Coupled CFD-STH modelling of the ATHENA lead-cooled pool-type facility

The Advanced Thermal-Hydraulic Experiment for Nuclear Applications (ATHENA) is a multipurpose pool-type facility located in Romania, designed for testing large to full-scale components of the Advanced Lead Fast Reactor European Demonstrator (ALFRED). This facility is representative in height of the ALFRED reactor and incorporates a barrel structure to drive the lead flow path within the pool. The internal structure's purpose is to prevent thermal stratification within the main vessel, which is a safety-relevant component in the reactor. Computational tools are required to analyse the thermal-hydraulics of pool facilities and reactors. Computational Fluid Dynamics (CFD) codes have the capabilities to simulate local phenomena (e. g., thermal stratification, fluid mixing and local distributions) by directly solving the three-dimensional Navier-Stokes equations. On the other hand, System Thermal Hydraulic (STH) codes solve a set of zero- and one-dimensional equations, even though at a considerably lower computational cost. Hence, a multiscale model of ATHENA has been developed in order to improve the capabilities to simulate the phenomena occurring within the facility at the different spatial scales, exploiting the strengths of both code families. In this paper, an in-house developed coupled tool that combines ANSYS CFX and RELAP5 Mod 3.3 has been applied to analyse the behaviour during a transient event involving the trip of the Main Pump with the consequent reduction of lead flow. In the work, the first step toward the identification of the strengths and weaknesses of the multiscale approach is made, and possible further model developments to validate the tool for safety related transients are proposed.