Concept Description and Thermalhydraulics of Liquid Surface FW/Blankets for High Power Density Reactors

The attractive features and scientific challenges offered by the liquid wall systems render them strong candidates for investigation in the APEX project[1]. In particular, their high power density capabilities make the fusion reactors economically competitive. In this paper, as part of evolving a practical design based on this evolutionary idea, issues concerning thermalhydraulics of liquid surface first wall/blankets were analyzed. Design approaches as presently envisioned include both liquid films over the solid surface and gravity driven thick liquid jets using lithium and flibe as working fluids. The analyses involved defining liquid systems operating conditions, such as velocity and inlet/outlet temperatures, as well as to calculate free surface temperature so that the evaporation rate from the free surface would not jeopardize plasma operation while maintaining the liquid temperature within the operating windows for high thermal efficiencies. All analyses were performed for a neutron wall load of 10 MW/m² and its corresponding surface heat flux of 2 MW/m². The results indicated that high velocities, hard x-ray spectra and turbulent heat transfer enhancement were necessary conditions for keeping flibe first wall temperature low. On the other hand, at velocities of 20 m/s or higher, it appears possible to maintain lithium film evaporation rate below 10²⁰#/m²s in an ARIES-RS type configuration. Nevertheless, present analyses have not uncovered any basic flaws or major shortcomings in the underlying scientific or technical arguments for the concepts. Yet, engineering innovations of how to maintain and control the flow and the associated analyses are still needed.