Neptunium incorporation into uranyl compounds that form as alteration products of spent nuclear fuel: Implications for geologic repository performance
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Peter C. Burns
Summary
Alteration of spent nuclear fuel in a geological repository under oxidizing conditions is likely to result in abundant uranyl compounds. Incorporation of radionuclides into the uranyl alteration phases may significantly reduce their mobility, thereby impacting repository performance. The following compounds have been synthesized from solutions containing from ∼10 to 500ppm Np5+: meta-schoepite, UO3·2H2O; Na-compreignacite, Na2[(UO2)3O2(OH)3]2(H2O)7; uranophane, Ca(UO2)2(SiO3OH)2(H2O)5; and β-(UO2)(OH)2. The structures of each involve sheets of uranyl polyhedra; the interlayers contain cations and H2O groups in Na-compreignacite and uranophane, only H2O in meta-schoepite, and β-(UO2)(OH)2 does not contain interlayer constituents. Synthesized powders were characterized by X-ray powder diffractometry, and were analyzed by ICP-AES (U, Na, Ca) and ICP-MS (Np). Aliquots of the powders were washed in 0.5M acetic acid to remove sorbed Np prior to analysis. The powders of meta-schoepite and β-(UO2)(OH)2 contained at most a few ppm Np5+. In contrast, powders of Na-compreignacite and uranophane contained Np5+ in proportion to the Np5+ concentration in the mother solution, and powders of each containing more than 400ppm Np5+ (of total Np + U) were obtained. Incorporation of Np5+ into uranyl compounds that form in a geological repository appears possible, and may impact the mobility of Np.
© 2004 Oldenbourg Wissenschaftsverlag GmbH
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Artikel in diesem Heft
- Deconvolution of alpha liquid scintillation spectra for quantitative analysis of actinide elements in water samples
- An EXAFS and TRLFS study of the sorption of trivalent actinides onto smectite and kaolinite
- New measurement of 239+240Pu concentration in the IAEA reference materials SOIL-6 and IAEA-375
- Reduction rate of neptunium(V) in heterogeneous solution with magnetite
- Neptunium incorporation into uranyl compounds that form as alteration products of spent nuclear fuel: Implications for geologic repository performance
- Preparation of U(VI) and Th(IV) alpha-sources from sea and fresh water samples by combining coprecipitation, solvent extraction and electrodeposition procedures
- Solvent extraction and separation of thorium(IV) and uranium(VI) by an ether-amide type tripodand
- Extraction of rubidium and caesium from strongly alkaline media
- Enhanced production possibility of the therapeutic radionuclides 64Cu, 67Cu and 89Sr via (n,p) reactions induced by fast spectral neutrons
