8 août 2012
Arrêt automatique du réacteur n° 2 (première divergence décembre 1978) suite à une pression excessive détectée au niveau de son circuit de refroidissement. Cette surpression a été provoquée par l’arrêt de a turbine principale, arrêt lui-même provoqué par une situation de vide dégradée au niveau du condenseur. Le réacteur est en arrêt à chaud. Le cœur étant critique, les systèmes de protection du réacteur se sont enclenché.
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Facility : ARKANSAS NUCLEAR - Region : 4 State : AR - Unit : [2]
Event Date : 08/08/2012 - Event Time : 08:23
Emergency Class : NON EMERGENCY
50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL
Unit SCRAM Code RX CRIT Initial PWR Initial RX Mode Current PWR Current RX Mode 2 A/R Y 100 Power Operation 0 Hot Standby
Event Text
AUTOMATIC REACTOR TRIP DUE TO HIGH REACTOR COOLANT SYSTEM PRESSURIZER PRESSURE
"At 0823 hours on August 8, 2012, Arkansas Nuclear One, Unit 2 (ANO-2) experienced an automatic reactor trip. The reactor automatically tripped due to High Reactor Coolant System Pressurizer Pressure that was caused by a Main Turbine trip due to high condenser back pressure from a degraded vacuum condition. The Reactor Protection System (RPS) performed as designed in response to the High Reactor Coolant System Pressurizer Pressure condition resulting in automatic shutdown of the reactor from approximately 100 percent power. All Control Element Assemblies (CEAs) fully inserted on the trip. The Emergency Feedwater Actuation System (EFAS) actuated for the ’A’ Steam Generator only due to level trending slightly below the setpoint. The plant has transitioned to supplying the steam generators using the Auxiliary Feedwater (AFW) system.
"The unit is currently in Mode 3 and implementing the transient response process. The investigation into the cause of the trip is ongoing and the local NRC Resident Inspectors have been notified."
The unit is in a normal electrical lineup, and the decay heat is being removed by the main condenser via the turbine bypass valves.
The State Department of Health was notified and ANO-2 will be issuing a press release.