SORPTION OF ACTIVATION PRODUCTS ON LONDON CLAY AND DUNGENESS AQUIFER GRAVEL

The sorption of a series of activation-product radionuclides onto London clay and Dungeness aquifer gravel from the nuclear reactor sites at Bradwell and Dungeness, has been examined. Batch sorption and through-diffusion experiments with clay determined chlorine as the chloride ion to be effectively non-sorbing; calcium to be weakly sorbing, whereas cobalt, nickel, niobium and samarium were moderately to strongly sorbing and silver was strongly sorbing. Distribution ratios (R(D) values) for Nb, Sm and Ag were found to have a strong dependence on the liquid-solid separation technique employed. The presence of high concentrations of calcium hydroxide led to lower values of R(D) for radioactive Ca but higher R(D) values for Sm and Ag. The sorption of Ni showed no apparent dependence on groundwater composition at low levels of dissolved organic carbon (DOC). The values of R(D) for Co decreased as the DOC content was increased by addition of humic materials. Batch sorption studies with aquifer gravel demonstrated that Ca is weakly sorbing whereas Nb, Ag and Eu are moderately to strongly sorbing. R(D) values for Ca and for Ag under neutral pH conditions show little sensitivity to the liquid/solid separation technique used. However, RD values for Nb and Eu under neutral pH conditions and for Ag in alkaline solution (pH = 11 - 12) show a marked effect. The aquifer gravel was found to be highly inhomogeneous unlike the clay and sorption was greatest on samples with a high proportion of sand, reflecting the clay mineral content.