ML20156A221
| ML20156A221 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-048 | |
| Download: ML20156A221 (6) | |
Text
B.30-1 B.30 LER Nos. 327/82-048 and -050 Event
Description:
Unavailability of One Emergency Diesel Generator and One Motor-Driven Auxiliary Feedwater Pump Date of Event:
April 13, 1982 Plant:
Sequoyah 1 B.30.1 Summary On April 8, 1982, an automatic control valve in the auxiliary feedwater (AFW) system at Sequoyah Unit I failed to open on demand. The failure was caused by a faulty soldered connection to the electrohydraulic actuator of the valve. A similar event occurred on April 10, 1982. In this case, it was found that the servo valve oil passages were blocked by an accumulation of foreign matter in the filters. In both instances, the motor-driven pump in train B was rendered inoperable by the failures. Five days later (April 13, 1982),
emergency diesel generator (EDG) IA-A was declared inoperable when power fuses opened in the control circuitry. The estimated increase in core damage probability, or importance, over the duration of the event is 2.6 x 10-'. The base-case core damage probability (CDP) over the duration of the event is 2.2 x 10', resulting in an estimated conditional core damage probability (CCDP) of 2.8 x 10--.
B.30.2 Event Description On April 8, 1982, Sequoyah Unit 1 was operating at 100% power when an automatic control valve (1 -PCV 132) in the AFW system was declared inoperable due to failure to open on demand. A similar event occurred on April 10, 1982. The first event was due to a faulty soldered connection to the electrohydraulic actuator of the valve. The connector was repaired and the valve was returned to service on April 8, 1982. In the second event, it was found that the servo valve oil passages were blocked by an accumulation of foreign matter in the filters. The valve was replaced, and the control valve was returned to service on April 11, 1982.
On April 13, 1982, with Unit I still at 100% power, emergency diesel generator 1 A-A was declared inoperable when power fuses opened in the control circuitry. The failure was due to a broken lead in the annunciator horn which had shorted to ground, causing the fuses to open due to excessive current. The horn was replaced, and the EDG was declared operable on April 13, 1982.
B.30.3 Additional Event-Related Information The failure of valve I-PCV-3-132 disables train B of the AFW system, since it is located in the discharge line of motor-driven pump (MDP) B. EDG lA-A is one of two diesel generators that provide emergency power to Unit 1.
LER Nos. 327/82-048 and -050
B.30-2 B.30.4 Modeling Assumptions These events are modeled as a combined unavailability of one EDG and an AFW MDP. EDG IA-A is assumed to have been inoperable for half of the 30-day surveillance period prior to April 13, 1982, i.e. starting on March 29, 1982. Similarly, MDP B is assumed to have been unavailable starting on March 24, 1982, 15 days prior to April 8, 1982. Using these assumptions, the period during which both systems were unavailable began on March 29, 1982. The end of the overlap period is April 8, 1982, when the valve which made MDP B inoperable was first returned to service and before EDG IA-A was discovered to be inoperable. This gives an overlap period of 10 days or 240 hours0.00278 days <br />0.0667 hours <br />3.968254e-4 weeks <br />9.132e-5 months <br />, longer than the overlap associated with the second valve failure on April 10, 1982. To reflect the inoperability of EDG IA-A, train 1 of the emergency power system was failed.
EDG I B-B was therefore subject to failure due to the same (common) cause. The potential for common cause failure exists, even when a component is failed. Therefore, the conditional probability of a common cause failure was included in the analysis for those components that were assumed to have been failed as part of the postulated event. In the AFW model, the unavailability of train B was represented by setting train 1 to failed.
This recognizes the potential for a similar failure in the other train due to common cause. To represent the unavailability of power from EDG 1A-A, the second AFW train was made unavailable. In the high-pressure injection (HPI) system model, the train 2 safety injection (SI) pump was made unavailable due to the loss of EDG lA-A. Train 1, the other SI pump, was thus susceptible only to random failures. Since train 3 of the HPI model represents the two charging pumps, which have a 2 of 2 success criterion, this train was made 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. In the HPR model, train 2, which represents the same SI pump used in the HPI system, was made unavailable due to the loss of EDG IA-A, leaving train 1 subject to random failures. Finally, train 2 in the RHR and RHR.AND.HPR models and the serial component in the RHR model (representing the series RHR suction valves) were also set to unavailable due to the loss of the EDG. A loss-of-offsite power (LOOP) was used as the potential initiator for the unavailability analysis. The base-case CDP (not shown in calculation) is 2.2 x 106 and the CCDP is 2.8 x 10'.
B.30.5 Analysis Results The increase in core damage probability over the duration of the event is 2.6 x 10.
The base-case CDP (not shown in calculation) is 2.2 x 10', resulting in an estimated CCDP of 2.8 x I0-. The dominant core damage sequence, shown in Figure B.30.1, involves a postulated LOOP, failure of emergency power, an RCP seal LOCA, and failure to recover offsite power prior to core uncovery.
LER Nos. 327/82-048 and -050
B.30-3
-18 8
2 V t2 V V8 8
N 00000000 000 000 000 00 000 000 000 00 w
IT-Cc, 0z 0
c CC R (
cc Figure B.30-1 Dominant core damage sequence for LER Nos. 327/82-048 and -050 LER Nos. 327/82-048 and -050
B.30-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
327/82-048 Event
Description:
EDG unavailable, AFW MOP discharge valve fails Event Date:
April 13, 1982 Plant:
Sequoyah I UNAVAILABILITY.
DURATION= 240 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 2.1E-03 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 2.6E-05 Total 2.6E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State 226 loop -rt(loop)
EP -afw/ep porv.chall/sbo -porv.reseat/ep seal CD
.loca offsite.pwr.rec/seal.loca 228 loop -rt(loop)
EP -afw/ep porv.chall/sbo -porv.reseat/ep -seal CD
,loca offsite.pwr.rec/-seal.loca 229 loop -rt(loop)
EP -afw/ep porv.chall/sbo porv.reseat/ep CD 239 loop -rt(loop)
EP afw/ep CD 215 loop -rt(loop) -EP AFW -offsite.pwr.rec/-ep.and.afw FEED.BLEED CO
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State 215 loop -rt(loop) -EP AFW -offsite.pwr.rec/-ep.and.afw FEED.BLEED CD 226 loop -rt(loop)
EP -afw/ep porv.chall/sbo -porv.reseat/ep seal CD loca offsite.pwr.rec/seal.loca 228 loop -rt(loop)
EP -afw/ep porv.chall/sbo -porv.reseat/ep -seal CD
.loca offsite.pwr.rec/-seal.loca 229 loop -rt(loop)
EP -afw/ep porv.chall/sbo porv.reseat/ep CD 239 loop -rt(loop)
EP afw/ep CD
- non-recovery credit for edited case Note:
For unavailabilities, conditional probability values are differential values added risk due to failures associated with an event.
Parenthetical values indicate risk compared to a similar period without the existing failures.
SEQUENCE MODEL:
c:\\asp\\1982-83\\pwrb8283.cmp Prob 1.5E-05 4.9E-06 2.OE-06 1.7E-06 1.6E-06 Prob 1.6E-06 1.5E-05 4.9E-06 2.OE-06 1.7E-06 N Rec**
4.7E-01 4.7E-01 4.7E-01 1.6E-01 2.4E-01 N Rec**
2.4E-01 4.7E-01 4.7E-01 4.7E-01 1.6E-01 which reflect the a reduction in LER Nos. 327/82-048 and -050
B.30-5 BRANCH MODEL:
PROBABILITY FILE:
c:\\asp\\1982-83\\sequoyl.82 c:\\asp\\1982-83\\pwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch trans loop loca sgtr rt rt(loop)
AFW Branch Model:
1.OF.3+ser Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
afw/atws afw/ep mfw porv.chall porv.chall/afw porv.chall/loop porv. chal l/sbo PORV. RESEAT Branch Model:
1.OF.1 Train 1 Cond Prob:
porv. reseat/ep srv. reseat (atws)
HPI System 1.6E-03 1.6E-05 2.4E-06 1.6E-06 2.8E-04 O.OE+O0 3.8E-04 > 5.0E-02 2.0E-02 > Failed 1.0E-01 > Unavailable 5.0E-02 2.8E-04 4.3E-03 5.OE-02 2.OE-01 4.OE-02 1.OE+O0 1.OE-01 1.0E+O0 2.0E-02 > 2.OE-02 2.0E-02 2.0E-02 1.OE-O1 1.0E-05 > 1.OE-02 Non-Recov 1.OE+0O 5.3E-01 5.4E-01 1.0E+00 iDOE-Ol 1.DE+00 4.5E-01 1.OE+DO 3.4E-01 3.4E-01 1.OE+OD 1.0E+00 1.DE+OD 1.OE+OD 1.1E-02 > 5.OE-O1 1-0E+00 1.OE+OO 8.9E-01 1.0F+00 Opr Fail 1.0E-03 Branch Model:
Train 1 Cond Train 2 Cond Train 3 Cond FEED.BLEED
- 1. OF.3 Prob:
Prob:
Prob:
1.DE-02 iDOE-Ol 1.OE-D2
- 2.
OE -02
> Unavailable
> Unavailable
> 3.0E-02 1.OE-02 Branch Model:
1.OF.3+ser+opr Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
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:
HPR 1.OE-02 1.OE-O1 > Unavailable 1.OE-02 > Unavailable 2.0E-02 O.OE+O0 2.0E-01 3.4E-01 3.0E-03 2.2E-02 > 1.0E+O0
- 1.
OE+OO
- 1.
OE+OO
- 1.
OE+OO
- 1.
OE+DO S.
7E-02 1.OE-02 1.0E-03 1.0E-03 2.OE -02 1.OE-D1>
2.OE-02>
1.OE-03>
Unavailable 1.0E+O0 1.0E-02 1.OE-02 I.OE-01 > Unavailable 4.DE-03 > 4.OE-02 1.DOE+OD
- 1.
OE+DO 1.OE-D3 1.DE-03 LER Nos. 327/82-048 and -050
B.30-6 Branch Model:
Train 1 Cond Train 2 Cond
- 1. OF. 2+opr Prob:
Prob:
EP Branch Model:
1.OF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
seal.loca offsite.pwr.rec/-ep.and.-afw offsite.pwr.rec/-ep.and.afw offsite.pwr.rec/seal.loca offsite.pwr.rec/-seal.loca sg.iso.and.rcs.cooldown rcs.cool.below.rhr prim.press.limited 4.OE-02 1.OE-01 > Unavailable 2.9E-03 > 5.7E-02 5.OE-02 > Failed 5.7E-02 2.7E-01 2.2E-01 6.7E-02 5.7E-01 7.OE-02 1.OE-02 3.OE-03
-8.F-03 8.9E-01 1.OE+O0
- 1.
0E+00 1.0 E+O0 1.OE+O0 1.OE+00 1.OE-01 1.OE+0O I.OF+O0 3.OE-03 branch model file
- forced LER Nos. 327/82-048 and -050