05000219/LER-2016-001, Regarding Failure of the 1 Emergency Diesel Generator During Surveillance Testing Due to a Cooling Water System Leak

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Regarding Failure of the 1 Emergency Diesel Generator During Surveillance Testing Due to a Cooling Water System Leak
ML16088A139
Person / Time
Site: Oyster Creek
(DPR-016)
Issue date: 03/04/2016
From: Gillin M
Exelon Generation Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-16-022 LER 16-001-00
Download: ML16088A139 (7)
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LER-2016-001, Regarding Failure of the 1 Emergency Diesel Generator During Surveillance Testing Due to a Cooling Water System Leak
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded
10 CFR 50.73(a)(2)(viii)(A)
10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
10 CFR 50.73(a)(2)(viii)(B)
10 CFR 50.73(a)(2)(ix)(A)
10 CFR 50.73(a)(2)(iv)(A), System Actuation
10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor
10 CFR 50.73(a)(2)(v), Loss of Safety Function
10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown
10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
10 CFR 50.73(a)(2)(i)
2192016001R00 - NRC Website
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text

I I L Exelon Generation© RA-16-022 March 4, 2016 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 - 0001 Oyster Creek Nuclear Generating Station Renewed Facility Operating License No. DPR-16 NRG Docket No. 50-219 10 CFR 50.73

Subject:

Licensee Event Report (LER) 2016-001-00, "Failure of the #1 Emergency Diesel Generator During Surveillance Testing due to a Cooling Water System Leak" Enclosed is LER 2016-001-00 reporting the failure of the #1 Emergency Diesel Generator during surveillance testing due to a cooling water system leak which occurred on January 4, 2016. A supplement to this report will be issued following the determination of the root and contributing causes of the event and all associated corrective actions.

This event did not affect the health and safety of the public or plant personnel. This event did not result in a safety system functional failure. There are no regulatory commitments made in this LER submittal.

Should you have any questions concerning this report, please contact Mike McKenna, Regulatory Assurance Manager, at (609) 971-4389.

Respectfully, Michael Gillin Plant Manager Oyster Creek Nuclear Generating Station Enclosure: NRG Form 366, LER 2016-001-00 cc:

Administrator, NRG Region I NRG Senior Resident Inspector - Oyster Creek Nuclear Generating Station NRG Project Manager - Oyster Creek Nuclear Generating Station

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE Oyster Creek, Unit 1 05000219 1 OF 4
4. TITLE Failure of the #1 Emergency Diesel Generator During Surveillance Testing due to a Cooling Water System Leak
5. EVENT DATE
6. LEA NUMBER
7. REPORT DATE
8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.

MONTH DAY YEAR N/A NIA FACILITY NAME DOCKET NUMBER 01 04 2016 2016 - 001

- 00 03 04 2016 N/A NIA
9. OPERATING MODE
11. THIS REPORT IS SUBMITIED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)

D 20.2201 (b)

D 20.2203(a)(3)(i)

D 50.73(a)(2)(ii)(A)

D 50.73(a)(2)(viii)(A)

N D 20.2201 (dl D 20.2203(a)(3)(ii)

D 50.73(a)(2)(ii)(B)

D 50.73(a)(2)(viii)(B)

D 20.2203(a)(1)

D 20.2203(a)(4)

D 50.13(a)(2)(m)

D 50.73(a)(2)(ix)(A)

D 20.2203(a)(2)(i)

D 50.36(c)(1)(i)(A)

D 50.73(a)(2)(iv)(A)

D 50. 73(a)(2)(x)

10. POWER LEVEL D 20.2203(a)(2J(iil D 50.36(c)(1)(ii)(A)

D 50.73(a)(2)(v)(A)

D 13.11(a)(4)

D 20.2203(a)(2)(iii)

D 5o.3a(cJ<2J D 50. 73(a)(2)(v)(B)

D 13.11(a)(5)

D 20.2203(a)(2)(iv)

D 5o.4a(a)(3l(ii) 0 50.73(a)(2)(v)(C)

D 73.77(aJ(1l 100 D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A)

D 50.73(a)(2)(v)(D)

D 13.77(a)(2)(i)

Q 20.2203(a)(2)(vi) 1:8] 50. 73(a)(2)(i)(B)

D 50.73(a)(2)(vii)

D 13.11(a)(2J(iil

  • l.P,;'<:,~

.::~c'.<'.)i~;,..

.. -:\\

D 50.73(a)(2)(i)(C)

D OTHER Specify in Abstract below or in

Analysis of Event

SEQUENTIAL NUMBER 001 REV NO.

00 The failed rubber pipe coupling was sent to Exelon's PowerLabs for functional testing and analysis. PowerLabs' Failure Analysis Report (OYS-34217) concluded that the observations and data from the EDG #1 ruptured rubber pipe coupling and the EDG #2 non-failed rubber provided support that the progression of degradation took place from the inner diameter of the rubber coupling to the outer diameter. The most likely failure scenario of the EDG #1 rubber coupling began with thermal degradation of the inner nitrile layer which caused it to harden and crack. This cracking allowed the coolant to come in contact with the rayon fabric reinforcement which degraded and weakened it. With the inner nitrile layer and the reinforcing layers compromised, the nitrile outer layer eventually became thermally degraded to a point that it could no longer withstand the pressure of the coolant during operation and the hose ruptured.

Assessment of Safety Consequences

Two EDG units serve as the Standby Power Supply for OCNGS by providing an emergency source of power to the 4.16 kV buses 1 C and 1 D in the event of a loss of normal power. The EDG units are designed to start and load automatically, if required. Non-essential loads are automatically shed by undervoltage sensing devices on loss of offsite power to ensure that the units are not overloaded. The capacity of the EOG units is sufficient to sequentially energize for starting all safety-related pumps and auxiliaries required for a safe shutdown of the reactor in the event of a Design Basis Accident. The EDG units are i_ndependent of each other, with the exception of a common bulk fuel storage supply, and are provided with auxiliary systems to ensure reliable starting and continuous operation with no Operator attention. Power to start the EDG units is self-contained and is not dependent on the availability of any other source of normal plant power at the moment of initiation.

There are two types of automatic start signals to the EOG units. The first signal will cause the EDGs to start and idle. The second signal is considered the Fast Start Signal. The EOG allowable time response to a Loss of Offsite Power (LOOP) event is 20 seconds as a basis for Core Spray System response to accident conditions. The time response period includes undervoltage (UV) sensor pick-up time, Emergency Bus logic to isolate and actuate the EDGs and the period to bring the Emergency Buses to nori:nal voltage level.

The failure of the rubber pipe coupling on the cooling water system could have precluded EDG #1 from being able to start, load, and operate without interruption in the event of a degraded or loss of voltage condition. EDG #2 would have continued to operate and would have supplied the 1 D 4160V bus as required to ensure power to the components required to achieve cold shutdown. Since the common cause for EOG #2 operability could not be clearly demonstrated based on available data, EDG #2 load test was successfully completed per TS Section 3.7.C., for common mode applicability requirements, and was maintained in an operable condition in accordance with station procedures.

Cause of Event

The root and contributing causes of the event and the associated extent of condition and extent of cause reviews are still being determined at this time and will be included in the supplement to this LER.

The following immediate actions were taken:

  • Complex Troubleshooting was commenced.
  • The #2 EDG was tested to eliminate the potential for a common cause failure.

SEQUENTIAL NUMBER 001 REV NO.

00

  • The failed rubber pipe coupling was replaced on EDG #1. (The opposite coupling was replaced in 2014)

Corrective Actions

Replaced both of the similar couplings on EDG #2.

  • Previous Occurrences There have been no similar, previous events resulting from a failure of a flexible fluid coupling on an EDG at Oyster Creek.

Component Data Component IEEE 805 System ID IEEE 803A Function Emergency Diesel Generator EK DG

Description of Event

On January 4, 2016, at approximately 0412 hours0.00477 days <br />0.114 hours <br />6.812169e-4 weeks <br />1.56766e-4 months <br />, the Oyster Creek Nuclear Generating Station (OCNGS)

Emergency Diesel Generator (EDG) #1 was started for the normal biweekly load test surveillance in accordance with Procedure 636.4.003 (Diesel Generator 1 Load Test). At 0414 hours0.00479 days <br />0.115 hours <br />6.845238e-4 weeks <br />1.57527e-4 months <br />, the EDG #1 came up to rated load and at 0440 hours0.00509 days <br />0.122 hours <br />7.275132e-4 weeks <br />1.6742e-4 months <br /> an unexpected alarm (T-4-b EDG 1 DISABLED), was received in the Main Control Room (MCR) when the EDG #1 controls processed a trip on low coolant pressure. MCR Operators noted the EDG #1 output breaker opened, the UNIT START light was not lit, and the UNIT IDLING light was briefly lit; then extinguished.

Operators discovered locally at the EDG enclosure that the rubber pipe coupling that connects the coolant surge tank to the right bank cooling water pump inlet tee had ruptured. The following local alarms were annunciated in the EDG #1 cubicle: ENG TRIP, GEN BKR TRIP, and LOW COOLANT PRESS. These indications were expected based on the "as found" condition of the hose and the mode of engine operation.

Following the trip, the EDG #1 was declared inoperable in accordance with the Technical Specification 3.7.C.2 LCO, which placed the plant in a 7-day action and resulted in an unplanned risk change from GREEN to YELLOW.

EOG #i was declared operable at 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br /> on January 5, 2016, and plant risk was returned to Green, following the replacement of the rubber pipe coupling and successful post maintenance testing.

Equipment Description OCNGS is equipped with two identical EDG units. The function of the EDGs is to provide AC power to the Class 1 E buses upon a loss of off-site power. The EDGs must be able to provide this power rapidly, within 1 O seconds, upon demand. This condition is referred to as a fast start signal. If started with a fast start signal, a high jacket water temperature condition will not trip the EDG.

The EDG units are General Motors Corporation, Electromotive Division (EMD) Model EMD 20-645E4, 20-cylinder, 2-cycle, turbo-intercooled diesel engines, which drive their respective EMD A20C AC generators. Each unit is normally operated bi-weekly to demonstrate the ability to carry rated loading upon loss of offsite power to their respective buses. The EDG units are self-contained in enclosures inside the EDG vaults and are provided with air-cooled radiators to remove waste heat.

Each engine is equipped with two engine-driven cooling water pumps to provide jacket water coolant flow to the power assemblies in each cylinder bank and the turbocharger after coolers. The cooling water, which is demineralized water treated with Nalcool 2000 corrosion inhibitor, is maintained in a closed loop with a surge tank connected to a tee in the suction side of the pumps. The tank is equipped to accommodate the volume of coolant that drains from the radiators in the standby condition and provides adequate coolant level for pump net positive suction head during operation. The rubber pipe coupling which failed on EDG #1 was one of two on that engine, which provided a flexible connection between the tee and the bottom of the tank.

To minimize the stress of a fast start, each engine is provided with an immersion heater in the coolant system and auxiliary oil pumps to circulate warm oil. The coolant system is designed for reverse natural circulation flow to provide for oil heating in standby conditions. In standby, the water level in the tank is approximately 14 inches higher than during operation, where the water is displaced into the piping above the radiator.

Analysis of Event

SEQUENTIAL NUMBER 001 REV NO.

00 The failed rubber pipe coupling was sent to Exelon's PowerLabs for functional testing and analysis. PowerLabs' Failure Analysis Report (OYS-34217) concluded that the observations and data from the EDG #1 ruptured rubber pipe coupling and the EDG #2 non-failed rubber provided support that the progression of degradation took place from the inner diameter of the rubber coupling to the outer diameter. The most likely failure scenario of the EDG #1 rubber coupling began with thermal degradation of the inner nitrile layer which caused it to harden and crack. This cracking allowed the coolant to come in contact with the rayon fabric reinforcement which degraded and weakened it. With the inner nitrile layer and the reinforcing layers compromised, the nitrile outer layer eventually became thermally degraded to a point that it could no longer withstand the pressure of the coolant during operation and the hose ruptured.

Assessment of Safety Consequences

Two EDG units serve as the Standby Power Supply for OCNGS by providing an emergency source of power to the 4.16 kV buses 1 C and 1 D in the event of a loss of normal power. The EDG units are designed to start and load automatically, if required. Non-essential loads are automatically shed by undervoltage sensing devices on loss of offsite power to ensure that the units are not overloaded. The capacity of the EOG units is sufficient to sequentially energize for starting all safety-related pumps and auxiliaries required for a safe shutdown of the reactor in the event of a Design Basis Accident. The EDG units are i_ndependent of each other, with the exception of a common bulk fuel storage supply, and are provided with auxiliary systems to ensure reliable starting and continuous operation with no Operator attention. Power to start the EDG units is self-contained and is not dependent on the availability of any other source of normal plant power at the moment of initiation.

There are two types of automatic start signals to the EOG units. The first signal will cause the EDGs to start and idle. The second signal is considered the Fast Start Signal. The EOG allowable time response to a Loss of Offsite Power (LOOP) event is 20 seconds as a basis for Core Spray System response to accident conditions. The time response period includes undervoltage (UV) sensor pick-up time, Emergency Bus logic to isolate and actuate the EDGs and the period to bring the Emergency Buses to nori:nal voltage level.

The failure of the rubber pipe coupling on the cooling water system could have precluded EDG #1 from being able to start, load, and operate without interruption in the event of a degraded or loss of voltage condition. EDG #2 would have continued to operate and would have supplied the 1 D 4160V bus as required to ensure power to the components required to achieve cold shutdown. Since the common cause for EOG #2 operability could not be clearly demonstrated based on available data, EDG #2 load test was successfully completed per TS Section 3.7.C., for common mode applicability requirements, and was maintained in an operable condition in accordance with station procedures.

Cause of Event

The root and contributing causes of the event and the associated extent of condition and extent of cause reviews are still being determined at this time and will be included in the supplement to this LER.

The following immediate actions were taken:

  • Complex Troubleshooting was commenced.
  • The #2 EDG was tested to eliminate the potential for a common cause failure.

SEQUENTIAL NUMBER 001 REV NO.

00

  • The failed rubber pipe coupling was replaced on EDG #1. (The opposite coupling was replaced in 2014)

Corrective Actions

Replaced both of the similar couplings on EDG #2.

  • Previous Occurrences There have been no similar, previous events resulting from a failure of a flexible fluid coupling on an EDG at Oyster Creek.

Component Data Component IEEE 805 System ID IEEE 803A Function Emergency Diesel Generator EK DG

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