Key factors to understand in-situ behavior of Cs in Callovo–Oxfordian clay-rock (France)

Effect of Water Saturation on the Diffusion/Adsorption of 22Na and Cesium onto the Callovo-Oxfordian Claystones

“…Moreover, at each suction level strictly higher than 0 MPa, compacted materials displayed saturation degree values about 10% lower as compared to the ones measured on intact materials. (2) At full saturation, a good consistency was evidenced between the K D values estimated on intact and compacted samples for 22 Na and Cs, in accordance with previous studies such as the one carried out by Chen et al [19] for cesium. (3) Independently of sample state (intact or compacted), one cannot conclude whether desaturation drastically impacted 22 Na adsorption, given the associated uncertainty bars.…”

“…However, such apparent contradiction can be related to the nonlinear behavior of cesium adsorption. Indeed, plotting all of these K D data as a function of their associated cesium concentrations in solution at equilibrium reveals that the higher the cesium concentration in solution is, the lower the K D values are (Figure 10), as already shown by Chen et al [19] on fully saturated intact or compacted samples originated from the Callovo-Oxfordian formation. This suggests that nonlinear cesium adsorption could be also responsible for the main features shown in Figure 9.…”

“…Thus its diffusive behavior is expected to be "intermediate" between cesium and HTO. Moreover, the purpose of using intact and compacted samples is twofold: (i) to verify if the extent of adsorption under partial water-saturated conditions is consistent with fully saturated conditions (see [19] for adsorption of cesium onto full-saturated Callovo-Oxfordian claystones) and (ii) to investigate the role played by the pore network geometry on diffusion.…”

Self-Diffusion of Water and Ions in Clay Barriers

“…In the important case of Cs þ diffusion in clay barriers, several studies have suggested that a values measured in batch experiments may not be relevant to diffusion in porous media (Tsai et al, 2001;Jakob et al, 2009;Shackelford and Moore, 2013). In at least one clay-rock, however, direct measurements of Cs þ adsorption in intact and crushed rock yielded identical results (Figure 6.2;Van Loon et al, 2009;Chen et al, 2014), and a values obtained by adsorption on crushed rock and by diffusion in intact rock could be reconciled by using Eqn (6.10) to account for the nonlinearity of the adsorption isotherm (Appelo et al, 2010). In the case of bentonite, adsorption experiments indicate that the K d value for Cs þ adsorption is independent of the solid-water ratio at low degrees of compaction (Montavon et al, 2006) but increases with the solid-water ratio in highly compacted clay (Van Loon and , a change in behavior that may reflect the higher affinity of Cs þ for clay mineral surfaces at lower levels of interlayer hydration (Laird and Shang, 1997;Bourg and Sposito, 2011b).…”

Molecular dynamics simulations of cesium adsorption on illite nanoparticles

“…Two isotopes of cesium, 135 Cs and 137 Cs, are among the most important contaminants associated with the nuclear fuel cycle because of their high fission yield, long half lives (2.3 Â 10 6 and 30 a, respectively), high solubility in water, and metabolic similarity to potassium. These radioisotopes are key concerns in the geologic storage of radioactive waste [60,35,17], the management of legacy sites contaminated during the development of nuclear power [28,70], and the remediation of soils contaminated by catastrophic releases such as those that occurred at the Chernobyl and Fukushima Daiichi nuclear power plants [31,104,105]. In the Fukushima region, in particular, 137 Cs is the main source of external radiation dose five years after the nuclear disaster of March 2011.…”