Preliminary design and analyses of the helium cooled ceramic breeder blanket for CFETR phase II

China Fusion Engineering Test Reactor (CFETR) has two operation phases: Phase I with P_f = 200 MW is to demonstrate the steady-state operation; Phase II with P_f = 1 GW is to validate the DEMO technology. Helium Cooled Ceramic Breeder (HCCB) blanket is one blanket candidate for CFETR, and several research institutes have conducted extensive conceptual designs and comprehensive analysis works for Phase I HCCB blanket. However, because the operation phase of CFETR has transformed from Phase I to Phase II and the latest physical design parameters have been just determined, the design and analysis works for HCCB blanket should be initialized. In this work, first, the basic structure design of CFETR Phase II HCCB blanket is performed and a design scheme is proposed according to the design principles and requirements of blanket. Besides, the material selection of each blanket component has been determined. Second, based on the global neutronics model of CFETR Phase II, the neutron wall loadings (NWL) on different blanket modules are calculated. Afterwards, the radial structure layout optimizations of all poloidal blanket modules arranged in a 22.5° toroidal sector are conducted by NTCOC. As for Phase II blanket, which operates under the high fusion power condition, it should be noted that a dynamic feedback is incorporated into the original one-way optimization method for solving the problems of inadequately optimized tritium breeding performance and insufficient tritium releasing ability. Finally, the radial structure layout parameters of all blanket modules in CFETR Phase II neutronics model are set as the obtained final optimal schemes. The calculation results show that the global TBR of CFETR Phase II is 1.182, which can well meet the tritium self-sustaining requirement. This work can provide worthy guidance and reference for further conceptual design, comprehensive analyses and optimizations of the CFETR Phase II HCCB blanket.