Radiation Chemical Effects in the Near Field of a Final Disposal Site–II: Simulation of the Radiolytic Processes in Concentrated NaCl Solutions

Abstract

The radiation chemical reactions in gamma-irradiated 2 to 5.3 mol/l NaCl solutions were mathematically modeled by elementary reactions proceeding in parallel. The calculations showed that if all radiolytic gases could escape from the solution, only three final compounds would be formed proportional to the dose and independent from the dose rate: H₂, O₂, and chlorate. All other products and intermediates reached a steady-state concentration after ~1 kGy. Within certain limits, the yields of final radiolytic products were determined solely by the primary G values of H₂ and H₂O₂. The results of the corresponding irradiation experiments carried out in glass ampoules up to ~1 MGy were in good agreement with the calculations. The simulation of the radiolysis under the condition that all gaseous products remain dissolved in the solution showed a nearly constant formation rate for hydrogen and oxygen. As opposed to this, the experiments conducted in autoclaves resulted in nearly steady-state conditions for the gases at some 100 kGy at a pressure of ~35 bars. For chlorate, the experiments and the calculation gave a constant concentration of a few micromoles per litre in 5.3 mol/l NaCl solution. A better correspondence between experiments and the simulation was achieved for the gases when the reaction model was extended for interaction of corrosion products from the autoclaves.