Themes: Engineering sciences: fluid mechanics, energetics
Corium Physics Study Laboratory (LEPC) - Cadarache (13)
Start: October 2021
M2 student in mechanics/energy or physics
Age limit: 26 years old unless otherwise stated.
IRSN coordinated from 2015 to 2019 the European IVMR (In-Vessel Melt Retention) project dealing with the In-Vessel Retention strategy in case of a severe accident in a nuclear plant. Following this project, a new evaluation methodology for this strategy was developed based on the simulation of the transient stratification of molten materials in the lower head of the vessel. The main uncertainties in the current evaluations have also been identified, with in particular, the maximal thermal flux reached at the external part of the vessel and located at the upper metallic layer elevation. This heat flux depends on the evaluation of heat transfer in the thin metallic layer and on the kinetics of growth of this layer above the oxide pool. This PhD thesis focuses on the convective heat transfers, which occur in such configuration of thin metal layer heated from below and cooled on the side. The proposed work is based on the following two aspects: 3D Direct Numerical Simulations with the Nek50000 computational code already used for 2D calculations (and some prospective 3D ones) of this problem and use/adaptation of an existing experimental device located in IRPHE lab. The latter allows obtaining some (similarity) results on the gas motion by Particle Image Velocimetry. The main objective is to establish scale laws on average properties (heat flux on the side, average temperature in volume and on the top surface...) but also various statistics on the flow (fluctuations, standard deviations, max/min,...) in order to characterize the heat transfers and define a model usable for reactor scale simulations.