DISPOSIT

1474359 Fuel elements; control elements COMMISSARIAT A L'ENERGIE ATOMIQUE 9 Jan 1976 [20 Jan 1975] 00870/76 Heading G6C A bracing device for a bundle of parallel pins in a reactor assembly, viz. a fuel, fertile or control assembly, comprises at least one compartment grid 1 formed by tube elements 4 of small height each traversed axially by one pin of the bundle, these elements 4 being rigidly fixed to each other as, for example, by spot welding and distributed within a wrapper 3 in at least one helix. This helical arrangement of the tube elements 4 results in stirring or mixing of the coolant as it flows through the wrapper 3. In the embodiment shown in Fig. 4, two grids 1a, 1b of a fuel assembly are disposed at opposite ends of the bundle and connected by means of longitudinal tie-rods 8 which replace a certain number of fuel pins within the bundle. The tierods 8 are provided at their lower ends with split end-caps 9 which co-operate with rounded portions 10 on the upper extremitites of support rails 11. In an alternative embodiment, Fig. 5, the bundle has a single compartment grid 1c which extends the full height of the fuel assembly. In the drawing only a few of the tube elements 4 are shown for clarity. The grid 1c is welded at its lower end to a component 12 having a positioning end-piece 13 into which the coolant 14 flows. In a further alternative embodiment, Fig. 6, the tube elements 4 of each compartment grid are welded or brazed to a certain number of fuel pins of the bundle at the level of intermediate plugs 15 provided within the cans 2 of the fuel pins. Each plug 15 has a bore 15a for the passage of fission product gases and forms a division between a fuel region 16 and a fertile region 17. The tube elements 4 may have oblique end faces with respect to the direction of the axis of the fuel pin bundle (Fig. 7, not shown).