Radiation chemistry of salt-mine brines and hydrates

Certain aspects of the radiation chemistry of NaCl-saturated MgCl2 solutions and MgCl2 hydrates at temperatures in the range of 30 to 1800C were investigated through experiments. A principal objective was to establish the values for the yields of H2 [G(H2)] and accompanying oxidants in the gamma-ray radiolysis of concentrated brines that might occur in waste repositories in salt. We concluded that G(H2) from gamma-irradiated brine solution into a simultaneously irradiated, deaerated atmosphere above the solution is between 0.48 and 0.49 over most of the range 30 to 1430C. The yield is probably somewhat lower at the lower end of this range, averaging 0.44 at 30 to 450C. Changes in the relative amounts of MgCl2 and NaCl in the NaCl-saturated solutions have negligible effects on the yield. The yield of O2 into the same atmosphere averages 0.13, independent of the temperature and brine composition, showing that only about 50% of the radiolytic oxidant that was formed along with the H2 was present as O2. We did not identify the species that compose the remainder of the oxidant. We concluded that the yield of H2 from a gamma-irradiated brine solution into a simultaneously irradiated atmosphere containing 5 to 8% air in He may be greater than the yield in deaerated systems by amounts ranging from 0% for temperatures of 73 to 850C, to about 30 and 40% for temperatures in the ranges 100 to 1430C and 30 to 450C, respectively. We did not establish the mechanism whereby the air affected the yields of H2 and O2. The values found in this work for G(H2) in deaerated systems are in approximate agreement with the value of 0.44 for the gamma-irradiation yield of H2 in pure H2O at room temperature. They are also in agreement with the values predicted by extrapolation from the findings of previous researchers for the value for G(H2) in 2 M NaCl solutions at room temperature