The nuclear radiation energy deposition rate (unit usually employed: W.g(-1)) is a key parameter for the thermal design of experiments on materials and nuclear fuel carried out in experimental channels of irradiation reactors, such as the French reactor in Saclay called OSIRIS or the Polish reactor named MARIA. In particular the quantification of nuclear heating allows the prediction of heat and thermal conditions induced in irradiated devices and/or structural materials. Various sensors are used to quantify this parameter, in particular radiometric calorimeters, also known as in-pile calorimeters. Two main kinds of in-pile calorimeter exist possessing two geometries and two measurement principles: the single-cell calorimeter and the differential calorimeter. The present work focuses on specific examples of these calorimeter types, from the step of their out-of-pile calibration (transient and steady experiments respectively) to the comparison between numerical and experimental results obtained from two irradiation campaigns (French and Polish reactors). The main aim of this paper is to propose a steady numerical approach to estimate the single-cell calorimeter response under irradiation conditions.