05000311/LER-2008-001
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3112008001R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse — Pressurized Water Reactor Pressurizer/Safety Valves {AB/RV}* *Energy Industry Identification System (EllS) codes and component function identifier codes appear as {SS/CC}
CONDITIONS PRIOR TO OCCURRENCE
The plant was in the shutdown condition for refueling outage 2R16. No structures, systems, or components were inoperable at the time of discovery that contributed to the event.
DESCRIPTION OF OCCURRENCE
On March 20, 2008, with Unit 2 in Mode 6 (Refueling) one of the three Pressurizer Safety Valves (PSV) 2PR3 {AB/RV} failed the as-found actuation pressure surveillance test, required by Technical Specification (TS) 4.4.2 and ASME OM-1987, Part 1, Requirements for Inservice Performance Testing of Nuclear Power Plant Pressure Relief Devices. The TS acceptance band for the as-found actuation pressure is ±3% of the nameplate setpoint pressure. The first (as-found) actuation pressure for PSV 2PR3 was below the lower limit of minus 3% of the nameplate setpoint. The removed 2PR3 valve passed a second (informational) pressure test with a lift pressure of 2440 psig (-1.8%). The valve remained leak tight following reseating after each lift test.
The actual test results of valve 2PR3 are:
Test # As found (psig) TS Setpoint (psig) Acceptable band (psig) % Difference 1 2402 2485 2410.45 — 2559.55 — 3.30 2 2440 2485 2410.45 — 2559.55 — 1.80 Because the first as-found lift set point of the 2PR3 was not within 3% of set point, expanded testing scope was performed in accordance with the In-Service Test (IST) program. The two remaining PSVs were removed and replaced with pre-tested spares. The removed valves were subsequently tested and found to lift within TS tolerances.
CAUSE OF OCCURRENCE
The 2PR3 valve was disassembled and all components were inspected. Valve critical dimensions were measured and all were within OEM tolerances. Three load tests were performed on the 2PR3 valve spring; the spring was found to be within OEM tolerance. A review of valve test data revealed that this was the first test of valve 2PR3 since it was received from the manufacturer in 1998. This valve was installed in the 2PR3 position in November 2003. Springs in a highly compressed state are known to relax over time. Other valves from this group of relief valves also lifted on the low side of the setpoint following their first installed operational cycle. This was the last valve of the group to complete its initial operational cycle.
�NRC FORM 366 (9-2007) PRINTED ON RECYCLED PAPER NW: FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (9-2007) 2. DOCKET1. FACILITY NAME 6. LER NUMBER 3. PAGE 08 0 0 1 0 Eu Edo CAUSE OF OCCURRENCE (continued) The apparent cause of the 2PR3 setpoint drifting low was due to valve spring relaxation during its first operational service cycle, possibly compounded by the time between valve tests.
PRIOR SIMILAR OCCURRENCES
A review of Salem LERs since 2001 identified one occurrence where PSVs exceeded the TS setpoint acceptance criteria of ±3%. The cause for that occurrence was that the valve internals were not lapped in place. The corrective actions associated with that LER would not have prevented this event.
SAFETY CONSEQUENCES AND IMPLICATIONS
Pressurizer safety valves are typically credited in the UFSAR Chapter 15 safety analyses for their pressure relief benefits, and these valves are modeled at the setpoint plus ±3% tolerance. Having one of these valves out of tolerance in the negative direction would be a direct benefit to all analyses that credit these valves for protection. For the UFSAR Chapter 15 safety analysis of Spurious Operation of the Safety Injection System at Power, an early lift of a safety relief could have the potential of liquid relief through the pressurizer safety valves. A review of this transient determined that the lower lift pressure of 2402 psig on the one out-of-tolerance PSV would have no affect on the calculated results, since it will not open given a spurious operation of the safety injection system. It was concluded that there were no safety consequences or implications involved as a result of the 2PR3 valve being below the lower limit of minus 3% by 0.3%. Therefore, the public health and safety was not affected.
A review of this condition determined that a Safety System Functional Failure (SSFF) did not occurred as defined in Nuclear Energy Institute (NEI) 99-02.
CORRECTIVE ACTIONS:
1. All Unit 2 PSVs were replaced with pre-tested valves.
2. The PSV testing was expanded to include the additional two PSVs in accordance with the IST Program, and both additional valves tested satisfactorily.
3. The tracking and scheduling basis for relief valve testing is being revised to assure that storage and shelf times, as well as service time, are factored into the ASME OM code testing periodicity of the valves.
COMMITMENTS
The corrective actions cited in this LER are voluntary enhancements and do not constitute commitments.