Although the distance is little more that 100 metres, the transfer of vacuum vessel sector 8 from the Assembly Hall, where it is presently stored, to the Cryostat Workshop, where it will be repaired, requires careful planning and preparation, according to the ITER Organisation.
Work has been underway since January to address defects identified in two key tokamak components during assembly of the International Thermonuclear Experimental Reactor (ITER), under construction in France. Defects were identified in the thermal shields and the vacuum vessel sectors and repairs to both are now underway.
Deviations during the welding process of the vacuum vessel sectors had led to dimensional ''non-conformities'' on the outer shells, affecting the geometry of the field joints where the sectors are to be welded together. “When a finalised component is made of several sections individually machined and welded together, and when it is as tall as a six-storey building like the ITER vacuum vessel, dimensional non-conformities are on par with the component's size,” ITER said in 2022.
In the case of the three vacuum vessel sectors that had already been delivered, the welding of the component's four individual segments caused deviations from nominal dimensions that were more substantial than the specified limit in different locations on the component's outer shell. “These dimensional non-conformities modified the geometry of the field joints where the sectors are to be welded together, thus compromising the access and operation of the bespoke automated welding tools,” ITER said.
After spending just about one year in vertical tooling, vacuum vessel sector 8 has now been returned to a horizontal orientation for removal from the Assembly Hall. In September 2022, the 440-tonne component had been moved into the sector sub-assembly tool that had been left vacant after the installation of sector module 6. However, plans for future installation activities had to be revised when it was reported that major repairs would be required to correct non-conformities in the geometry of the vacuum vessel sectors.
Vacuum vessel sector 8 was removed from the sector sub-assembly tool to an "upending" cradle. And from there it was recently moved to a horizontal platform. The component was carefully wrapped in order to leave the controlled environment of the Assembly Hall for a period of storage in the Cryostat Workshop. Sector 8 is the third of three sectors needing repair, so work will not begin immediately.
Image courtesy of ITER