Hydraulic assessment of an upgraded pipework arrangement for the DEMO divertor plasma facing components cooling circuit

Abstract

In the context of the Work Package DIVertor (WPDIV) of the EUROfusion action, a research campaign has been carried out by University of Palermo in cooperation with ENEA to assess the thermal-hydraulic performances of the DEMO divertor cooling system, concentrating the attention on its 2019 Plasma Facing Components (PFCs) configuration, relevant to DEMO baseline 2017. The research activity has been performed following a theoretical-numerical technique based on the finite volume method and adopting the well-known ANSYS CFX CFD code. The PFCs cooling circuit thermal-hydraulic performances under nominal steady-state conditions, assessed mainly in terms of coolant total pressure drop, coolant axial flow speed and margin against Critical Heat Flux (CHF) distributions among the plasma-facing channels, have been evaluated with a CFD analysis to check their compliance with the corresponding limits. Results have highlighted serious critical issues, such as an intolerable total pressure drop (significantly higher than 1.4 MPa) as well as an insufficient margin against CHF onset (lower than 1.4) within all the PFU channels. Therefore, an optimization study has been performed to investigate the potential improvements of the PFCs cooling circuit thermal-hydraulic performances due to proper changes of its geometric configuration, focussing the attention on the inlet manifold branch. The study has allowed selecting the most effective cooling circuit configuration, that fulfils the maximum pressure drop requirement (Δp<1.4 MPa) while raising the minimum CHF margin within the PFU channels. Moreover, it would allow reducing the ex-vessel total pressure drop, while decreasing the average coolant flow velocity up to values lower than 10 m/s. Models, loads and boundary conditions assumed for the analyses are herewith reported and critically discussed, together with the main results obtained.