Neutronics Design and Analysis of a Novel Liquid-Solid Space Nuclear Reactor Based on Cross-shaped Spiral Fuel

摘要: As the key technology of space exploration, space power has always been a research interest of international researchers. A lot of research work has been carried out around the world for the space nuclear reactor using heat pipe, liquid metal and gas cooling method. With the development of molten salt reactor of IV generation reactor system, molten salt dissolving fissile material and acting as a coolant at the same time has become a new cooling scheme, which provides new ideas for the design of space nuclear reactor. In this study, a novel reactor Liquid-Solid Dual-Fuel Space Nuclear Reactor (LSSNR) was preliminarily proposed combining the molten salt fuel and cross-shaped spiral solid fuel for the design goals of 30-year lifetime and active core weight less than 200 kg. Monte Carlo neutron transport code OpenMC based on ENDF/B-VII.1 library was employed for neutronics design in aspect of fuel type, cladding material, reflector material and spectral shift absorber. Then, the thickness of control drum absorber was optimized to meet the requirement of the sufficient shutdown margin, lower solid fuel enrichment, and 30 EFPY operation lifetime. Finally , UC solid fuel with U-235 enrichment of 80.98 wt.% and B4C thickness of 0.75 cm were adopted in LSSNR, and BeO was adopted as reflector and matrix material of control drum. A spectral shift absorber Gd2O3 was used to avoid the sub-critical LSSNR returning to criticality at a launch accident. The keff with control drum rotating innermost position is 0. 954949, and the keff reaches 1.00592 after 30 EFPY operation. The total mass of the active core is 160.65 kg. In addition, the thermal-hydraulic feasibility of LSSNR using cross-shaped spiral fuel was analyzed based on a 4/61 reactor core model. The structure of cross-shaped spiral fuel achieves enhanced heat transfer by generating turbulence, leads to a uniform temperature distribution of the coolant flow field, and reduces local temperature peaks. Based on LSSNR scheme, some neutronic characteristics were analyzed. Results demonstrate that the LSSNR has strongly negative reactivity coefficients due to the thermal expansion of liquid fuel, and the fission gas-induced pressure meets safety requirements. After 100 years of the end of core life, the total radioactivity of reactor core is reduced by 99% and is 7.1305 Ci.