A two-dimensional mathematical model has been developed for unsteady thermophysical processes in the industrial duct of an uranium-graphite reactor with conversion fuel elements of the bush type. The numerical algorithm and computer code have been developed on the basis of the proposed model to investigate the temperature fields in an aluminum core, fuel, shell as well as in the cooling water with regard for the design and technological assembly peculiarities. The results of some computational experiments are presented, which characterize the distribution of temperature fields in the column of fuel elements and in the cooling water.