One of the UO2 fuel element designs proposed for use in the PTRT is the nested tubular concepts. This configuration compromises a central fuel todo surrounded by two concentric tubes of fuel (see sketch, appenx I.) . These UO2 shapes are to be jacketed in the Zircaloy and must be separated from each other and the procuresses tyvm vt annular spaces for the passage of coolant. The annuli are established and and maintained by the longitudinal ribs on the outer surface of all three jacketed fuel elements.

It is well known that neutron damage generally causes increases in the yield and ultimate strength and a decrease in ductility of a metal. There is a continuing program at HAPO to determine the extent of these changes in Zircaloy-2 as functions of integrated neutron exposure, irradiation temperature, and reactor atmosphere. Three investigations from this program will be described and the results summarized. The first investigation deals with both annealed and cold worked Zircaloy-2 irradiated at approximately 50 C. and the other two investigations deal with annealed Zircaloy-2 irradiated at approximately 100 and 280 C respectively. In each investigation tensile testing was performed at room temperature.