Abstract
The fission gas escape during fissioning in fuel was interpreted with a newly proposed escape mechanism which comprises the three successive processes of release from trapping sites, diffusion of the released fission gas nuclides, and desorption from the fuel surface. The expression for the release rate of fission gas was derived from a simple mathematical model postulating a continuous activation energy spectrum for the release reaction of trapped nuclides. The proposed mechanism satisfactorily explains observed data reported in literature on the dependence of the escape rate on decay constant, the contribution of the precursor, and the change of escape rate with irradiation time. There appears to be only a small effect brought by diffusion of the released nuclides on the escape rate, which can thus be considered to be controlled mainly by the release reaction from the the trapping sites. The present model based on the release from trapping sites can also qualitatively explain the influence of differences in irradiation conditions such as time and neutron flux.
