Experimental simulation of hydrocarbons transfer and deposition in ITER

The deposited films of hydrocarbons radicals forming during plasma interaction with carbon composites, which are supposed to be used in ITER (International Thermonuclear Experimental Reactor), can contain considerable quantity of tied-up tritium. The processes of transport, condensation and recombination of CH3-radicals carrying by carrier gas (CH4/C2Hn/H2, n = 2, 4, 6) in quartz tube with cylindrical inserts from Cu, Ni, Fe, W and stainless steels (SS), both initial and covered with thin films of Pd and Rh, are studied. It is shown, that within the 380-800 K temperature range CH3-radicals don not deposit but destroy with some probability on the surface of inserts from Si, Fe, Cu, Ni, W, SS and SS with thin films of Pd and Rh. This temperature interval is called temperature transport window. The most effective catalyst of radicals recombination and hydrogenation in temperature transport window is SS, thin film of Rh increases the effectiveness of hydrogenation reactions of CH3-radicals and other unsaturated hydrocarbons (T = 380-420 K). On the basis of SS a model of recombination filter of CH3-radicals with methane formation is suggested. Such filter will decrease flow capacity of ITER pumping-out system not more than 10%