Joint modeling of thermal creep and radiation damage interaction with gas permeability and release dynamics: The role of percolation

• Dynamical percolation leads to a time-dependent gas flux in a percolating pore system.
• The roles of various damage mechanisms can be assessed.
• We study the effect of microcrack healing on percolation and gas release.

Nuclear fuel material is an example of a sintered, porous ceramic material. We formulate a two-dimensional model which couples three physical mechanisms in the material: (scalar) damage accumulation by thermal creep and radiation effects, porosity changes due to the damage, and the time-dependent diffusion of (radiation-induced) gases in the pore system thus created. The most important effect in the dynamics arises from the process where the pore system is swept through the percolation transition. The main conclusions that can be drawn concern the fractional gas release and its dependence on the three effects present in the damage dynamics: creep, radiation-induced bubble formation, and recovery due to bubble closure. In the main, the model reproduces the experimentally observed quick gas release phenomenon qualitatively.