ML13190A465

LER 12-002-01 for Oyster Creek, Unit 1, Regarding Loss of Offsite Power During Hurricane Sandy

ML13190A465
Person / Time
Site:
Issue date:	06/26/2013
From:	Peak R R Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 12-002-01
Download: ML13190A465 (4)

Text

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10/31/2013 (10-2010)

Estimated burden per response to comply with this mandatory collection request:

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Send comments regarding burdenestimate to the FOIA/Pdvacy Section (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail toinfocollects.resource@nrc.gov, and to the Desk Officer, Office of Information LICENSEE EVENT REPORT (LER) and Regulatory

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1. FACILITY NAME 2. DOCKET NUMBER 3. PAGEOyster Creek, Unit 1 05000219 1 OF 34. TITLELoss of Offsite Power During Hurricane Sandy5. EVENT DATE 6. LER NUMBER 7. REPORT DATE 8. OTHER FACILITIES INVOLVEDRFACILITY NAME DOCKET NUMBERMONTH DAY YEAR YEAR SUE REV MONTH DAY YEAR N/A N/AM O T_ D Y Y AR Y A NUM BER NO. _ _ _ _____ __FACILITY NAME DOCKET NUMBER10 29 2012 2012 -002 01 06 20 2013 N/A N/A9. OPERATING MODE 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)[1 20.2201(b)

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Specify in Abstract belowor in NRC Form 366A12. LICENSEE CONTACT FOR THIS LERMikeILI NAMcEn e rMike McKenna, Regulatory Assurance ManagerI TLEPH IOIUMBER (InclIuoe Area LCode)(609) 971-4389[E YES (If yes, complete

15. EXPECTED SUBMISSION DATE),BSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)At 20:18 on October, 29, 2012, while the reactor was in the Cold Shutdown Condition during a planned refueling outage, Oyster Creek experienced a Loss of Offsite Power (LOOP) event. The LOOP resulted in a valid automatic actuation signal for both the Emergency Diesel Generators (EDGs) to start, a valid Reactor Protection System (RPS)actuation with automatic containment isolations, and a trip of Shutdown Cooling to the reactor.

Shutdown Cooling wasexpeditiously

restored, following the initial EDG loading sequence, with electrical power from the EDGs.The primary cause of the LOOP is attributed to equipment damage caused by the winds associated with Hurricane Sandy. Prior to reactor startup from the Refueling Outage, Oyster Creek verified that all required electrical distribution power lines and equipment required by Technical Specifications were available,

operable, and functioning as required.

There were no Emergency Plan (EP) Emergency Action Levels (EALs) applicable for this event.A detailed investigation was performed and found that the root cause of this event was a wall falling in the switchyard causing a ground fault on the 34.5KV system. Contributing to this event was a stuck breaker which allowed the groundfault to propagate to the 34.5KV system resulting in a local loss of the 34.5KV system. To prevent recurrence, the wallwas removed and a stuck breaker modification was performed.

This event is being reported pursuant to 1OCFR50.73(a)(2)(iv)(A) due to automatic actuation of the EDGs, RPSactuation, and containment isolation.

NRC FORM 366 (10-2010)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)CONTINUATION SHEET1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGEYEAR SEQUENTIAL REV1 YEAR NUMBER NO.Oyster Creek, Unit 1 05000219 2 OF 32012 002 -01NARRATIVE Plant Conditions Prior To EventEvent Date: October 29, 2012 Event Time: 2018 EDTUnit 1 Mode: Cold Shutdown Power Level: 0%Description of EventOn October 22, 2012, Oyster Creek completed a plant shutdown to the Cold Shutdown Condition for the 1 R24Refueling Outage. On October 28, 2012, prior to the arrival of Hurricane Sandy; refueling activities weresuspended, all switchyard work was secured, and full power supply redundancy was reestablished.

The reactorand cavity were flooded to 585 inches above the top of the fuel.On 10/29/12 at 20:18 hours, a dividing wall between Startup Transformer Banks 5 and 6 voltage regulators fell onthe 'C' phase of the Bank 6 Voltage Regulator during high winds from Hurricane Sandy. The damage to the 'C'phase of the voltage regulator resulted in a phase to ground fault at the regulator.

Upon sensing the fault, thesecondary side of Bank 6, the S1 B 4160V, breaker opened as designed.

However, the primary side of Bank 6, the34.5KV Oil Circuit Breaker (OCB) stuck and failed to clear the fault as required.

Oyster Creek's switchyard consists of two 230KV busses which power two 34.5KV busses through 230KV /34.5KVtransformers:

230KV bus C powers 34.5KV bus B though the Bank 7 Transformer; 230KV bus D powers 34.5KVbus A through the Bank 8 Transformer.

The normal configuration for Oyster Creek is that the A and B 34.5KVbusses are tied together through a bus tie OCB. In addition, there are 2 express feeders that power the 34.5KVbusses should the 230KV power be lost: The 34.5KV 0121 line is connected to the B 34.5KV bus; the 34.5KV Z52line is connected to the A 34.5KV bus.Oyster Creek's Startup (S/U) Transformers are 34.5KV / 4160v transformers that are normally powered by the34.5KV busses through single phase voltage regulators:

Bank 5 S/U Transformer is connected to 34.5KV bus B;Bank 6 S/U Transformer is connected to 34.5KV bus A. The S/U Transformers and their associated voltageregulators can be isolated via 34.5KV OCB's (Bank 5 and Bank 6 OCBs for the primary side) and 4160V air circuitbreakers (S1A and S1B for the secondary side, respectively).

Since the 34.5KV Bus Tie OCB is not designed to trip during a ground fault condition and the bus tie is normallyclosed, the sustained fault on the 34.5KV system was detected by the Bank 7 and Bank 8 (230KV / 34.5KV)Transformers neutral ground fault protection relays. Additionally, since the fault was 'close-in' to Bank 7 and Bank8, the transformer neutral ground fault relays actuated prior to the A and B 34.5KV Bus Backup Protection relays,which are set at 3.5 seconds to protect the bus from any associated line stuck breaker condition.

Therefore, theBank 7 and Bank 8 Transformer neutral ground fault protection relays tripped the 230KV bus breakers connected tothe C and D 230KV buses, respectively, to clear the 34.5KV fault.In addition, since the 34.5KV Bus Tie OCB is not designed to trip during a ground fault condition and the bus tie isnormally closed, the protective relay systems (remote backup) for the Q121 and Z52 express feeder lines openedthe remote 34.5KV breakers located at Whiting and Manitou Substations, respectively.

As a result of losing theQ121 and Z52 express feeders combined with the previously mentioned trip of the 230KV bus breakers, power tothe Oyster Creek Bank 5 and Bank 6 S/U Transformers was lost- creating a Loss of Offsite Power (LOOP)condition.

Upon the loss of power to Banks 5 and 6, both Emergency Diesel Generators (EDGs) responded as expected, andreenergized their respective safety buses. The LOOP caused a valid Reactor Protection System (RPS) actuation with automatic containment isolations, and resulted in a trip of Shutdown Cooling to the reactor and a trip of FuelPool Cooling.

Shutdown Cooling and Fuel Pool Cooling were both expeditiously restored with power provided byINAC FORM 366A(10-2010)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)CONTINUATION SHEET1. FACILITY NAME 2. DOCKET 6. LER NUMBER 3. PAGEYEAR SEQUENTIAL REVYEAR NUMBER NO.Oyster Creek, Unit 1 05000219 3 OF 32012 002 -01NARRATIVE the EDGs. Emergency Plan (EP) Emergency Action Levels (EALs) were reviewed by the Shift Manager and foundto be not applicable in the Cold Shutdown mode of operation since both EDGs started and loaded as required.

At 10:39 on October 30, 2012, power was restored to Startup Transformer Bank 5 and EDG #1 was secured.

Dueto equipment damage to the Bank 6 Voltage Regulator, Startup Transformer Bank 6 was not returned to service atthat time. At 3:46 on October 31, 2012, a planned contingency offsite power backfeed path was established torepower plant loads associated with EDG#2 and EDG #2 was secured.

At 21:32 on November 1, 2012, with theBank 6 Voltage Regulator repair complete and power restored to Startup Transformer Bank 6, the plannedcontingency offsite power backfeed was secured.Analysis of EventThis event was of low significance since Oyster Creek was in Cold Shutdown with reactor water level at 585 inchesabove the fuel, and both EDGs fast started as designed repowering all required emergency loads.Prior to the arrival of Hurricane Sandy, Oyster Creek ensured that both EDGs and the associated safety systemelectrical buses were available and operable.

Oyster Creek also ensured that an adequate amount of fuel oil wasavailable for sustained EDG operation.

The Operations Department was prepared and briefed for the oncomingstorm. The Operators were prepared for and briefed for the LOOP, loss of Shutdown

Cooling, as well as the loss ofFuel Pool Cooling.

The Operators took appropriate actions and expeditiously recovered Shutdown Cooling andFuel Pool Cooling following the initial EDG loading sequence.

There were no significant equipment problems notedrelated to maintaining the reactor in a safe Cold Shutdown Condition during the LOOP. There were no safetyconsequences impacting the plant or public safety as a result of this event.Cause of EventA detailed root cause investigation was performed and found that the wall falling onto the 'C' phase of the Bank 6Voltage Regulator was the root cause of the event. When the wall fell onto the 'C' phase of the Bank 6 VoltageRegulator a ground fault condition

occurred, and due to the Bank 6 OCB failing to clear the fault, resulted inisolation of the local 34.5KV system, resulting in the Oyster Creek LOOP. The wall was installed as part of amodification, performed in the mid 1980s, and was not built to withstand the winds experienced during the storm.Oyster Creek license conditions require that switchyard equipment be inspected under the 'Structures Monitoring Program' every 4 years. The wall has been regularly inspected without detection of any structural deficiencies-withthe last inspection being performed in September 2012. No deficiencies with the wall were documented.

Contributing to the LOOP was the stuck breaker condition on the Bank 6 OCB, which failed to clear the fault asdesigned.

Corrective maintenance on Bank 6 OCB after the event discovered that the trip coil had failed whichwould have prevented the breaker from opening.

With the Bank 6 OCB stuck, the fault was propagated throughout the local 34.5KV system resulting in the LOOP.Corrective ActionsPrior to reactor startup from the Refueling Outage, Oyster Creek verified that all required electrical distribution power lines and equipment required by Technical Specifications were available,

operable, and functioning asrequired.

This verification included ensuring that the transmission owner/operator completed the replacement andtesting of the failed trip coil and the Bank 6 OCB.In order to prevent recurrence it was verified that the defective wall was not part of Oyster Creek's currentlicense or design basis and the wall was removed.

Additionally, the transmission system owner/operator hasperformed a modification in the Oyster Creek switchyard to provide stuck breaker protection for the 34.5KVbreakers.

NRC FORM 366A (10-2010)