05000458/LER-2015-001, Operations Prohibited by Technical Specifications Due to Deficient Local Leak Rate Test Procedures Containing Erroneous Valve Alignments
| River Bend Station - Unit 1 | |
| Event date: | 2-18-2015 |
|---|---|
| Report date: | 04-16-2015 |
| 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 |
| 4582015001R00 - NRC Website | |
REPORTED CONDITION
On February 18, 2015, while the plant was operating at approximately 98% power, it was discovered that four local leak rate each procedure erroneously required the closure of the respective motor-operated valve in the packing leak-off line for the outboard main steam isolation valve being tested, when the proper test configuration would require the valve to be open. This condition had existed since the procedures were revised in 1992 to add specific valve lineup checklists, where the error existed. The net effect of the error was to partially negate the effectiveness of a surveillance test required by Technical Specifications.
This condition is being reported in accordance with 10CFR50.73(a)(2)(v) as operations prohibited by Technical Specifications.
BACKGROUND
supplements the isolation function of the MSIVs. The MS-PLCS consists of two independent subsystems: an inboard subsystem, which is connected between the inboard and outboard MSIVs; and an outboard subsystem, which is connected between the double disk of main steam line shutoff valves and the valve stem packing glands of the outboard MSIVs. The system supplies pressurized air to those components following system actuation to provide positive sealing of each penetration. Each subsystem is powered by the respective emergency diesel generator.
Surveillance Requirement (SR) 3.6.1.3.10 requires the verification that the total leakage rate through the valves served by each affected procedures are the outboard main steam isolation valves (MSIVs), and the test boundary includes the MSIV packing leak-off lines.
be manually initiated following an event postulated in the site accident analysis, as documented in the Updated Safety Analysis assumptions supporting the accident analysis.
If the MS-PLCS system is placed into service, the MSIV packing leak-off isolation valves would be open. Having the valves closed isolates the outboard MSIV packing glands leak-off lines, and thus artificially confines the boundary of the potential leakage paths.
INVESTIGATION and IMMEDIATE ACTIONS This condition was discovered as the station was preparing to enter a scheduled refueling outage. The plant was taken offline on February 22, and entered cold shutdown later that day.
This condition was discovered during development of a new procedure for combined steam line MSIV and outboard drain isolation valve leak rate testing. During development of the new STP, it was recognized that the existing procedures specify an incorrect position for motor-operated valves B21-MOVF027A, B, C, and D (main steam isolation valve stem leak-off drain). Because these 00 2015 - 001 were specified to be in the closed position, outboard MSIV stem packing leakage, if any, was not included in the leakage total for the outboard MSIVs, and has not been included in past testing as required to support the 150 scfh limit documented in SR 3.6.1.3.10. The Division I (outboard) main steam line and steam line drain penetration leakage rate summation documented at the end of the previous refueling outage was 101.35 scfh, compared to an allowable rate of 150 scfh indicating a margin of approximately 48 scfh.
The incorrect valve position for the subject test procedures was caused by lack of attention to detail when the procedures were developed. The procedure preparer and reviewers failed to recognize that the closed position for the subject valves would not allow for inclusion of potential packing leakage in the total leakage summation for the outboard MSIVs.
The affected procedures were revised and performed to establish the correct test configuration and confirm compliance with the applicable surveillance requirement.
PREVIOUS OCCURRENCE EVALUATION
No similar occurrences have been reported by River Bend Station in the past five years.
SAFETY SIGNIFICANCE
An assessment of effects of the procedure error was conducted. Reasonable assurance was established that the safety function of the outboard MSIVs was not compromised by this condition. Additionally, since the outboard MSIV packing leak-off isolation valves were required to be open by the system operating procedure, this condition did not adversely affect the ability of the MS-PLCS system to perform its design function. This conclusion is based on review of test results for the previous three operating cycles.