Design and Research on Anti-assembly Drop of Integrated Fast Reactor Cantilever Transfer Mechanism

Nuclear energy is a high-tech strategic industry and a crucial support for fulfilling emission reduction commitments. The integrated fast reactor represents the world’s mainstream development direction and offers the highest nuclear fuel cycle efficiency. The reactor is the core component of the integrated fast reactor and the largest facility within the integrated closed fuel nuclear energy cycle system. In the integrated fast reactor, the reactor equipment adopts a compact and integrated design, further enhancing its economic efficiency. Unlike previous fast reactor refuelling systems, the straight-pull refuelling system was adopted in the Chinese integrated fast reactor for the first time, which combined the cantilever transfer mechanism, straight-pull elevator, and translation transporter. This design makes the reactor more compact and improves its economic efficiency. The cantilever transfer mechanism is a specialized device for in-pile transfer of fuel assemblies. It was fixed on the small rotary plug and can cover an area exceeding the diameter of the rotary plug. This design offers a significant advantage when the top arrangement space is limited and the size of the rotary plug is constrained. By using the cantilever transfer mechanism, the number of rotary plugs can be reduced from 3 to 2. Fuel assembly drop is one of the most harmful and serious accidents. Analysis of the gripper components reveals two scenarios that may cause the fuel assembly to fall: severe plastic deformation or fracture of the gripping glove (including strength failure and fatigue failure) and operational flow errors. Reliability can be improved by increasing the mechanical strength of the gripping gloves. Based on strength and fatigue calculations, the probability of gripping glove failure is very low. Process errors can be avoided by fully controlling the refuelling system and implementing necessary interlocks. Human intervention is minimized during fully automatic operation. While errors caused by human factors cannot be entirely eliminated, the drop height of the fuel assembly can be minimized by rationally designing the movement stroke of the guide tube, thereby reducing potential harm. According to drop test results of the CFR600 fuel assembly, free fall from this height does not cause damage to the fuel assembly. Therefore, the probability of fuel assembly drops in the transfer mechanism is extremely low, and even if a drop occurs, it will not affect the safety of the reactor.