Effect of Zn- and Ca-oxides on the structure and chemical durability of simulant alkali borosilicate glasses for immobilisation of UK high level wastes

Abstract

Article available under the terms of the CC-BY-NC-ND licence (https://creativecommons.org/licenses/by-nc-nd/4.0/) eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse This article is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) licence. This licence only allows you to download this work and share it with others as long as you credit the authors, but you can't change the article in any way or use it commercially. More information and the full terms of the licence here: https://creativecommons.org/licenses/ Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. alter the glass structure, with changes identified in both borate and silicate glass networks using Raman 50 spectroscopy. In particular, these glasses were characterised by a significantly higher Q 3 species, which we 51 attribute to Si-O-Zn linkages; addition of ZnO and CaO to the glass composition therefore enhanced glass 52 network polymerisation. The increase in network polymerisation, and the presence of spinel crystallites, were 53 found to increase the glass viscosity of the ZnO / CaO modified base glass; however the viscosities were within 54 the accepted range for nuclear waste glass processing. The ZnO / CaO modified glass compositions were 55 observed to be significantly more durable than the Na 2 O / Li 2 O base glass up to 28 days, due to a combination 56 of the enhanced network polymerisation and the formation of Ca / Si containing alteration layers.

Comment on “Preliminary assessment of modified borosilicate glasses for chromium and ruthenium immobilization”, by Farid and Rahman

“…In a recent publication, Farid and Rahman reported an investigation of alkali borosilicate glasses applied for the immobilisation of UK radioactive wastes [1]. Aspects of this study are inconsistent with previous investigation of these materials [2][3][4][5] and require clarification, as we highlight in this comment on their study.…”

“…In fact, Zn K-edge X-ray absorption spectroscopy has demonstrated Zn to primarily participate in network formation in such glasses, as ZnO 4 polyhedra (Zn-O distance of 1.95 ± 0.01Å), linking, on average, to 2 ± 1 SiO 4 units via bridging oxygen atoms [2]. This conclusion was later verified by Raman spectroscopy investigation and molecular dynamics simulations of the structure of closely related UK HLW glass compositions [3,4].…”

“…CaO and ZnO modified glass, prepared in our laboratory, for the immobilisation of HLW derived principally from Magnox fuel reprocessing [2,4,5]. Farid and Rahman incorrectly attribute the source of Cr 2 O 3 in this glass to "the result of Magnox declading and dissolution processes" [1].…”

“…In the UK, and internationally, alkali borosilicate glasses are the material of choice for vitrification of the fission products and minor actinides arising from nuclear fuel reprocessing, classified as High Level Waste (HLW) [2][3][4][5][6][7]. Modification of the UK HLW glass composition, by addition of CaO and ZnO, has been studied with the aim of improving processing characteristics and long term durability, as discussed elsewhere [2][3][4][5][6].…”

Structural characterization of sulphate and chloride doped glasses for radioactive waste immobilisation

“…It also inhibited surface swelling, thereby decreasing transport rates of ions (Lyle et al 1936;Wassick et al 1983;McGrail et al 1984). Small additions of ZnO and CaO to the glass frit further enhanced the corrosion resistance and chemical durability of the glass (Tait & Jensen 1982;Calestani et al 1986;Zhang et al 2015;Frugier et al 2005;Smets et al 1984). The oxides also decrease the viscosity of the glass at high temperatures (1000-1200 o C) (Gehlhoff & Thomas 1926).…”