ML20149K391
| ML20149K391 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 05/28/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1984-011-00 | |
| Download: ML20149K391 (6) | |
Text
PRECURSOR DESCRIPTION SHEET LER No.:
409/84-011 Event
Description:
LOOP with DG Failure to Load and Associated HPCS-Unavailability Date of Event:
July 16, 1984 Plant:
LaCrosse EVENT DESCRIPTION Sequence At 1750 h while in hot shutdown, the potential *transformer in. the switchyard shorted out during a storm, causing breakers to open and resulting in an LOOP.
Although both EDGs started, the 1B EDO output breaker, 452 EGB, did not close, leaving the 1B essential bus without power.
The breaker could not be closed using the control switch in the control room.
When offsite power was regained at 1810 h, the, 1B essential bus could not be energized.
A successful attempt was made to close the lB EDG output breaker locally, which reenergized the 1B essential bus.
The normal alignment was then tried with 452-52B, the normal feed breaker, closed and 452 EGB open.
This also worked.
The 1B EDG was then re-turned to "auto."
Breaker 452-52B immediately tripped open,,ieaving the bus deenergized again. Breaker 452 EGB did not close.
Only placing~the lB EDG control switch to Off allowed breaker 452-52B to be closed, re-energizing the bus.
This action was completed at -1915 h.
At 1920 h the operating crew attempted to start HPCS Pump 1B but could not.
The 1A HPCS pump, which was tagged out, was checked to see if maintenance were in progress.
Because the pump appeared intact, the tags were cleared at 2000 h, and the 1A HPCS pump started.
At -~0350 h a static inverter annunciated because of decreased input voltage.
The input breaker to the diesel building battery, charger was open and probably had been since the power transient.
An overvoltage trip probably actuated during the electrical transient before the pro-tective devices operated.
The breaker was closed.
Event Identifier:
409/84-O11 D-250
Corrective Action Troubleshooting was conducted on the 1B EDG output breaker.
A blown fuse was found in the control power circuit for 452 EGB.
The breaker's 'spring release coil, which allows the breaker to close, was found burnt out.
This could have caused the fuse to blow.
The coil and fuse were replaced.
Further troubleshooting led to the discovery that two of four primary fuses for the undervoltage potential transformer on LB essential bus were also blown.
The breaker was bench tested; and the toggle rolinut, which knocks the latch off center during the closing cycle, was lubricated.
At 1801 h on July 17, a successful breaker test, which checked the diesel s.8tart ing and 1B essential bus loading on an undervoltage con~di-tion,,was performed.
Following additional successful tests of the system on July 18, it was determined that during the loss of power, the 1B EDG output breaker received a closing signal but did not close.
The spring release coil burnt out because of the sustained closure signal, which, in turn, caused the control power circuit fuse to blow.
The two undervoltage fuses on the 1B essential bus blew during the electrical transient.
These fuses did not affect the closing ability of the 1B EDG output breaker but did simulate the existence of an undervoltage con di-tion on the bus.
Bus undervoltage logic prevents HPCS pump starting if an under-voltage condition exists, or existed, on the essential bus until af,ter the EDG output breaker closes, which clears the undervoltage signal.
The blown undervoltage fuses continued to simulate an undervoltage-con-dition on the bus after power was restored, precluding closure of the HPLCS pump breaker.
A generator plant 125-V-dc ground alarm had annunciated during LOOP and had not cleared when power was restored.
The ground was traced to the closing circuit of breaker 452 MIB, the lB 480-V bus main feed breaker.
While offsite power was disconnected on July 18, this breaker and its circuitry were examined; no problems were identified.
The ground did not return when the circuit was reenergized.
Plant/Event Data Systems Involved:
Emergency power, SI Event Identifier:
409/84-011 D-251
Components and Failure Modes.Involved:
"1B" DG breaker -
failed to close on demand "lA" SI pump
-failed on demand Component Unavailability Duration:
NA Plant Operating Mode:
3 (0% power)
Discovery Method:
Operational event Reactor Age:
17 years Plant Type:
BWR Comments The LaCrosse high-pressure safety injection system consists of two trains of high-pressure core spray pumps driven by two trains of dedi-cated power supplies.
MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate LOOP Base case Branches Impacted and Branch Nonrecovery Estimate Emergency power Base case Base case Degraded; one train failed HPCS The train in maintenance was assumed recoverable locally Plant Models Utilized Specialized model for LOOP at LaCrosse Event Identifier:
409/84-011 D-252
CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 409/84-011 Event
Description:
LOOP and OS Failure to Load and Associated HPCS Unavailability Event Date:
7/16/84 Plant:
LaCrosse INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP SEQUENCE CONDITIONAL PROBABILITY SUIMS' End State/Initiator 3.4E-01 Probability CD LOOP Total 9.9E-04 9.9E-04 CV LOOP Total 0.OE+00 0.0E+00 ATWS LOOP Total 5.5E-05 5.5E-05 DOMINANT SEQUENCES End State:
CD Conditional Probability:
205 LOOP -EMERG.POWER -SCRAM HPCS HPSW End State:
ATWS Conditional Probability:
207 LOOP -EMERS.POWER SCRAM HPCS SEQUENCE CONDITIONAL PROBABILITIES 5
.6E-04 4.6E-05 Event Identifier: 409/84-011 D-253
Sequence SeueceEnd State Prob N Rec**
202 LOOP -EMERS.POWER -SCRAM HPCS -HPSW -SRV.CLOSE SHUTDOWN.COND ENSER MANUAL.DEPRESS 204 LOOP -EMERG.POWER -SCRAM HPCS -HPSW SRV.CLOSE MANUAL.DEPRES S
CD CD 1.3E-04 1.1E-0l 1.3E-04 1.1E-01 205 206 207 210 211 212 LOOP LOOP LOOP LOOP LOOP LOOP
-EMERG.POWER
-EMER6.POWER
-EMERG.POI'ER EMERS.POWER EMERS.POWER EMERG POWER
-SCRAM HPCS HPSW SCRAM -HPCS SLC.OR.RODS SCRAM HPCS
-SCRAM -HPSW SRV.CLOSE
-SCRAM HPSW SCRAM CD ATWS ATWS CD CD ATWS 5.6E-04
- 4.4E-06 4.6E-05
- 9.8E-05 4.9E-05
- 4. 1E-06 1.1E-01 2.2E-01 1.1E-01 1.7E-01 1.7E-01
- 1. 7E-0 I
- dominant sequence for end state
- 1non-recovery credit for edited case MODEL:
b \\l actree.cmp DATA:
b:-\\lacprob.cmp No Recovery Limit BRANCH FREQUENCIES/PROBABILITIES Branch System Non-Recov Opr Fail TRANS LOOP LOCA SCRAM SLC.OR.RODS EMERG.POWER Branch Model:
1.OF.2 Train 1 Cond Prob:
Train 2 Cond Prob:
FW HPSW SHUTDOWN.CONDENSER HPCS Branch Model: 1.OF.1 Train 1 Cond Prob:
LPCS SRY.CLOSE DH MANUAL.DEPRESS 1.1E-03 1.3E-05 3.3E-06
- 4. 1 E-04 I.OE-02 2.9E-03 > 5.7E-02 5.OE-02 > Failed 5
.7E-02 1
.OE-01 5
.OE-03 I
.OE-02 5.OE-03 > 1.OE+00 5.OE-03 > Unavailable 1.OE-03 1.OE-02 I
.OE-02 1
.2E-01 1.OE+00 3.4E-01 3.4E-01 1.OE+00 1
.OE+00 5.1IE-01 3.4E-01 1.OE+00 1.OE+00 1.0E+00 > 3.4E-01 1.OE+00 1.OE+00 1
.OE+00 1.OE+00 4.OE-02 forced Event Identifier: 409/84-011 D-254
Minarick 04-12-1987 12 :46:30 Event Identifier: 409/84-011 D-255