05000341/LER-2010-004
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 12-28-2010 |
|---|---|
| Report date: | 02-23-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 46515 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3412010004R00 - NRC Website | |
Initial Plant Conditions:
Mode� 1 Reactor Power� 75 percent
Description of the Event
On December 28, 2010 at approximately 0950 EST the quarterly High Pressure Coolant Injection (HPCI) [BJ] system surveillance procedure was released for performance. The system and the minimum flow valve (E4150F012) performed as expected during the startup of the HPCI System.
During the HPCI turbine trip portion of the surveillance, however, the HPCI minimum flow valve open and close indicating lights in the control room began blinking simultaneously. After a short duration (approximately 1 minute) the blinking faded and both indicators went out at 1220 EST. The HPCI minimum flow valve did not fully close as expected. Operations manually operated and closed the valve. Upon discovery of the problem and performance of minor troubleshooting, Operations determined that the ability of the HPCI minimum flow valve to perform its intended function was unreliable, and the valve was declared inoperable at 1220 EST. With an inoperable minimum flow valve, the system may not have been able to perform its intended function since the valve is relied upon for pump protection under low flow and high discharge pressure conditions that accompany system startup.
System troubleshooting, diagnostic testing, and analysis were performed, and a number of components were identified that could be responsible for the problem. These components were replaced. Post maintenance testing was successfully completed on December 30, 2010 at 1027 EST. The HPCI minimum flow valve was closed, and the system returned to service on December 30, 2010 at 1042 EST.
Significant Safety Consequences and Implications The HPCI system, a single train safety system, was rendered inoperable when the operation of the HPCI minimum flow valve was determined to be unreliable and the valve was declared inoperable. The purpose of the HPCI system is to provide emergency core cooling in the event of an accident involving loss of coolant from a small break. Reactor steam is used to drive the HPCI turbine, which in turn drives the main and booster pumps to provide a source of high pressure water to the reactor. The Reactor Core Isolation Cooling [BN] and Standby Feedwater [SJ] systems remained available for high pressure injection in the event of an emergency. Additionally, the Automatic Depressurization System [JE] was available to reduce reactor pressure to within the capabilities of the low pressure Emergency Core Cooling Systems.
This event resulted in approximately 46-hours where HPCI was inoperable. Technical Specification 3.5.1 allows HPCI to be taken out of service for planned outages for up to 14 days. This risk increase associated with HPCI being out of service for approximately 46-hours has been evaluated by the Probabilistic Safety Analysis (PSA) group and determined to be low.
This report is made in accordance with 10 CFR 50.73(a)(2)(v)(D), for any event or condition that could have prevented the fulfillment of a safety function of structures or systems that are needed to mitigate the consequences of an accident. An eight-hour non-emergency notification was made pursuant to 10 CFR 50.72(b)(3)(v)(D) as a condition that at the time of discovery could have prevented the fulfillment of a safety function to mitigate the consequences of an accident based on loss of a single train safety system (EN 46515).
Cause of the Event
A number of potential causes were identified related to the HPCI minimum flow valve. The potential causes that were not ruled out by troubleshooting and failure analysis were the close contactor, auxiliary contact alignment or high resistance, and high resistance connections (power fuse clip, loose leads).
Corrective Actions
The close contactor was replaced. The auxiliary contacts were removed, inspected and cleaned, and proper operation verified following installation. Circuit leads were inspected and tightened, and power fuse tightness verified during fuse replacement. This event has been documented in the Fermi 2 Corrective Action Program and additional actions may be taken as determined by the program.
Additional Information
A. Failed Component:
Component: Contactor Function: Controls power to the valve actuator motor Manufacturer: General Electric Model Number: CR305T026 Failure Cause: Internal contactor failure B. Previous LERs on Similar Problems:
There are no other LERs on similar problems noted within the past five years