05000387/LER-2015-002
| Susquehanna Steam Electric Station Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| Initial Reporting | |
| ENS 50974 | 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 3872015002R00 - NRC Website | |
the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Susquehanna Steam Electric Station, Unit 1 05000387
CONDITIONS PRIOR TO THE EVENT
Unit 1 — Mode 1, 100 percent Rated Thermal Power Unit 2 — Mode 3, Hot Shutdown, 0 percent Rated Thermal Power There were no systems, structures, or components that were inoperable at the start of the event and contributed to the event.
EVENT DESCRIPTION
On April 11, 2015, at 0051 hours5.902778e-4 days <br />0.0142 hours <br />8.43254e-5 weeks <br />1.94055e-5 months <br />, the ventilation system that maintains Secondary Containment at a negative pressure failed requiring entry into the Action Statement for Technical Specification (TS) 3.6.4.1, Condition A, for failure to meet Surveillance Requirement (SR) 3.6.4.1.1 for Susquehanna Steam Electric Station (SSES) Unit 1 and Unit 2. The Reactor Building (RB) Zone II differential pressure fell below the TS limit of 0.25 inches water column (in. w.c.) vacuum when both RB Zone II exhaust fans (2V205A and B) [EllS System Code VA] would not develop flow. Operators found the Zone II exhaust fan B discharge damper control air solenoid valve (SV27578B) to be porting air, such that both exhaust fans could not continue to run. The failed solenoid valve was isolated and replaced. TS 3.6.4.1, Condition A, was exited at 0320 hours0.0037 days <br />0.0889 hours <br />5.291005e-4 weeks <br />1.2176e-4 months <br /> when the differential pressure was restored to meet the TS limit of 0.25 in. w.c. vacuum.
On April 11, 2015, at 0522 hours0.00604 days <br />0.145 hours <br />8.630952e-4 weeks <br />1.98621e-4 months <br />, this condition was reported as an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> Event Notification#50974 in accordance with 10 CFR 50.72(b)(3)(v)(C) for any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.
SSES has no redundant Secondary Containment system.
In accordance with 10 CFR 50.73(a)(2)(v)(C), this LER is being submitted for an event or condition that at the time of discovery, could have prevented the fulfillment of the safety function of Secondary Containment to control the release of radioactive material.
CAUSE OF THE EVENT
The cause of the event is the storage practice for the solenoid valve and preventive maintenance (PM) strategy were both improper. The failure analysis of the solenoid valve has not yet been completed but will be addressed by the station's Corrective Action Program. If other cause(s) of this failure are found, then additional corrective action(s) will be identified to prevent a recurrence, and a supplement to this LER will be provided.
ANALYSIS/SAFETY SIGNIFICANCE
The actual consequence of this event was a degradation of the Secondary Containment vacuum which led to an unplanned entry into the Action Statement for TS 3.6.4.1, Condition A, for Unit 1 and Unit 2. An Engineering evaluation was performed which concluded that Secondary Containment could have performed its safety function of isolating as assumed in the SSES accident analysis and also of re-establishing 0.25 in. w.c. vacuum (i.e., drawdown time) within the assumed accident analysis time of 10 minutes. Therefore, the safety function of the Secondary Containment boundary and Standby Gas Treatment systems were unaffected and capable of performing their safety function during this event. As such, there were no actual consequences to the health and safety of the public.
Additionally, this event will not be counted as a safety system functional failure (SSFF) for the NRC performance indicator based on the engineering evaluation that concluded there was no loss of Secondary Containment's ability to fulfill its safety function.
CORRECTIVE ACTIONS
Immediate compensatory action was performed by isolating and replacing the failed solenoid valve. The TS 3.6.4.1, Condition A was exited when differential pressure for Secondary Containment was restored to meet the required TS limit in SR 3.6.4.1.1.
Corrective action will be pursued with additional failure analysis, and the following to prevent recurrence:
1. Storage practices for these solenoid valves will be changed to use an appropriate standard.
2. A preventive maintenance strategy change for Zones I, II and III solenoid valves will be to replace these valves more frequently than the current practice.
PREVIOUS SIMILAR EVENTS
This event was similar to another malfunction of this type of solenoid valve, occurring on November 27, 2013, and reported in Licensee Event Report (LER) 2013-008-00, dated January 23, 2014.
Other events that more generally involve the entry into the TS 3.6.4.1, Condition A for a failure to maintain differential pressure requirements includes:
- LER 50-388/2014-001: Secondary Containment Personnel Airlock Doors Both Opened Resulting in Failure to meet TS 3.6.4.1
- LER 50-387(388)/2013-003-00: Loss of Secondary Containment
- LER 50-387(388)/2013-004-00: Loss of Secondary Containment Due to Differential Pressure Not Meeting Technical Specification 3.6.4.1
- LER 20-387(388)/2013-005-00: Loss of Secondary Containment
COMPONENT INFORMATION
Manufacturer: ASCO Services Type: 3-way electrical solenoid valve Process fluid: Air Model: ASCO 8320 Solenoid Valve, General Use Model 8320G003 Voltage: 120 VAC