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Etats-Unis : Watts-Bar : deux vannes de limitation thermique de confinement ont refusé de s’ouvrir

4 février 2018

Au cours d’essais de surveillance, les clapets anti-retour ont refusé de s’ouvrir pour laisser passer un débit acceptable. Suite à ce problème, un excès de pressurisation pourrait entrainer un rejet radioactif direct dans l’environnement.

 Type : PWR - Puissance : 3 459 MWth - Première divergence : 1 / 1996 -

Available in english only

Event Number : 53196

Facility : WATTS BAR

Region : 2 State : TN - Unit : [1] - RX Type : [1] W-4-LP -

Event Date : 02/04/2018 - Event Time : 04:45 [EST]

Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(3)(v)(C) - POT UNCNTRL RAD REL

Initial PWR  : 100 % Current PWR  : 100 %


"At 0445 [EST] on February 4, 2018, Watts Bar Unit 1 entered Technical Specification 3.6.1 condition A and 3.6.3 condition A.1 and A.2 due to inoperable containment penetration thermal relief check valves 1-CKV-31-3407 and 1-CKV-31-3421 associated with one train of the Containment Incore Instrument Room Chiller system. During surveillance testing, the thermal relief check valves failed to open and pass flow as required by acceptance criteria. The two penetrations were subsequently drained and isolated in accordance with the surveillance procedure to remove any thermal expansion concerns. Technical Specification 3.6.1 was exited February 4, 2018 at 0512 once the two penetrations were drained and isolated.

"The purpose of the thermal relief check valves is to allow flow from an isolated penetration back into the upstream containment piping to prevent over-pressurization due to thermal expansion. Over-pressurization of an isolated containment penetration could potentially cause the penetration or both of the isolation valves to fail and provide a direct flow path to the environment from the potentially contaminated containment atmosphere under certain Design Basis Accidents. Therefore, failure of the thermal relief check valves to open could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.

"This event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(C).

"NRC Resident Inspector has been notified."