On the formation of gas bubbles in fissile material during reactor irradiation

Abstract

Abstract The formation of fission gas bubbles in solids has been considered in conditions where the re-solution of gas from bubbles is appreciable. In such conditions the Greenwood theory is shown to apply only at high temperatures and short irradiation times. At low temperatures precipitation is delayed at short irradiation times. For longer irradiation times at all temperatures, the irradiation-enhanced generation rate due to re-solution of gas from bubbles outweights the natural generation rate and the number of nuclei increases linearly with time until numbers are eventually limited by the agglomeration of bubbles by random motion. The number of bubbles predicted by this nucleation-agglomeration theory agrees with experimental observation in the case of uranium dioxide, but may not agree in the case of uranium, for which the re-solution parameter may not be high enough. The effect of the theoretical predictions of bubble number and size on swelling and gas migration is discussed for uranium dioxide.