4.7 Article

Effect of solution chemistry on the iodine release from iodoapatite in aqueous environments

Journal

JOURNAL OF NUCLEAR MATERIALS
Volume 525, Issue -, Pages 161-170

Publisher

ELSEVIER
DOI: 10.1016/j.jnucmat.2019.07.034

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Funding

  1. Center for Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0016584]

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To ensure the safe disposal of nuclear waste, understanding the release process of radionuclides retained in the nuclear waste forms is of vital importance. Iodoapatite Pb-9.85(VO4)(6)I-1.7, a potential waste form for iodine-129, was selected as a model system for ceramic waste forms in this study to understand the effect of aqueous species on iodine release. Semi-dynamic leaching tests were conducted on bulk samples in cap-sealed Teflon vessels with 0.1 mol/L NaCl, Na2CO3, Na3PO4, and Na2SO4 solutions under 90 degrees C, fixed sample surface area to solution volume ratio of 5/m, and periodic replacement of leaching solutions. The reacted solutions were then analyzed by Inductively Coupled Plasma-Mass Spectrometry and Inductively Coupled Plasma-Optical Emission Spectrometry; the leached surfaces were characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. The result shows that, compared to deionized water, the ion-rich solutions enhanced the iodine release as a result of the increased ionic strength, reduced activity coefficient of dissolved species, and increased solution pH. Surface reactions can lead to the formations of secondary phases by ion-exchange and precipitation. These findings suggest that an ion-rich environment in the geological repository can be detrimental to the disposal safety of the nuclear waste form. (C) 2019 Elsevier B.V. All rights reserved.

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