This telephone report is being made in accordance with
10 CFR 50.73(a)(2)(iv)(A) as an event or condition caused by an invalid signal that resulted in an automatic Group 6 isolation. On August 31, 2010 at 1737
CDT, Group 6 of
Primary Containment Isolation System (
PCIS) actuated. This resulted in completion of
Secondary Containment isolation, initiation of the
Standby Gas Treatment System and
Control Room Emergency Filtration System. An invalid signal occurred apparently as a result of a voltage
transient on the
Nebraska City
345kV line. This was from a 3-phase fault to ground due to a structural failure during a severe thunder storm with
high winds.
The equipment associated with the Group 6 isolation functioned successfully and the isolation was complete. The Group 6 PCIS was reset. Cooper Nuclear Station operators reviewed the parameters that would cause a Group 6 trip signal (i.e. reactor water level, drywell pressure, reactor building radiation) and determined there were no valid conditions that would have caused the isolation.
This event was most likely due an act of nature, thus no corrective actions were required.
The NRC Resident Inspector will be notified.
