Analyses of vacuum vessel pressure suppression system during divertor LOCA for Helium cooled pebble bed DEMO

An important aspect under investigation for several years in the EU-DEMO reactor is the mitigation of hydrogen concentration - mainly tritium and deuterium - in the Vacuum Vessel (VV) and the surrounding volumes. This accumulation poses risks, including potential explosion hazards, which could damage confinement barriers. One of the possible solutions, applicable to both water and helium-cooled blanket concepts, involves the use of Passive Autocatalytic Recombines (PAR). These devices, representing a cross-cutting technology between fission and fusion facilities, are being considered for integration into the Vacuum Vessel Pressure Suppression System (VVPSS) and related systems. This paper focuses on the hydrogen transport analysis, specifically the inVV tritium and deuterium inventory mobilization towards the VVPSS designed for - Helium-Cooled Pebble Bed (HCPB) concept for which a model was developed by means of MELCOR 1.8.6 for fusion applications. Previous work on the HCPB Loss of Coolant Accident (LOCA) analyses suggests that inert helium resulting from Helium coolant blowdown can significantly mitigate the risk of hydrogen deflagration. The paper explores a new scenario, the Divertor in-vessel LOCA, which may lead to increased hydrogen mass due to the water-metal reaction. The paper discusses the integration of PAR technology within the operational range of fusion devices, specifically focusing on its potential to recombine hydrogen within the Expansion Volumes.