05000272/LER-2001-003
| Docket Number | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2722001003R00 - NRC Website | |
FACILITY NAME (1) DOCKET (2) LER NUMBER (6) PAGE (3) SALEM UNIT 1 05000272 YEAR NUMBER NUMBER 01 � - � 003 � - � 00 2 � OF � 4
PLANT AND SYSTEM IDENTIFICATION
Westinghouse - Pressurized Water Reactor Main Steam / Safety Valves (SB/RV)* * Energy Industry Identification System (EIIS) codes and component function identifier codes appear in the text as {SS/CCC}.
IDENTIFICATION OF OCCURRENCE
Event Date: April 13, 2001
CONDITIONS PRIOR TO OCCURRENCE
Mode 6 — Refueling
DESCRIPTION OF OCCURRENCE
On April 13, 2001, with Unit 1 in Mode 5 (Refueling) one of five Main Steam Safety Valves (MSSV) {SB/RV} that was tested failed the as-found actuation pressure surveillance test, required by ASME OM-1987, Part 1, Requirements for Inservice Performance Testing of Nuclear Power Plant Pressure Relief Devices. The Technical Specification (TS) acceptance band for the as-found actuation pressure is ± 1% of the nameplate setpoint pressure. The as-found actuation pressure for MSSV 11MS11{SB/RV) was below the lower limit of minus 1% of the nameplate setpoint.
The actual test results of the failed valve is:
Valve Id As found TS Setpoint Acceptable band % Difference (psig) (psig) (psig) (psig) 11MS11 1111 1125 1113.8 — 1136.3 1.3% Because the actual lift set point of the 11MS11 was not within 1% of set point, expanded testing scope was performed in accordance with the In-Service Test (IST) program. Two additional MSSV's were tested and met the Technical Specification required acceptance criteria. A review of this event determined that a Safety System Functional Failure (SSFF), as defined in NEI 99-02, did not occur. No structures, systems or components were inoperable at the time of this event that contributed to this event.
FACILITY NAME (1) DOCKET (2) LER NUMBER (6) PAGE (3) SALEM UNIT 1 05000272 YEAR NUMBER NUMBER
CAUSE OF OCCURRENCE
The apparent cause of the valves failing to meet the Technical Specification acceptance criteria was attributed to excessive seat leakage. The MSSV leakage is a result of steam cutting between the disc and nozzle seating area. Steam cutting can occur when system pressure reaches greater than 90% of set pressure, which typically occurs during a unit start-up. At this point, system pressure is sufficient to allow the relief valve(s) to simmer. If this simmering condition is allowed to exist for an extended period (e.g., during a unit start-up), the steam flow has the potential to erode small grooves into the seating surface. These small grooves create a permanent leak path by which steam continues to erode the disc and nozzle. This condition was confirmed when the valve was tested at the vendors test facility.
From a process point of view, there were no program or process deviations that contributed to this event. As described in AEOD/S92-02, Safety and Safety / Relief Valve Reliability, a set-point variance (drift) of greater than ±1.0% but less than ±3.0% is not unusual for these valves.
PRIOR SIMILAR OCCURRENCES
A review of 1999 and 2000 LERs for both Salem and Hope Creek identified 3 similar occurrelAces.
attributed to set point variance (drift). Setpoint variance, as discussed in the AEOD/S92-02, is a result of aging.
Aging is the effect seen by a component that remained unexercised for an extended period of time at extreme temperatures. Lubrication dries out due to high temperature, and due to component design, there is no lubricity provided by system fluid. Therefore, a ± 1.0% tolerance may be too restrictive for this application. These failures were also within the ± 3.0% tolerance.
acceptance criteria of ± 1.0%. The apparent cause of this event was attributed to excessive seat leakage as indicated by steam cutting of valve disc and nozzle. Again, as discussed in the AEOD/S92-02, a set-point variance of greater than 1.0% but less than ± 3.0% is not unusual for these valves.
FACILITY NAME (1) DOCKET (2) LER NUMBER (6) PAGE (3) PRIOR SIMILAR OCCURRENCES (cont'd) acceptance criteria by 3.1%. The apparent cause of this event was attributed to friction on the sliding surfaces resulting from poorly controlled vendor's maintenance. These practices were addressed via a NUPIC audit.
Corrective actions associated with the Salem LER would have not precluded this event, since they did not involve the failure of a process or program. The safety relief valve associated with the Hope Creek LER was a two- stage power operated valve, therefore the corrective actions would not have been appropriate for this event.
SAFETY CONSEQUENCES AND IMPLICATIONS
There were no safety consequences associated with this event. The Salem licensing basis UFSAR Chapter 15 accident analyses were re-analyzed in support of a Fuel Upgrade/Margin Recovery Program (FUMRP), the Unit 1 Steam Generators Replacement Project, and NSAL 98-007 "Analysis of Pressurizer Heaters". These analyses support a ±3% to;erance that bounds the as found condition of the valve and provides the justification for a license change request submitted on September 26, 2000.
Based on the above, the valve would have performed its intended safety function although the set point was found to be outside the Technical Specification tolerances, and the health and safety of the public and plant personnel were not affected.
CORRECTIVE ACTIONS
1. The MSSV has been refurbished to assure seat tightness to 95% of Setpoint pressure and tested to ensure compliance with the ±1% Technical Specification tolerance. NOTE: Valves are tested offsite every 72 months to ensure seat leakage criterion as well as compliance with the Technical Specification Setpoint tolerance is satisfied.
2. A license change request to increase the Technical Specification set-point tolerance from ±1% to ±3% was submitted to the NRC on September 26, 2000.
3. Two additional valves were tested in accordance with the IST program. The two additional valves tested were within the ±1% Technical Specification set-point tolerance.
COMMITMENTS
The corrective actions cited in this LER are voluntary enhancements and do not constitute commitments.