On the mechanisms associated with the chemical reactivity of Be in steam

One safety concern surrounding beryllium as a plasma-facing material in a w ater-cooled Tokamak is steam interactions with hot beryllium and the produc tion of significant quantities of hydrogen. We have tested several differen t product forms of Be with different densities and levels of porosity. Oxid ation kinetics has been determined by measurements of hydrogen release with a mass spectrometer, volumetric measurements of the product gas and weight change of the sample. We discuss and compare with the literature the funda mental mechanisms and kinetics controlling the oxidation of Be in steam. Fu lly dense beryllium exhibits parabolic, linear and accelerating modes of ox idation as temperature increases from 450 degreesC to 1200 degreesC. The ox idation mechanisms and temperature trends are similar for other product for ms. Oxidation rates are higher, however, when processing or annealing signi ficantly increases the extent of interconnected porosity and consequently t he effective surface area. The effective surface area as measured by BET su rface analyses is a key parameter when comparing oxidation rates. (C) 2000 Elsevier Science B.V. All rights reserved.