ML20161A173
| ML20161A173 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1987-020-00 | |
| Download: ML20161A173 (4) | |
Text
B-122 PRECURSOR DESCRIPTION SHEET LER No.: 382/87-020 Event
Description:
Reactor trip 'with partial loss of both main and emergency feedwater Date of Event: 7/31/87 Plant: Waterford 3 EVENT DESCRIPTION Sequence With the reactor at 100% power, operations personnel began isolat-ing main condenser waterbox C2 for cleaning of the circulating water inlet box. As the C2 waterbox inlet isolation valve was shut, satura-tion pressure and temperature increased, causing a surge of condensate to the A and B hotwells where the condensate pump suction lines and hot-well level instrumentation are located. Observing alarms and wide fluctuations of hotwell level, the control room supervisor ordered power reduction by boration and unisolation of the C2 waterbox.
Before these steps could be initiated, the A main feed pump tripped on high-high level in its turbine casing drain tank, a result of increased B condenser pressure. On trip of the A main feed pump, a group of four control element assemblies did not drop as required on reactor runback (caused by a loose semiconductor connection in the reactor power cutback system). This caused a load differential between the primary and secondary system and resulted in reactor trip on high pressurizer pressure. While verifying plant response during the per-formance of the emergency entry procedure, an operator noticed that the A/B emergency feedwater pump had tripped on mechanical overspeed and could not be restarted.
Corrective Action Short-term corrective action was initiated to inspect the A/B EWF pump (no cause for the multiple trips) and the failed reactor power cut-back system component. Longer-term corrective action included revisions to procedures for isolating a waterbox and potential design changes allowing incremental closing of the waterbox inlet isolation valves and increased condenser instrumentation.
Plant/Event Data Systems Involved:
Main feedwater Emergency feedwater Reactor power cutback Event Identifier: 382/87-020
B-123 Components and Failure Modes Involved:
Main feedwater pump A - tripped on hotwell hi-hi level Emergency feedwater pump A/B - tripped on overspeed Control element essemblies - did not insert on demand due to failure in reactor power cutback system Component Unavailability Duration: N/A Plant Operating Mode: 1(100% power)
Discovery Method: Operational event Reactor Age: 2.4 y Plant Type: PWR Comments MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient No recovery assumed possible Branches Impacted and Branch Nonrecovery Estimate AFW Base case Turbine-driven train unavailable Plant Models Utilized PWR plant Class C Event Identifier: 382/87-020
B-124 CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 382/87-020 Event
Description:
Reactor trip with partial loss of emergency feedwat er Event Date: 07/31/87 Plant: Waterford 3 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS 1.0E+00 SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator Probability CD TRANS 1.5E-05 Total 1.5E-05 CV TRANS 2.7E-05 Total 2.7E-05 ATWS TRANS 3.4E-05 Total 3.4E-05 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)
Sequence End State Prob N Rec**
120 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open -ss.depress CD 1.3E-05 3.OE-02 cond/mfw 121 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open ss.depress CD 1.5E-06 8.8E-02 119 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open -ss.depress - CV 2.5E-05 5.8E-02 cond/mfw 109 trans -rt -AFW -porv.or.srv.chall ss.releas.term hpi CV 1.3E-06 2.9E-01 128 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**
109 trans -rt -AFW -porv.or.srv.chall ss.releas.term hpi CV 1.3E-06 2.9E-01 119 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open -ss.depress - CV 2.5E-05 5.BE-02 cond/mfw 120 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open -ss.depress CD 1.3E-05 3.OE-02 cond/mfw 121 trans -rt AFW mfw -hpi(f/b) -hpr/-hpi porv.open ss.depress CD 1.5E-06 8.8E-02 128 trans rt ATWS 3.4E-05 1.2E-01
- non-recovery credit for edited case SEQUENCE MODEL: c:\asp\newmodel\pwrgnew.cmp BRANCH MODEL: c:\asp\newmodeliwaterfd.new PROBABILITY FILE: c:\asp\newmodel\pwrbnew.pro No Recovery Limit Event Identifier: 382/87-020
B-125 BRANCH FREOUENCIES/PROBABILITIESi Branch System Non-Recov Opr Fail trans 4.8E-04 1.OE+00 loop 4.6E-06 3. 9E-01 loca 2.4E-06 4.3E-01 rt 2.8E-04 1.2E-01 rt/loop O.OE+OO I.OE+00 emerg .power 2. 9E-03 8.OE-01 ep.rec 1.OE+OO 1.7E-01 AFW 31.BE-04 > 2.3E-03 2.6E-01 Branch Model: l.OF.3+ser Train 1 Cond Prob: 2.OE-02 Train 2 Cond Prob: l.OE-Ol Train 3 Cond Prob: 5.OE-02 > Unavailable Serial Component Prob: 2.8E-04 afw/emerg .power 5.OE-02 3.4E-01 mfw 2.OE-O1 3.4E-01 porv.or.srv.chall 2. OE-02 1.OE+O0 porv.or. srv. reseat 1 .OE-O2 1.1E-02 porv.or. srv.reseat/emerg.power 1.OE-02 I.OE+00 ss. releas .term 1.5E-02 3.4E-01 ss.depress 3.6E-02 1.OE+00 cond/mfw l.OE+OO 3.4E-01 1.OE-02 hpi 3.OE-04 8.4E-01 hpi (f/b) 3.OE-04 8.4E-01 1.OE-02 porv .open 1.OE+OO 1.OE+00 O.OE+00 hpr/-hpi 1.5E-04 1.OE+00 csr 2.OE-03 3.4E-01
- branch model file
- forced Minarick 05-16-1989 07:01:46 Event Identifier: 382/87-020