Design and analysis of a remote, robot-mounted cutting tool for SS316L pipes in the EU DEMO environment

Abstract

This bachelor's thesis presents the conceptual design and engineering analysis of a remote, robot-mounted cutting tool for austenitic stainless steel 316L (SS316L) cooling pipes in the EU DEMO fusion reactor environment. A key maintenance challenge within this tokamak is the remote cutting of pipes located in the ultra-high vacuum (UHV) vessel, where extreme gamma radiation (up to 300 Gy/h), elevated temperatures (up to 60 °C), and strong magnetic fields (up to 3 mT) prohibit conventional cutting technologies. Through a systematic comparative evaluation of existing pipe cutting technologies including laser cutting, orbital turning, sawing, and swage cutting a lathe based orbital cutting system was selected as the optimal solution. This hybrid mechanical approach combines the swarf-free cutting principle of the swage cutter with the robust sleeve-cutter construction, offering weld-ready surface quality (target Ra < 6.3 µm), negligible heat-affected zones, and minimal particulate generation. The proposed end-effector features a dual-drive mechanical architecture with a high-torque orbital rotation system employing a harmonic drive and external gear reduction, and a precision radial feed mechanism utilizing a worm-driven leadscrew. The tool integrates a three-point hydraulic clamping system for pipe fixation across different pipe diameters and a mechanical vacuum shroud for swarf containment. Finite element analysis (ANSYS) was conducted to validate the structural integrity of critical components, comparing SS316L and 17-4PH H900 materials for the orbital gear mechanism and assessing the hydraulic actuator under operational pressures.