Analysis of the Structure of Heavy Ion Irradiated LaFeO3 Using Grazing Angle X-ray Absorption Spectroscopy.

Crystalline ceramics are candidate materials for the immobilization of radionuclides, particularly transuranics (such as U, Pu, and Am), arising from the nuclear fuel cycle. Due to the α-decay of transuranics and the associated recoil of the parent nucleus, crystalline materials may eventually be rendered amorphous through changes to the crystal lattice caused by these recoil events. Previous work has shown irradiation of titanate-based ceramics to change the local cation environment significantly, particularly in the case of Ti which was shown to change from 6- to 5-fold coordination. Here, this work expands the Ti-based study to investigate the behavior in Fe-based materials, using LaFeO3 as an example material. Irradiation was simulated by heavy ion implantation of the bulk LaFeO3 ceramic, with the resulting amorphous layer characterized with grazing angle X-ray absorption spectroscopy (GA-XAS). Insights into the Fe speciation changes exhibited by the amorphized surface layer were provided through quantitative analysis, including pre-edge analysis, and modeling of the extended X-ray absorption fine structure (EXAFS), of the GA-XAS data.

A multimodal X-ray spectroscopy investigation of uranium speciation in ThTi2O6 compounds with the brannerite structure.

ThTi2O6 derived compounds with the brannerite structure were designed, synthesised, and characterised with the aim of stabilising incorporation of U5+ or U6+, at dilute concentration. Appropriate charge compensation was targeted by co-substitution of Gd3+, Ca2+, Al3+, or Cr3+, on the Th or Ti site. U L3 edge X-ray Absorption Near Edge Spectroscopy (XANES) and High Energy Resolution Fluorescence Detected U M4 edge XANES evidenced U5+ as the major oxidation state in all compounds, with a minor fraction of U6+ (2-13%). The balance of X-ray and Raman spectroscopy data support uranate, rather than uranyl, as the dominant U6+ speciation in the reported brannerites. It is considered that the U6+ concentration was limited by unfavourable electrostatic repulsion arising from substitution in the octahedral Th or Ti sites, which share two or three edges, respectively, with neighbouring polyhedra in the brannerite structure.

Underpinning the use of indium as a neutron absorbing additive in zirconolite by X-ray absorption spectroscopy.

Indium (In) is a neutron absorbing additive that could feasibly be used to mitigate criticality in ceramic wasteforms containing Pu in the immobilised form, for which zirconolite (nominally CaZrTi2O7) is a candidate host phase. Herein, the solid solutions Ca1-xZr1-xIn2xTi2O7 (0.10 ≤ x ≤ 1.00; air synthesis) and Ca1-xUxZrTi2-2xIn2xO7 (x = 0.05, 0.10; air and argon synthesis) were investigated by conventional solid state sintering at a temperature of 1350 °C maintained for 20 h, with a view to characterise In3+ substitution behaviour in the zirconolite phase across the Ca2+, Zr4+ and Ti4+ sites. When targeting Ca1-xZr1-xIn2xTi2O7, single phase zirconolite-2M was formed at In concentrations of 0.10 ≤ x ≤ 0.20; beyond x ≥ 0.20, a number of secondary In-containing phases were stabilised. Zirconolite-2M remained a constituent of the phase assemblage up to a concentration of x = 0.80, albeit at relatively low concentration beyond x ≥ 0.40. It was not possible to synthesise the In2Ti2O7 end member compound using a solid state route. Analysis of the In K-edge XANES spectra in the single phase zirconolite-2M compounds confirmed that the In inventory was speciated as trivalent In3+, consistent with targeted oxidation state. However, fitting of the EXAFS region using the zirconolite-2M structural model was consistent with In3+ cations accommodated within the Ti4+ site, contrary to the targeted substitution scheme. When deploying U as a surrogate for immobilised Pu in the Ca1-xUxZrTi2-2xIn2xO7 solid solution, it was demonstrated that, for both x = 0.05 and 0.10, In3+ was successfully able to stabilise zirconolite-2M when U was distributed predominantly as both U4+ and average U5+, when synthesised under argon and air, respectively, determined by U L3-edge XANES analysis.

Spectroscopic identification of Ca-bearing uranyl silicates formed in C-S-H systems.

Portland cement-based grouts used for radioactive waste immobilisation contain a Ca- and Si-rich binder phase, known as calcium-silicate-hydrate (C-S-H). Depending on the blend of cement used, the Ca/Si ratio can vary considerably. A range of C-S-H minerals with Ca/Si ratios from 0.6 to 1.6 were synthesised and contacted with aqueous U(VI) at 0.5 mM and 10 mM concentrations. Solid-state 29Si MAS-NMR spectroscopy was applied to probe the Si coordination environment in U(VI)-contacted C-S-H minerals and, in conjunction with U LIII-edge X-ray absorption spectroscopy analysis, inferences of the fate of U(VI) in these systems were made. At moderate or high Ca/Si ratios, uranophane-type uranyl silicates or Ca-uranates dominated, while at the lowest Ca/Si ratios, the formation of a Ca-bearing uranyl silicate mineral, similar to haiweeite (Ca[(UO2)2Si5O12(OH)2]·3H2O) or Ca-bearing weeksite (Ca2(UO2)2Si6O15·10H2O) was identified. This study highlights the influence of Ca/Si ratio on uranyl sequestration, of interest in the development of post-closure safety models for U-bearing radioactive waste disposal.

Sulfidation and Reoxidation of U(VI)-Incorporated Goethite: Implications for U Retention during Sub-Surface Redox Cycling.

Over 60 years of nuclear activity have resulted in a global legacy of contaminated land and radioactive waste. Uranium (U) is a significant component of this legacy and is present in radioactive wastes and at many contaminated sites. U-incorporated iron (oxyhydr)oxides may provide a long-term barrier to U migration in the environment. However, reductive dissolution of iron (oxyhydr)oxides can occur on reaction with aqueous sulfide (sulfidation), a common environmental species, due to the microbial reduction of sulfate. In this work, U(VI)-goethite was initially reacted with aqueous sulfide, followed by a reoxidation reaction, to further understand the long-term fate of U species under fluctuating environmental conditions. Over the first day of sulfidation, a transient release of aqueous U was observed, likely due to intermediate uranyl(VI)-persulfide species. Despite this, overall U was retained in the solid phase, with the formation of nanocrystalline U(IV)O2 in the sulfidized system along with a persistent U(V) component. On reoxidation, U was associated with an iron (oxyhydr)oxide phase either as an adsorbed uranyl (approximately 65%) or an incorporated U (35%) species. These findings support the overarching concept of iron (oxyhydr)oxides acting as a barrier to U migration in the environment, even under fluctuating redox conditions.

Phase Evolution in the CaZrTi2O7-Dy2Ti2O7 System: A Potential Host Phase for Minor Actinide Immobilization.

Zirconolite is considered to be a suitable wasteform material for the immobilization of Pu and other minor actinide species produced through advanced nuclear separations. Here, we present a comprehensive investigation of Dy3+ incorporation within the self-charge balancing zirconolite Ca1-xZr1-xDy2xTi2O7 solid solution, with the view to simulate trivalent minor actinide immobilization. Compositions in the substitution range 0.10 ≤ x ≤ 1.00 (Δx = 0.10) were fabricated by a conventional mixed oxide synthesis, with a two-step sintering regime at 1400 °C in air for 48 h. Three distinct coexisting phase fields were identified, with single-phase zirconolite-2M identified only for x = 0.10. A structural transformation from zirconolite-2M to zirconolite-4M occurred in the range 0.20 ≤ x ≤ 0.30, while a mixed-phase assemblage of zirconolite-4M and cubic pyrochlore was evident at Dy concentrations 0.40 ≤ x ≤ 0.50. Compositions for which x ≥ 0.60 were consistent with single-phase pyrochlore. The formation of zirconolite-4M and pyrochlore polytype phases, with increasing Dy content, was confirmed by high-resolution transmission electron microscopy, coupled with selected area electron diffraction. Analysis of the Dy L3-edge XANES region confirmed that Dy was present uniformly as Dy3+, remaining analogous to Am3+. Fitting of the EXAFS region was consistent with Dy3+ cations distributed across both Ca2+ and Zr4+ sites in both zirconolite-2M and 4M, in agreement with the targeted self-compensating substitution scheme, whereas Dy3+ was 8-fold coordinated in the pyrochlore structure. The observed phase fields were contextualized within the existing literature, demonstrating that phase transitions in CaZrTi2O7-REE3+Ti2O7 binary solid solutions are fundamentally controlled by the ratio of ionic radius of REE3+ cations.

Cr2+ solid solution in UO2 evidenced by advanced spectroscopy.

Advanced Cr-doped UO2 fuels are essential for driving safe and efficient generation of nuclear energy. Although widely deployed, little is known about their fundamental chemistry, which is a critical gap for development of new fuel materials and radioactive waste management strategies. Utilising an original approach, we directly evidence the chemistry of Cr(3+)2O3-doped U(4+)O2. Advanced high-flux, high-spectral purity X-ray absorption spectroscopy (XAS), corroborated by diffraction, Raman spectroscopy and high energy resolved fluorescence detection-XAS, is used to establish that Cr2+ directly substitutes for U4+, accompanied by U5+ and oxygen vacancy charge compensation. Extension of the analysis to heat-treated simulant nuclear fuel reveals a mixed Cr2+/3+ oxidation state, with Cr in more than one physical form, explaining the substantial discrepancies that exist in the literature. Successful demonstration of this analytical advance, and the scientific underpinning it provides, opens opportunities for an expansion in the range of dopants utilised in advanced UO2 fuels.

Biogenic Sulfidation of U(VI) and Ferrihydrite Mediated by Sulfate-Reducing Bacteria at Elevated pH.

Globally, the need for radioactive waste disposal and contaminated land management is clear. Here, gaining an improved understanding of how biogeochemical processes, such as Fe(III) and sulfate reduction, may control the environmental mobility of radionuclides is important. Uranium (U), typically the most abundant radionuclide by mass in radioactive wastes and contaminated land scenarios, may have its environmental mobility impacted by biogeochemical processes within the subsurface. This study investigated the fate of U(VI) in an alkaline (pH ∼9.6) sulfate-reducing enrichment culture obtained from a high-pH environment. To explore the mobility of U(VI) under alkaline conditions where iron minerals are ubiquitous, a range of conditions were tested, including high (30 mM) and low (1 mM) carbonate concentrations and the presence and absence of Fe(III). At high carbonate concentrations, the pH was buffered to approximately pH 9.6, which delayed the onset of sulfate reduction and meant that the reduction of U(VI)(aq) to poorly soluble U(IV)(s) was slowed. Low carbonate conditions allowed microbial sulfate reduction to proceed and caused the pH to fall to ∼7.5. This drop in pH was likely due to the presence of volatile fatty acids from the microbial respiration of gluconate. Here, aqueous sulfide accumulated and U was removed from solution as a mixture of U(IV) and U(VI) phosphate species. In addition, sulfate-reducing bacteria, such as Desulfosporosinus species, were enriched during development of sulfate-reducing conditions. Results highlight the impact of carbonate concentrations on U speciation and solubility in alkaline conditions, informing intermediate-level radioactive waste disposal and radioactively contaminated land management.

Sulfidation of magnetite with incorporated uranium.

Uranium (U) is a radionuclide of key environmental interest due its abundance by mass within radioactive waste and presence in contaminated land scenarios. Ubiquitously present iron (oxyhydr)oxide mineral phases, such as (nano)magnetite, have been identified as candidates for immobilisation of U via incorporation into the mineral structure. Studies of how biogeochemical processes, such as sulfidation from the presence of sulfate-reducing bacteria, may affect iron (oxyhydr)oxides and impact radionuclide mobility are important in order to underpin geological disposal of radioactive waste and manage radioactively contaminated land. Here, this study utilised a highly controlled abiotic method for sulfidation of U(V) incorporated into nanomagnetite to determine the fate and speciation of U. Upon sulfidation, transient release of U into solution occurred (∼8.6% total U) for up to 3 days, despite the highly reducing conditions. As the system evolved, lepidocrocite was observed to form over a period of days to weeks. After 10 months, XAS and geochemical data showed all U was partitioned to the solid phase, as both nanoparticulate uraninite (U(IV)O2) and a percentage of retained U(V). Further EXAFS analysis showed incorporation of the residual U(V) fraction into an iron (oxyhydr)oxide mineral phase, likely nanomagnetite or lepidocrocite. Overall, these results provide new insights into the stability of U(V) incorporated iron (oxyhydr)oxides during sulfidation, confirming the longer term retention of U in the solid phase under complex, environmentally relevant conditions.

Biomineralization of Uranium-Phosphates Fueled by Microbial Degradation of Isosaccharinic Acid (ISA).

Geological disposal is the globally preferred long-term solution for higher activity radioactive wastes (HAW) including intermediate level waste (ILW). In a cementitious disposal system, cellulosic waste items present in ILW may undergo alkaline hydrolysis, producing significant quantities of isosaccharinic acid (ISA), a chelating agent for radionuclides. Although microbial degradation of ISA has been demonstrated, its impact upon the fate of radionuclides in a geological disposal facility (GDF) is a topic of ongoing research. This study investigates the fate of U(VI) in pH-neutral, anoxic, microbial enrichment cultures, approaching conditions similar to the far field of a GDF, containing ISA as the sole carbon source, and elevated phosphate concentrations, incubated both (i) under fermentation and (ii) Fe(III)-reducing conditions. In the ISA-fermentation experiment, U(VI) was precipitated as insoluble U(VI)-phosphates, whereas under Fe(III)-reducing conditions, the majority of the uranium was precipitated as reduced U(IV)-phosphates, presumably formed via enzymatic reduction mediated by metal-reducing bacteria, including Geobacter species. Overall, this suggests the establishment of a microbially mediated "bio-barrier" extending into the far field geosphere surrounding a GDF is possible and this biobarrier has the potential to evolve in response to GDF evolution and can have a controlling impact on the fate of radionuclides.

Survival benefit associated with early detection of spontaneous bacterial peritonitis in veteran inpatients with cirrhotic ascites.

BACKGROUND: Spontaneous bacterial peritonitis (SBP) is common in hospitalized cirrhotic patients with ascites and carries high mortality. This study aimed to determine whether early diagnostic paracentesis (EDP) <12 h of hospitalization conveys an intermediate-term (6-month) survival benefit in cirrhotic patients diagnosed with SBP. METHODS: Consecutive US veterans with cirrhosis diagnosed with SBP over 13 years at a single VA medical center were reviewed retrospectively. Kaplan-Meyer analyses assessed the effects of EDP on survival. RESULTS: A total of 79 cirrhotic patients were diagnosed with SBP (61.8 ± 8.8 years, n = 77 male, n = 52 [66.8%] Caucasian, n = 23 [29.1%] African-American). Underlying liver diseases included hepatitis c viral infection (HCV) (17.5%), alcohol (28.6%), alcohol and HCV (30.1%), and cryptogenic/metabolic (15.9%). Median baseline model for end-stage liver disease (MELD) was 12 (range 6-34), and median MELD at presentation was 18. Seven subjects had a history of hepatocellular carcinoma (11.1%), and 26 (41.3%) presented with sepsis. Thirty-three (52.4%) subjects died within 6 months after the SBP admission. Of the subjects, 41 (65.1%) underwent EDP, of which 23 (56.0%) survived at least 6 months, compared to only 7 of the 22 patients (31.8%) undergoing paracentesis >12 h from presentation (P = 0.057). The maximal benefit of EDP on survival was observed beyond days 14 and 30; at these time points, no statistical difference in mortality was discernable (P = 0.55 and 0.71). In a multivariate model including age, MELD at admission, hepatocellular cancer, and sepsis criteria, EDP (p 0.034) positively impacted patient survival at 6 months. CONCLUSIONS: EDP is associated with improved 6-month mortality in cirrhotic patients with ascites. In this veteran cohort, EDP was as important as MELD as a predictor of intermediate-term survival.

Formation of a U(VI)-Persulfide Complex during Environmentally Relevant Sulfidation of Iron (Oxyhydr)oxides.

Uranium is a risk-driving radionuclide in both radioactive waste disposal and contaminated land scenarios. In these environments, a range of biogeochemical processes can occur, including sulfate reduction, which can induce sulfidation of iron (oxyhydr)oxide mineral phases. During sulfidation, labile U(VI) is known to reduce to relatively immobile U(IV); however, the detailed mechanisms of the changes in U speciation during these biogeochemical reactions are poorly constrained. Here, we performed highly controlled sulfidation experiments at pH 7 and pH 9.5 on U(VI) adsorbed to ferrihydrite and investigated the system using geochemical analyses, X-ray absorption spectroscopy (XAS), and computational modeling. Analysis of the XAS data indicated the formation of a novel, transient U(VI)-persulfide complex as an intermediate species during the sulfidation reaction, concomitant with the transient release of uranium to the solution. Extended X-ray absorption fine structure (EXAFS) modeling showed that a persulfide ligand was coordinated in the equatorial plane of the uranyl moiety, and formation of this species was supported by computational modeling. The final speciation of U was nanoparticulate U(IV) uraninite, and this phase was evident at 2 days at pH 7 and 1 year at pH 9.5. Our identification of a new, labile U(VI)-persulfide species under environmentally relevant conditions may have implications for U mobility in sulfidic environments pertinent to radioactive waste disposal and contaminated land scenarios.

Impact of Age on Patient-Reported Outcome Measures in Total Knee Arthroplasty.

Patient expectations and demographics are vital factors in determining patient satisfaction and outcomes from total knee arthroplasty (TKA). This study was a retrospective chart review that analyzed data from TKA patients to determine the impact of age on patient-reported outcomes measures following TKA. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Oxford knee scores were collected as primary outcome measures from 356 consecutive patients who underwent TKA. Oxford knee scores were further divided into pain and function subscores. Patients were age categorized as <50, 50 to 59, 60 to 69, 70 to 79, and >79. Preoperative scores were compared among age categories including age category, gender, body mass index (BMI), and length of stay (LOS) in the model as fixed effects. Scores collected postoperatively (∼10, 30, 90, and 180 days postoperation) were analyzed as repeated measures including age category, day and their interaction, gender, BMI, LOS, and preoperative score in the model. Preoperative OXFORD scores significantly differed among age categories (p < 0.05) and were numerically higher for the older (≥60 years old) compared with younger patients (<60 years old). After adjusting for preoperative scores, postoperative WOMAC and overall, pain, and function OXFORD scores significantly differed among the age groups (p < 0.05), with patients younger than 60 years reporting the worst scores in the postoperative time period. Older patients reported better preoperative overall, pain, and function scores and greater post-TKA outcomes than younger patients. A better understanding of factors that influence patient-reported outcomes can help providers to better manage patient expectations.

Does Marital Status Impact Outcomes After Total Knee Arthroplasty?

BACKGROUND: There is a paucity of research on the relationship between marital status and patient outcomes following total knee arthroplasty (TKA). METHODS: This was a retrospective chart review of patients who underwent TKA by a single surgeon at a university-based orthopedic practice. Data abstracted included age, gender, marital status, body mass index, length of hospital stay, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Oxford Knee Score (OKS). The WOMAC and OKS were administered at the preoperative visit and at approximately 10, 30, 90, and 180 days after TKA. Multivariate analyses with patient-reported outcomes as repeated measures, marital status, day of assessment; and the interaction of marital status and day of assessment as fixed effects; and age, gender, body mass index, and length of hospital stay as covariates were conducted as well as analyses in which preoperative patient-reported outcomes were treated as fixed effects. RESULTS: Of 422 patients who underwent TKA during the study period, complete data were available for 249, of whom 124 were married and 125 unmarried. Married patients had significantly higher WOMAC scores than unmarried patients at all postoperative assessments, even after controlling for preoperative scores. Although married patients also had significantly higher postoperative OKS scores than their unmarried peers, differences between groups were attenuated after adjusting for preoperative OKS scores. CONCLUSION: This study found that married patients have better overall outcomes after TKA but yielded conflicting results as to whether the positive effects of marriage are specific to the postoperative period.