Thermal–hydraulic analysis and optimization of breeder unit for EU helium cooled pebble bed blanket

As a European reference concept of blanket for a DEMO fusion reactor, the helium cooled pebble bed (HCPB) blanket is introduced a novel design of a cellular structure with breeder units (BUs) to fulfil functional blanket requirements. The BU is a stack of shallow ceramic breeders and beryllium pebble beds separated by cooling plates. The helium coolant in the dense array of channels inside the cooling plates is the key to achieve a good thermal layout of the BU, it has to secure bed temperatures high enough for a good tritium production while staying within material temperature limits. Given the complexity of the system, with non-symmetric helium headers and collectors, a multitude of parallel helium channels and spatially varying heat sources, a refined numerical model was applied to understand in detail the BUʹs thermal–hydraulic behaviours. The results will be used to identify testing conditions for an HCPB BU mock-up.