Pre-test Analysis of Low Power Operations of STEAM, the EU-DEMO Steam Generator Mock-Up Facility

While nuclear fusion reactors hold promise, their realization faces significant complexities, not only in the construction but also in managing the auxiliary systems required for safely operating plasmas. Pulsed plasma regime, integral to reactor normal operations, determines atypical operative conditions that can cause high thermal stresses on the components and generate instabilities. R&D activities are therefore required to characterize the components behavior in the extremely severe conditions of pressure and temperatures associated with fusion, especially during sudden power transitions. ENEA, as part of the EUROfusion consortium, is planning the construction of STEAM, an experimental facility aimed at qualifying the DEMO Steam Generator during pulse-dwell-pulse transitions within the W-HYDRA platform. Dedicated experimental campaigns will reproduce the low-power phase associated with the only material activation (dwell), the full-power phase (pulse) and the corresponding power transitions. This paper focuses on the low-power phase, presenting the performed RELAP5/Mod3.3 simulations, investigating the thermal-hydraulic performances of the system at 1 %, 5 % and 10 % of the nominal power, hence in conditions considerably different from fission standard practices. The simulation results are essential for defining regulation strategies for the SG test section and ensuring the correct operation of the entire system.