New insight studies of the secondary phase formation under repository conditions. (2020)

• Record Type: Journal Article
• Authors: Rodríguez-Villagra, N.; Bonales, L.J.; Cobos, J.
• Is Part Of: MRS advances. Volume 5:Number 11(2020)
• Page Start: 539
• Page End: 547
• Publication Date: 2020
• Subjects: nuclear materials, -- waste management, -- radiation effects, -- Raman spectroscopy, -- U; Electrical engineering -- Congresses; Physics -- Congresses; Materials -- Research -- Congresses; Materials science -- Congresses; 620.11
• DOI: 10.1557/adv.2020.120
• Languages: English
• ISSNs: 2059-8521

Abstract

ABSTRACT: In a deep geological repository (DGR) scenario, uranium oxidized in aqueous systems will be stabilized as UO2 2+ (hexavalent uranium), as a consequence of tetravalent uranium oxidation by radiolytic byproducts. Uranyl cationic species (UO2 2+ ) in different speciation forms are expected to be found at the whole pH range conditions. The importance of UO2 2+ lies in its potential incorporation of trace radioelements onto secondary uranyl phases. In view of the difficulty of U chemistry in natural groundwater, it is necessary to improve speciation assessment techniques so as to understand chemical processes. Raman spectroscopy has been shown as a powerful tool to analyze the speciation of various actinyl (UO2 2+, NpO2 + and PuO2 2+ ) and to determine the distribution of those elements which are more likely to be stable in a near-field groundwater environment. Therefore, the aim of this work is to follow UO2 2+ changes as a consequence of γ radiation in aqueous media under DGR conditions, and to understand the behavior of UO2 2+ as a function of aqueous media, which help to understand and predict the potential precipitation of the solid phases formed. In this work, the use of Raman spectroscopy adapted to the empirical analysis of different nuclear applications for initial uranium concentrations 0.04M at ambient atmosphere is shown, i.e. as monitoring tool for UO2 2+ precipitation as a function of pH, studying UO2 (NO3 )2 ·6H2 O stability in aqueous solutions representative of groundwater, in particular at ionic strength I = 0.02 – 0.4 M and pH from 7 to 13.2; and to evaluate the effect of γ radiation fields. At 10 −4 -10 -3 M of radiolytically formed H2 O2 concentration, the amount of uranium in solution decreased, as a results of secondary phases precipitation. The results obtained will be useful to the performance assessment studies of the Spent Nuclear Fuel (SNF) stored in DGRs. The work performed provides a partial picture of secondary phase formations, as a result of corrosion of SNF in a DGR.