LOCA Accident for the DEMO Helium Cooled Blanket

The exploitation of Fusion as energy source requires also the demonstration of a limited impact in terms of risk to the staff, 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 proposed solution. This analysis points out the dominant accident sequences and outlines the possible prevention, protection and mitigation actions and their associated systems. This analysis points out the dominant accident sequences and outlines the possible prevention, protection and mitigation actions and their associated systems. One of the most challenging accidents is a large break Loss of Coolant Accident (LOCA) of the Primary Heat Transfer System (PHTS) outside the Vacuum Vessel (VV), due to the possible consequences in terms of radiological releases to the environment. However, because of 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.  Nevertheless the consequent peak of pressure in the Expansion Volume located within the Tokamak Building could severely impact the confinement function, hence the overall safety of the plant. For this purpose a numerical assessment of a blanket PHTS ex-vessel LOCA 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 considerations.