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Remote in-bore cutting & welding for nuclear fusion reactors

Remote in-bore cutting & welding for nuclear fusion reactors

TWI has worked with RACE (Remote Applications in Challenging Environments), part of UKAEA (the UK Atomic Energy Authority), to help in the development of the remote, in-bore, laser-based cutting and welding maintenance technologies that will be needed for future nuclear fusion reactors.

Background

Nuclear fusion is one candidate technology aiming to develop a safe, abundant, sustainable energy source, helping to meet society’s energy needs over the coming decades. In step by step developments, the first short term milestone within Europe will be the completion and operation of the ITER reactor (targeted in the 2020s). The next step thereafter will be the construction of DEMO, a viable, electricity-generating nuclear fusion plant (targeted by 2050).

During their operational lifetimes, these reactors will inevitably require maintenance, including the disconnecting (e.g. cutting out) of service pipes to remove neutron-damaged components and their subsequent replacement (e.g. by welding back new pipes).

Attracted by TWI’s recent design, build and test of a snake arm-mounted in-bore orbital laser welding head, RACE is now working with TWI in its own development of miniaturised laser welding and cutting tools, for the future needs of in-bore pipe cut-and-replace operations.

Schematic of one design of a nuclear fusion reactor, highlighting an example of in-bore pipe maintenance requirements (circled)

Example of a RACE-designed miniaturised in-bore laser processing head

Head inserted (robotically) into a 90mm bore pipe, prior to initiation of processing

Work Programme

TWI’s support to RACE includes:

Connection of TWI’s Yb-fibre laser source facilities with RACE’s gas-cooled cutting and welding head designs
Characterisation of the multi-kilowatt beam power transmissions through those heads, including profiling of the resulting beam caustics
Guiding and carrying out cutting and welding trials using those heads, on representative steel and stainless steel grades and thicknesses
Tests on plates, followed by the transfer of selected procedures to orbital in-bore work on DN90 pipe
Remote operations - preliminarily using a robot supplied by TWI, then in later trials using the completely integrated in-bore tools designed and manufactured by RACE

Results

Multi-kilowatt plate and pipe cutting conditions have been developed that result in full through-thickness cutting of 5mm thickness pipes in under 40 seconds. The cut kerf produced, although unsuitable for re-use without further processing, could then allow an affected component to be removed from the reactor assembly and replaced.

With a change in head design and processing parameters, multi-kilowatt laser butt welding of 3mm thickness ferritic-martensitic or stainless steels is also possible. This, again, then provides a possible means of meeting future fabrication in-situ needs.

Going forwards from this work, optimisation of the designs of these miniaturised heads, and the associated parameters for the in-bore cutting and welding that they can carry out, will lead to credible maintenance solutions for the fusion reactors of the future, in the wake of these promising initial results.

Images in this article have been reproduced courtesy of UKAEA.

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No. 633053.

The views and opinions expressed herein do not necessarily reflect those of the European Commission.

TWI is now part of the UK small modular reactor consortium discover more here.

Pipe cutting rig (top), cut coupons (middle) and integrated in-bore cutting tool (bottom)

Example of an orbital through-thickness cut in 5mm wall thickness stainless steel pipe

Example of an orbital weld made between two 3mm wall thickness stainless steel pipe sections and (inset) a typical weld cross-section

Chris Allen Principal Project Leader- Laser Welding

Dr. Chris Allen is a Principal Project Leader in the Laser and Sheet Processes Section at TWI Ltd, having joined TWI in 2002.

He has an MA (Hons) in Natural Sciences from the University of Cambridge and, after working in civil engineering in Hong Kong during a gap year, a Doctorate from the University of Oxford. This specialised in calorimetric and electron microscopy studies of the nucleation of intermetallic phases during solidification of 1xxx series aluminium casting alloys, and was supported by Alcan.

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