The EU-DEMO must demonstrate the possibility of generating electricity through nuclear fusion reactions. Moreover, it must denote the necessary technologies to control a powerful plasma with adequate availability and to meet the safety requirements for plant licensing. However, the extensive radioactive materials inventory, the complexity of the plant, and the presence of massive energy sources require a rigorous safety approach to fully realize fusion power’s environmental advantages. The Tokamak building barrier design must address two main issues: radioactive mass transport hazards and energy-related or pressure/vacuum hazards. Safety studies are performed in the frame of the EUROfusion Safety And Environment (SAE) work package to support design improvement and evaluate the thermal-hydraulic behavior of confinement building environments during accident conditions in addition to source term mobilization. This paper focuses on developing a thermal-hydraulic model of the EU-DEMO Tokamak building. A preliminary model of the heat ventilation and air conditioning system and vent detritiation system is developed. A loss-of-coolant accident is studied by investigating the Tokamak building pressurization, source term mobilization, and release. Different nodalizations were compared, highlighting their effects on source term estimation. Results suggest that the building design should be improved to maintain the pressure below safety limits; some mitigative systems are preliminarily investigated for this purpose.

One of the most important environmental and safety concerns in nuclear fusion plants is the confinement of radioactive substances into the reactor buildings during both normal operations and accidental conditions. For this reason, hydrogen build-up and subsequent ignition must be avoided, since the pressure and energy generated may threaten the integrity of the confinement structures, causing the dispersion of radioactive and toxic products toward the public environment. Potentially dangerous sources of hydrogen are related to the exothermal oxidation reactions between steam and plasma-facing components or hot dust, which could occur during accidents such as the in-vessel loss of coolant or a wet bypass. The research of technical solutions to avoid the risk of a hydrogen explosion in large fusion power plants is still in progress. In the safety and environment work package of the EUROfusion consortium, activities are ongoing to study solutions to mitigate the hydrogen explosion risk. The main objective is to preclude the occurrence of flammable gas mixtures. One identified solution could deal with the installation of passive autocatalytic recombiners into the atmosphere of the vacuum vessel pressure suppression system tanks. A model to control the PARs recombination capacity as a function of thermal-hydraulic parameters of suppression tanks has been modeled in MELCOR. This paper aims to test the theoretical effectiveness of the PAR intervention during an in-vessel loss of coolant accident without the intervention of the decay heat removal system for the Water-Cooled LithiumLead concept of EU-DEMO.

European DEMOnstration (EU-DEMO) fusion reactor is currently progressing through its conceptual design phase. Reliability assessments play a key role in demonstrating that the system architecture can fulfill its intended functions over a defined lifespan. In the current approach, availability assessments begin with a failure mode and effects analysis (FMEA) to systematically identify potential failure events affecting system performance. Fault tree (FT) models are developed for subsystems exhibiting multiple failure modes, while the overall system configuration is modeled using a reliability block diagram (RBD). This study focuses on the electron cyclotron (EC) heating system, which supports plasma heating during ramp-up and ramp-down phases, stabilizes neoclassical tearing modes, and mitigates radiative instabilities. The analysis targets the current design of the transmission line (TL) and launcher subsystems, excluding gyrotrons from the current scope. Availability simulations have been performed over a 20-year operational period. Parametric analyses are also conducted to quantify the sensitivity of availability to maintenance duration and restoration parameters, providing key insights into design robustness and operational planning.

This work presents a code-to-code comparison of a loss of coolant accident (LOCA) scenario in the European DEMOnstration (EU-DEMO) fusion reactor. The analysis involves GOTHIC and MELCOR, two well-established system codes commonly used for thermal-hydraulic simulations of nuclear reactors under accident conditions. Containment models were developed in both codes to predict the thermal-hydraulic response of the system with a particular focus on the pressure evolution in different compartments of the building. Key physical phenomena influencing pressure behavior, namely flashing, condensation, heat exchange, and choked flow have been examined. For each phenomenon, its relevance to the accident scenario was discussed, followed by a comparative analysis of the modeling approaches adopted by each code. Finally, the resulting differences in the main thermal-hydraulic variables were analyzed and interpreted on the basis of the underlying physical models.