Incorporation of strontium and europium in crystals of α-calcium isosaccharinate.

Song Chen,Kerstin Forsberg,Le Fu,Mats Jonsson,Ahmed F Abdel-Magied

doi:10.1016/j.jhazmat.2018.10.001

Song Chen, Kerstin Forsberg + Show 3 more

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https://doi.org/10.1016/j.jhazmat.2018.10.001

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Abstract

The final repository for short-lived, low and intermediate level radioactive waste in Sweden is built to act as a passive repository. Already within a few years after closure water will penetrate the repository and conditions of high alkalinity (pH 10.5-13.5) and low temperature (< 7 °C) will prevail. The mobility of radionuclides in the repository is dependent on the radionuclides distribution between solid and liquid phases. In the present work the incorporation of strontium (II) and europium (III) in α-calcium isosaccharinate (ISA) under alkaline conditions (pH ∼10) at 5 °C and 50 °C have been studied. The results show that strontium and europium are incorporated into α-Ca(ISA)2 when crystallized both at 5 °C and 50 °C. Europium is incorporated to a greater extent than strontium. The highest incorporation of europium and strontium at 5 °C rendered the phase compositions Ca0.986Eu0.014(ISA)2 (2.4% of Eu(ISA)3 by mass) and Ca0.98Sr0.02(ISA)2 (2.2% of Sr(ISA)2 by mass). XPS spectra show that both trivalent and divalent Eu coexist in the Eu incorporated samples. Strontium ions were found to retard the elongated growth of the Ca(ISA)2 crystals. The incorporation of Sr2+ and Eu3+ into the solid phase of Ca(ISA)2 is expected to contribute to a decreased mobility of these ions in the repository.

Highlights

The final repository for short-lived, low and intermediate level radioactive waste in Sweden, SFR1, is designed to retain the radioactive elements during thousands of years [1]
As it is not clear whether the drying conditions affect the phases of recrystallized calcium isosaccharinate, we compared the results obtained by drying the crystals at room temperature and at 50 °C
Together these results indicate that Sr(II) is incorporated into the crystal lattice of Ca(ISA)2 substituting for calcium due to molecular resemblance

Summary

Introduction

The final repository for short-lived, low and intermediate level radioactive waste in Sweden, SFR1, is designed to retain the radioactive elements during thousands of years [1]. Journal of Hazardous Materials 364 (2019) 309–316 ions in SFR, and isotopes of actinides such as Pu, Am and Cm [2]. Groundwater is expected to penetrate into the repository so that the vaults will be completely filled already a few years after closure [3]. Parts of the engineered barriers in the repository are made of cementitious materials, which will give a high basicity of the aqueous phase. Alkali hydroxides will maintain the pH at about 13.5, the pH will be kept at about 12.5 in equilibrium with portlandite and decalcification of calcium-silica hydrate phases will maintain the pH in the range 12.5–10.5. Alkaline and anoxic conditions are expected to remain for more than 20 000 years and the temperature will remain about 5–7 °C for about 50 000 years [4,5,6]

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