ML20135G956
| ML20135G956 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 05/14/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1990-017-01 | |
| Download: ML20135G956 (6) | |
Text
B- 103 ACCIDENT SEQUENCE PRECURSOR PROGRAM EVENT ANALYSIS LER No.: 244/90-017 R1 Event
Description:
Trip with manual and auto safeguards initiation disabled Date of Event: December 12, 1990 Plant: Ginna Summary While performing a troubleshooting procedure on engineered safeguards features (ESF) bus 14, DC control power was removed from the manual and automatic actuation circuitry for the plant engineered safeguards systems. This condition existed for approximately 20 min, during which time a reactor trip occurred.
The conditional probability of core damage associated with this event is 2.0 x 10-6. The relative significance of the event compared to other postulated events at Ginna is shown below.
-LER 244/90-017 R1 1E-7 IE-6 1EF IE-4 IE-3 1E-2 Trip]J 360 h EP precursor cutoff.J
-j MR AFW 360 h AFW Event Description During the course of a startup, an apparently false indication of undervoltage on ESF bus 14 was given when an undervoltage relay failed. The relay failure caused the associated diesel generator to start, but its output breaker did not close in to feed the bus as the normal source continued to provide power.
In the course of troubleshooting the bus 14 undervoltage monitoring system, a procedure was initiated which required that the bus be transferred to its alternate feeder, supplied from the diesel generator. This procedure, written for use while at cold shutdown, incorrectly indicated that it could be performed during any operational mode. One step of
B- 104 the procedure required that two DC switches be opened, removing power from the circuits providing manual and automatic initiation of the plant engineered safeguards.
This step was performed at 2310 on the day of the event. (This step had been initially questioned by the Control Room Foreman, but subsequently accepted following verification that the procedure requirements were being adhered to.)
A subsequent step in the procedure required that the normal bus 14 feeder be opened to allow the "A" diesel generator output breaker to close in on the bus. This step was performed at 2322. When this occurred, the 1B instrument bus was briefly deenergized, resulting in trip of nuclear instrumentation intermediate range channel N-36 and reactor trip. After stabilizing the plant in hot shutdown, the procedure to transfer bus 14 was continued.
At about 2330, the operators reached a step in the procedure requiring that the safeguards DC control power switches be closed, and they placed them back in the closed position.
This restored the engineered safeguards systems to operability.
It was subsequently recognized that, for the 20 min that the safeguards system DC control power switches were open, the associated systems could not have performed their design functions. Had an accident requiring them taken place, no automatic initiation would have occurred. In addition, manual (pushbutton) initiation of the system was disabled. The individual components - pumps, valves, etc. - were still individually operable, however.
Licensee Event Reports 244/90-0 13 and 244/90-0 16 also described circumstances relating to this event.
Additional Event-Related Information The engineered safety features actuation system (ESFAS) is powered from the two battery-backed DC buses. DC power to the applicable ESFAS train is required for actuation. The analog protection circuits that detect out-of-range process parameters are powered from four 120-V AC vital power. Theses circuits trip on loss of power.
ASP Modeling Assumptions and Approach This event has been modeled as a trip with automatic safeguards initiation disabled.
Failure to manually initiate safety injection (via operator action or at the component level) was assigned a failure probability of 0. 12, consistent with other ASP event assessments (see Appendix A). This probability was also utilized for failure of feed and bleed, since manual actuation of SI which is required during feed and bleed initiation, was also
B- 105 unavailable.
Analysis Results The conditional probability of subsequent severe core damage for this event is 2.0 x 10-6.
The dominant core damage sequence, highlighted on the following event tree, involves a transient-induced loss-of-coolant accident (LOCA) with failure to initiate high-pressure injection (HPI).
B-106 TA RT* IW M W POR V/I SRV I SRV PORV / HPI H IPR IOPEN OR SEQ END 1TRANS 1 1 NO STATE I CHAL ~RESEATIOE I OK OK 11 CD 12 CD OK OK OK 13 CD 14 CD OK OK 15 CD (1) 16 OD 17 CD 1s ATWS (1) OK for Class D Dominant core damage sequence for LER 244/90-017
B-107 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 244/90-017 Event
Description:
Trip with manual and auto safeguards initiation disabled Event Date: 12/12/90 Plant: Ginna INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1 .OE-40O SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 2 .OE-06 Total 2 .DE-06 ATWS TRANS 3 .4E-05 Total 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec-*
12 trans -rt -afw porv.or.srv.chall porv.or.srv.reseat HPI CD 1.1E-06 1.3E-03 17 trans -rt afw mfw HPI(F/B) CD 8.4E-07 2.2E-03 18 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**
12 trans -rt -afw porv.or.srv.chall porv.or.srv.reseat iiPI CD 1.15-06 1.3E-03 17 trans -rt afw mfw HPI(F/B) CD 8.4E-07 2.2E-03 1s trans rt ATWS 3.4E-05 1.2E-01
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\1989\pwrbseal.cmp BRANCH MODEL: c:\asp\1989\ginna.sll PROBABILITY FILE: c:\asp\1989\pwrbpsll.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 1.3E-04 1.05+00 Event Identifier: 244/90-017
B- 108 loop 1.6E-05 3. 6E-01 loca 2A.E-06 4.3E-01 rt 2 .8E-04 1.2 E-01 rt /loop 0 .OE+00 1.OE+00 eme rg *power 2.9E-03 8.OE-01 afw 3.SE-04 2.6E-01 afw/emerg.power 5.OE-02 3.4E-0l mfw 1 .OE+00 7. OE-02 porv.or.srv.chall 4.OE-02 1.OE+O0 porv.or.srv.reseat 2.OE-02 1.1E-02 porv.or . rv. reseat/emerg.power 2 .OE-02 1.OE+00 seal. loca 2 .3E-01 1. OE+00 ep.rec(sl) 6.OE-O1 1. OE+00 ep .rec 8 .2E-03 1.OE+00 HPI 3.OE-04 > 1.OE+00 8.4E-O1 > 1.2E-01 Brench Model: 1.OF.3 Trein 1 Cond Prob: 1.OE-02 Unavailable Train 2 Cond Prob: 1 .OE-01 Unavailable Train 3 Cond Prob: 3.OE-01 Unavailable HPI (F/B) 3.OE-04 1.OE+00 8.4E-01 > 1.2E-01 1.OE-02 > 0.OE+00 Branch Model: 1.OF.3+opr Train 1 Cond Prob: 1.OE-02 Unavailable Train 2 Cond Prob: 1 .OE-0l Unavailable Train 3 Cond Prob: 3.OE-01 Unavailable hpr/-hpi 1.5E-04 1.OE+00 1.OE-03 porv.open 1.OE-02 1. OE+0O 4.OE-04 branch model file
- forced Minarick 08-06-1991 17 :33: 31 Event Identifier: 244/90-017