GB1222718A - Improvements in or relating to nuclear reactors - Google Patents

Abstract

1,222,718. Reactors. H. BENZLER. 18 Oct., 1968, No.49407/68. Heading G6C. A fast gas-cooled nuclear reactor comprises a plurality of flat plate-shaped fuel elements each including ceramic fuel and a metallic casing. The thickness of the fuel and the spacing between adjacent elements in each part of the reactor are so arranged that throughout the reactor at full load the inner parts of the fuel are at the same temperature, also the fuel casings are at the same temperature. The pressure loss can be reduced to at least one half in comparison with an equivalent reactor core having rod-shaped elements, which is particularly important for gas-cooled reactors. If the elements of the breeding cover, i.e. the cover of a jacket around the reactor core, are formed in a similar way to the core elements, then a reduction of the pressure loss by a factor of from 4 to 6 is achieved. Furthermore, the volume of the cooling medium in the outer radial zones can be reduced, resulting in the reactor accommodating more fuel and the thermal loading of the outer cooling channels being advantageously raised. Also, by achieving the maximum permissible fuel temperature in the whole reactor core, the negative temperature coefficient of the reactivity is advantageously increased. The fuel elements may be assembled in bundles with the aid of spacers and each bundle inserted in an outer casing or in a support member. In a particular .construction, several bundles of fuel elements are stacked one upon another in each outer easing with adjacent bundles angular staggered, e.g. by 90 degrees. In order to avoid the pressure build-up of fission product gases, the interior of each fuel element is maintained by suction through a communicating duct system at a pressure below that of the cooling medium. The ceramic fuel may be inserted and fixed in the metallic casings in the form of prepressed panels. The metallic casings may be interrupted as in a cage, by which means a free diffusion of the fission products is made possible which results in a reduction of the metallic components in the reactor core and a simultaneous increase in the breeding rate. In an example, the fuel is a UO 2 -PuO 2 mixture of 20 to 25% by wt. fission material (U-235 and Pu) enrichment within a casing of austenitic steel. The cooling medium is CO 2 . The reactor core is surrounded on all sides by a jacket formed from a plurality of casings each containing stacked bundles of plate-shaped breeding elements.