AbstractA computer program has been developed and used to validate and adjust models for predicting fuel-pin deformations. An existing computer program, DEFORM, was combined with a clad swelling model to be a subroutine for calculating fuel-pin deformations. Predictions of deformations made with this subroutine are compared with measured deformations in a parameter fitting program, SIMPLEX. A comparison of analyses made with this program, using input data collected from experiments on four irradiated fuel pins, indicated that the program version assuming only a clad swelling model predicted the mean deformations of these pins better than the program version assuming both clad swelling and a mechanical interaction between the fuel material and the clad material.