25 février 2013
Arrêt d’urgence du réacteur n° 3 suite à la perte de la turbine, perte elle-même due à un vide trop faible du condenseur. Le problème du condenseur est dû à une fuite sur le circuit de recirculation : les vannes ont été fermées manuellement pour isoler la fuite.
Première divergence : août 1976 - Puissance 1 105 MW - Type : Mark I -
Available in english only.
Pendant les transitoires, aucune soupape de sécurité n’a fonctionné et une vanne a été actionnée manuellement pour maintenir la pression dans le circuit du réacteur.
Suite à l’injection haute pression de liquide de refroidissement, la piscine de surpression a dépassé son seuil maximum autorisé : ce dépassement a duré plus de 2 heures, contrairement aux prescriptions réglementaires.
Cette situation aurait dû conduire à la mise à l’arrêt des deux autres réacteurs du site.
La situation d’arrêt normal a fini par être atteinte.
Facility : BROWNS FERRY - State : AL - Unit : [3] GE-4
Event Date : 02/25/2013 - Event Time : 13:13
Emergency Class : NON EMERGENCY
50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL 50.72(b)(3)(iv)(A) - VALID SPECIF SYS ACTUATION
Initial PWR 92 % - Current PWR 0 % Hot Shutdown
Event Text
AUTOMATIC SCRAM DUE TO A TURBINE TRIP FROM A LOSS OF CONDENSER VACUUM
"At 1313 [CST] on 02/25/2013, the Unit 3 reactor automatically scrammed due to actuation of the Reactor Protection System from a turbine trip. Preliminary indications show the turbine tripped on low condenser vacuum. Cause of loss of condenser vacuum has been identified as Reactor Feedwater recirculation piping separation. Main Steam Isolation Valves (MSIVs) were manually closed to isolate the leak. None of the Safety Relief Valves (SRVs) automatically cycled during the transient, and one Safety Relief Valve (SRV) was manually operated to maintain Reactor Pressure due to the Main Turbine Bypass Valves unavailability because of loss of condenser vacuum. All systems responded as expected to the turbine trip. No Emergency Core Cooling System (ECCS) or Reactor Core Isolation Cooling (RCIC), reactor water level initiation set points were reached. Reactor water level is being controlled by the RCIC system and Reactor Pressure is being controlled with the High Pressure Coolant Injection (HPCI) system.
"All expected containment isolation and initiation signals (Groups 2, 3, 6, and 8) were received. Upon receipt of these signals all required components actuated, with the exception of one valve in Group 6. Drywell Continuous Air Monitor (CAM) Inboard Return Isolation Valve 3-FSV-90-257 did not have indication following isolation signal and was not able to be verified locally. Indication was subsequently restored following restoration of containment isolation signals, and the Drywell CAM was manually isolated at 1422 [CST] with positive indication of isolation, and isolation valves deactivated at time 1514 [CST] to satisfy TS LCO 3.6.1.3 required actions.
"This event is reportable within 4 hours per 10CFR50.72(b)(2)( iv)(B), ’Any event or condition that results in actuation of the reactor protection system (RPS) when the reactor is critical except when the actuation results from and is part of a pre-planned sequence during testing or reactor operation’. It is also reportable within 8 hours per 10CFR 50.72(b)(3)(iv)(A) and requires an LER within 60 days per 10CFR 50.73(a)(2)(iv)(A).
"At 1415 [CST], Suppression Pool Water level exceeded -1 inch due to operation with HPCI in pressure control mode, and required entry into TS LCO 3.6.2.2 condition A to restore level within 2 hours. Efforts are being made to lower suppression pool water level within limits. At 1615 [CST], water level remains above -1 inch requiring entry into TS LCO 3.6.2.2 condition B requiring action to be in MODE 3 in 12 hours and MODE 4 within 36 hours.
"This event is reportable within 4 hours per 10CFR 50.72(b)(2)(i), ’The initiation of any nuclear plant shutdown required by the plant’s Technical Specifications.’
"The NRC Resident Inspector has been notified."
All control rods fully inserted and electrical offsite power is in a normal shutdown configuration. Residual Heat Removal is aligned for suppression pool cooling. There was no impact on either Unit 1 or 2.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2013/20130226en.html
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