Thermal-hydraulic optimisation of the DEMO divertor cassette body cooling circuit equipped with a liner

•Estimation of major criticalities in the CB thermal-hydraulic performances.•Adoption of a theoretical approach based on a lumped parameter 1D model.•Assessment of several CB configurations thermal-hydraulic performances.•Identification of the most promising CB layout configuration to be further improved. Within 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 thermal-hydraulic performances of the DEMO divertor cassette cooling system. The research activity has been focused onto the most recent design of the Cassette Body (CB) cooling circuit equipped with a Liner, whose main function is to protect the underlying vacuum pump hole from the radiation arising from the plasma. 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 code ANSYS-CFX. The CB thermal-hydraulic performances have been assessed in terms of coolant and structure temperature, coolant overall pressure drop, flow velocity distribution and mass flow rate fed to the Liner cooling circuit, mainly in order to check coolant aptitude to provide a uniform and effective cooling to both CB and Liner structures. The outcomes of the study have shown some major criticalities, mainly in terms of water coolant vaporization as well as non-symmetric coolant distribution between the two Liner inlets. As a consequence, the following potential solutions have been successfully explored in order to allow the CB to safely operate while complying with its design constraints: •revising the CB design layout in order to increase the coolant mass flow rate fed to Liner;•increasing coolant inlet pressure to rise water saturation temperature and, hence, its margin against vaporization;•increasing coolant mass flow rate to reduce its overall thermal rise. The main results and the achieved optimized model are herewith described and critically discussed.