Book Description

Three separate irradiation experiments were completed with Th and Th-U alloys. In the first experiment, three-rolled plates of Th and Th-5 wt% U alloy irradiated to total atom burnups up to 1.5% at 200 deg C showed no anisotropic growth and decreased in density at a rate of 1% per wt.% burnup. In the second experiment, 15 swaged specimens of Th and of the alloys Th-0.1 wt% U, Th-1.4 wt% U, and Th-5.5 wt% U were irradiated to burnups ranging from 0.3 to 3.6% of all atoms at temperatures in the range of 45 to 200 deg C. Again, no anisotropic growth was observed and densities decreased at rates near 1% per wt.% burnup. A Th-1.4 wt% U alloy specimen with 2.0 wt.% burnup was found to have retained significant room-temperature ductility. In the final experiment, a group of 44 chill-cast specimens of Th alloys containing 10, 15, 20, 25, and 31 wt% U were irradiated to burnups ranging from 0.16 to 10.1% of all atoms. Maximum irradiation temperatures ranged from 260 to over 1000 deg C. Surface roughening occurred in the alloys containing 25 and 31 wt% U. Volume increases at any given temperature for all alloys were linear with increasing burnup. The rate of volume increase for all alloys rose from approximately 1% per wt.% burnup at the lower temperatures to a value of 2.5 at 650 deg C. Thereafter the swelling rate increased somewhat, reaching a value of 6% volume increase per wt.% burnup at 800 deg C. The rates of volume increase under irradiation of Th-U alloys in the entire temperature range studied were significantly less than those reported for the best U-base alloys. It is suggested that the excellent resistance to high- temperature swelling of the cast Th-U alloys resulted from the fact that a dispersion of very thin U particles was obtained. A high probability, therefore, existed for fission recoils to escape from the U particles into the isotropic and less densely packed Th matrix.