DEVELOPMENT OF METALLIC URANIUM FUEL ELEMENTS OF IMPROVED IRRADIATION STABILITY. Semiannual Progress Report No. 1

The feasibility of improving swelling resistance in metallic uranium by increasing the dislocation density is under investigation. Increasing the density of dislocations is expected to increase the number of sites at which fission product gas atoms are "pinned," increase the number of gas bubble nuclei, and increase mechanical strength. Dislocations are introduced by a treatment which involves deformation of metastable beta or gamma phase in uranium-rich alloys, followed by transformation. Activity has been concerned primarily with selection of uraniurnbase alloys for initial evaluation, procurement of materials, installation of specialized equipment, and development of techniques. A number of small ingots were produced, and screening tests were carried out on several analyses. These preliminary experiments were designed to show the deformation characteristics of the alloys in the metastable state as a function of rolling temperature and time. Initial results on gamma-stabilized binary alloys containing 2, 3.5, 5, and 7 wt. % Mo showed that large reductions are possible in 5 and 7 wt. % Mo alloys at450 deg C. The more dilute alloys are relatively difficult to roll, although small reductions were achieved. Aging experiments on deformed and undeformed 5 wt. % Mo alloys indicate that deformation accelerates the aging process and retards growth of the "pearlitic" eutectoid transformation product. Results with dilute chromium and chromium- molybdenum alloys showed that rolling is possible in the metastable beta phase for a short time at temperatures as low as 450 deg C. The beta phase is quite hard at lower temperatures, however, and cracking occurs in some alloys at relatively small reductions. Beta phase deformation of these alloys resulted in no significant hardness increase, although final grain size was reduced appreciably. .Additional experimental work is required to complete the screening of uranium alloys for application to the current program. Following this activity, several of the most promising alloys will be selected for an intensive investigation of the effect of processing variables on mechanical properties, microstructure, and structural stability. Irradiation testing and post- irradiation evaluation of treated alloys will be undertaken later as Phase II of the over-all program. (auth