19 décembre 2017
Cette indisponibilité est due à un problème commun sur les voyants indicateurs et sur les prises associées installées sur divers circuits de commande et auxiliaires des deux générateurs. Ces problèmes auraient engendré des délais de démarrage, de passage en charge et de fonctionnement des groupes diesels trop longs pour assurrer l’atténuation des conséquences d’un accident. Le système de filtrage d’urgence de la salle de commande était également inopérent.
Lors d’une mise à jour du 14 février 2018, soit 55 jours après la déclaration de ce problème, la NRC retire la notification en précisant que le défaut n’aurait pas eu d’incidence sur sur la capacité de fonctionnement des diesels ni sur la filtration de l’air de la salle de commande...
Type : Fukushima 1 (BWR Mark 1) - Puissance : 2 419 MWth - Première divergence : 2 / 1974 -
Available in english only
Event Number : 53128
Facility : COOPER - State : NE
Unit : [1] - RX Type : [1] GE-4
Event Date : 12/19/2017 - Event Time : 13:40 [CST]
Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(3)(v)(D) - ACCIDENT MITIGATION
Initial PWR : 100 % Current PWR : 100 %
Event Text
DIESEL GENERATORS (DGs) DECLARED INOPERABLE DUE TO A COMMON ISSUE
"During regular power operations at 100% power, DG#1 and DG#2 were declared inoperable due to a common issue associated with indicating lights and the associated sockets installed in various control and auxiliary circuits for both DG’s.
"The indicating lights in question are incandescent 120V AC style 120MB bulbs in a socket with a 550 ohm resistor. Style 120MB light bulbs have a failure mechanism where the bulb can cause a short circuit rather than the more common open circuit that is expected when an incandescent bulb filament fails. Cooper originally believed that the socket’s integral resistor was sufficient to protect the circuit. In testing performed by an outside laboratory and confirmed on-site using warehouse stock, it was determined that the integral resistor may not have the power dissipation capability to protect the circuit ln which the light and socket are installed if a bulb fails in short circuit.
"This condition resulted in both DG’s being declared inoperable at 1340 [CST] due to a loss of reasonable expectation that they would meet their safety function required action to start, load and run to support loads required to mitigate the consequences of an accident. This is a loss of safety function under 10CFR 50.72(b)(3)(v)(D) subject to an 8 hour report.
"As a result of both DG’s being inoperable, the Control Room Emergency Filtration System is also inoperable. This is also a loss of safety function subject to an 8 hour report for the same criterion.
"The Senior Resident has been notified."
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2017/20171220en.html