Activation energy for diffusion of helium in water-saturated, compacted Na-montmorillonite

Abstract

It is important to clarify the migration behavior of hydrogen gas dissolved in water-saturated, compacted bentonite, which is a promising material for geologic disposal of high-level waste and TRU waste disposal. The diffusion coefficients of helium, which can be detected under extremely low background conditions, in water-saturated, compacted Na-montmorillonite were determined as a function of temperature by a transient diffusion method. The activation energies for diffusion of helium were then obtained. The activation energies were from 6.9 ± 4.8 to 19 ± 2.8 kJ mol -1 and were regarded to be independent of dry density. The activation energies of helium in water-saturated Na-montmorillonite were roughly equal to those in bulk water, 14.9 kJ mol -1, and in ice, from 11 to 13 kJ mol -1. It is possible that helium diffuses not only in pore water but also in interlayer water.

Isotopic fractionation of noble gases by diffusion in liquid water: Molecular dynamics simulations and hydrologic applications

“…Dissolved noble gases have emerged as important geochemical indicators of both continental paleoclimate (Stute et al, 1995;Peeters et al, 2003;Hall et al, 2005) and mass transport in hydrological basins (Price et al, 2003;LaBolle et al, 2006), hydrocarbon reservoirs (Torgersen and Kennedy, 1999;Zhou et al, 2005), lacustrine sediments (Poreda et al, 2004;Brennwald et al, 2005), aquitards (Rü bel et al, 2002;Hendry et al, 2005), engineered clay barriers (Higashihara et al, 2005) and the oceans (Rodehacke et al, 2007). Despite this importance of noble gases in low-temperature geochemistry, remarkably few measurements of noble gas diffusion coefficients in liquid water have been reported.…”

Self-Diffusion of Water and Ions in Clay Barriers

“…As evidenced below, this simplicity is instrumental in identifying the key trends associated with water and ion diffusion in clay materials. The diffusion of more complex or less extensively studied species such as oxyanions (Aertsens et al, 2003;Jansson and Eriksen, 2004;Sato and Miyamoto, 2004), actinides Joseph et al, 2013), lanthanides , trace metals (Lange et al, 2009), dissolved gases (Higashihara et al, 2004(Higashihara et al, , 2005, and organic molecules (Chapman and Parker, 2005;Martens et al, 2010) is not addressed here despite its interest in a range of areas. Diffusion in unsaturated conditionsdan important phenomenon in soils (Calvet, 1973;Nye, 1979) and, potentially, in HLRW repositories in certain conditions (Savoye et al, 2010)dis not discussed.…”

Salt effects on Re(VII) and Se(IV) diffusion in bentonite

“…In general, radionuclide diffusion is governed by the pore water chemistry (Molera et al, 2003), the microstructure of the clays (Glaus et al, 2010;González Sánchez et al, 2008), the orientation of clay particles (Sato, 2005), and temperature (Higashihara et al, 2005;Joseph et al, 2013). In the case of pore water chemistry, the salt concentration is an important factor because it will affect the diffusion of radionuclides in clays.…”