ML20161A159
| ML20161A159 | |
| 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 1989-021-00 | |
| Download: ML20161A159 (5) | |
Text
B-260 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No:
Event
Description:
Date of Event:
Plant:
344/89-021 HHSI inoperable due to unavailability of VCT isolation during testing October 30, 1989 Trojan Summary The potential existed for the high head safety injection (HHSI) system to be inoperable during performance of portions of a surveillance test. This test involves bypassing the charging pumps' suction isolation valves from the volume control tank. If a safety injection were required during this time, hydrogen cover gas from the volume control tanks could become entrained in both charging pumps. This would render safety injection inoperable. The conditional probability of core damage associated with this event is estimated to be 2.1 x 10-6. The relative significance of this event compared with other potential events at Trojan is shown below.
-LER 344/89-021 1E-7 1E61E-5 1E-4 1E-3 1E-2 L T~r ip 360 hAFW1 36OhP L-precursor cutoff MflX A.FW Event Description During review of procedures an operator trainee discovered that performance of portions of periodic operating test (POT) 2-3, "Safety Injection System Emergency Core Cooling System (ECCS) Valve In Service Test," could render both trains of centrifugal charging pumps (CCPs) inoperable if a safety injection signal (SIS) occurred while the POT was in progress. POT 2-3 requires that the volume control tank (VCT) isolation valves be bypassed during portions of the test. If an SIS occurred while in this bypassed state, the pressure from the VCT hydrogen cover gas, depending on safety injection flow and VCT
B-261 level and pressure, could cause the VCT to preferentially provide the CCP suctions, with subsequent entrainment of the VCT cover gas in both CCPs.
ASP Modeling Assumptions and Approach This event was modeled as a potential loss of safety injection for 2 h/year.
Analysis Results The conditional probability of subsequent severe core damage estimated for this event is 2.1 x 10-6. Such an event is of low significance from an ASP standpoint.
The dominant sequence leading to core damage for this event involves a postulated loss of coolant accident and failure of high-pressure injection. The conditional probability of severe core damage for the dominant sequence is 1.7 x 10-6.
This sequence is highlighted on the following event tree.
B-262 LOA RT AFW MFW HI-P HPR OPEN SEQ END NO STATE 71 72 73 74 OK OK CD CD OK 75 GO0(1) 76 CD 77 0D 78 ATWS (1)0OK for Class D Dominant core damage sequence for LER 344/89-02 1
B-263 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
344/89-021 Event
Description:
HHSI inoperable due to unavailability of VCT isolation Event Date:
10/30/89 Plant:
Trojan UNAVAILABILITY, DURATION= 2 NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.lE-03 LOOP 1.2E-05 LOCA
- 2. lE-OG SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS
- 0. OE+00 LOOP
- 0. 0E+00 LOCA
- 0. 0E+00 Total
- 0. OE+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
72 loca -ft -afw ((PT CD 2.1E-06 4.3E-01 17 trans -rt afw mfw HPI(F/B)
CD 6.7E-08 2.4E-02 non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
17 trans -rt afw mfw HPI(F/B)
CD 6.7E-08 2.4E-02 72 loca -ft -afw NPI CD 2.1E-0S 4.3E-0l non-recovery credit for edited case Note:
For unavailabilitles, 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\\1989\\pwrbseal.cmp BRANCN MODEL:
c:\\asp\\1989\\trojan.sll PROBABILITY FILE:
c:\\asp\\1989\\pwr~bsll.pro No Recovery Limit BRANCN FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 5.6E-04 l.OE+00 loop 1.6E-05 3.GE-01 loca 2.4E-06 4.3E-01 Event Identifier: 344/89-021
B-264 rt rt/loop emerg.power afw afw/emerq.power mfw porv.or.srv.chall porv.or.srv. reseat porv.or.srv. reaeat/emerg.power aeal.loca ep.rec Cal) ep. rec HPIF Branch Model:
l.OF.2 Train 1 Cond Prob:
Train 2 Cond Frob:
HPIFTF/B)
Branch Model:
l.OF.2+opr Train 1 Cond Prob:
Train 2 Cond Prob:
hpr/-hpi porv.open 2.8 E-04
- 0. OE+00 2.9E-03 2.5E-03 2.5E-03
- 1. 0E+00 4.0 E-02 2.0 E-02 2.OE-02
- 2. 3E-01
- 5. 9E-01
- 6. IE-02 1.06-03 > 1.06+00
- l.0E-02 > Failed 1.06-01 > Failed 1.06-03 > 1.06+00 1.06-02 > Failed 1.06-01 > Failed
- 1. 5E-04 1.06-02 1.2E-01 1.06+00 8.0OE-01 3.4E-01 3.46-01 7.0 6-02 1.06+00 1.1E-02 1.06+00 1.06E+00 1.06E+00
- 1. 06+00 8.46-01 > 1.06+00 8.4E-01 > 1.06+00
- 1. OE+00
- 1. 06+00
- 1. 06-02 1.06-03 4 O0E-04
- branch model file
- forced Minarick 06-14-1990 15:59:46 Event Identifier: 344/89-021