In the search of the optimal combination of low-carbon energy sources to address the challenge of climate change, nuclear energy plays a crucial role alongside intermittent renewable energies. In this context, the performance and safety of Pressurized Water Reactors (PWRs), which make up the French nuclear fleet, remain an active and high-value research area.
In these reactors, a subcooled nucleate boiling regime can occur, particularly when the local temperature of the coolant exceeds its saturation temperature. This wall boiling promotes the formation of porous deposits of metallic oxides. Within the porosities of these deposits, gas nuclei can be trapped and lead to the onset of nucleate boiling on these surfaces. The vapor formed through a wick boiling or capillary vaporization mechanism then escapes through the chimneys of the deposit. The chemistry of the coolant affects not only the thermodynamic properties of the fluid (such as saturation temperature and latent heat) but, more importantly, its interfacial properties (surface tension and solid/liquid/gas contact angles). These interfacial properties directly control the capillary forces within the deposits, and thus the onset and dynamics of subcooled boiling. As of today, the influence of coolant chemistry on the initiation and development of subcooled nucleate boiling within porous heated surfaces remains poorly understood.
The objective of this PhD is therefore to systematically study the coupled influence of coolant composition and capillary vaporization on nucleate boiling within porous substrates heated by conduction.
The research will follow an experimental approach to investigate how coolant chemistry affects surface tension and contact angles, in order to characterize fluid wetting on idealized porous substrates. Subcooled convective boiling experiments will also be conducted, with the phenomena characterized by shadowgraphy and fiber-optic thermometry.
The PhD will take place within the Thermal Hydraulics of Core and Circuits Laboratory (LTHC) and the Contamination Control, Coolant Chemistry and Tritium Management Laboratory (LMCT) at CEA IRESNE (Cadarache, France). The work will be supervised by Prof. Benoît Stutz of the University of Savoie Mont Blanc. Throughout this project, the doctoral student will develop expertise in interfacial physico-chemistry and two-phase thermohydraulics through the observation, characterization, and modeling of complex multiphysics phenomena.