On the thermal-hydraulic performances of the DEMO divertor cassette body cooling circuit equipped with a liner

In the framework of the Work Package DIV 1 - “Divertor Cassette Design and Integration” of the EUROfusion action, a research campaign has been jointly carried out by University of Palermo and ENEA to investigate the steady-state thermal-hydraulic performances of the DEMO divertor cassette cooling system. The research activity has been focussed onto the most recent design of the Cassette Body (CB) cooling circuit, consistent with the DEMO baseline 2017 and equipped with a liner, whose main function is to protect the underlying vacuum pump CB opening from plasma radiation. The research campaign has been carried out following a theoretical-computational approach based on the finite volume method and adopting the commercial Computational Fluid-Dynamic (CFD) code ANSYS-CFX. The CB thermal-hydraulic performances have been assessed in terms of coolant and structure temperature, coolant overall total pressure drop and flow velocity distribution, mainly in order to check its aptitude to provide a uniform and effective cooling to both CB and liner structures. Moreover, the margin against coolant saturation has been evaluated in order investigate whether any risk of its bulk vaporisation is prevented. The outcomes of the study have shown some criticalities, mainly in terms of structure maximum temperature and coolant vaporization occurrence within the liner. As a consequence, some minor design variations have been suggested within the paper. Models, loads and boundary conditions assumed for the analyses are herewith reported and critically discussed, together with the main results obtained.