Patent Number: 048030414
Section: summary

BACKGROUND OF THE INVENTION The invention relates to a process for the recycling of nuclear fuels contained in a first metal can, within which said pellets have previously been irradiated in a fast neutron nuclear reactor. In fast neutron nuclear reactors, the fissile material is in the form of pellets, normally constituted by a mixed uranium and plutonium oxide (UO.sub.2, PuO.sub.2). These pellets are stacked within metal cans to form the nuclear fuel rods. These rods are arranged in bundles in sleeves with a hexagonal cross-section, so as to form nuclear fuel assemblies. When a new assembly is placed in a fast neutron nuclear reactor core, there is a certain radial clearance between the nuclear fuel pellets and the cans containing said pellets. This initial clearance is provided to take account of the swelling of the pellets occurring under irradiation and to ensure a satisfactory introduction of the oxide pellets into the can during production. Moreover, the irradiation time of the assemblies in the core of a fast neutron nuclear reactor is limited by the deformation undergone by the fuel rod and the hexagonal tube, said deformations being essentially caused by the swelling of the steel. In the present state of the art, the nuclear fuel assemblies are then dismantled, the rods cut up and the fuel removed. These operations obviously take a long time and are very expensive, the latter particularly penalizing the costs of the fuel cycle of fast neutron nuclear reactors. The present invention is based on the observation that when the irradiated assemblies are removed as a result of the swelling of the cans, the combustion level of the fuel pellets is low compared with the combustion possibilities intrinsically offered by said fuel. In the particular case of a fast neutron clear reactor comprising a zero reactivity drop core, such as is proposed in French patent applications Nos. 84 12123 and 85 01203, reprocessing would be considerably spaced if the irradiation time of the assemblies was not limited by the swelling of the cans. It would therefore appear that the limitation of the irradiation time of the assemblies imposed by the swelling of the cans leads to a mediocre exploitation of the possibilities offered by the actual fuel. In particular, the reprocessing of the fuel after a single irradiation period of limited duration is not justified and considerably increases operating costs. SUMMARY OF THE INVENTION The present invention relates to a process making it possible to recycle nuclear fuel pellets after they have undergone one or more irradiations. Thus, the reprocessing of the fuel can be eliminated or limited to the fuel which has reached very high combustion levels and namely roughly three times those presently achieved following a single irradiation. This leads to a considerable drop in operating costs. The present invention therefore proposes a process for the recycling of nuclear fuel pellets contained in a first metal can in which these pellets have previously been irradiated in a fast neutron nuclear reactor, wherein the process comprises extracting the pellets from the first can and introducing them into a new metal can having a slightly larger internal diameter than that of the first can. According to a preferred embodiment of the invention, the pellets are extracted from the first can by progressively melting the latter from one of its ends, the thus exposed pellets then being introduced immediately into the new can. Preferably, the first can is then melted by means of a coil supplied by a high frequency electric current producing a thermal skin effect by induction. In order to ensure that the melted can does not stick again to the remainder of the can, the melted part of the can is removed either by means of a refractory material deflector to which the first can only adheres after melting, or by blowing a neutral gas onto the melted part of the can. According to another feature of the invention, the introduction of the pellets into the new can is facilitated by preheating the latter. Moreover, to limit contamination of the new can, it is preferable to place the latter within a sleeve.