9 septembre 2014
Après avoir considéré comme hautement improbable la menace d’une tornade et assuré que les systèmes électroniques seraient capables d’assurer leurs fonctions de sécurité, un nouvel examen a été réalisé. Ce dernier a montré une possible atteinte des systèmes de ventilation de l’unité 1 et 2 de la ligne de vie 480 v AC, de l’onduleur et des batteries. En conséquence, la déclaration a été effectuée suite à un risque d’impossibilité d’accomplissement de fonctions de sécurité et des mesures compensatoires sont développées pour résoudre les problèmes.
Type : PWR - Puissance : 3 411 MWTh - Première divergence n° 1 : 04/1984 ; n° 2 : 08/1985
Available in english only.
Event Number : 49879
Facility : DIABLO CANYON
State : CA - Unit : [1] [2]
RX Type : [1] W-4-LP,[2] W-4-LP
Event Date : 03/06/2014 - Event Time : 09:06 -
Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(3)(ii)(B) - UNANALYZED CONDITION 50.72(b)(3)(v)(A) - POT UNABLE TO SAFE SD
Initial PWR : 100 % - Current PWR : 100 %
Event Text
UNANALYZED CONDITION REGARDING POTENTIAL TORNADO MISSILE DAMAGE TO EMERGENCY DIESEL EXHAUST PLENUM
"The condition described below is being reported as an unanalyzed condition per 10 CFR 50.72(b)(3)(ii)(B) and per the guidance of NUREG-1022, Rev. 3.
"On 03/06/2014 at 0906 PST, Diablo Canyon Power Plant (DCPP) identified a nonconforming condition involving the Emergency Diesel Generator (EDG) ventilation exhaust plenums installed in Unit 1 and Unit 2. Specifically, the radiator exhaust plenums and exhaust piping need to be re-evaluated to ensure adequate protection against flying debris that could be generated by a tornado.
"The occurrence of such an event is highly unlikely and there is no imminent concern regarding severe weather involving tornados. The EDGs are located inside the power plant structure and are capable of performing their safety function. Compensatory measures are being developed to address the associated nonconformance.
"This event does not adversely affect the health and safety of the public.
"The licensee informed the NRC Resident Inspector."
* * * UPDATE PROVIDED BY RUSS CRUZEN TO JEFF ROTTON AT 2245 EDT ON 09/09/2014 * * *
"This condition does not adversely affect the health and safety of the public.
"Based on an extent of condition review being performed for this event, the issue identified in the original event notification 49879 has also been determined to similarly affect the ventilation systems associated with the Unit 1 and 2 Vital 480 volt AC switchgear and battery/inverter equipment.
"The condition described in this update is being reported as an unanalyzed condition per 10 CFR 50.72(b)(3)(ii)(B) and as an event or condition that could have prevented the fulfillment of a safety function per 10 CFR 50.72(b)(3)(v)(A).
"Compensatory measures are being developed to address the associated condition.
"The licensee informed the NRC Resident Inspector."
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2014/20140910en.html#en49879
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