ML20147A518
| ML20147A518 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1989-023-00 | |
| Download: ML20147A518 (5) | |
Text
B-70 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No: 302/89-023 Event
Description:
Loss, of offsite power with degraded emergency feedwater Date of Event: June 16, 1989 Plant: Crystal River 3 Summary A loss of offsite power (LOOP) was initiated at Crystal River 3 with the plant at 12%
power when a technician bumped a test trip button. Automatic transfer to another source did not occur because a relay failed and indicated that a breaker was closed when it was not. The emergency diesel generators (EDGs) automatically started and reenergized their respective engineered safeguards (ES) buses. Also, the motor-driven emergency feedwater pump failed to automatically start because of two faulted relays and was manually started.
The conditional core damage probability estimated for this event is 3.5 x 10-5. The relative significance of this event compared with other postulated events at Crystal River 3 is shown below.
1 LER 302/89-023 1E-7 1E-6 1E-5 E-4 1E-3 1E-2 L Tip 1 I
360OhAFWi Lo LOFW +1I L
L360 hEP precursor cutoff TAF Event Description On June 16, 1989, Crystal River 3 was operating at 12% of rated power with the main generator latched and rolling. An electrical technician accidently bumped the test trip button in the Brookridge (230-ky) line metering cabinet, opening switchyard breakers 1690 and 1691. This alone should have only de-energized the Brookridge line. However, a fault detector relay in breaker 1691 failed, causing a false breaker-closed indication. The fault detection scheme opened breaker 1692 to clear the indicated fault. As a result, power to the startup transformer was lost. ED~s 3A and 3B automatically started and reenergized their
B-71 respective 4160-V ES buses. All operating reactor coolant pumps and both operating main feedwater pumps tripped because of the loss of power on the startup transformer. This caused an automatic initiation of the emergency feedwater (EFW) system. The turbine-driven EFW pump started. However, the motor-driven EFW pump had to be started manually. This was caused by the failure of two series relays. The startup transformer was returned to service approximately 1 h after the event began.
Additional Event-Related Information Crystal River 3's normal offsite source of power to the ES buses 3A and 3B is from the 230-ky switchyard (five possible sources) stepped down through the Unit 3 startup transformer. Alternate offsite power to the ES buses is from the Unit 3 auxiliary transformer supplied by the main generator. Backup offsite power to the ES buses is from the Units 1 and 2 startup transformer. EDGs 3A and 3B supply emergency power to the ES buses in the event that all other sources of power are lost. In this event, the plant was in power operation, but the main generator was separated from the grid even though it was latched and rolling. Thus, the alternate source of power to the ES buses was unavailable.
The EFW system consists of two 100% capacity trains, one with a motor-driven pump and the other with a turbine-driven pump. The motor-driven pump receives power from 3A ES bus.
ASP Modeling Assumptions and Approach This event has been modeled as a plant-centered loss of offsite power with one train of EFW initially unavailable. No change in the EFW system nonrecovery estimate was assumed in the analysis.
Analysis Results The conditional probability of severe core damage for this event is 3.5 x 10-5. The dominant core damage sequence involves successful emergency power following the LOOP, with subsequent failure of AFW and feed and bleed. This sequence is highlighted on the following event tree. If the failure of the motor-driven EFW pump is not addressed in the analysis (since it was manually started shortly after the LOOP), the core damage probability estimate is reduced to 1.3 x 10-5 . In this case, the dominant sequence involves failure of emergency power and failure of the turbine-driven AFW train.
B-72 i h iI Z
LO RT/L8 O E I
AFW IPSRV ORV /
OHALL PSRV ORV / ý S RESEAT LCA p EA,_HPE (LONG)
HR I I P. P I PO V OPE
,RJ SEO NOl END STATE OK OK 41 CD 42 CO OK<
OK 43 CD (1) 44 CD 45 CD OK<
46 CD 47 CD 48 CO OK 49 CD so Go OK 51 CD 52 CO 53 GD OK 54 CO 55 CD 40 ATWS (1) OK for Class D Dominant core damage sequence for LER 302/89-023
B-73 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 302/89-023 Event
Description:
LOOP with degraded emergency feedwater Event Date: 06/16/89 Plant: Crystal River 3 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 1. 5E-01 SEQUENCE CONDITIONAL PROBABILITY SUNS End State/Initiator Probability CD LOOP 3. 5E-05 Total 3. 5E-05 ATWS LOOP 0. OE-400 Total 0 . OE+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
45 LOOP -rt/loop -emerg.power AFW hpi(f/b) CD 2. QE-OS 3 . 3E-02 55 LOOP -rt/loop emerg.power afw/emerg.power CD 5.8E-06 4 . 1E-02 54 LOOP -rt/ioop emerg.power -afw/emerg.power -porv.or.srv.chali CD 4. 9E-0 6 1.2E-01 SEAL.LOCA EP.REC 44 LOOP -rt/loop -emerg.power AFW -hpi(f/b) hpr/-hpi CD 2. 2E-06 3. 9E-02 53 LOOP -rt/loop emerg.power -afw/emerg.power -porv.or.srv.chall CD 1.3E-06 1.2E-01 SEAL.LOCA EP.REC(SL)
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State P rob, N Rec**
44 LOOP -rt/ioop -emerg.power AFW -hpi(f/b) hpr/-hpi CD 2.2E-06 3. 9E-02 45 LOOP -rt/loop -eslerg.power AFW hpi(f/b) CD 2. OE-05 3. 3E-02 53 LOOP -rt/loop emerg.power -afw/emerg.power -porv.or.srv.chall CD 1. 3E-06 1 .2E-01 SEAL.LOCA EP.REC(SL) 54 LOOP -rt/loop emerg.power -afw/emerg.power -porv.or.srv.chall- CD 4 . 9E-0 6 1 .2E-01 SEAL.LOCA EP.REC 55 LOOP -rt/loop emerg.power afw/emerg.power CD 5. 8E-06 4 . 1E-02
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\1989\pwrdseal.cinp BRANCH MODEL: c:\asp\1989\crystal3.sll PROBABILITY FILE: c:\asp\1989\pwr~bsll.pro No Recovery Limit BRANCN FREQUENCIES/PROBABILITIES Branch System Non-Re coy Opr Fail trans 3.9E-04 l.OE+0 0 LOOP 1.8E-05 > 1.8E-05 3.3E-0 1 > 1.5E-01 Branch Model: INITOR Event Identifier: 302/89-023
B-74 Initiator Freq: 1.8E-05 loca 2.4E-06 4. 3E-01 rt 2. 8E-04 1. 2E-01 rt/loop 0.OE+00 1. OE+00 emerq.power 2. 9E-03 8. CE-0l AFW 1.3E-03 > 5.OE-02 2. 6E-0l Branch Model: 1.OF.2+ser Train 1 Cond Prob: 2.OE-02 > Failed Train 2 Cond Prob: 5.0 E-02 Serial Component Prob: 2. 8E-04 afw/emerg .power 5.OE-02 3.4 E-01 mfw 2.OE-0l 3.4E-01 porv.or.srv.chall 8.0 E-02 1. CE+00C porv .or -srv .reseat l.OE-02 l.IE-02 porv.or.srv.reseat/emerg.power l.OE-02 1. CE+CC SEAL.LOCA 6.OE-02 > 1.5E-02 1.OE+CC Branch Model: l.OF.l Train 1 Cond Prob: 6.OE-02 > l.5E-02 EP.REC (SL) 7.6E-01 > 2.8E-0l 1. CE+C0 Branch Model: l.OF.l Train 1 Cond Prob: 7.6E-01 > 2.8E-01 EP.REC 3.1E-0l > 1.6E-02 1. CE+/-00 Branch Model: l.OF.1 Train 1 Cond Prob: 3.1E-0l > l.6E-02 hpi 3. OE-04 8.4E-Cl hpi (f/b) 3.OE-04 8 .4 E-01 l.CE-02 hpr/-hpi 1. 5E-04 1. CE+CC l.CE-03
- branch model file
- forced Minarick 06-15-1990 09:30:26 Event Identifier: 302/89-023