The Oyster Creek Nuclear Power Plant in Lacey Township, Ocean County, is among 21 plants nationwide being ordered by the Nuclear Regulatory Commission to conduct in-depth analyses of earthquake risk.

NRC spokesman Neil Sheehan said safety upgrades were already planned, but the Japan disaster highlighted the importance of seismic issues.

"This is related very specifically to the Fukushima disaster in March 2011," Sheehan said. "We were already on course to have plants do these updates. Fukushima lent greater urgency to that."

The spokesman said plants like Oyster Creek that were built in the 1960s haven't had earthquake assessments since they were designed.

The agency reviewed updated earthquake hazard information for 59 reactor sites that were due in March. The review was part of a priority list of actions that was developed by the NRC to implement in the wake of the 2011 Fukushima nuclear accident.

The list takes into account a limited number of seismic experts in the industry available to complete the effort.

"So we wanted to use those resources on the plants where the greatest increase in ground motion was seen," Sheehan said.

Plants included in the first tier of the priority list must detail their risk by June 30, 2017. Oyster Creek is among the second-tier plants, which have until Dec. 31, 2019 to complete the analysis.

Although Oyster Creek is scheduled to close in 2019, Sheehan said the shutdown process could take several years and that the seismic analysis will still be very valuable in terms of increasing safety at the facility.

"We do expect them to take some interim actions to make sure that the plant could withstand this higher level of earthquake activity," Sheehan said.

You can view the full list of central and eastern U.S. plants included on the NRC's priority list at