GB1139990A - Nuclear fuel element - Google Patents

Abstract

1,139,990. Fuel elements. COMMISSARIAT A L'ENERGIE ATOMIQUE. 27 Dec., 1967 [25 Jan., 1967], No. 58735/67. Heading G6C. A fuel element comprises a mass of ceramic fuel 14, e.g. an oxide (UO 2 , PuO 2 or a mixed oxide of U and Pu), carbide or nitride, in finely divided form, compacted in a tubular zone between a metallic can 6 and a core 12 of a porous, non-fissile refractory material retaining a substantial resistance to compression and creep at the working temperature of the fuel element and having end parts that project out from the fuel material and are covered by the end plugs 10 of the can. The core 12, which may be of graphite, Al 2 O 3 , MgO, ZrO 2 or SiO 2 , serves to absorb fission product gases and to secure the mechanical rigidity of the element. A graphite core has the disadvantage of reacting with the oxide fuel materials but the reaction kinetics, which are slow if the contact temperature between the fuel and the graphite is low and if the external pressure of the coolant gas is high, result in acceptable valves in the case of a reactor operating with a coolant gas at a high pressure, e.g. 60 bars. In order to avoid any reaction, however, the graphite core may be coated with a refractory oxide, e.g. Al 2 O 3 , MgO or ZrO 2 , by spraying it with a suspension of the refractory oxide in a flow of hot gas. In a process of manufacturing such a fuel element, a graphite core is prepared by machining or extruding a carbon mixture which is subjected to a graphitizing treatment and also to a treatment for increasing its porosity. The can 6 previously equipped with the lower plug 10 is placed vertically on a frame 18 and fitted with a loading funnel 20 provided with a central hub 22 through which the core 12 is slipped into position in the can 6. The fuel material is then poured into the funnel 20 and compacted in the can 6 by vibration of the frame 18. These operations are performed within a gas-tight vessel 24 in which a vacuum is maintained. When the filling is completed, the funnel 20 is removed and the end plug placed in position and screwed to the can 6, e.g. by electron beam welding.