A rational incorporation of hydrostatic stress into the rate theory models for fission-gas behavior in U₃Si₂ dispersion fuels

The current method of incorporation of hydrostatic stress into rate theory models for fission-gas behavior of nuclear fuels is simple and rough, treating the hydrostatic stress as a constant irrespective of the deformation and stress state of fuels. The constant hydrostatic stress is typically derived from some empirical estimate or lower-scale simulations. For dispersion fuels, the fuel particles are constrained by the surrounding matrix and undergo inhomogeneous deformation. The hydrostatic stress should depend on the deformation and stress states within the fuel particles. A more rational approach to doing this is to calculate the stress distribution of the constrained fuel particles and extract the hydrostatic stress. Using the amorphous U₃Si₂ dispersion fuels as an example, this paper presents the implementation of the rate theory model for the fission-gas behavior of U₃Si₂ based on Rest's model in a commercially available finite element software, ABAQUS. The swelling associated with the fission-gas behavior of U₃Si₂ fuels was captured and validated against reported simulation and experimental data. A representative volume element (RVE) model was constructed to simulate the swelling of U₃Si₂/Al dispersion fuel meat. The numerical results were compared with the reported experiments, and good agreement was achieved. The user-defined subroutine codes and the ABAQUS input files are publicized, which offer a powerful and realistic tool for modeling the fission-gas swelling in fuels.