An experiment set up to investigate the scientific feasibility of using nuclear fusion as a new energy source called on TWI's expertise. The Joint European Torus project (JET) was based at Culham, near Abingdon, Oxfordshire, UK.
The original design of the JET specified a plasma current of 4.8MA but, this has been increased subsequently to 7MA. At these high currents, large mechanical forces can be exerted on the vacuum vessel structure, so the inner wall of the vacuum vessel had to be stiffened by using restraining rings on the outside. A team at TWI was asked to develop welding procedures.
The vessel is a huge toroid, which is a complex shape, built of high nickel stainless steel and Inconel. The stiffening needed required very high quality welding.
TWI's work had two distinct phases: the first was to select a suitable welding technique; the second to qualify a welding procedure. Hot wire TIG, manual cold wire TIG and automatic cold wire TIG were identified as potential processes.
TWI recommended using a special item of equipment for mechanised cold wire feed, manual TIG welding. This was selected in preference to hot wire TIG welding equipment for this application.
The procedures were successfully adopted by an outside contractor and by working round the clock, the modifications were completed to specification and on time.