05000443/LER-2012-002
| Seabrook Station | |
| Event date: | 9-25-2012 |
|---|---|
| Report date: | 11-08-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4432012002R00 - NRC Website | |
Description of Event
On September 25, 2012 with the unit in a refueling outage and defueled, station personnel, while reviewing a design change for installation of new circuit boards in the solid state protection system [JE], identified a deficiency in the procedure that performs response time testing of the reactor trip breakers (RTB) [JC, 52]. The RTB have two diverse trip methods: the undervoltage circuit and the shunt trip circuit. When a RTB is opened through the shunt trip circuit, two coils (STA and SH TR) [JC, RLY] must function in order to open the breaker. A review of the existing test method found that the shunt trip circuits for both RTB had not been adequately tested. Further, a review of previous revisions of the surveillance procedures concluded that the response time of the shunt trip circuit had never been adequately tested.
Cause of Event
This event is similar to and has the same cause as the inadequate time response testing reported September 13, 2012, in LER 2012-001, Inadequate Testing of Certain Emergency Feedwater Actuation System Relays [BA, RLY].
The root cause of the event was that the procedure development process in effect prior to station operation did not require validation of technical bases when surveillance procedures were initially developed. However, current programmatic guidance for procedure development is substantially more robust.
Analysis of the Event
Two separate and independent RTB connected in series provide power to the control rod drive mechanisms. When either of the RTB opens, power is interrupted to the rod drive power supply, and the control rods fall into the core. The RTB have two diverse trip methods: the undervoltage circuit and the shunt trip circuit. When a RTB is opened through the shunt trip circuit, two coils (STA and SH TR) must function in order to open the breaker. During review of a design change for installation of new circuit boards in the solid state protection system, station personnel discovered that the surveillance procedure that performs response time testing of the RTB does not measure the response time of the STA relay in the shunt trip circuit. Further review concluded that the response time of the shunt trip circuit had never been adequately tested. However, surveillance procedures adequately test the response time of the undervoltage trip circuit and perform appropriate functional tests of the undervoltage and shunt trip circuits.
This condition was discovered while the plant was shutdown for a refueling outage. During the outage in October 2012, technicians used a revised procedure to obtain response times for the RTB that included both devices STA and SH TR in the shunt trip circuit. The measured response times were 0.036 second and 0.046 second for RTB A and B, respectively. Because the as-found response times were well below the limit of 0.120 second, this event had no potential safety consequences.
This event met the reporting criterion of 10 CFR 50.73 (a)(2)(i)(B) for a condition prohibited by the TS. However, this event had no adverse impact on the health and safety of the public or the plant and its personnel. Although the response time for the shunt trip circuit of the RTB had never been adequately tested, measurements obtained after discovery of the condition found the response time within acceptable limits. No plant transients, systems actuations, or consequences resulted from this event. This event did not involve a safety system functional failure.
Corrective Actions
The corrective actions for this condition included revising the surveillance procedure and obtaining response times, which were found to be within acceptable limits. A review of the adequacy of time response testing is ongoing to address the extent of condition.
Similar Events In March of 2011, Seabrook personnel identified that feedwater isolation on hi-hi steam generator level was not being adequately tested as required by TS 4.3.2.2, which resulted in declaration of a missed surveillance.
time for starting and loading of the motor-driven emergency feedwater pump had not been adequately tested.
Additional Information
The Energy Industry Identification System (El IS) codes are included in this LER in the following format: [Ell S system identifier, EIIS component identifier].