CFD ANALYSES OF THE INTERNAL BLOCKAGE IN THE NACIE-UP FUEL PIN BUNDLE SIMULATOR

In the context of GEN-IV heavy liquid metal-cooled reactors safety studies, the flow blockage in a fuel sub-assembly is considered one of the main issues to be addressed and one of the most important accidents for Lead Fast Reactors (LFR). In order to model the temperature and velocity field inside a wrapped fuel assembly under unblocked and blocked conditions, a detailed experimental campaign as well as 3D thermal hydraulic analyses of the fuel assembly are required. The present paper is focused on the CFD modelling and preliminary computational analysis of the new experimental facility ‘Blocked’ Fuel Pin bundle Simulator (BFPS) that will be inserted in the heavy liquid metal NACIE-UP (NAtural CIrculation Experiment-UPgrade) facility located at the ENEA Brasimone Research Center (Italy). The BFPS test section aims to carry out suitable experiments to fully investigate different flow blockage regimes in a 19-pin fuel bundle providing experimental data in support of the development of the ALFRED (Advanced Lead-cooled Fast Reactor European Demonstrator) LFR DEMO. The BFPS test section, cooled by lead bismuth eutectic, was conceived with a thermal power of about 250 kW and a wall heat flux up to 0.7 MW/m2, which are relevant values for a LFR. It consists of 19 grid-spaced electrical pins placed on a hexagonal lattice with a pitch to diameter ratio of 1.4 and a diameter of 10 mm. The geometrical domain of the fuel pin bundle simulator was designed to reproduce the geometrical features of ALFRED, e.g. the external wrapper in the active region and the spacer grids. Different modelling approaches (e.g. meshing, turbulence modelling, codes and users) in RANS, URANS and LES will be compared to each other. The pre-test analyses presented here will facilitate the post-test analysis of the experimental data expected in 2017-2018. These calculations were carried out by applying unambiguous boundary conditions. In addition conjugate heat transfer is also considered. The comparison among different codes and turbulence models allows to make an overall assessment of different approaches to CFD modelling and simulation. ANSYS CFX, ANSYS FLUENT, STAR-CCM+ and OpenFoam simulations are compared to each other.