The radiolysis of simple gas mixtures—I: Rates of production and destruction of methane in mixtures with carbon dioxide as a major constituent

Abstract

Carbon dioxide based gas mixtures, similar to those used as coolants in the Advanced Gas-Cooled Nuclear Reactors have been radiolysed at the comparatively low dose rate of 3Gy s -1 using y-radiation from a 60Co source. The variation in the methane concentration (initially in the range 60–70 volume parts per million) with dose, temperature, pressure and gas composition was determined. The gas mixtures were radiolysed in sealed stainless steel capsules and it was found that for a wide range of conditions a steady-state methane concentration was obtained irrespective of the initial methane content of the gas mixture. Packing the irradiation vessel with mild steel, stainless steel or graphite demonstrated that heterogeneous processes played a significant role in the reaction scheme. A mechanism involving the deposition of reactive carbon on surface is outlined.