Effect of Exchangeable Cation on Radionuclide Diffusion In Compacted Bentonite

  • Park, Jong-Won (Korea Atomic Energy Research Institute) ;
  • Park, Hyun-Soo (Korea Atomic Energy Research Institute) ;
  • Dennis W. Oscarson (AECL Whiteshell Laboratories, Canada)
  • Published : 1996.06.01


Diffusion coefficient is a critical parameter for predicting radiological source term(migration rate and flux of radionuclide) through given near field conditions in spent fuel or high level waste repository. The effect of exchangeable cation-$Na^+$ and $Ca^{2+} - on the diffusion of $I^- \;and^3H$ (as HTO) in compacted bentonite was examined using a through-diffusion method. Bentonite material used here was compacted to a density of 1.3 Mg/m$^3$, and Na-bentonite was saturated with a solution of 100 mol NaCl/m$^3$ and Ca-bentonite with 50 $mol\;CaCl_2$/m$^3$. The results show that effective diffusion coefficients are generally higher by a factor of two to five in Ca-than Na-clay. This is attributed to the larger particle size of Ca-compared to Na-bentonite; hence, Ca-bentonite has a greater proportion of relatively large pores, which make a greater contribution to mass transport than small pores. Although the nature of the exchangeable cation affects mass diffusion in compacted bentonite, the effect is small and not likely to influence performance assessment modeling of compacted bentonite-based barriers.



  1. Nucl. Eng. Des. v.129 The Canadian approach to safe, permanent disposal of nuclear fuel waste W.T. Hancox;K. Nuttall
  2. AECL. Research Report, AECL-9891 Elemental, mineralogical, and poresolution compositions of selected Canadian clays D.W. Oscarson;D.A. Dixon
  3. Proc. of Clay Conf. Factors affecting the microstructure of smectites : Role of cation and history of applied stresses H. Ben Rhaiem;C.H. Pons;D. Tessier
  4. Soil Sci. v.93 Relationship between the activation energies for deuterium oxide diffusion and exchangeable ion conductance in clay systems G.R. Dutt;P.F. Low
  5. Can. Geotech. J. v.21 Diffusion of nonreactive and reactive solutes through fine-grained barrier materials R.W. Gillham;M.J. Robin;D.J. Dytynyshyn;H.M. Johnston
  6. AECL Research Report, AECL-10981 Procedures and apparatus for measuring diffusion and distribution coefficients in compacted clays H.B. Hume
  7. Geochim. Cosmochim. Acta v.48 Water-rock interaction and chemistry of groundwaters from the Canadian Shield S.K. Frape;P. Fritz;R.H. Mcnutt
  8. Eng. Geol. v.28 Swelling capacity and permeability of an unprocessed and a processed bentonitic clay D.W. Oscarson;D.A. Dixon;M. Gray
  9. Materials Research Society Symposium Proceedings 127, Scientific Basis for Nuclear Wsate Management XⅢ Diffusion of plutonium(Ⅳ) in dense bentonite-based materials H.D. Sharma;D.W. Oscarson;W. Lutze(ed.);R.C. Ewing(ed.)
  10. Soil Sci. Soc. Am. Proc. v.28 Mobility of water adjacent to mineral surfaces W.D. Kemper;D.E.L. Maasland;L.K. Porter
  11. J. Phys. Chem. v.69 The effect of ions on the self-diffusion of water. Ⅰ. Concentration dependence D. Mccall;D. Douglass
  12. Soil Sci. Soc. Am. J. v.55 Diffusion of technetium in dense bentonite under oxidizing and reducing conditions N.G. Sawatsky;D.W. Oscarson
  13. J. Phys. Chem. v.63 Phenomenological theory of ion solvation. Effective radii of hydrated ions E.R. Nightingale
  14. The Surface Chemistry of Soils G. Sposito
  15. Envir. Geol. v.4 A tabulation and evaluation of ion exchange data on smectites L.V. Benson
  16. Clays Clay Miner v.36 Effect of magnesium on the hydraulic conductivity of Na-smectite-sand mixtures I. Shainberg;N. Alperovitch;R. Keren
  17. Soil Sci. Soc. Am. J. v.56 Diffusion of iodide in compacted bentonite D.W. Oscarson;H.B. Hume;N.G. Sawatsky;S.C.H. Cheung
  18. Appl. Clay Sci. v.8 The measurement of apparent diffusion coefficients in compacted clays : an assessment of methods W.J. Cho;D.W. Oscarson;P.S. Hahn