Book Description

The swelling of uranium and of a few selected uranium alloys on post-irradiation annealing was investigated by utilizing density measurements in conjunction with the observation of pores in the microstructures of annealed specimens. Specimens were irradiated to about 0.3 at.% burnup in a constrained condition at approximately 275 deg C and were subsequently pulse annealed. The amount of swelling was found to be less than 1% for U specimens that were pulse annealed up to 75 hr at temperatures below 550 deg C; the amount of swelling, however, increased considerably on annealing at temperatures between 550 and 650 deg C. Specimens pulse annealed up to 75 hr at 618 deg C decreased in density by approximately 18%. The swelling was accompanied by the formation of bubbles on grain boundaries in recrystallized regions. The observations suggest that recrystallization is a necessary prerequisite for pronounced swelling in the alpha phase.