05000321/LER-2008-002
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 03-29-2008 |
|---|---|
| Report date: | 05-27-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3212008002R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code XX).
DESCRIPTION OF EVENT
On March 29, at approximately 1104 EDT, Unit 1 was at 1697 CMWTh, which is 60.5 percent RTP. On that day it was identified during bench testing that two Safety Relief Valves (SRVs) (EIIS Code SB) experienced setpoint drift that exceeded the allowable plant Technical Specifications (TS) limit At the conclusion of bench testing, a total of three of the eleven SRVs were identified as having setpoint drift in excess of the TS limit which is +1- 3%. The setpoint for each of the eleven SRVs is 1150 +1- 34.5 psig. The following is a tabulation of the test results for the eleven SRVs:
MPL Number Pilot Serial Number As-Found Lift Pressure Percent Drift 1B21-F013A 1190 1165 101.3 1B21-F013B 1003 1316 114.4 1B21-F013C 312 1177 102.3 1B21-F013D 1009 1161 101.0 1B21-F013E 311 1182 102.8 1B21-F013F 1227 1162 101.0 1B21-F013G 1226 1175 102.2 1B21-F013H 1011 1187 103.2 1B21-F013J 303 1180 102.6 1B21-F013K 1008 1175 102.2 1B21-F013L 301 1230 107.0 These valves were removed from service during the Spring 2008 refueling outage and replaced with like kind valves that were serviced and tested in accordance with plant procedures. These replacement valves had pilot discs made from Stellite 21 material, which is more resistant to corrosion bonding in this application.
CAUSE OF EVENT
The cause of the SRV setpoint drift exceeding the allowable plant TS limit is corrosion induced bonding between the pilot disc and seating surface.
4 by Technical Specifications (TS). Specifically, multiple test failures of the SRVs is defined as reportable in NUREG-1022, Revision 2, dated October 2000, in section 3.2.2, example 3, titled "Multiple Test Failures.
The 11 SRVs, which are located on the four main steam lines within the drywell between the reactor vessel and the inboard main steam isolation valves (MSIV EIIS Code SB), are required during Modes 1, 2, and 3 to limit the peak pressure in the nuclear system such that it will not exceed the applicable ASME Boiler and Pressure Vessel Code limits for the reactor coolant pressure boundary. Per TS Surveillance Requirement 3.4.3.1, the valves are tested in accordance with the In-service Testing Program to verify the safety function lift setpoints are within the specified limits The SRVs must accommodate the most severe pressurization transient which, for the purposes of demonstrating compliance with the ASME Code limit of 1375 psig peak vessel pressure, has been defined as a closure of all MSIVs with a failure of the direct reactor protection system trip from the MSIV position switches; the reactor ultimately shutdowns from a high neutron flux trip. Analysis of this event using the as-found bench test results for SRV actuation pressures has demonstrated that the resultant peak pressure was within the ASME Code limit Furthermore, the plant TS overpressure safety limit of 1325 psig dome pressure must be met during normal operations and for anticipated operational occurrences (AOOs). The analysis of the as-found test results also showed that for the MSIV Closure A00 with the MSW position switches providing the reactor protection system trip, the resultant dome pressure was within the plant TS Safety Limit.
In addition, a non-credited electrical actuation system was installed in 1993 to ensure proper actuation of the SRVs. This system provides a redundant, independent method (i.e., electrical signal) to actuate the SRVs. During the run cycle the redundant electrical system was available. The system was procured to Class lE environmental and seismic standards, and is deemed highly reliable.
Based on this analysis, it is concluded that this event had no adverse impact on nuclear safety.
SNC will continue to participate in industry working groups in evaluating potential solutions to this industry issue. Any additional actions to further improve SRV performance will be tracked under the plant's corrective action program.
ADDITIONAL INFORMATION
Other Systems Affected: None Failed Components Information:
Master Parts List Number: 1B21-F013 EIIS System Code: SB Manufacturer: Target Rock Reportable to EPIX: Yes Model Number: 7567F Root Cause Code: B Type: Relief Valve EIIS Component Code: RV Manufacturer Code: T020 Commitment Information: This report does not create any new permanent licensing commitments.
Previous Similar Events:
Corrective actions for that LER were not yet implemented for the Unit 1 SRV's and thus were replaced with pilot discs made from Stellite 21 material.
described results from the previous three outages where multiple SRV setpoint drift had occurred. Corrective actions for that LER focused on ensuring proper reporting of SRV setpoint drift was performed.