In large-scale nuclear facilities involving fission reactions, electricity production is the result of converting nuclear energy into electricity via numerous heat transfers. In fusion machines, which are currently used only for Research purposes, heat transfer is also a major scientific issue. For various reasons, a number of these issues are common to both current and future energy production methods. Indeed, the materials used and the thermal diagnostics used to control and monitor installations are often subject to the same constraints. The aim of this cross-disciplinary axis is to share the skills and experimental resources of the Institute's various laboratories, in order to make progress in characterizing, developing and optimizing the thermal and thermodynamic properties of the materials used (including in the context of waste management), as well as in thermal diagnostics and the analysis of measurements produced in these facilities.