Thermodynamics, kinetics, and mechanics of cesium sorption in cement paste: A multiscale assessment

Abstract

Cesium-137 is a common radioactive byproduct found in nuclear spent fuel. Given its 30 year half life, its interactions with potential storage materials-such as cement paste-is of crucial importance. In this paper, simulations are used to establish the interaction of calcium silicate hydrates (C-S-H)-the main binding phase of cement paste-with Cs at the nano-and mesoscale. Different C-S-H compositions are explored, including a range of Ca/Si ratios from 1.0 to 2.0. These calculations are based on a set of 150 atomistic models, which qualitatively and quantitatively reproduce a number of experimentally measured features of C-S-H-within limits intrinsic to the approximations imposed by classical molecular dynamics and the steps followed when building the models. A procedure where hydrated Ca 2+ ions are swapped for Cs 1+ ions shows that Cs adsorption in the C-S-H interlayer is preferred to Cs adsorption at the nanopore surface when Cs concentrations are lower than 0.19 Mol/kg. Interlayer sorption decreases as the Ca/Si ratio increases. The activation relaxation technique nouveau is used to access timescales out of the reach of traditional molecular dynamics (MD). It indicates that characteristic diffusion time for Cs 1+ in the C-S-H interlayer is on the order of a few hours. Cs uptake in the interlayer has little impact on the elastic response of C-S-H. It leads to swelling of the C-S-H grains, but mesoscale calculations that access length scales out of the range of MD indicate that this leads to practically negligible expansive pressures for Cs concentrations relevant to nuclear waste repositories.

Time resolved alkali silicate decondensation by sodium hydroxide solution

“…The rich and complex chemistry of silicate species motivates the study of the dissolution and polymerization of silica [12][13][14]. The role of ions, such as alkali, has long being studied [15] because it varies according to the type of material (glass, hydrated glass, gel, zeolite, mineral) and on the chemical environment [16][17][18]. In recent decades, silicates glasses or aluminosilicates binders have been widely studied in the construction industry and other specific areas.…”

Molecular Dynamics Study of the Beryllium Interaction with C-S-H Phases

“…It was found that the disordered structure of C-S-H provides multiple acceptor sites for hydrogen bonds, and therefore is significantly more hydrophilic compared to cationic clays that are often used for comparison. Abdolhosseini Qomi and co-workers 8 constructed bulk C-S-H models that correspond to a wide range of compositions that could be used successfully to study both the mechanical and the sorption properties of C-S-H. 11,12 A number of computational studies describe the behavior of beryllium in aqueous solutions on the molecular level. Beryllium preferentially coordinates ligands in tetrahedral geometry, has strong hydrolyzing and polarizing abilities, and shows complex pH-dependent solution chemistry.…”

Experimental Study Investigating the Effects of Concrete Conditions on the Penetration Behaviors of Cs and Sr at Low Concentration Ranges

“…Calcium silicate hydrate (C-S-H) is the most significant cement hydrate phase that interacts with Cs, and these interactions have been investigated extensively (Missan et al 2018;Haga et al 2019). These interactions have also been studied using atomistic models that considered molecular dynamics or quantum chemistry (Arayro et al 2018;Jian et al 2017;Duque-Redondo et al 2018;Tachikawa et al 2020). The contribution of aggregates in concrete has also been considered (Idemitsu et al 1992;Fuller et al 2014).…”