DIFFUSION BONDING OF ZIRCALOY PLATE-TYPE FUEL ELEMENTS

A program on the diffusion bending of plate type, compartmented ceramic- fuel, Zircaloy nuclear elements was completed. The fuel element consists essentially of a punched receptacle sheet of Zircaloy-2 bonded to two cover sheets of Zircaloy-2. The receptacle sheet forms the frames or compartments for the ceramic UO/sub 2/ fuel. By chemical displacement plating, the punched receptacle sheet was coated with a bonding agent such as copper, iron, or nickel. The element was assembled with the ceramic fuel platelets in their compartments, and the three sheets joined around their periphery by tungsten-inert-gas edge arc welding. The ceramic fuel platelets were coated with graphite prior to assembly to inhibit reaction between the UO/sub 2/ and the Zircaloy-2 bonding. The element was heated in helium atmosphere furnace to temperatures from 1600 to 1900 ts F, under positive pressures from 1 to 30 psi, and held from 1/4 to 3 1/2 hr. Bonding was achieved over the entire faying surface areas by formation of low-melting eutectics between the bending agent and the Zircaloy, and diffusion of the eutectic into the Zircaloy. Based on the mechanical properties and corrosion resistance of bonded elements and on metallographic observations, copper served best as the diffusion bondingmore » medium. The behavior of elements plated with iron was undependable, and voids generally formed in the bend. The effect of geometry on mechanical properties the effects of temperature, time, and heating and cooling rates on the interface reactions. (auth)« less