GB981957A - Improvements in or relating to the production of sheathed articles - Google Patents

Abstract

981,957. Casting composite articles. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. April 30, 1963 [May 4, 1962], No. 17159/62. Heading B3F. [Also in Division G6] A sheathed article is produced by passing a molten material into a sheath of a material of considerably lower melting point than the first material, and effecting control of the temperature of the sheath by heat exchange means during solidification. As applied to the manufacture of a nuclear fuel element, uranium is cast into a magnesium alloy sheath under vacuum. The sheathing may have internal circumferential or helical recesses so that the uranium is keyed thereto, and have preformed heat transfer surfaces; alternatively said surfaces may be formed by subsequent working. The interior of the sheath may be inhibited to prevent alloying of the uranium and sheath or alloying may be encouraged by providing a bonding material, e.g. A1, Si, on the wall of the sheath. The ends of the sheath are completed by fitting an insulation disc of sintered magnesium oxide followed by edge welding an end cap into position. A suitable amount of helium is introduced into the sheath so that subsequent leak testing may be effected with a mass spectrometer. Good contact between the uranium and sheath, despite shrinkage of the uranium during cooling may be ensured by pressurization of the sheath by known gaseous or hydraulic means. A number of sheaths may be supported for top pouring in a structure with parallel passages for liquid or gaseous coolants, and at a suitable temperature the coolant may be replaced by a heating fluid, with or without additional heating, to effect annealing &c. In a modification the sheaths are supported in a solid or liquid refrigerantfilled container. Alternatively the sheaths are bottom poured by supporting them in a vessel into which the uranium is poured. The elements may be made from ceramic fuel material, e.g. uranium dioxide or carbide, and sheaths of metal, e.g. stainless steel, or ceramic material, e.g. beryllia for uranium dioxide or silicon carbide for uranium carbide. Specifications 790,389, 806,971, 812,123, 863,492, 921,484, 935,510, 974,887 and 981,956 are referred to.