Nuclear reactor fuel element subassembly - with variable spread pitch helical spacers between adjacent elements

摘要

A nuclear reactor subassembly comprises a bundle of fuel elements in a peripheral wrapper. The elemtns are spaced by helically wound fins, which, as the outermost elements have half the dimension and half the pitch of the fins on the other elements. The outermost elements are secured in positions such that adjacent elements have a fin-on-fin relationship. The structure may be used in a sodium cooled fast reactor with a hexagonal core structure. The gap between the outer elements and the wrapper is halved so as to reduce over-cooling of the outer elements and increase allowable fuel content.