During the early stages of cement hydration, the heat released can significantly increase the temperature, potentially causing fractures that compromise radionuclide retention in radioactive waste packages. Understanding the heat generation and temperature distribution within the structure is fundamental for preventing such issues. While a full-scale experimental setup with embedded thermocouples provides comprehensive data, it is costly and challenging. An alternative approach involves conducting calorimetric tests to measure the heat released from a sample, using the results to simulate the thermal behavior of the waste package through FEM analysis. Modelling the structure is complex, as the matrix often contains non-cementitious components randomly dispersed. A simplified and computationally efficient approach assigns homogeneous properties to the matrix using averaged thermal coefficients, offering an indicative assessment of its thermal behavior. Another possibility is to employ a Representative Volume Element (RVE) approach to determine effective thermal characteristics at the microscopic level, which can then be applied uniformly across the structure for a more detailed macroscopic analysis. This study compares these two simplified approaches applied to real data, that come from study about three cementitious formulations derived from experiments aimed at developing matrices for immobilizing ILW radioactive waste.