GB920343A - Improvements in or relating to fuel element assembly for nuclear reactors - Google Patents

Abstract

920,343. Fuel elements. BABCOCK & WILCOX CO. April 28, 1960 [April 30, 1959], No. 15027/60. Class 39 (4). In a fuel element for a reactor in which pressurized water acts as both a coolant and moderator, fuel pins are spaced apart within a chamber and the outer layer of pins, adjacent the chamber inside surface, have a lower fissionable content than the inner pins, to avoid a higher rate of heat generation at the surface than in the element interior. In addition, where the pins are in square cross-section groups, the four corner pins have a further reduced fissionable content such that a reduction of coolant flow past the corner pins due to diagonal bowing does not cause overheating of the corners. Each pin contains both fissionable and a fertile material, thorium. As shown, the assembly 10 comprises a flow chamber 12 with coolant inlet and outlet 14 and 16 respectively, and contains fuel pins 18. Each pin is formed of fuel cylinders 24 within tube 22 which is sealed by cap 28 with insulating pellet 26 between the cap and fuel. Spacing members 30, 32 are brazed to the fuel pins and permit the flow of coolant with a small pressure drop. The outer layer pins are connected together by spacers 32 which project outwards and maintain a space between the pins and wall 11. The complete pin assembly 20 is positioned within 12 by the shoulder 34 which engages the outer fuel pins 18A. Specification 913,653 is referred to.