ITER dome fabrication processes

Abstract

Ahstrucl -The 3/4-ton International Thermonuclear ExperimentalRcactor (ITER) divertor dome component is fabricated from three dissimilar metals-stainless steel, copper, and tungsten. It is actively cooled to withstand heat loads of 5 MW/m2 during nominal operation, transient heat loads of I5 MW/m2 for 1-2 seconds, and volumetric heating of 0.5-5 MW/m3.The divertor dome is comprised of two subcomponents: a 3 16L cast stainless steel dome shicld block with internal coolant passages and a CuCrZr plasmafacing component (PFC) with internal coolant passages and a 15-mm-thick layer of diffusion bonded W-brush armor. This paper describes the processes developed for fabricating the stainless steel dome shield block and CuCrZr plasma-facing component (PFC) and the resulting mechanical properties of the copper and stainless steel joined by the hot-isostatic-pressing assisted diffusion bonding techniques. FABRICATION OF DOME SHIELD BLOCKThe complete divertor dome is shown in Fig. I . The dome shield block of the divertor dome was fabricated using a 900-kg, 316LN stainless steel sand casting (Fig. 2).No internal discontinuities were detected in the prototype cassette castings under radiographic examination. The casting was poured with the parting line between the cope and drag along the 1.5" plane. A riser was located on the 3" side. An allowance of 14-mm excess material on all surfaces of the casting eliminated surface connected porosity. Extensive tensile testing performed on the cast material showed that the cast allowable membrane stress is approximately 25% lower than wrought at 200°C, but ductility is approximately 25% higher than the wrought form [I]. The reduced allowable is not a problem for the dome block since the design exceeds all reference loading conditions. The dome proximity to the plasma necessitates increased cooling compared to the cassette body. A 30-mm minimum spacing is required between adjacent channels while attaching the 13-mmthick cover plates onto the cassette body. This spacing was reduced on the dome block to IO-mm using hot-isostatic-pressing (HIP) assisted diffusion bonding [2]. This is depicted in Fig. 3. A 15-mmthick backing plate was diffusion bonded to each side of the dome with the aid of thin cover plates welded over the manifolds. The thin cover plates provide a vacuum tight seal between the dome body and the backing plate.The internal dome block cooling channels were incorporated by boring 30-mm holes through the thickness which connected to coolant manifolds at the 0" and 3" sides as shown in Fig. 4. One-mm-thick 3 16L stainless steel cover plates were gas-tungstenarc (GTA) welded over the side manifolds (Fig. 3) to provide the pressure boundary between the coolant passages and the cover plates in preparation for HIP bonding. The 15-mm-thick backing plates were welded around the periphery to form a pressure boundary to the outside of the dome block and form a HIP-canister assembly.The HIP-canister assembly (Fig. 4) includes evacuation pipe stems on both sides for He-leak checking of th...