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Retardation of uranium and thorium by a cementitious backfill developed for radioactive waste disposal

Felipe-Sotelo, Monica, Hinchliff, J, Field, LP, Milodowski, AE, Preedy, O and Read, David (2017) Retardation of uranium and thorium by a cementitious backfill developed for radioactive waste disposal Chemosphere, 179. pp. 127-138.

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Abstract

The solubility of uranium and thorium has been measured under the conditions anticipated in a cementitious, geological disposal facility for low and intermediate level radioactive waste. Similar solubilities were obtained for thorium in all media, comprising NaOH, Ca(OH)2 and water equilibrated with a cement designed as repository backfill (NRVB, Nirex Reference Vault Backfill). In contrast, the solubility of U(VI) was one order of magnitude higher in NaOH than in the remaining solutions. The presence of cellulose degradation products (CDP) results in a comparable solubility increase for both elements. Extended X-ray Absorption Fine Structure (EXAFS) data suggest that the solubility-limiting phase for uranium corresponds to a becquerelite-type solid whereas thermodynamic modelling predicts a poorly crystalline, hydrated calcium uranate phase. The solubility-limiting phase for thorium was ThO2 of intermediate crystallinity. No breakthrough of either uranium or thorium was observed in diffusion experiments involving NRVB after three years. Nevertheless, backscattering electron microscopy and microfocus X-ray fluorescence confirmed that uranium had penetrated about 40µm into the cement, implying active diffusion governed by slow dissolution-precipitation kinetics. Precise identification of the uranium solid proved difficult, displaying characteristics of both calcium uranate and becquerelite.

Item Type: Article
Subjects : Chemistry
Divisions : Faculty of Engineering and Physical Sciences > Chemistry
Authors :
NameEmailORCID
Felipe-Sotelo, Monicam.felipe-sotelo@surrey.ac.ukUNSPECIFIED
Hinchliff, JUNSPECIFIEDUNSPECIFIED
Field, LPUNSPECIFIEDUNSPECIFIED
Milodowski, AEUNSPECIFIEDUNSPECIFIED
Preedy, OUNSPECIFIEDUNSPECIFIED
Read, Davidd.read@surrey.ac.ukUNSPECIFIED
Date : 26 March 2017
Identification Number : https://doi.org/10.1016/j.chemosphere.2017.03.109
Copyright Disclaimer : © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
Uncontrolled Keywords : uranium, thorium, solubility, through-diffusion, cement.
Related URLs :
Depositing User : Symplectic Elements
Date Deposited : 29 Mar 2017 11:29
Last Modified : 04 Jul 2017 16:46
URI: http://epubs.surrey.ac.uk/id/eprint/813880

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