Thermal-Hydraulic Modeling and Code Benchmark of the EU-DEMO TOKAMAK Building Under Accident Conditions

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.