24 février 2013
Arrêt manuel du réacteur 2 qui était à 25 % de sa puissance nominale suite à la perte de l’indication du niveau de vide au condenseur. Cette perte a provoqué la fermeture des décharges de condenseur vapeur et l’ouverture de soupapes à l’atmosphère : la perte des pompes principales était imminente.
Première divergence : novembre 1981 -Puissance : 1 126 MW - Type : PWR -
Available in english only.
Le défaut a été localisé au niveau du pressostat de vide d’un condenseur. Pendant ce problème, il y a eu plusieurs lâchés de pression à l’atmosphère, mais toujours affirmés sans impact sur l’homme ou sur l’environnement. Les conditions d’arrêt seraient correctes.
Facility : SEQUOYAH - State : TN
Unit :[2] RX Type : W-4-LP
Event Date : 02/24/2013 - Event Time : 12:05
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 25 % Courant PWR 0 % Hot Standby
Event Text
MANUAL REACTOR TRIP DUE TO LOSS OF CONDENSER VACUUM INDICATION
"On February 24, 2013 at 1205 [EST] with reactor power at 25% and the turbine offline, a manual reactor trip for Sequoyah Unit 2 was initiated due to loss of condenser vacuum indication causing closure of condenser steam dumps, opening of the Steam Generator Atmospheric Relief Valves, and lowering hotwell level resulting in imminent loss of hotwell pumps. The cause of the event was determined to be a faulty test connection on B Condenser vacuum pressure switch.
"During the event, steam pressure rose to the setpoint for the first Steam Generator code safety valve (1064 psig). [The safety valve opened, then reseated].
"Following the reactor trip, all safety related equipment operated as designed. Auxiliary feedwater actuated as expected on loss of the operating main feedwater pumps. The reactor trip was uncomplicated.
"Unit 2 is currently being maintained in Mode 3 at NOP/NOT [Normal Pressure and Temperature], with auxiliary feedwater supplying the steam generators and maintaining level at approximately 33% narrow range.
"Method of decay heat removal is via atmospheric reliefs to the atmosphere. Current RCS conditions : temperature [is] 547 degrees F and stable. Pressure [is] 2235 psig and stable. [There is] no indication of any primary/secondary leakage. All rods are inserted. Electrical alignment is normal and supplied from offsite power. [There is] no impact to Unit 1. Unit 1 is operating at 100% power / Mode 1.
"There was no impact on public health and safety. Post-trip investigation is in progress and planned restart is 02/25/2013. [The licensee plans a press release.]"
The licensee notified the NRC Resident Inspector.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2013/20130225en.html
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