GB1461288A - Fuel assembly for a high-power nuclear reactor - Google Patents

Abstract

1461288 Fuel elements COMMISSARIAT A L'ENERGIE ATOMIQUE 3 May 1974 [4 May 1973] 19576/74 Heading G6C A fuel assembly comprises within a polygonal outer can 3 a cluster of fuel pins 4 retained parallel to one another at the junctions of a regular network with a bracing or support wire wound as a coarse helix between the two end plugs 5, 6 of each fuel pin 4. At least the non- peripheral fuel pins 4, i.e. those not in contact with the outer cam 3, belong to one of two types 1 and 2, one of the types (e.g. type 1 as in the Figure 5 embodiment) having a bracing or support wire 9 of diameter d 1 equal to the maximum spacing which exists between two adjacent fuel pins when in operation and the other type (e.g. type 2) having a bracing or support wire 11 of diameter d 2 less than the diameter d 1 . The cross-sections of the wires 9, 11 are indicated in Fig. 5 by 10, 12, respectively. The fuel pins 4 are clad in stainless steel sheaths, the end plugs 5, 6, wires 9, 11 and the outer can 3 also being of stainless steel. The above arrangement of two types of fuel pin with support wires of different diameter obviates some of the contact points otherwise occurring between adjacent fuel pins so as to facilitate longitudinal bending of the pins resulting from distortion and swelling of the pins during irradiation while making it impossible for adjacent pins to contact one another other than via support wires. As regards the peripheral fuel pins, either only those having a d 1 -diameter wire are placed at the periphery or, alternatively, both type fuel pins are placed peripherally in an arrangement similar to the fuel pins inside the cluster. Those fuel pins having a d 2 -diameter wire can then be arranged to bear on the can 3 only at the top plug 5, e.g. by using a large diameter plug, or the d 2 - diameter wires can be sheathed by tubular pieces of outside diameter d 1 at regular intervals so as to maintain a spacing d 1 between the outer can 3 and the peripheral fuel pins. Alternatively, each peripheral fuel pin has a d 2 -diameter wire with regular sheathing of the wire of some of the peripheral fuel pins by means of d 1 - diameter tubular members disposed opposite adjacent fuel pins so as to achieve a similar patterning to that specified for the inner fuel pins of the cluster. The cam 3 may be formed with longitudinal thickenings and/or longitudinal recesses on its inside surface.