ML20140A195

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Final ASP Analysis - San Onofre 1 (LER 206-90-006)
ML20140A195
Person / Time
Site: San Onofre Southern California Edison icon.png
Issue date: 05/19/2020
From:
NRC/RES/DRA/PRB
To:
Littlejohn J (301) 415-0428
References
LER 1990-006-00
Download: ML20140A195 (12)
v • d • e


Text

B-6 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No.: 206/90-006 Event

Description:

Wrong failure mode for a chemical and volume control valve Date of Event: February 20, 1990 Plant: San Onofre 1 Summary San Onofre 1 was operating at 90% of rated power when it was determined during surveillance testing that a chemical volume and control system (CVCS) pneumatic control valve had a non-conservative failure mode and potentially could cause failure of the charging pumps. The conditional core damage probability estimated for this event is 6.0 x 10-5. The relative significance of this event compared to other postulated events at San Onofre 1 is shown below.

FLER 206/90-006 IE-7 1E-6 1E-5 1E-4 IE-3 1E-2 I

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precursor cutoff .4 Event Description While San Onofire 1 was performing fail-safe position testing of pneumatic control valves for the CYCS, it was discovered that the blended boric acid supply valve to the charging pump suction, CV-406B, had failed-open and not failed-closed upon a loss of the instrument air (IA) system as required by plant design. Failure of this valve to close when required during postulated accidents could result in inadvertent injection of the volume control tank (VCT) hydrogen gas into the suction of the charging pumps, potentially causing the pumps to gas bind and fail. Subsequent investigations revealed that the valve had been installed, since the plant's initial construction in 1967, as a fail-open valve.

B-7 Additional Event-Related Information Loss of two support systems can fail CV-406B: (1) the IA system, which is a non-safety-related system, and (2) the valve control power supply (120 VAC).

The CVCS is designed to charge to and let down from the reactor coolant system (RCS) during normal operations, and assists in the recirculation of borated water to the RCS following a loss-of-coolant-accident (LOCA). The charging pumps usually take a suction from the VCT, which maintains a hydrogen overpressure during normal plant power operations to control oxygen levels in the RCS. During accident scenarios, the VCT is isolated from the charging pump suction by closing a motor-operated valve; however, if the IA system were to coincidentally fail also, there would exist a flow path available for the hydrogen gas in the VCT to become entrained in the charging pump suction.

The safety injection (SI) system at San Onofre 1 has two separate and independent trains that use the main feedwater pumps (MFWPs) for injecting borated water into the RCS at a rate of 10,500 GPM per train following a LOCA, which depressurizes the RCS. Each MFWP is supplied with borated water by one of two SI pumps. The two charging pumps are 12 stage centrifugal pumps with a design flow rate of 213 GPM. They are the primary means for injecting water into the core during the recirculation phase following a LOCA. It is estimated that the recirculation phase would be required about 5 h after the injection phase began.

ASP Modeling Assumptions and Approach This event has been modeled with the assumption that both charging pumps would fail upon loss of instrument air if the charging pumps were taking suction from the RWST.

Charging pump operation is assumed required for small-break LOCA mitigation and for feed and bleed. Postulated scenarios that have been modeled are transient-induced LOCAs and loss of secondary-side cooling and feed and bleed following a postulated loss of offsite power (LOOP) or loss of instrument air. Loss of instrument air was also assumed to result in a loss of feedwater.

Analysis Results The estimated conditional probability of severe core damage for this event over a 1-yr period is 6.0 x M0-5. The dominant sequence involves loss of secondary-side cooling and failure of feed and bleed following a postulated LOOP. The dominant sequence to core damage is highlighted on the following event tree.

B-8 The conditional probability for the event was calculated by first estimating a conditional core damage probability for the IA and LOOP initiators over a 1-yr period assuming HPI and feed and bleed would be unavailable (first two calculations) and subtracting the conditional probability for the two initiators for 1-yr assuming HPI and feed and bleed were nominally available (reference calculations). This approach is consistent with the core damage probability algorithm used in the ASP Program and had to be used because loss of IA is not directly addressed in the models.

B-9 LOOP R/OP E AFW ISRRVVI PSRRVVI SEAL BIEC Ný[

PI HPR PORV SEO END NO STATE ICE HALL RESEAT LOCA "xqG OPEN OK OK 41 CD 42 CD OK OK 43 OD0(1) 44 00 45 CD OK 46 CD 47 CD 48 CD OK 40 CD so 00 OK 51 CID 52 00 53 00D OK 54 CD 55 CD 40 ATWS (1)OK forClass D Dominant core damage sequence for LER 206/90-006

B-10 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 206/90-006 Event

Description:

wrong failure mode for CVCS valve (postulated loss of IA)

Event Date: 02/20/90 Plant: San Onofr Io INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1. OE-02 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 6 .0E-06 Total 6.OE-06 ATHS TRANS 3.4E-07 Total 3.4E-07 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence End State P rob N Rec**

17 TRANS -rt afw NFW EPI (F/B) CD 5. 9E-06 2. 6E-03 18 TRANS rt ATWS 3 .4E-07 1.2E-03

    • non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)

Sequence End State Prob N Rec**

17 TRANS -rt afw MFW )IPI(F/B) CD 5.9E-06 2. 6E-D3 lB TRANS rt ATWS 3. 4E-07 1.2E-03

    • non-recovery credit for edited case SEQUENCE MODEL: C: \asp\lBBQ\pwrbseal.crnp BRANCN MODEL: c:\asp\1999\sanonol.sll PROBABILITY FILE: c:\asp\19B9\pwr~bsll.pro No Recovery Limit BRANCH FREQUENCIES/PRDBABILITIES Branch System Non-Recov Opr Fail TRANS 1.2E-04 > 1 .2E-04 l.OE+00 > l.OE-02 Branch Model: INITOR Initiator Freq: 1 .2E-04 Event Identifier: 206/90-006

B-11 loop 2.02-05 5.82-01 loca 2.42-06 4.3E-01 rt 2.82-04 1.2E-01 rt/loop 0.OE+00 1.02+00 aenerg.power 2.9E-03 8.02-01 1. 02-03 afw 2.3E-03 2.6E-01 afw/emerg.power 5.OE-02 3.4E-O1 MFW 1.9E-01 > 1.02+00 3.42-01 > 1.02+00 Branch model: 1.0F.1 Train 1 Cond Prob: 1.9E-01 > Unavailable POrv.or.arv.chall 4.02-02 1.02+00 porv.or. arv. reseat 2.OE-02 1.12-02 porv. O.oarv. reseat/amerg .power 2.02-02 1.0E+00 seal *loca 3.2E-01 1.02+00 ep.rec (al) 7.6E-01 1.02+00 ep. rec 1.62-01 1.02+00 H9 I 1.02-03 > 1.0E+00 8.42-01 > 1.OE+00 Branch Model: l.OF.2 Train I Cond Prob: 1.02-02 > Failed Train 2 Cond Prob: l.OE-01 > Failed liPI (B) 1.02-03 > 1.0E+00 8.42-01 > 1.0E+00 1.02-02 Branch Model: l.OF.2+opr Train 1 Cond Prob: 1.02-02 > Failed Train 2 Cond Prob: 1.0E-01 > Failed hpr/-hpi 1.5E-04 1.0E+00 1.02-03 porv .Open 1 .02-02 1. 02+00 4.OE-04

  • branch model file
    • forced Minarick 08-06-1991 17:29:52 Event Identifier% 206/90-006

B-12 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 206/90-006 Event

Description:

Wrong failure made for CVSC valve (postulated LOOP)

Event Date: 02/20/90 Plant: San Onofre 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 7 .1E-02 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 1.4E-04 Total 1 .4E-04 ATWS LOOP D.DE+DD Total D.DE+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence End State Prob N Rec**

53 LOOP -rt/loop, emerg.power -afw/emerg.power -porv.or.srv.chall CD 5.3E-05 5.6E-02 seal.loca ep.rec(sl) 45 LOOP -rt/loop -emerg.power afw HPI(F/B) CO 4.2E-D5 l.BE-D2 54 LOOP -rt/loop emerg.power -afw/emerg.power -porv.or.srv.chall - CO 2.4E-05 5.6E-02 seal.loca ep.rec 52 LOOP -rt/loop emerg.power -afw/emerq.power -porv.or.arv.chell CD 1.7E-05 5.6E-02 seal.loca -ep.rec(sl) HPI 55 LOOP -rt/loop, emerg.power afw/emerg.power CO 4.OE-06 1.9E-02 48 LOOP -rt/loop, emerg.power -afw/emerg.powuer porv.or.srv.chall - CD 2.2E-06 5.6E-02 porv.or.arv.reseat/emerg.power seal.loca ep.recial)

    • non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)

Sequence End State Prob N Rec~*

45 LOOP -rt/loop, -emerg.power sfw HPI(F/B) CD 4.2E-05 1.8E-02 48 LOOP -rt/loop emerg.power -afw/emerg.power porv.or.srv.ckiall - CD 2.2E-06 5.6E-02 porv.or.srv.reseat/emerg.power seel.loca ep.rec(sl) 52 LOOP -rt/loop emerg.power -aflE/emerg.power -porv.or.srv.chall CD 1.7E-05 5.6E-02 seal.loca -ep.rec(sl) HPI 53 LOOP -rt/loop emerg.power -afw/emerg.power -porv.or.srv.chall CD 5.3E-D5 5.6E-02 seal.loca ep.rec(sl) 54 LOOP -rt/loop emerg.power -afw/emerg.power -porv.or.srv.chall - CD 2.4E-05 5.6E-02 aeal.loca ep.rec 55 LOOP -It/loop emerq.power afw/emerg.power CO 4.OE-06 1.9E-02 Event Identifier: 206/90-006

B- 13

    • non-recovery credit for edited case SEQUENCE MODEL: c :\asp\1889\pwrbaeal .cmp BRANCH MODEL: c: \asp\1989\aanonol .all PROBABILITY FILE: c: \aap\l9B9\pwr~bsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS l.2K-C4 > l.2E-04 l.CK+CC > l.CK-C2 Branch Model: INITOR Initiator Freg: 1 .2E-04 LOOP 2.CE-C5 > 2.0K-CS 5.8E-Cl > 7.lE-C2 Branch Model: INITOR Initiator Freq: 2 .0K-CS loca 2 .4E-06 4.3E-01 rt 2.8E-C4 1.2E-01 rtlloop C .CE+CC 1.0K+00 eieerg. power 2.9E-03 8.0K-01 l.CK-C3 afw 2 .3E-03 2.6K-Cl afw/emerg.power 5.CK-C2 3.4K-0l MFW 1.9K-Cl > l.CK+CC 3.4K-Cl > l.CK+CC Branch Model: l.OF.l Train 1 Cond Prob: 1.9E-Cl > Unavailable porv.or.arv.chall 4.CE-02 l.0E+00 porv.or. arv. reseat 2.CE-C2 1.lE-02 porv.or.arv. reseat/emerg.power 2 .CE-C2 l.CK+CC seal
  • bca 3.2E-al l.0z+0O ep.rec(sl) 7.6E-01 l.CK+CC ep. rec 1.6K-0l l.CK+00 HPi l.CK-C3 > l.CKE+CC 8.4K-Cl > l.CK+CC Branch Model: l.OF.2 Train 1 Cond Prob: 1.CK-C2 > Failed Train 2 Cond Prob: 1.0K-Cl > Failed HPI (F/B) l.CK-C3 > l.CE+00 8.4K-Cl > l.CE+CC l.CE-C2 Branch Model: l.OF.2+opr Train 1 Cond Prob: l.CE-C2 > Failed Train 2 Cond Prob: 1.0K-Cl > Failed hpr/-hpi 1.5E-04 l.CE+00 l.CE-C3 porv.open 1.0K-02 1.CE+00 4.OE-04
  • branch model file
    • forced Nina rick 08-06-1991 17:29:55 Event Identifier: 206/90-006

B-14 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 206/90-006 Event

Description:

Wrong failure mode for CVCS valve (reference loss of IA)

Event Date: 02/20/90 Plant: San Onofre 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS l.0E-02 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD TRANS 1 .3E-07 Total 1.3E-07 ATWS TRANS 3.4E-07 Total 3.4E-07 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence End State Prob, N Rec**

18 TRANS rt. ATWS 3.4E-07 1.2E-03

    • non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)

Sequence End State Prob N Rec~*

18 TRANS rt ATWlS 3.4E-07 1.2E-03

    • non-recovery credit for edited case SEQUENCE MODEL: c :\asp\1989\pwrbseal .cmp BRANCH MODEL: c:\asp\l989\sanonol.sll PROBABILITY FILE: c:\asp\19B9\pwr__ball .pro No Recovery Limit BRANCN FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.2E-04 > 12E-0 l.OE+0O > l.DE-D2 Branch Model: INITOR Initiator Freq: 1 .2E-04 LOOP 2.OE-05 > 2.DE-05 5.8E-01 > 7.1E-02 Branch Model: INITOR Event Identifier: 206/90-006

B-15 Initiator Freq: 2 .09-05 loca 2 .4E-06 4.3E-01 rt 2 .SE-04 1.2E-01 rt/loop 0.OE+ 00 1.OE+00 emerg.poller 2.9E-03 S. OE-01 1.OE-03 afw 2 .3E-03 2. 6E-01 afw/emerg.power S .OE-02 3.4E-01 MFW 1.9E-01 > 1.ýOE+00 3.4E-01 > 1.OE+00 Branch Model: 1.OF.l Train 1 Cond Prob: 1. 9E-01 > Unavailable porv.or.srv.chall 4 .OE-02 1.OE+00 porv.or.srv. reseat 2 .OE-02 1.1E-02 porv.or.srv. reseat/emerg.power 2 .OE-02 1.OE+O0 seal. loca 3.2E-01 1.OE+00 ep. rec (sll 7.*6E-01 1. OE+00 ep *rec 1.6E-01 1.OE+00 hpi 1 .OE-03 S. 4E-01 hpi (f/b) 1.OE-03 8.4E-01 1. OE-02 hpr/-hpi 1 .5E-04 1.OE+00 1.OE-03 porv.open l.OE-02 1.OE+00 4. OE-04

  • branch model file
    • forced

?4inarick 08-06-1991 17:29:57

-- i Event Identifier: 206/90-006

B-16 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 206/90-006 Event

Description:

Wrong failure mode for CVCS valve (reference LOOP)

Event Date: 02/20/90 Plant: San Onofre I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 7 .1E-02 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD LOOP 8.6E-05 Total 9.6E-05 ATWS LOOP D.DE+DO Total 0.OE+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence End State Prob N Rec**

53 LOOP -rt/loop, emerg.power -afw/emerg.power -porv.or.arv.chall CD 5.3E-05 5.6E-02 aeal.loca ep.rec(al) 54 LOOP -rt/loop emerg.power -afw/emerg.power -porv.or.arv.chall - CD 2.4E-05 5.6E-02 seal.loca ep.rec 55 LOOP -rt/loop emerg.power afw/emerg.power CD 4.OE-06 1.9E-02 48 LOOP -rt/loop emerg.power -afw/emerg.power porv.or.srv.chall - CD 2.2E-06 5.6E-02 porv.or.arv.reseat/emerg.power seal.loca ep.rec(al)

Snon-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)

Sequence End State Prob N Rec**

48 LOOP -rt/loop emerg.power -afw/emerg.power porv.or.arv.chall - CD 2.2E-06 5.6E-02 porv.or.arv.reseat/emerg.power. seal. loca ep.rec (si) 53 LOOP -rt/loop emerg.power -afw/emerg.power -porv.or.arv.chall CD 5.3E-05 5.6E-D2 seal.loca ep.rec(sl) 54 LOOP -rt/ioop emerg.power -afw/emerg.power -porv.or.srv.chall - CD 2.4E-05 5.6E-02 seal.loca ep.rec 55 LOOP -rt/loop emerg.power afwr/emerg.power CD 4.OE-06 1.9E-02

    • non-recovery credit for edited case SEQUENCE MODEL: c: \asp\1989\pwrbseal.cmp BRANCH MODEL: c:\asp\1989\sanonol.sll PROBABILITY FILE: c :\asp\1989\pwr ba~ll.pro Event Identifier: 206/90-006

B-17 No Recovery Limit BRANCH FREQU2NCIES/PI4DBABILITIES Branch System Non-Recov Opr Fail TRANS 1.2E-04 > 1.2E-04 1.02+00 > 1.02-02 Branch Model: INITOR Initiator Freq: 1.2E-04 LOOP 2.02-05 > 2.02-05 5.8E-01 > 7.1E-02 Branch Model: INITOR Initiator Freq: 2.02-05 loca 2.4E-06 4.3E-01 rt 2 .82-04 1.2E-01 fl/loop 0.02+00 1.0E+00 emerg.power 2.9E-03 8.02-01 1. 02-03 afw 2.3E-03 2.6E-01 afw/emerg. power 5.02-02 3.4E-01 NFW 1.9E-01 > 1.02+00 3.4E-01 > 1.OE+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 1. 9E-01 > Unavailable porv.or.srv.chall 4.02-02 1.02+00 porv.or. srv. reseat 2.02-02 1.1E-02 parv.or.srv. reseat/emerg.power 2.02-02 1.02+00 seal .loca 3.2E-01 1.02+00 ep. rec (sl) 7.6E-01 1.0E+00 ep. rec 1. 6E-01 1.02+00 hpi 1.02-03 8. 4E-01 hpi (f/b) 1. 02-03 8.4E-01 1. 02-02 hpr/-hpi 1.5E-04 1.02+00 1.02-03 porv.open 1.02-02 1.02+00 4.02-04

  • branch model file
    • forced Mina rick 08-0 6-19 91 17:30:00 Event Identifier: 206/90-006
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