Radiation Chemical Effects in the Near Field of a Final Disposal Site - I: Radiolytic Products Formed in Concentrated NaCl Solutions

The yields of the different radiolytic products formed by gamma radiolysis from NaCl brines at ambient temperature and dose rates between 0.1 and 1 kGy/h were determined. At a chloride concentration of 5.3 mol/l, H₂, O₂, and ClO₃^- were formed proportional to the dose and independent from the dose rate with G values of 0.6, 0.16, and 0.074, respectively. At a concentration of 2 mol/l, the chlorate yield dropped to a value close to zero, and the gas composition became stoichiometric. At pH 12 and in the presence of heavy metal ions, the yield of oxygen increased at the expense of chlorate. The concentrations of hypochlorite and chlorite were usually in the micromole per litre range. In pressurized solutions of 5.3 mol/l Cl^- where all radiolytic gases were kept dissolved, equilibrium concentrations of radiolytic products were almost reached at a dose of ~1 MGy. The partial pressure of radiolytic gases was ~35 bars, and the chlorate concentration was ~170 mol/l.