ML20161A152
| ML20161A152 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 06/09/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-017-00 | |
| Download: ML20161A152 (5) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.:
344/84-017 Event
Description:
Steam Generator Safety Valve Fails Open and Subsequent Reactor Trip Date of Event:
September 26, 1984 Plant:
Trojan EVENT DESCRIPTION Sequence The event began on September 26, 1984, just after a power distribu-tion flux map had been taken at power [_.500 MW(e)].
The control rods were in manual mode to facilitate rod repositioning to compensate for boron dilution and to achieve varying axial flux differences for the Cycle 7 physics testing program.
At 2208 h a plant computer alarm indi-cated low suction pressure (caused by a cracked bourdon tube in the suc-tion pressure transmitter) on the only operatingMFWP' pump.
When the control room personnel first started reducing turbine load by manually closing the control valves-, they noticed the mismatch between turbine demand and reactor power, which caused the RCS average temperature CTave) to increase.
They attributed this mismatch to the load runback.
The control room personnel failed to realize that RCS Taviý was not decreasing because the, control rods were ýin manual.
In.addition, SG pressure increased from --970 psig to the set point of the first set of safety valves (1170 psig)-on all four SGs.
At 2230 h, the oncoming crew informed the control room personnel that the safety valves were open.
It was also noticed that the "A" steam-line PORV was open 30% and that the steam pressure was -1130 psig in the S~s.
The PORV was later deter-mined to have, been set to relieve at 1260 psig instead of 1125 psig.
The PORV was closed and reactor temperature and pressure were re-duced so that the SRVs could close.
The "D" SRV remained open.
At about 2310 h, the shift maintenance mechanics tried unsuccessfully to force the "D" safety valve closed.
Reduction in reactor and turbine power was continued, and the turbine generator was taken off line at 2326 h. Level control problems in the "D" SG resulted in a reactor trip at 2329 h due to low-low level.
At 2335 h, the "D" saf ety valve re-seated when the SG pressure reached -890 psig.
Corrective Action The immediate corrective action was to reduce steam pressure to reseat the stuck-open steam-line safety valve.
Additional corrective actions were developed later and reported to NRC in separate corre-spondence.
Event Identifier: 344/84-017 D-1 80
Plant/Event Data Systems Involved:
Nonnuclear instrumentation system, secondary-side relief system Components and Failure Modes Involved:
failed to close Component Unavailability Duration:
NA Plant Operating Mode:
1 (50% power)
Discovery Method:
Operational event Reactor Age:
8.8 years Plant Type:
PWR Comments None MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate Secondary-side 1.0 SRV could not be closed release terminated
,given MFW success Secondary-side 1.0 SRV could not be closed release terminated given MFW failure Plant Models Utilized
.PWR plant Class C Event Identifier: 344/84-017 D-181
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 344/84-017 Event
Description:
S6 Relief Valve Fails Open and Subsequent Reactor Trip Event Date:
9/26/84 Plant:
Trojan INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator 1.0E+00 Probability CV TRANS Total 5
.4E-04 5
.4E-04 CD TRANS Total 1
IE-05 1
.E-05 ATWS TRANS Total 3
.OE-05 3
.OE-05 DOMINANT SEQUENCES End State: CV Conditional Probability:
109 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERII HPI End State: CD Conditional Probability:
126 TRANS -RT AFW MFW HPI (F/B) -SS.DEPRESS COND/MFW End State:
ATWS Conditional Probability-5.OE-04 3.8E-06 3.OE-05 Event Identifier: 344/84-017 D-182
128 TRANS RT SEQUENCE CONDITIONAL PROBABILITIES Sequence End State Prab N Rec**
101 TRANS -RT -AFW PORV.OR.SRV.CHALL -PORV.OR.SRV.RESEAT SS.RELE AS.TERM HPI 103 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP R/-HPI -SS.DEPRESS LPR/-HPI.HPR 109 TRANS -RT -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI 120 TRANS -RT AFW MFW -HPI(F/B) -HPR/-HPI PORV.GPEN -SS.OEPRESS COND/MFW 123 TRANS -RT AFW MFW -HP! (FIB)
HPR/-HPI -SS.DEPRESS COND/MFW 124 TRANS -RT AFW MFW
-HP!CF/B)
HPR/-HPI SS.DEPRESS 126 TRANS -RT AFW MFW HP! (F/B) -SS.DEPRESS COND/MFW 127 TRANS -RT AFW MFW HPI (F/B)
SS.DEPRESS 128 TRANS RT CV CD CV CD 2.1E-05 5.2E-01 1.1E-06 2.8E-02 5.OE 04
- 5.2E-01 8.7E-07 3.9E-02 CO CD CD CO ATWS 3.8E-06 4.2E-07 3.BE-06
- 4.2E-07 3.OE-05
- 2.2E-02 6.5E-02 2.OE-02 6.OE-02 1.2E-01
- dominant sequence for enid state
- 1non-recovery credit for edited case' MODEL:
DATA:
b
- \\pwrbtree.cmp b :\\tr~ojprob.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS LOOP LOCA RT RT/LOOP EMERS.POWER AFW AFW/EMERS.POWER MFW PORV.OR.SR V.CHALL PORY.OR.SRV.RESEAT PORY.OR SSRV.RESEAT/EMER6.POWER SS.RELEAS.TERM Branch Model:
1.OF.1 Train 1 Cond Prob:
69.RELEAS.TERM/-MFW' Branch Model:
1.OF.1 Train I Cond Prob:
Event Identifier: 344/84-017 1.OE-03 2.3E-05 4.2E-06 2.5E-04 0.OE+00 2.9E-03 2.5E-03 5.0E-_02 I. OE+00 4.OE-02 2.OE-02 2.OE-02 1.5E-02 > 1.0E+00 1.5E-02 > Failed 1.5E-02 > 1.0E+00 1.5E-02 > Failed 1.OE+00 3.4E-01 3.4E-01 1.2E-01 1.0E+00 5.1E-01 3.4E-01 3.4E-01 3.4E-01 1.0E+00 5.OE-02 5
.OE-02 3.4E-01 > 1.OE+00 3.4E-01 > 1.0E+00 I>-1 83
HPI HPI (F/B)
HPR/-HPI PORY.OPEN SS.DEPRESS COND/MFW LPI /HPI LPR/-HPI.HPR LPR/HPI
- forced Minarick 04-12-1987 10:34 :2h Event Identifier: 344/84-017 1.OE-03 1
.0E-03 3
.0E-03 L.OE-02 3
.6E-02 I.OE400 I.0E-03 M.E-01 I.OE-03
.5.2E-01 5.2E-01 5.6E-01I I
.OE+00 1.OE+00 3.4E-01 3.E-01 I.OE+00 1.OE+00 4.E-02 4.OE-02 D-184