Themes: Engineering sciences: fluid mechanics, energetics
Thesis location: Laboratoire de Statistique et des Méthodes Avancées (LSMA) - Cadarache (13)
Start: October 2021
Master 2 research with specialization: thermics, fluid mechanics, energetics, numerical simulation
Age limit: 26 years old unless otherwise stated.
Fuel-coolant interaction could occur during hypothetical accident scenarios of pressurized water reactors (PWR). Following a reactivity initiated accident scenario that would lead to fuel’s rod failure, some hot fuel fragments could interact with coolant. Resulting intense heat transfer leads to pressure peaks and vaporization. Consequences of those phenomena required to be evaluated that remains a complex issue. Recent lab experiments and tests within the CIP (CABRI International program) bring experimental data about the phenomena. The main objective of this PhD is to contribute to the modelling of the phenomena thanks to the development of numerical tools and to the simulation of experiments. Lab experimental data concern an analytical study of thermal interaction within a coolant. A dedicated experimental device allowed to reproduce the phenomenology of interest and to get rather fine measurements of both pressure and vaporization dynamics. Their analysis also revealed a strong coupling of heat and mass transfer with acoustic within the experimental device. Otherwise, in the frame of the CIP program, tests on fuel rodlets will be performed in a near future; those rodlets will be submitted to high power peaks to induce their failure leading to a fuel-coolant interaction in PWR conditions that will be recorded by dedicated instrumentation. During this study, two different simulation tools will be considered: the CIGALON software allowing to estimate a transient interaction thanks to a simplified approach and the EUROPLEXUS software, a finite volume approach for solving compressible fluid flows with heat and mass transfers. The simplified approach can successfully simulate fuel-coolant interactions in large devices but has some drawbacks by neglecting acoustic phenomena for more realistic evaluations. The finite volume approach allows for a more generic solving of the governing equations but requires some adaptations of models for describing accurately fuel-coolant interaction. The 3 years PhD project has the following roadmap. The first year (at EDF R&D Saclay) will be devoted to the first adaptation of the finite volume approach to deal with the phenomenology by developing ad-hoc thermodynamics and transfers models. During the second year (at IRSN Cadarache), numerical simulations using the two approaches will be confronted to experimental results. Discrepancies will be analyzed. The third year (at IRSN Cadarache) will allow improving the numerical simulation tools.