05000443/LER-2006-005
| Docket Number | |
| Event date: | 07-03-2006 |
|---|---|
| Report date: | 07-27-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4432006005R00 - NRC Website | |
I. Description of Event
On July 3, 2006 at 0615, during operation at 100% power, Seabrook Station determined that the unit had been operated in a condition prohibited by the Technical Specifications (TS). Specifically, at 1949 on June 30, 2006, an alarm annunciated in the Main Control Room indicating a malfunction of a power supply associated with the control cabinet that contains the Train A controls for two Main Steam Isolation Valves (MSIV) [SB, V]. Subsequent troubleshooting identified a problem with the valve control module for Train A MSIV (MS-V88). The MSIV was declared inoperable on July 1 at 1318 to facilitate additional troubleshooting and eventual replacement of the failed control module.
Following replacement of the module the MSIV was declared operable on July 1 at 1559. A subsequent examination of the failed valve control module on July 3 identified both power supply fuses open. This condition would have prevented the control module from functioning and would have rendered the MSIV inoperable. As a result of this discovery, a Reportability Determination was performed on July 3, 2006. The Reportability Determination concluded that the MSIV was inoperable from receipt of the control room alarm until the failed valve control module was replaced, a duration of approximately 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />. The plant operated at full power during this time with the MSIV open. TS 3.7.1.5, Main Steam Isolation Valves allow only four hours to restore a MSIV to operable status before requiring a plant shutdown. The MSIVs are also containment isolation valves (CIV). TS 3.6.3, Containment Isolation Valves allow only 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to restore a CIV to operable before requiring either the CIV be closed or the plant shutdown. Consequently, this event resulted in a condition prohibited by the TS. The condition did not involve a safety system functional failure.
II. Cause of Event
The cause of this event was a random failure of a MSIV control module printed circuit board. This is the first confirmed valve control module failure at Seabrook Station. The system is qualified for a 40- year life.
III. Analysis of Event
One MSIV is provided on each steam generator to provide positive shutoff of steam flow during emergency as well as normal operation. Each MSIV receives closure signals from both Train A and Train B instruments and logic circuits. The MSIVs are located in two separate pipe chases, two MSIVs in each pipe chase. Open, close and partial stroke test signals to each MSIV are processed through the MSIV logic cabinets. There are four MSIV control cabinets. Each cabinet processes either the Train A or Train B signals to the MSIVs. The alarm received in the Main Control Room was indicative of a problem with the cabinet that processes the Train A signal for two MSIVs (MS-V88 and MS-V90).
Troubleshooting into the cause for the alarm ultimately determined that the alarm was due to a faulty valve control module for MS-V-88 and that the nature of the fault rendered MS-V-88 inoperable.
However, during the period of inoperability, MS-V-88 remained capable of closing automatically via Train B closure signals and circuitry.
This was a random failure of a printed circuit board in the Train A MSIV logic cabinet. Review of the failure history of MSIV logic failures indicates relatively few failures of MSIV logic boards. There are no systematic failures occurring with these boards. Based on the random nature of this failure there is no transportability to other printed circuit boards in the MSIV logic cabinets.
The event had no adverse impact on the plant or on the health and safety of the public or plant personnel. No plant transients, systems actuations, or consequences resulted from the event. No other inoperable structures, systems, or components contributed to this event.
This event is of regulatory significance because it met the reporting criterion of 10CFR50.73(a)(2)(i)(B) for a condition prohibited by the TS. The event was reported to the NRC on July 3, 2006 at 1623 (event #42684) in accordance with the Seabrook Station operating license condition 2.G for a violation of the TS.
IV. Corrective Action The failed MSIV valve control module printed circuit board was replaced.
V. Similar Events This is the first confirmed valve control module failure at Seabrook Station.
VI. Manufacturer Data The valve control module was originally manufactured by Consolidated Control P/N 6N372-1.