ML20147A346
| ML20147A346 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1987-036-00 | |
| Download: ML20147A346 (4) | |
Text
3-145 PRECURSOR DESCRIPTION SHEET LER No.:
412/87-036 Event
Description:
Trip and subsequent loss of offsite power Date of Event:
11/17/87 Plant:
Beaver Valley 2 EVENT DESCRIPTION Sequence An I&C technician bumped and tripped the power supply switch to the turbine thrust-bearing circuit supervisory instrument.
The resultant spike caused a turbine trip followed by a reactor trip.
A fast bus transfer from the unit station service transformers (USST) to the system station service transformers (SSST) was automatically initiated.
After the transfer, the USST breakers immediately reclosed since the trip signal was not designed to seal-in.
This resulted in an overcurrent condition that tripped the A, B,
C, and D 4-kV buses and resulted in an effective loss of offsite power.
Both emergency diesel generators started and energized the emergency buses.
The supply breaker for the A and B 4-kV buses reclosed, and RCP A and B were restarted.
Corrective Action To ensure that the turbine-thrust bearing trip signal is maintained to the circuit after a trip signal has occurred, the self reset relays were to be replaced with lockout type relays.
To prevent the USST breakers from reclosing on a transfer from onsite to offsite
- power, a
reclosure blocking scheme was added to the circuit (knife switches were added, which are administratively controlled).
Plant/Event Data Systems Involved:
Electrical Components and Failure Modes Involved:
Relay cycles opened then closed in operation Component Unavailability Duration:
4 min Plant Operating Mode:
1 (98%)
Discovery Method:
Operational event Reactor Age:
0.3 y Plant Type:
PWR Comments None.
MODELING CONSIDERATION AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP 0.04 Recoverable from the control room Event Identifier:
412/87-036
B-146 Branches Impacted and Branch Nonrecovery Estimate None Plant Models Utilized PWR plant Class A Event Identifier:
412/87-036
B-147 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:
412/87-036 Event
Description:
Trip with subsequent loss of offsite power Event Date:
11/17/87 Plant:
Beaver Valley 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 4.OE-02 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD LOOP 1.7E-05 Total 1.7E-05 CV LOOP 4.3E-07 Total 4.3E-07 ATWS LOOP 0.0E+00 Total 0.OE+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec*
217 LOOP -rt/loop emerg.power ep.rec CD 1.6E-05 5.4E-03 216 LOOP -rt/loop emerg.power -ep.rec afw/ep CD 1.3E-06 9.OE-03 215 LOOP -rt/loop emerg.power -ep.rec -afw/ep -porv.or.srv.chall s
CV 3.6E-07 8.9E-03 s.releas.term 209 LOOP -rt/loop
-emerg.power -afw -porv.or.srv.chall ss.releas.te CV 4.9E-08 I.1E-02 rm hpi 213 LOOP -rt/loop emerg.power -ep.rec -afw/ep porv.or.srv.chall -p CV 1.5E-08 8.9E-03 orv.or.srv.reseat/emerq.power ss.releas.term
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
209 LOOP -rt/loop -emerg.power -afw -porv.or.srv.chall ss.releas.te CV 4.9E-08 l.1E-02 rm hpi 213 LOOP -rt/loop emerg.power -ep.rec -afw/ep porv.or.srv.chall -p CV 1.5E-08 8.9E-03 orv.or.srv.reseat/emerg.power ss.releas.term 215 LOOP -rt/loop emerg.power -ep.rec -afw/ep -porv.or.srv.chall s
CV 3.6E-07 8.9E-03 s.releas.term 216 LOOP -rt/loop emerg.power -ep.rec afw/ep CD 1.3E-06 9.OE-03 217 LOOP -rt/loop emerg.power ep.rec CD 1.6E-05 5.4E-03 non-recovery credit for edited case SEQUENCE MODEL:
c:\\asp\\newmodel\\pwranew.cmp BRANCH MODEL:
c:\\asp\\newmodel\\beaver2.new PROBABILITY FILE:
c:\\asp\\newmodel\\pwr-bnew.pro Event Identifier:
412/87-036
B-148 No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov.
Opr Fail trans 4.8E-04 I.OE+O0*
LOOP 4.6E-06 > 4.6E-06 3.9E-01 >.4.OE-02 Branch Model:
INITOR Initiator Freq:
4.6E-06 loca 2.4E-06 4.3E-01 rt 2.8E-04 1.2E-O1 rt/loop O.OE+O0 1.OE+O0 emerg.power 2.9E-03 8.OE-01 ep.rec 1.OE+00 1.7E-01 afw 3.8E-04 2.6E-01 afw/ep 5.OE-02 3.4E-01 mfw 2.OE-01 3.4E-01 porv.or.srv.chall 4.OE-02 1.OE+00 porv.or.srv.reseat 3.OE-02 I.IE-02 porv.or.srv.reseat/emerg.power 3.OE-02 I.OE+00 ss.releas.term 1.5E-02 3.4E-01 ss.depress 3.6E-02 1.OE+00 cond/mfw 1.OE+00 3.4E-01 1.OE-02 hpi 3.OE-04 8.4E-01 hpi(f/b) 3.OE-04 8.4E-01 I.OE-02 porv.open 1.OE-02 1.OE+00 4.OE-04 hpr/-hpi 1.5E-04 1.OE+00 1.OE-03 csr 1.OE-02 1.OE+00 ipi/hpi.
1.5E-04 3.4E-01 lpr/-hpi 6.7E-01 1.OE+00 lpr/hpi 1.5E-04 1.OE+O0 branch model file
- forced Minarick 05-16-1989 07:02:21 Event Identifier:
412/87-036