INES-event
INES 2

Reactor trip wth complications

On 31 August 1999, the unit tripped from 100% power due to a spurious reactor trip signal. Several minutes after the trip, a 480 VAC safety bus sensed an undervoltage condition, causing all emergency diesel generators (EDGs) to automatically start and load to their respective emergency buses. However, the output breaker for one of the EDGs tripped open immediately, and its associated 480 VAC safety bus was deenergized. One of the motor driven auxiliary feedwater pumps was lost due to lack of electrical power. The loss of AC power also resulted in the loss of a safety related battery charger and the eventual discharge of a 24 VDC battery, which supplies power to control room annuciators, among other loads. The licensee declared an Unusual Event emergency classification due to the loss of the control room annunciators. This event may be a significant precursor, and the USNRC is continuing to evaluate its risk significance.
Justification of the Rating: This event was rated as level 1 in accordance with Section IV-3.2.1.3(a) of the 1998 Draft INES Users Manual, as an event with an expected initiator and safety function operability within operating limits and conditions. However, the rating was increased due to the unexpected complications caused by the discharged battery, for a final rating of level 2.

Location: INDIAN POINT-2
Event date: Tue, 31-08-1999
Nuclear event report
Legenda & explanation