ML20156A246
| ML20156A246 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1982-040-00 | |
| Download: ML20156A246 (5) | |
Text
B.34-1 B.34 LER No. 335/82-040 Event
Description:
Reactor Trip and Loss of Grid Synchronization Due to Shorting of Generator Relay During Testing Date of Event: September 2, 1982 Plant: St. Lucie I B.34.1 Summary On September 2, 1982, personnel conducting a test of a generator trip relay short circuited it, which caused the generator breakers to open and a reactor/turbine trip. The spurious operation of the generator breakers allowed the unit to slip out of synchronization with the grid. Transfer of the vital buses to startup power did not occur and the emergency power system was actuated. The conditional core damage probability estimated for this event is 3.1 x 10'.
B.34.2 Event Description During full power operation, a generator trip relay was briefly shorted while being tested. This caused the generator breakers to open and a synchronizing inhibit timer to start. By the time the reactor tripped'due to a turbine overspeed trip, the timer had cycled, so transfer of the vital buses to startup power did not occur. The diesel generators started automatically and loaded properly. Offsite power and normal plant status were restored about 28 minutes after the short circuit occurred.
B.34.3 Additional Event-Related Information A similar bus loss was reported in LER 335/79-028.
B.34.4 Modelling Assumptions Since this event, in effect, isolated the plant from offsite power, it was modeled as a plant-centered loss of offsite power (LOOP). However, this is probably conservative since the event involved a failure to transfer only the vital buses. Changes to LOOP-related branch probabilities to reflect the plant-centered LOOP are shown in the following table:
LER No. 335/82-040
B.34-2 Branch Description Probability SEAL.LOCA Probability that an RCP seal LOCA will occur. 4.0 x 10.2 OFFSITE.PWR.REC/ Probability of failing to recover offsite power 1.4 x 10-'
-EP.AND-AFW within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> given that EP and AFW are successful.
OFFSITE.PWR.REC/ Probability of failing to recover offsite power 9.9 x 104
-EP.AND.AFW within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> given that EP is successful but AFW fails.
OFFSITE.PWR.REC/ Probability of failing to recover offsite power 4.8 x 10' SEAL.LOCA given the occurrence of an RCP seal LOCA.
OFFSITE.PWR.REC/ Probability of failing to recover offsite power 2.2 x 10-'
-SEAL.LOCA given that there is no RCP seal LOCA.
EP - emergency power AFW - auxiliary feedwater RCP - reactor coolant pump B.34.5 Analysis Results The conditional core damage probability (CCDP) estimated for this event is 3.1 x 10-. The dominant core damage sequence, shown in Figure. B.34. 1, involves the effective LOOP, successful reactor trip, failure of emergency power (EP), success of AFW, power-operated relief valve (PORV) challenge, and failure of the PORVs to reseat.
LER No. 335/82-040
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LER No. 335/82-040
B.34-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 335/82-040 Event
Description:
Reactor trip due to shorted generator relay Event Date: 9/2/82 Plant: St. Lucie 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 2,1E-01 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 3.1E-05 Total 3.IE-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
231 loop -rt(loop) ep -afw/ep porv.chall/sbo porv.reseat/ep CD 1.OE-05 1.8E-01 228 loop -rt(loop) ep -afw/ep porv.chall/sbo -porv.reseat/ep SEAL CD 9.9E-06 1.8E-01
.LOCA OFFSITE.PWR.REC/SEAL.LOCA 241 loop -rt(loop) ep afw/ep CD 9.1E-06 6.4E-02 216 loop -rt(loop) -ep afw -OFFSITE.PWR.REC/-EP.AND.AFW feed.bleed CD 1.1E-06 9.4E-02
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
216 loop -rt(loop) -ep afw -OFFSITE.PWR.REC/-EP.AND.AFW feed.bleed CD 1.1E-06 9.4E-02 228 loop -rt(loop) ep -afw/ep porv.chall/sbo -porv.reseat/ep SEAL CD 9.9E-06 1.8E-01
.LOCA OFFSITE.PWR.REC/SEAL.LOCA 231 loop -rt(loop) ep -afw/ep porv.chall/sbo porv.reseat/ep CD 1.0E-05 1.8E-01 241 loop -rt(loop) ep afw/ep CD 9.1E-06 6.4E-02
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\models\pwrg8283.cmp BRANCH MODEL: c:\asp\models\sluciel.82 PROBABILITY FILE: c:\asp\models\pwr8283.pro No Recovery Limit LER No. 335/82-040
B.34-5 BRANCH FREQUENCIES/PROBABILITIES Branch System Non- Recov Opr Fail trans 7.2E-04 1.OE.-00 loop 6.7E-05 2.1E-01 loca 2.4E-06 5.4E-01 sgtr 1.6E-06 1.OE+OO rt 2.8E-04 I.QE-Ol rt(loop) O.OE+00 1.OE+/-OO afw 3.8E-04 4.5E-01 afw/atws 4.3E-03 1.OE+0O afw/ep 5.OE-02 3.4E-01 mfw 1.9E-O1 3.4E-01 porv.chall 4.OE-02 1.OE+00 porv chall/afw 1.OE+O0 1.OE+0O porv.chall/loop I.OE-OI 1.OE+00 porv.chall/sbo 1.OE+O0 1.OE+0O porv.reseat 2.OE-02 1.1E-02 porv.reseat/ep 2.OE-02 1.OE+OO srv.reseat(atws) 1.0E-01 1.OE+OO hpi 3.OE-04 8.9E-01 feed.bleed 2.OE-02 1.0 E+OO 1.OE-02 emrg.boration O.OE+O0 l.OE+00 1.OE-02 recov.sec.cool 2.OE-O1 1.OE+00 recov.sec.cool/offsite.pwr 3.4E-O1 1.CE+0O rcs.cooldown 3.OE-03 1.0E+00 1.OE-03 rhr 8.OE-03 7.OE-02 1.OE-03 csr 4.OE-03 1.OE+OO 1.OE-03 hpr 1.5E- 04 1.OE+/-OO ep 2.9E-03 8.9E-01 SEAL.LOCA 4.8E-02 > 4.OE-02 1.OE+OO Branch Model: 1.OF.1 Train 1 Cond Prob: 4.BE-02 > 4.OE-02 OFFSITE.PWR.REC/-EP.AND.-AFW 2.5E-01 > 1.4E-O1 1.OE+OO Branch Model: 1.OF.1 Train 1 Cond Prob: 2.5E-01 > 1.4E-01 OFFSITE.PWR.REC/-EP.AND.AFW 5.7E-02 > 9.9E-04 1.OE+OO Branch Model: 1.OF.1 Train I Cond Prob: 5.7E-02 > 9.9E-04 OFFSITE.PWR.REC/SEAL.LOCA 6.OE-O1 > 4.8E-01 1.OE+0O Branch Model: I.OF.1 Train I Cond Prob: 6.OE-O1 > 4.8E-01 OFFSITE.PWR.REC/-SEAL.LOCA 1.1E-02 > 2.2E-05 1.OE+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 1.1E-02 > 2.2E-05 sg.iso.and.rcs.cooldown 1.OE-02 1.QE-0l rcs.cool.below.rhr 3.OE-03 1.OE+00 3.OE-03 prim.press.limited 8.8E-03 1.OE+00
- branch model file
- forced LER No. 335/82-040