05000395/LER-2008-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 01-24-2008 |
|---|---|
| Report date: | 07-30-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3952008001R01 - NRC Website | |
PLANT IDENTIFICATION
Westinghouse - Pressurized Water Reactor
EQUIPMENT IDENTIFICATION
IFV00498 Feedwater Flow Control Valve
IDENTIFICATION OF EVENT
On January 24, 2008, the C feedwater flow control valve (IFV00498) exhibited oscillations as indicated by the plant computer and on the Main Control Board (MCB). As the feedwater flow oscillations increased in size, the Shift Supervisor directed the operator to take manual control of the valve. Feedwater flow was greater than steam flow when manual control was implemented. When the operator decreased flow demand on the manual/auto station, IFV-498 indicated closed and feedwater flow decreased to zero.
Due to a rapidly decreasing level in C Steam Generator, the Shift Supervisor directed a manual reactor trip at 1604 hours0.0186 days <br />0.446 hours <br />0.00265 weeks <br />6.10322e-4 months <br />. The operations crew entered the reactor trip procedure. All systems responded as required. The plant was stabilized in Mode 3.
EVENT DATE
1/24/2008 Condition Report CR-08-00292 was initiated to address this event.
REPORT DATE
07/30/2008
CONDITIONS PRIOR TO EVENT
Mode 1, 100% Power
DESCRIPTION OF EVENT
On January 24, 2008, the C feedwater flow control valve (IFV00498) exhibited oscillations as indicated by the plant computer and on the MCB. As the feedwater flow oscillations increased in size, the Shift Supervisor directed the operator to take manual control of the valve. Feedwater flow was greater than steam flow when manual control was implemented. When the operator decreased flow demand on the manual/auto station, IFV00498 indicated closed and feedwater flow decreased to zero. Due to a rapidly decreasing level in C Steam Generator, the Shift Supervisor directed a manual reactor trip at 1604 hours0.0186 days <br />0.446 hours <br />0.00265 weeks <br />6.10322e-4 months <br />. The operations crew entered the reactor trip procedure. The Emergency Feedwater Pumps automatically started on Lo-Lo Steam Generator level.
Steam Generator levels recovered quickly. Cycling of the Pressurizer Level Control System resulted in the Letdown Relief Valve lifting due to high temperature and pressure. The Letdown Relief Valve reseated with no further anomalies. One Moisture Separator Reheater relief valve lifted momentarily, as expected during a turbine trip, and promptly reseated. All systems responded as required. The plant was stabilized in Mode 3.
CAUSE OF EVENT
The root cause was determined to be the failure of the feedwater flow control valve positioner pilot valve. The failure was due to either fretting as a result of normal operation or foreign material inclusion into the component's air system due to insufficient filtration and vibration induced component wear.
ANALYSIS OF EVENT
Flow Control Valve IFV00498 is a design backup to the associated Feedwater Isolation Valve (FWIV). The condition of IFV00498 did not affect the ability of the FWIV to perform its function. Only the flow control function of IFV00498 was impacted by this condition. However, the capability of the valve to close on an isolation signal and meet its safety function was not impacted.
CORRECTIVE ACTIONS
On each feedwater flow control valve, the positioners, check valves, and pressure regulators were replaced, and additional filtration was installed. Copper tubing and the brass check valves were replaced with stainless steel to minimize particulate intrusion. In addition, components susceptible to vibration were relocated. To address future problems, an "air-gag" device was installed on each feedwater flow control valve to facilitate on-line maintenance without loss of safety function.
PRIOR OCCURRENCES
There have been two other instances of Feedwater Flow Control Valve malfunctions in the past. A similar event occurred on March 30, 2004 and was reported by Licensee Event Report (LER) 2004-001-00. Valve positioners on all three feedwater flow control valves were replaced. An engineering evaluation was initiated to address resolution of pilot valve performance issues.
VCSNS subsequently experienced degraded response of IFV00498 while shutting down the reactor on December 4, 2004. All three valve positioners were replaced on January 28, 2005.