Water Corrosion and Release Mechanism of Cement Matrix Incorporating Simulated Medium-Level Waste

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Abstract
Previous works on cement leached in water and containing radioactive wastes like cesium and strontium agree to attribute the release in the liquid phase to a diffusion mechanism. The kinetic release can be represented by an empirical relationship in which the dependence of the leached fraction Fr = C/C0 versus time t assumes the form Fr = Btn and the factor n = 0.5 is typical of a diffusion process. On the other hand, the results of our studies on cement leached in static water demonstrate that the release of calcium, considered to be representative of matrix degradation, follows a time dependence of t0.25. A model is suggested for which the release of calcium depends on superposition of two processes: a diffusion through a reaction layer of calcium silicate hydrate around the cement particles during the hydration step and a diffusion of elements from the bulk of cement toward the external surface of the specimen. Based on this schematic diffusion mechanism, some suggestions are advanced to improve the ph...

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