Sub-channel analysis of the MYRRHA reactor with OpenFOAM: Numerical assessment of turbulence models

The heavy liquid metal Lead-Bismuth Eutectic (LBE) is the primary coolant of the MYRRHA reactor, chosen because of its high heat removal capability, low melting point, non-violent reactivity to water and low neutron absorption. One of the phenomena to be considered for the operation of the reactor with LBE-coolant is the erosion/corrosion of the fuel pin cladding. For this reason, it is key to provide accurate estimations of the cladding outer temperature and LBE velocity during operation. In this work, I investigate the thermal-hydraulic behaviour of LBE in the MYRRHA IPS sub-channel (i.e., In-Pile test Section, core design version 1.8), with the perspective of constructing boundary conditions for fuel pin thermo-mechanical analyses. One of the main challenges in the numerical simulation of liquid metals flows with low Prandtl number (∼ 0.025 for LBE) is to establish a reliable turbulent heat transfer modelling, not being possible to rely on the Reynolds analogy based on the direct proportionality between momentum and thermal boundary layers. A comparative study of different turbulence models is presented for studying the low-Prandtl turbulent flow of LBE in the MYRRHA hexagonal rod bundle characterized by a pitch-to-diameter ratio of 1.28. To this end, the Reynolds-Average Simulation (RAS) models available in the open-source fluid dynamics software OpenFOAM have been applied and compared with each other. The comparison focuses on key thermal-hydraulic parameters, such as the sub-channel temperature field, velocity field, pressure drops, and Nusselt number during reactor normal operation.