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EFFECT OF CARBONATE ON THE SOLUBILITY OF NEPTUNIUM IN NATURAL GRANITIC GROUNDWATER

  • Kim, B.Y. (Department of Nuclear & Quantum Engineering, KAIST) ;
  • Oh, J.Y. (Department of Nuclear & Quantum Engineering, KAIST) ;
  • Baik, M.H. (Radioactive Waste Technology Development Division, Korea Atomic Energy Research Institute) ;
  • Yun, J.I. (Department of Nuclear & Quantum Engineering, KAIST)
  • Received : 2010.02.23
  • Accepted : 2010.07.24
  • Published : 2010.10.31

Abstract

This study investigates the solubility of neptunium (Np) in the deep natural groundwater of the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT). According to a Pourbaix diagram (pH-$E_h$ diagram) that was calculated using the geochemical modeling program PHREEQC 2.0, the redox potential and the carbonate ion concentration both control the solubility of neptunium. The carbonate effect becomes pronounced when the total carbonate concentration is higher than $1.5\;{\times}\;10^{-2}$ M at $E_h$ = -200 mV and the pH value is 10. Given the assumption that the solubility-limiting stable solid phase is $Np(OH)_4(am)$ under the reducing condition relevant to KURT, the soluble neptunium concentrations were in the range of $1\;{\times}\;10^{-9}$ M to $3\;{\times}\;10^{-9}$ M under natural groundwater conditions. However, the solubility of neptunium, which was calculated with the formation constants of neptunium complexes selected in an OECD-NEA TDB review, strongly deviates from the value measured in natural groundwater. Thus, it is highly recommended that a prediction of neptunium solubility is based on the formation constants of ternary Np(IV) hydroxo-carbonato complexes, even though the presence of those complexes is deficient in terms of the characterization of neptunium species. Based on a comparison of the measurements and calculations of geochemical modeling, the formation constants for the "upper limit" of the Np(IV) hydroxo-carbonato complexes, namely $Np(OH)_y(CO_3)_z^{4-y-2z}$, were appraised as follows: log $K^{\circ}_{122}\;=\;-3.0{\pm}0.5$ for $Np(OH)_2(CO_3)_2^{2-}$, log $K^{\circ}_{131}\;=\;-5.0{\pm}0.5$ for $Np(OH)_3(CO_3)^-$, and log $K^{\circ}_{141}\;=\;-6.0{\pm}0.5$ for $Np(OH)_4(CO_3)^{2-}$.

Keywords

References

  1. J. P. Kaszuba and W. H. Runde, “The aqueous geochemistry of neptunium: Dynamic control of soluble concentrations with applications to nuclear waste disposal”, Environ. Sci. Technol., 33, 4427 (1999). https://doi.org/10.1021/es990470x
  2. J. I. Kim, “Significance of actinide chemistry for the longterm safety of waste disposal”, Nucl. Eng. Technol., 38, 459 (2006).
  3. C. Lierse, W. Treiber, and J. I. Kim, “Hydrolysis reactions of neptunium(V)”, Radiochim. Acta., 38, 27 (1985).
  4. V. Neck, J. I. Kim, and B. Kanellakopulos, “Solubility and hydrolysis behavior of neptunium(V)”, Radiochim. Acta., 56, 25 (1992).
  5. L. Merli and J. Fuger, “Thermochemistry of a Few Neptunium and Neodymium Oxides and Hydroxides”, Radiochim. Acta., 66/67, 109 (1994).
  6. D.W. Efurd, W. Runde, J. C. Banar, D. R. Janecky, J. P. Kaszuba, P. D. Palmer, F. R. Roensch, and C. D. Tait, “Neptunium and plutonium solubilities in a Yucca Mountain groundwater”, Environ. Sci. Technol., 32, 3893 (1998). https://doi.org/10.1021/es980591h
  7. L. Maya, “Hydrolysis and carbonate complexation of dioxoneptunium(V) in 1.0-M $NaClO_4$ at 25${\circ}$C”, lnorg. Chem., 22, 2093 (1983). https://doi.org/10.1021/ic00156a031
  8. I. Grenthe, P. Robouch, and P. Vitorge, “Chemical equilibria in actinide carbonate systems”, J. Less-Common Met., 122, 225 (1986). https://doi.org/10.1016/0022-5088(86)90415-7
  9. V. Neck, W. Runde, J. I. Kim, and B. Kanellakopulos, “Solidliquid equilibrium reactions of neptunium(V) in carbonate solution at different ionic strength”, Radiochim. Acta., 65, 29 (1994).
  10. V. Neck, W. Runde, and J. I. Kim, “Solid-liquid equilibria of neptunium(V) in carbonate solutions of different ionic strengths: II. Stability of the solid phases”, J. Alloys Comp., 225, 295 (1995). https://doi.org/10.1016/0925-8388(94)07099-7
  11. C. F. Novak, I. Al Mahamid, K. A. Becraft, S. A. Carpenter, N. Hakem, and T. Prussin, “Measurement and Thermodynamic Modeling of Np(V) Solubility in Aqueous $K_{2}CO_{3}$ Solutions to High Concentrations”, J. Sol. Chem., 26, 681 (1997). https://doi.org/10.1007/BF02767621
  12. I. A. Mahamid, C.F. Novak, K.A Becraft, S. A. Carpenter, and N. Hakem, “Solubility of Np(V) in K-Cl-$CO_3$ and Na-K-Cl-$CO_3$ Solutions to High Concentrations: Measurements and Thermodynamic Model Predictions”, Radiochim. Acta., 81, 93 (1998).
  13. D. Rai and J. L. Ryan, “Neptunium(IV) hydrous oxide solubility under reducing and carbonate conditions”, Inorg. Chem., 24, 247 (1985). https://doi.org/10.1021/ic00197a001
  14. R. M. Pratopo, H. Moriyama, and K. Higashi, “The behaviour of Neptunium under reducing conditions”, Proceedings of 1989 Joint International Waste Management Conference, Kyoto, Japan, Oct. 22-28, 1989.
  15. M. Yui, “Database development of glass dissolution and radionuclide migration for performance analysis of HLW repository in Japan”, J. Nucl. Mater., 298, 136 (2001). https://doi.org/10.1016/S0022-3115(01)00578-5
  16. J. H. Rees, “The theoretical derivation of solubilities of longlived radionuclides in disposal”, J. Nucl. Mater., 130, 336 (1985). https://doi.org/10.1016/0022-3115(85)90322-8
  17. V. Neck and J. I. Kim, “Solubility and hydrolysis of tetravalent actinides”, Radiochim. Acta, 89, 1 (2001). https://doi.org/10.1524/ract.2001.89.1.001
  18. F. J. Mompean, M. Illemassene, C. D. Orti, and K. B. Said, Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Vol. 5, ELSEVIER B.V., Amsterdam (2003).
  19. A. Kitamura and Y. Kohara, “Carbonate complexation of neptunium(IV) in highly basic solutions”, Radiochim. Acta, 92, 583 (2004). https://doi.org/10.1524/ract.92.9.583.55002
  20. D. Rai, N. J. Hess, A. R. Felmy, and D. A. Moore, “A thermodynamic model for the solubility of $NpO_2$(am) in the aqueous $K^{+}-HCO_{3}^{-}-CO_{3}^{2-}-OH^{-}-H_{2}O$ system”, Radiochim. Acta, 84, 159 (1999).
  21. T. E. Eriksen, P. Ndalamba, D. Cui, J. Bruno, M. Caceci, and K. Spahiu, “Solubility of the redox-sensitive radionuclides $^{99}$Tc and $^{237}$Np under reducing conditions in neutral to alkaline solutions; effect of carbonate”, SKB-TR-93-18, Swedish Nuclear Fuel and Waste Management Co. (1993).
  22. M. I. Pratopo, H. Moriyama, and K. Higashi, “Carbonate complexation of neptunium(IV) and analogous complexation of ground-water uranium”, Radiochim. Acta, 51, 27 (1990).
  23. S. Kwon, C. S. Lee, S. J. Cho, S. W. Jeon, and W. J. Cho, “An investigation of the excavation damaged zone at KAERI underground research tunnel”, Tunn. Undergr. Sp. Tech., 24, 1 (2009). https://doi.org/10.1016/j.tust.2008.01.004
  24. W. -J. Cho, S. Kwon, and J. H. Park, “KURT, a small-scale underground research laboratory for the research on a highlevel waste disposal”, Ann. Nucl. Energy, 35, 132-140 (2008). https://doi.org/10.1016/j.anucene.2007.05.011
  25. D. S. Bae, C. S. Kim, K. S. Kim, Y. K. Koh, J. H. Hwang, and J. R. Kim, “Assessment of deep geological environment condition”, KAERI /RR-2783/2006, Korea Atomic Energy Research Institute (2007).
  26. S. S. Kim, M. H. Baik, and K. C. Kang, “Solubility of neptunium oxide in the KURT (KAERI Underground Research Tunnel) groundwater”, J. Radioanal. Nucl. Chem., 280, 577 (2009). https://doi.org/10.1007/s10967-009-7481-y
  27. A. Kitamura and Y. Kohara, “Solubility of Np(IV) under carbonate conditions”, Report JNC TC8400 2001-006, Japan Nuclear Fuel Cycle Development Institute (2001).
  28. H. Moriyama, M. I. Pratopo, and K. Higashi, “The solubility and colloidal behavior of Neptunium(IV)”, Sci. Tot. Environ., 83, 227 (1989). https://doi.org/10.1016/0048-9697(89)90095-8
  29. V. Neck, Th. Fanghanel, and J. I. Kim, “Mixed hydroxocarbonato complexes of neptunium(V)”, Radiochim. Acta, 77, 167 (1997).