ML20161A180
| ML20161A180 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-009-00 | |
| Download: ML20161A180 (6) | |
Text
B.18-1 B.18 LER No. 304/82-009 Event
Description:
Unavailability of Two Motor-Driven AFW Pumps Date of Event:
April 9, 1982 Plant:
Zion 2 B.18.1 Summary On April 9, 1982, while monthly periodic testing of the auxiliary feedwater (AFW) pumps was being performed, service water valves 2SVSW 131 and 2SVSW 130 failed to open to supply cooling to motor-driven AFW pumps 2B and 2C oil coolers upon the start of the pumps. Accumulation of silt from the service water system caused the valves to stick closed. The event was modeled as an unavailability of both AFW motor-driven pumps. The estimated increase in core damage probability, or importance, over the duration of this event is 3.4 x 105. The base-case core damage probability (CDP) over the duration of the event is 1.9 x 106, resulting in an estimated conditional core damage probability (CCDP) of 3.6 x I10.
B.18.2 Event Description On April 9, 1982, during monthly periodic testing of the AFW pumps, service water valves 2SVSW131 and 2SVSW130 failed to open to supply cooling to motor-driven AFW pumps 2B and 2C oil coolers upon the start of the pumps. After valve 2SVSW130 for pump 2C was tapped, the valve opened and service water flowed to the 2C pump oil cooler. The AFW turbine-driven pump was operable during the time of this event.
Investigation revealed that years of accumulation of silt from the service water system caused the valves to stick closed. The valves were cleaned and opened properly when tested again.
B.18.3 Additional Event-Related Information The AFW system of Zion 2 has three pumps. Two pumps are motor driven and one is turbine driven. Each motor-driven pump can supply cooling to two of four steam generators. The single turbine-driven pump is capable of providing cooling to all four steam generators and can provide cooling in the event of a loss of offsite power as well as a loss of emergency power.
B.18.4 Modeling Assumptions This event was modeled as an unavailability of both motor-driven AFW pumps. Since the length of time in which both service water valves were stuck closed is unknown, the duration of the event was taken to be half the surveillance period of the AFW pumps (15 days or 360 hours0.00417 days <br />0.1 hours <br />5.952381e-4 weeks <br />1.3698e-4 months <br />). All four initiating events were examined, each with its default value as the initiating event frequency.
LER No. 304/82-009
B.18-2 B.18.5 Analysis Results The estimated increase in core damage probability over the duration of this event is 3.4 x 10"'. The base-case CDP (not shown in calculation) is 1.9 x 106, resulting in an estimated CCDP of 3.6 x 10.'. The dominant sequence involved a postulated transient with a successful reactor trip, failure of AFW, failure of main feedwater (MFW), and failure of feed and bleed and is shown on the event tree in Figure B. 18.1.
LER No. 304/82-009
B.18-3 cIz
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cc M
000 azo Oo I
WLU U-rn I
0 (n a.WL 02
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Cr I-Figure B. 18.1 Dominant core damage sequence for 304/82-009 LER No. 304182-009
B.18-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
304/82-009 Event
Description:
Unavailability of two motor-driven AFW pumps Event Date:
April 19. 1982 Plant:
Zion 2 UNAVAILABILITY, DURATION= 360 NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS LOOP LOCA SGTR SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 5.4E-01 3.1E-03 4.7E-04 5.9E-04 Probability CD TRANS LOOP LOCA SGTR Total 3.1E-05 2.1E-06 2.2E-08 9.1E-07 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State 120 trans -rt AFW mfw feed.bleed CD 508 trans rt -prim.press.limited AFW/ATWS CD 215 loop -rt(loop) -ep AFW -offsite.pwr.rec/-ep.and.afw feed.bleed CD 411 sgtr -rt AFW mfw CD 119 trans -rt AFW mfw -feed.bleed recov.sec.cool hpr CD
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State 119 trans -rt AFW mfw -feed.bleed recov.sec.cool hpr CD 120 trans -rt AFW mfw feed.bleed CD 508 trans rt -prim.press.limited AFW/ATWS CD 215 loop -rt(loop) -ep AFW -offsite.pwr.rec/-ep.and.afw feed.bleed CD 411 sgtr -rt AFW mfw CD
- non-recovery credit for edited case Note:
For unavailabilities. conditional probability values are differential values Prob 1.9E-05 1.2E-05 1.9E-06
.9.1E-07 6.2E-07 Prob 6.2E-07 1.9E-05 1.2E-05 1.9E-06 9.1E-07 N Rec**
1.5E-OI 1,0E-OI 2.4E-01 1.5E-O1 1.5E-01 N Rec**
1.5E-01 i1SE-OI I.OE-01 2.4E-01 1.5E-01 which reflect the LER No. 304/82-009
B.18-5 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:
BRANCH MODEL:
PROBABILITY FILE:
c:\\aspcode\\models\\pwrb8283.cmp c:\\aspcode\\models\\zion2.82 c:\\aspcode\\models\\pwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System trans l
oop loca sgtr rt rt(loop)
AFW Branch Model:
l.OF.3+ser Train 1 Cond Prob:
Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
AFW/ATWS Branch Model:
1.OF.1 Train 1 Cond Prob:
afw/ep mfw porv.chal1 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/offsite.pwr rcs. cool down rhr rhr.and.hpr hpr ep seal.loca offsite.pwr. rec/-epand. -afw offsite.pwr.rec/-ep.and.afw offsite.pwr.rec/seal loca offsite.pwr.rec/-seal.loca sg. iso. and. rcs.cool down rcs.cool.below.rhr prim.press. limi ted 1.5E-03 1.6E-05 2.4E-06 1.6E-06 2.8E-04 O. OE+O0 3.8E-04 > 5.OE-02 2.OE-02 > Failed I.OE-01 > Failed 5.OE-02 2.8E-04 4.3E-03 > I.OE+O0 4.3E-03 > Failed 5.OE-02 2.OE-O1 4.OE-02 I.OE+O0 I.OE-01 1.OE+00 2.OE-02 2.OE-02 i.OE-OI 1.OE-05 2.OE-02 O.OE+O0 2.OE-O1 3.4E-O1 3.OE-03 2.2E-02 1.OE-03 4.OE-03 5.4E-04 2.7E-01 2.2E-01 6.7E-02 5.7E-01 3.1E-02 1.OE-02 3.OE-03 8.8E-03 Non-Recov 1.OE+00 5.3E-01 5.4E-01 1.OE+00 I.DE-01 1.OE+0O 4.5E-01 1.OE+00 3.4E-01 3.4E-01 1.OE+O0 1.OE+O0 1.OE+O0 1.OE+00 1.1E-02 1.OE+O0 1.OE+O0 8.9E-01 1.OE+00 1.OE+00 1.OE+00 1.OE+O0 1.0E+00 7.OE-02 1.OE+00 1.OE+00 8.9E-01 1.OE+00 1.OE+00 1.0 E+0O 1.OE+00 1.OE+00 1.DE-01 1.OE+00 1.0E+00 Opr Fail 1.OE-03 1.OE-02 1.OE-02 1.OE-03 1.OE-03 1.OE-03 1.OE-03
- 3.
OE -03 LER No. 304/82-009
B.18-6 branch model file
- forced LER No. 304/82-009