Radiation chemical effects in the near-field environment of a radwaste repository: γ radiolysis in 6 molal NaCl solutions

The radiation emitted from high-level radioactive wastes in a radwaste repository causes radiolysis products to be formed in brines resulting from water intrusion. The products may alter via redox and complexing reactions the mobilisation processes of radionuclides. The major products of γ radiolysis determined in 6 molal NaCl solution as a function of radiation dose are hydrogen, oxygen, and chlorate. Hypochlorite and chlorite were found to have concentrations in the μMol/kg range. There was no dependence on dose rate. For the experiments under atmospheric pressure, which allowed radiolytic gas to escape from the solution, the G values measured are 0.46 (H2), 0.16 (O2), and 0.074 (ClO3). In pressurized experiments, with radiolytic gas remaining contained in the solution, the radiolytic effect was much smaller. After approx. 100 days, at a dose of about 2 MGy, gas equilibrium concentrations of some mMol/kg were measured. The results can be qualitatively described by a system of parallel running reaction rate equations. As to quantitative analysis, the reaction model needs to be refined. (orig./CB)