Comparison o RANS and LES heat transfer results for a 19-rod bundle experiment with wire spaces cooled by lead bismuth eutectic

This work presents the main results of a CFD benchmark exercise completed by partner institutions from Europe and USA aiming to achieve a better understanding of the heat transfer characteristics and flow behavior in fuel assemblies cooled by heavy liquid metals. The selected scenario is a 19-rod bundle with wire spacers representative of the MYRRHA reactor under development at SCK CEN (Belgium), with uniform heat flux and cooled by lead-bismuth eutectic (LBE) in steady state conditions of forced convection. Reynolds Averaged Navier Stokes (RANS) simulations using commercially available CFD codes were performed by NRG (Netherlands), UGent (Belgium) and ENEA (Italy). These partial results were presented previously, focusing on a code to code comparison. Experimental data from an LBE test at ENEA became later available, including temperature measured at selected sub-channels. High fidelity Large Eddy Simulation (LES) were recently performed by ANL (USA) using spectral elements. Comparing the two types of numerical results and including the experimental data, is an important step towards a verification and validation of numerical tools used in design and licensing. The comparison of RANS with LES indicates to which extent the current liquid metal modeling methods are sufficiently capable of capturing the most relevant thermal-hydraulic features and helps to highlight remaining issues. Preferably, experimental data are used for validation, although at a lower level of detail. Two cases are studied, representative of nominal conditions (high power and flow) and of conditions after a protected loss of flow accident (PLOFA) (low power and flow).