The current baseline for the conditioning of most UK intermediate-level radioactive waste (ILW) is immobilisation using cement. However, vitrification of some UK ILW is being considered as an ...alternative. One option for the disposal of the resulting vitrified ILW would be to place it in a geological disposal facility in a high-pH environment with cemented ILW and a cement-based backfill. Therefore, the potential effects of such a high pH (∼12.5), calcium-rich cement-based environment on the dissolution behaviour of simulant ILW glasses have been studied using the product consistency test (PCT). Three non-radioactive waste compositions were assessed: a laboratory simulant ILW vitrified in a borosilicate glass and two full-scale simulant vitrified products (a slag containing simulant plutonium-contaminated material and Magnox sludge; and a glass containing clinoptilolite). Powdered samples were leached in saturated Ca(OH)2 solutions for up to 42days at temperatures between 30 and 90°C.
In general the rates of dissolution were lower than expected at such a high pH compared to studies in the literature under alkaline conditions. In contrast to the typical dissolution behaviour of high level waste (HLW) glasses, dissolution of the simulant borosilicate ILW glass was initially slow, followed by a period of faster boron and alkali metal release. The saturation/residual regime was not reached within experimental timescales. The rate of dissolution during the period of faster release increased with increasing temperature; the activation energy for this stage of dissolution was calculated to be 47±2kJmol−1 based on boron release. The two full-scale simulant glasses, which contained negligible boric oxide, exhibited conventional static dissolution profiles, and entered the residual rate regime after 7-14days at 50°C. The greater durability of the full-scale simulants is thought to be due to the greater content of network-forming oxides in these glasses compared to the borosilicate glass. It is also suggested that the formation of calcium borates may delay initial hydration of the borosilicate glass in a similar manner to the retardation of cement hydration by soluble borates. More generally, the formation of calcium- and magnesium-containing precipitates on the surface of the vitrified wastes, and agglomeration of the powder, appeared to act to reduce the dissolution rate. Overall these results suggest that calcium has an important role in the long-term durability of vitrified wastes at high pH.
Research and innovation is key to delivering UK Government's civil nuclear energy policy, in particular to accelerate reduction in the hazard, timescale and cost of legacy decommissioning and ...geological disposal of radioactive wastes. To address this challenge, a national centre of excellence, the HADES Facility, has been established to support research and innovation in High Activity Decommissioning Engineering & Science, as part of the wider network of UK National Nuclear User Facilities. Herein, we describe the development of this user facility, the current status of its capability, and functional equipment specifications. The unique capabilities of the HADES Facility, in the UK academic landscape, are emphasised, including: handling of weighable quantities of 99Tc and transuranics; quantitative electron probe microanalysis of radioactive materials; hot isostatic pressing of radioactive materials; and laboratory-based X-ray absorption and emission spectroscopy. An example case study of the application of the HADES capability is described, involving thermal treatment of a real radioactive ion exchange resin waste to produce a conceptual vitrified waste form.
Ti3SiC2 was deposited onto titanium substrates using electrophoretic deposition; a 4.3 wt% suspension of Ti3SiC2 in water at pH 9 was used with 10 V field applied across the substrates. After 10 min ...of deposition, the coating surface density was 1.89 ± 0.26 mg/cm2. The thin coatings were then rapidly densified using a Renishaw AM250 3D printing laser to scan the surface. Cross sections of the substrate post sintering, showed the coating thickness to be 10–30 μm and densified with silicon loss constrained to the surface, although the overall coverage and adhesion varies. Preliminary Raman spectroscopy results suggest some MAX phase remains after sintering, but further characterisation is required to confirm.
•1.89 ± 0.26 mg/cm2 green coatings of Ti3SiC2 deposited on titanium via EPD•10–30 μm coating bands with varying adhesion achieved via laser densification•Raman indicates some Ti3SiC2 present in sintered coating.
Rare earth zirconates, such as Nd
2
Zr
2
O
7
, crystallise with the pyrochlore structure and are a group of materials which have been suggested as potential nuclear waste forms for actinide ...immobilisation. In this work, a new hydroxide co-precipitation route is presented to investigate the incorporation of Pu into Nd
2
Zr
2
O
7
. The plutonium content was varied between 5 and 10 mol% and the structural uptake and Pu oxidation state were probed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray absorption spectroscopy (XAS). The experimental findings were complemented by DFT
ab initio
calculations. For all the incorporation mechanisms studied PuO
2
was used as the reference reactant state to allow for a direct comparison between the possible Pu uptake scenarios. Analysis of the experimental data suggests that Pu(
iv
) cations substitute for Nd(
iii
) cations leading to structural distortion of the pyrochlore A-sites. The computed solution energies and bond-distances corroborate the experimental findings and indicate that the excess charge is balanced
via
the introduction of oxygen at formerly vacant sites.
Experimental & theoretical insights into the structural response of complex oxides to dopant elements - the example of plutonium within pyrochlore.
SEM–EDX and Raman spectroscopy analysis of radioactive compounds is often restricted to dedicated instrumentation, within radiological working areas, to manage the hazard and risk of contamination. ...Here, we demonstrate application of WetSEM® capsules for containment of technetium powder materials, enabling routine multimodal characterisation with general user instrumentation, outside of a controlled radiological working area. The electron transparent membrane of WetSEM® capsules enables SEM imaging of submicron non-conducting technetium powders and acquisition of Tc Lα X-ray emission, using a low cost desktop SEM–EDX system, as well as acquisition of good quality μ-Raman spectra using a 532 nm laser.
To study radiation stability of iron phosphate glasses, cerium is used as surrogate of actinides. Cerium doped iron phosphate glasses have been synthesised. Heavy gold ion irradiations have been ...performed on pure and cerium doped iron phosphate glasses to mimic ballistic damage due to cascade of recoil atoms. Pure and cerium doped glasses are irradiated with gold ions of energy 750 keV at fluence of 2 × 10
15
ions/cm
2
. In this paper, ion irradiation effects on glass network modification and change in speciation of network former have been discussed. Significant changes in glass network structure and speciation of network former is observed.
A suite of uranium brannerites for the disposal of MOX residues, formulated (U
0.9
Ce
0.1
)
1−
x
M
x
Ti
2
O
6
(M = Ca
2+
and/or Gd
3+
), were prepared using a mixed oxide route under oxidising, inert ...and reducing atmospheres (air, argon and H
2
/N
2
). Gd
3+
was added to act as a neutron absorber in the final Pu bearing wasteform and Ce added to function as a structural analogue for Pu. X-ray powder diffraction of the synthesised specimens found that phase distribution was strongly affected by the processing atmosphere and Gd content. In all cases prototypical brannerite was formed, accompanied by different secondary phases dependent on processing atmosphere. Microstructural analysis (SEM) of the sintered samples confirmed the results of the X-ray powder diffraction. Bulk XANES found that Ti remained in the Ti
4+
oxidation state whereas Ce was uniformly reduced to the Ce
3+
oxidation state regardless of processing conditions or stoichiometry. Micro-focus XANES was used to determine U oxidation in the brannerite phase and showed that U oxidised to higher U oxidation states to charge compensate. It was concluded that the charge balance mechanism was a combination of U oxidation and A-site vacancies.
This work presents the synthesis and characterisation of novel brannerite ceramics designed for the disposal of mixed oxide fuel residues.
The basic principles of incorporating high level radioactive waste into glasses, ceramics (Synroc type) and glass composites including glass ceramics are described. Current UK technology uses glass ...wasteforms for the products of reprocessing, although many countries are temporarily storing the ceramic spent fuel for eventual disposal. Some waste streams may be incorporated into ceramics, but difficult or legacy wastes will require the development of other wasteforms comprising composite systems of crystals and glass. The importance of processing-property-structure (especially durability) relations in such systems over size scales from the atomic to the geological and on timescales to hundreds of thousands of years is highlighted.
Abstract
Radioactive waste streams that include metallic uranium are incompatible with conventional ordinary Portland cement (OPC)-based encapsulation matrices. These encapsulation systems are ...essentially composite materials that incorporate high replacement levels of pulverised fly ash (PFA) or blast furnace slag (BFS). A potential alternative encapsulant for the treatment of problematic waste streams is magnesium phosphate cement. This paper discusses the fundamental characterisation results obtained from two magnesium phosphate cement formulations being developed in the UK for the encapsulation of metallic intermediate level waste (ILW). When compared to conventional OPC based systems, the two magnesium phosphate cement formulations investigated have lower pH, are able to chemically combine more mix water into the system and provide sufficient workability at water/solid ratios close to the theoretical confines needed for paste saturation. The results presented have confirmed compliance of this material against NDA RWMD guidelines for strength and expansion. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results obtained for both formulations up to 360 days cure time have indicated that the cement system shows evidence of chemical stability.
Primary progressive aphasia (PPA) is comprised of three subtypes: logopenic (lvPPA), non-fluent (nfvPPA), and semantic (svPPA). We used magnetic resonance spectroscopy (MRS) to measure ...tissue-corrected metabolite levels in the left inferior frontal gyrus (IFG) and right sensorimotor cortex (SMC) from 61 PPA patients. We aimed to: (1) characterize subtype differences in metabolites; and (2) test for metabolite associations with symptom severity. tCr differed by subtype across the left IFG and right SMC. tCr levels were lowest in lvPPA and highest in svPPA. tCr levels predicted lvPPA versus svPPA diagnosis. Higher IFG tCr and lower Glx correlated with greater disease severity. As tCr is involved in brain energy metabolism, svPPA pathology might involve changes in specific cellular energy processes. Perturbations to cellular energy homeostasis in language areas may contribute to symptoms. Reduced cortical excitatory capacity (i.e. lower Glx) in language regions may also contribute to symptoms. Thus, tCr may be useful for differentiating between PPA subtypes, and both tCr and Glx might have utility in understanding PPA mechanisms and tracking progression.
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