Validation of a coupled STH and low-fidelity CFD approach using experimental data from NACIE-UP test facility

The IAEA CRP "Benchmark of Transition from Forced to Natural Circulation Experiment with Heavy Liquid Metal Loop" aims to support the development of numerical models suitable for the investigation of thermal-hydraulic analysis of liquid metal cooled reactors. In particular, this work presents a multiscale approach developed to assess cases where the addressed facility experiences a simulated Loss Of Flow Accident. A domain decomposition approach was used together with an explicit scheme, adopting a novel application philosophy for CFD modelling. Indeed, the CFD model was built to simplify as much as possible the wrapped wires design, since a detailed description of such components increases the cell count exponentially. The "simplified" model allows for a shorter running time of the simulation with an equivalent number of CPUs used, making this approach appealing for preliminary estimations of the main thermal-hydraulics phenomena involved. The results show that suitable predictions were usually achieved both for the initial and final steady-state conditions; improvements can be obtained in the transient phase working on the considered boundary conditions.