Development of cutting and welding methods for thick-walled stainless steel support and containment structures for ITER

In ITER the containment and support structures are made from 316L(N)-IG (ITER Grade) stainless steel plate, 40 to 70 mm thick. The structures are divided into twenty sectors which have to be welded together in situ. The three areas of work described in this paper are, CO2 laser welding, plasma cutting and CO2 laser cutting. CO2 laser welding offers significant advantages due to its high speed and low distortion and the most powerful commercial laser in Europe has been used to investigate single pass welding of thick plates, with strong welds up to 35 mm thick being achieved in one pass. For cutting, the space available on the back-side to collect debris and protect fragile components from damage is limited to 30 mm. A static, water-cooled backside protection plate proved unable to contain the debris from plasma cutting so a reciprocating backside protection system with dry ceramic heat shield demonstrated a solution. A 10 kW CO2 laser system for nitrogen-assisted laser cutting, provided successful results at 40 mm thickness. This technique shows considerable promise as significant reductions in through power and rate of debris production are expected compared with plasma cutting and thicker cuts appear feasible. The results presented herein represent significant technical advances and will be strong candidates for the mix of methods which will have to be used for the assembly and maintenance of the ITER machine. (authors)