31 juillet 2014
Alors que les réacteurs ont divergé depuis 30 ans, un problème de sûreté vient d’être découvert : des alimentations électriques de sûreté en 4 160 volts pourraient être indisponibles suite à la survenue d’une rupture sur une ligne de vapeur principale. En effet, suite à une fuite de vapeur, l’humidité relative dans le local électrique pourrait atteindre 100 %. Des mesures ont été prises pour isoler de la vapeur, les 3 bus de 4 kV 160 de chaque unité.
Type : PWR - Puissance : 3 411 MWth - Première divergence n° 1 : 04/1984 ; n° 2 : 08/1985
Available in english only.
Event Number : 50334
Facility : DIABLO CANYON
State : CA - Unit : [1] [2] - RX Type : [1] W-4-LP,[2] W-4-LP
Event Date : 07/31/2014 - Event Time : 17:29
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 50.72(b)(3)(v)(B) - POT RHR INOP 50.72(b)(3)(v)(C) - POT UNCNTRL RAD REL
Unit SCRAM Code RX CRIT Initial PWR Initial RX Mode Current PWR Current RX Mode 1 N Y 100 % Power Operation 100 % Power Operation 2 N Y 100 % Power Operation 100 % Power Operation
Event Text
UNANALYZED CONDITION
"On 07/31/2014 at 1729 PDT, Diablo Canyon Power Plant (DCPP) identified an unanalyzed condition involving the three class 1E 4160 volt buses on Unit 1 and on Unit 2. Following a postulated main steam line High Energy Line Break (HELB) in the Turbine Building, steam could enter the 4160 volt bus rooms through ventilation ducts that exhaust to the turbine deck where the steam lines are located. New analysis identified that the relative humidity (RH) of the 4160 volt bus rooms could reach 100%, which exceeds the design RH used in the analyses for the protective devices in the room. The high-humidity could possibly prevent the protective devices from operating as intended and could therefore result in the unavailability of the 4160 volt buses to supply power to engineered safety feature systems.
"This concern is being reported as an unanalyzed condition per 10 CFR 50.72(b)(3)(ii)(B) and as a condition that could have prevented fulfillment of a safety function per 10 CFR 50.72(b)(3)(v).
"Compensatory measures were taken to isolate the ventilation ducts between the 4160 volt bus rooms and the turbine deck, thereby preventing steam entry into the 4160 volt bus rooms, assuring the protective devices would not be subjected to conditions exceeding the design RH. With this compensatory measure all three 4160 buses on each unit are assured of performing their expected design function following the postulated main steam line break.
"This concern did not result in any adverse affect on the health and safety of the public.
"The licensee informed the NRC Resident Inspector."
In addition to the 10 CFR sections listed in the header of this event notification, the licensee is also reporting this under 10 CFR 50.72(b)(3)(v)(D).
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2014/20140804en.html
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