Analysis on the Improved Control Rod Drop Behavior among Deformation Channels Based on the Rigid-flexible Coupling

The fuel assembly is prone to bend after long-term irradiation in the core, which affects the safe drop of the control rod. Therefore, it is urgent to study the influence mechanism of the control rod drop behavior under the deformation channel. By means of numerical simulation, the law of rod drop behavior after bending deformation of guide tube is analyzed and studied, the rigid-flexible coupling method is used to calculate the rod drop behaviors in the straight, C-shaped and S-shaped guide tubes respectively, analyze the variation of the entire rod drop journey, velocity, acceleration, and collision force along the journey with time, and the effects of straight and two different deformation channels on rod drop behavior are compared. The results show that the rigid flexible coupling method can better simulate the rod drop behavior under the deformation channel. The C-shaped rod drop does not get stuck, and the S-shaped rod drop is stuck at the second bend. This study will help to provide a basis for judging the ultimate bending threshold of the problem of rod drop sticking caused by bending deformation, and provide a reference for engineering design.