05000443/LER-2005-003
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. N/A 05000 | |
| Event date: | 3-22-2005 |
|---|---|
| Report date: | 05-16-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 4432005003R00 - NRC Website | |
I. Description of Event
On March 22, 2005 at 1022 during operation in Mode 1 at 100% power, Seabrook Station entered the action statement of Technical Specification (TS) 3.3.1, Reactor Trip System Instrumentation, for an inoperable train A reactor trip breaker (RTA) [JE, 52]. While performing a routine actuation logic surveillance test on the solid state protection system (SSPS) [JE], the reactor trip breaker unexpectedly tripped open and subsequently failed to close upon initiation of a close signal. As a result, the station entered action 9 of TS Table 3.3-1, which requires the unit to be in Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. A plant shutdown commenced at 1102. The NRC was notified of the initiation of this TS-required shutdown in a four-hour report (event # 41513) in accordance with 10CFR50.72(b)(2)(i). The plant entered Mode 3 at 1547 on March 22, 2005. The reactor trip breaker was restored to operable status at 0101 on March 23, 2005.
II. Cause of Event
The apparent cause of this event was a malfunctioning switch [JC, 17] associated with the Auto Shunt Trip Test pushbutton (Grayhill Inc., part number 7-26RED). This feature is used to test the shunt trip device on the reactor trip breakers. Industry experience has shown that these switches become unreliable due to sub-component wear and time in service and should be replaced periodically. The failure of the switch caused actuation of the shunt trip coil, providing a trip open signal to RTA, and prevented closure of the breaker.
The station became aware of the switch reliability issue in 2002 and developed a preventative maintenance activity to replace the switches on a 6th refueling outage interval. In 2004, a switch with a new design became available, and replacement of the switches was scheduled for the refueling outage that was scheduled to commence on April 1, 2005. Prior to this event, the switches neither performed erratically nor experienced any failures. A review of the extent of condition identified that the switch unreliability concern also existed with the Auto Shunt Trip Block pushbutton associated with the reactor trip breakers.
III. Analysis of Event
This event met the reporting criteria of 10CFR50.72(b)(2)(i) and 50.73(a)(2)(i)(A) for initiation and completion of a plant shutdown required by the TS. This event is of regulatory significance because the condition was sufficiently serious to warrant a plant shutdown. Nonetheless, no consequences resulted from the event and, therefore, this occurrence had no adverse impact on the plant or on the health and safety of the public. No inoperable structures, systems, or components other than RTA contributed to the event.
The malfunction of the reactor trip breaker was classified as a Maintenance Rule Functional Failure. However, this condition did not result in a loss of safety function since the redundant train of the reactor protection system, including the reactor trip and bypass breakers, remained operable during the event.
IV. Corrective Action The interim corrective action consisted of implementing a temporary modification that installed a jumper around the Auto Shunt Trip Test pushbutton. Replacement of the train A and train B switches for the Auto Shunt Trip Test and Auto Shunt Trip Block devices was completed in the April 2005 refueling outage.
V. Additional Information
The Energy Industry Identification System (EIIS) codes are included in this LER in the following format: [EIIS system identifier, EIIS component identifier].
VI. Similar Events The station has had no previous occurrences of malfunctions of the switches in the reactor trip breaker Auto Shunt Trip Test device.