Analysis and Research on Axial Stiffness Model and Influencing Factors of PWR Fuel Assembly

Currently, the axial analysis model for domestic commercial PWR fuel assembly accident condition mainly relies on foreign technology transfer, and the theoretical mechanism research depth is obviously insufficient. Based on the basic structural characteristics of fuel assembly and the basic mechanical theory, a small basic structure element model is established in this paper and its axial stiffness is analyzed, and then the basic model is reasonably extended to establish the entire fuel assembly axial analysis model. With the obtained analysis model, the sensitivity analysis of axial stiffness is conducted from three aspects of grid number, clamping system and guide thimble thickness. The analysis results show that the number of grid is negatively correlated with the axial stiffness of the assembly, the clamping force of the grid affects the sliding force threshold of the fuel rod, and the axial stiffness increases with the guide thimble thickness. The research results of this paper can provide new ideas for axial model research of new type fuel assembly under accident conditions.