LOCA Accident for the DEMO Helium Cooled Blanket

The exploitation of Fusion as energy source requires also the demonstration of a limited impact in term of risk to the sta, to the public, and to the environment, well below the limits established by international committees and national safety authorities. Therefore, a systematic safety analysis has to follow the design development to demonstrate that the safety objectives are met for each solution proposed. This analysis points out the dominant accident sequences as well as outlines the possible prevention, protection and mitigation actions and relevant systems. One of the most challenging accidents is a large break of the primary cooling system, due to the possible consequences in terms of radiological releases to the environment. However, thanks to the relative small radiological inventory and to the lower decay heat density, the risk associated with a break of the primary cooling loop in a fusion reactor is lower than the risk of the same event in a fission reactor. However, this event should be detected as soon as possible to limit the consequences: e.g. limiting radioactive inventory from the primary confinement, impairment of secondary confinement due to the enthalpy of the helium mass released. Therefore, the Primary Heat Transfer System (PHTS) of the DEMO helium cooled Blanket requires system performances far dierent to that one of the fission reactors cooled by pressurized water. For this purpose a numerical assessment of PHTS has been carried out, considering two possible layout solutions. This analysis has been performed employing MELCOR 1.8.2 and aims to support the design of the Blanket and its PHTS with some safety-related consideration.