Theoretical models are used in support of the I2S-LWR (Integral Inherently Safe LWR) project for a direct comparison of fuel swelling and fission gas bubble formation between U₃Si₂ and UO₂ fuels. Uranium silicide is evaluated using a model developed by Dr. J. Rest with the fuel in a amorphous state. The uranium dioxide is examined with two separate models developed using a number of papers. One model calculates the swelling behavior with a fixed grain radius while the second incorporates grain growth into the model. Uranium silicide rapidly becomes amorphous under irradiation. The different mechanisms controlling the swelling of the fuels are introduced including the knee point caused by the amorphous state for the U₃Si₂. The outputs of each model are used to compare the fuels.