In the frame of EUROfusion Work Package Breeding Blanket and Horizon2020 thermal-hydraulic analyses have been carried out at ENEA, in close cooperation with Sapienza University of Rome, to investigate and evaluate the thermal and fluid-dynamic behaviour of the Water Cooled Lithium Lead Breeding Blanket (WCLL), which is a candidate option for the European DEMO nuclear fusion reactor.
Several layouts of the Breeding Zone coolant system have been investigated in the last years in order to identify the optimum configuration that guarantee Eurofer temperature below the limit (550°C) and good thermal-hydraulic performances (i.e. water outlet temperature 328 °C). A research activity will be conducted to study a new configuration of WCLL design, characterized by horizontal tubes and PbLi flow path mainly in radial direction. The objective is to investigate the feasibility of this layout and to identify pro and cons from the thermal-hydraulic point of view, also comparing it with the other configurations. The analysis will be carried out using a CFD approach, thus a three-dimensional finite volume model of an elementary cell of the outboard segment will be developed, adopting the commercial ANSYS CFX 19.2 code. The thermal-hydraulic results will be discussed, highlighting open issues and suggesting pertinent modifications to DEMO WCLL coolant system layout aimed at optimizing the design. The research activity aims at laying the groundwork for the finalization of the Water Cooled Lithium Lead blanket design, pointing out relevant thermal-hydraulic aspects.
Nuclear fusion is considered the most promising energy source to meet the ever-increasing demand by the world for electricity consumption in the 21th century due to virtual carbon-free emissions, very limited production of only short-lived radioactive wastes and employing as fuel deuterium (cheap, uniformly distributed and virtually inexhaustible). However, the most promising fusion reaction involves the use of tritium that, as opposed as deuterium, as no significant natural source. Therefore, the design of a blanket able to breed tritium from lithium due to neutron capture reactions to an extent required to guarantee the self-sufficiency of the fusion reactor is a non-negotiable condition to develop this source to a commercial level.
This proposal aims to extend the available tubes layout configuration of the BB, and extend the thermal-hydraulics features that can be expected in a fusion reactor breeding blanket with an innovative tubes disposition. The horizontal DWTs have demonstrated the feasibility of the layout during normal operation with promising results, but no analysis is conducted to evaluate the thermal-hydraulics behavior during operational transients, hence the reason to extend the analysis to these conditions. DEMO, as a pulsed reactor, is subject to fluctuation of thermal fields with high peaks of heat flux on the FW, moreover, there is the requirement to guarantee adequate water conditions at the FW and BZ cooling systems outlet to ensure electricity production even during the phases of: ramp-up, ramp-down and dwell. To perform this activity, the commercial CFD code ANSYS CFX 19.2 is employed to simulate the thermal-hydraulics behavior of the BZ and FW with heat generation into the breeder and structures and transferred to the water-cooling systems. The imposed boundary conditions of the model will correspond to the physical parameters of DEMO, in order to have an accurate simulation that respect all the parameters. These parameters will be check in the results analysis to analyze the CFD code response to the implementation of this model. These analyses will be pioneering analyses from the thermo-hydraulic point of view trying to verify the effective refrigeration of the BB during these transient conditions. Demonstrating the efficient refrigeration of the BB in this situation is a fundamental step for the optimization and finalization of the design of this component, since the goal is the constant production electrical energy from a pulsed reactor.