ML20149K463
| ML20149K463 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1988-007-01 | |
| Download: ML20149K463 (5) | |
Text
B- 276 Accident Sequence Precursor Program Event Analysis LER No.: 369/88-007 Ri Event
Description:
Trip and the turbine-driven AFW pump fails to start Date of Event: April 16, 1988 Plant: McGuire Unit 1 Summnary While at 100% power, a feedwater regulating valve spuriously closed, causing a steam generator level decrease. Recognizing an imminent automatic trip, operators manually tripped the turbine generator and the reactor. Following the trip, the turbine auxiliary feedwater pump failed to start as designed. The conditional probability for core damage has been calculated at 1.0 x 10-6. The relative significance of this event compared with other potential events at Mc~uire 1 is shown below.
LER 369/88-007 RI 1E-8 IE-7 1E-6 1E-5 I1E-4 IE-3 IE-2 Trip LEP Uavail Trip w/1 AFW AFW Unavail Train Unavail (360 hrs)
Event Description While at 100% power, the controller card for the power supply to valve ICF-20 failed, causing the valve to close. This valve closure caused the level in the steam generator 1C to decrease at the rate of 25% per minute. Recognizing that the unit would trip on low steam generator signal, operators manually tripped the turbine generator, which sub-sequently tripped the reactor. On reactor trip, the main feedwater valves closed and auxiliary feedwater was initiated; however, the tur-bine-driven auxiliary feedwater failed when the steam supply failed to actuate due to damage to the valve 1SA49 limit switch. This damage was caused by valve packing leakage.
B-277 Corrective actions included replacing the power controller card for valve 1CF-20 and the limit switch for valve 1SA-49.
Event-Related Plant Design Information The main feedwater system includes a feedwater regulating valve and an isolation valve in the flow path to each steam generator. These valves are designed to fail in the closed position. If either valve fails closed during full-power operation, the water level in the affected steam generator would begin to rapidly decrease.
ASP Modeling Assumptions and Approach This event has been modeled as a trip with the turbine-driven auxiliary feedwater pump failed.
Analysis Results The conditional probability of core damage is estimated to be 1.0 x 10-6. The dominant core damage sequence (highlighted on the following event tree) is associated with a failure of the remaining trains of AFW (p = 6.0 x 10-4), failure to reinitiate main feedwater (p =0.071), and failure of feed and bleed (p = 0.012).
- B-278 PORV/ PORV/ PR SEQ END TRANS RT AFW MFW SRV SRV HP HPR OPORN NO STATE CHAL RESEAT OPE OK OK 12 OD OK OK OK 13 ao 14 CD~
OK OK 15 16 17 18 ATWS Dominant Core Damage Sequence for LER 369/88-007 Ri
B-279 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 369/88-007 Event
Description:
Trip and the turbine-driven AFW train fails to start Event Date: 04/16/88 Plant: McGuire 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD TRANS 1.09-06 Total l.OE-.06 ATWS TRANS 3.4E-~05 Total 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
17 trans -rt AFW mfw hpi(f/b) CD 5.0E-07 1.5E-02 15 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open CD 4.3E-07 1 .SE-02 16 trans -rt AFW mfw -hpi(f/b) hpr/-hpi 4.8E-08 1.8E-02 CD 11 trans -rt -AFW porv.or.srv.chall porv.or.srv.reseat -hpi hpr/ l.5E-08 1 . 1E-02
-hp i 1B 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**
11 trans -rt -AFW porv.or.srv.chall pory.or.srv.reaeat -hpi hpr/ CD l.5E-08 1 . E-02
-hpi 15 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open CD 4 . 3E-07 1 . 8E-02 16 trans -rt AFW mEw -hpi(f/bl hpr/-hpi CD 4 .8E-08 1.8R-02 17 trans -rt AFW mfw hpi(f/b) CD 5.OE-07 1 . 5E-02 18 trans rt ATWS 3.4E-05 1 .2E-01
~*non-recovery credit for edited case SEQUENCE MODEL: c:\asp\sealmod\pwrbseal.cmep BRANCH MODEL: c:\asp\seaimod\mcguire.sll PROBABILITY FILE: c:\asp\sealmod\pwr~bsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 4.3E-04 1.0 E+00 loop 1.6E-05 3. 6E-01 loca 2.4E-06 4.3E-01 rt 2.SE-04 1.2E-01 rt/loop 0.OE+00 l.OE+00 Event Identifier: 369/88-007
B-230 eme rg .power 2. 9E-03 8. OE-01 AFW 3.8E-04 > 2.3E-03 2.68E-01 Branch Model: 1.OF.3+ser Train 1 Cond Prob: 2.0E-02 Train 2 Cond Prob: 1.OE-01 Train 3 Cond Prob: 5.OE-02 > Failed Serial Component Prob: 2.8E-04 afw/emerg .power 5.OE-02 3.4E-01 mfw 1.OE+00 7. OE-02 1.OE-03 porv.or.srv.chaii 4 . OE-02 1.OE+00 porv.or.srv. reseat 3.OE-02 1 . IE-02 porv.or.srv.reseat/emerg.power 3.OE-02 1.OE+00 seal .loca 0.09+00 1 *OE+00 ep.rec(sl) 0.OE+00 1. OE+00 ep. rec 4.5E-01 1.OE+00 hpi 1.OE-03 8.4 E-01 hpi (f/b) 2.2E-03 8 .4E-01 1 .OE-02 hpr/-hpi 1.5E-04 1.OE+00 1 .OE-03 porv .open 1.0 E-02 1.OE+00 4 O0E-04
- branch model file
- forced Minarick 11-09-1989 12:58:22 Event Identifier: 369/88-007