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This progress report covers the ninth year of operation under Contract AT(11-1)-1436. The principal area of research is ternary diffusion in solid solution alloys. Specific research projects deal with diffusion in the Cu-Zn-Ni, Ag-Zn and Ni-Al systems (three projects). Each of the projects is carried out

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U-10Zr is a nuclear fuel proposed for use in the Integral Fast Reactor (IFR). Possible mechanical interaction between the swelling metal fuel and its cladding which may cause cladding failure is a safety and operational issue. Specimens prepared from uranium and zirconium powders (meta] and hydride) were sintered in a purified argon atmosphere to entrap gas and simulate fission gas bubbles in irradiated fuel. The specimens were hot isostatically pressed to study the fuels' densification under external pressure. Hot-pressing was not detected at 600°C, but U-10Zr hot-presses at 700°C by a coupled creep/grain boundary diffusion mechanism. The measured stress dependence (n=3.4x'-0.3) indicates a dislocation creep mechanism and the measured activation energy (187+10 KJ/mole) agrees with the reported value for grain boundary diffusion of y-U. This is contrary to observations for UO2 and other materials where hot-pressing is controlled by diffusion.