Structural concept of Japanese solid breeder test blanket modules for ITER

A solid breeder blanket was selected as the primary candidate blanket of the fusion power demonstration plant (DEMO plant) in Japan. Test blanket module (TBM) testing in ITER is the most important milestone for the development of the blanket of the DEMO plant. Therefore, the major development effort has been focused on the development of the TBMs in Japan. This paper presents a structural concept of solid breeder TBMs cooled by pressurized water and helium gas. In the sub-module concept which was developed, a slitted box structure was adopted for both TBMs to simulate the DEMO blanket structure and to endure the over-pressurization in case of the coolant ingress to box structure. The breeder and neutron multiplier formed by small pebbles are packed separately in a layered structure. Detailed internal structure was developed with consideration of fabrication procedure, coolant flow route and purge gas flow route. Coolant flow route was considered from the view points of thermal–hydraulic and heat transfer performances. As for He purge gas flow passages, separated passages for tritium breeder layers and neutron multiplier layers were adapted to avoid tritium migration to the neutron multiplier layers.