A Calculation on the Migration of Fission Gas in Material Exhibiting Precipitation and Re-solution of Gas Atoms Under Irradiation

TLDR

Bubbles in irradiated material are unstable because an irradiation‑induced resolution process tends to dissolve the gas they contain. The study evaluates how intragranular bubbles, acting as efficient trapping sites, influence fission‑gas migration under irradiation. By modeling a grain as a spherical perfect sink, the authors derive analytical expressions for intragranular gas concentrations in bubbles and solution, and for gas released to grain boundaries, incorporating the effects of bubble resolution and intragranular trapping. The derived expressions simplify under realistic irradiation conditions and provide a basis for calculating the external release of gas from intergranular bubbles that grow large enough to interlink.

Abstract

AbstractThe influence of intragranular bubbles, acting as efficient trapping sites, on the migration of fission gas atoms in material under irradiation is assessed. It is considered that the bubbles are unstable due to the operation of an irradiation-induced resolution process tending to dissolve their enclosed gas. Treating an individual grain within the material as a sphere whose boundary behaves as a perfect sink, general expressions are derived for the intragranular concentrations of gas existing instantaneously within bubbles and in solution. It is shown that the relationships may be simplified for the range of irradiation times and conditions likely to be encountered in practice. Under these conditions, an expression is obtained for the quantity of gas released to the grain boundary, and this is compared with the analogous expression derived previously by Booth for the case where there are no intragranular traps.The fact that the resolution process through its effects on bubbles at the grain boundary will return some gas to the matrix and in so doing destroy the property of perfect-sink behavior is later considered. By an approximate method the appropriate modification to the formula describing the quantity of gas released to the boundary is deduced. This final expression, including the complete effects of intragranular trapping and irradiation-induced resolution on gas migration, may provide the basis on which to calculate the amount of gas which is eventually released external to the material from regions where intergranular bubbles grow so large that they interlink.