05000400/LER-2005-003
| Harris Nuclear Plant - | |
| Event date: | 06-05-2005 |
|---|---|
| Report date: | 08-03-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4002005003R00 - NRC Website | |
I. DESCRIPTION OF EVENT
On June 8, 2005 at 1:15 p.m., with the reactor at approximately 100% power and upon review of troubleshooting data for an equipment drain system isolation valve [WK-ISV] (1ED-125, Reactor Coolant Drain Tank Pump Discharge Isolation Valve), the Harris Nuclear Plant (HNP) identified that the valve had sufficient leakage past its seat to result in declaring the valve inoperable: Operations was notified .
immediately, and the valve was declared inoperable per Technical Specifications (TS) 3.6.3 (Containment Isolation Valves [NH-ISV]). Upon review, it was determined that this condition had existed since June 5, 2005. Thus, the approximately three-day delay before completing the review of the troubleshooting data and declaring the valve inoperable resulted in exceeding the allowed outage time for this condition (i.e., the 4- hour action statement per TS 3.6.3). The condition was rectified immediately upon discovery.
On June 1, 2005, preliminary troubleshooting data had been collected and reviewed for the equipment drain system penetration. The troubleshooting data indicated a liquid leak rate of approximately 0.014 gpm through both closed valves (1ED-125 and 1ED-121, Reactor Coolant Drain Tank Pump Discharge Level Control Valve [LCV]) for this penetration. The leakage was not measured individually. When converted from a liquid leak rate to an estimated air leak rate, this leak rate was approximately 1500 sccm at normal operating pressures, which, when compared to values associated with local leak rate testing (LLRT), were minor and well within limits specified in the Containment Leakage Rate Testing Program of 101,200 sccm, which is 60% of the maximum containment leakage rate (La) at peak containment pressure (Pa). This condition was documented in the corrective action program at HNP. Thus, this preliminary troubleshooting data had indicated that the estimated leak rate would not have impacted the operability of the valves.
On June 5, 2005, to support a revised troubleshooting plan to better quantify the suspected leakage associated with each valve in the containment penetration for the equipment drain system, additional liquid data was collected by operations. The review of this troubleshooting data was not completed until June 8, 2005. This review revealed that the estimated leak rate for the outboard containment isolation valve for this penetration (1ED-125) would have been sufficient to declare the valve inoperable (i.e., approximately 1.63 gpm, which when converted is approximately 171,400 sccm at normal operating pressures). Operations was immediately notified, and the valve was declared inoperable on June 8, 2005 per TS 3.6.3.
Since there was firm evidence that this condition had existed since June 5, 2005, this condition is reportable as a condition prohibited by TS pursuant to 10 CFR 50.73(a)(2)(i)(B) since the condition existed for a time longer than the allowed outage time. This condition was neither recognized nor discovered until after the allowed outage time for this condition had elapsed, and the condition was rectified immediately upon discovery.
The equipment drain system collects liquids from the various plant operational systems and transfers them to appropriate collection tanks. The portion of the equipment drain system piping and associated valves that penetrate the containment building are designed to Seismic Category I and Safety Class 2 requirements for containment isolation. The equipment drain system isolation valves for this penetration (1ED-121 and 1ED- 125) are containment isolation valves specified in the Technical Specification Equipment List Program.
These valves are air-operated valves that have a safety function in the closed position for containment isolation. They are capable of automatic closure. The valves are installed in series and are provided power from separate emergency power sources to satisfy single failure criteria. Both valves fail to the closed position upon loss of actuating air.
Energy Industry Identification System (BUS) codes are identified in the text within brackets [ ].
II. CAUSE OF EVENT
The root cause of this event is that the troubleshooting procedure did not provide guidance specific to troubleshooting this operable equipment. This lack of guidance allowed troubleshooting to be performed on this equipment without fully understanding the limits for operability.
III. SAFETY SIGNIFICANCE
There were no actual significant safety consequences as a result of this condition. The redundant inboard containment isolation valve (1ED-121) for the same penetration remained operable during this time, so any postulated leakage through this penetration was bounded by the values assumed in the Final Safety Analysis Report (FSAR) at peak containment pressure during a Design Basis Accident (DBA).
The potential safety consequences under other alternate conditions, such as a DBA coincident with a postulated failure of the redundant inboard containment isolation valve, may have increased the severity of this condition. The potential safety consequences under this postulated alternate condition may have resulted in containment leakage through this penetration above the amounts assumed in the FSAR and may have resulted in increased dose rates.
This condition is reportable as a condition prohibited by Technical Specifications pursuant to 10 CFR 50.73(a)(2)(i)(B) since the condition existed for a time longer than its allowed outage time. This condition was neither recognized nor discovered until after the allowed outage time for this condition had elapsed, and the condition was rectified immediately upon discovery.
IV. CORRECTIVE ACTIONS
As immediate corrective action, the valve was repaired, tested satisfactorily, and returned to operation.
The corrective action to prevent recurrence is to revise the troubleshooting procedure to provide specific guidance requiring acceptance criteria to be established for troubleshooting on operable components.
V. PREVIOUS SIMILAR EVENTS
No previous HNP events or conditions are known within the last ten years related to a containment isolation valve that exceeded its allowed outage time due to leakage past its seat.