29 décembre 2012
Problème générique découvert à Anchor Darling : de grosses vannes de commandes seraient inopérantes suite à des défauts de conception.
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Liste des 43 centrales pouvant être affectées par le problème :
ANO 1 - Browns Ferry - Brunswick - Callaway - Catawba - Clinton - Columbia - Cook - Cooper - Crystal River - Dresden - Diablo Canyon - Duane Arnold - Fitzpatrick - Fort Calhoun - Grand Gulf - Hatch - Indian Point - Kewaunee - LaSalle - Limerick - Maine Yankee - Millstone - Monticello - Nine Mile - North Anna - Oconee - Oyster Creek - Peach Bottom - Perry - Pilgrim - Prairie Island - Quad Cities - River Bend - Robinson - San Onofre - St. Lucie - Surry - Three Mile Island 2 - Waterford - VC Summer - Vermont Yankee - Wolf Creek.
Event Number : 48797
Licensee : ANCHOR DARLING - State : NC
Event Date : 12/29/2012 -
Emergency Class : NON EMERGENCY 10 CFR Section : 21.21(d)(3)(i) - DEFECTS AND NONCOMPLIANCE
Event Text
PART 21 - WEDGE PIN FAILURE IN ANCHOR DARLING MOTOR OPERATED DOUBLE DISC GATE VALVES WITH THREADED STEM TO UPPER WEDGE CONNECTIONS
The following is a summary of information received from Flowserve via facsimile :
"This is to notify the US Nuclear Regulatory Commission that, in accordance with the provisions of 10CFR Part 21, we have identified a potential issue and are submitting our evaluation of the event.
"Flowserve has been working with the Tennessee Valley Authority’s (TVA) Browns Ferry Nuclear Plant to investigate the failure of a Size 10, Class 900 Anchor/Darling motor-operated double-disc gate valve. The failure was due to the shearing of the wedge pin which serves a joint locking function at the threaded interface between the valve stem and upper wedge. The pin is designed to ensure that the joint does not loosen due to vibration and other secondary loads. On some valve designs, the pin also is used to attach the disc retainers to the upper wedge. The pin shearing allowed rotation of the stem during the closing stroke when the valve was seating and ultimately resulted in loss of the stem to upper wedge joint integrity.
"Flowserve has completed an evaluation of the failure and concluded the root cause of the wedge pin failure was excessive load on the pin. The stem operating torque exceeded the torque to tighten the stem into the upper wedge before installation of the wedge pin. The additional stem torque produced a load on the wedge pin creating a stress which exceeded the pin shear strength causing the failure. The recommended assembly stem torque did not envelope the operating torque for the TVA application providing the potential for an over load situation and ultimate failure. The operating torque for the TVA valve was unusually high due to the fast closing time of the actuator and very conservative closing thrust margin.
"This situation can potentially occur on any Anchor/Darling type double-disc gate valve with a threaded stem to upper wedge connection, typically size 2.5" and larger, operated by an actuator that applies torque on the stem to produce the required valve operating thrust. An operating stem torque greater than the assembly stem torque can provide the opportunity for excessive pin load and potentially failure.
"We have reviewed our records, and the only similar wedge pin failure that we can identify, in addition to the Browns Ferry problems, is a sheared wedge pin at LaSalle Nuclear Station in 1993. Our investigation of the LaSalle failure concluded that the wedge pin failed due to excessive torque in the opening direction due to bonnet over pressurization.
"Flowserve recommends that all critical Anchor/Darling Double-Disc Gate valves with threaded stem to upper wedge connections and actuators that produce a torque on the stem be evaluated for potential wedge pin failure. Valves with electric motor actuators which produce high output torques are the most susceptible to failure. Valves which were assembled with stem torques that exceed the operating torque are not candidates for failure.
"Below is a list, based on our records, of customers, utilities and nuclear plants which were supplied with Anchor/Darling Double-Disc Gate valves with motor actuators on contracts with ASME Section III and/or 10 CFR 21 imposed.
"Flowserve plans to provide each of the customers identified [below] with a copy of this notification letter."
The following facilities in the United States may be affected :
ANO 1, Browns Ferry, Brunswick, Callaway, Catawba, Clinton, Columbia, Cook, Cooper, Crystal River, Dresden, Diablo Canyon, Duane Arnold, Fitzpatrick, Fort Calhoun, Grand Gulf, Hatch, Indian Point, Kewaunee, LaSalle, Limerick, Maine Yankee, Millstone, Monticello, Nine Mile, North Anna, Oconee, Oyster Creek, Peach Bottom, Perry, Pilgrim, Prairie Island, Quad Cities, River Bend, Robinson, San Onofre, St. Lucie, Surry, Three Mile Island 2, Waterford, VC Summer, Vermont Yankee, Wolf Creek.
See Related Part 21 EN #48650.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2013/20130304en.html
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