Fission-Gas Release During Fissioning in UO2

The results of in-pile tests on UO2 specimens of fine-grain and single-crystal structure led to the formation of a defect-trap theory to describe fission-gas release. The theory, which applies only when the UO2 temperature is below the grain growth region (≍1600° C), is described, and confirming experiments are cited.Experimental results are given to support the contention that a knock-out mechanism accounts for the majority of the fission-gas release at UO2 temperatures under 600° C.An oscillating experimental technique developed to evaluate the defect-trap theory is described, and the initial results are interpreted in terms of the theory.