ML20161A156
| ML20161A156 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-027-01 | |
| Download: ML20161A156 (5) | |
Text
B-209 Accident Sequence Precursor Program Event Analysis LER No:
Event
Description:
Date of Event:
Plant:
344/88-027 Ri Loss of volume control tank isolation capability results in potential for charging pump inoperability September 15, 1988 Trojan Summnary The ability to isolate the volume control tank from the charging pump suctions was lost for approximately 2.33 h because of failure of control power to one isolation valve and maintenance activities on the series valve.
The conditional probability of core damage associated with the event is estimated to be 2.8 x 10-6.
Relative significance compared with other potential events at Trojan is shown below.
LER 344/88-027 RI IE-5 IE4 IE-3 I E-2 IE-8 I
E-7 IE-6 Trip I
L EP Unavail (360 hrs)
Trip w/t AEW Train Unavail LOOP Event Description The train B suction valve (MO-122C) for the centrifugal charging pumps from the volume control tank (VCT) was open and incapable of automatic closure due to performance of a design change.
It was discovered that control power had been lost to the train A suction valve (MO-112B) for the centrifugal charging pumps.
This combination of valve unavail-abilities resulted in the inability to isolate the centrifugal charging pump suction line from the VCT on a safety-injection signal.
In the event of a safety-injection signal and realignment of the charging pump suctions to the RWST, hydrogen gas in the VCT would be drawn into the pumps, failing the pumps.
It was estimated that the capability to isolate the VCT was lost for approximately 2 h and 19 min.
B-210 ASP Modeling Assumptions and Approach This event was modeled as an unavailability of high-pressure injection and of feed and bleed capabilities because the inability to isolate the volume control tank from the charging pumps could render both of these functions inoperative.
These functions were inoperable for approxi-mately 2.33 h.
Analysis Results The conditional probability of severe core damage estimated for this event is 2.8 x 10-6.
The dominant core damage sequence (higlighted on the following event tree) involves a postulated small-break LOCA during the vulnerability period (p = 2.4 x 10-6), with unavailability of UPI.
B-211 LOCA RT jAFW jMFW HPI HPR OPEN SEQ END NO STATE OK 71 CD 72 CD OK 73 CD 74 CO OK 75 CD 76 CD 77 CD 78 ATWS Dominant Core Damage Sequence for LER 344/88-027 Ri
B-212 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
344/88-027 Event
Description:
Loss of volume control tank isolation capability Event Date:
09/15/88 Plant:
Trojan UNAVAILABILITY, DURATION= 2.33 NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS
- 1. 3E-03 LOOP 1.4E-05 LOCA 2.4E-06 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD TRANS
- 2. 4E-06 Total
- 0. OE+00 LOOP 0.05+00 LOCA 0.0E+00 Total 0.0E+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec t5 72 boce -rt -afw RPI CD 2.4E-06 4.3E-01 17 trans -rt afw mfw BPI(F/B)
CD 3.8E-07 1.2E-01
-' non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec t
- 17 trans -rt afw mfw HPI(F/B)
CD 3.8E-07 1.2E-01 7?2 inca -rt -afw NPI CD 2.4E-06 4.3E-01 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:\\asp\\sealmod\\pwrbseal.cmp BRANCH MODEL:
c:\\asp\\sealmod\\trnjan.sll PROBABILITY FILE:
c:\\asp\\sealmnd\\pwr-bsll.prn No Recovery Limit BRANCH FREQUENCIES /PROBABILITIES Branch System Non-Recnv Opt Fail trans 5.6E-04 l.0E-*00 loop l.EE-05 3.6E-01 inca 2.4E-06 4.3E-01 Event Identifier: 344/88-027
B-213 rt ni loop emerg.power afw afwl emerg.power mfw porv.or.srv.chall porv.or.srv. reseat porv.or.srv.reseat/emerg.power seal.loca ep.rec(sl) ep. rec HPI Branch Model:
l.CF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
HPI (F/B)
Branch Model:
1.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
hpr/-hpl porv.open 2.8E-04 O.06+00
- 2. 9E-03
- 2. 5E-03
- 2. 5E-03 1.OE+00 4.OE702 2.0E-02 2.OE-02 2.3E-01
- 5. 9E-01
- 6. 1E-02 1.06-03 > 1.OE+00 1.06-02 > Failed 1.OE-01 > Failed 1.06-03 > 1.06+00 1.OE-02 > Failed 1.06-01 > Failed
- 1. 5E-04 1.0OE-02 1.2E-01 1.06+/-00 8.06-01
- 3. 4E6-01
- 3. 4E-01 3.4E-01 1.06+00 1.1E-02
- 1. 0 +00 1.06+00 1.06+00 1.06+00 8.46-01 > 1.06+00 8.4E-01 > 1.06+00 1.06+/-+00
- 1. 0 +00 1.06-02 1.06-0 3 4.06-04
- branch model file
- forced Minarick 11-10-1989 15: 2 5: 54 Event Identifier: 344/88-027