05000305/LER-2012-002
| Docket | |
| Event date: | 02-29-2012 |
|---|---|
| Report date: | 04-29-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3052012002R00 - NRC Website | |
Event Description:
On February 29, 2012, during the start of safety injection pump B [P] for surveillance testing, the 4160 volt breaker [52] functioned correctly to start the pump but the breaker charging spring motor [MO] did not stop after charging the breaker springs.
The event occurred during routine surveillance testing. Safety injection pump B was started at approximately 1206 hours0.014 days <br />0.335 hours <br />0.00199 weeks <br />4.58883e-4 months <br />, the breaker at location 1-606BKR closed, and the spring charging motor for the breaker began to run, as expected. However, the spring charging motor failed to stop after sufficient time had elapsed for the springs to fully charge. Control room personnel directed electricians to open the knife switch for the charging control circuit associated with breaker 1-606BKR. Once the knife switch was opened, the charging motor stopped, as expected. Performance of the surveillance continued. At approximately 1230 hours0.0142 days <br />0.342 hours <br />0.00203 weeks <br />4.68015e-4 months <br />, the control switch for safety injection pump B was taken to the STOP position per the surveillance procedure.
The breaker at location 1-606BKR opened and safety injection pump B stopped, as expected.
The breaker was removed from its switchgear cubicle for troubleshooting. Following visual inspection, the breaker was cycled multiple times at the local test station without incident. Since the initial troubleshooting was unable to identify a definite cause for the original condition, a decision was made to obtain a spare replacement breaker, and quarantine the original breaker. Following installation of the replacement breaker, surveillance was performed to demonstrate operability. All equipment operated as designed during the surveillance procedure. Safety injection pump B and associated safety injection train B were declared operable and returned to service at 2110 hours0.0244 days <br />0.586 hours <br />0.00349 weeks <br />8.02855e-4 months <br /> on 02/29/2012.
A review of work history found the breaker had been installed at location 1-606BKR on 12/07/2011 shortly after it had been refurbished by an outside vendor. A search in the work management system did not indicate any corrective maintenance work orders had been initiated against this breaker prior to its refurbishment.
With this Westinghouse model PSD-5VR circuit breaker in the condition where it's charging motor would continue to run after breaker closure, there is a postulated scenario impacting safety injection pump operability. If the safety injection pump were stopped with the breaker charging motor continuing to run and the breaker was called upon to close, it would not cycle closed due to the breaker's closing circuit design.
The safety injection pump B breaker was previously cycled successfully on December 7, 2011. Between the period of December 7 through February 29, 2012, safety injection pump A was inoperable on January 16, 2012 and February 7, 2012. Thus, it can be postulated that both trains of safety injection were inoperable at the same time.
Per Technical Specifications 3.5.2, ECCS — Operating: Limiting Condition for Operation (LCO) 3.5.2 requires "Two ECCS trains shall be OPERABLE." For CONDITION A with one or more trains inoperable, REQUIRED ACTION A.1 requires restoring train(s) to OPERABLE status with a COMPLETION TIME of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This time was exceeded.
Therefore, this event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) for any operation or condition which was prohibited by the plant's Technical Specifications and 50.73(a)(2)(v), for any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to:
(A) Shut down the reactor and maintain it in a safe shutdown condition; (B) Remove residual heat; or (D) Mitigate the consequences of an accident.
.i.
An assessment was made of the risk associated with this scenario. Common cause was explicitly included in this assessment. It was conservatively assumed that SI pump B had no chance of starting in recirculation mode although the actual failure was intermittent. With this conservative methodology, the calculated risk for the period in which the faulty breaker was installed was below the threshold for a very low risk (green) in the Significance Determination Process.
Cause:
A bent main charging shaft on the 4160 volt breaker caused the charging motor at location 1-606BKR failure to stop. Troubleshooting confirmed the motor failing to stop was an intermittent condition. Troubleshooting and inspections identified the bent main charging shaft as the only significant anomaly within the breaker.
The cause for the bent shaft could not be determined.
Corrective Actions:
The breaker was replaced with a spare breaker following completion of the surveillance testing.
Additionally, the vendor has revised their refurbishment procedure for Westinghouse model PSD-5VR circuit breakers to include a procedure step to specifically inspect the charging main shaft for straightness.
Similar Events:
A review of Licensee Event Reports covering the previous three years did not identify any similar events.