ML20149K492
| ML20149K492 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1985-012-00 | |
| Download: ML20149K492 (5) | |
Text
PRECURSOR DESCRIPTION AND ANALYSIS LER No.: 219/85-012 Rev. 0 Event
Description:
MSIV Closure and Scram with Subsequent SDV Isolation Problems Date of Event: June 12, 1985 Plant: Oyster Creek 1 EVENT DESCRIPTION Sequence During power operation, failure of the plant's electric pressure regulator (EPR) resulted in a decrease in reactor pressure, which then initiated automatic closure of the MSIVs. MSIV closure automatically initiated a reactor scram. Several failures occurred in the ensuing transient.
The scram discharge volume (SDV) did not fully isolate, resulting in overheating of equipment downstream of the SDV, evolution of steam and paint fumes, and activation of the deluge fire system. The deluge had the potential to render other safety-related systems inoperable, but this equipment (unspecified in LER) was verified operable either during or shortly after the event. Scram could not be reset until reactor pressure was reduced to <600 psig.
The control room operator raised- reactor water level by the feedwater system to compensate for reactor level shrink that accompanied the initial pressure drop. That combined with feedwater'in-leakage resulted in high level and prevented determination of how high the level was.
Thus, use of the isolation condensers to control pressure early in the transient was precluded to prevent water hammer.
While attempting to place the Reactor Water Cleanup System (RWCS) in service to lower reactor water level, an RWCS isolation valve failed to open. The electromatic relief valves (ERV) were then used to control pressure until the RWCS could lower water level sufficiently to operate the isolation condensers. Reactor pressure was reduced, the scram sig-nal was reset and the, plant was placed in cold shutdown. The contain-ment spray system was successfully initiated during use of the ERVs.
Corrective Action Repairs to the EPR, the faulted SDV valves, and the RWCS valve were completed before plant startup. The EPR filtration system was reviewed for possible improvements to prevent recurrence of the EPR because of impurities. An investigation was conducted to determine why a closing spring in one of the two failed SDV valves was improperly sized.
Event Identifier 219/85-012 E-2 1
Plant/Event Data Systems Involved:
Reactor scram, isolation condenser, reactor isolation, RWCS, operator Components and Failure Modes Involved:
South SDVs - fail to close on demand One RWCS valve - failed to open on demand Isolation condensers - unavailable because of operator error EPR - failed during operation (initiator)
Component Unavailability Duration: NA Plant Operating Mode: 100% power Discovery Method: During operation Reactor Age: 16.11 years - Criticality Date: 5/3/69 Plant Type: BWR Comments Trip plus multiple train failures MODELING CONSIDERATIONS AN~D DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate Power conversion 1.0 Because of MSIV closure system Isolation condensers 0.05 0.04 for operator to restore because they had been isolated in the event, plus 0.01 for equipment failure probability CRD cooling 1.0 With leakage from the RCS, the CED pumps assumed inadequate for makeup, given loss of feedwater flow Plant Models Utilized BWR plant Class A model Event Identifier: 219/85-0 12 E-2 2
COY' ITIONAL CORE DAMAGE CALCULATIONS LER Number: 219/B5-012 Event
Description:
MSIV Closure -and Sr ram with Subsequent SDV Isolation Problems Event Date: 1112/85OF Plant: Oyster Crepik INITIATING EVENT/
NON-RECOVERABLE IN]TIATIjWG EVENT PROBABILITIES TRANS 1.000E+00 SEQUENCE' CONDITIONAL PROBABILITY SUMS End Sta~te/Initiator Probability CD TRANS 2.284E-04 Total 2.2 84E-04 CV TRANS 3.664E-05 Total 3.664E-05 AIWS TRANS 2.034E-05 Total 2.034E-05 DOMINANT SEQUENCES End State: CD Conditional Probability: 2.261E-04 108 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM -SRV.CLOSE ISOL.COND FW/PCS.TRANS FWCI/FW.TRANS CRD SRV. ADS End State: CV Conditional Probability: 2.401E-05 127 TRANS SCRAM -SLC.OR.RODS PCS/TRANS FN/PCS.TRANS FWCI/FW.TRANS -SRV.ADS -COND/FW.PCS -SDC End State. ATWS Conditional Probability: 2.034E-05 Event Identifier: 219/85-012 E-2 3
1414 TRANS SCRAM SLC.OR.RODS SEQUJENCE CONDITIONAL PROBABILITIES Sequence End State Seg. Prob Non-Recov~l 108 TRANS -SCRAM PCS/TRANS SRV.CHALL/TRANS.-SCRAM -SRV.CLOSE IS COD\ 2.261E-04 I 5.256E-02 OL.COND FW/PCS.TRANS FWC]/FW.TRANS CR0 SRV.ADS 127 TRANS SCRAM -SLC.OR.RODS PCS/TRANS FW/PCS.TRANS FWCI/FW.TR CV 2>#1'JE-05 I 2.05SE-0l ANS -SRV.ADS -CONO/FW.PCS -SOC 131 TRANS SCRAM -SLC.OR.ROOS PCS/TRANS FW/PCS.TRANS FWCIIFW.TR CV 1.237E\05 1.060OE-01 ANS -SRV.ADS COND/FW.PCS -LPCS -SOC 141 TRANS SCRAM SLC.OR.RODS ATWS 2.034E-05, 1 2.IBIE-Ol I dominant sequence for end state tt non-recovery credit for edited Ease Note:
Conditional probability values are differential values which reflect the added risk due to observed failures.
Parenthetical values indicate a reduction in risk compared to a similar period without the existing failures.
MODEL: A:bwratree. cap DATA- A:ocprob.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS 1.142E-03 1.O0OE+00 LOOP 1.305E-05 3.400E-01 LOCA 3.250E-06 3.400E-01 SCRAM 4.IOOE-04 1.C'OOE+00 SLC.OR.RODS 1.OO0E-02 1.OOOE+00 4. DOOE-02 PCSITRANS 1.700E-01 > 1.000E+00 1.000E+00 Branch Model: I.OF.1 Train 1 Cond Prob: 1.700E-01 > Failed PCSILOCA 1.OO0E+00 1.OOOE+00 SRV. CHALL/TRANS. -SCRAM l.000E+00 1.OOOE+00 SRV.CHALL/TRANS. SCRAM 1.OOOE+00 1.OOOE+00 SRV.CHALL/LOOP.-SCRAM 1.OOOE+00 1.OOQE+00 SRV. CHALL/LOOP. SCRAM 1.OOOE+00 1.O0OE+00 SRV. CLOSE 1.200E-02 1.OOOE+00 EMERG. POWER 2.850E-0.3 5. IOOE-01 FW/PCS. TRANS I.000OE+00 1.OOOE+OC:
FW/PCS. LOCA 1.000OE+00 1.000E+00 ISOL.COND l.000E-02 > 5.OOOE-02 *11 1.OOOE+00 Branch Model: 1.OF.1 Event Identifier: 219/85-012 E-24
Train 1 Cond Prob: 1.OOOE-02 FWCI/FW. TRANS 2.900E-01 3.400E-01 FWCI/LOOP 1. O0OE+00 1.OOOE+00 FWCI/FW. LOCA 1.OOOE-03 3. 400E-01 CR0 1.000E-02 > 1.000E+60 1.OOOE+00 4. OOOE-02 Branch Model: 1.OF.1+opr Train 1 Cond Prob; 1.OOOE-02 > Unavailable SRV. ADS 6.700E-03 1.000E+00 4.OOOE-02 COND/FW. PCS 1.000E+00 3. 400E-01 LPCS 3.OOOE-04 3. 400E-01 FIREWTR. DR.OTHER/LPCS. TRANS 1.000E+00 1. OOOE+00 FIREWTR. OR. OTHER/LPCS. LOOP 1.OOOE+00 1.OOOE+00 FIRE WTR. OR. OTHER/LPCS. LOCA I.OOOE+00 1.OOOE+00 SOC 2. 088E-02 3.400E-01 CC/SOC 1.OOOE-03 1.000E+00 C.I.AND.V 1.000OE+00 It$ forced Austin 08-12-1986 13:48:58 Event Identifier: 219/85-012 E-2 5