Patent Number: 049816403
Section: summary

BACKGROUND OF THE INVENTION 1. Technical Field The invention relates to a reception and dismantling cell for a nuclear fuel assembly of the type comprising a bundle of fuel rods retained at the nodes of a regular lattice by a skeleton formed of two end pieces connected together by tie rods and grids spaced apart along the tie rods. When such fuel assemblies are removed from a reactor after irradiation, they must be stored in a swimming pool until the deactivation is sufficient to make it possible to remove the rods. It is desirable to reduce as much as possible the volume occupied by the elements of the assembly during deactivation so as to increase the storage capacity of the swimming pool. 2. Prior Art An installation is already known (Beneck et al. U.S. Pat. No. 4,731,219) for separating a fuel assembly into a skeleton and rods, which form the most active elements, and consolidating the rods in the form of a bunch of jointing rods distributed according to a triangular lattice. The installation comprises a cell receiving the fuel assembly to be dismantled for successively removing an end piece then extracting the rods. The cell comprises a vertical structure with a cross-section corresponding to that of the assembly to be received, having mechanisms for retaining the grids and the lower end piece and a mechanism for holding the rods at their nominal spacing with combs movable between a position in which they are outside the assembly and a position in which the fingers of the combs are engaged between the rods, above the highest remaining grid after removal of the upper end piece. SUMMARY OF THE INVENTION An object of the invention is to provide a fuel assembly reception and dismantling cell for holding the assembly firmly in position, avoiding any risk of damaging the rods during separation of the upper end piece (generally by severing the tie rods formed by guide tubes) and avoiding jamming of the rods during subsequent extraction thereof. To this end, the invention provides a fuel assembly reception and dismantling cell characterized in that the comb mechanism comprises at least two sets of combs carried by a frame solidly joined to said structure, the combs of each set being guided over the frame and having jacks for moving them toward and away from each other in a direction transversal to the move direction along which the combs of the other set move toward and away from each other. The grid retention mechanisms comprise jaws pivotally mounted on the structure and connected to jacks for simultaneous control, arranged for moving the jaws between a position in which they release the grid situated immediately below the comb mechanism and a predetermined position with respect to the structure in which the jaws grip the grid on all sides thereof. With such an arrangement, the top ends of the fuel rods are held accurately in position at the nodes of a regular lattice when the unit formed of the upper end piece of the assembly, a section of the guide tubes separated by cutting and possibly the uppermost grid of the assembly, is withdrawn. If the fuel assembly has a square cross-section and the rods are retained at the nodal points of a square lattice, the comb mechanism typically comprises two sets of orthogonally movable combs and the mechanism for retaining the highest grid remaining after removal of the upper end piece comprises two sets of two jaws, one of the sets at least having studs for engaging the grid and preventing upward movement thereof.