The ability of crystalline rocks to adsorb radionuclides after exposure to aggressive environments

Crystalline rock massif of the Yeniseiskiy site (Krasnoyarsk region) is considered for the disposal of radioactive waste in the Russian Federation. In this study the resistance of different types of rocks located at target depths in the site of geological disposal facility (gneisses, dolerites, and carbonatized fissure filling) to dissolution by groundwater was simulated by short-term stage-by-stage treatment with 18 % HCl solution and aqua regia. The impact of dissolution on isolation properties was also investigated. A high sorption capacity to Cs(I) and Eu(III) which chemical behavior is similar to Am (III) and Pu (III) of gneiss, dolerite, and fissure filling samples was established. During the studies of sorption properties, it was found that the greatest influence on the retention of Cs by gneiss and dolerite have the specific surface area (SSA) value. This effect is most pronounced for gneiss due to the increased available surface area of mica minerals biotite and muscovite. The retention effect of the fissure filling material is mainly determined by the content of mixed-layer illite-smectite clay minerals and chlorite. It was found that the greatest influence on the retention of europium by gneiss and mineral fissure filling is the content of chlorite in the samples. The obtained results reflect the resistance of the host rock of the Yeniseiskiy site to the most aggressive acid environments, which allows assessing the stability of their isolation properties for a long-term perspective.