Effects of Relative Surface Area and Leachant Composition on the ¹³⁷Cs Leach Rate from Cement Waste Forms

Abstract

Cement matrices, doped with ¹³⁷Cs, were investigated to establish their physicochemical properties, mainly ¹³⁷Cs leach-rate. Experiments were carried out in leachant media with different degrees of aggressiveness on the cement matrix, e.g., distilled water, Na₂SO₄ and NaCl solutions. A series of six cement samples, which were orthocylindrically-shaped, were treated in each of three leachant media. For each sample, the surface area exposed to leaching relative to the total surface area was increased from 1:6 to 6:6, at increments of 1/6 of the total surface area. Expected higher ¹³⁷Cs leach-rates of the samples immersed in the more aggressive environment show very specific behavior and functional relations with respect to the exposed surface area. Radionuclide leach-rate coefficients did not exhibit linear behavior. Instead, leach-rate values were best fit by exponential equations to describe cement matrix behavior in the leachants. Different empirical equations were established to describe ¹³⁷Cs leach-rates in the various leachants as a function of the relative surface area of the cement matrix exposed to the leachant.