The North Anna nuclear facility in Virgina issued an update to its Event Report from last week, when a 5.8 earthquake struck the East Coast and closed both reactors at the plant. Pardon the Nuclearese: “Other conditions exist(ed) which … warrant declaration of an alert. Initial review of seismic response data from the earthquake on 8/23/11 (1348 hours) indicates that design spectrum input assumptions (i.e. Design Basis Earthquake [DBE] limits) may have been exceeded above 5 HZ. This would have resulted in classification of an Alert under EAL HA1.1.”
In essence, operators feel that movement at the plant was more severe than previously estimated, and that the emergency declaration was made under the wrong section of emergency procedures.
North Anna suffered an aftershock on Thursday which delayed exiting the Unusual Event until Sunday. Both reactors at the site remain shut down as of Monday morning.