Modifications of the Fuel Rod Analysis Program FRAP-S3 to Account for the Effects of Fuel Initial Density

The Fuel Rod Analysis Program (FRAP-S3) is a fairly comprehensive computer code that is developed for the analysis of light water reactor fuel elements during steady-state operation. However, the code pre dicts an increase in the fuel radial temperature dis tribution with an increase in the fuel density, which is contrary to experiments. A simple modification of the code was used where the thermal conductivity is treated as porosity independent in the inner iteration loops of the program. The resulting temperature pro file is corrected for the effects of porosity after it has converged. The modified code shows good agree ment with the IFA-11 series of experiments using the Halden Boiling Water Reactor in Sweden.