Development and application of a neutronics/thermal-hydraulics coupling optimization code for the CFETR helium cooled solid breeder blanket with mixed pebble beds

As one of the most important components of fusion reactor, breeding blanket mainly accounts for tritium self-sufficiency, shielding and fusion energy collection. The performance of the blanket is mainly determined by the internal structural arrangement and material composition. However, if we directly adopt a three-dimensional calculation model for the blanket design and optimization, not only will it consume extensive human and computer resources, but also make the computational process extremely complicated and lengthy. Considering that the radial arrangement of the functional zones, which has the greatest influence on the performance, is the basis of the detailed and accurate 3D design of the blanket, NTCOC, a Neutronics/Thermal-hydraulics Coupling Optimization Code, which adopts simplified 1D neutronics and 2D thermal-hydraulic calculation models, is developed for accelerating the radial build design and optimization of the blanket in this work. This code realizes the functions of both the automatic iterative updating the temperature-dependent cross-section libraries and the data transmission between the neutronics and thermal-hydraulic calculation results through the inner and external coupling between the MCNP4C and CFD software, respectively. Therefore, this can make the comprehensive optimization analyses progress much faster and more accurate. In addition, a variable step length method is adopted to further improve the coupling optimization speed of this code, and several leading design objectives are set as the optimization criteria instead of taking all the possible practical engineering constrains into account. Finally, this code has been applied to optimize the radially arranged zones of a conceptual design scheme of Chinese Fusion Engineering Test Reactor (CFETR) helium cooled solid breeder blanket, which adopts mixed pebble beds as both the tritium breeder and neutron multiplier, under both the normal and critical conditions.