05000461/LER-2011-006

LER-2011-006, Condition Prohibited by Technical Specifications Due to Failed Missed Surveillance

Clinton Power Station, Unit 1
Event date:	12-07-2011
Report date:	01-26-2012
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
4612011006R00 - NRC Website

PLANT AND SYSTEM IDENTIFICATION

General Electric — Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EllS) codes are identified in the text as [XX].

EVENT IDENTIFICATION

Condition Prohibited by Technical Specifications Due to Failed Missed Surveillance

B. DESCRIPTION OF EVENT

On December 7, 2011, Clinton Power Station (CPS) was in Mode 5 (Refueling) for refueling outage Cl R13. During leakage testing of Reactor Coolant System (RCS) Pressure Isolation Valve (PIV) [ISV], 1E12-F042C, Low Pressure Coolant Injection [BO] from Residual Heat Removal (RHR) C Shutoff Valve, was performed in accordance with Technical Specification (TS) Surveillance Requirement (SR) 3.4.6.1. This test was performed in accordance with SR 3.0.3 to address a missed surveillance that was discovered on April 7, 2011. During the test, the valve would not pressurize due to the amount of water passing through the seat at low pressure. The test pressure for the surveillance test is 1000 to 1025 pounds per square inch gauge (psig). Since the valve would not pressurize, the leakage was determined to be in excess of the specified leakage criteria of five gallons per minute (gpm) and was declared an as-found failure.

During the operating cycle following refueling outage Cl R12 completed in February 2010, it was discovered on April 7, 2011, that valve 1E12-F042C was tested at a higher pressure than the range specified in SR 3.4.6.1. SR 3.0.3 was entered for a Surveillance not performed within its specified frequency, which allows a delay period for declaring the Limiting Condition for Operation (LCO) not met. Since SR 3.4.6.1 failed in C1R13 during the delay period, LCO 3.4.6 was not met for the entire cycle for valve 1E12-F042C.

There were no structures, systems, or components that were inoperable at the start of the event that contributed to this event.

This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS LCO 3.4.6, RCS PIV Leakage. TS LCO 3.4.6 requires RCS PIV leakage to be within the specified limits during plant operation in Modes 1 (Power Operation) and 2 (Startup).

C. CAUSE OF EVENT

The valve repair team identified wear on the guide ribs and excessive disc to rib clearances. Based upon the valve repair team personnel input, the excessive clearances appeared to be original dimensional tolerances rather than recent wear. Engineering determined the cause of the C1R13 as-found failure was that the disc became cocked when closing, was not fully seated, and subsequently failed the as-found leak rate test.

D. SAFETY CONSEQUENCES

There were no actual safety consequences for this event.

For the RCS PIV function, 1E12-F042C is one of two redundant pressure isolation valves in the RHR C injection line. The redundant isolation valve is the inboard check valve, 1E12-F041C. To lose the required function of isolating the RHR system (low pressure) piping from the reactor pressure, both the 1E12-F041C and the 1E12- F042C would have to fail leakage testing with seat leakage in excess of the allowable TS SR 3.4.6.1 requirements.

Valve 1E12-F041C passed surveillance testing in C1 R12 and passed surveillance testing with 0.5 gpm measured leakage in C1R13. Therefore, valve 1E12-F041C maintained the RCS PIV function of providing overpressure protection of the low pressure RHR C piping for the C1R12 to C1R13 operating cycle.

Valve 1E12-F042C is also the first of two redundant primary containment isolation barriers to prevent loss of containment integrity. The second barrier is the RHR C Closed Loop Outside Containment (CLOC). This barrier provides a water seal beyond 1 E12-F042C and is historically extremely reliable. The RHR C CLOC was tested in C1R13 and passed leakage rate testing with a measured leakage rate of 0.25 gpm as compared to an acceptance criteria of five gpm. Therefore, there is reasonable assurance that primary containment integrity was maintained for containment penetration 1MC-017.

E. CORRECTIVE ACTIONS

The valve was repaired by performing weld build-up of the internal guide ribs, which tightened the valve internal tolerances. Following repairs, the valve was restored to an operable status by satisfactorily testing the valve within allowable limits.

F. PREVIOUS OCCURRENCES

In C1R12, 1E12-F042C (plus four other RCS PIVs) were tested at a pressure slightly higher than the pressure specified in SR 3.4.6.1. This condition was identified on April 7, 2011 which resulted in missed surveillances per SR 3.0.3 for these valves. The other four RCS PIVs passed their leakage tests in C1R13. No other occurrences of leakage test failures were identified for these RCS PIVs.