An investigation of the effects of irradiation on uranium containing 0.52 and 1.62 w/o zirconium was made. Specimens of wrought material, variously heat treated, were studied as well as castings of the alloys. It was found that, although the wrought and heat-treated alloys were reportedly stable under thermal cycling, they elongated rapidly under irradiation. The best material studied was the 1.62% alloy in the as-cast condition. It was found to increase in length initially at a rate of about 5% per a/o burnup, after which the rate steadily diminished. Up to burnups of at least 5.3 a/o it retained a smooth surface. Two specimens of the cast 1.62% alloy, one irradiated to 2.1 a/o burnup at a calculated central temperature of 690°C and the other irradiated to 5.3 a/o burnupat a calculated central temperature of 620°C, swelled and increased in volume with the formation of a large central void surrounded by highly porous metal. The critical swelling temperature of uranium-1.62 w/o zirconium alloy was found to lie between 300 and 620°C, with some indications that it may be near 500°C.
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