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Archaeological glasses with prolonged exposure to biogeochemical processes in the environment can be used to understand glass alteration, which is important for the safe disposal of vitrified nuclear waste. Samples of mafic and felsic glasses with different chemistries, formed from melting amphibolitic and granitoid rocks, were obtained from Broborg, a Swedish Iron Age hillfort. Glasses were excavated from the top of the hillfort wall and from the wall interior. A detailed microscopic, spectroscopic, and diffraction study of surficial textures and chemistries were conducted on these glasses. Felsic glass chemistry was uniform, with a smooth surface showing limited chemical alteration (

Reactive spark plasma sintering has been utilised as a high-throughput processing route for the synthesis of two simulant zirconolite wasteform materials, targeting Ca0.80Ce0.20ZrTi1.60M0.40O7 (M = Fe3+ and Al3+). Materials were processed under 15 MPa uniaxial pressure, with heating/cooling rates of 100 °C/min to 1320 °C, maintained under vacuum. Despite moderate yield (> 80 wt%) of zirconolite-2M, a considerable Ce-rich perovskite phase was formed in both formulations, attributed to complete reduction of the Ce inventory to Ce3+, as determined by Ce L3-edge XANES analysis. The composition charge balanced with Al3+ was favoured on the basis of lower accompanying perovskite fraction. Graphical abstract

Altering the CaO to ZnO ratio of alkali borosilicate glass, in favour of ZnO, causes phase separation with hardystonite-like (Ca2ZnSi2O7) and willemite-like (ZnSi2O4) structures identified. This is concurrent with increased glass durability.

This work elaborates and evaluates approaches to the construction of 2D speciation maps, in an effort to maximize sensitivity to the U oxidation state at the U L 3-edge, applied to a suite of synthetic Chernobyl lava specimens., Uranium speciation and redox behaviour is of critical importance in the nuclear fuel cycle. X-ray absorption near-edge spectroscopy (XANES) is commonly used to probe the oxidation state and speciation of uranium, and other elements, at the macroscopic and microscopic scale, within nuclear materials. Two-dimensional (2D) speciation maps, derived from microfocus X-ray fluorescence and XANES data, provide essential information on the spatial variation and gradients of the oxidation state of redox active elements such as uranium. In the present work, we elaborate and evaluate approaches to the construction of 2D speciation maps, in an effort to maximize sensitivity to the U oxidation state at the U L 3-edge, applied to a suite of synthetic Chernobyl lava specimens. Our analysis shows that calibration of speciation maps can be improved by determination of the normalized X-ray absorption at excitation energies selected to maximize oxidation state contrast. The maps are calibrated to the normalized absorption of U L 3 XANES spectra of relevant reference compounds, modelled using a combination of arctangent and pseudo-Voigt functions (to represent the photoelectric absorption and multiple-scattering contributions). We validate this approach by microfocus X-ray diffraction and XANES analysis of points of interest, which afford average U oxidation states in excellent agreement with those estimated from the chemical state maps. This simple and easy-to-implement approach is general and transferrable, and will assist in the future analysis of real lava-like fuel-containing materials to understand their environmental degradation, which is a source of radioactive dust production within the Chernobyl shelter.

Fenton or Fenton-like oxidation for treatment of organic radioactive wastes is a promising technology with applications to a range of organic wastes. This review details this process; exploring potential challenges, pitfalls and opportunities for industrial usage with radioactive wastes. The application of this process to real radioactive wastes within pilot-plant settings has been documented, with key findings critically assessed in the context of future waste production. Although this oxidation process has not found mainstream success in treatment of radioactive wastes, a lower temperature oxidation system bring certain benefits, specifically for higher volume or problematic organic wastestreams.

Abstract Refractory ‘stuffed’ pyrochlores such as Gd2TiO5 are of interest for nuclear applications, including as matrices for actinide disposition and as neutron absorbers in control rods. Here, we report the results of a preliminary comparative investigation of the synthesis of Gd2TiO5 by molten salt and conventional solid-state synthesis. We show that synthesis of Gd2TiO5 proceeds from the pyrochlore phase Gd2Ti2O7 which is first formed as a kinetic product. Molten salt synthesis afforded single phase Gd2TiO5 at 1300 °C in 2 h, via a template growth mechanism, and is effective for the synthesis of these refractory materials. This work demonstrates molten salt mediated synthesis of ‘stuffed’ pyrochlore for the first time. Graphic abstract

Disposal of spent nuclear fuel poses significant challenges, as the UO2 and fission products are under constant irradiation and must be safely stored for millennia. CeO2 is a non-radioactive analog for UO2 for studying microstructure and its evolution. Many techniques have been applied to uranium and cerium oxides to investigate point defects. Positron annihilation spectroscopies (PAS) are sensitive to neutral and negatively charged vacancy-like point defects and impurity vacancy complexes. PAS has been applied previously to UO2+x to investigate nuclear fuels, but virtually no PAS work exists on CeO2. Here, the basics of positron annihilation spectroscopy is reviewed, and preliminary work on undoped and doped CeO2 is shown and compared to the literature results from UO2. To simulate fission product incorporation in spent nuclear fuels, CeO2 samples were doped at different concentration with yttrium. Select samples were irradiated with heavy ions at different doses. Doping and irradiation are shown to give rise to different defect characteristics.

A sample of zirconolite with nominal composition Ca0.80Ce0.20ZrTi1.60Cr0.40O7was processed via Hot Isostatic Pressing (HIP), with a dwell temperature and pressure of 1320 °C/100 MPa maintained for 4 h. The produced wasteform was characterised by powder XRD, SEM–EDS, Ce L3and Cr K-edge XANES. A significant portion of the Ce inventory did not fully partition within the zirconolite phase, instead remaining as CeO2within the microstructure. Inspection of the stainless steel–ceramic interface detailed the presence of an interaction region dominated by a Cr-rich oxide layer. No significant Cr or Fe migration was observed, although a greater concentration of perovskite was observed at the periphery, relative to the bulk ceramic matrix. The X-ray absorption features of Cr remained analogous with Cr3+accommodation within TiO6octahedra in the zirconolite matrix. The absorption edge of Ce was comprised of contributions from zirconolite-2M and unincorporated CeO2, with an average oxidation state of Ce3.9+. As zirconolite-2M accounted for > 92 wt% of the overall phase assemblage, it is clear that the dominant oxidation state of Ce in this phase was Ce4+.Graphic abstract

A series of zirconolite ceramics with composition CaZr1‐xThxTi2O7 (Δx = 0.10) were reactively sintered at 1350 ˚C for 20 h, in air (0 ≤ x ≤ 0.60) and 5% H2/N2 (0 ≤ x ≤ 0.40). A sample with composition corresponding to x = 0.20 was also produced by hot isostatic pressing (HIP) at 1300 ˚C and 100 MPa for 4 h. Th4+ immobilisation was most readily achieved under oxidising conditions, with Th4+ preferentially incorporated within a pyrochlore‐structured phase in the range 0.10 ≤ x ≤ 0.50, yet formation of the zirconolite‐4M polytype was not observed. We report the novel synthesis of single phase pyrochlore with nominal composition CaZr0.40Th0.60Ti2O7 when targeting x = 0.60. Th4+ incorporation under reducing conditions produced a secondary Th‐bearing perovskite, comprising 24.2 ± 0.6 wt. % of the phase assemblage when targeting x = 0.40, alongside 8.8 ± 0.3 wt. % undigested ThO2. Under reducing conditions, powder XRD data were consistent with zirconolite adopting the 3T polytype structure. The sample produced by HIP presented a non‐equilibrium phase assemblage, yielding a major phase of zirconolite‐2M alongside accessory Th4+ bearing phases ThTi2O6, ThO2 and perovskite. These data highlight the efficacy of Th4+ as a Pu4+ surrogate, with implications for the formation of Zr‐stabilised Th‐pyrochlore phases as matrices for waste with elevated Th4+ content.

The influence of increasing the waste loading of Ca- and Zn-containing MW high-level-waste glass, from 20 to 35 wt%, on the chemical durability was investigated using 112-day PCT-B tests at 90 °C in ultra-high-quality water. During the initial stage of dissolution, from 0 to 3 days, increased waste loadings corresponded to reduced boron dissolution rates. By 112 days, however, there was no difference in the normalised mass loss of boron as a function of waste loading, within experimental uncertainty. In comparison to literature values obtained for traditional MW high-level-waste glasses, containing no Ca and Zn, the boron dissolution rates of CaZn MW glasses in the residual stage of dissolution, > 28 days, were greater by at least an order of magnitude. Analysis of secondary phases, combined with geochemical modelling of the solutions, indicate that the dual formation of Mg- and Zn-smectite phyllosilicate clays, potentially saponite (Ca0.2Mg3(Si,Al)4O10(OH)2·4H2O) and sauconite (Na0.3Zn3(Si, Al)4O10(OH)2·nH2O), respectively, may be the cause of this enhanced dissolution.

Zirconolite (CaZrTi2O7) has been identified as a candidate ceramic wasteform for the immobilisation and disposal of Pu inventories, for which there is no foreseen future use. Here, we provide an ov...

Low-temperature soft chemical synthesis routes to transition-metal nitrides are of interest as an alternative to conventional high-temperature ammonolysis reactions involving large volumes of chemotoxic NH3 gas. One such method is the reaction between metal oxides and NaNH2 at ca. 200 °C to yield the counterpart nitrides; however, there remains uncertainty regarding the reaction mechanism and product phase assemblage (in particular, noncrystalline components). Here, we extend the chemical tool box and mechanistic understanding of such reactions, demonstrating the nitridation of Fe3O4 by reaction with NaNH2 at 170–190 °C, via a pseudomorphic reaction. The more reduced Fe3O4 precursor enabled nitride formation at lower temperatures than the previously reported equivalent reaction with Fe2O3. The product phase assemblage, characterized by X-ray diffraction, thermogravimetric analysis, and 57Fe Mossbauer spectroscopy, comprised 49–59 mol % e-Fe2+xN, accompanied by 29–39 mol % FeO1–xNx and 8–14 mol % γ″-FeN. The oxynitride phase was apparently noncrystalline in the recovered product but could be crystallized by heating at 180 °C. Although synthesis of transition-metal nitrides is achieved by reaction of the counterpart oxide with NaNH2, it is evident from this investigation that the product phase assemblage may be complex, which could prove a limitation if the objective is to produce a single-phase product with well-defined electrical, magnetic, or other physical properties for applications. However, the significant yield of the FeO1–xNx oxynitride phase identified in this study opens the possibility for the synthesis of metastable oxynitride phases in high yield, by reaction of a metal oxide substrate with NaNH2, with either careful control of H2O concentration in the system or postsynthetic hydrolysis and crystallization.

Detailed chemical analysis of the solidified molten fuel still residing in the stricken Chernobyl reactor unit 4 are inferred using multi-modal micro-focus X-ray analysis of a low-radioactivity proxy. A fascinating mixture of molten UO2, nuclear fuel cladding, concrete, stainless steel and other nuclear reactor components, these materials behaved like lava, solidifying to form a complex, highly radioactive glass-ceramic. Using element-specific chemical probes (micro-X-ray fluorescence and X-ray absorption spectroscopy), coupled with micro-diffraction analysis, the crystalline phase assemblage of simulants of these heterogeneous materials was established, which included “chernobylite” and a range of compositions in the (U1−xZrx)O2 solid solution. Novel insight to nuclear accident fuel chemistry was obtained by establishing the oxidation state and local coordination of uranium not only in these crystalline phases, but uniquely in the amorphous fraction of the material, which varied depending on the history of the nuclear lava as it flowed through the reactor. This study demonstrates that micro-focus X-ray analysis of very small fractions of material can yield rich chemical information, which can be applied to nuclear-melt down materials to aid decommissioning and nuclear fuel management at nuclear accident sites.

Struvite-K (MgKPO4·6H2O) is a magnesium potassium phosphate mineral with naturally cementitious properties, which is finding increasing usage as an inorganic cement for niche applications including...

A series of Ca1-xCexZrTi2-2xCr2xO7 zirconolite ceramics (0 ≤ x ≤ 0.35) were reactively sintered in air at 1350 °C for 20 h. Single phase zirconolite-2M was formed for x ≤ 0.15, with Cr2O3 and an undesirable Ce-bearing perovskite phase present above x = 0.20. Electron diffraction analysis confirmed that the zirconolite-2M polytype was maintained over the solid solution. X-ray absorption near edge structure (XANES) data determined that between 10–20% Ce was speciated as Ce3+, and Cr was present uniformly as Cr3+ with near edge features consistent with occupation of octahedral sites within the zirconolite-2M structure. A sample corresponding to x = 0.20 was processed by reactive spark plasma sintering (RSPS), with a rapid processing time of less than 1 h. XANES data confirmed complete reduction to Ce3+ during RSPS, promoting the formation of a Ce-bearing perovskite, comprising 19.3 ± 0.4 wt. % of the phase assemblage.

Technetium-99 immobilization in low-temperature nuclear waste forms often relies on additives that reduce environmentally mobile pertechnetate (TcO4-) to insoluble Tc(IV) species. However, this is ...

The synthesis, characterization, and crystal structure of a novel (dominant) uranium(V) brannerite of composition U

The Black Death had a devastating impact on communities living in Europe during the mid-14th century. The devastation wreaked by the epidemic was thought to lead to the disruption of social norms, including those surrounding the burial of the dead. Some scholars have, however, suggested this was not always the case, in particular for those communities living in rural settings (Kacki et al., 2011). Recent excavation at Thornton Abbey in Lincolnshire revealed two burial populations; one associated with the abbey’s medieval hospital, and the other a mass grave that was in use during the Black Death epidemic. Together with the mass grave and post-epidemic burials from East Smithfield, London, these two populations presented an opportunity to explore the early taphonomic histories of the plague dead through the inspection of bone diagenesis associated with bacterial soft tissue decomposition. The histological analysis of 81 skeletons revealed striking differences in the post-mortem treatment of the plague dead in rural Lincolnshire compared to those buried in urban London, and in this paper we explore the possible scenarios that may account for this variability. We also present three cases where the individuals’ status in life may have led to attempts at inhibiting their corporeal decay.

The influence of A-site vacancies on zirconate perovskite structured ceramics of formula A1−xLa2x/3ZrO3 (A = Ca, Sr, Ba) has been investigated using 400 keV Kr+in situ ion irradiation in a TEM with varied temperature from 100 K to 673 K. The solubility limit of La within the Ba1−xLa2x/3ZrO3 system was 5.33 ml% (x = 0.08) using a solid-state synthesis route, with space group symmetry of Pmm for x ≤ 0.08. The Ca0.9La0.067ZrO3 and Sr0.9La0.067ZrO3 samples were found to synthesise single-phase with the Pcmn and Pbnm symmetries of their respective end member structures. The addition of 6.67 ml% La (x = 0.1) in CaZrO3 and SrZrO3 was found to decrease the critical temperature of amorphisation, Tc, in comparison with the undoped structures. A similar decrease was found for the 5.33 ml% La doped BaZrO3 structure. Namely, values were observed for doped samples of ≈404 K, ≈520 K and ≈621 K (A = Sr, Ca, Ba respectively), compared to ≈440 K, ≈623 K and ≈675 K for SrZrO3, CaZrO3 and BaZrO3, respectively. This follows similar behaviour to that observed in titanate systems at low dopant levels, and these findings have been discussed in relation to both the presence of cation vacancies in the doped samples and the presence of the La cation. Void formation, growth and induced morphology changes have also been characterised, onset by ion irradiation.

Understanding the physical and chemical properties of materials arising from nuclear meltdowns, such as the Chernobyl and Fukushima accidents, is critical to supporting decommissioning operations and reducing the hazard to personnel and the environment surrounding the stricken reactors. Relatively few samples of meltdown materials are available for study, and their analysis is made challenging due to the radiation hazard associated with handling them. In this study, small-scale batches of low radioactivity (i.e., containing depleted uranium only) simulants for Chernobyl lava-like fuel-containing materials (LFCMs) have been prepared, and were found to closely approximate the microstructure and mineralogy of real LFCM. The addition of excess of ZrO2 to the composition resulted in the first successful synthesis of high uranium–zircon (chernobylite) by crystallisation from a glass melt. Use of these simulant materials allowed further analysis of the thermal characteristics of LFCM and the corrosion kinetics, giving results that are in good agreement with the limited available literature on real samples. It should, therefore, be possible to use these new simulant materials to support decommissioning operations of nuclear reactors post-accident.

The dissolution of the United Kingdom’s vitrified high-level-waste simulant, CaZn MW28, was investigated following the Product Consistency Test-B protocol for 112 d at 90 °C and in ultra-high-quality water. Residual rate dissolution (stage II) and rate resumption (stage III), after 28 d, was observed. Thermodynamic modelling suggested that solutions were saturated with respect to Mg- and Zn-bearing phases, and the presence of Mg- and Zn-smectite clays was tentatively observed. The formation of these phases was concurrent with a significant increase in the dissolution rate, similar to Stage III behavior seen in other nuclear waste simulant glass materials, indicating that the addition of Mg and Zn to high-level-waste glass (7.3 wt. % combined) significantly influences the dissolution rate.

Nuclear fuel debris generated at the Fukushima Daiichi nuclear power plant during the loss of coolant accident in 2011, still resides within the reactor units, constantly cooled by water. Until it is retrieved, the fuel debris will corrode, releasing radioactive elements into the coolant water and the ground surrounding the reactors. To predict the corrosion behaviour of these materials, and to establish parameters for experiments with U-containing and real fuel debris, the corrosion of two surrogate fuel debris materials, with a composition of Ce(1-x)ZrxO2 (x = 0.2 and 0.4), was investigated. Materials were synthesised by a wet chemistry route and pellets were sintered at 1700°C in air atmosphere. Due to the slow corrosion kinetics, aggressive conditions were applied, and corrosion experiments were performed in 9 mol.L^-1 HNO3 under static conditions. The incorporation of Zr into the structure of Ce reduced the normalised dissolution rate; from (3.75 ± 0.15) × 10-6 g.m-2.d-1 to (4.96 ± 0.28) × 10^-6 g.m^-2.d^-1 for RL(Ce) of Ce0.8Zr0.2O2 and Ce0.6Zr0.4O2, respectively.

The synthesis of a palladium-containing iodovanadinite derivative, hypothetically “PdPb9(VO4)6I2”, was attempted using PdI2 as a source of iodine in searching for a novel waste form for radioiodine. Stoichiometric amounts of Pb3(VO4)2 and PdI2 were batched and reacted at elevated temperatures in sealed vessels. Batched material was also subjected to high-energy ball-milling (HEBM) in order to reduce reaction time and the potential for iodine volatilization during subsequent reaction at 200–500 °C. The resulting products were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, IR spectroscopy, thermal analysis and Pd K XANES. Results showed that PdI2 can function as a sacrificial iodine source for the formation of iodovanadinite, prototypically Pb10(VO4)6I2, however, the incorporation of Pd into this phase was not definitively observed. The sacrificial reaction mechanism involved the decomposition of PdI2 to Pd metal and nascent I2, with the latter incorporated into the iodovanadinite Pb10(VO4)6I2 phase. In comparison to processing using standard solid state reaction techniques, the use of HEBM prior to high temperature reaction generates a more homogeneous end-product with better iodine retention for this system. Overall, the key novelty and importance of this work is in demonstrating a method for direct immobilisation of undissolved PdI2 from nuclear fuel reprocessing, in a composite wasteform in which I-129 is immobilised within a durable iodovandinite ceramic, encapsulating Pd metal.

X-ray Absorption Spectroscopy is a technique of fundamental importance in nuclear waste management, as an element specific probe of speciation, which governs radionuclide solubility, immobilisation and migration. Here, we exploit recent developments in laboratory instrumentation for X-ray Absorption Spectroscopy, based on a Rowland circle geometry with a spherically bent crystal analyser, to demonstrate speciation in prototype ceramic and glass-ceramic waste forms. Laboratory and synchrotron XANES data acquired from the same materials, at the Ce and U L3 edges, were found to be in excellent quantitative agreement. We establish that analysable laboratory XANES data may be acquired, and interpreted for speciation, even from quite dilute absorber concentrations of a few mol%, albeit with data acquisition times of several hours. For materials with suitable absorber concentrations, this approach will enable routine element specific speciation studies to support rapid optimisation of radioactive waste forms and analysis of radiological materials in a purpose designed laboratory, without the risk associated with transport and manipulation at a synchrotron radiation facility.

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.