ML20147A339
| ML20147A339 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 02/14/1983 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1983-007-00, LER 1983-011-00, LER 1983-012-00 | |
| Download: ML20147A339 (5) | |
Text
B.45-1 B.45 LER No. 368/83-007, -011, and -012 Event
Description:
Transient with One Train of EFW Inoperable Date of Event: February 14, 1983 Plant: ANO 2 B.45.1 Summary On February 22, 1983, emergency feedwater (EFW) turbine-driven pump 2P-7A would not attain rated speed or discharge pressure during surveillance testing. A plant trip had occurred on February 14 (NUREG-0020).
Between February 3 and February 18, several EFW system valve failures also occurred. The estimated conditional core damage probability for this event is 4.1 x 10-5.
B.45.2 Event Description On February 3, 1983, during power operations, the hydraulic pump for the operator for the EFW control valve 2CV- 1075-1 was determined to be in need of replacement during the performance of preventive maintenance.
On February 4 and 17, 2CV-1075-1 failed to close when attempts were made to decrease flow to steam generator B. The failure of 2CV- 1075-1 to close on the 17th of February was attributed to improperly set manifold block relief valves. The relief valve settings were lower than 1000 psi, which caused the relief valves to be challenged by the normal hydraulic operating pressure.
On February 18,1983, while in Mode 3 with pump 2P-7B feeding the steam generators, control valve 2CV-1036 failed to close. Control valve 2CV-1075-1 was inoperable for repairs. The ability to feed the steam generators with pump 2P-7B through a cross-connect through valves 2EFW-11B and 2EFW-8A was maintained. Investigation revealed that the failure of the valve to close was due to a shorted relay coil which caused the control power fuse in control panel 2C-17 for 2CV-1036 to open. Both the relay and fuse were replaced.
On February 22, 1983 while in Mode i, the steam-driven EFW pump 2P-7A would not attain rated speed or discharge pressure during a surveillance test. The cause was attributed to setpoint drift in the speed controller.
The converter gain on the speed controller was adjusted so the pump would run at the desired speed.
B.45.3 Additional Event-Related Information The EFW system at Arkansas Nuclear One (ANO) I is a two-train system. One motor-driven (2P-7B) and one turbine-driven pump (2P-7A) provide coolant flow to two steam generators (A and B). Successful accident mitigation under most circumstances requires the use of one pump supplying water to one steam generator.
Control valves 2CV-1075-1 and 2CV-l1036 allow pump 2P-7B to supply coolant to steam generator B. There are two separate flow paths for pump 2P-7B to supply coolant to steam generator B (through 2CV-1075-1 and 2CV-1036 or through 2EFW-I lB and 2EFW-8A).
LER No. 368/83-007, -011, and -012
B.45-2 B.45.4 Modeling Assumptions A plant trip occurred on February 14, 1983. Assuming that both valves and EFW pump 2P-7A would have been inoperable at the time of the trip, this event was modeled as a transient with one train (the turbine-driven train) of EFW failed. Since pump 2P-7B could still supply both steam generators with both control valves failed, it was assumed that train B would still function as needed. To reflect the inoperability of the turbine-driven pump, one train of EFW was set to failed. EFW/anticipated transient without scram (ATWS) was also set to failed to reflect the fact that only one pump remained operable, and flow from two pumps is required for mitigation given ATWS.
B.45.5 Analysis Results The estimated conditional core damage probability for this event is 4.1 x 10'. The dominant sequence highlighted on the event tree in Figure B.45.1 is an ATWS sequence involving the failure to trip, and the failure of EFW given ATWS.
LER No. 368/83-007, -011, and -012
B.45-3
~
w 0 ~00
~1-NCOv c O Wr, O ctw O,.
CL0>L Cn OL
~ O O to L O
O L LU z
wcjU) 1- 0 0 0 0 Figure B.45.1 Dominant core damage sequence for LER 368/83-007, -011, and -012 LER No. 368/83-007, -011, and -012
B.45-4 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 368/83-007, -011, and -012 Event
Description:
Transient with one train of EFW inoperable Event Date: February 14. 1983 Plant: AND 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS I.OE+O0 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 4.1E-05 Total 4.1E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
508 trans rt -prim.press.limited AFW/ATWS CD 2.BE-05 I.OE-O1 121 trans -rt AFW mfw feed.bleed CD 1.3E-05 1.5E-01
- non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)
Sequence End State Prob N Rec**
121 trans -rt AFW mfw feed.bleed CD 1.3E-05 1.5E-01 508 trans rt -prim.press.limited AFW/ATWS CD 2.8E-05 I1OE-OI
- non-recovery credit for edited case SEQUENCE MODEL: c:\aspcode\models\pwrg8283.cmp BRANCH MODEL: c:\aspcode\models\ano2.82 PROBABILITY FILE: c:\aspcode\models\pwr8283.pro No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail trans 2.4E-03 1.OE+00 loop 1.6E-05 3.6E-01 loca 2.4E-06 5.4E-01 LER No. 368/83-007, -011, and -012
B.45-5 sgtr 1.6E-06 1.OE+/-00 rt 2.8E-04 I.QE-01 rt(loop) 0.OE+00 1.OE+/-00 AFW 1.3E-03 > 2.OE-02 4.5E-01 Branch Model: 1.OF.2+ser Train I Cond Prob: 2.OE-02 Train 2 Cond Prob: 5.OE-02 > Failed Serial Component Prob: 2.8E-04 AFW/ATWS 7.OE-02 > 1.OE+00 1.OE+/-00 Branch Model: 1.OF.1 Train 1 Cond Prob: 7.OE-02 > Failed AFW/EP 5.OE-02 3.4E-01 mfw 2.OE-01 3.4E-01 porv.chall 4.OE-02 1.OE+00 porv.chall/afw 1.OE+00 1.OE+00 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) LDE-0l 1.OE.00 hpi 3.OE-04 8.9E-01 feed.bleed 1.OE-02 1.OE+00 1.CE-02 emrg.boration 0.0 E+00 1.OE+00 1.CE-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.CE-03 rhr 3.1E- 02 7.0E-02 1.CE-03 csr 4.OE -03 1.0E+00 1.CE-03 hpr 1.5E-04 1.OE+00 ep 2.9E-03 8.9E-01 seal.loca 4.OE-02 1.OE+00 offsite.pwr.rec/-ep.and.-afw 2.1E-01 1.OE+00 offsite.pwr.rec/-ep.and.afw 9.9E-02 1.OE+00 offsite.pwr.rec/seal.loca 5.9E-01 1.OE+00 offsite.pwr.rec/-seal.loca 2.1E-02 1.OE+00 sg.iso.and.rcs.cooldown l.OE-02 iCE-0l rcs.cool.below.rhr 3.OE-03 1.OE+00 3.OE-03 prim.press.limited 8.8E-03 L.OE+00
- branch model file
- forced LER No. 368/83-007, -011, and -012