05000461/LER-2010-002
| Clinton Power Station | |
| Event date: | 02-03-2010 |
|---|---|
| Report date: | 08-23-2010 |
| 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 10 CFR 50.73(a)(2)(ii) |
| 4612010002R01 - NRC Website | |
EVENT DESCRIPTION
On February 3, 2010, after entering Mode 2 (Startup) following refueling outage Cl R12, it was discovered that a primary containment local leak rate test (LLRT) performed on feedwater [SJ] check valve [ISV], 1B21-F032B, exceeded its acceptance criteria. Technical Specification (TS) Surveillance Requirement (SR) 3.6.1.3.11 requires that the combined leakage rate for the primary containment feedwater penetrations to be less than or equal to 2 gallons per minute (gpm) through the worst of the isolation valves. The measured leakage rate for 1B21-F032B was reported to be 2.5 gpm. This leakage rate is greater than that assumed in the plant safety analysis.
The unit was placed in Mode 4 (Cold Shutdown) to repair the valve and to re-perform the LLRT. After lubricating the valve actuator and stroking the check valve, the LLRT was performed to confirm the valve could meet its safety function for the Feedwater Leakage Control System (FWLCS). Following the satisfactory completion of the LLRT, plant startup was re-commenced on February 4, 2010.
Time line of events 1/18/2010 0100 Local Leak Rate Test performed for 1B21F032B with 2.5 gpm leakage rate 2/2/2010 2138 Plant entered Mode 2 (Startup) 2/3/2010 0730 Issue Report 1025446 written for failed LLRT not identified, discovered by Engineering reviewer 2/3/2010 1100 Operations notified of condition; Control Room declared 1B21-F032B inoperable and initiated action in accordance with TS 3.6.1.3 to close the feedwater inlet shutoff valve, 1B21F065B, to isolate the affected penetration.
2/3/2010 1136 1B21-F065B closed and breaker turned off to comply with TS 3.6.1.3, Condition C Required Actions 2/3/2010 1447 FWLCS declared inoperable in accordance with TS LCO 3.6.1.9; entered 30-day action to restore FWLCS to an operable condition.
2/3/2010 1930 Plant entered Mode 3 (Hot Shutdown) 2/4/2010 0521 Plant entered Mode 4 (Cold Shutdown) 2/4/2010 1000 Lubricated actuator and stroked valve 2/4/2010 1330 Performed LLRT 2/4/2010 1533 Entered Mode 2; recommenced plant startup This issue was entered into the corrective action program as issue report (IR) number 1025446.
CAUSE OF EVENT
The cause of the 1B21-F032B check valve to fail its leak rate test was age-related degradation of the lubrication causing increased friction in the actuator. The actuator had not been re-lubricated since initial installation during a refueling outage that ended in May 1999. No preventive maintenance activities existed to lubricate or overhaul the actuator.
SAFETY ANALYSIS
This event is reportable under the provisions of: 10 CFR 50.73(a)(2)(i)(B) due to a condition prohibited by the plant Technical Specifications; 10 CFR 50.73(a)(2)(ii) due to a degraded or unanalyzed condition; and 10 CFR 50.73(a)(2)(v) due to a condition that could have prevented fulfillment of the safety function of the feedwater containment isolation valves to ensure offsite doses are not exceeded following a design basis loss of coolant accident (DBA LOCA).
The feedwater isolation valves and the FWLCS provide a sealing system to ensure that following a design basis accident loss of coolant accident (DBA LOCA), offsite doses are not exceeded. The 2 gpm leakage limit in TS SR 3.6.1.3.11 has been shown by testing and analysis to bound the condition following a DBA LOCA where, for a limited time, both air and water are postulated to leak through this pathway. The leakage rate of each primary containment feedwater penetration is assumed to be the maximum pathway leakage, i.e., the worst of the two isolation valves in each penetration.
Once the condition was identified, prompt actions were taken to ensure that the affected penetration was isolated to comply with TS. Once the plant was in Mode 4, corrective actions were taken to repair and re-test the valve to ensure leakage rates were restored to within acceptance limits.
No actual leakage path existed. The motor operated feedwater containment isolation valve, 1B21-F065B, had been in the closed position prior to plant startup. Once the condition was identified, 1B21-F065B was verified to be in the closed position, and the power was removed from its operator.
CORRECTIVE ACTIONS
The valve was repaired by lubricating the valve actuator. Following completion of repairs, the valve was stroked.
An LLRT was completed at 1330 on February 4, 2010 with satisfactory results (0.15 gpm). Mode 2 was entered at 1533 on February 4, 2010.
A service request has been approved for preventive maintenance activities to rebuild the 1B21-F032 actuators every 12 years and to lubricate and exercise the valve linkage every refueling outage.
PREVIOUS OCCURRENCES
This is the first failure of the 1B21-F032B since the installation and implementation of a Feedwater Leakage Control system in 2000. In refueling outage Cl R11, which occurred in January 2008, a similar testing failure occurred on valve1B21-F032A with a leak rate result of 3.75 gpm. Following the LLRT failure, the internals of the valve were inspected and found to be satisfactory. Observation of a valve stroke with the valve partially disassembled revealed uneven and un-repeatable side to side movement of the actuator. The disc was cleaned and the actuator was re-lubricated resulting in proper seating of the valve. This event was not reported, and no causal analysis was performed. The testing failure of valve 1B21-F032A is being reported under this LER.
The following LERs occurred prior to the installation of a Feedwater Leakage Control system:
Results in Total Leakage Rates in Excess of Technical Specification and 10CFR50 Appendix J Limits.
Results in Total Leakage Rates Greater than Technical Specification and 10CFR50, Appendix J Limits.
Resilient Seat Design Result in Local Leak Rate Test Failures of Feedwater Containment Isolation Valves and Total Leakage Rates Greater than Technical Specification and 10CFR50, Appendix J Limits.
COMPONENT FAILURE DATA
Feedwater valves 1B21-F032A and 1B21-F032B are 20-inch, air assisted, non-slam tilting disc check valves, manufactured by Anchor Darling Valve Company.