A comprehensive investigation of SM reactor fuel elements with 20% higher nuclear fuel load after reactor tests with elevated parameter values is performed. The radial swelling behavior of fuel elements and their kernels as a function of the fission products concentration, fission density, heat-flux density, and test temperature is presented. The swelling behavior of fuel particles in the transfer cross section of a fuel element kernel is examined. The dependences found make it possible to evaluate quantitatively the swelling of fuel elements for different values of the thermophysical parameters and choose safe values for the parameters taking account of the maximum swelling of the fuel elements and the technical possibilities.