Preliminary development of a conceptual first wall for DEMO

Abstract

The first wall is one of the key components in a tokamak, in particular, for DEMO in the future. The conceptual first wall for a DEMO reactor is designed, fabricated and tested in this paper. It has a sandwich-like structure, which consists of a reduced activation ferritic/martensitic (RAFM) substrate, an interlayer and a plasma-facing material of tungsten produced by chemical vapor deposition (CVD-W) due to its characteristics of high density, high purity and superior thermal shock resistance. The interlayer is required to not only have good adhesion between CVD-W and the CLF-1 substrate, which is a type of RAFM developed by the Southwestern Institute of Physics, but also the capability of tritium transport prevention due to the great importance of controlling the tritium buildup in the first wall, improving the fuel efficiency and conforming to the safety regulations of tritium. Titanium nitride (TiN), a well-known tritium barrier, is selected as the interlayer material in this work. In total, eight sandwich-like first wall samples have been fabricated, and thermal cycle tests and plasma exposure tests are implemented. The results of material analysis show that the quality of the TiN coating layer is critical for good adhesion and tritium prevention. At the defects of the TiN interlayer, fluorine (F) penetrated into the CLF-1 during the CVD-W fabrication and, as a result, the sandwich-like structure was broken near the CLF-1 side. For some samples, the TiN interlayer made by CVD has sufficient adhesion as an interlayer between CVD-W and CLF-1 during tests so far. These encouraging test results support further examination of TiN as an interlayer material for W on an RAFM steel as a first wall material. Preliminary results indicate that the design and fabrication of the conceptual first wall are feasible. Further tests, including the improvement of the interlayer quality and the tritium permeation test, are necessary in the future.

Recent progress of thick tungsten coating prepared by chemical vapor deposition as the plasma-facing material

“…However, more attention should be paid to deal with the higher D permeability. Indeed, a sandwich-like structure, which consists of reduced activation ferritic/martensitic steel (structural material), titanium nitride interlayer (T barrier), and CVD-W (PFM) has been proposed for the first wall of the DEMO reactor [54]. The interlayer was not only designed to mitigate the stresses between the PFM and the structural materials, but also act as a T permeation barrier.…”

Progress in developing ITER and DEMO first wall technologies at SWIP

“…A couple of CVD-W/CuCrZr mock-ups were made with a gradient material interface, which successfully survived an 11 MW m −2 heat load for 1000 cycles [20]. In developing the W coating on CLF-1 RAFM steel recently, a CVD TiN coating was firstly applied on the steel surface as a tritium permeation barrier [21]. SEM observation shows a good bonding structure and an Fe transition interlayer formed between the TiN and the CLF-1 substrate, which may act as a stress-releasing layer.…”