ML20149K406
| ML20149K406 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-024-00 | |
| Download: ML20149K406 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.: 369/84-024 Event
Description:
LOOP at McGuire 1 Affects Unit 2 Date of Event: August 21, 1984 Plant: McGuire 1 EVENT DESCRIPTION Sequence At ~-2400 h on August 20, 1984, the McGuire switchyard computer was reported inoperable. On August 21, computer and inverter maintenance personnel performed corrective maintenance on the switchyard computer and static inverter. At 2114 h, the switchyard computer was restarted, checked for operability, and returned to service. At 2148 h, when the switchyard operator reenabled the computer control outputs, 30 power circuit breakers and associated disconnects opened, resulting in McGuire Unit 1 reactor trip and turbine trip, loss of Unit 1 offsite ac power,,
and startup of Unit 1 DGs A and B.
Unit 1 was in mode 1 at 100% power at the time and supplying steam to the Unit 2 MFWP turbines. Unit 2 was in startup at 0% power. The trip at Unit 1 also caused a loss of MFWP turbine steam at Unit 2.
This incident was classified as a component malf unct ion/f ai lure because the control circuits were changed to an undesirable state with-out a command from the computer, apparently during computer and inverter maintenance. A design deficiency also contributed because the computer program did not include a function to reset the computer-output control circuits to a predetermined state when the computer was restarted.
Corrective Action Corrective action was not stated in the LER.
Plant/Event Data Systems Involved:
Electrical and computer Components and Failure Modes Involved:
LOOP during operation Event Identifier: 369/84-024 D- 202
Component Unavailability Duration: NA Plant Operating Mode: Unit 1, mode 1 (100% power); Unit 2, mode 2 (0%
power)
Discovery Method: Maintenance Reactor Age: Unit 1, 3 years; Unit 2, 2.2 years Plant Type: PWR Comments Reference LER 370/84-020 MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP Base case Branches Impacted and Branch Nonrecovery Estimate None Plant Models Utilized PWR plant Class F Event Identifier: 369/84-024 D- 203
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 369/84-024 Event Descript ion. LOOP at Mc~uire 1 Affects Unit 2 Event Date: 8/21/84 Plant: McGuire I INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 3.4E-01 SEQUE NCE CONDITIONAL PROBABILITY SUMS End State/initiator Probability CV LOOP 2 .SE-06 Total 2 .8E-06 CD LOOP 1.7E-05 Total 1.7E-05 ATWS LOOP 0.OE+00 Total o.OE+O0 DOMINANT SEQUENCES End State: CV Conditional Probability: 2.4E-06 217 LOOP -RT/LOOP EMERG .POWER -AFW/EMERG .POWER -PORV .OR .SRV .CHALL SS .RELEAS .TERM End State: CD Conditional Probability: 8.4E-06 218 LOOP -RT/LOOP EMERG .POWER AFW/EMERG .POWER SEQUENCE CONDITIONAL PROBABILITIES Event Identifier: 369/84-024 D- 204
Sequence SeueceEnd State Prob N Rec**
203 LOOP -RT/LOOP -EMERG.POWER -AFW PORV.OR.SRY.CHALL PORV.OR.SR cv 2.7E-07 9.5E-03 V.RESEAT -HPI HPR/-HPI -SS.DEPRESS -LPRI-FfPI.HPR 204 LOOP -RT/LOOP -EMERG.POWER -AFW PORV.OR.SRY.CHALL PORV.OR.SR CD 5.5E-07 9.5E-03 V.RESEAT -HPI HPR/-HPI -SS.DEPRESS LPR/-HPI.HPR 212 LOOP -RT/LOOP -EMERG.POWER AFW -HPI(F/B) -HPR/-HPI PORYSOPEN CD 8.6E-07 9.2E-02 213 LOOP -RT/LOOP -EMERG-POWER AFW -HPI(F/B) HPR/-HPI CD 3.7E-06 5.1E-02 214 LOOP -RT/LOOP -EMERG.POWER AFW HPI(F/B) CD 3.8E-06 4.8E-02 215 LOOP -RT/LOOP EMERG.POWER -AFW/EMERS.POWER PORV.OR.SRV.CHALL Cv 9.9E-08 5.8E-02
-PORY .OR .SRV .RESEAT/EMERG SPOWER SS .RELEAS STERM 217 LOOP -RT/LOOP EMERG.POWER -AFW/EMERG.POWER -PORY.OR.SRV.CHALL Cv 2.4E-06
- 5.9E-02
- dominant sequence for end state
- non-recovery credit for edited case MODEL:- b:\pwrbtree.cmp DATA: b:\mcgurpro.cinp No Recovery Limit BRANCH FREQUENCIES/PROBABIL ITIES Branch System Non-Recov Opr Fail TRANS 1.OE-03 1.0E+00 LOOP 4.3E-05 3.4E-01 LOCA 4.2E-06 3.4E-01 RT 21.5E-04 1.2E-01 RT/LOOP 0.OE+00 1.0E+00 EMERS .POWER £ .9E-03 5.IE-01 AFW 1.0E-03 2.7E-01 AFW/EMERG .POWER 5.OE-02 3.4E-01 MFW 2.OE-01 3.4E-01 POR . OR .SR . CHALL 4.0E-02 1.0E+00 PORV .OR .SRY .RESEAT 3.OE-02 5.OE-02 PORY .OR SSRY .RESEAT/EMERG.POWER 3.OE-02 5.OE-02 55 .RELEAS.TR 1.5E-02 3.4E-01 SS .RELEAS .TERM/-MFW 1.5E-02 3.4E-01 HPI 1.OE-03 5.2E-01 HPI (F/B) I.OE-03 5.2E-01 4.OE-02 HPR/-HPI 3.OE-03 5.6E-01 4.OE-02 PORY .OPEN 1.OE-02 1.OE+00 SS .DEPRESS 3.6E-02 1.OE+00 COND/MFW 1.0OE+00 3.4E-01 LPI/HPI 1.OE-03 3.4E-01 LPR/-HPI .HPR 6.7E-01 1.0E+00 Event Identifier: 369/84-024 D- 205
.OE-03 I.OE+00
- forced Minarick 04-12-1987 10:53:42 Event Identifier: 369/84-024 D- 206