WATER RADIOLYSIS UNDER NET CONDITIONS

Radiolytic decomposition of the NET-plasma Facing Component and Blanket water coolant is expected due to the intense radiation fields present inside the vacuum vessel. A sensitivity analysis has been performed by computer simulation to study the formation and the suppression of the radiolytic products under NET conditions. The formation of the stable radiolytic products (oxygen, hydrogen and hydrogen peroxide) formed within the water due to the decomposition induced by mixed neutron and gamma irradiation is given for several cases, which are relevant to the First Wall water coolant. The influence of coolant temperature (20-degrees-C, 70-degrees-C, 130-degrees-C, 200-degrees-C), heterogeneous decomposition of H2O2, added solutes such as hydrogen, and ferrous ions simulating possible corrosion products has been studied. There are still large discrepancies in the literature on the radiation chemical yields (G-values) in the case of the neutron irradiation. Therefore three sets of G-values have been considered, and the sensitivity of the applied G-values for mixed neutron and gamma irradiation has been investigated as well. For all these cases, the hydrogen concentration required to suppress the water radiolysis is given, and some critical issues with respect to the specific contribution of neutrons with high energy typical for the fusion spectrum (10-14 MeV) on the radiolytic water decomposition have been discussed.