At 0225 hrs on April 19, 2006, a container storing in-core instrument pieces rose to the surface of the flooded reactor cavity under its own bouyancy, causing unexpected high radiation readings in the general vicinity of the reactor cavity for a few seconds before the container returned to the bottom of the reactor cavity. Emergency Action Level RU2.2 was promptly reviewed, and it was determined that the threshold for an unusual event was not exceeded, because the area radiation monitors rose by a factor of approximately 100 versus the
EAL setpoint of 1000 over normal levels.
Subsequently, at 1750 hrs, during post event investigation, it was discovered that dose rates indicated by an electronic dosimeter worn by an individual in the area at the time of the event may have exceeded the EAL setpoint of 1000 times the normal radiation levels for that area of containment for a few seconds. The total exposure received by the individual was less than 50 millirem. Therefore, this event is being reported in accordance with NUREG 1022, Revision 2, Section 3, "Discussion." as a potential event discovered after-the fact.
The licensee notified the NRC Resident Inspector, and Al Svilpe, Emergency Management Office in Van Buren County, MI. There is also expected to be some media attention from this incident.
