Effects of High Burnup on Natural Uranium

Results are given from experiments in which unrestrained specimens of unalloyed natural uranium were irradiated to total atom burnups ranging up to 1.82% (15,500 Mwd/T) at temperatures from 50° to 220°C. A few specimens were also thermally cycled. The specimens represented material with four different fabrication histories: (1) rolled at 300°C, (2) rolled at 300°C and quenched from the beta phase, (3) rolled at 300°C, quenched from the beta phase, and recrystallized in the alpha phase, and (4) rolled at 600°C. It was found that the 300°C rolled specimens in the as-rolled condition grew in length at a rapid rate when subjected to irradiation, although they maintained relatively smooth surfaces. The growth rate of this material appeared to decrease with increasing irradiation temperature. The beta-quenched specimens were much more stable dimensionally but developed roughened surfaces. The 600°C rolled material showed intermediate behavior. It was concluded that 300°C rolled and beta-quenched uranium can withstand at least 2 atomic per cent burnup without disintegration due to irradiation damage. A qualitative similarity was found between the irradiation growth rates of the four materials and their growth rates under thermal cycling.