The Cesium Leaching Resistance of Cement Matrices for Secondary Processing and Solidification of Cemented Radioactive Waste Materials

Abstract

This study is part of a broader investigation on the processing and re-solidification of cemented radioactive wastes (CRW) for the production of stabilized waste materials suitable for disposal. One of the objectives of the study is to develop and assess various cementing matrices for the solidified material. The leaching resistance of those potential matrices has to be assessed. A series of tests on the leaching of cesium was performed and the results are presented in this paper.

Surrogate Cemented Waste (SCW), representative of the CRW, was reduced to a particle size suitable for mixing with cementing material (cement and other cementitious materials) and water to produce mortars. The mixture optimization program included several parameters such as the composition of the SCW, the cement-to-SCW (C/SCW) and the water-to-cementitious materials (W/C) ratios of the mortars, and the use of different types and proportions of supplementary cementing materials (SCMs). In this part of the study, the cesium leaching resistance was determined on a number of mortars of different compositions at various ages using the ANSI leach test. As an indicator of the durability, the calcium leaching resistance was also determined on selected specimens.

Reducing the water-to-cementitious materials ratio (W/CM) of the mixtures resulted in the improvement of the leaching resistance of the mortars, however, the effect of the use of SCMs was not clear. In general, the use of zeolites resulted in a relatively good performance in the leaching.

The amount of calcium leached from the mortar exposed to water, an indication of the long-term durability, was determined during the extended cesium leaching test. The calcium leaching appeared significant, however, the extended-test leachability index values for cesium indicate that the integrity of the cement matrix was not much affected by the longer exposure to water, at least not enough to affect significantly the cesium leaching resistance of the mortars.