Journal Article

FZJ-2020-03142

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Recrystallization and Uptake of 226Ra into Ba-Rich (Ba,Sr)SO4 Solid Solutions

Brandt, F. (Corresponding author)FZJ* ; Klinkenberg, M.FZJ* ; Poonoosamy, J.FZJ* ; Bosbach, D.FZJ*

2020
MDPI Basel

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Please use a persistent id in citations: http://hdl.handle.net/2128/25683  doi:10.3390/min10090812

Abstract: $^{226}$Ra is an important contributor to naturally occurring radioactive materials (NORM) and also considered in safety cases related to the disposal of spent nuclear fuel in a deep geological repository. Recrystallization and solid solution formation with sulfates is regarded as an important retention mechanism for $^{226}$Ra. In natural systems sulfates often occur as (Ba,Sr)SO$_4$. Therefore, we have chosen this solid solution at the Ba-rich end for investigations of the $^{226}$Ra uptake. The resulting $^{226}$Ra-solubility in aqueous solution was assessed in comparison with a thermodynamic model of the solid solution-aqueous solution system (Ba,Sr,Ra)SO$_4$ + H$_2$O. The temperature and composition of the initial (Ba,Sr)SO$_4$ solid solution were varied. Measurements of the solution composition were combined with microscopic observations of the solid and thermodynamic modeling. A complex recrystallization behavior of the solid was observed, including the dissolution of significant amounts of the solid and formation of metastable phases. The re-equilibration of Ba-rich (Ba,Sr)SO$_4$ to (Ba,Sr,Ra)SO$_4$ leads to a major reconstruction of the solid. Already trace amounts of Sr in the solid solution can have a significant impact on the $^{226}$Ra solubility, depending on the temperature. The experimental findings confirm the thermodynamic model, although not all solids reached equilibrium with respect to all cations.

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Contributing Institute(s):

1. Nukleare Entsorgung und Reaktorsicherheit (IEK-6)

Research Program(s):

1. 161 - Nuclear Waste Management (POF3-161) (POF3-161)

Appears in the scientific report 2020

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