05000354/LER-2013-010
| Hope Creek Generating Station | |
| Event date: | 1-20-2013 |
|---|---|
| Report date: | 03-14-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 49671 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3542013000R01 - NRC Website | |
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PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor (BWR/4) Control Building Environmental Control System - EllS Identifier (VI) Control Room Chiller - EllS Identifier (CHU) Pressure Control Valve - IEEE Identifier (PCV) * Energy Industry Identification System (EllS) codes and component function identifier codes appear as (SS/CCC)
IDENTIFICATION OF EVENT
Event Date: December 20, 2013 Discovery Date: December 20, 2013
CONDITIONS PRIOR TO EVENT
Hope Creek was in Operational Condition (OPCON) 1, operating at 100 percent rated thermal power. The B Control Room Chiller (CHU) was inoperable following planned maintenance. There was no other equipment out of service that would have impacted this event.
DESCRIPTION OF EVENT
On 12/20/13 at 1303, while the B Control Room Chiller was inoperable following planned maintenance, the A Control Room Chiller (CHU) was manually secured due to excessive fluctuations in load. The Technical Specification action statement (TS 3.7.2.2 Action a.2) for both Control Room Air Conditioning (VI) subsystems inoperable was entered.
An eight-hour NRC ENS notification was required by 10CFR50.72(b)(3)(v)(D) for an event or condition that could have prevented fulfillment of a safety function of structures or systems needed to mitigate the consequences of an accident.
The ENS notification (#49671) was completed at 2010 on 12/20/13. This LER is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(v)(D).
At 2120 on 12/20/13, the B Control Area Ventilation Train and Chiller were placed in service for post-maintenance testing, returned to operable status, and the action statement was exited.
CAUSE OF EVENT
The cause of this event was the concurrent loss of operability of both control room chillers.
The B Control Room Chiller, while available, was inoperable as it had not yet been tested following planned maintenance.
The A Control Room Chiller was removed from service due to excessive fluctuations in load.
An evaluation was performed to determine the cause of the excessive load fluctuations in the A Control Room Chiller.
The positioner for the pressure control valve (PCV), which provides cooling water flow to the chiller condenser, had failed. The failure analysis indicated that the positioner's internal relay assembly, which is made up of a series of diaphragms, had a damaged diaphragm. This allowed an internal leakage path for the air, resulting in the failure of the positioner to operate properly. This failure was determined to be age-related.
This is a legacy issue resulting from a design change that was implemented circa 1998. Evaluation of the design change failed to identify that the purchase class of the positioner for the chiller condenser cooling water pressure control valve should have been changed from non-safety related to safety related. The purchase class was not changed.
Consequently, shelf life of the diaphragms was not tracked, leading to this failure.
SAFETY CONSEQUENCES AND IMPLICATIONS
The Control Room Envelope (CRE) Heating, Ventilation and Air Conditioning (HVAC) Systems are designed to ensure habitability during any design basis radiological accident. Redundant HVAC systems are provided to control the ambient conditions for safety related equipment, to ensure operating temperature limits are not exceeded. The chillers provide the accident function of maintaining the temperature of the CRE for equipment performance and operator comfort.
There were no actual safety consequences because of this event and potential safety consequences were minimal. The B Control Room Chiller was available and was returned to service at 2120 on 12/20/13.
Throughout the time both chillers were inoperable, the control room temperature was maintained below the TS limit of 90 degrees F.
SAFETY SYSTEM FUNCTIONAL FAILURE
A review of this event determined that a Safety System Functional Failure (SSFF) did occur as defined in Nuclear Energy Institute (NEI) 99-02, "Regulatory Assessment Performance Indicator Guideline.
The control room chillers provide the accident function of maintaining the temperature of the control room envelope for equipment performance and operator comfort. Therefore, both chillers being out of service at the same time was an event or condition that could have prevented the fulfilment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
PREVIOUS EVENTS
A review of events for the past three years at Hope Creek was performed to determine if a similar event had occurred. No similar events were identified.
CORRECTIVE ACTIONS
1. At 2120 on 12/20/13, the B Control Area. Ventilation Train and Chiller were placed in service for post-maintenance testing, returned to operable status, and the action statement was exited.
2. The failed positioner on the A Chiller condenser pressure control valve was replaced, and the A Control Area Ventilation Train and Chiller were returned to operable status.
3. The purchase class for the chiller condenser cooling water pressure control valve positioner will be changed to safety-related.
4. Safety related replacements for the A and B Chiller condenser cooling water pressure control valve positioners will be installed.
COMMITMENTS
This LER contains no commitments.