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Etats-Unis : Diablo Canyon : manchon de couplage mal engagé sur une conduite principale de vapeur




20 septembre 2016


Ce manchon constitutif d’un système anti coup de bélier n’aurait pas pu assurer sa fonction. La fixation de la douille d’accouplement a été restaurée. D’autres défauts d’accouplement n’ont pas été relevés sur d’autres lignes de la centrale. Ce problème était susceptible de dégrader fortement la sécurité et il nécessite donc une analyse plus approfondie.

Type : PWR - Puissance : 3 411 MWth - Première divergence n° 1 : 04/1984

Available in english only


Event Number : 52260

Facility : DIABLO CANYON - State : CA

Unit : [2] - RX Type : [2] W-4-LP

Event Date : 09/20/2016 - Event Time : 20:47 [PDT] -

Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(3)(ii)(B) - UNANALYZED CONDITION

Initial PWR  : 100 % Current PWR  : 100 %

Event Text

STEAM LINE PIPE WHIP RESTRAINT COUPLING SLEEVE FOUND NOT ENGAGED

"On 9/20/2016, a coupling sleeve on a pipe whip restraint located on the 119 foot elevation of the turbine building associated with Unit 2 main steam line 4 was found to be not engaged. As a result of the detached coupling, the restraint was not capable of performing its restraint function for a postulated pipe whip event on the main steam line. The coupling was reconnected on 9/20/2016, restoring its functionality. An extent of condition walkdown was subsequently performed for the other Unit 1 and Unit 2 steam line restraints and no similar issues were identified.

"This concern did not result in any adverse effect on the radiological health and safety of the public.

"The purpose of this whip restraint is to restrain the steam line for a postulated loss at the G-line anchor (east side of Turbine Building above the 104 foot elevation). The restraint protects the floor slab at the 104 foot elevation, which extends over the Unit 2 component cooling water heat exchangers.

"With the detached coupling, equipment in the area may have been vulnerable to damage if a pipe whip event occurred. Further analysis is needed to conclude whether the heat exchangers and other equipment would have remained protected in such an event and whether this would have significantly affected the designed plant response to a pipe event.

"Based on the need for further analysis, this event is being reported as an unanalyzed condition that may have significantly degraded plant safety in accordance with 10 CFR 50.72(b)(3)(ii)(B).

"The NRC Senior Resident Inspector was notified."

http://www.nrc.gov/reading-rm/doc-collections/event-status/event/2016/20160926en.html#en52260