Chemical and elemental mapping of spent nuclear fuel sections by soft X-ray spectromicroscopy.

Soft X-ray spectromicroscopy at the O K-edge, U N4,5-edges and Ce M4,5-edges has been performed on focused ion beam sections of spent nuclear fuel for the first time, yielding chemical information on the sub-micrometer scale. To analyze these data, a modification to non-negative matrix factorization (NMF) was developed, in which the data are no longer required to be non-negative, but the non-negativity of the spectral components and fit coefficients is largely preserved. The modified NMF method was utilized at the O K-edge to distinguish between two components, one present in the bulk of the sample similar to UO2 and one present at the interface of the sample which is a hyperstoichiometric UO2+x species. The species maps are consistent with a model of a thin layer of UO2+x over the entire sample, which is likely explained by oxidation after focused ion beam (FIB) sectioning. In addition to the uranium oxide bulk of the sample, Ce measurements were also performed to investigate the oxidation state of that fission product, which is the subject of considerable interest. Analysis of the Ce spectra shows that Ce is in a predominantly trivalent state, with a possible contribution from tetravalent Ce. Atom probe analysis was performed to provide confirmation of the presence and localization of Ce in the spent fuel.

Short life fission products extracted from molten salt reactor fuel for radiopharmaceutical applications.

This work studies the potential of using short life fission product (AFp) radioisotopes e.g. 82Br, 86Rb, (90Sr) - 90mY, (99Mo) - 99mTc, 103Ru - 103mRh, 111Ag, 127Sb - 127(m)Te, 126I, 131I, 133Xe, 136Cs, 141Ce, 143Ce, 143Pr, 147Nd - 147Pm, 149Pm, 153Sm, 156Eu, 159Gd and 161Tb, extracted from a molten salt reactor and their separation using specific thermodynamic and radiochemical conditions. Their utilisation for coupled radiodiagnostics and radiotherapy is a key consideration. A molten salt reactor produces fission products during operation. These radioisotopes can be separated at line from the liquid fuel by evaporation/distillation, chemical reduction (using H2 doped gas), electro-deposition and/or chemical oxidation (using Cl2 doped gas). They can be refined and chemically treated for radiopharmaceutical use for imaging and radiodiagnostics utilising γ radioscopy or positron emission tomography, and potentially in radiotherapy to target specific cancers or viral diseases using ß- emitters. Some of the AFp isotopes are currently used for radiodiagnostics because they emit γ rays of energy 50-200 keV. However, some may also be used in parallel for radiotherapy utilising their ß- (EMean ≈ 100 keV) emission whose mean free pathway of c.a. 100 nm in biological tissue is much smaller than their penetration depth. Focus is given to 86Rb, 90Y, 99mTc, 131I and 133Xe as well as on the ALn isotopes (141Ce, 143Ce - 143Pr, 147Nd - 147Pm, 149Pm and 153Sm) because of their strong potential for complexation with bio-ligands (e.g. DOTA) or for their ability to form micro-nano-spheres, and because of their potential for dual radiodiagnostics and radiotherapy. It is shown that these radio-lanthanides could also replace 177Lu for the treatment of specific cancers.

Single virus inductively coupled plasma mass spectroscopy analysis: A comprehensive study.

The characterisation of individual nanoparticles by single particle ICP-MS (SP-ICP-MS) has paved the way for the analysis of smallest biological systems. This study suggests to adapting this method for single viruses (SV) identification and counting. With high resolution multi-channel sector field (MC SF) ICP-MS records in SV detection mode, the counting of master and key ions can allow analysis and identification of single viruses. The counting of 2-500 virial units can be performed in 20 s. Analyses are proposed to be carried out in Ar torch for master ions: 12C+, 13C+, 14N+, 15N+, and key ions 31P+, 32S+, 33S+ and 34S+. All interferences are discussed in detail. The use of high resolution SF ICP-MS is recommended while options with anaerobic/aerobic atmospheres are explored to upgrade the analysis when using quadrupole ICP-MS. Application for two virus types (SARS-COV2 and bacteriophage T5) is investigated using time scan and fixed mass analysis for the selected virus ions allowing characterisation of the species using the N/C, P/C and S/C molar ratio's and quantification of their number concentration.

Local and global trace plutonium contributions in fast breeder legacy soils.

Trace-level plutonium in the environment often comprises local and global contributions, and is usually anthropogenic in origin. Here, we report estimates of local and global contributions to trace-level plutonium in soil from a former, fast-breeder reactor site. The measured 240Pu/239Pu ratio is anomalously low, as per the reduced 240Pu yield expected in plutonium bred with fast neutrons. Anomalies in plutonium concentration and isotopic ratio suggest forensic insight into specific activities on site, such as clean-up or structural change. Local and global 239Pu contributions on-site are estimated at (34 ± 1)% and (66 ± 3)%, respectively, with mass concentrations of (183 ± 6) fg g-1 and (362 ± 13) fg g-1. The latter is consistent with levels at undisturbed and distant sites, (384 ± 44) fg g-1, where no local contribution is expected. The 240Pu/239Pu ratio for site-derived material is estimated at 0.05 ± 0.04. Our study demonstrates the multi-faceted potential of trace plutonium assay to inform clean-up strategies of fast breeder legacies.

Simulating uranium sorption onto inorganic particles: The effect of redox potential.

An analytical expression is proposed to simulate the effects of pH and redox potential (E) on the sorption of uranium onto model inorganic particles in aquatic environments instead of following an experimental approach providing a list of empirical sorption data. The expression provides a distribution coefficient (Kd) as function of pH, E and ligand concentration (complex formation) applying a surface complexation model on one type of surface sites (>SuOH). The formulation makes use of the complexation and hydrolysis constants for all species in solution and those sorbed at the surface, using correlations between hydrolysis constants and surface complexation constants, for the specific sorption sites. The model was applied for the sorption of uranium onto aluminol, iron hydroxide and silanol sites, mimicking respectively 'clean' clay or 'dirty' clay and 'clean' sand or 'dirty' sand ('dirty' referring to iron hydroxide contaminated), in absence or presence of carbonates in solution. The calculated distribution coefficients are very sensitive with the presence or absence of carbonates. The Kd values obtained by applying the model are compared with values reported in the literature for the sorption of uranium onto specific adsorbents. It is known that in surface water, U(VI) and its hydroxides are the primary stable species usually observed. However, reduction to U(IV) is possible and may be simulated during sorption or when the redox potential (E) decreases. Similar simulations are also applicable to study the sorption of other redox sensitive elements.

Pore water colloid properties in argillaceous sedimentary rocks.

The focus of this work is to evaluate the colloid nature, concentration and size distribution in the pore water of Opalinus Clay and other sedimentary host rocks identified for a potential radioactive waste repository in Switzerland. Because colloids could not be measured in representative undisturbed porewater of these host rocks, predictive modelling based on data from field and laboratory studies is applied. This approach allowed estimating the nature, concentration and size distributions of the colloids in the pore water of these host rocks. As a result of field campaigns, groundwater colloid concentrations are investigated on the basis of their size distribution quantified experimentally using single particle counting techniques. The colloid properties are estimated considering data gained from analogue hydrogeochemical systems ranging from mylonite features in crystalline fissures to sedimentary formations. The colloid concentrations were analysed as a function of the alkaline and alkaline earth element concentrations. Laboratory batch results on clay colloid generation from compacted pellets in quasi-stagnant water are also reported. Experiments with colloids in batch containers indicate that the size distribution of a colloidal suspension evolves toward a common particle size distribution independently of initial conditions. The final suspension size distribution was found to be a function of the attachment factor of the colloids. Finally, calculations were performed using a novel colloid distribution model based on colloid generation, aggregation and sedimentation rates to predict under in-situ conditions what makes colloid concentrations and size distributions batch- or fracture-size dependent. The data presented so far are compared with the field and laboratory data. The colloid occurrence, stability and mobility have been evaluated for the water of the considered potential host rocks. In the pore water of the considered sedimentary host rocks, the clay colloid concentration is expected to be very low (<1ppb, for 10-100nm) which restricts their relevance for radionuclide transport.

Predictions of TiO2-driven migration of Se(IV) based on an integrated study of TiO2 colloid stability and Se(IV) surface adsorption.

Colloids (ex. nanoparticles) may be relevant in contaminant migration in groundwater if the contaminant is strongly adsorbed onto colloids and they are stable in the environment. An integrated study of Se(IV) sorption and TiO2 colloid stability was performed in this work. This integrated study includes the experimental analysis and modelling of Se(IV) sorption onto TiO2 particle surface and the evaluation of the influence of adsorbed Se(IV) on TiO2 stability. Results indicated that low ionic strength and acid pH favour both high Se(IV) sorption and TiO2 colloid stability. However, at medium-high surface occupancy, sorbed Se(IV) highly affected TiO2 colloid stability. Anion adsorption decreases the positive surface charge shifting the TiO2 isoelectric point, thus promoting particle aggregation under acid pH. Nevertheless, the application of the single particle counting technique allowed determination of the presence of a significant fraction of TiO2 nanoparticles which are highly susceptible to migrate even under favourable conditions for aggregation. Therefore, although part of the TiO2 is disabled for migration by sorbed Se at acid conditions, still a considerable percentage that remains disaggregated could move together with Se. The developed Se(IV) sorption model can inform about the extent and type of sorption under specific geochemical conditions.

Electron energy loss spectroscopy investigation through a nano ablated uranium dioxide sample.

A lamella of uranium dioxide (∼10 × âˆ¼10 × âˆ¼0.02-0.20 µm) was produced by focused ion beam for transmission electron and electron energy loss spectroscopy (EELS) examinations. This sample allows quantitative analysis of the EEL spectra recorded for UO2 as a function of the thickness. The M, N, O and P edges were recorded over zero loss to 4000 eV loss. The edges allow reconstruction of the electronic transitions, the lowest energy loss edges for P transitions corresponds to P3 electron transition (17.2 eV) from U6p3/2 level. The edge analysis allows also better interpretation of the loss spectrum with identification of the plasmon peak of the core electron transition edges. In addition, the energy lost was studied through a range of thicknesses going from ∼20 to ∼200 nm to derive the electron mean free path and cross section for inelastic scattering in the plasmon part of the spectrum. The mean free path of inelastic electron for uranium dioxide is compared with that reported earlier for other oxides from Be to Bi and for 200 keV incidents electrons. The present study emphasises the potential of combining FIB and EELS for the analysis of actinide compounds.

Determining pseudo-equilibrium of montmorillonite colloids in generation and sedimentation experiments as a function of ionic strength, cationic form, and elevation.

Colloid generation and sedimentation experiments were carried out on Na- and Ca-montmorillonite in order to verify whether pseudo-equilibrium concentrations are reached at the same level in both types of experiments. The size and concentration of colloidal Na- and Ca-montmorillonite particles were monitored as a function of time and distance from the colloid bed in different ionic strength solutions. A stable pseudo-equilibrium concentration was reached after time in generation and sedimentation experiments. The colloid concentration decreased sharply at distances near to the colloid source. Na-montmorillonite concentration at pseudo-equilibrium (roughly quantified at distances > or = 7 cm from the colloid source) was 5.2 +/- 0.5, 0.5 +/- 0.1, and 0.2 +/- 0.1 mg L(-1) in 0.001, 0.01, and 0.1 M NaCl solution, respectively, while the Ca-montmorillonite concentration was 0.4 +/- 0.2 mg L(-1) in 0.001 M NaCl.

Variable incidence angle X-ray absorption fine structure spectroscopy: a zirconia film study.

Variable incidence angle X-ray absorption fine structure (VIAXAFS) spectroscopy offers a non-destructive ability to investigate film nano-structures. This technique was applied, spanning sample-beam angles from a grazing to normal incidence on a film obtained by zirconia sputtering on flat sample of stainless steel. X-ray absorption fine structure analysis on the Zr K edge identified chemical, defects and fractal structures through the film depth. VIAXAFS revealed occurrence of zirconium monoxide fractions at the surface a reduced state of zirconium oxide vs. the zirconium dioxide bulk. The discussion underlines that the technique may quantify the profile of various sub-layers, nano-pores, dislocations, vacancies or defect features.

XAFS study of americium sorbed onto groundwater colloids.

The sorption of americium, as Am(III), onto groundwater colloids obtained from a marl aquifer was studied in 2 x 10(-2)M sodium bicarbonate groundwater and 2 x 10(-2)M sodium chloride bicarbonate-free solutions. At the in situ groundwater pH of 8.6, the americium was strongly sorbed onto the colloids. XAFS analyses were performed on these sorbed Am species to establish the oxidation state and its near-neighbour bonding. These XAFS data, obtained at 400 mg l(-1) colloid concentrations and total Am concentration of 1.53 x 10(-5)M (dissolved and onto colloids), indicated that Am remains trivalent, and that surface complexes are formed with the colloids without surface precipitation. This conclusion is based on the absence of Am-Am interactions in the second or third shells. The surface complexes generated by the Am(III) sorbed onto active sites are described on the basis of the XAFS data. They include the presence of about seven water molecules around the ternary surface complexes of this trivalent actinide.