Patent Number: 054250714
Section: summary

This invention relates to loading nuclear fuel pellets into a cladding tube to form a nuclear fuel pin for use in a nuclear reactor. In particular, the invention is concerned with inserting an end plug into the cladding tube after loading a stack of fuel pellets into the cladding tube where the pellets are made of a mixed oxide fuel comprising a mixture of uranium dioxide and plutonium dioxide. Because of the radiological hazards involved in handling fuel pellets containing plutonium they are manufactured in a containment area enclosed by alpha radiation shielding. When loading the pellets from the containment area into a cladding tube located outside the containment area, the end of the tube through which the pellets are inserted protrudes into the containment area. As a result, the end portion of the tube becomes radioactively contaminated. This necesitates subjecting the pin to a decontamination process, which is undesirable since it increases manuacturing costs. It is an object of this invention to obviate the need for decontamination of the pin following the fuel pellet loading operation. According to one aspect of the invention there is provided apparatus for inserting an end plug into a fuel pin cladding tube after loading nuclear fuel pellets into said cladding tube, said apparatus comprising a sleeve removably mounted on one end of the cladding tube, said sleeve being slidably locatable in a resilient seal, a carrier having a closed recess for locating therein an end plug for closing said one end of the cladding tube, the carrier being slidable in the sleeve so that on moving the carrier through the sleeve the end plug is inserted into said one end of the cladding tube, the arrangement being such that on withdrawal of the cladding tube with the end plug therein leaves the sleeve and carrier trapped in the seal. Preferably, the sleeve has an internal seating surface comprising a reduced diameter portion extending from one end of the sleeve, the seating surface being adapted to fit on the end of the cladding tube. The seating surface preferably extends from the said one end of the sleeve to an internal end surface which is coincident with an end surface of the cladding tube. The seating surface may be a press fit on the cladding tube. In a preferred embodiment the end plug has a head portion having an end surface and a peripheral surface, the depth of the recess in the carrier being sufficient to surround the end surface and the peripheral surface. Preferably, stop means are provided to retain the sleeve and carrier in the resilient seal upon withdrawal of the cladding tube. The resilient seal may be of the sphincter seal type having a plurality of resilient rings adapted so as to press against the sleeve. According to a further aspect of the invention there is provided a method of inserting an end plug into a fuel pin cladding tube after loading nuclear fuel pellets into said cladding tube, said method comprising the steps of mounting a sleeve on one end of the cladding tube, inserting the sleeve in a resilient seal, introducing a carrier into said sleeve, said carrier having a closed recess containing therein an end plug which is inserted into said one end of the cladding tube upon introduction of the carrier into the sleeve, and withdrawing said cladding tube with the end plug inserted therein while leaving the sleeve and carrier located in the seal. Preferably, the method includes the further step of displacing the sleeve and carrier from the seal by a sleeve mounted on a fresh fue pin cladding tube during a subsequent pellet loading sequence.