ML20135G965
| ML20135G965 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 05/14/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1991-001-00 | |
| Download: ML20135G965 (5) | |
Text
B-37 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No.:
Event
Description:
Date of Event:
Plant:
247/9 1-00 1 Reactor trip and auxiliary feedwater pump failure January 7, 1991 Indian Point 2 Summary Maintenance errors resulted in a spurious low pressurizer pressure reactor trip. A subsequent low steam generator (SG) level signal initiated an automatic start of both motor-driven auxiliary feedwater (AFW) pumps. After about two min, faulty protective circuitry caused one auxiliary feedwater pump to trip. The conditional probability of subsequent core damage estimated for the event is 2.0 x 10-6. The relative significance of the event compared to other postulated events at Indian Point 2 is shown below.
[LER 247/91-001 1E-7 IE-6 F 1E-5 1E-4 IE-3 IE-2 I
L 360 hEP LOFW +]LLOP 1MTRAFWAFW Event Description Indian Point 2 was operating at 97% power when repair work was begun on a leaky compression fitting in a pressurizer pressure transmitter sensing line. The transmitter was isolated and repairs effected. During this time, the affected transmitter falsely indicated a low pressurizer pressure. While the sensing line was being restored to service, a pressure transient in the sensing line resulted that caused a second pressure transmitter to indicate low. Coincidence of low pressurizer pressure indication from the two transmitters caused a reactor trip.
A short time later, low levels in the SGs resulted in actuation of the AFW system.
Motor-driven AFW pumps 21 and 23 started and began supplying feedwater. About two min later, AFW pump 21 tripped and would not restart. This resulted in a loss of feedwater flow to SGs 21 and 22. Subsequent investigation revealed that the pump
B-38 motor breaker spuriously tripped on overcurrent as a result of miscalibration of an associated overcurrent protective device. The device, an Amptector, was set to trip at 540 A instead of at 725 A.
Normal operating current for the motor is -530 A.
Operators did not initially know that the pump had tripped on overcurrent as faulty relay contacts in the breaker resulted in control room indication that the pump was off, but not that it had tripped. The 22 AFW turbine-driven pump was started and used to supply the affected steam generators.
ASP Modeling Assumptions and Approach This event was modeled as a reactor trip with loss of one motor-driven AFW pump.
Analysis Results The estimated core damage probability associated with a reactor trip and failure of one motor-driven AFW pump was calculated as 2.0 x 10-6.
The dominant core-damage sequences involve failure of main feedwater, failure of the remaining AFW systems, and failures in systems required for feed-and-bleed heat removal. The two dominant sequences are shown on the following event tree.
B-39 IPOR VIII PORVI PORV TRANS RT AFW IMFW SRV SRV iHPI IHPR OPEN CHAL RESEAT I
I SEQ END NO STATE OK 11 CD 12 CD OK OK OK 13 CO 14 C
OK OK 15 00 (1) 16 Go 17 CO 1s ATWS (1) OK for Ciass D Dominant core damage sequ~ence for LER 247/9 1-001
B-40 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
247/91-001 Event
Description:
Reactor trip and AFN pump failure Event Date:
01/07/91 Plant:
Indian Point 2 INITIATING EVENT NON-RECOVERAB3LE INITIATING EVENT PROBABILITIES TRANS 1.OE+00 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD TRANS 2.0E-06 Total 2.OE-06 ATNS TRANS 3.4E-05 Iotal1 3.4E-05 SEQUENCE CONDITIONAL PROBABI1LITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
15 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open CD 9.6E-07 8.8E-02 17 trans -rt AFW rsfw hpi(f/b)
CD 9.6E-07 7.4E-02 16 trans -rt AFW raN -hpi(f/b(
hpr/-hpi CD 1.1E-07 8.8E-02 18 trans rt ATWS 3.4E-05 1.2E-01
-* non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
15 trans -rt AFW mfw -bpi(f/b) -hpr/-hpi porv.open CD 9.6E-07 8.BE-02 16 trans -rt AFW mfw -hpi(f/b(
hpr/-hpi CD 1.1E-07 8.8E-02 17 trans -ft AFW mfw hpi(f/b(
CD 9.6E-07 7.4E-02 18 trans rt ATWS 3.4E-05 1.2E-01 non-recovery credit for edited case SEQUENCE MODEL:
c:\\asp\\1989\\pwrbseal.cmp BRANCH MODEL:
c:\\asp\\1989\\indpolnt.s~l PROBAB3ILITY FILE:
c:\\asp\\1989\\pwr~bsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail Event Identifier: 247/91-001
B-41 trans loop loca rt rt/loop emerg.power AFW Branch Model:
l.OF.3+/-ser Train 1 CondProb:
Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
afw/ernerg.power mfw porv.or.srv.chall porv.or. srv. reseat porv.or. arv. reseat /emerg.power seal. loca ep.tee (st) ep. rec hpi hpi (f/b).
hpr/-hpi porv.open 4.6E-04 3.1E-05 2.4E-06 2. BE-04 0.OE+00
- 5.45-04 3.8E-04 > 5.3E-03 2.OE-02 > Failed 1. 0-01
- 5. OE-02 5.0E-02
- 2. OE-01 4.OE-02
- 2. OE-02 2.05-02 2.1E-01 6.05-01
- 5. 6E-02 3.05-04 3.OE-04
- 1. 5E-04 1 05-02
- 1. OE+00
- 1. 7E-01 4.35-01 1.2E-01 1.OE+00 B.OE-01 2.6E-01 3.4E-01 3.4E-01
- 1. OE+00 1.1E-02 l.OE+00 1.05+00 1.05+00
- 1. 05+00
- 8. 4E-01
- 8. 4E-01
- 1. OE+00 1.05+00 1.OE-02 1.OET03 4.05-04
- branch model file
- forced Minarick 03-11-1992 11:10:46 Event Identifier: 247/91-001