Thermofluid-dynamic assessment of the dual cooling scheme EU-DEMO divertor cassette

The EU-DEMO divertor is currently foreseen to employ a dual cooling scheme, which involves two separate cooling circuits for the Cassette Body (CB) and the Vertical Targets (VTs), provided with cooling water at distinct operating conditions. Following the EU-DEMO project Gate Review 1, the cassette design has been revised to employ a high-temperature (295-328 °C) and high-pressure (15.5 MPa) coolant for the CB cooling circuit. These design assumptions present novel challenges in achieving uniform and effective cooling of the structure, to ensure reliable operation over the intended lifetime. Furthermore, alternative materials for the VTs-supporting Target Support Bodies (TSBs), namely CuCrZr, SS 316Ti and Eurofer97, are currently being evaluated to extend the operational lifetime of these components under irradiation. The University of Palermo, in collaboration with EUROfusion and ENEA, analysed the steady-state thermal-hydraulic performance of the EU-DEMO divertor cooling circuits with an integrated conjugate heat transfer analysis campaign of the entire divertor cassette, with the twofold aim to evaluate the CB thermal performance under the revised coolant conditions and to compare the temperature distribution in the TSBs with the different materials considered. The work was carried out following a numerical approach based on the finite volume method and adopting the ANSYS CFX computational fluid-dynamic commercial code. Models, loads and boundary conditions are herewith reported and critically discussed, together with the main outcomes obtained. • The cooling performances of a DEMO dual cooling divertor are investigated. • PWR-like coolant operating conditions are adopted for the cassette cooling circuit. • The VTs connected in series require a higher coolant pressure for their circuit. • Thermal hot spots and CHF issues are found in the cassette, needing design revision. • Simulation of the entire cassette required to predict the VT support temperature.