Abstract: The device comprises at least one compartment grid formed by tube elements of small height placed in juxtaposed relation and each traversed axially by one pin of the bundle. The tube elements are rigidly fixed to each other at successive points in the grid and relatively displaced along the height of the pins so as to be distributed in at least one helix.

Abstract: The fuel assembly comprises at least one cluster of canned-fuel pins disposed on a uniform lattice within a sleeve defining a duct through which a coolant is circulated. Each fuel pin is provided at least over the greater part of its length with a helical spacer member which determines the minimum spacing between the fuel pin and the adjacent pins or the sleeve. The internal face of the sleeve is provided with recesses in which the spacer members of the lateral pins of the cluster are partially engaged.The fuel assembly finds an application in nuclear reactors of the liquid-sodium-cooled fast breeder type.This is a continuation, of application Ser. No, 395,454 filed Sept. 10, 1973 now abandoned.

Abstract: A nuclear fuel sub-assembly comprises a bundle of fuel pins provided with helical spacers and located within a shroud for the coolant. The sub-channels at the periphery of the bundle are restricted in order that the rate of flow matches the heat transfer surfaces in all sub-channels. For this purpose the spacers of the outer pins project radially by an extent smaller than the spacers of the inner pins. In addition longitudinal ribs may be provided in the outer sub-channels.