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Compatibility Relationships in the U-Fe-O(-H) System at 400°C: The Implications of the Ferric-Ferrous Buffer for the Immobilization of Uranium and Transuranic Elements

Published online by Cambridge University Press:  21 February 2011

Deane K. Smith ,
W. Phelps Freeborn  and
Barry E. Scheetz
Deane K. Smith*
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802
W. Phelps Freeborn
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802
Barry E. Scheetz
Affiliation:
Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802
*
* Also associated with the Department of Geosciences.
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Abstract

The current strategy for the immobilization of nuclear wastes is based upon a system of multiply redundant barriers for which geological containment is the final barrier to the migration of radionuclides in the biosphere. The ability of the respository host rock to buffer the oxygen fugacity of the pore waters is a critical concern for the evaluation of the far-field migration of selected elements; notable Tc, U and TRU elements. The buffer capacity of all proposed host rocks, with the exception of salt, is based upon the presence of both ferric and ferrous iron in the host rock phases.

The system U-Fe-O(-H) was selected for study because of its significance on the role of Fe in controlling the oxidation state of the U. It has been established that the Fe2+/Fe3+ couple is the controlling factor in limiting the uranium oxidation to the U4+ state.

The results from this experimental study at 400° C (the maximum worse case temperature for a repository) verified the existence of the compatibility triangles between hematite and UO2.00 and magnetite and between U4O9 and UO2.00 and hematite. These data indicate that in the presence both ferric and ferrous ions, the form of the uranium dioxide is retained as stoichiometric UO2.00 and not as an intermediate member of the UO2+x solid solution series or other higher oxide. These experimental results are in concert with the phase relationships predicted by Freeborn et al. (1980) based upon thermochemical calculations.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 15: Symposium D – Scientific Basis for Nuclear Waste Management VI , 1982 , 91
Copyright
Copyright © Materials Research Society 1983

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References

REFERENCES

1. NRC, Disposal of High-Level Radioactive Wastes in Geologic Repositories- Performance Objectives and Technical Criteria: 10 CER 60 (Draft 7), Code of Federal Regulations, U.S. Nuclear Regulatory Commission, Washington, DC (1980).Google Scholar
2. Evans, W.D.J. and White, J., “Equilibrium Relationships in the System UO2-Fe3O3-O,” Trans. Brit. Ceram. Soc. 63, 705 (1964).Google Scholar
3. Rich, R.A., Holland, H.D. and Peterson, U., Hydrothermal Uranium Deposits, Elsevier Publishing Co., Inc., New York (1977).Google Scholar
4. Badham, J.P.N., “Magnetite-Apatite-Amphibole-Uranium and Silver-Arsenide Mineralizations in Lower Protozoic Igneous Rocks, East Arm, Great Slave Lake, Canada,” Econ. Geol. 73, 1474 (1978).Google Scholar
5. Freeborn, W.P., Zolensky, M.E., Scheetz, B.E., Komarneni, S., McCarthy, G.J. and White, W.B., “Shale Rocks as Nuclear Waste Repositories: Hydrothermal Reactions with Glass, Ceramics and Spent Fuel Waste Forms,” Scientific Basis for Nuclear Waste Management 2, (Northrup, C.J.M. Jr., ed; Plenum Press, NY, 499–406, 1980).Google Scholar
6. Naumov, G.B., Ryzhenko, B.N. and Khodakovsky, I.L., Handbook of Thermodynamic Data, (Trans. Russian Rpt.) NTIS PB, 266 722, 327 (1974).Google Scholar