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Thermodynamic Modeling of Neptunium(V) Solubility in Concentrated Na-CO3-HCO3-Cl-ClO4-H-OH-H2O Systems

Published online by Cambridge University Press:  15 February 2011

Craig F. Novak  and
Kevin E. Roberts
Craig F. Novak
Affiliation:
Sandia National Laboratories, MS 1320, P.O. Box 5800, Albuquerque, NM 87185-1320USA
Kevin E. Roberts
Affiliation:
Lawrence Berkeley Laboratory, MS 70A-1115, 1 Cyclotron Road, Berkeley, CA 94270USA
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Abstract

Safety assessments of nuclear waste repositories often require estimation of actinide solubilities as they vary with groundwater composition. Although a considerable amount of research has been done on the solubility and speciation of actinides,1,2 relatively little has been done to unify these data into a model applicable to concentrated brines. Numerous authors report data on the aqueous chemical properties of Np(V) in NaClO4, Na2CO3, and NaCl media, but a consistent thermodynamic model for predicting these properties is not available. To meet this need, a model was developed to describe the solubility of Np(V) in Na-Cl-ClO4-CO3 aqueous systems, based on the Pitzer activity coefficient formalism for concentrated electrolytes. Hydrolysis and/or carbonate complexation are the dominant aqueous reactions with the neptunyl ion in these systems. Literature data for neptunyl ion extraction and solubility are used to parameterize an integrated model for Np(V) solubility in the Np(V)-Na-CO3-HCO3-Cl-ClO4-H-OH-H2O system. The resulting model is tested against additional solubility and extraction data, and compared with Np(V) solubility experiments in complex synthetic brines.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 353: Symposium – Scientific Basis for Nuclear Waste Management XVIII , 1994 , 1119
Copyright
Copyright © Materials Research Society 1995

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