ML20140A209
| ML20140A209 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 05/19/2020 |
| From: | NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1990-001-00 | |
| Download: ML20140A209 (5) | |
Text
B-322 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No.: 389/90-001 Event
Description:
Loss of feedwater with one train of AFW unavailable Date of Event: January 14, 1990 Plant: St. Lucie 2 Summary The reactor tripped on a steam generator (SG) low-low level. Shortly after the automatic initiation of the auxiliary feedwater system (AFW), the turbine-driven AFW pump tripped off due to an overspeed trip signal. Thus, one of three trains of AFW was lost during this event. The conditional core damage probability estimated for this event is 4.7 x 10-6. The relative significance of this event compared to other postulated events at St. Lucie 2 is shown below.
_LER 389/90-001 1E-7 IE-6 IE51E-4 IE-3 1E-2 TripL 360 h A1F LOFW +
precuxsor cutoff _.J ILMM AF Event Description On January 14, 1990, St. Lucie 2 was at 50% power with one SG feed pump and one condensate pump running; however, this is the upper power limit for this configuration, and as the operators attempted to increase power, the feed pump tripped off on low suction pressure. The second condensate pump failed to start because its control power fuses had not been re-installed following maintenance. While the operators were trying to re-establish feed and condensate flow, the reactor tripped on low SG level. This was followed almost immediately by a turbine trip. AFW automatically initiated and all three AFW pumps started, but the turbine-driven AFW pump tripped off shortly after it had started due to an overspeed signal from the turbine tachometer. The motor-driven AFW pumps continued supplying water to the SGs until the plant was stabilized in hot
B-323 standby. It was determined later that the turbine governor hydraulic oil contained foreign matter and caused the AFW pump turbine overspeed.
Additional Event-Related Information St. Lucie's AFW system consists of two 100% capacity motor-driven pumps and one 100% capacity turbine-driven pump. All three pumps share a common normal suction from the condensate storage tank. The turbine-driven pump supplies both SGs while each motor-driven pump can supply one SG. The discharges of the motor-driven pumps can be cross connected.
ASP Modeling Assumptions and Approach This event has been modeled as a reactor scram with a recoverable loss of feedwater and one of three trains of AFW unavailable.
Analysis Results The conditional probability of severe core damage estimated for this event is 4.7 x 10-6.
The dominant core damage sequences, highlighted on the following event tree, involve failure of secondary-side cooling and failure of feed and bleed.
B-324 FI ~~IIF I I TRANS I S AFW WW SRV PORV/I SRV PORV/I CHALL RESEAT IHPI I HP P ORV OE SEC NO END STATE OK OK 11 CD 12 CO OK OK OK 13 CD 14 CD OK OK 10 CD 15 CD is CD 17 CD Is ATWS Dominant core damage sequence for LER 389/90-001
B-325 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 389/90-001 Event
Description:
LOFW with one train of AFW unavailable Event Date: 01/14/90 Plant: St Lucie 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1 .0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 4 .7E-06 Total 4 .7E-06 ATWS TRANS 3. 4E-05 Total 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
15 trans -rt AFW MFW -hpi(f/b) -hpr/-hpi porv.open CD 2 .1E-06 8.8E-02 17 trans -rt AFW MFW hpi(f/b) CD 2 .1E-06 7 .4E-02 19 trans -rt AFW MFW -hpi(f/b) -hpr/-hpi -porv.open csr CD 3.3E-07 3.OE-02 16 trans -rt AFW MFW -hpi(f/b) hpr/-hpi CD 2 .3E-07 8.8E-02 18 trans rt ATWS 3.4 E-05 1 .2E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State P rob N Rec**
19 trans -rt AFW MFW -hpi(f/b) -hpr/-hpi -porv.open csr CD 3. 3E-07 3.05-02 15 trans -rt AEW MFW -hpi(f/b) -hpr/-hpi porv.open CD 2 .IE-06 8.8E-02 16 trans -rt AFW MEW -hpi(f/b) hpr/-hpi CD 2.3E-07 8.8E-02 17 trans -rt AFW MFW hpi(f/b) CD 2.1E-06 7 .4E-02 18 trans rt ATWS 3.4E5-05 1 .2E-01
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\1989\pwrgseal.cmp BRANCH MODEL: c:\asp\1989\lucie2.sll PROBABILITY FILE: c:\asp\1989\pwrb.ksll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Event Identifier: 389/90-001
B-326 Branch System Non-Recov Opr Fail trans 1.42-04 1.02+00 loop 6.7 2-05 2.1E-01 loca 2.42-06 4.3E-01 rt 2.8E-04 1.2E-01 nt/loop 0.02+00 1.02+00 emerg. power 2.9E-03 8.02-01 AMW 3.8E-04 > 2.32-03 2.6E-01 Branch Model: l.OF.3+ser Train 1 Cond Prob: 2.02-02 Train 2 Cond Prob: 1.02-01 Train 3 Cond Prob: 5.02-02 > Failed Serial Component Prob: 2.8E-04 AEW/EMERG. POWER 5.02-02 > 1.02+00 3.42-01 > 1.02+00 Branch Model: l.OF.l Train 1 Cond Prob: 5.02-02 > Failed MFW 1.92-01 > 1.02+00 3. 4-01 Branch Model: l.OF.1 Train 1 Cond Prob: 1.92-01 > Failed porv.or.srv.chall 4.02-02 1.02+00 porv.or. srv. reseat 2.02-02 1. 1E-02 porv.or. srv. reseat/emerg.power 2.02-02 1. 02+00 seal. loca 4.8E-02 1.02+00 ep.rec(sl) 6.02-01 1.02+00 ep. rec l.1E-02 1.02+00 hpi 3.02-04 8. 4-01 hpi(f/b) 3.02-04 8.42-01 1.02-02 porv.open 1.02-02 1.02+00 4. 02-04 hpr/-hpi 1.5E-04 1.02+00 2.02-03 3. 4-01
- branch model file
- forced Minarick 08-06-1991 17:31:06 Event Identifier: 389/90-001