The partial differential equations describing thermal processes in the reactor core are solved with respect to the coolant temperature in two cases: (1) when the fuel element temperature is averaged over the fuel element cross sectional area, (2) when the temperature distribution in this cross section is taken into account. It is assumed that the fuel element is of the rod type, there is no conduction in the longitudinal direction, and the inlet coolant temperature is a constant. The results obtained as solutions of these equations are discussed from the point of view of the application of an analogue computer to the exact simulation of thermal processes in the reactor core.