05000374/LER-2015-002
| Lasalle County Station, Unit 2 | |
| Event date: | 02-14-2015 |
|---|---|
| Report date: | 07-15-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| Initial Reporting | |
| 3742015002R01 - NRC Website | |
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U.S. NUCLEAR REGULATORY COMMISSION I APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 LaSalle County Station Unit 2 is a General Electric Company Boiling Water Reactor with 3546 Megawatts Rated Core Thermal Power.
A. CONDITION PRIOR TO EVENT:
Unit(s): 2 Reactor Mode(s): 5 Event Date: February 14, 2015 Event Time: 1530 CST Mode(s) Name: Refueling Power Level: 0%
B. DESCRIPTION OF EVENT:
During the February 2015 Unit 2 refueling outage L2R15, two main steam safety relief valves (SRV)[AD] did not pass Technical Specification (TS) Surveillance Requirement 3.4.4.1 and Inservice Testing Program lift pressure requirements. Both SRVs lifted below their expected lift pressures. SRV 2621-F013S was required to lift within plus or minus three percent of 1150 psi (i.e., 1150 psi plus or minus 34.5 psi), but actually lifted at 1099 psi. SRV 2B21-F013M was required to lift within plus or minus three percent of 1195 psi (i.e., 1195 psi plus or minus 35.8 psi), but actually lifted at 1145 psi.
This condition was discovered while Unit 2 was outside the mode of applicability for TS 3.4.4, Safety/Relief Valves (Modes 1, 2 and 3); however, multiple test failures are reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by the plant's Technical Specifications.
C. CAUSE OF EVENT:
Disassembly and inspection of both valves was performed at NWS Technologies to determine the cause for failure. The vendor reported that for both valves all of the spring tolerances were within the acceptance limits.
There were no other signs of degradation or any other issue that would affect the setpoint. Second lift tests for both valves were satisfactory and were within the plus or minus three percent tolerance of the set pressure.
The cause for 2B21-F013S and 2621-F013M to fail their set pressure test in L2R15 was found to be indeterminate.
D. SAFETY ANALYSIS:
The safety significance of this condition was minimal. The out-of-tolerance lift pressures were discovered while the plant was in Mode 5 during a refueling outage and the SRVs were not required to be operable. Both SRVs lifted prior to their expected lift pressures, which is conservative in regards to maintaining reactor pressure vessel overpressure limits.
LaSalle County Station, Unit 2 05000374
E. CORRECTIVE ACTIONS:
Both SRVs were replaced during the outage.
F. PREVIOUS OCCURRENCES:
A review of past events identified one additional occurrence of out-of-tolerance safety relief valve pressures in the previous ten years. On February 17, 2014 the 1621-F013R Safety Relief Valve failed a pressure test by lifting at 1154 psi against a set pressure of 1205 psi.
G. COMPONENT FAILURE DATA:
Crosby Safety Relief Valves for Main Steam Service, Style HB-65-BP, Size 6R10. ASME Section III, Class I