INES-event
INES 0

Loss of shutdown cooling

On 13 February 1998, shutdown cooling of the reactor vessel was lost for several hours when suction isolation valves for the residual heat removal (RHR) system automatically closed. These valves closed due to the loss of the primary power supply to Division 2 of the Nuclear Safety Protection System, while the alternate power supply was unavailable because of maintenance. The unit had been shut down since 5 September 1996, and decay heat loads were relatively low. During the period the shutdown cooling system was unavailable, water in the reactor vessel began to heat up at a rate of approximately 0.6 deg. F per hour. The licensee declared an ALERT Emergency Classification at the discretion of the control room supervisor, who desired to bring additional personnel onsite to assist in restoring the RHR system. The RHR system was restarted approximately six hours after the initial event.
Justification:
This event is rated at level 0/below scale in accordance with Part III-3.1.1 of the INES User's Manual as a minor change in coolant temperature due to some degradation of cooling with a comparable large time available for corrective actions.

Location: CLINTON-1
Event date: Fri, 13-02-1998
Nuclear event report
Legenda & explanation