Computation of Gap Conductance in Different Fuel Assemblies in VVER-1000 Type Reactors

In this paper, a calculation for fresh fuels gap conductance at different axial lengths of fuel assemblies of the VVER-1000 type reactors has been made using two models of Calza-Bini and Relap5. By applying these two models, the dependency of the fuel outer surface temperature and the clad inner surface temperature of the gap conductance has been determined upon using following procedures: Coupling gap conductance model computer programming to obtain temperature at different axial lengths of the fuel and clad; and coupling gap conductance model to the COBRA-EN output code. The results of calculations and comparison with the FSAR results showed that the Relap5 model is less accurate than the Calza-Bini model. The Calza-Bini model agrees well with the FSAR results. By combining these two models, a new model with a better accuracy was proposed for the gap conductance.