Clay and carbon materials-based engineered barriers for technetium immobilization

Abstract

Immobilization of long-lived 99Tc is one of the most complicated tasks faced during disposal of radioactive waste. Bentonite clays, which are common components used for construction of engineered barriers are not capable of preventing migration of highly soluble oxidized technetium forms. Modification of bentonite clay materials with natural and industrial coals of various genesis, added in amount of 5 mass %, was carried out as part of this research. The anthracite from Omsukchan coal cluster, coke of Kuznetsk basin and activated carbons of AG-3 and CAU marks have demonstrated high ability to immobilize technetium under oxidizing conditions with values of partition coefficient exceeding 103 ml/g. The resulting composite materials are characterized by low water permeability (Kp < 1–5·10−11 m/s at a dry density of 1.1–1.2 g/cm3), which is mandatory for engineered barriers. Dispersed materials are easy-flowing (ff > 4), which allows the construction of clay barriers by dry, cavity-free backfilling. Quantitative immobilization of technetium occurs during the first day of interaction, with strongly-bonded forms accounting for over 90% of all technetium in the barrier material.