A Study of the Dissolution of Nuclear Waste Glasses in Highly-Alkaline Conditions

Long-term disposal of nuclear waste is a problem for the world’s nuclear energy industry. The preferred option for the UK for Intermediate- and High-Level Waste (ILW & HLW) is for long-term emplacement in a Geological Disposal Facility (GDF), which requires a robust safety case based on the long-term behaviour of the waste. This work investigates one aspect of the long-term behaviour: the dissolution of the waste in highly-alkaline conditions, in the case of the formation of a highly-alkaline plume within the GDF by the interaction of groundwater with cementitious materials. Dissolution experiments were performed on a range of glass compositions with varying CaO and MgO contents and B/Al ratios to analyse their effects on glass dissolution at high-pH. Ca and Mg are expected to be present in the GDF and in UK HLW, and are known to significantly affect glass dissolution. The effect of varying B/Al ratio is relevant to the comparison of natural glasses (B/Al = 0), with nuclear waste glasses (B/Al ~ 1 – 10). Magic-Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy was performed to identify the effects of composition on glass structure. Dissolution experiments were also performed on existing glasses pertinent to UK nuclear waste disposal to determine their performance. The addition of CaO and MgO, in replacement for Na2O, was found to lead to a decrease in IVB units, due to the inability of the divalent Ca2+ and Mg2+ cations to charge-compensate for two IVB tetrahedra each. The increased strength of this effect in the Mg-containing glasses suggests that Mg may be behaving as an intermediate oxide. Increasing the ratio of B/Al in aluminoborosilicate glasses was found to lead to an increase in the proportion of IVB units. Glass dissolution resistance was found to correlate with replacement of Na2O for CaO and MgO. Ca-containing glasses displayed a higher dissolution resistance than those containing Mg, due to a combination of structural and solution factors. Increasing the B/Al ratio of the glasses led to a decrease in dissolution resistance, believed to be due to the greater resistance of Si – O – Al bonds to hydrolysis compared to Si – O – B bonds. The leachant cation (Ca or K) was found to have a significant effect on dissolution behaviour. The International Simple Glass (ISG) was found to behave differently to MW-25% (UK simulant HLW glass) in Ca-rich, high-pH solutions, suggesting that it is not helpful as an analogue for the dissolution of UK nuclear waste glasses. The dissolution of a laboratory-made basaltic glass was found to be partially comparable to that of natural basaltic glasses, indicating that care must be taken when comparing the dissolution resistance of natural basaltic glasses with nuclear waste glasses. Significant localisation of elements in alteration layers during dissolution, e.g. Zr for ISG, suggests that the mechanism of dissolution in these experiments was coupled dissolution-reprecipitation

Investigation of the role of Mg and Ca in the structure and durability of aluminoborosilicate glass

The structure and dissolution behaviour of Na 2 O·CaO·(15–x)Al 2 O 3 ·xB 2 O 3 ·SiO 2 and Na 2 O·MgO·(15–x)Al 2 O 3 ·xB 2 O 3 ·SiO 2 glasses, relevant to compositions of UK nuclear waste glass, have been investigated using nuclear magnetic resonance (NMR) spectroscopy and static dissolution experiments using the PCT protocol. Structural data from 11 B, 27 Al and 29 Si NMR analyses show that increasing the [B 2 O 3 ]/([Al 2 O 3 ] + [B 2 O 3 ]) ratio of the alkali-alkaline-earth aluminoborosilicate glasses led to an overall decrease in the proportion of non-silicate tetrahedral species ( IV Al + IV B) and a decrease in Si–O–X bonds (X[dbnd]B, Al). The Mg-containing glasses exhibited lower IV B fractions than their Ca-containing counterparts, which is thought to be due to the presence of IV Mg tetrahedra in the network. The measured corrosion rates were similar for both Ca and Mg-containing glasses although unexpectedly some Ca-containing glasses exhibited higher corrosion losses than the Mg-containing ones for time periods up to 112 d. However, there was evidence of a greater tendency to rate resumption in the Mg containing than the Ca containing ones. Alteration products were found to contain Ca, Si and Al with the Ca containing glasses and Ca, Mg, Si and Al with the Mg containing glasses; Na was not detected in the alteration products although its presence cannot be ruled out based on the data obtained

X-Ray fluorescence analysis of feldspars and silicate glass: effects of melting time on fused bead consistency and volatilisation

Reproducible preparation of lithium tetraborate fused beads for XRF analysis of glass and mineral samples is of paramount importance for analytical repeatability. However, as with all glass melting processes, losses due to volatilization must be taken into account and their effects are not negligible. Here the effects of fused bead melting time have been studied for four Certified Reference Materials (CRM’s-three feldspars, one silicate glass), in terms of their effects on analytical variability and volatilization losses arising from fused bead preparation. At melting temperatures of 1065 °C, and for feldspar samples, fused bead melting times shorter than approximately 25 minutes generally gave rise to greater deviation of XRF-analyzed composition from certified composition. This variation might be due to incomplete fusion and / or fused bead inhomogeneity but further research is needed. In contrast, the shortest fused bead melting time for the silicate glass CRM gave an XRF-analyzed composition closer to the certified values than longer melting times. This may suggest a faster rate of glass-in-glass dissolution and homogenization during fused bead preparation. For all samples, longer melting times gave rise to greater volatilization losses (including sulphates and halides) during fusion. This was demonstrated by a linear relationship between SO3 mass loss and time1/2, as predicted by a simple diffusion-based model. Iodine volatilization displays a more complex relationship, suggestive of diffusion plus additional mechanisms. This conclusion may have implications for vitrification of iodine-bearing radioactive wastes. Our research demonstrates that the nature of the sample material impacts on the most appropriate fusion times. For feldspars no less than ~25 min and no more than ~60 min of fusion at 1065 °C, using Li2B4O7 as the fusion medium and in the context of feldspar samples and the automatic fusion equipment used here, strikes an acceptable (albeit non-ideal) balance between the competing factors of fused bead quality, analytical consistency and mitigating volatilization losses. Conversely, for the silicate glass sample, shorter fusion times of less than ~30 minutes under the same conditions provided more accurate analyses whilst limiting volatile losses

Using iPads to increase the level of student engagement in the peer review and feedback process.

This investigation explored the use of iPads in an HE setting in order to evaluate how and if they could enhance an already established approach to peer review and feedback. The context centred on a cohort of 140 pre-service teacher education students engaged in small group assessed activities in one of their modules. Although some aspects of the existing formative assessment process worked well, the level of student engagement in peer review was felt to need improvement. An opportunity to explore the use of iPads in group work and collaborative learning environments arose as part of the York St John University (YSJ) iPad Project. The management and deployment of the iPads was based on Apple’s ‘institutional’ model and was informed by the YSJ Technology Enhanced Learning quality framework

X-ray Fluorescence Analysis of Feldspars and Silicate Glass: Effects of Melting Time on Fused Bead Consistency and Volatilisation

Reproducible preparation of lithium tetraborate fused beads for XRF analysis of glass and mineral samples is of paramount importance for analytical repeatability. However, as with all glass melting processes, losses due to volatilisation must be taken into account and their effects are not negligible. Here the effects of fused bead melting time have been studied for four Certified Reference Materials (CRM’s: three feldspars, one silicate glass), in terms of their effects on analytical variability and volatilisation losses arising from fused bead preparation. At melting temperatures of 1065 °C, and for feldspar samples, fused bead melting times shorter than approximately 25 min generally gave rise to a greater deviation of the XRF-analysed composition from the certified composition. This variation might be due to incomplete fusion and/or fused bead inhomogeneity but further research is needed. In contrast, the shortest fused bead melting time for the silicate glass CRM gave an XRF-analysed composition closer to the certified values than longer melting times. This may suggest a faster rate of glass-in-glass dissolution and homogenization during fused bead preparation. For all samples, longer melting times gave rise to greater volatilisation losses (including sulphates and halides) during fusion. This was demonstrated by a linear relationship between SO3 mass loss and time1/2, as predicted by a simple diffusion-based model. Iodine volatilisation displays a more complex relationship, suggestive of diffusion plus additional mechanisms. This conclusion may have implications for vitrification of iodine-bearing radioactive wastes. Our research demonstrates that the nature of the sample material impacts on the most appropriate fusion times. For feldspars no less than ~25 min and no more than ~60 min of fusion at 1065 °C, using Li2B4O7 as the fusion medium and in the context of feldspar samples and the automatic fusion equipment used here, strikes an acceptable (albeit non-ideal) balance between the competing factors of fused bead quality, analytical consistency and mitigating volatilisation losses. Conversely, for the silicate glass sample, shorter fusion times of less than ~30 min under the same conditions provided more accurate analyses whilst limiting volatile losses

A study of risk-aware program transformation

In the trend towards tolerating hardware unreliability, accuracy is exchanged for cost savings. Running on less reliable machines, functionally correct code becomes risky and one needs to know how risk propagates so as to mitigate it. Risk estimation, however, seems to live outside the average programmer’s technical competence and core practice. In this paper we propose that program design by source-to-source transformation be risk-aware in the sense of making probabilistic faults visible and supporting equational reasoning on the probabilistic behaviour of programs caused by faults. This reasoning is carried out in a linear algebra extension to the standard, `a la Bird-Moor algebra of programming. This paper studies, in particular, the propagation of faults across standard program transformation techniques known as tupling and fusion, enabling the fault of the whole to be expressed in terms of the faults of its parts.Fundação para a Ciência e a Tecnologia, Portugal, under grant number BI1-2012 PTDC/EIA-CCO/122240/2010 UMINHO

COVID 19:Seroprevalence and vaccine responses in UK dental care professionals

Dental care professionals (DCPs) are thought to be at enhanced risk of occupational exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, robust data to support this from large-scale seroepidemiological studies are lacking. We report a longitudinal seroprevalence analysis of antibodies to SARS-CoV-2 spike glycoprotein, with baseline sampling prior to large-scale practice reopening in July 2020 and follow-up postimplementation of new public health guidance on infection prevention control (IPC) and enhanced personal protective equipment (PPE). In total, 1,507 West Midlands DCPs were recruited into this study in June 2020. Baseline seroprevalence was determined using a combined IgGAM enzyme-linked immunosorbent assay and the cohort followed longitudinally for 6 mo until January/February 2021 through the second wave of the coronavirus disease 2019 pandemic in the United Kingdom and vaccination commencement. Baseline seroprevalence was 16.3%, compared to estimates in the regional population of 6% to 7%. Seropositivity was retained in over 70% of participants at 3- and 6-mo follow-up and conferred a 75% reduced risk of infection. Nonwhite ethnicity and living in areas of greater deprivation were associated with increased baseline seroprevalence. During follow-up, no polymerase chain reaction–proven infections occurred in individuals with a baseline anti–SARS-CoV-2 IgG level greater than 147.6 IU/ml with respect to the World Health Organization international standard 20-136. After vaccination, antibody responses were more rapid and of higher magnitude in those individuals who were seropositive at baseline. Natural infection with SARS-CoV-2 prior to enhanced PPE was significantly higher in DCPs than the regional population. Natural infection leads to a serological response that remains detectable in over 70% of individuals 6 mo after initial sampling and 9 mo from the peak of the first wave of the pandemic. This response is associated with protection from future infection. Even if serological responses wane, a single dose of the Pfizer-BioNTech 162b vaccine is associated with an antibody response indicative of immunological memory

Biomass Ashes as Potential Raw Materials for Mineral Wool Manufacture: Initial Studies of Glass Structure and Chemistry

The energy intensive and CO2-generating nature of commercial mineral wool and glass production necessitates advances and changes in materials and processes. The derivation of raw materials from waste products arising from biomass energy generation offers the possibility of a two-fold environmental benefit: partial replacement of carbonate raw minerals in production, leading to lower CO2 release during melting; and the utilisation and valorisation of byproducts which may otherwise be sent to landfill. Glass samples with a basaltic mineral wool composition were produced with additions to the raw materials of 0, 1, 5 and 10 wt% of a fly ash and a bottom ash arising from biomass combustion. The resulting glasses were analysed by x-ray fluorescence (XRF), x-ray diffraction (XRD), dilatometry, 57 Fe Mössbauer and Raman spectroscopies, and their densities, molar volumes and viscosity–temperature profiles were calculated and compared against benchmark glass samples. All biomass ash-containing glasses were closely similar in both composition and properties to the benchmark glass, with up to 10 wt% ash additions to the raw materials. In addition, the use of the biomass fly ash led to a reduction in batch CO2 content estimated to be 1 · 5 kg CO2 per tonne of batch for each 1 wt% addition. These initial results provide evidence supporting the further development of these ash materials as potential value-added raw materials for mineral wool manufacture