The Influence of Titanium Dioxide on Silicate-Based Glasses: An Evaluation of the Mechanical and Radiation Shielding Properties

The mechanical and radiation shielding features were reported for a quaternary Na2 O-CaO-SiO2-TiO2 glass system used in radiation protection. The fundamentals of the Makishima– Mazinize model were applied to evaluate the elastic moduli of the glass samples. The elastic moduli, dissociation energy, and packing density increased as TiO2 increased. The glasses’ dissociation energy increased from 62.82 to 65.33 kJ/cm3, while the packing factor slightly increased between 12.97 and 13.00 as the TiO2 content increased. The MCNP-5 code was used to evaluate the gamma-ray shielding properties. The best linear attenuation coefficient was achieved for glass samples with a TiO2 content of 9 mol%: the coefficient decreased from 5.20 to 0.14 cm−1 as the photon energy increased from 0.015 to 15 MeV. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This research was funded by the Deanship of Scientific Research at Princess Nourah bint Abdulrahman University through the Fast-Track Research Funding Program

Novel wasteforms for caesium-containing spent adsorbents from Fukushima Daiichi: a study of volatilisation and low-temperature glass processing

Remediation activities at Fukushima Daiichi have produced large volumes of highly radioactive adsorbents. These require immobilisation but are contaminated with Cs which volatilises at the temperatures typical for common methods like vitrification. Here a low temperature immobilisation process was developed. Cs volatilisation studies were conducted for three commercial adsorbents: A-51 JHP, IE-911 and IE-96. These were loaded with 8 wt.% Cs, and heated in air to establish the highest temperature that avoided volatilisation. Any Cs evolved was measured using atomic absorption spectroscopy, in the range 600-1000 C. Volatilisation started at 700ºC in all samples, with a relative volatilisation of 1.67% ±0.15% and 0.097% ±0.0080 for A-51 JHP and IE-96 respectively at 1000 C and 7.71% ± 0.66% at 900 C for IE-911 (which degraded at high temperature preventing examination at higher temperatures). This established a maximum process temperature of 600 C. Glass-Composite Material (GCM) waste forms were designed within this processing envelope. Lead borosilicate (PBS) and a lead borate (PB) compositions were chosen due to their low working temperatures. These were used to encapsulate Cs exchanged chabazite and IE-96 by low temperature sintering. A 15 wt.% mass loss, observed at 350 C, was confirmed, using evolved gas analysis mass spectroscopy, to be due to adsorbed water. Its release led to trapped gases during sintering, resulting in closed porosity in the final waste forms. A thermal treatment was developed to reduce closed porosity in the final waste form with pre-treatment (600 C) of the adsorbent prior to mixing, followed by degasification (350 C), sintering (either 400 C or 500 C) and annealing (350 C and 450 C) produced dense waste forms for both PB and PBS respectively. Wasteloadings of 50 wt.% (72.6 vol.%) in PBS GCM and 40 wt.% (65.2 vol.%) in PB GCM were achieved. No influence of Cs on the sintering behaviour was found as Cs remained sequestered in the adsorbent during sintering.Open Acces

The Influence of BaO on the Mechanical and Gamma / Fast Neutron Shielding Properties of Lead Phosphate Glasses

The mechanical features evaluated theoretically using Makishima-Mackenzie's model for glasses xBaO-(50-x) PbO–50P2O5 where x = 0, 5, 10, 15, 20, 30, 40, and 50 mol%. Wherefore, the elastic characteristics; Young's, bulk, shear, and longitudinal modulus calculated. The obtained result showed an increase in the calculated values of elastic moduli with the replacement of the PbO by BaO contents. Moreover, the Poisson ratio, micro-hardness, and the softening temperature calculated for the investigated glasses. Besides, gamma and neutron shielding ability evaluated for the barium doped lead phosphate glasses. Monte Caro code (MCNP-5) and the Phy-X/PSD program applied to estimate the mass attenuation coefficient of the studied glasses. The decrease in the PbO ratio has a negative effect on the MAC. The highest MAC decreased from 65.896 cm2/g to 32.711 cm2/g at 0.015 MeV for BPP0 and BPP7, respectively. The calculated values of EBF and EABF showed that replacement of PbO with BaO contents in the studied BPP glasses helps to reduce the number of photons accumulated inside the studied BPP glasses. © 2021 Korean Nuclear Society.Taif University, Saudi Arabia is kindly acknowledged for Supporting our work through the Project number (TURSP-2020/84)

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

Silicate and borosilicate glasses are of great importance for both the commercial and nuclear waste glass industries. Anionic species such as chloride and, more famously, sulphate are known to play a role in melting, fining and homogenization of commercial silicate glasses. At the same time, these anions can be present in abundance in several kinds of nuclear wastes destined for confinement in a multi-oxide borosilicate glass matrix (the most widely employed glass for radioactive waste immobilisation). Beyond a certain extent, it is difficult to incorporate the anionic species in commercially used radioactive waste borosilicate glasses due to their poor solubility in the molten glass and this can limit waste loading in the final waste forms, thus increasing the waste volumes and having substantial logistical and economic impacts. Besides the technological and economic repercussions faced by the waste vitrification facilities, the undissolved sulphates that precipitate as a water-soluble salt layer, are often enriched in 137Cs, 99Tc and 90Sr and can dissolve in the groundwater in geological waste repositories which raises environmental concerns. Similarly, the pyrochemical reprocessed chloride containing waste contains significant quantities of actinides such as 239Pu and 241Am which have low solubilities in the borosilicate waste glasses. Therefore, in order to formulate glass compositions with enhanced anionic capacities, a careful investigation is required to determine the anion solubility factors in such glasses. Since the structural characterisation of the industrially used borosilicate glass compositions is challenging due to the presence of multiple elements in the glass, we have designed a simplerapproach by developing binary and ternary silicate and borosilicate glasses with and without the anions added. The key focus of the thesis is to look at largely sulphate capacities of two glass systems: silicate and borosilicate glasses. Thorough spectroscopic investigation of chloride doped glasses has not been carried out due to insufficient levels of chloride retained in the two glass systems and hence makes just a side-study for the research. The undoped and sulphate doped glasses are subjected to comparative compositional and structural investigation using a range of techniques including density measurements, XRF, ICP, XRD, MAS - NMR, Raman spectroscopy, ND, and DTA, SEM - EDS, and Mössbauer spectroscopy. This thesis mostly elucidates the influence of different essential modifier oxides that are either already present or can be added / removed in the industrial waste glass compositions to enhance sulphate solubility. Density measurements show that incorporation of sulphate slightly decreases the densities of the doped glasses. XRF, ICP, SEM-EDS analyses identify the dependence of sulphate capacity on glass composition. Raman spectroscopy and 29Si MAS-NMR techniques provide measures to link sulphate capacity with structural changes in the Si/O and B/O/Si network. 23Na, 7Li MAS-NMR, though less informative, suggest changes in modifier environment with sulphate addition. Raman spectroscopy of sulphate doped glasses shows distinct bands corresponding to S-O stretching modes in silicate and borosilicate systems. The centre position of these modes is compared with S-O modes for corresponding crystalline sulphates to establish the cation environment around the sulphate ions. The increase in the degree of polymerisation of the glass network upon sulphate addition is consistent between silicate and borosilicate systems, with only a few exceptions. Neutron Diffraction is employed to study the change in coordination environment of the cations and anions in the glass upon sulphate addition. The results were collectively put intodifferent empirical models proposed to study sulphate solubility and checked for the models’ versatility. Simulated sulphate doped, multi-oxide borosilicate glasses which are broadly representative of industrial U.S. HLW / LAW waste glasses, are prepared and modified as per our investigations on simpler glasses, to study changes in its sulphur solubility. Additionally, we have also considered the effect of V2O5 addition on sulphate incorporation in the simulated radioactive waste glasses

Terbium doped glasses: their optical properties and potential applications

The optical properties of inorganic glasses doped with terbium have been investigated with particular emphasis on silicate glass systems. The effect of increasing terbium concentration on the refractive index of silicate glasses has been investigated and the optical absorption from 0.2 to 40 microns has also been studied. The energy levels of the trivalent terbium ions involved in the various optical processes have been identified by reference to theoretical predictions and spectra in other media. Glasses doped with terbium show intense series of blue and green luminescence emissions when excited by ultra-violet or X-ray radiation. Emissions from the (^5) D (_3) level of the Tb (^3+) ions produce the blue luminescence while the green emission results from transitions from the (^5) D (_4) level. At terbium concentrations above 0.3 mole % the blue emissions are quenched by multipolar transitions from the (^5) D (_3) level to the (^5) d (_4) level. The green emissions are quenched at concentrations above 6 mole % by an exchange-dipole mechanism. The effect of temperature on the emission characteristics has been determined. Intense luminescence persists to temperatures above 500 C in silicate glasses. The reduction in temperature does not greatly change the emission intensity. Inhomogeneous broadening, due to the random nature of the glass matrix, persists even at liquid helium temperatures. Decay rates have been measured at various temperatures with both ultra-violet and X-ray excitation. The effect of other rare earths on the photoluminescence has also been investigated, and a model for the lanthanide ion site is proposed. The thermoluminescence characteristics of terbium doped silicate glasses have also been measured. Increased terbium concentration reduces the glow peak intensity. A model of the mechanism producing thermoluminescence is proposed. Differences between binary (sodium silicate) and ternary (lithium aluminosilicate) glasses, observed in both photo- and thermoluminescence, are discussed. Other optical properties, such as the Faraday Effect and cathodoluminescence, are reviewed in a survey of the literature

Glassy materials for Silicon-based solar panels: present and future

About 2/3 of a commercial solar panel's weight is glass. This material should provide mechanical, chemical, and UV protection, contributing to the device's overall net energy production. Here we discuss some current trends in glassy materials for Silicon photovoltaics. The search for environmentally friendly glasses and new features such as anti-reflection, self-cleaning, and spectral conversion is reviewed. A conceptual model to compare UV-blocking and spectral converter materials is proposed, and the potential of these features to improve solar power production and its sustainability are discussed.Comment: 47 pages, 4 figure

Application of effective concrete composites to increase radiation protection of residential areas

The scientific article presents the analysis of studies of radiation safety of residential buildings in the city of Yekaterinburg, Sverdlovsk region and the results of the development of new building materials with protective properties. The review of available statistical data on the specified subject is carried out. It is revealed that the most simple and economically justified method of increasing the protection of the population from the radiation impact of man-made or natural environment is the construction of buildings with the use of innovative building materials or reconstruction of existing ones with the use of heavy concrete with effective radiation-protective aggregates. © Published under licence by IOP Publishing Ltd

Molecular Dynamics Simulations of the Structures of Europium Containing Silicate and Cerium Containing Aluminophosphate Glasses

Rare earth ion doped glasses find applications in optical and photonic devices such as optical windows, laser, and optical amplifiers, and as model systems for immobilization of nuclear waste. Macroscopic properties of these materials, such as luminescence efficiency and phase stability, depend strongly on the atomic structure of these glasses. In this thesis, I have studied the atomic level structure of rare earth doped silicate and aluminophosphate glasses by using molecular dynamics simulations. Extensive comparisons with experimental diffraction and NMR data were made to validate the structure models. Insights on the local environments of rare earth ions and their clustering behaviors and their dependence on glass compositions have been obtained. In this thesis, MD simulations have been used to investigate the structure of Eu2O3-doped silica and sodium silicate glasses to understand the glass composition effect on the rare earth ions local environment and their clustering behaviors in the glass matrix, for compositions with low rare earth oxide concentration (~1mol%). It was found that Eu–O distances and coordination numbers were different in silica (2.19-2.22 Å and 4.6-4.8) from those in sodium silicate (2.32 Å and 5.8). High tendencies of Eu clustering and short Eu-Eu distances in the range 3.40-3.90 Å were observed in pure silica glasses as compared to those of silicate glasses with much better dispersed Eu3+ ions and lower probability to form clusters. The results show Eu3+ clustering behavior dependence on the system size and suggest for low doping levels, over 12,000 atoms to obtain statistical meaningful results on the local environment and clustering for rigid silica-based glasses. The structures of four cerium aluminophosphate glasses have also been studied using MD simulations for systems of about 13,000 atoms to investigate aluminum and cerium ion environment and their distribution. P5+ and Al3+ local structures were found stable while those of Ce3+ and Ce4+ ions, through their coordination numbers and bond lengths, are glass composition-dependence. Cerium clusters were found in the high cerium glasses.P5+ coordination numbers around cerium revealed the preference of phosphorus ions in the second coordination shell. Total structure factors from MD simulations and experimental diffraction results show a general agreement from comparison for all the cerium aluminophosphate glasses and with compositional changes up to 25 Å-1. Aluminum enters the phosphate glass network mainly as AlO4 and AlO5 polyhedra only connected through corner sharing to PO4 tetrahedra identified by Q11(1 AlOx), Q12(2 AlOx), Q21(1 AlOx), and Q22(2 AlOx) species

Dissolution behavior of phosphate glasses

The solubility of phosphate glasses in aqueous solutions can be tailored through compositional control to obtain a wide range of ion release rates required for a variety of applications. The principal objective of this dissertation is to advance the understanding of the dissolution behavior of phosphate glasses in aqueous environments. Two families of glasses, sodium-iron phosphate (NFP) glasses and sodium-calcium phosphate (NCP) glasses, were evaluated. The dissolution behavior depends on the phosphate anions that constitute the glass structure and the associated metal (Me) cations. The phosphate glass structure, defined by the distribution and average size of phosphate anions and depending on the O/P and Me/P ratios, was determined by high-pressure liquid chromatography and Raman spectroscopy; Mössbauer spectrometry provided information about the coordination environment of iron. This structural information is used to explain the compositional dependence of the thermal properties and crystallization tendency of NFP glasses and melts, and the aqueous corrosion behavior of NFP and NCP glasses. Phosphate glass dissolution data are fit to different kinetic models which describe the glass dissolution mechanisms. Information about the glass composition and structure is used to predict changes in the pH of leachate solutions, and a model based on the Gibbs free energy of hydration used to explain the compositional dependence of the glass dissolution rates --Abstract, page iv

Novel method for the determination of radionuclides and their precursors in concrete using LA-ICP-MS

During the decommissioning of nuclear facilities, a range of materials are generated and need careful characterisation in order to segregate them into their appropriate waste stream. The procedures involved demand significant time and investments to accurately determine the radionuclide inventory necessary to proceed. Methodology requires sampling, homogenisation, dissolution and sometimes a separation step to measure radionuclides using their decay properties. The approach proposed here is to spatially resolve the distribution of major and trace elements in concretes, and by inference important neutron activation-induced radionuclides, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The technique offers the possibility of an onsite sampling tool for the different concrete constituents such as aggregates and sand/cement mixes at the micron scale, with typical detection limits in the ng.g-1 range for most elements. Several shielding concrete samples from Windscale (Cumbria) and CONSORT research reactor hosted by Imperial College (Silwood Park campus) are investigated. Initial work focussed on the identification and main chemistry of the aggregate types involved, using a set of chemical characteristics to fingerprint the ablated phases. Subsequently, available and manufactured calibration materials are evaluated for direct quantification purposes, together with wet chemistry reference values obtained for each concrete constituent for validation. Typical chemistry can thereafter be linked to each phase and build the overall bulk information. Finally, the potential to measure 3H directly using ICP-MS is investigated. This theoretical approach describes the conventional analysis methods and problems with ICP-MS analysis and considers several technological advances from the original instrumentation to overcome these, including the latest instrument available and figures of merit based on practical data