3.3 x 10-.
B.32.2 Event Description During performance of surveillance testing of emergency diesel generator lA-A on December 12, 1983, it tripped due to high crankcase pressure. Unit I was operating at 100% power at the time of the event.
Investigation of the failure revealed significant damage to the diesel, which resulted from improper torquing of the wrist pin bolts on one cylinder. The EDG was repaired and returned to service on December 12, 1983.
This event was reported under LER 327/83-186. On December 2, 1983, with Unit 1 at 0% power, stroke testing of the turbine-driven auxiliary feedwater pump revealed that the steam supply valve was inoperable.
The cause was a failed limitorque operator-geared limit switch. The switch was replaced and the valve was verified operable on December 12, 1983.
This event was reported under LER 327/83-183.
B.32.3 Additional Event-Related Information LER 327/83-183 states that the steam supply valve could have been in a failed condition during power operation. EDG IA-A is one of two diesel generators that provide emergency power to Unit 1.
B.32.4 Modelling Assumptions These events are modeled as a combined unavailability of one EDG and the TDAFW pump. Since steam supply valve 1-FCV-I-18 was found to be failed on December 2, 1983, it was assumed that it was failed on November 17, 1983, 15 days after the last pump test one month earlier. On December 12, 1983, EDG IA-A was found to be failed. Given the fact that the failure was due to incorrect assembly, it was assumed that it would have been unavailable since the last test one month earlier on November 11, 1983. Therefore, both LER Nos. 327/83-183 and -186
B.32-2 systems would have been unavailable from November 17, 1983 until December 12, 1983 when the EDG was the first of the two systems to be returned to service. This unavailability period of 25 days (600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br />) was reduced to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> to reflect the fact that the unit tripped on November 24, 1983. With EDG I A-A inoperable, train 2 of the emergency power system model was failed to reflect the assumption that EDG 1 B-B would not be likely to fail due to the same cause since, according to LER 327/83-186, a similar failure had not occurred in a factory-assembled unit since 1979. In the AFW model, train 3, which represents the TDP, was failed. The single train in the AFW/EP model represents the TDP, so it was also failed. Trains I and 2 represent the two motor-driven pumps (MDPs). Since one MDP would be unavailable due to the failure of EDG I A-A, train 2 was set to unavailable, making train 1 only susceptible to independent (random) failures.
Similarly, the high-pressure injection (HPI) and high-pressure recirculation (HPR) system models were modified by setting train 2 to unavailable due to the loss of EDG 1 A-A. Since train 3 of the HPI model represents the two charging pumps, which have a 2 of 2 success criteria, the failure probability was also set to unavailable. Feed-and-bleed operations use the HPI system. Therefore, the modifications made to the HPI model were also made to the FEED.BLEED model. A loss of offsite power (LOOP) was used as the potential initiator for the unavailability analysis.
B.32.5 Analysis Results The estimated increase in core damage probability over the duration of the event is 3.1 x 10'. The base-case CDP (not shown in calculation) is 1.6 x 10', resulting in an estimated CCDP of 3.3 x 10". The dominant core damage sequence, shown in Figure B.32. 1, involves a postulated LOOP, failure of emergency power, and loss of AFW.
LER Nos. 327/83-183 and -186
B.32-3 VN SVSNSS RN 8
SN~8 AN C94 92 w
I-0ý J 0 8
ow w 0.
Figure B.32.1 Dominant core damage sequence for LER Nos. 327/83-183 and -186 LER Nos. 327/83-183 and -186
B.32-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
327/83-183 and -186 Event
Description:
EDG trips during test, valve on TDAFW pump fails test Event Date:
December 2. 1983 Plant:
Sequoyah 1 UNAVAILABILITY.
DURATION= 168 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 1.SE-03 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 3.1E-05 Total 3.1E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
239 loop -rt(loop)
EP AFW/EP CD 2.2E-05 1.6E-01 226 loop ýrt(loop)
EP -AFW/EP porv.chall/sbo -porv.reseat/ep seal CD 5.9E-06 3.1E-01
.loca offsite.pwr.rec/seal.loca 228 loop -rt(loop)
EP -AFW/EP porv.chall/sbo -porv.reseat/ep -seal CD 2.OE-06 3.1E-O1
.loca offsite.pwr.rec/-seal.loca 229 loop -rt(loop)
EP -AFW/EP porv.chall/sbo porv.reseat/ep CD 7.8E-07 3.1E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
226 loop -rt(loop)
EP -AFW/EP porv.chall/sbo -porv.reseat/ep seal CD 5.9E-06 3.1E-01
.loca offsite.pwr.rec/seal.loca 228 loop -rt(loop)
EP -AFW/EP porv.chall/sbo -porv.reseat/ep -seal CD 2.OE-06 3,1E-01
,loca offsite.pwr.rec/-seal.loca 229 loop -rt(1pop)
EP -AFW/EP porv.chall/sbo porv.reseat/ep CD 7.8E-07 3.1E-O1 239 loop -rt(loop)
EP AFW/EP CD 2.2E-05 1.6E-O1
- non-recovery credit for edited case Note:
For unavailabilities. conditional probability values are differential values which reflect the added risk due to failures associated with an event.
Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
SEQUENCE MODEL:
c:\\asp\\1982-83\\pwrb8283.cmp BRANCH MODEL:
c:\\asp\\1982-83\\sequoyl.82 PROBABILITY FILE:
c:\\asp\\1982-83\\pwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES LER Nos. 327/83-183 and -186
B.32-5 Branch System Non-Recov Opr Fail trans 1 oop I oca sgtr rt rt(loop)
AFW Branch Model:
1.OF.3+ser Train I Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
afw/atws AFW/EP Branch Model:
1.OF.1 Train 1 Cond Prob:
mfw porv.chall porv.chall/afw porv.cha 11/loop porv.chall/sbo PORV. RESEAT Branch Model:
I.OF.1 Train 1 Cond Prob:
porv. reseat/ep srv.reseat(atws)
HPI Branch Model:
Train 1 Cond Train 2 Cond Train 3 Cond FEED.BLEED Branch Model:
Train 1 Cond Train 2 Cond Train 3 Cond 1.OF.3 Prob:
Prob:
Prob:
1.OF.3+ser+opr Prob:
Prob:
Prob:
1.6E-03 1.6E-05 2.4E-06 1.6E-06 2.8E-04 O.OE+O0 3.8E-04 > 2.OE-02 2.OE-02 1.0E-01 > Unavailable 5.OE-02 > Failed 2.8E-04 4.3E-03 5.OE-02 > 1.OE+O0 5.OE-02 > Failed 2.OE-01 4.OE-02 1.0E+O0 1.E-01 1.OE+O0 2.OE-02 > 2.OE-02 2.OE-02 2.OE-02 1.E-01 1*OE-05 > 1.OE-02 1.OE-02 1.0E-01 > Unavailable 1.OE-02 > Unavailable 2.OE-02 > 3.OE-02 1.OE-02 i.E-01 > Unavailable 1.OE-02 > Unavailable 2.OE-02 O.OE+O0 2.OE-01 3.4E-01 3.OE-03 2.2E-02 > 1.OE+O0 2.OE-02 i.E-01 > Unavailable 2.OE-02 > 1.OE+O0 1.OE-03 > 1.OE-02 1.OE-02 1i0E-01 > Unavailable 4.OE-03 > 4.OE-02 4.OE-02 i.E-01 > Unavailable 2.9E-03 > S.0E-02 1.OE+OO 5.3E-01 5.4E-01 1.OE+OO 1.DE-0 1
- 1.
OE+OD 4.5E-01 1.OE+OO 34E -01 3.4E-01
- 1.
OE+OO
- 1.
OE+OO
- 1.
OE+OO
- 1.
OE+OO 1.1E-02 > 5.OE-O1 1.OE+OO 1.OE+OO 8.9E-01 1.OE+OO 1.OE+OO 1.OE+OO 1.OE+OO 1.OE+OO 5.7E-02 1.OE+OO 1.OE+0O 1.OE-03 Serial Component Prob:
emrg.boration recov.sec.cool recov.sec.cool/offsite.pwr rcs.cooldown RHR Branch Model:
1.OF.2+ser+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Serial Component Prob:
RHR.AND.HPR Branch Model:
1.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
1.OE-02 1.OE-02
- 1.
OE-03 1.OE-03 1.OE-03 1.OE-03 HPR EP Branch Model:
1.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
8.9E-01 Branch Model:
Train I Cond Train 2 Cond 1.OF.2 Prob:
Prob:
5.OE-02 5.7E-02 > Failed LER Nos. 327/83-183 and -186
B.32-6 seal.loca 2.7E-01 1.OE+O0 offsite.pwr.rec/-ep.and.-afw 2.2E-01 LOE+O0.
offsite.pwr.rec/-ep.and.afw 6.7E-02 1.OE+O0 offsite.pwr.rec/seal.loca 5.7E-01 I.OE+O0 offsite.pwr.rec/-seal.loca 7.OE-02 1.OE+O0 sg.iso.and.rcs.cooldown I.OE-02 1.OE-O1 rcs.cool.below.rhr 3.0E-03 I.OE+O0 3.OE-03 prim.press.limited 8.8E-03 1.OE+O0
- branch model file
- forced LER Nos. 327/83-183 and -186