Steam radiolysis by alpha-particle irradiation

In order to better understand the processes occurring in defective fuel rods in a nuclear reactor, radiolysis of saturated steam by Cm-244 alpha particles was investigated at temperatures between 250 and 300 deg. C. Radiolysis took place in gold-plated steel chambers and the yields of H2 and of O2 were measured mass spectrometrically as functions of dose up to 5x1020 eV/g. The H2 integral yields were constant up to a critical dose and decreased thereafter. G(H2) values on the initial plateau increased with steam temperature (or density). At 250 deg. C (20 mg/ml), G(H2) was 2 molecules/100 eV and increased to 8 molecules/100 eV at 300 deg. C (50 mg/ml). The O2 integral yield was measured at 288 deg. C (36 mg/ml) where it was found to be 1.1 molecules/100 eV, or ∼1/6 of the H2 yield. Addition of H2 to the steam markedly decreased G(O2); beyond 10 mole percent H2, the O2 product was too small to detect. A ten-reaction model that included thermal decomposition of H2O was fitted to the data. The model reproduced the observed hydrogen yields in general but not in detail. Achieving the optimum fit required primary-product yields nearly 50% larger than those reported in the literature