ML20147A515

Final ASP Analysis - Crystal River (LER 302-82-007)

ML20147A515
Person / Time
Site:	Crystal River
Issue date:	05/26/2020
From:	Christopher Hunter NRC/RES/DRA/PRB
To:
Littlejohn J (301) 415-0428
References
LER 1982-007-00
Download: ML20147A515 (5)

Text

B.17-1 B.17 LER No. 302/82-007 Event

Description:

Two EDGs Inoperable Date of Event:

January 23, 1982 Plant:

Crystal River 3 B.17.1 Summary On January 23, 1982, during normal operation, the starting air pressure for emergency diesel generator (EDG)

B was too low for automatic start and the air pressure low alarm did not alarm. On January 25, EDG A was fast started but did not excite and maintain voltage. Thus, both EDGs were inoperable.

The estimated increase in core damage probability, or importance, over the duration of this event is 2.8 x 10'. The base-case core damage probability (CDP) over the duration of the event is 3.4 x 10', resulting in an estimated conditional core damge probability (CCDP) of 2.8 x 10-5.

B.17.2 Event Description At 0700 on January 23, 1982, during normal operation, the starting air pressure for EDG B was found to be too low for automatic start and the air pressure low alarm did not alarm. The air tank blowdown valve EGV-1 6 was not completely shut. The valve was shut and EDG B was fast started and restored to operation at 0705.

Maintenance was initiated on the alarm circuit. Investigation revealed that a bad circuit card had led to the alarm malfunction. The circuit card was replaced and the alarm circuit tested satisfactorily. At 0714 on January 25, EDG A was fast started but did not excite and maintain voltage.

Maintenance was initiated on the excitation and voltage control circuit but no problem could be found. EDG A was restored at 1307 the same day.

B.17.3 Additional Event-Related Information Crystal River 3 has two EDGs which provide power to two engineered safeguards (ESF) buses in the event of a loss of normal power supply to the ESF buses. Both EDGs automatically start on either a low ESF bus voltage or an ESF actuation signal.

B.17.4 Modeling Assumptions This event is modeled as an unavailability of both EDGs for a period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> given a postulated LOOP.

The cause for the failure of EDG A was never determined, so EDG A was assumed to be failed for a period of 15 days (half the surveillance period) prior to the discovery of the failure. EDG B was assumed to be failed for a period of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (approximately two shifts) since the diesel generator rooms are frequently checked, the leaking air would make a noticeable noise, and the air compressor would run continuously. Thus, both trains were assumed inoperable for approximately 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Both trains of emergency power (EP) were set LER No. 302/82-007

B.17-2 to failed and the recovery probability was modified to reflect the ability of the operators to recover the EDGs locally (p=0. 55, see Appendix A of this report).

B.17.5 Analysis Results The estimated increase in core damage probability over the duration of this event is 2.8 x 10'. The base-case CDP (not shown in calculation) is 3.4 x 10-7, resulting in an estimated CCDP of 2.8 x 10'. The dominant sequence involves a successful reactor shutdown following a postulated LOOP, failure of emergency power (station blackout) and failure to recover offsite power prior to battery depletion and is highlighted in the event tree in Figure B. 17. 1.

LER No. 302/82-007

B.17-3 0

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Figure B.17.1 Dominant core damage sequence for LER 302/82-007 LER No. 302/82-007

B.17-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:

302/82-007 Event

Description:

Two EDGs inoperable Event Date:

January 23. 1982 Plant:

Crystal River 3 UNAVAILABILITY.

DURATION= 24 NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 1.4E-04 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 2.8E-05 Total 2.BE-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence End State Prob N Rec**

228 loop -rt(loop)

EP -afw/ep porv.chall/sbo -porv.reseat/ep -seal CD 2.2E-05 1.8E-01

.loca offsite.pwr.rec/-seal.loca 226 loop -rt(loop)

EP -afw/ep porv.chall/sbo -porv.reseat/ep seal CD 3.4E-06 1.8E-01

.loca offsite.pwr.rec/seal.loca 239 loop -rt(loop)

EP afw/ep CD 1.3E-06 6.2E-02 229 loop -rt(loop)

EP -afw/ep porv.chall/sbo porv.reseat/ep CD 7.6E-07 1.8E-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 3.4E-06 1.8E-01

.loca offsite.pwr.rec/seal.loca 228 loop -rt(loop)

EP -afw/ep porv.chall/sbo -porv.reseat/ep -seal CD 2.2E-05 1.8E-01

.loca offsite.pwr.rec/-seal.loca 229 loop -rt(loop)

EP -afw/ep porv.chall/sbo porv.reseat/ep CD 7.6E-07 1.8E-01 239 loop -rt(loop)

EP afw/ep CD 1.3E-06 6.2E-02

• • 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:\\aspcode\\models\\pwrb8283.cmp LER No. 302/82-007

B.17-5 BRANCH MODEL:

PROBABILITY FILE:

c:\\aspcode\\models\\criver3.82 c:\\aspcode\\models\\pwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 1 oop 1 oca sgtr rt rt (loop) afw afw/atws afw/ep mfw porv.chall porv.chall/afw porv.chall/loop porv.chall/sbo porv. reseat porv. reseat/ep, srv.reseat(atws) hpi feed.bleed emrg.boration recov.sec. cool recov.sec. cool/offsi te. pwr rcs.cooldown rhr rhr.and.hpr hpr EP 1.8E-03 1.8E-05 2.4E-06 1.6E-06 2.8E-04 O.OE+O0 1.3E-03 7.OE-02 5.OE-02 2.OE-01 8.0E-02 1.OE+O0 I.OE-O1 1.OE+O0 I.OE-02

1.

OE-02 1.OE-O1 3.OE-04 3.OE-04 O.OE+O0 2.OE-O1 3.4E-01

3. OE-03 2.2E-02 I.OE-03 4.OE-03 2.9E-03 > 1.OE+O0 5.OE-02 > Failed 5.7E-02 > Failed 6.OE-02 4.3E-01 2.1E-01 7.6E-01 3.1E-01 1.OE-02 3.0E-03 8.8E-03

1.

OE+00 3.3E-01 5.4E-01 1.OE+00 1.DE-01 1.OE+00 4.5E-01

1.

OE+00 3.4E-01 3.4E-01 1.OE+00 1.OE+00 1.OE+00 1.OE+00 1.1E-02

1.

OE+00

1.

OE+00 8.9E-01 1.OE+00 1.OE+00 1.OE+00 1.OE+0O

1.

OE+00

7.

OE-02

1.

OE+00 1.OE+00 8.9E-01 > 5.5E-01 1.OE+0O 1.0E+00 1.OE+OO

1.

OE+0O 1.OE+OO 1.OE-01 1.0E+00 1.OE+00 Branch Model:

Train 1 Cond Train 2 Cond seal.loca 1.OF.2 Prob:

Prob:

1.

OE- 02 1.OE-02 1.OE-03 1.OE-03 1.OE-03 1.OE-03

3.

OE- 03 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 branch model file

• • forced LER No. 302/82-007