Wolf Creek Nuclear Station still shutdown over 1 month after loss of off-site power

At 2:03 in the afternoon on January 13th, officials at the Wolf Creek Nuclear Operating Co., declared a Notice of Unusual Event after the failure of a main generator electrical breaker, followed by an unexplained loss of power to an electrical transformer.

This caused the switchyard to become de-energized, which removed the plant’s connection to the electrical power grid. This is an especially precarious position for a nuclear plant, as the offsite power that is supplied to the nuclear power station is one of the key backup safety systems. While working to restore the power the plant also lost 1 of it’s 2 emergency diesel generators and suffered problems associated with the turbine-driven AFW pump.

The plant is mysteriously still shut down over a month later, and the augmented (specialized) NRC inspection team has come and gone. In an emailed statement to Power Engineering magazine on Jan. 16, Wolf Creek spokesperson Jenny Hageman said plant operators were not speculating as to when the plant will be back online.

Two full-time NRC resident inspectors responded to the control room to monitor site activities during the event and were onsite a week after to monitor licensee activities and initial recovery actions.

By January 25th, the Nuclear Regulatory Commission (NRC) said it would dispatch an Augmented Inspection Team (AIT) to the Wolf Station to review the circumstances surrounding the automatic reactor trip and loss of offsite power.

AIT’s are used by the NRC to review more significant events or issues at NRC-licensed facilities. The six-member team is typically responsible for coordinating with the resident inspectors for gathering information about the shutdown event, putting together a detailed chronology of the event, evaluate the adequacy of licensee actions in response to the incident and assess the impact of the prolonged loss of off-site power to non-safety related equipment.

How significant is the loss of off-site power?

While the NRC and the Utility assert that the event was not as significant as it may appear, operators and regulators in Japan might have a significantly different opinion. During the March 11^th disaster, and for an extended period afterwards, both nuclear power stations in Fukushima, Daiichi and Daini were facing potentially catastrophic events as they tried to cool down the reactors.

Japanese officials assert that the only reason that the reactors at Fukushima Daini did not fall to the same fate as its sister-station Fukushima Daiichi was because off-site power was available at the Daini facility, as opposed to the complete loss of off-site power at Daiichi.

This is not the first switchyard issue at Wolf Creek, and the actual number of problems will never be identified as one or more transmission lines between the plant and the electrical grid had failed 31 times since 2004, but under 20% of them were entered into corrective action programs. The January 2012 shutdown at Wolf Creek was eerily similar in some aspects to a switchyard outage and emergency diesel problems the station suffered in 2009.

Report Summary of Wolf Creek Incident

On August 19, 2009, a lightning bolt hit dangerously close to the station and disconnected the plant from the electrical grid. The reactor and turbine automatically shut down in response and the onsite emergency diesel generators started automatically, to provide electrical power to essential safety equipment. Essential service water (ESW) pumps also started automatically.

However, a pressure spike in the ESW system after the pumps started created a 3/8-inch-diameter hole in the piping. The SIT investigated the loss of offsite power and the ensuing damage to the ESW system (NRC 2010y).

The SIT found that a 2007 internal study had forecast leakage in the ESW piping, and that leakage had actually occurred in April 2008 in an event similar to that in August 2009. The NRC sanctioned the company for having identified this safety problem but having failed to correct it.

Greater potential of earthquake risk

At the beginning of February, the NRC announced that new data had been revealed that might show that the nation’s nuclear reactors were not as safeguarded against earthquakes as previously estimated. The new data surprisingly was not related to the plants on the west coast, which are under constant scrutiny, especially in California where the citizens are growing visibly irritated with what they perceive as a growing threat to their celebrated way of embracing life on the edge of the ocean and in its waves.

A picture of a collapsed electrical supply tower at Fukushima Daiichi

Instead the new data highlighted new potential risk to nuclear power plants in the Midwest and Eastern United States, which were before thought to be well above any levels of risk or reassessment. Wolf Creek is one of the nuclear power stations that is highlighted as having a potentially greater threat and subsequently mandated upgrades to ensure safety during operations.

There has been no timetable released for reactor restart, and while the root cause of the switchyard problem remains unidentified the station will remain shutdown. While waiting for news to surface, it appears that the mounting problems at Wolf Creek will prove to be a much more critical issue than initially assumed.