GB1251400A - - Google Patents

Abstract

1,251,400. Fuel elements. ATOMIC ENERGY OF CANADA Ltd. 23 May, 1969 [4 June, 1968 (2)], No. 26568/69. Addition to 1,118,850. Heading G6C. A fuel element comprises a core of U metal alloyed with from 2 to 7À3 wt. per cent Si, the core containing one or more void spaces, and a sheath of corrosion resistant alloy, e.g. Zr alloy. The core is heat-treated so as to form a corrosion-resistant alloy, preferably the delta phase U 3 Si. The total volume of the void space(s) is between 3 and 25%, preferably 15%, of that of the U-Si alloy, its purpose being to accommodate any swelling of the alloy and also the fission products produced. The fuel element is fabricated by one of the following methods: (a) casting the U-Si alloy in the form of a rod having a central void, heat-treating the rod at 750‹ to 900‹ C. for 2 to 300 hours to peritectoidally transform the alloy to the delta (U 3 Si) form, machining the rod to predetermined dimensions, and slip fitting the rod into a protective sheath; (b) casting the U-Si alloy in the form of a billet, heat-treating the billet at 750‹ to 900‹ C. for 2 to 300 hours to peritectoidally transform the alloy to the delta phase, extruding the billet at less than 930‹ C.(the peritectoid temperature) such that a void is formed in the rod, machining the rod to predetermined dimensions, and slip fitting the rod into a protective sheath; (c), as (b) above, but extruding the billet before the heat-treatment; (d) casting the U-Si alloy in the form of a billet, heat-treating the billet at 750‹ to 900‹ C. for 2 to 300 hours to peritectoidally transform the alloy to the delta phase, and co-extruding the billet inside a corrosionresistant sheath at less than 930‹ C. to form a U 3 Si core having a central void; and (e), as (d) above, but co-extruding the billet before the heat-treatment. A plug of U 3 Si may be bonded to one or both ends of the core so that the void is enclosed by the core. The U-Si alloy may alternatively be cast as a rod having a uniformly dispersed porosity produced by the introduction of an inert gas, e.g. helium, as by bubbling the gas through the molten alloy or exposing the molten alloy, typically at 1500‹ C., to an atmosphere of the inert gas so that sufficient of the inert gas is absorbed by the alloy, or by placing a gas-generating liquid or solid, e.g. magnesium, in the mould cavity in which the core is to be formed. The rod is heat-treated as in method (a) above to transform it peritectoidally to the delta phase and then machined to its final dimensions before being slip fitted into a protective sheath.