A metallurgical bond can be effected between a Zircaloy-2 jacket and a thin walled uranium tube by treatment in a high temperature, high pressure gas autoclave. Bonding is independent of core history, provided that all surfaces are free from contamination. Gas pressure bonding causes the fuel element jacket to conform to the core, which promotes bonding on all surfaces including the ends. Grain growth occurred in some instances between the jacket and end cap interface. A three phase system (alpha, delta and epsilon) was identified across the interface at the bonding conditions of 845 C (1500 F), 10,000 psi and a time of four hours. Four structures were observed; these were epsilon, epsilon plus delta, delta, and alpha plus delta. Microhardness tests were used to identify the various phases. Also, thickness measurements were made of each component in the interface. The normal pressure bonded interface consists mainly of epsilon and delta phases. A cast bonded sample, subjected to the pressure bonding treatment, consists predominantly of alpha plus delta material while an interface bonded during casting is primarily alpha plus delta phases and epsilon phase.