Numerical study of the thermal and geometrical characteristics of the WWER fuel rods at normal operation conditions of the Kozloduy NPP units for application in neutronics calculations

In this paper, a methodological approach and results of its application for steady-state thermo-mechanical study of the WWER-440 and WWER-1000 fuel rods, by means of the TRANSURANUS code, to obtain dependencies of fuel rod temperatures and radii on the linear heat rate (LHR) and burnup, are presented. The dependencies are intended to be applied in neutron-physical calculations of the WWER reactors at the Kozloduy NPP, for steady-state and transient regimes. The thermo-mechanical effects for this kind of applications are considered for the first time in Bulgaria. Selected calculated results of the WWER fuel rod thermophysical characteristics, obtained by the TRANSURANUS and the TOPRA-s codes are presented and compared. The comparison shows reasonable compliance of the fuel temperatures calculated by the two codes