ML20149K489
| ML20149K489 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-011-00 | |
| Download: ML20149K489 (5) | |
Text
B.14-1 B.14 LER No. 287/83-011 Event
Description:
Loss of Feedwater Transient with One EFW Pump Inoperable Date of Event: October 13, 1983 Plant: Oconee 3 B.14.1 Summary On October 13, 1983, following a loss of main feedwater, the 3B motor-driven emergency feedwater (EFW) pump started. Approximately 30 minutes later, it was discovered that there was no low pressure service water (LPSW) flow through the 3B EFW pump due to a failed solenoid valve. The pump was declared inoperable.
The estimated conditional core damage probability for this event is 3.2 x 10'.
B.14.2 Event Description On October 13, 1983, following a loss of main feedwater (MFW) caused by a loss of instrument air pressure, the 3B motor-driven EFW pump emergency started. Approximately 45 minutes later, it was discovered that no LPSW was flowing through the 3B EFW pump. The pump was shut down and declared inoperable.
Investigation revealed that the solenoid that operates 3B EFW motor cooler outlet valve 3SV-203 had failed.
The outlet valve did not open when the pump was started. The plunger of valve 3SV-203 was found to be stuck. The valve was replaced and the 3B EFW pump was declared operable the next day. To help identify low LPSW flow to the EFW pumps, the computer points for flow were to be changed to provide an alarm if flow is low while the pumps are running.
On October 18, 1983, an additional problem was found related to the 3B EFW pump. While operating at 100% power, a performance test on 3B EFW pump was performed. Feedwater valve 3FDW-382 was closed per procedure. Upon completion of the test, the valve was reopened by placing the valve position switch to its normally open position in the control room. The control panel indicated the valve was open when it was only partially open. Visual inspection of the valve during the next shift revealed that the valve was only 10%
open. Attempts to close the valve from the control room failed, and the valve and the pump were declared inoperable. The direct cause was unknown, but the valve was successfully cycled from the control room approximately 40 minutes later. This event was reported in LER 287/83-012.
B.14.3 Additional Event-Related Information Oconee 3 has a three-train EFW system. Two trains have motor-driven EFW pumps (3A and 313). Each motor-driven pump is aligned to one steam generator. The third train has a turbine-driven pump which is aligned to both steam generators. In the event that main feedwater is lost, the EFW pumps provide secondary side cooling to the steam generators. One pump delivering flow to one steam generator provides sufficient secondary side cooling in the event that main feedwater is lost and the reactor has tripped. LPSW provides LER No. 287/83-011
B.14-2 motor cooling to both motor-driven EFW pumps and turbine jacket cooling and bearing oil cooling for the turbine-driven EFW pump.
B.14.4 Modeling Assumptions The event was modeled as a transient with loss of MFW and one motor-driven EFW pump inoperable because of the loss of LPSW cooling. The valve failure reported in LER 287/83-012 was assumed not to further impact the EFW system during the loss of feedwater. MFW was set to failed to reflect the loss of feedwater. Because of the loss of instrument air pressure, MFW was assumed to be nonrecoverable. In revising the EFW system failure probability, it was assumed that the type of valve fault observed on pump 3B could also have affected the motor-driven pump 3A. The potential for common cause failure exists, even when a component is failed.
Therefore, the conditional probability of a common cause failure was included in the analysis for those components that failed as part of the event.
B.14.5 Analysis Results The estimated conditional core damage probability for this event is 3.2 x 10'. The dominant sequence, highlighted on the event tree in Figure B. 14.1, involved a plant trip with the failure of EFW, the failure of MFW and the failure of feed and bleed.
LER No. 287/83-011
B.14-3 00 N8 M8 8 8ý! v ý t ýe : ý? Cn LU W in a-CL M
w03 08)0 ca.
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0 (n I-(0 zL Figure B. 14.1 Dominant core damage sequence for LER 287/83-011.
LER No. 287/83-011
B.14-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 287/83-011 Event
Description:
LOFW transient with one EFW pump inop Event Date: October 13. 1983 Plant: Oconee 3 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.OE+OO SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 3.2E-05 Total 3.2E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
120 trans -rt AFW MFW feed.bleed CD 2.4E-05 4.5E-01 508 trans rt -prim.press.limited AFW/ATWS CD 4.2E-06 1.0E-B1 119 trans -rt AFW MFW-feed.bleed recov.sec.cool hpr CD 2.3E-06 4.5E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
119 trans -rt AFW MFW-feed.bleed recov.sec.cool hpr CD 2.3E-06 4.5E-01 120 trans -rt AFW MFW feed.bleed CD 2.4E-05 4.5E-01 508 trans rt -prim.press.limited AFW/ATWS CD 4.2E-06 1.0E-01
- non-recovery credit for edited case SEQUENCE MODEL: d:\asp\models\pwrb8283.cmp BRANCH MODEL: d:\asp\models\oconee3.82 PROBABILITY FILE: d:\asp\models\pwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 2.4E-04 1.OE+O0 loop 1.6E-05 2.4E-01 loca 2.4E-06 5.4E-01 LER No. 287/83-011
B.14-5 sgtr 1.6E-06 1.OE+00 rt 2.8E-04 1.OE-01 rt(loop) 0.0 E+00 1.OE+00 AFW 3.8E-04 > 5.3E-03 4.5E-01 Branch Model: 1.OF.3+ser Train 1 Cond Prob: 2.OE-02 > 1.0E+00 Train 2 Cond Prob: 1.OE-01 Train 3 Cond Prob: 5.OE-02 Serial Component Prob: 2.8E-04 AFW/ATWS 4.3E-03 > 1.5E-01 1.OE+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 4.3E-03 > 1.5E-01 afw/ep 5.OE-02 3.4E-01 MFW 2.OE-01 > 1.OE+00 3.4E-01 > 1.OE+00 Branch Model: 1.OF.1 Train 1 Cond Prob: 2.OE-01 > 1.OE+00 porv.chall 8.OE-02 1.OE+00 porv.chall/afw 1.QE+00 1.OE.-OO porv.chall/loop 1.OE-01 1.OE+00 porv.chall/sbo 1. OE+00 1.OE+00 porv.reseat 1.OE-02 1.1E-02 porv.reseat/ep 1.OE-02 1.OE+00 srv.reseat(atws) 1.OE-01 1.OE+00 hpi 3.OE-04 8.9E-01 feed.bleed 3.OE-04 1.OE+00 1..1OE-02 emrg.boration 0.OE+00 1.OE+00 1.QE-02 recov.sec.cool 2.OE-01 1.OE+00 recov.sec.cool/offsite.pwr 3.4E-01 1.OE+00 rcs.cooldown 3.OE-03 1.OE+00 1.OE-03 rhr 2.2E-02 5.7E-02 1.OE-03 rhr.and.hpr 1.OE-03 1.OE+00 1.OE-03 hpr 4.OE-03 1.OE+00 1.OE-03 ep 6.OE-04 8.9E-01 seal.loca 0.OE+00 1.OE+00 offsite.pwr.rec/-ep.and.-afw 2.7E-01 1.OE+00 offsite.pwr.rec/-ep.and.afw 1.6E-01 1.OE+00 offsite.pwr.rec/seal.loca 0.OE+00 1.OE+00 offsite.pwr.rec/-seal loca 4.5E-01 1.OE+00 sg.iso.and.rcs.cooldown 1.OE-02 1.OE-01 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. 287/83-011