The role of Na-Al-P glass leachates in speciation and sorption of radionuclides on crystalline rocks

Abstract

Radioactive waste of the 1^st and 2^nd class, including radioactive wastes vitrified in a sodium-alumophosphate glass matrix, are planned to be buried in a deep underground disposal site (PGZRO) at the Yeniseisky site, Krasnoyarsk Region. The host rock massive is considered as a natural barrier to the radionuclides migration in the environment. The radionuclides release into the environment is possible if when they are leached from the matrix. At the same time, the macro components of the matrix are leached and released to the groundwater, and the resulting leachate will significantly differ in properties from the groundwater of the horizon under consideration. Such a change in the composition of the liquid phase can affect the behavior of radionuclides and their interaction with the rocks of the host massif. The paper presents the results of a study of the sorption of radionuclides ⁹⁰Sr, ¹³⁷Cs, ²³³U, ²³⁷Np, ²³⁹Pu, ²⁴¹Am from simulated groundwater and simulated alumophosphate glass leachate on crushed rock samples collected at the Yeniseisky site. It has been shown that the presence of sodium-alumophosphate glass leaching products in the liquid phase reduces the sorption of cesium and, in some cases, to americium on rock samples. At the same time, for strontium and plutonium, the radionuclide distribution coefficients between the rock and the simulated liquid phase increase significantly, while for neptunium and uranium, the corresponding coefficients increase by orders of magnitude. The redistribution of the forms of sorbed radionuclides is observed for all studied radionuclides and depends on the chemical properties of radionuclides and the composition of the liquid phase.