Fission gas release and swelling model of metallic fast reactor fuel

A mechanistic model of fission gas release and swelling for the U–Pu–10Zr metallic fuel in a fast reactor, GRSIS (Gas Release and Swelling in ISotropic fuel matrix), was developed. Fission gas bubbles are assumed to nucleate isotropically from gas atoms in the metallic fuel matrix since they could nucleate at both the grain boundaries and the phase boundaries, which are randomly distributed inside the grain. Bubbles can grow to larger sizes by gas atom diffusion and coalescence with other bubbles. When bubble density or swelling due to bubbles reaches a threshold value, bubbles are assumed to be interconnected to each other to form an open channel to the external free space and then the fission gases inside the interconnected open bubbles are released instantaneously. During the irradiation, fission gases are successively released through the open bubbles. The GRSIS model was validated by comparison with the irradiation test results of U–Pu–10Zr fuels as well as parametric studies of the key variables in the model.