Comparison of fission gas swelling models for amorphous U3Si2 and crystalline UO2

Abstract Theoretical models are used in support of the I 2 S-LWR (Integral Inherently Safe LWR) project for a direct comparison of fuel swelling and fission gas bubble formation between U 3 Si 2 and UO 2 fuels. Swelling in uranium silicide is evaluated by analyzing the bubble coarsening process’ effects on the bubble population and size distribution. The uranium dioxide is examined with two models: one which calculates the swelling behavior with a fixed grain radius and a second which incorporates grain growth into the model. These two models use the diffusion of gas atoms to the grain boundaries to calculate the swelling. The different mechanisms controlling the swelling of the fuels are introduced including the “knee point” caused by the amorphous state for the U 3 Si 2 . The U 3 Si 2 model shows that, for the burnup expected for the I 2 S reactor, swelling in U 3 Si 2 will not reach the “knee point” with accelerated swelling. The results from the fixed grain UO 2 model and U 3 Si 2 model are used to compare the swelling of each fuel at the same fission rate.