"Entergy officials failed to ensure that a control room simulator used to train reactor operators was capable of reproducing all of the challenges those operators might encounter during a specific unplanned reactor shutdown scenario," NRC Region IV Administrator Marc Dapas said. "As a result of this training program deficiency, the operators took some actions that unnecessarily complicated the plant’s response to the unplanned shutdown on Dec. 25, 2014."

River Bend was operating at 85 percent capacity Christmas morning when the shutdown occurred. Following the shutdown, some problems were experienced with the plant’s feedwater system, which supplies short-term cooling water to the reactor core. Several electrical circuit breakers also failed to operate properly. Operators took compensatory actions to ensure the plant would remain in a safe shutdown mode.

The NRC conducted a special inspection to better understand the circumstances surrounding the event, determine if there were any generic implications and review the licensee’s corrective actions. The team identified an apparent violation of NRC requirements for failing to maintain a training simulator that accurately reproduced the kinds of conditions that control room operators faced on that day, complicating the operators’ efforts to respond to the event. The finding is discussed in a July 7 inspection report. Entergy officials notified the NRC on July 30 that they agreed with the preliminary finding.

The NRC evaluates regulatory performance at commercial nuclear plants with a color-coded process that classifies inspection findings as green, white, yellow or red in order of increasing safety significance. The NRC has determined that the inspection finding has low to moderate (white) safety significance which may require additional inspections, regulatory actions and oversight.