Rotary Joint Design for High Payload Remote Handling System for a Tokamak Reactor

A general-purpose high payload in-vessel remote handling (RH) system is required for fusion reactors such as China fusion engineering test reactor (CFETR). One of the key technical challenges to implement a high payload RH system is its rotary joints that should be able to handle various in-vessel components having both high and small payload and requiring high precision within a constrained in-vessel space. In addition, it needs to withstand seismic loads, high radiation, to get low contamination during maintenance operation, and to be easily decontaminated. This article presents the design and analysis results of one of the key rotary joints that takes the most significant cantilever loading within a tight space constraint, which is the first rolling joint. Design requirements of the rotary joint are investigated considering its normal operation, seismic event, failure conditions, and recovery operations. The configuration having three-stage reducers and three independent servomotors is selected. The final-stage gearbox that takes the highest loading is designed by using cycloid gears which are driven by second-stage planetary gears whose sun gear is driven by the three independent geared servo motors. Mechanical design is carried out to fit into the available space within the rotary joint body frame. Finite element analysis is performed to assess the deformation and stress of the rotary joint body frame and the cycloid gear internal components. The analysis result shows that the rotary joint is feasible to cope with the required loading conditions.