Oxidative dissolution is the key stage of uranium oxide spent nuclear fuel (SNF) reprocessing technology in carbonate media. The ability to quickly and completely dissolve the main component of the SNF matrix - UO ₂ in sodium or ammonium carbonate solutions in the presence of hydrogen peroxide at room temperature made it possible to substantiate carbonate media as an alternative to nitric acid media in the SNF reprocessing technology. Before the SNF oxidative dissolution stage, in the CARBEX (CARBonate EXtraction) process, voloxidation (volume oxidation) is carried out. As a result, UO₂ completely turns into U₃O₈. In this work, the dissolution of U₃O ₈ in sodium carbonate solutions, in the presence of hydrogen peroxide, and sodium percarbonate was studied. The optimal dissolution conditions were determined. With the help of mathematical experimental data processing, the dissolution rates and the apparent activation energy values were calculated.

1. H. Tomiyasu, Y. Asano, “Environmentally acceptable nuclear fuel cycle development of a new reprocessing system”, Prog. Nucl. Energ., vol. 32, no. 3–4 pp. 421–427, 1998.
   DOI: https://doi.org/10.1016/S0149-1970(97)00037-1
2. G. S. Goff et al., “Development of a novel alkaline based process for spent nuclear fuel recycling”, AIChE Annual Meeting, Nuclear Engineering Division, Salt Lake City (Utah), USA, Nov. 4–9, 2007.
3. K. W. Kim et al., “A study on a process for recovery of uranium alone from spent nuclear fuel in a high alkaline carbonate media”, NRC 7, Budapest, Hungary, Aug. 24–29, 2008.
4. S. I. Stepanov, A. M. Chekmarev, “Concept of spent nuclear fuel reprocessing”, Dokl. Chem., vol. 423 no. 1, pp. 276–278, 2008.
   DOI: https://doi.org/10.1134/S0012500808110037
5. C. Z. Soderquist et al., “Dissolution of irradiated commercial UO₂ fuels in ammonium carbonate and hydrogen peroxide”, Ind. Eng. Chem. Res., vol. 50 no. 4, pp. 1813–1818, 2011.
   DOI: https://doi.org/10.1021/ie101386n
6. N. Asanuma, M. Harada, Y. Ikeda, H. Tomiyasu, “New approach to the nuclear fuel reprocessing in non–acidic aqueous solutions”, J. Nucl. Sci. Technol. vol. 38, no. 10, pp. 866–871, 2001.
   DOI: https://doi.org/10.1080/18811248.2001.9715107
7. K. W. Kim et al., “A conceptual process study for recovery of uranium alone from spent nuclear fuel by using high–alkaline carbonate media”, Nucl. Technol., vol. 166, no. 2, pp. 170–179, 2009.
   DOI: https://doi.org/10.13182/NT09-A7403
8. S. M. Peper et al., “Kinetic study of the oxidative dissolution of UO ₂ in aqueous carbonate media”, Ind. Eng. Chem. Res ., vol. 43, no. 26, pp. 8188–8193, 2004.
   DOI: https://doi.org/10.1021/ie049457y
9. S. C. Smith, S. M. Peper, M. Douglas K. L. Ziegelgruber, E. C. Finn, “Dissolution of uranium oxides under alkaline oxidizing conditions”, J. Radioanal. Nucl. Chem., vol. 282, no. 3, pp. 617–621, 2009.
   DOI: https://doi.org/10.1007/s10967-009-0182-8
10. S. A. Steward, E. T. Mones, “Aqueous dissolution rates of uranium oxides”, in American Nuclear Society's International High Level Waste Management Conference , Las Vegas (Nevada), USA, 1995.
11. D. Y. Chung et al., “Oxidative leaching of uranium from SIMFUEL using Na₂CO₃–H₂O₂ solution”, J. Radioanal. Nucl. Chem., vol. 284, pp. 123–129, 2010.
    DOI: https://doi.org/10.1007/s10967-009-0443-6
12. K. W. Kim et al., “An oxidative leaching of uranium in a H₂O ₂–CO₃^2– system for a recovery of U alone from spent fuel without TRU”, GLOBAL 2009 Congress: The Nuclear Fuel Cycle: Sustainable Options and Industrial Perspectives , Paris, France, Sep. 6–11, 2009.
13. K. W. Kim et al., “Preparation of uranium oxide powder for nuclear fuel pellet fabrication with uranium peroxide recovered from uranium oxide scraps by using a carbonate–hydrogen peroxide solution”, J. Radioanal. Nucl. Chem., vol. 292 pp. 909–916, 2012.
    DOI: https://doi.org/10.1007/s10967-011-1534-8
14. S. I. Stepanov, A. V. Boyarintsev, A. M. Chekmarev, “Physicochemical foundations of spent nuclear fuel leaching in carbonate solutions”, Dokl. Chem. vol. 427, no. 2, pp. 202–206, 2009.
    DOI: https://doi.org/10.1134/S0012500809080060
15. F. Clarens et al., “The oxidative dissolution of unirradiated UO₂ by hydrogen peroxide as a function of pH”, J. Nucl. Mater., vol. 345, no. 2–3, pp. 225–231, 2005.
    DOI: https://doi.org/10.1016/j.jnucmat.2005.06.002
16. S. A. Steward, W. J. Gray, “Comparison of uranium dissolution rates from spent fuel and uranium dioxide”, International high level radioactive waste management conference , UCRL–JC–115355, Las Vegas, NV, USA, May 1994.
    DOI: https://doi.org/10.2172/10163296
17. S. A. Steward, E. T. Mones, “Comparison and modeling of aqueous dissolution rates of various uranium oxides”, Materials Research Society Conference, UCRL–JC–124602, Boston, MA, USA, 1996.
    Retrieved from: https://www.nrc.gov/docs/ML0334/ML033490600.pdf
    Retrieved on: Jun. 15, 2021
18. S. N. Nguyen, H. C. Weed, H. R. Leider, R. B. Stout, “Dissolution kinetics of UO₂, Flow–through tests, on UO_2,00 pellets and polycrystalline schoepite samples in oxygenated, carbonate/bicarbonate buffer solutions at 25°C”, Material Research Society Conference UCRL–JC–107478, Strasbourg, France, 1991.
    Retrieved from: https://www.osti.gov/servlets/purl/6021724
    Retrieved on: Jun. 15, 2021
19. E. Ekeroth, M. Jonsson, “Oxidation of UO₂ by radiolytic oxidants”, J. Nucl. Mater., vol. 322, no. 2–3, pp. 242–248, 2003.
    DOI: https://doi.org/10.1016/j.jnucmat.2003.07.001
20. J. S. Goldik, J. J. Noël, D. W. Shoesmith, “Surface electrochemistry of UO₂ in dilute alkaline hydrogen peroxide solutions: Part II. Effects of carbonate ions”, Eletrochim. Acta., vol. 51, no. 16, pp. 3278–3286, 2006.
    DOI: https://doi.org/10.1016/j.electacta.2005.09.019
21. T. Suzuki, A. Abdelouas, B. Grambow, T. Mennecart, G. Blondiaux, “Oxidation and dissolution rates of UO₂(s) in carbonate–rich solutions under external alpha irradiation in initially reducing conditions”, Radiochim. Acta., vol. 94, no. 9–11, pp. 567–573, 2006.
    DOI: https://doi.org/10.1524/ract.2006.94.9-11.567
22. J. de Pablo, I. Casas, F. Clarens, F. El. Aamrani, M. Rtovira,“The effect of hydrogen peroxide concentration on the oxidative dissolution of unirradiated uranium dioxide”, MRS Online Proceedings Library, vol. 663, article no. 409, 2000.
    DOI: https://doi.org/10.1557/PROC-663-409
23. J. B. Hiskey, “Hydrogen peroxide leaching of uranium in carbonate solutions”, Transactions of the Institution of Mining and Metallurgy, Section C: Mineral Processing and Extractive Metallurgy vol. 89, pp. 145–152, 1980.
24. В. К. Марков, А. В. Виноградов, С. В. Елинсон, Уран, методы его определения, Москва, Россия: Атомиздат, 1960.(V. K. Markov, E. A. Vernyi, A. V. Vinogradov, Uranium, methods of its definition, Moscow, Russia: Atomizdat, 1960.)
25. Analytical Spectroscopy Library Volume 10 : Separation, preconcentration, and spectrophotometry in inorganic analysis , Z. Marczenko, M. Balcerzak, Eds., 1st ed., New York (NY), USA: Elsevier Science, 2000.
26. B. Bertsch-Frank, A. Dorfer, G. Goor, H. U. Süss, “Hydrogen peroxide and inorganic peroxy compounds,” Ind. Inorg. Chem.: Prod. Uses pp. 175–198, 1995.

N.M. Chervyakov , A.V. Boyarintsev , A.V. Andreev, S.I. Stepanov, "Oxidative dissolution of triuranium octoxide in carbonate solutions",RAD Conf. Proc, vol. 5, 2021, pp. 68-74, http://doi.org/10.21175/RadProc.2021.13