05000387/LER-2012-005
| Susquehanna, Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 3872012005R00 - NRC Website | |
EVENT DESCRIPTION
While in Mode 5, Refueling, in shutdown temperature and pressure bands, two (2) Main Steam Safety Relief Valves (SRVs) (EllS Code: SB and RV) failed to meet the setpoint criteria of +3/-5% set forth in Technical Specification 3.4.3. The two SRVs actuated at a pressure less than the -5% setpoint criteria.
The affected SRVs were installed on March 17, 2008 during the Susquehanna Unit 1 15th Refueling and Inspection Outage. They were tested prior to the subsequent post-outage start-up. The tests included stroking the valves using the valves' actuator assemblies in accordance with station procedures. The SRVs were removed from the plant on April 11, 2012 and sent to Wyle Labs for routine testing and refurbishment. The valves were tested by Wyle Labs on April 24 and April 25, 2012. The following are the April 24 and April 25, 2012 test results:
Valve Serial #� Setpoint (psig) As Found (psig)� Deviation N63790-00-0112 1205 1142 -5.23% N63790-00-0133 1195 1133 -5.19% On June 12, 2012, based on the conclusions of the component failure analysis performed by the valve manufacturer, it was identified by Susquehanna personnel that the two SRVs actuated below their required setpoints because of a misalignment of valve internals. Having two SRVs inoperable due to the same cause constitutes a Common-Cause Inoperability of Independent Trains or Channels and is reportable under 10 CFR 50.73(a)(2)(vii). Each of the SRVs remained functional and would have relieved pressure.
There were no actual adverse consequences to the fuel, any plant equipment, or to the health and safety of the public as a result of this event.
CAUSE OF THE EVENT
The cause of the event was determined to be two SRVs inoperable at the same time during the operating cycle. The inoperability of the SRVs was apparently caused by misalignment of valve internals due to actuation of the valves, prior to start-up with the actuator assembly. Upon de-pressurization of the accumulator and subsequent closing of the main valve, a misalignment of the valve internals may have occurred.
ANALYSIS/SAFETY SIGNIFICANCE
This event was determined to be reportable under 10 CFR 50.73(a)(2)(vii) in that two (2) SRVs were inoperable at the same time during the past operating cycle due to misalignment of valve internals. There were no actual adverse consequences to the fuel, any plant equipment, or to the health and safety of the public as a result of the 2 SRVs not lifting within +3%/-5% of their design set point. The SRVs remained functional and would have relieved pressure. There were no safety or operational concerns associated with premature SRV lift since all SRVs tested lifted at pressures that were greater than the minimum relief mode lift pressure and because there was no effect to the manual operation of the SRVs. Therefore, the SRVs did not challenge the operators due to inadvertant actuation or prevent them from actuating the valves and still provided reactor pressure boundary overpressurization protection.
CORRECTIVE ACTIONS
The following corrective actions have been completed:
- The SRVs were replaced with SRVs having a setpoint tolerance of +/- 1% of nameplate setpoint pressure.
The following corrective action is planned:
- The SRVs that failed their setpoint tolerance will be refurbished to have an actuation pressure within +/- 1% of nameplate setpoint pressure.
- Pending a license amendment and In-Service Testing (IST) Relief Request, procedures for post-installation testing of SRVs will be modified to test the SRVs using altemative methods.
No regulatory commitments are associated with this report.
ADDITIONAL INFORMATION
Component Information:
Component: Main Steam Safety Relief Valve Manufacturer: Crosby Valve and Gage Co.
Model Number. HB-65-BP-DF Size: 6R10
Previous Similar Events:
- Safety Relief"Multiple Test Failures of Main SteamLER 2000-007-00, Valves" Docket No. 387/License No. NPF-14,
- Safety Relief"Multiple Test Failures of Main SteamLER 2001-005-00, Valves" Docket No. 388/License No. NPF-22,
- Safety Relief"Multiple Test Failures of Main SteamLER 2009-001-00, Valves" Docket No. 388/License No. NPF-22,
- Safety Relief"Multiple Test Failures of Main SteamLER 2011-001-00, Valves" Docket No. 388/License No. NPF-22,