Thermalassessment of the operational conditions for the determination of the pre-heating strategy for the DONES Target Assembly

The European Roadmap to the realisation of fusion energy foresees the construction of the DEMO Oriented NEutron Source (DONES). It is a 5 MW accelerator-based neutron source capable of producing, by Li(d,n) stripping reactions, a neutron flux of ∼ 5 ∙ 10 14 neutrons/(cm 2 s) with a broad energy peak around the relevant value of 14 MeV, typical of the d -T fusion reactions in the fusion power plants. Its main scope will be the test and qualification under a fully fusion-relevant neutronic spectrum of the materials that will be exposed to the plasma in the future fusion power plants. The core of the DONES facility is the Target Assembly (TAA), integrated within the Target System (TSY), as it is devoted to creating and stabilizing the Li film for the d,n reactions, which take place within the TAA Back-Plate (BPL). Since the Li flowing through the TSY in nominal conditions enters the BPL at 300 °C, a pre-heating of the whole TSY is necessary to ensure that the BPL lithium channel minimum temperature is above 200 °C before the lithium starts flowing. In this way one can exclude, from one side, possible local Li solidification and, from another side, potential structural issues of the BPL structural material. In this context, a campaign of steady state thermal analysis has been performed to determine a proper pre-heating strategy for the DONES TSY. To this purpose, different combinations of operational conditions have been conceived and the TSY thermal behaviour has been investigated in order to select the best strategy to ensure that, at steady state, the BPL Li channel is warmed up above 200 °C even in case of heaters failure. The impact of the atmosphere surrounding the TSY on the pre-heating effectiveness has been assessed too. Results allowed selecting a suitable pre-heating strategy for the DONES TSY, provided that the Test Cell housing the TSY foresees an Argon atmosphere instead of the Helium envisaged during the beam-on phase, regardless of its temperature. The study has been performed following a numerical approach based on the Finite Element Method (FEM) and adopting the Abaqus FEM code. The models, the assumptions and the obtained results are herewith presented and critically discussed.