GB989889A - Fuel element for a nuclear reactor - Google Patents

Abstract

989, 889. Nuclear fuel elements. FULCRUM A.B. March 9, 1962, No. 9224/62. Heading G6C. A fuel element for a nuclear reactor comprises a central core 3 of fissile material capable of withstanding the high temperatures prevailing in the central part of the fuel element during operation, an outer mantle 1 of fissile material and an intermediate layer 2 of non-fissile material for transferring heat from the core 3 to the mantle 1, the non-fissile material being of low neutron absorption cross-section and chemically inert towards the fissile material, the core 3 being of higher thermal stability than the mantle 1 and the mantle 1 being of higher thermal conductivity than the core 3. The mantle 1 comprises metallic uranium and/or plutonium which may be alloyed with one or more of aluminium, silicon, magnesium, titanium, zirconium, vanadium, inobium, tantalum, chromium, molybdenum and tungsten. The core 3 comprises a thermally stable compound of a fissile metal, e.g. the oxide, carbide, silicide, nitride, boride or sulphide of uranium or plutonium, and may be mixed with a suitable metal in order to increase the thermal conductivity and the mechanical stability. The fissile material of the core 3 may also be mixed with materials other than metals such as Cr-Al 2 O 3 , SiC-Si, ZrC-Fe and MgO-Ni. The intermediate layer 2 may be a gas, advantageously argon, helium or hydrogen, a material liquid at the operating temperature of the fuel element, lead-bismuth or sodium-potassium eutectic alloys being particularly suitable, or a solid such as a metal or metal alloy. If desired, the core may be enriched by the inclusion of U-235, either unalloyed or alloyed with other substances, or the central part 4 of the core 3 may consist of an enriched fissile material. In one method of producing a fuel element according to the invention, a metal or metal alloy tube is externally ground so as to fit the inside of the mantle as snugly as possible and filled with powdered core material. It is then closed by a suitable end plug, placed in a press holder and pressure applied to the end plug to increase the density of the powder. Thereafter the tubular member is removed from the holder and inserted in the mantle. The powder sinters when the fuel element commences to operate in the reactor. Alternatively, presintered fuel slugs are used in which case an accurate tolerance should be provided on the inside of the metal or metal alloy tube with respect to the diameter of the slugs. Alternatives to the fuel element of circular cross-section shown in Fig. 1 are a fuel element having a flat oval cross-section (Fig. 2, not shown) and a fuel element consisting of a rectangular or circular disc 3 and two mantle plates 1 (Fig. 3, not shown). An element having an increased radiation surface is shown in Fig. 4.