05000354/LER-2015-001
| Hope Creek Generating Station | |
| Event date: | 03-31-2015 |
|---|---|
| Report date: | 06-30-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3542015001R01 - NRC Website | |
the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to Impose an Information collection does not display a currently vafid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection,
2. DOCKET
Hope Creek Generating Station 05000354
PLANT AND SYSTEM IDENTIFICATION
General Electric — Boiling Water Reactor (BWR/4) Core Spray System {BM/BKR}* *Energy Industry Identification System {EMS} codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF OCCURRENCE
Event Date: 03/31/15 Discovery Date: 03/31/15
CONDITIONS PRIOR TO OCCURRENCE
Hope Creek was in Operational Condition 1 at 100 percent rated thermal power (RTP). There was no other equipment out of service that would have impacted this event.
DESCRIPTION OF OCCURRRENCE
On 03/31/2015 at 1342, the breaker {BM/BKR} for 'A' Core Spray Pump failed to close during normal surveillance testing. No alarms were received in the Main Control Room when the start pushbutton was depressed. A second start attempt had the same results. Technical Specification (TS) 3.5.1.a was entered for one inoperable Core Spray Subsystem {BM}. The breaker was replaced and the surveillance was satisfactorily performed. 'A' Core Spray Subsystem was declared OPERABLE on 03/31/2015 at 2000 and the TS was exited.
Initial troubleshooting indicated that the failure in the breaker most likely existed since the last breaker operation in January 2015. Consequently, 'A' Core Spray Subsystem was inoperable for longer than the TS allowed outage time.
Therefore, the condition was determined to be reportable per 10 CFR 50.73(a)(2)(i)(B) as any operation or condition prohibited by TS. During the review of this event, it was determined that '13' Core Spray Subsystem was inoperable from 02/09/2015 at 0300 until 02/10/2015 at 1532 (36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> and 32 minutes) when planned maintenance was performed on the 'B' Emergency Diesel Generator (EDG). This condition is reportable per 10 CFR 50.73(a)(2)(v) as an event or condition that could have prevented the fulfillment of a safety function.
Plant TS require two Core Spray Subsystems, each comprised of two OPERABLE Core Spray pumps and an OPERABLE flow path. Provided that at least two Low Pressure Coolant Injection (LPCI) subsystems are OPERABLE, with one Core Spray Subsystem inoperable, the inoperable Core Spray Subsystem must be restored to OPERABLE within seven days, or the plant shall be in HOT SHUTDOWN within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and COLD SHUTDOWN within the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. With both Core Spray Subsystems inoperable, the plant shall be in HOT SHUTDOWN within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in COLD SHUTDOWN within the next 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Contrary to these requirements, the 'A' Core I Spray Subsystem was inoperable from 01/08/2015 at 1000 when the 'A' Core Spray Pump breaker was opened, until 03/31/2015 at 2000, a period of 82 days, 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />. Both Core Spray Subsystems were inoperable from 02/09/2015 at 0300 until 02/10/2015 at 1532 (36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> and 32 minutes) when planned maintenance was performed on the '13' EDG.
6. LERNUNIBER
the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to Impose an Information collection does not display a currently vafid OMB control number, the NRC may not conduct or sponsor, and a person Is not required to respond to, the Information collection,
2. DOCKET
6. LERNUMBER 3. PAGE 1. FACILITY NAME
CAUSE OF EVENT
A broken spring was found inside the breaker 125 VDC control device. The control device operates when the breaker closes to recharge the closing springs and other breaker control functions. The closing springs were found charged on 03/31/15 when the Core Spray breaker failed to close. This indicates that the control device operated properly to recharge the closing springs when the breaker was closed on 01/08/15 during the quarterly surveillance test. Once the closing springs are charged, the control device does not operate again until the next closing cycle. Failure analysis indicated fatigue where the spring coil begins to bend to form the hook that attaches to the pin on the contact carrier. The fracture exhibited multiple initiation sites where an apparent shallow kink was present on the spring. The bend for the hook is a high stress location and the kink likely introduced an additional stress riser that promoted fatigue crack initiation. Fatigue is a progressive failure mechanism that occurs over several stress cycles, suggesting that the spring failed due to an accumulation of operations of the control device. Based on a review of corrective action program data, this failure has not been seen on any other breakers and is considered to be an isolated event.
SAFETY CONSEQUENCES AND IMPLICATIONS
The Core Spray System consists of two independent subsystems or loops. Each subsystem consists of two centrifugal pumps that can be powered by normal or emergency AC power; a spray sparger in the reactor vessel; piping and valves to convey water from the suppression pool to the sparger; and associated controls and instrumentation. If there is low water level in the reactor vessel or high pressure in the drywell, the core spray system automatically sprays water onto the top of the fuel assemblies in time and at a sufficient flow rate to cool the core and prevent excessive fuel temperature. The Low Pressure Coolant Injection (LPCI) system starts from the same signals that initiate the core spray system and operates independently to achieve the same objective by flooding the reactor vessel.
The Emergency Core Cooling System (ECCS) network has built-in redundancy so that adequate reactor core cooling can be provided, even with other failures. The primary purpose of Core Spray is to provide reactor vessel inventory makeup and spray cooling during large breaks in which the reactor core is calculated to uncover. LPCI is an operating mode of the RHR system. Four pumps deliver water from the suppression chamber to four separate reactor vessel nozzles and inject directly into the core shroud region. The primary purpose of LPCI is to provide reactor vessel coolant inventory makeup following large break loss of coolant accidents. The Core Spray System and LPCI also both provide reactor vessel inventory makeup and core cooling following small break loss of coolant accidents after automatic depressurization.
The accident analyses require various combinations of ECCS components. To meet these combinations, at least one Core Spray Subsystem must remain available. The 'B' Emergency Diesel Generator (EDG) was inoperable for planned maintenance from 02/09/2015 at 0300 until 02/10/2015 at 1532 (36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> and 32 minutes). Consequently, one Core Spray Pump in each subsystem was unavailable, resulting in two inoperable Core Spray Subsystems and a non-compliance with TS 3.5.1 Action a.2.
There were no actual consequences due to the failure of the 'A' Core Spray Pump breaker and the potential impact on nuclear safety was minimal. There were no actual consequences due to theinoperability of both Core Spray Subsystems and there was no significant impact on nuclear safety.
SAFETY SYSTEM FUNCTIONAL FAILURE
During the period when the 'A' Core Spray Subsystem was inoperable, planned maintenance was performed on 'B' EDG, resulting in two inoperable Core Spray Subsystems. This condition existed for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> and 32 minutes. This condition is a safety system functional failure as defined in NEI 99-02, Revision 7, Regulatory Assessment Performance Indicator Guideline.
the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently vafid OMB control number, the NRC may not conduct or sponsor, and a person Is not required to respond to, the information collection.
Hope Creek Generating Station 05000354
PREVIOUS EVENTS
A review of events at Hope Creek for the past three years was performed to determine if any similar events had occurred. No similar events were identified.
CORRECTIVE ACTIONS
The 'A' Core Spray Pump breaker was replaced. 'A' Core Spray Pump was declared operable after completion of the surveillance test on 03/31/2015 at 2000.
The preventative maintenance template for the ABB HK breakers used in safety-related applications will be reviewed and revised as necessary to include periodic replacement of the breaker control device.
Other corrective actions are being tracked in the licensee's Corrective Action Program.
COMMITMENTS
This LER contains no regulatory commitments.