Where are we at?
From a strict industrial point of view, repairing the dimensional non-conformities that affect the ITER vacuum vessel sectors is not an insurmountable task. What needs to be done can be formulated quite simply: filling the "valleys" or shaving the "hills" along the bevel joint region in order to restore geometry to nominal and recover the ability to weld the sectors together. Sectors, however, are not ordinary chunks of steel; their geometry is complex and their weight (~440 tonnes) is comparable to that of a jumbo airliner. Once assembled and welded to form the fusion reaction chamber they will act as the installation's first nuclear safety barrier and, as such, are subject to very stringent regulations. Whereas two of the three sectors present on site are already positioned in the sub-assembly tools where they will be repaired (#6 and #7), the handling and positioning of the third (#8) requires adapting and manufacturing heavy bespoke tooling.
Operations will begin in parallel on sectors #6 and #7 by the end of February/beginning of March when all tests and qualification procedures are complete. The first operation will consist of grinding the bevel joint regions, followed by manual metal build-up and final machining to restore the bevels' nominal dimensions. As machining is simpler and does not alter mechanical properties, build-up will be minimized as much as possible. Optimizations are still under assessment, but it is estimated that sectors #6 and #7 will each require approximately 24 kgs of metal to fill the "valleys" in the bevels. Grinding, metal build-up and machining will be performed under local protections in order to avoid altering the Assembly Hall's controlled environment. Sectors #6 and #7 will remain in the giant sector sub-assembly tools for the duration of the repair operations.
If the second upending tool is not available in time, the only remaining solution consists in transferring sector #8 to the assembly pit to "park" it there while the existing upending tool is modified to accommodate the sector in its flipped position. This of course would be a much heavier and longer operation but there might be no other choice.
Thermal shield repair is also moving forward. We will report on progress in an upcoming issue of the ITER Newsline.
Thermal shield repair is also moving forward. We will report on progress in an upcoming issue of the ITER Newsline.