The combined effect of radiation and carbonation on the immobilization of Sr and Cs ions in cementitious pastes

In the present study the effect of gamma irradiation on the transport of immobilized Sr and Cs ions in cementitious paste samples is described. During the irradiation process, the samples were exposed to atmospheric conditions. Hence, atmospheric carbonation of samples could takes place. Cementitious pastes, differing in their w/c ratio (0.3, 0.45), were exposed to an integral dose of 10⁷ grays (Gy) of γ irradiation during a period of approximately 6 months. The effect of irradiation on the transport properties of the immobilized Sr and Cs ions was studied by leaching experiments. The carbonation depth of the different samples was measured and found to markedly increase in the case of irradiated samples compared to samples not exposed to irradiation. The enhanced carbonation is associated with the dehydration due to radiolysis of pore water in the paste. It was found that the irradiation resulted in a marked decrease in the leached fraction of Sr ions. This is related to the increased carbonation found for the irradiated samples. On the other hand, a small increase in Cs diffusivity was found for irradiated samples. This increase in leachability might be associated with the formation of microcracks in the irradiated sample.