Kernbrennstoffelement

955, 485. Nuclear fuel elements. SOC. NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION. Dec. 6,1960 [Dec. 11, 1959], No. 42002/60. Heading G6C. The component parts of a fuel element for a nuclear reactor contain an active material, i.e. a mixture of a fissile material with an isotope which is not (or only very slightly) fissile, and are in the form of bundles of rods or concentric cylindrical rings, the cross-sectional area and the concentration of active material of each of the component parts being so correlated that the surface thermal flow is the same for all the component parts. The component parts (i.e. rods or rings) may have the same cross-sectional area and an active material concentration which increases towards the centre of the element, a uniform concentration of active material and a cross-sectional area which increases towards the centre of the element, or, both a concentration and a cross-sectional area which increase towards the centre of the element. In one example, six peripheral rods 1 surround a central rod 2, both rods 1 and 2 being of 10 mm dia. and clad in sheaths 3 of an alloy of 80% by wt. Ni and 20% by wt. Cr of 1 mm thickness. The material of the six peripheral rods 1 comprises 40% by wt. UO 2 (20% by wt. U-235) in a homogenous mixture with 60% by wt. MgO while the material of the central rod 2 comprises 48% by wt. of the same UO 2 and 52% by wt. MgO. The element is housed in a channel 18 of 40 mm dia.