Concerning the radioactive waste management, thermoaeraulic of a new horizontal and passive concept in a closed space is studied. Corrosion is avoided, as heat transfer use confined air in natural convection. An experimental real scale mock-up has been carried out to demonstrate feasibility of this new concept and to provide reliable data for the validation of numerical simulation methods. The design of such facilities implies thermal-aeraulic studies in order to predict air and wall temperatures. For that reason, numerical CFD tools have to be validate in order to model the cooling of spent nuclear fuel in a real interim storage and make sure that safety thresholds never exceed critical values. The experimental loop represents a slice of the real module at the same scale in height and length. It consists of four superposed horizontally annular spaces (length: 5m; air gap: 5cm) where inner cylinder is equipped with electrical wires, aiming to reach a uniform and controlled power density. A natural air circulation appears between the tubes and a special cooled roof. The whole system is inside an air-conditioned building. For each annular space, inner surfaces are painted in black with a known emissivity. Instrumentation includes thermocouples in the air flow channel on the cylinders and on the roof wall, and air velocity measurement (hot wire transducer and Laser Doppler Velocimetry). During experiments, the external temperature and the heating power have been controlled and adjusted to simulate various thermal conditions. Numerous configurations and geometrical parameters have been studied to optimize the cooling conditions. The main experimental results obtained with different values of the parameters like the kind of cooling (water or air), power density (500 to 750W/m2) are presented as well as the heterogeneous power distribution on the four channels. Steady-state local temperatures are presented, with air flow distribution within annular space. Using this database, a special CFD tool has been developed to model complex and coupled phenomena. Then, numerical simulations results have been compared on a reference test case, firstly with water cooling and secondly with natural air cooling. Experimental and numerical data are presented and analysed. From that numerical validation, thermohydraulic model’s extrapolation is now in progress to design a real interim storage with 49 heated sub-channels and propose power loading in order to respect safety rules, especially temperature criteria on the wall.

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