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Modelling Ra-bearing baryte nucleation/precipitation kinetics at the pore scale; application to radioactive waste disposal

Enzo Curti, Jacinta Xto, Camelia N. Borca, Katja Henzler, Thomas Huthwelker and Nikolaos I. Prasianakis
Modelling Ra-bearing baryte nucleation/precipitation kinetics at the pore scale; application to radioactive waste disposal
European Journal of Mineralogy (November 2018) 31 (2): 247-262

Abstract

Baryte is of interest to nuclear waste disposal as the main scavenger of (super 226) Ra, a long-lived nuclide playing a major role in the safety assessment of planned disposal sites. In specific repository setups, Ba and Ra released from the nuclear waste will react with sulphate-rich pore water, potentially leading to formation of Ra-bearing baryte. Baryte has a complex kinetic behaviour and its precipitation may strongly be inhibited. Because highly supersaturated solutions may persist metastably, it can be anticipated that the migration of Ra through the repository near-field will strongly depend on parameters related to nucleation and precipitation kinetics, so that thermodynamic equilibrium calculations will not be sufficient for a reliable prediction of (super 226) Ra mobility. In this study, we implement Classical Nucleation Theory (CNT) and a saturation-state dependent precipitation rate equation into a Lattice-Boltzmann (LB) reactive transport code to model Ra-bearing baryte precipitation within a porous medium analogous to fragmented nuclear waste glass. In the simulations, baryte precipitation is induced by counter-diffusion of BaCl (sub 2) and Na (sub 2) SO (sub 4) solutions. Radium co-precipitation is taken into account by assuming a fixed partition coefficient and constant Ra concentration at the BaCl (sub 2) injection boundary. Both homogeneous and heterogeneous growth were considered. Critical CNT parameters, particularly supersaturation-dependent induction times, were calibrated against independent turbidity and X-ray absorption experiments. The model allows exploring the influence of baryte nucleation/precipitation kinetics on the partitioning of Ra between aqueous phase and solid at the pore (micrometre) scale. Our results indicate that quantitative knowledge of kinetic and nucleation parameters is essential to predict radionuclide transport towards the geosphere in nuclear waste repository systems.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 31
Serial Issue: 2
Title: Modelling Ra-bearing baryte nucleation/precipitation kinetics at the pore scale; application to radioactive waste disposal
Affiliation: Paul Scherrer Institut, Laboratory for Waste Management, Villigen, Switzerland
Pages: 247-262
Published: 20181127
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 71
Accession Number: 2019-003823
Categories: Isotope geochemistryEnvironmental geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: Swiss Federal Institute of Technology, CHE, Switzerland
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201904
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