# A Six-Year Hydration Evaluation of Cs-Bearing Materials at Room Temperature and 55% Relative Humidity Simulating Radioactive Waste with Different Crystallinities

## TL;DR

This study evaluates how different crystalline and amorphous materials containing cesium hydrate over six years under controlled conditions, affecting their durability.

## Contribution

The study provides new insights into hydration behavior of cesium-bearing materials with varying crystallinity over an extended period.

## Key findings

- Hydration levels increased logarithmically with time and were directly related to the amount of amorphous phase.
- The most amorphous sample absorbed 1.95% water, while the most crystalline absorbed only 0.07%.
- Samples with ≤19% amorphous phase showed higher durability due to lower cesium content in the amorphous phase.

## Abstract

Radioactive wastes often contain amorphous and crystalline phases, and vapor hydration can affect their durability. In this study, Cs-clinoptilolite was heated (at 1100 °C and for 2–36 h) to prepare the samples that were composed mainly of an amorphous phase (AmP) and CsAlSi5O12 (≥94%) with minor CsAlSi2O6. Six samples with an AmP/CsAlSi5O12 ratio from 26.5 to 0.1 were kept at 21 °C and 55% relative humidity, and their hydration was measured via thermogravimetry (TG) over a period of almost six years. The hydration that resulted was directly related to the AmP quantity. The increase in water content followed a logarithmic trend over time. It reached 1.95% in the AmP-richest material, while it attained only 0.07% in the most crystalline sample. The hydrolysis of the AmP led to an increase over time in the tightly bound water. Samples with an AmP of ≤19% demonstrated slightly higher durability due to the lower Cs content in the AmP.