Exploratory thermal and fluid-dynamic assessment of a pin of the Helium cooled pebble bed breeding blanket concept with a modular pin monoblock design for the EU DEMO nuclear fusion reactor

The Helium-Cooled Pebble-Bed (HCPB) Breeding Blanket (BB) concept is one of the two candidates eligible for the driver blanket for the EU-DEMO nuclear fusion reactor. It foresees gaseous helium at high pressure as a coolant and tritium carrier, and solid tritium breeder and neutron multiplier. In order to overcome the potential showstoppers that emerged during its pre-conceptual design phase, alternative HCPB BB variants are under consideration in the frame of the DEMO studies. Among them, the concept envisaging a modular pin monoblock presents the advantages of having all the functional materials contained in a pin structure and of avoiding the need for a first wall, remarkably simplifying manufacturing. Hence, in this work, a campaign of thermofluid-dynamic scoping analyses aimed at assessing the performances of this novel BB concept is presented. To this scope, different geometric layouts have been assessed under a wide range of loading conditions and evaluating the sensitivity to key parameters, through cost-effective 2D CFD models. As an outcome, two promising geometric configurations ensuring both temperatures in line with the design requirements and an acceptable pressure drop have been found to be further assessed from the structural standpoint in a second phase of the activity.