Abstract: Calculations and analyses of Halden IFA519.9 DK fuel rod irradiation test were carried out using the fuel performance code COPERNIC. Investigations on the high burnup fission gas release behaviors were implemented. Comparison between predictions and experimental results were performed. The results indicate that, during high burnup to ~100 GW?d/t(U) irradiation, the code predictions show good agreement with experimental data in terms of fission gas release. The code does not particularly model the evolution of fuel porosity within high burnup rim structure, however, the accuracy and rationality on fuel rod integrated performance analysis would not be affected.