Development of a DEMO helium cooled pebble bed (HCPB) breeder unit featured in flat plates with meandering channels

Abstract

During the design review in 2003, the modular HCPB blanket concept with a cellular breeding region was proposed and accepted as an EU reference. The concept offers the flexibility of designing 200 x 200 x 500 mm 3 breeder units virtually independently of the blanket box. Recently it has been found that ceramic breeder containers featured in the current breeder unit design could see high levels of secondary stress and need to be amended. Scoping calculations have shown, however, that an alternative design based on flat plates with meandering cooling channels meets neutronics requirements, despite a decrease in the content of ceramic breeder and beryllium. This design would also help increase the common features and manufacturing steps of HCPB and HCLL concepts. In this report, a new HCPB breeder unit based on the design featured in flat plates is developed. Supporting analyses in neutron physics, thermal-hydraulics and structure mechanics are carried out to check (i) the capability of reaching tritium breeding sufficiency, (ii) the adherence to maximum temperatures in structural and functional materials and (iii) the abidance by the stress criterion imposed by the structural material. Manufacturing sequences of the breeder unit are defined. Finally possible improvements of the new designed breeder unit are proposed.