Yuanzineng kexue jishu (Jan 2022)
Research on Neutronics/Thermal-hydraulics Coupling Effect of CFETR Blanket
Abstract
Chinese Fusion Engineering Test Reactor (CFETR) has been proposed to bridge the technology gap between the International Thermonuclear Experimental Reactor (ITER) and the Fusion Demonstration Reactor (DEMO). As the most crucial nuclear component, fusion blanket undertakes the functionalities of tritium breeding, energy extraction and radiation shielding. The design of fusion blanket directly determines whether the fusion reactor can operate in a safety and steady way. In the design of fusion blanket, the neutronics and thermal-hydraulics are the most associated aspects. Actually, the neutronics and thermal-hydraulics are closely coupled to each other in the fission reactor. The effect caused by the interaction between neutronics and thermal-hydraulics is called the neutronics/thermal-hydraulics coupling effect. In the fission reactor, the neutronics/thermal-hydraulics coupling effect will lead to significant impact on both of neutronics and thermal-hydraulics, e.g., change the effective multiplication factor, and influence power distribution and temperature distribution. Therefore, the neutronics/thermal-hydraulics coupling effect must be taken into account in the design work of fission reactor. However, the influences of the neutronics/thermal-hydraulics coupling effect are still not clear in the fusion reactor. The key point to perform the neutronics/thermal-hydraulics coupling calculation of fusion blanket is to choose rational solvers and coupling method. Considering the complicated structure of the fusion blanket, Monte-Carlo code MCNP and computational fluid dynamics code FLUENT, which have good geometric adaptability, are selected as the neutronics solver and the thermal-hydraulics solver, respectively. Nevertheless, the direct three-dimensional coupling calculation is still difficult because of the complicated geometric mapping relationship and huge amount of calculation. Thus, a hybrid 3D-1D-2D coupling method is used to deal with the spatial mapping between neutronics model and thermal-hydraulics model. Moreover, the pseudo material method is adopted to efficiently handle the variation of neutron cross sections under different temperatures. In this paper, the main conceptual blanket designs of CFETR, including the helium cooled solid blanket design under 200 MW, and the water cooled solid blanket designs under 200 MW and 1.5 GW, were selected as the research objects to study the neutronics/thermal-hydraulics coupling effect on the CFETR. Above all, the neutronics sensitivity analysis of material temperature of fusion blanket was conducted to demonstrate how temperature influenced the tritium breeding capability and nuclear heat deposition. The results of sensitivity analysis indicate that the thermal scattering effect of beryllium and the density of water are the decisive factors of temperature effect. Subsequently, the neutronics/thermal-hydraulics coupling calculation was carried out. The coupling results show that, in the helium cooled solid blanket, the neutronics/thermal-hydraulics coupling effect is small and can be ignored, and in the water cooled solid blanket, the neutronics/thermal-hydraulics coupling effect will slightly influence the tritium breeding capability and temperature distribution.
