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(FTP1/29) Oxidation of Carbon Based First Wall Materials of ITER

R. R. M. Moormann1), H. K. Hinssen1), C. H. Wu2)
 
1) Forschungszentrum Jülich/ISR, D-52425 Jülich, Germany
2) EFDA/Max-Planck Institut für Plasmaphysik, D-85748 Garching, Germany

Abstract.  The safety relevance of oxidation reactions on carbon materials in fusion reactors is discussed. Becau-se tritium codeposited in ITER will probably exceed tolerable limits, countermeasures have to be developed: In this paper ozone is tested as oxidising agent for removal of codeposited layers on thick a-C:D-flakes from TEXTOR. In preceeding experiments the advantageous features of using ozonised air instead of ozonised oxygen, reported in literature for reactions with graphite, is not found for nuclear grade graphite. At 185oC = 458 K ozone (0.8-3.4 vol-% in oxygen) is able to gasify the carbon content of these flakes with initial rates, comparable to initial rates in oxygen (21 kPa) for the same material at > 200K higher temperatures. The layer reduction rate in ozone drops with increasing burn-off rapidly from about 0.9-2.0 $ \mu$m/h to 0.20-0.25 $ \mu$m/h, but in oxygen it drops to zero for all temperatures $ \leq$ 450 oC = 723 K, before carbon is completely gasified. Alltogether, ozone seems to be a promising oxidising agent for removal of codeposited layers, but further studies are necessary with respect to rate dependence on temperature and ozone concentration even on other kinds of codeposited layers. Furtheron, the optimum reaction temperature considering the limited thermal stability of ozone has to be found out and studies on the general reaction mechanism have to be done. Besides these examinations on codeposited layers, a short overview on the status of our oxidation studies on different types of fusion relevant C-based materials is given; open problems in this field are outlined.

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IAEA 2001