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On June 19, 2016, while operating at 82% power, two secondary containment access airlock doors were briefly opened simultaneously during a surveillance test. This event was a momentary inoperability of secondary containment integrity, which is an 8 hour reportable event. The Resident Inspector was notified, and an Event Notification made pursuant to 10 CFR 50.72(b)(3)(v)(C). (Reference EN#52022). Following the event, the door controls were adjusted and verified to function properly. On June 29, 2016, at 100% power, workers opened two doors concurrently when entering a secondary containment access airlock. The individuals promptly closed their respective doors. The event was a brief inoperability of secondary containment integrity as above, notifications were made, and repairs completed. (Reference EN#52053) The root causes were determined to be inadequate procedural guidance and equipment design not being able to prevent the simultaneous opening of an inner and outer door at all times, under all possible conditions. Corrective actions include modification of the interlock tests, and replacement of key door interlock components.

These events did not result in a safety system functional failure. There were no radiological releases associated with these events.

On March 21, 2015, while operating at 100% power, workers opened doors concurrently when entering a secondary containment access airlock. The individuals involved each closed their respective doors upon encountering this unexpected condition; however, the result was a brief inoperability of secondary containment integrity. This resulted in an 8 hour reportable event. The Resident Inspector was notified, and an Event Notification was made pursuant to 10 CFR 50.72(b)(3)(v)(C) due to a condition at the time of discovery that prevented the fulfillment of the Secondary Containment safety function (Reference EN#50914).

Following the event, the doors were verified to be functioning properly and no deficiencies were noted on either door.

A Root Cause Evaluation was conducted and determined the root cause of this event is that the airlock door interlock is not designed to prevent more than one airlock door from opening under all possible conditions.

This event did not result in a safety system functional failure. There were no radiological releases associated with this event.

On June 30, 2014, at 1913, while operating at 98% power, a grid disturbance resulted in an automatic start of both of the site's Emergency Diesel Generators (EDGs) (IEE Code EK). Neither EDG loaded onto its respective essential bus. The cause of the EDG starts was a momentary (approximately 13 cycles) dip in essential bus voltage to 62%. A review of the system design showed that since the EDGs started on an automatic start signal of essential bus voltage less than 65% for greater than 12 cycles, the EDGs operated as designed. Both EDGs were secured and returned to their normal standby readiness condition at 2116 on June 30, 2014. This event resulted in an 8 hour reportable event. The Resident Inspector was notified, and Event Notification Number 50246 was made pursuant to 10 CFR 50.72(b)(3)(iv)(A) due to a valid system actuation.

The apparent cause of the event was determined to be a valid start of the EDGs per design. This event did not result in a safety system functional failure. There were no radiological releases associated with this event.

On May 30, 2014, while operating at 100% power, workers opened doors concurrently when entering a secondary containment access airlock. The individuals involved each closed their respective doors upon encountering this unexpected condition; however, the result was a brief inoperability of secondary containment integrity. This resulted in an 8 hour reportable event. The Resident Inspector was notified, and Event Notification Number 50153 was made pursuant to 10 CFR 50.72(b)(3)(v)(C) due to a condition at the time of discovery that prevented the fulfillment of the Secondary Containment safety function.

The apparent cause of the event was determined to be excess strength of a permanent magnet on one of the doors. The monthly surveillance test will be revised to address the lag between the interlock lights turning off and the door latching, to document maintenance actions to allow trending and to quantify the gap between the interlock light turning off and the door latching.

This event did not result in a safety system functional failure. There were no radiological releases associated with this event.

On January 17, 2014, while operating at 100% power, Standby Transformer 1X4 Undervoltage Relay 127/SB2 failed to meet requirements of Surveillance Test Procedure (STP) 3.3.8.1-05B, 1A4 4KV Emergency Transformer Supply Undervoltage Calibration. Two relay trip circuit contacts were found to be incorrectly configured such that the relay could not perform the intended function to actuate on loss-of-voltage to trip the Standby Transformer supply breaker. A past operability review determined that the relay had been inoperable for 120 days, 8 hours and 5 minutes. The relay is required to be operable in Modes 1, 2, and 3, and when the associated "B" Emergency Diesel Generator is required to be operable by Limiting Condition for Operation (LCO) 3.8.2, AC Sources-Shutdown. The event resulted in a condition prohibited by Technical Specifications and is reportable pursuant to 10CFR50.73(a)(2)(i)(B). The safety significance is minimized due to the fact that degraded voltage relays perform a similar function and would trip the Standby Transformer supply breaker to allow the "B" Emergency Diesel Generator to carry essential loads during a Loss-of-Offsite-Power.

The root cause of this event was inadequate procedural guidance for both preplanned maintenance and post maintenance testing. This event did not result in a safety system functional failure. There were no radiological releases associated with this event.