On the numerical assessment of the thermal-hydraulic operating map of the DEMO Divertor Plasma Facing Components cooling circuit

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 behaviour of the DEMO divertor cassette cooling system, focussing the attention on the 2018 configuration of the Plasma Facing Components (PFCs) circuit consistent with the DEMO baseline 2017. 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. A steady-state CFD analysis has been carried out for the PFCs cooling circuit under nominal conditions and its thermal-hydraulic performances have been assessed in terms of coolant total pressure drop, flow velocity and Critical Heat Flux (CHF) margin distributions among the Plasma Facing Units (PFUs) channels, to check whether they comply with the corresponding limits. Results obtained have clearly predicted a total pressure drop of ≈1.7 MPa, slightly higher than the prescribed limit of 1.4 MPa, as well as a sufficient margin against CHF onset, higher than 1.4 except for three IVT PFU channels where a minimum value of 1.39 is predicted. Moreover, a parametric study has been performed in order to assess the operating map of the cooling circuit in the phase-space of coolant inlet temperature, pressure and mass flow rate, to be intended as that domain where the circuit thermal-hydraulic performances let it stay within the prescribed requirements. Models, loads and boundary conditions assumed for the analyses are herewith reported and critically discussed, together with the main results obtained