Patent ID: 6980620

Claim:
In a water-cooled nuclear reactor having: a core that includes juxtaposed fuel assemblies of straight prismatic shape with their vertical axes orthogonal to the horizontal core support plate; positioning elements for the fuel assemblies, each element received in a respective opening formed in a lower end piece of the fuel assembly, the positioning element including— a) a pin having a stud portion received within a respective opening and projecting from the core support plate, a threaded portion of the pin being screwed into a threaded vertical opening formed in the core support plate; b) a securing washer received within a counterbore formed around the threaded opening in the core support plate and axially mounted on the pin; a restoration process for replacing a defective positioning element of a fuel assembly, the process performed under water and comprising the steps: removing the fuel assemblies from the core; removing the defective positioning pin from its threaded opening; machining the threaded opening in the support plate, under water, to remove the securing washer and to eliminate a original screw thread from the threaded opening; machining a new screw thread where the original screw thread was removed; inserting a modified replacement positioning pin in an associated opening in the lower end piece of the fuel assembly, a threaded portion of the replacement positioning pin being screwed into the new screw thread; screwing the replacement positioning pin until an integral annular flange thereof contacts the counterbore, the flange having a diameter that is substantially equal to the diameter of the counterbore; and continuing to screw the replacement positioning pin with a torque which eliminates play between the flange and the core support plate during operation of the reactor.