Applicability study of mechanical multi-pipe connections for DEMO breeding blanket maintenance concept

Abstract

Maintenance of DEMO breeding blanket includes the removal and replacement of plasma facing components, for example the breeding blankets (BB). For access, multiple coolant pipes need to be removed. As an option to reduce downtime and increase maintenance speed, a so-called mechanical multi-pipe connection (MPC) concept is developed to allow removal of multiple pipes at the same time using remotely operated mechanical connections. MPC is one promising candidate to allow fast remotely controlled opening and closing of multiple pipe connections by using flanges and bolts.Some major challenges for the application of MPC are highly constrained space on top of the BBs, accessibility for appropriate tools and homogenous distribution of sealing forces on the gaskets. Numerous studies on arrangement and force application methods were performed to identify suitable concepts – of which a compact flange design using direct bolted connection is favourable. Finite Element Analyses on the shape and geometry optimization of the MPC led to analytically verified solutions. Furthermore, material selection and behaviour under radiation, vacuum, and thermal cycling at high temperature conditions requires advancement of available material treatment solutions in terms of things such as coated surfaces of threads and contact areas on flanges to avoid diffusion bonding.