05000334/LER-2006-004
| Beaver Valley Power Station | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3342006004R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse-Pressurized Water Reactor {PWR} Solid State Protection System {JG}
CONDITIONS PRIOR TO OCCURRENCE
Unit 1: Mode 1 at 100 percent power. There were no systems, structures, or components that were inoperable at the start of the event that contributed to the event other than as described below.
DESCRIPTION OF EVENT
On September 7, 2006, the Beaver Valley Power Station (BVPS) Unit No. 1 experienced an unexpected reactor trip at 21:57 while operating at full power. The reactor trip then caused a Main Turbine trip. The first out computer point for the reactor trip was Turbine Trip due to Reactor Trip. The operating crew entered Emergency procedure E-0 (Reactor Trip or Safety Injection), and transitioned to ES-0.1 (Reactor Trip Response) in response to the trip.
Following the reactor trip, safety systems functioned as designed. The safety related 4160v emergency busses correctly switched automatically to their respective offsite power feed when the Main Generator tripped after the reactor trip. All three Auxiliary Feedwater System pumps started as expected on low steam generator levels. The plant was stabilized in Mode 3 with primary and secondary parameters returned to normal hot standby values.
N-36 intermediate range power instrument failed off scale low following the reactor trip, but was unrelated to the cause of the reactor trip.
CAUSE OF EVENT
The cause of the reactor trip was the unexpected opening of the "B" Reactor Trip Breaker caused by a random failure of universal logic card A312B output gate in the Solid State Protection System (SSPS) that produced an invalid SSPS signal to the trip breaker. The cause of the Universal Logic Board (ULB) failure was a manufacturing defect (corrosion) on the integrated circuit Z9 that was not identified by pre and post manufacturing testing. An assessment of ULB failures demonstrates that the failures occur in a random, unpredictable manner.
REPORTABILITY
On September 7, 2006, BVPS Unit 1 experienced a reactor trip at 21:57. This was reportable pursuant to 10 CFR 50.72(b)(2)(iv)(B) as an actuation of the Reactor Protection System when the reactor is critical and pursuant to 10 CFR 50.72(b)(3)(iv)(A) as an event that resulted in the valid automatic actuation of the Auxiliary Feedwater System. BVPS notified the Nuclear Regulatory Commission per 10 CFR 50.72 via EN 42834 at 23:23 EDT on September 7, 2006.
This reactor trip is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event that was not part of a pre-planned sequence which resulted in the automatic actuation of: the Reactor Protection System per 10 CFR 50.73(a)(2)(iv)(B)(1) and of the Auxiliary Feedwater System per 10 CFR 50.73(a)(2)(iv)(B)(6).
SAFETY IMPLICATIONS
At the time of the BVPS Unit 1 reactor trip due to the unexpected opening of the "B" Reactor Trip Breaker on September 7, 2006, there were no other PRA modeled components that were unavailable. Plant safety systems functioned as designed following the reactor trip. This event is bounded by the Design Basis "Loss of External Updated Final Safety Analysis Report (UFSAR).
The cause of the reactor trip was due to the unexpected opening of the "B" Reactor Trip Breaker caused by a defective logic card that produced an invalid SSPS signal to the trip breaker. Therefore, a spurious reactor trip initiating event was used to analyze the risk associated with this event.
The plant risk associated with the BVPS Unit 1 reactor trip that occurred on September 7, 2006, due to the unexpected opening of the "B" Reactor Trip Breaker is considered to be very low. This is based on the conditional core damage probability for the event when considering the actual component unavailability that was present at the time of the reactor trip.
CORRECTIVE ACTIONS
1. The failed SSPS Universal Logic Board (ULB) card was replaced.
CORRECTIVE ACTIONS (Continued) 2. Initial laboratory analysis confirmed that the failure was in the Integrated Circuit portion of the logic card. The failed SSPS logic card received additional Westinghouse destructive failure analysis.
3. FirstEnergy Nuclear Operating Corp. (FENOC) is participating with Westinghouse on performing additional generic investigations on ULB cards. This will include evaluating methods to ensure more reliable ceramic MHTL (Motorola High Threshold Logic) devices are used when manufacturing SSPS boards and will include evaluating SSPS board replacement strategy considerations.
Completion of the above and other corrective actions are being tracked through the BVPS corrective action program.
PREVIOUS SIMILAR EVENTS
A review found two prior BVPS Unit 1 and one prior BVPS Unit 2 Licensee Event Reports (LERs) within the last five years involving the a Solid State Protection System issue:
- LER 1-2006-002 LER 1-06-002, "Unit Shutdown Completed as Required by Plant Technical Specification for Failed Solid State Protection System Memory Card.
This event involved a failed SSPS testing circuit (bent card pin).
- LER 1-2003-007, "Inadvertent Reactor Trip During Solid State Protection System Testing." This event did not involve a failed SSPS component.
- LER 2-2001-003, "Condition Inadvertently Exceeds Technical Specification Allowed Outage Time." This involved a human performance event associated with a failed SSPS component.
Though not LERs, there have been other SSPS ULB failures and non-ULB failures noted within the last two years at BVPS. Although no specific common mode failures have been identified, FENOC continues to work with Westinghouse on addressing SSPS related failures.
COMMITMENTS
There are no new commitments made by FENOC for BVPS Unit No. 1 in this document.