Development of an In-Bore welding tool prototype for DEMO's in-vessel pipes

The development of a remote maintenance strategy for the replacement of the in-vessel components of the DEMO reactor is one of the key issues on the path to the realization of fusion energy. A critical aspect is the maintenance of the service pipes that supply coolant and remove the tritium that is bred in the Breeding Blankets (BB). Pipe service technologies are available from industrial applications and specific ITER developments, but these are not fully compliant with the requirements and pipe sizes defined for DEMO. In order to carry out the maintenance of the in-situ pipelines foreseen in DEMO, it is sometimes necessary, due to space constraints, to use equipment that operates from inside the pipelines for both cutting and welding, known as in-bore tools. This article is focused on the development of the in-bore welding tool for the large DN200 cooling pipes of the water-cooled BB. A stepwise approach was adopted: 1) Identification of the maintenance strategy and tool requirements. 2) Realization of a prototype with the purpose of demonstrating principal functions. This prototype has been a key step to validate the solution achieved and/or to address issues that arose during the project, highlighting any potential problems. 3) Preliminary design of the in-bore welding tool for DN200 pipes, followed by a first prototype in full scale to test key functions, including the clamping system inside the pipe. The prototype has been realized through additive manufacturing. It has enabled the qualification and resolution of the following points: (i) the design of the engagement system; (ii) the design of the welding torch positioning system; and (iii) initially encountered issues related to the control system and the cabling.