ML20156A242
| ML20156A242 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1989-006-00 | |
| Download: ML20156A242 (5) | |
Text
B-366 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No:
Event
Description:
Date of Event:
Plant:
400/89-006 Reactor trip with one AFW pump out of service March 14, 1989 Shearon Harris Summary Shearon Harris was operating at 100% of rated power when the "B" main feedwater pump (MFP) tripped off because of an inadvertent fire protection spray actuation. An automatic turbine runback reduced the turbine load to 60%; however, with all control systems in automatic, the plant was unable to maintain level in the steam generators with the remaining MFP. An SG low-low level tripped the reactor approximately 71 s after the "B" MFP tripped. The two motor-driven auxiliary feedwater (AFW) system pumps started automatically and began supplying water to the SG, but the turbine-driven AFW pump was out of service for maintenance. The conditional core damage probability estimated for this event is 4.4 x 10-6. The relative significance of this event compared with other postulated events at Shearon Harris is shown below.
LER 400/89-006 IE-7 1E-6 1E-5 1E-4 1E-3 1E-2 Trip 1 LOFW +1J 360 hAFW-'
[30E MM MTAFW LO I...precursor cutoff Event Description On March 14, 1989, Shearon Harris was operating at 100% of rated power when a technician opened an upstream manual isolation valve in the supply line to a fire protection sprinkler deluge valve. Following maintenance on the system, the solenoid-operated deluge valve had not reseated, and fire protection personnel, thinking that the sprinkler head downstream of the deluge valve was closed, cracked open the isolation
B-367 valve; some water sprayed ftrom the sprinkler head onto the "B" MFP junction box. This was unexpected; however, the junction boxes were rain-and drip-proof. A short time later a short circuit due to water accumulation blew the "B" MFP junction box apart, and the pump tripped. The plant automatically responded by reducing the turbine load to 60%, dumping steam, inserting control rods, and trying to control water level in the SGs.
SG low-low level during the subsequent transient initiated auxiliary feedwater, which started both motor-driven AFW pumps, and they began supplying water to the SGs. The turbine-driven AFW pump was out of service for maintenance. The remaining MFW pump tripped on low flow 26 s after the SG low-low level signal.
Additional Event-Related Information Shearon Harris' AFW system consists of two motor-driven pumps and one turbine-driven pump. All three pumps share a common suction from the condensate storage tank (CST). AFW supplies the three SGs through separate lines (one for each SG); however, any of the AFW pumps can supply the SGs.
ASP Modeling Assumptions and Approach This event has been modeled as a reactor scram and locally recoverable loss of main feedwater, with the turbine-driven AFW pump unavailable.
Analysis Results The conditional probability of severe core damage for this event is 4.4 x 10-6. The dominant sequence associated with the event (highlighted on the following event tree) involves failure of secondary-side cooling and failure to initiate feed and bleed. Note that two other events at this plant involved a turbine trip with one train of AFW unavailable (see LERs 400/89-001 and -017).
PORV/
HI HR PR TRANAFW MFW SRV SRV OP P
ENOR LIJLCHAL IRESEAT IPEN SEO END NO STATE OK OK 11 CD 12 C
OK OK OK 13 CD 14 C0 OK 15 16 17 OK CD0(1)
CD CD 1B ATWS (1) OK for Class D Dominant core damage sequence for LER 400/89-006
B-369 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 400/89-006 Event
Description:
Reactor trip with one ASH pump out of service Event Date:
03/14/89 Plant:
Harris 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS l.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD TRANS 4.4E-06 Total 4.4E-06 ATWS TRANS 3.4E-05 Total 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
15 trans -rt AFN NFW -hpi(f/b) -hpr/-hpi porv.open CD 2.1E-06 8.BE-02 17 trans -rt APH NFN hpicf/b)
CD 2.1E-06 7.4E-02 16 trans -rt ATH NFN -hpi(f/b) hpr/-hpi CD 2.3E-07 8.BE-02 18 trans rt ATNS 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 Alit NFN -hpi(f/b) -hpr/-hpi porv.open CD 2.lE-06 8.8E-02 16 trans -rt AFN MFN -hpi(f/b) hpr/-hpi CD 2.3E-07 8.8E-02 17 trans -rt Alit MPH hpi(f/b)
CD 2.1E-06 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\\harris.sil PROBABILITY FILE:
c:\\asp\\1989\\pwrý_bsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 5.5E-04 l.OE+00 loop 1.6E-05 5.3E-01 loca 2.4E-06 4.3E-01 rt.
2.8E-04 1.2E-01 rt/loop, 0.OE+00 l.OE+00 enwrg.pover 2.9E-03 8.OE-01 ASH 3.8E-04 > 2.3E-03 2.6E-01 Branch Model:
l.OF.3+ser Train 1 Cond Prob:
2.OE-02 Event Identifier: 400/89-006
B-370 Train 2 Cond Prob:
Train 3 Cond Prob:
Serial Component Prob:
afw/emerg.power MFW Branch Model:
l.OF.l+opr Train 1 Cond prob:
porv.or.srv.chall porv.or.srv. reseat porv.or.srv. reseat/emerg.power seal. loca-ep. rec (si) ep. rec hpi hpi (f/b) hpr/-hpi porv.open l.OE-0l 5.OE-02 > Unavailable 2.
E-04
- 5. OE-02 l.OE+00 > 1.OE+0O
- 1. OE-400 4. OE-02 2.OE-02 2.OE-02 2.7E-01 5.7E-01 7.0 E-02
- 3. OE-04
- 3. OE-04
- 1. 5E-04
- 1. OE-02
- 3. E-0l 7.OE-02 > 3.4E-0l
- 1. OE+00
- 1. lE-02
- 1. OE+00
- 1. OE+00
- 1. OE+00
- 1. OE+00 8.4E-0l 8.4E-0l
- 1. OE+00
- 1. OE+00 l.OE-03 1.OE-02 l.OE-03 4.OE-04
- branch model file
- forced Minarick 06-13-1990 17:40:39 Event Identifier: 400/89-006