05000339/LER-2015-001
| North Anna Power Station, Unit 2 | |
| Event date: | 10-07-2015 |
|---|---|
| Report date: | 12-02-2015 |
| 3392015001R00 - NRC Website | |
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1.0 DESCRIPTION OF THE EVENT On October 7, 2015, at approximately 2147 hours0.0248 days <br />0.596 hours <br />0.00355 weeks <br />8.169335e-4 months <br />, a high energy line break (HELB) door, 2-BLD-STR-S54-11, between the Unit 1 Turbine Building (TB) and the safety related Unit 2 Emergency Switchgear Room (ESGR) was determined to be slightly open and unlatched. This was discovered by a Security Officer completing rounds. The door was subsequently latched closed. There were no systems, structures, or components that were inoperable at the start of the event that contributed to the event.
An investigation determined a company employee exited .the door at 2101 hours0.0243 days <br />0.584 hours <br />0.00347 weeks <br />7.994305e-4 months <br />. The door (EIIS — DR) had closed enough to prevent the security door open alarm but not enough to allow the magnetic lock to engage. As a result the door was unlatched for approximately 46 minutes. In this condition, operability of one train of equipment in the Unit 2 ESGR (EIIS — SWGR) required for safe shutdown was not met.
The existing calculation basis for the effects of a Unit 1 Turbine Building (EIIS — NM) High Energy Line Break on equipment in the Unit 2 Emergency Switchgear Room with Door S54-11 in the unlatched condition was reviewed. This equipment included transformers, 4160 volt and 480 volt busses, DC cabinets, vital bus inverters, and battery chargers. Electrical equipment in the Control Room Envelope (Main Control Room and Emergency Switchgear Rooms) is qualified to operate in 120 Fahrenheit and 95 percent non-condensing relative humidity. The computer models to determine conditions (temperature, relative humidity) in the Control Room Envelope were run.
Temperatures in several areas in the Unit 2 ESGR remained below 120 Fahrenheit, but relative humidity in the areas containing both trains of inverters and chargers quickly reached 100% and remained at that level for approximately five minutes. As such, no ESGR required for safe shutdown in the event of Unit 1 TB HELB with Door S54-11 unlatched.
At 1823 hours0.0211 days <br />0.506 hours <br />0.00301 weeks <br />6.936515e-4 months <br /> on October 8, 2015, an 8-hour Non-Emergency Report was made to the NRC in accordance with 10 CFR 50.72(b)(3)(ii)(B) as an unanalyzed condition and in accordance with 10 CFR 50.72(b)(3)(v)(A) & (D) as a condition that could have prevented the fulfillment of safety functions to shutdown the reactor and maintain it in a safe shutdown condition and mitigate the consequences of an accident.
North Anna Power Station, Unit 2 05000339 2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS Given the low likelihood of a TB HELB occurring during the time the door was unlatched there were no significant safety consequences. The health and safety of the public were not affected by this event.
3.0 CAUSE The cause of the event was a human performance error where an employee did not follow standards for ensuring the door closed and latched as expected.
4.0 IMMEDIATE CORRECTIVE ACTION(S) The door was closed by Security personnel, regaining functionality. The employee's conduct was addressed by the company performance management processes.
5.0 ADDITIONAL CORRECTIVE ACTIONS While repeated attempts could not get the door to duplicate the as-found condition, the door closure was adjusted on October 13, 2015. Security equipment associated with the open door alarm was tested and proven to have been functioning properly. An Apparent Cause Evaluation has been completed for this event.
6.0 ACTIONS TO PREVENT RECURRENCE A Performance Improvement Plan will be implemented to track employee improvement regarding standards compliance in accordance with the Crew Performance Review Board process. A site expectation briefing sheet or similar document for proper door check behaviors will be developed and distributed to all plant personnel. A training analysis regarding changes to North Anna expectations/standards for checking doors will be conducted.
7.0 SIMILAR EVENTS None 8.0 ADDITIONAL INFORMATION North Anna Unit 1 continued operating in Mode 1, 100 percent power and was not affected during this event.