Radiation level in the DEMO tokamak complex due to activated flowing water: Impact on the architecture of the building

The radiation protection issues linked to the activated cooling water coming from the in-vessel components of a fusion reactor to the ex-vessel regions are important design and safety constraints in the building layout definition, as demonstrated at ITER. To tackle these issues more rigorously already in the pre-conceptual design of DEMO some relevant activation and neutronic studies have been performed for the re-definition of a preliminary architecture of the tokamak complex. The design conditions of the Water Cooled Lithium Lead (WCLL) Breeding Blanket (BB) concept have been considered as well as those of the Helium Cooled Pebble Bed (HCPB). The radiation environment in those areas of the building hosting the pipes carrying activated water devoted to the cooling of the First Wall/limiter and divertor has been characterized in terms of decay photons and secondary neutron emissions, which are emitted by N16 and N17 radionuclides. In particular, the feasibility of placing radiation sensitive equipment near flowing activated water is evaluated by calculating accumulated dose in silicon and neutron flux. Viability for manual maintenance activities is assessed by calculating biological dose rate for workers due to Activated Corrosion Products (ACP). The values achieved are then compared to applicable limits. Identification of problematic areas stimulated the examination of some design proposals to improve shielding materials and components.