10 avril 2015
Le réacteur était en cours d’arrêt pour rechargement à 37 % de sa puissance. Le vide s’est dégradé trop rapidement pour permettre l’enclenchement d’un arrêt manuel. Les barres de contrôle se sont correctement insérées, mais un niveau d’eau du réacteur trop bas a engendré un isolement du circuit. Le niveau d’eau a été rétabli par le circuit d’isolement de refroidissement du coeur du réacteur (RCIC). Les pompes de recirculation du réacteur se sont arrêtées suite à l’arrêt de la turbine en puissance. Le vide au condenseur a été restauré et la chaleur évacuée par dérivation de la vapeur vers ce condenseur.
Type : BWR Mark II - Puissance : 3 952 MWTh - Première divergence : 05/1984
Available in english only.
Event Number : 50973
Facility : SUSQUEHANNA - State : PA
Unit : [2] - RX Type : [2] GE-4
Event Date : 04/10/2015 - Event Time : 23:46
Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL 50.72(b)(3)(iv)(A) - VALID SPECIF SYS ACTUATION
Initial PWR : 37 % Current PWR : 0 %
Event Text
AUTOMATIC REACTOR SCRAM CAUSED BY MAIN TURBINE TRIP DUE TO DEGRADING MAIN CONDENSER VACUUM
"At 2346 EDT on April 10, 2015, Susquehanna Steam Electric Station Unit 2 reactor automatically scrammed due to a main turbine trip caused by loss of turbine steam seals and degrading main condenser vacuum.
"Unit 2 reactor was being shutdown for a refueling outage. At approximately 37 percent power, turbine steam seals were lost resulting in a degrading vacuum. The vacuum degraded quickly, resulting in a main turbine trip before the reactor operator could insert a manual scram. At 37 percent power, the turbine trip caused an automatic scram. This occurred during a transfer from normal steam seal supply to the auxiliary boiler supply. All control rods [fully] inserted. Reactor water level lowered to +2 inches causing Level 3 (+13 inches) isolation. No ECCS actuations occurred. The Operations crew subsequently maintained reactor water level at the normal operating band using RCIC [Reactor Core Isolation Cooling]. No steam relief valves opened. The reactor recirculation pumps tripped on EOC-RPT due to the turbine trip at power.
"The reactor is currently stable in Mode 3. Investigation into the cause of the loss of turbine steam seals is underway.
"The NRC Resident Inspector was notified. A voluntary notification to PEMA [Pennsylvania Emergency Management Agency] and press release will occur."
Unit 2 is in a normal shutdown electrical lineup. Turbine steam seals were restored to the normal steam supply and condenser vacuum was restored. Decay heat is being removed via the steam bypass valves to the condenser. Unit 2 is proceeding with their cooldown to support the scheduled refueling outage.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2015/20150413en.html#en50973
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