The basic principles of incorporating high level radioactive waste into glasses, ceramics (Synroc type) and glass composites including are described. Current UK technology uses wasteforms for the products reprocessing, although many countries temporarily storing ceramic spent fuel eventual disposal. Some streams may be incorporated ceramics, but difficult or legacy wastes will require development other comprising composite systems crystals glass. importance processing–property–structure...

Tetragonal tungsten bronzes (TTBs), an important class of oxides known to exhibit ferroelectricity, undergo complex distortions, including rotations oxygen octahedra, which give rise either incommensurately or commensurately modulated superstructures. Many TTBs display broad, frequency-dependent relaxor dielectric behavior rather than sharper frequency-independent normal ferroelectric anomalies, but the exact reasons that favor a particular type response for given composition remain unclear....

X-ray absorption fine structure (XAFS) and x-ray emission spectroscopy (XES) are advanced spectroscopies that impact a wide range of disciplines. However, unlike the majority other spectroscopic methods, XAFS XES accompanied by an unusual access model, wherein dominant use technique is for premier research studies at world-class facilities, i.e., synchrotron light sources. In this paper, we report design performance improved spectrometer based on general conceptual Seidler et al. [Rev. Sci....

Abstract Uranium (U) is a ubiquitous element in the Earth’s crust at ~2 ppm. In anoxic environments, soluble hexavalent uranium (U(VI)) reduced and immobilized. The underlying reduction mechanism unknown but likely of critical importance to explain geochemical behavior U. Here, we tackle U(VI) by mixed-valence iron oxide, magnetite. Through high-end spectroscopic microscopic tools, demonstrate that proceeds first through surface-associated form pentavalent U, U(V). U(V) persists on surface...

Strong coupling between local polar displacements and a commensurate octahedral tilting is proposed to explain the onset of classic ferroelectric behavior in tetragonal tungsten bronzelike dielectrics Ba2LaxNd1−xNb3Ti2O15. The phase transition associated with discontinuous non-lock-in transformation an incommensurate tilted structure superstructure. In manner reminiscent perovskitelike oxides, driving force for increases as average ionic radius rare-earth ion decreases; no classical observed...

The structure and dielectric properties of a new family tetragonal tungsten bronze (TTB) ceramics with the general formula, Ba2MTi2Nb3O15 where M=Bi3+,La3+,Nd3+,Sm3+,Gd3+, have been investigated. Hereafter compositions will be referred to by abbreviation BMTNO15 M=B(Bi3+), L(La3+), N(Nd3+), S(Sm3+) or G(Gd3+). BLTNO15 [permittivity maximum (Tm)∼−80°C] BBTNO15 (Tm∼−100°C) exhibited relaxorlike behavior. In contrast, BNTNO15 (Tm∼165°C), BSTNO15 (Tm∼250°C), BGTNO15 (Tm∼320°C) were classic...

The release of radionuclides from spent fuel in a geological disposal facility is controlled by the surface mediated dissolution UO2 groundwater. In this study we investigate influence reactive sites on synthesized CeO2 analogue for fuel. Dissolution was performed following: annealed at high temperature, which eliminated intrinsic defects (point and dislocations); CeO2-x inert reducing atmospheres to induce oxygen vacancy crushed particles different size fractions. BET area measurements were...

Abstract Research and innovation is key to delivering UK Government’s civil nuclear energy policy, in particular accelerate reduction the hazard, timescale cost of legacy decommissioning geological disposal radioactive wastes. To address this challenge, a national centre excellence, HADES Facility, has been established support research High Activity Decommissioning Engineering & Science, as part wider network National Nuclear User Facilities. Herein, we describe development user...

In this study, a multi-technique approach was utilised to determine the high temperature performance of magnesium potassium phosphate cement (MKPC) blended with fly ash (FA) or ground granulated blast furnace slag (GBFS) respect nuclear waste immobilisation applications. Conceptual fire conditions were employed (up 1200 °C, 30 min) simulate scenarios that could occur during interim storage, transportation within final geological disposal facility. After exposure up 400 main crystalline...

Zirconolite (CaZrTi2O7) has been identified as a candidate ceramic wasteform for the immobilisation and disposal of Pu inventories, which there is no foreseen future use. Here, we provide an overview relevant zirconolite solid solution chemistry with respect to Ce, U incorporation, alongside summary available literature on aqueous durability. The phase may accommodate wide variety tri- tetravalent actinide rare-earth dopants through isovalent heterovalent solution, e.g. CaZr1–xPuxTi2O7 or...

An iodide sodalite wasteform has been prepared by Hot Isostatic Pressing of powder produced hydrothermal synthesis. The was free leachable secondary phases which can mask leaching mechanisms. Leaching is congruent dissolution and leach rates decrease as Si Al accumulate in the leachate. Differential normalised are 0.005–0.01 g m−2 d−1 during 7–14 day period. This indicates that natural groundwater, already saturated these elements, will be very low.

A diverse range of materials and properties are exhibited by layered perovskites. We report on the synthesis, characterization, computational investigation a new ferroelectric—CsBi2Ti2NbO10—an n = 3 member Dion–Jacobson (DJ) family. Structural studies using variable-temperature neutron powder diffraction indicate that combination octahedral rotations polar displacements result in structure. Density functional theory calculations reveal wider perovskite blocks CsBi2Ti2NbO0 stabilize proper...

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 0.15, with Cr2O3 and an undesirable Ce-bearing perovskite present above = 0.20. Electron diffraction analysis confirmed that the polytype maintained over solid solution. X-ray absorption near edge structure (XANES) data determined between 10–20% Ce speciated as Ce3+, Cr uniformly Cr3+ features consistent occupation octahedral sites...

There is interest in identifying novel materials for use radioactive waste applications and studying their behavior under high pressure conditions. The mineral zirconolite (CaZrTi(2)O(7)) exists naturally trace amounts diamond-bearing deep-seated metamorphic/igneous environments, it also identified as a potential ceramic phase radionuclide sequestration. However, has been shown to undergo radiation-induced metamictization resulting amorphous forms. In this study we probed the structural...

In the safety case for geological disposal of nuclear waste, release radioactivity from repository is controlled by dissolution spent fuel in groundwater. There remain several uncertainties associated with understanding dissolution, including contribution energetically reactive surface sites to rate. this study, we investigate how features influence rate synthetic CeO2 and ThO2, analogues that approximate as closely possible microstructure characteristics fuel-grade UO2 but are not sensitive...

Bulk properties such as glass transition temperature, density and thermal expansion of iron phosphate compositions, with replacement Cs by Ba, are investigated a surrogate for the transmutation 137Cs to 137Ba, relevant immobilisation in glass. These studies required establish appropriate incorporation rate Density temperature increases addition BaO indicating shrinkage reticulation network. The average coefficient reduces from 19.8 × 10−6 K−1 13.4 K−1, when 25 wt. % Cs2O was replaced caesium...