An inspection has shown that loss of offsite power at the Wolf Creek nuclear power plant near Burlington, Kan., in January had substantial safety significance and will result in additional inspections and regulatory oversight, the Nuclear Regulatory Commission (NRC) said on Friday.

Operators of the Wolf Creek Nuclear Operating Corp. on Jan. 31 declared an "Unusual Event"—the lowest of four levels of nuclear emergency—after the failure of a main generator electrical breaker, followed by an unexplained loss of power to a transformer. This caused the switchyard to lose power, which cut off the plant from the power grid, the NRC said. All safety systems responded as expected, and emergency diesel generators automatically power safety-related equipment, the regulator added.

But an augmented inspection conducted later by the NRC determined that company actions had "set the stage for the incident because the company failed to provide adequate oversight of contractors while they performed work that could affect safety-related equipment in April 2011." Wolf Creek Nuclear Operating Corp. failed to identify that electrical maintenance contractors had "improperly connected wires on an electrical component," the NRC alleged.  "This allowed an electrical short to prevent transfer of power to a transformer on Jan. 13."

The "yellow" finding—ranked just below "red" findings, which have "high safety significance"—puts Wolf Creek into the "degraded cornerstone" column of the NRC action matrix. Other reactors in that column include Hope Creek 1, Palisades, Perry 1, Saint Lucie 1, and Salem 1 and 2.

Sources: POWERnews, NRC, Wolf Creek
–Sonal Patel, Senior Writer (@POWERmagazine)