15 février 2018
Le réacteur était à pleine puissance quand le problème s’est produit. Les opérateurs sont entrés dans les procédures d’opérations d’urgence, et selon la NRC : "sans complication" alors que les deux pompes de refroidissement du cœur du réacteur ne fonctionnaient plus : elles venaient de perdre leur alimentation électrique suite à l’impossibilité de transférer leur bus d’alimentation. L’ébullition est un des pire phénomènes qui puisse se produire dans le cœur d’un réacteur puisque les bulles empêchent le refroidissement des barres de combustible. Rassurons nous, l’autorité parle d’un départ d’un faible niveau d’ébullition nucléaire... au moment du problème un groupe électrogène était hors service pour maintenance. Toutes les barres de contrôles se sont insérées dans le cœur. Il n’y aurait pas eu de nécessité de classement d’urgence.
Type : PWR - Puissance : 3 990 MWth - Première divergence : 5 / 1985 -
Available in english only
Event Number : 53215
Facility : PALO VERDE - 4 State : AZ - Unit : [1] - RX Type : [1] -
Event Date : 02/15/2018 - Event Time : 21:53 [MST]
Emergency Class : NON EMERGENCY - 10 CFR Section : 50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL
Initial PWR : 100% Current PWR : 0 %
Event Text
AUTOMATIC REACTOR TRIP DUE TO LOW DEPARTURE FROM NUCLEATE BOILING SIGNAL
"The following event description is based on information currently available. If through subsequent reviews of this event additional information is identified that is pertinent to this event or alters the information being provided at this time a follow-up notification will be made via the ENS or under the reporting requirements of 10CFR50.73.
"On February 15, 2018, at approximately 2153 Mountain Standard Time (MST), the Palo Verde Generating Station (PVGS) Unit 1 Control Room received Reactor Protection System alarms for Low Departure from Nucleate Boiling Ratio and an automatic reactor trip occurred. Prior to the reactor trip, Unit 1 was operating normally at 100 percent power. Plant operators entered the emergency operations procedures and diagnosed an uncomplicated reactor trip but noted that Reactor Coolant Pumps 1B and 2B were not running due to a loss of power. All CEAs [Control Element Assemblies] fully inserted into the core. Following the reactor trip, all nuclear instruments responded normally. No emergency classification was required per the PVGS Emergency Plan.
"The PVGS Unit 1 safety related electrical busses remained energized from normal offsite power during the event. The Unit 1 ’B’ Diesel Generator is currently removed from service for maintenance. Due to ongoing planned maintenance on NAN-X02, Startup Transformer 2, fast bus transfer for NAN-S02 (from NAN-S04) was blocked. This resulted in a loss of offsite power to NAN-S02 and NBN-S02. The offsite power grid is stable. Unit 1 is currently stable in Mode 3 with the reactor coolant system at normal operating temperature and pressure.
"The event did not result in any challenges to fission product barriers and there were no adverse safety consequences as a result of this event. The event did not adversely affect the safe operation of the plant or the health and safety of the public.
"The NRC Resident Inspector has been informed of the Unit 1 reactor trip."
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2018/20180216en.html
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