The ITER divertor cassette body is a large (>20 tonne) stainless steel (316LN) structure that supports the plasma facing components (PFCs), distributes cooling water to the PFCs, and provides radiation shielding for the vacuum vessel and magnets. It also must withstand electromagnetic loads, and includes an intricate matrix of cooling holes connected by side coolant distribution / collection channels to remove nuclear heating. It is designed to be a re-usable component, accommodating several sets of PFCs over the life of ITER.

Divertor production involves the fabrication of 60 cassette bodies over a 2-year period. Production cost considerations have led the US Home Team to select Hot-Isostatically-Pressed (HIPped) castings for this component. HIP eliminates porosity due to shrinkage, greatly enhancing the consistency of mechanical properties in castings. Because the size of the cassette body exceeds that of the largest HIP vessel in the world, the body is made of two, mirror-image halves that are built-up from four large castings (segments) joined using 80 mm deep structural welds. Body cooling is provided by 50-mm diameter cross-holes connected by machined-in side-channels closed by 13-mm-thick, welded-on cover plates. Each half-body involves over 80 m of controlled-root-melt, gas-tungsten-arc welding and full weld inspection to attach the cover plates.

Manufacturing development efforts are underway at Atlas and PCC to establish and demonstrate the necessary procedures for manufacturing the cassette body structures. These include casting design and fabrication, segment welding, and cover plate welding. Current progress, results, and future plans will be discussed. These lead to the fabrication of a full-scale prototype of one half cassette body in FY'98.

* Work supported by US DOE under Contract AC-3013 with Sandia National Laboratories