ML20156A240
| ML20156A240 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-006-00 | |
| Download: ML20156A240 (6) | |
Text
B-294 Accident Sequence Precursor Program Event Analysis LER No: 400/88-006 Rl Event
Description:
SWS pump seal water unavailable Date of Event: February 8, 1988 Plant: Shearon Harris Unit 1 Summnary During surveillance testing of the emergency service water system, the nonsafety-related portion of the ESW pump seal water supply system failed to isolate as required due to an accumulation in two valves of debris from the raw lake water supply. The significance of the event is estimated to be 4.8 x 10-4 (this value may be conservative). The rela-tive significance of this event compared with other potential events at Harris is shown below.
Event Description During surveillance testing of the emergency service water system, the nonsafety-related portion of the ESW pump seal water supply system failed to isolate as required when valves 1SW-1335 and 1SW-1336 failed to close on demand due to accumulated debris from the ESW raw lake water supply. Additionally, check valve 1SW-1336 failed to properly seat.
Upon confirming valve failure, both ESW trains were declared inoperable.
Manual valves 1SW-1332 and 1SW-1324 were then closed, which restored operability of train A emergency service water, since the train was now isolated from the nonsafety-related piping.
Four days later, a concern was raised that the seal water piping con-figuration may be vulnerable to single passive failures that could
3-29 5 render both emergency service water trains inoperable. This problem was temporarily resolved by isolating the two ESW trains by a locked closed valve pending design changes to the system. Additional corrective action was taken to clean the debris from the valves.
Event-Related Plant Design Information The ESW pumps are normally not in service; however, they will start on SIAS, LOOP, or low SWS header pressure. When ESW is not in use, one of the ESW pump seal/bearing water booster pumps (nonsafety) draws raw lake water from the ESW header and supplies clean water via a cyclone separator to the ESP pump seals and bearings. The separator is used to prevent debris accumulation between the bearing and shaft seals. The failure of the subject valves to close prevents the isolation of the nonsafety seal water booster pump and both trains of the safety-related ESW pump seal water supplies. Valves 1SW-1332 and 1SW-1324 were manually closed to provide isolation and restore ESW train "A" to operability. Since valve ISW-1338 could not close, ESW train "B" was considered inoperable, although the valve could be manually closed if required.
Normally when ESW starts, the booster pumps trip off and the valves close to isolate the nonsafety portions of the system. Qualified ESW water is then provided by the safety-related ESW screen wash pumps, which tie into the seal water supply header downstream from the isola-tion valves.
ASP Modeling Assumptions and Approach The event has been modeled as a potential ESW unavailability for one-half of a test period (360 h). This results in unavailability of emergency power, high-pressure injection, feed and bleed, and high-pressure recirculation. A value of 0.34 has been assigned to the likelihood of not recovering ESW prior to equipment damage.
Because the impact of the existing ESW seal diversion and debris on the systems cannot be fully ascertained from the LER, this assessment may be conservative.
Analysis Results The significance of the event is estimated to be 4.8 x 10-4, a signifi-cant event from an ASP standpoint. Dominant sequences involve:
(1) a postulated LOOP during the vulnerability period (p = 3.1 x1-)
failure to recover ESW and therefore emergency power (p = 0.34), a 1b
B-296 subsequent RCP seal. LOCA (p = 0.27), and failure to recover AC power prior to core uncovery (p = 0.57); and (2) a postulated small-break LOCA (p = 3.7 x 10-4), with failure to recover ESW and subsequent HPI failure (p =0.34).
Sequence (1) is highlighted on the following event tree.
B-297 LOOP RT/LOOP EP AFW IO FVV E EPORVI SEQL E END CHALL RESEAT LCC (LONG) OPE O~ STATE OK OK 41 CD 42 CD OK OK 43 CD 44 CD 45 D-OK 46 CD 47 CO 48 CD OK 49 CD 50 CD OK 51 51 CD 52 CD 53 CD OK 54 CD 55 CD 40 ATWS Dominant Core Damage Sequence for LER 400/88-006 Ri
B- 298 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 400/88-006 Event
Description:
SMS pump seal water is unavailable Event Date: 02/08/88 Plant: Harris 1 UNAVAILABILITY, DURATION- 360 NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 2.OE-01 LOOP 3.1E-03 LOCA 3.7E-04 SEQUENCE CONDITIONAL PROBABILITY SUMS End state/Initiator Probability CO TRANS 2.8SE-06 LOOP 1. OE-03 LOCA 3. 7E-04 Total 1.4E-03 ATMO TRANS 0 .OE*00 LOOP 0. OE+00 LOCA 0. OFi00 Total 0. OE+/-00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER) tt Sequence End State Prob N Rec 53 loop -rI/loop EMERG.POWER -atw/emerg.power -perv.or.srv.cball CD 4.5E-04 5.2E-0l seal. loca ep. rec (sl) 72 boca -rt -afw EPI CD 3.7E-04 4.3E-01 52 loop -rt/loop EMERG.POWER -afw/emerg.power -porv.or.srv.chall CD 3.4E-04 5.2E-Ol seal.loca -ep.rec(sl) BPI 54 loop -rt/loop ENERG.PONER -afw/emerg.power -porv.oI.srv.cball - CD 1.5Z-04 5.2E-01 seal.loca ep.rec 55 loop -rt/loop ENERO.POMER afw/erserq.power CD 5. 3E-05 1. 5-01 4S loop -rt/loop EMERG.POMER -afw/emerg.power porv.or.srv.chall - CD 1.8SE-O5 5. 2E-01 porv.or.srv.reseat/exserg.power seal.loca ep.rec(sl) 47 loop -rt/loop EMERG.POMER -afw/emerg.power porv.or.srv.chall - CD 1. E-05 5. 2E-01 porv.or.srv.reseat/emerq~power seal.loca -ep.rec(sl) BPI
-* non-recovery credit tot edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER) t Sequence End State Prob N Rec' 47 loop -rI/loop EMERG.POMER -afw/emetg.power porv.or.srv.chall - CD 1.4E-05 5. 2E-0l porv.or.srv.reseat/emerq.power seallioca -ep~rec(sl) NPI 45 loop -rtlloop EMERG.POMER -afw/emerg.power porv.or.srv.chall - CD 1. SE-O5 5, 2E-01 pcrv.or.srv.reseatlemerg.power seal.boca ep.rec (sI) 52 loop -rI/loop ENERG.POMER -afw/emerq.power -porv.or.srv.chall CD 3.4E-04 5. 2E-01 seal.loca -ep.rec(sl) NPI 53 loop -rtlloop ENENO.POMER -afw/emerg.power -porv.or.srv.chall CO 4.5E-04 5.2E-Ol seal.loca ep.rec(sl) 54 loop -rI/loop ENERG.PONER -afw/emerg.powver -porv.cr.srv.chall - CD l.SE-04 5.2E-01 seal.loca ep.rec 55 loop -rt/loop ENERG.POMER afwlemerg.power CD 5.3E-05 1.8E-01 72 loca -rt -afw BPI CD 3.7E-04 4.3E-01 Event Identifier: 400/88-006
B-299
- 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 NODEL: c:\asp\sealmod\pwrbseal .cmp BRANCH MODEL: c:\asp\sealmod\harris.sll PROBABILITY FILE: c:\asp\sealmod\pwr_bsll.pro No Recovery Limit BRANCH FREQUENCIES/PRPBABILITIES Branch System Non-Recov Cpr Fail trans 5.5E-04 1.OE+00 loop 1. 6E-O05 5. 3E-01 lot a 2. 4E-O06 4 .3E-01 rt 2.8E-04 1. 2E-01 rt/ loop 0.O+0 1. 0E+00 EMERG. POWER 2.9E-03 > l.0E+/-00 8.05-01 > 1.05+00 Branch Nodal: l.OF.2 Train 1 Good Prob: 5.0E-02 > Unavailable Train 2 Gond Prob: 5.7E-02 > Unavailable a fw 3. BE-04 2.6E5-01 afw/emerg .power 5.0OE-02 3. 4E-01 mfw l.0E-*00 7. OE-02 1.0E-03 porv.or.srv.chall 4.0E-02 1 .OE-'0O porv.or.srv. reseat 2. 0E-02 1. 1E-02 porv.or.srv.reseat/emerg.power 2. OE-02 1. 0E+00 seal.boca 2. 7E-01 1 .05+00 ep. ret (sl) 5.7E-01 1. OE+s00 ep. ret 7. 0E-02 1. QEtOS BPI 3.0E-04 > 1.OE05-- 8.4E-01 > 1.OE+/-00 Branch Nodal: l.UF.3 Train 1 Coed Prob: 1. OE-02 " Unavailable Train 2 Coed Prob: l.OE-0l " Unavailable Train 3 Cond Prob: 3.0OE-01 " Unavailable HPI (FIB) 3.OE-04 " l.OE-r00 8.45-01 > l.OE+s00 1 .0E-02 Branch Nodal: l.OF.3ropr Train 1 toed Prob: l.OE-02 " Unavailable Train 2 Cond Prob: 1.OE-0l " Unavailable Train 3 Good Prob: 3.OE-01 " Unavailable NPRI-NPI 1. 5E-04 " l.0E+00 1. OE+00 I O0E-03 Branch Nodal: l.OF.2+opr Train 1 Good Prob: 1 .OE-02 " Unavailable Train 2 Cond Prob: 1 .5E-02 " Unavailable porv .open 1. 0E-02 1. OE+00 4 .0E-04
- branch model file
- forced Minarick 11-13-1989 14:25:45 Event Identifier: 400/88-006