Myths and Methodologies: Understanding the health impact of head down bedrest for the benefit of older adults and astronauts. Study protocol of the Canadian Bedrest Study.

Weightlessness during spaceflight can harm various bodily systems, including bone density, muscle mass, strength and cognitive functions. Exercise appears to somewhat counteract these effects. A terrestrial model for this is head-down bedrest (HDBR), simulating gravity loss. This mirrors challenges faced by older adults in extended bedrest and space environments. The first Canadian study, backed by the Canadian Space Agency, Canadian Institutes of Health Research, and Canadian Frailty Network, aims to explore these issues. The study seeks to: (1) scrutinize the impact of 14-day HDBR on physiological, psychological and neurocognitive systems, and (2) assess the benefits of exercise during HDBR. Eight teams developed distinct protocols, harmonized in three videoconferences, at the McGill University Health Center. Over 26 days, 23 participants aged 55-65 underwent baseline measurements, 14 days of -6° HDBR, and 7 days of recovery. Half did prescribed exercise thrice daily combining resistance and endurance exercise for a total duration of 1 h. Assessments included demographics, cardiorespiratory fitness, bone health, body composition, quality of life, mental health, cognition, muscle health and biomarkers. This study has yielded some published outcomes, with more forthcoming. Findings will enrich our comprehension of HDBR effects, guiding future strategies for astronaut well-being and aiding bedrest-bound older adults. By outlining evidence-based interventions, this research supports both space travellers and those enduring prolonged bedrest.

Including land management in a European carbon model with lateral transfer to the oceans.

The use of cover crops (CCs) is a promising cropland management practice with multiple benefits, notably in reducing soil erosion and increasing soil organic carbon (SOC) storage. However, the current ability to represent these factors in land surface models remains limited to small scales or simplified and lumped approaches due to the lack of a sediment-carbon erosion displacement scheme. This precludes a thorough understanding of the consequences of introducing a CC into agricultural systems. In this work, this problem was addressed in two steps with the spatially distributed CE-DYNAM model. First, the historical effect of soil erosion, transport, and deposition on the soil carbon budget at a continental scale in Europe was characterized since the early industrial era, using reconstructed climate and land use forcings. Then, the impact of two distinct policy-oriented scenarios for the introduction of CCs were evaluated, covering the European cropping systems where surface erosion rates or nitrate susceptibility are critical. The evaluation focused on the increase in SOC storage and the export of particulate organic carbon (POC) to the oceans, compiling a continental-scale carbon budget. The results indicated that Europe exported 1.95 TgC/year of POC to the oceans in the last decade, and that CCs can contribute to reducing this amount while increasing SOC storage. Compared to the simulation without CCs, the additional rate of SOC storage induced by CCs peaked after 10 years of their adoption, followed by a decrease, and the cumulative POC export reduction stabilized after around 13 years. The findings indicate that the impacts of CCs on SOC and reduced POC export are persistent regardless of their spatial allocation adopted in the scenarios. Together, the results highlight the importance of taking the temporal aspect of CC adoption into account and indicate that CCs alone are not sufficient to meet the targets of the 4‰ initiative. Despite some known model limitations, which include the lack of feedback of erosion on the net primary productivity and the representation of carbon fluxes with an emulator, the current work constitutes the first approach to successfully couple a distributed routing scheme of eroded carbon to a land carbon model emulator at a reasonably high resolution and continental scale. SHORT ABSTRACT: A spatially distributed model coupling erosion, transport, and deposition to the carbon cycle was developed. Then, it was used to simulate the impact of cover crops on both erosion and carbon, to show that cover crops can simultaneously increase organic carbon storage and reduce particulate organic carbon export to the oceans. The results seemed persistent regardless of the spatial distribution of cover crops.

New frontiers in the measurement of energy metabolism.

This perspective highlights three key areas of current and future energy metabolism research: intergenerational health, climate change, and interplanetary exploration. We describe the recent advances in determining estimated energy requirements for a large subset of the general population using the gold standard method for free-living total daily energy expenditure estimates, the doubly labeled water method. The global rise in overweight and obesity demands particular attention to energy requirements in pregnancy and early life, as accumulating evidence contributes to our understanding of intergenerational health transmission and the potential for epigenetic programming in utero. We also acknowledge some gaps in necessary guidelines and understandings of energy requirements for underrepresented populations (i.e., individuals from low and middle-income countries) or those who undergo major physiological changes in new environment (e.g., astronauts). The rising prevalence of excess weight gain, together with climate change, cumulate into a global syndemic exposing vulnerable populations to both malnutrition and the effects of unpredictable and severe weather events, emphasizing the need for varied energetic data accounting for rapid physiological and socioeconomic changes. Finally, we relate how specific estimated energy requirements are needed to account for the energetic challenges specific to extended space travel and ensure the success of interplanetary exploration.

Influence of Sintering Conditions on the Structure and Redox Speciation of Homogeneous (U,Ce)O2+δ Ceramics: A Synchrotron Study.

Although uranium-cerium dioxides are frequently used as a surrogate material for (U,Pu)O2-δ nuclear fuels, there is currently no reliable data regarding the oxygen stoichiometry and redox speciation of the cations in such samples. In order to fill this gap, this manuscript details a synchrotron study of highly homogeneous (U,Ce)O2±Î´ sintered samples prepared by a wet-chemistry route. HERFD-XANES spectroscopy led to determining accurately the O/M ratios (with M = U + Ce). Under a reducing atmosphere (pO2 ≈ 6 × 10-29 atm at 650 °C), the oxides were found to be close to O/M = 2.00, while the O/M ratio varied with the sintering conditions under argon (pO2 ≈ 3 × 10-6 atm at 650 °C). They globally appeared to be hyperstoichiometric (i.e., O/M > 2.00) with the departure from the dioxide stoichiometry decreasing with both the cerium content in the sample and the sintering temperature. Nevertheless, such a deviation from the ideal O/M = 2.00 ratio was found to generate only moderate structural disorder from EXAFS data at the U-L3 edge as all the samples retained the fluorite-type structure of the UO2 and CeO2 parent compounds. The determination of accurate lattice parameters owing to S-PXRD measurements led to complementing the data reported in the literature by various authors. These data were consistent with an empirical relation linking the unit cell parameter, the chemical composition, and the O/M stoichiometry, showing that the latter can be evaluated simply within a ± 0.02 uncertainty.

Impact of 14 Days of Bed Rest in Older Adults and an Exercise Countermeasure on Body Composition, Muscle Strength, and Cardiovascular Function: Canadian Space Agency Standard Measures.

INTRODUCTION: Head-down bed rest (HDBR) has long been used as an analog to microgravity, and it also enables studying the changes occurring with aging. Exercise is the most effective countermeasure for the deleterious effects of inactivity. The aim of this study was to investigate the efficacy of an exercise countermeasure in healthy older participants on attenuating musculoskeletal deconditioning, cardiovascular fitness level, and muscle strength during 14 days of HDBR as part of the standard measures of the Canadian Space Agency. METHODS: Twenty-three participants (12 males and 11 females), aged 55-65 years, were admitted for a 26-day inpatient stay at the McGill University Health Centre. After 5 days of baseline assessment tests, they underwent 14 days of continuous HDBR followed by 7 days of recovery with repeated tests. Participants were randomized to passive physiotherapy or an exercise countermeasure during the HDBR period consisting of 3 sessions per day of either high-intensity interval training (HIIT) or low-intensity cycling or strength exercises for the lower and upper body. Peak aerobic power (V̇O2peak) was determined using indirect calorimetry. Body composition was assessed by dual-energy X-ray absorptiometry, and several muscle group strengths were evaluated using an adjustable chair dynamometer. A vertical jump was used to assess whole-body power output, and a tilt test was used to measure cardiovascular and orthostatic challenges. Additionally, changes in various blood parameters were measured as well as the effects of exercise countermeasure on these measurements. RESULTS: There were no differences at baseline in main characteristics between the control and exercise groups. The exercise group maintained V̇O2peak levels similar to baseline, whereas it decreased in the control group following 14 days of HDBR. Body weight significantly decreased in both groups. Total and leg lean masses decreased in both groups. However, total body fat mass decreased only in the exercise group. Isometric and isokinetic knee extension muscle strength were significantly reduced in both groups. Peak velocity, flight height, and flight time were significantly reduced in both groups with HDBR. CONCLUSION: In this first Canadian HDBR study in older adults, an exercise countermeasure helped maintain aerobic fitness and lean body mass without affecting the reduction of knee extension strength. However, it was ineffective in protecting against orthostatic intolerance. These results support HIIT as a promising approach to preserve astronaut health and functioning during space missions, and to prevent deconditioning as a result of hospitalization in older adults.

Young people's proposals for a web-based intervention for sexual health promotion: a French qualitative study.

BACKGROUND: Promoting sexual health is key to improving the supportive behaviors and well-being of young people. With the advent of the Internet, web-based features for sexual health promotion may be attractive to a diverse range of young people. This study aims to assess young people's proposals regarding a web-based intervention for sexual health promotion. METHODS: Nineteen French young people aged 15-24 years participated to the study. In a semi-structured interview, they presented their views on a web-based intervention for sexual promotion. Data were coded with N'Vivo and subjected to qualitative thematic analysis to explore their proposals. RESULTS: The majority of participants (n = 18) thought that a web-based intervention for sexual health promotion would be attractive. Young people interviewed made 31 concrete proposals for sexual health promotion on the Internet. Participatory and interactive dimensions on the internet appeared essential, with the need for stimulating activities and interaction with peers, but also with competent professionals and moderation. Face to the risks of the internet, they expressed the need of a secure and confidential space, to generate trust and participation in intervention. For participants, sexual health should be addressed in all its dimensions, taking into account the relational, sexual, and gender dimensions, and by incrementing on the internet valid, credible and personalized content. CONCLUSIONS: In sexual health promotion, young people are indispensable stakeholders who can make concrete proposals and can also participate in content creation and research. More broadly, in health promotion, involving target audiences in decisions represents a promising perspective.

Diversity of farmland management practices (FMP) and their nexus to environment: A review.

We examined the environmental impacts of farmland management practices (FMPs), considering FMPs as frequent or single actions that change both land use AND use rights (land and property relations). Based on a review of the international literature in both the social and life sciences and using an analytical framework of landscape agronomy, we explored the links between FMPs and changes in agricultural practices designed for the achievement of environmental goals. The Web of Science (WOS) and SCOPUS bibliographic databases were used to identify references on FMP types and their environmental effects based on the following search equations: 1- " Farmland tenure OR cropland tenure OR farm size and environment " and 2- "Farmland use rights OR farmland property rights AND environment OR pollution OR biodiversity." Ninety references were selected from these databases and read in depth. Google scholar enabled us to identify an additional 20 papers, using the snowball approach. From this analysis, we present a typology of FMPs based on the distinction between bottom-up strategies, which rely on local initiatives from farmers to improve the overall functioning of their farms, and top-down strategies, which originate from public bodies or private organizations. Our results also highlight the environmental impacts of FMPs considered in the literature: tenure arrangements, whether rental or exchange of land parcels, may alter crop succession and reduce phytosanitary pressure without changing cropping plans. Considering the direct agronomic implications of farmers' land dynamics, we conclude that the area of FMPs is a potential tool for reducing the environmental impacts of agricultural activities and protecting natural resources. This is the subject of ongoing research that seeks to explore a particular FMP in greater depth, along with temporary exchanges of plots between farmers as an agri-environmental tool to reduce agricultural impacts on environment.

A spectroscopic hike in the U-O phase diagram.

The U-O phase diagram is of paramount interest for nuclear-related applications and has therefore been extensively studied. Experimental data have been gathered to feed the thermodynamic calculations and achieve an optimization of the U-O system modelling. Although considered as well established, a critical assessment of this large body of experimental data is necessary, especially in light of the recent development of new techniques applicable to actinide materials. Here we show how in situ X-ray absorption near-edge structure (XANES) is suitable and relevant for phase diagram determination. New experimental data points have been collected using this method and discussed in regard to the available data. Comparing our experimental data with thermodynamic calculations, we observe that the current version of the U-O phase diagram misses some experimental data in specific domains. This lack of experimental data generates inaccuracy in the model, which can be overcome using in situ XANES. Indeed, as shown in the paper, this method is suitable for collecting experimental data in non-ambient conditions and for multiphasic systems.

Comparison of saliva with oral and nasopharyngeal swabs for SARS-CoV-2 detection on various commercial and laboratory-developed assays.

The accurate laboratory detection of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a crucial element in the fight against coronavirus disease 2019 (COVID-19). Reverse transcription-polymerase chain reaction testing on combined oral and nasopharyngeal swab (ONPS) suffers from several limitations, including the need for qualified personnel, the discomfort caused by invasive nasopharyngeal sample collection, and the possibility of swab and transport media shortage. Testing on saliva would represent an advancement. The aim of this study was to compare the concordance between saliva samples and ONPS for the detection of SARS-CoV-2 on various commercial and laboratory-developed tests (LDT). Individuals were recruited from eight institutions in Quebec, Canada, if they had SARS-CoV-2 RNA detected on a recently collected ONPS, and accepted to provide another ONPS, paired with saliva. Assays available in the different laboratories (Abbott RealTime SARS-CoV-2, Cobas® SARS-CoV-2, Simplexa™ COVID-19 Direct, Allplex™ 2019-nCoV, RIDA®GENE SARS-CoV-2, and an LDT preceded by three different extraction methods) were used to determine the concordance between saliva and ONPS results. Overall, 320 tests were run from a total of 125 saliva and ONPS sample pairs. All assays yielded similar sensitivity when saliva was compared to ONPS, with the exception of one LDT (67% vs. 93%). The mean difference in cycle threshold (∆C t ) was generally (but not significantly) in favor of the ONPS for all nucleic acid amplification tests. The maximum mean ∆​​​​​C t was 2.0, while individual ∆C t varied importantly from -17.5 to 12.4. Saliva seems to be associated with sensitivity similar to ONPS for the detection of SARS-CoV-2 by various assays.

SARS-CoV-2 seroprevalence in health care workers from 10 hospitals in Quebec, Canada: a cross-sectional study.

BACKGROUND: The COVID-19 pandemic has disproportionately affected health care workers. We sought to estimate SARS-CoV-2 seroprevalence among hospital health care workers in Quebec, Canada, after the first wave of the pandemic and to explore factors associated with SARS-CoV-2 seropositivity. METHODS: Between July 6 and Sept. 24, 2020, we enrolled health care workers from 10 hospitals, including 8 from a region with a high incidence of COVID-19 (the Montréal area) and 2 from low-incidence regions of Quebec. Eligible health care workers were physicians, nurses, orderlies and cleaning staff working in 4 types of care units (emergency department, intensive care unit, COVID-19 inpatient unit and non-COVID-19 inpatient unit). Participants completed a questionnaire and underwent SARS-CoV-2 serology testing. We identified factors independently associated with higher seroprevalence. RESULTS: Among 2056 enrolled health care workers, 241 (11.7%) had positive SARS-CoV-2 serology. Of these, 171 (71.0%) had been previously diagnosed with COVID-19. Seroprevalence varied among hospitals, from 2.4% to 3.7% in low-incidence regions to 17.9% to 32.0% in hospitals with outbreaks involving 5 or more health care workers. Higher seroprevalence was associated with working in a hospital where outbreaks occurred (adjusted prevalence ratio 4.16, 95% confidence interval [CI] 2.63-6.57), being a nurse or nursing assistant (adjusted prevalence ratio 1.34, 95% CI 1.03-1.74) or an orderly (adjusted prevalence ratio 1.49, 95% CI 1.12-1.97), and Black or Hispanic ethnicity (adjusted prevalence ratio 1.41, 95% CI 1.13-1.76). Lower seroprevalence was associated with working in the intensive care unit (adjusted prevalence ratio 0.47, 95% CI 0.30-0.71) or the emergency department (adjusted prevalence ratio 0.61, 95% CI 0.39-0.98). INTERPRETATION: Health care workers in Quebec hospitals were at high risk of SARS-CoV-2 infection, particularly in outbreak settings. More work is needed to better understand SARS-CoV-2 transmission dynamics in health care settings.

Probing the Local Coordination of Hexavalent Uranium and the Splitting of 5f Orbitals Induced by Chemical Bonding.

We report here a detailed experimental and theoretical investigation of hexavalent uranium in various local configurations with a high-energy-resolution fluorescence-detected X-ray absorption near-edge structure at the U M4 edge. We show the pronounced sensitivity of the technique to the arrangement of atoms around the absorber and provide a detailed theoretical interpretation revealing the nature of spectral features. Calculations based on density functional theory and on crystal field multiplet theory indicate that for all local configurations analyzed, the main peak corresponds to nonbonding 5f orbitals, and the highest energy peak corresponds to antibonding 5f orbitals. Our findings agree with the accepted interpretation of uranyl spectral features and embed the latter in a broader field of view, which interprets the spectra of a large variety of U6+-containing samples on a common theoretical ground.

Charge Distribution in U1-xCexO2+y Nanoparticles.

In view of safe management of the nuclear wastes, a sound knowledge of the atomic-scale properties of U1-xMxO2+y nanoparticles is essential. In particular, their cation valences and oxygen stoichiometries are of great interest as these properties drive their diffusion and migration behaviors into the environment. Here, we present an in-depth study of U1-xCexO2+y, over the full compositional domain, by combining X-ray diffraction and high-energy resolution fluorescence detection X-ray absorption near-edge structure. We show, on one hand, the coexistence of UIV, UV, and UVI and, on the other hand, that the fluorite structure is maintained despite this charge distribution.

Resources Assessment for Penicillin Allergy Testing Performed by Pharmacists at the Patient's Bedside.

BACKGROUND: False penicillin allergies lead to increased antimicrobial resistance, adverse effects, and health care costs by promoting the use of broad-spectrum antibiotics. The Infectious Diseases Society of America recommends the implementation of allergy testing. OBJECTIVES: The primary objective of this research was to estimate the number of pharmacist full-time equivalents (FTEs) required for an intervention aimed at determining penicillin allergy in hospitalized patients. Acceptance of pharmacists' suggestions on antibiotic therapy are described. METHODS: A quasi-experimental study was conducted in a 712-bed university hospital involving hospitalized patients with a suspected penicillin allergy and an infection treatable with penicillin. The time required for the intervention, which included a questionnaire, penicillin allergy testing (skin-prick test, intradermal injection, and oral provocation test), and recommendations on antibiotic therapy were measured to calculate the number of pharmacist FTEs. RESULTS: A total of 55 patients were included. Scarification allergy testing was performed on 37, intradermal allergy test on 33, and oral provocation test on 26 patients. The intervention ruled out penicillin allergy in 26 patients, with no serious adverse effects. The intervention was associated with a median weekly pharmacist FTE of 0.15 (interquartile range = 0.12-0.25). The acceptance of pharmacists' suggestions was high and led to 9 patients being switched to an antibiotic with a narrower spectrum of activity. CONCLUSIONS AND RELEVANCE: This study describes penicillin allergy testing and the number of median weekly hospital pharmacist FTEs required, which was approximately 0.15. These data may aid in the implementation of this safe intervention that promotes narrower-spectrum antibiotherapy.

Soil chemistry drives below ground traits in an alternate successional pathway from forest to heath.

To understand impacts of post-disturbance assembly mechanisms on the functional diversity (FD) of plant communities, it is necessary to determine how the environment drives their functional trait composition. In the boreal forest, post-fire abiotic filters may control community assembly by selecting plants with specific traits. Ericaceous heaths are characterized by low FD and are thought to be subject to such filters. We hypothesized that soil parameters select for a specific suite of traits and act as a secondary abiotic filter in post-fire ericaceous heath and contribute to the observed reduction of FD. We measured six soil parameters, five functional traits, and plant species abundances in eight post-fire heath and four regenerating forest sites in Eastern Canada. We conducted a combined analysis of RLQ (R-table Linked to Q-table) and fourth-corner methods to examine the links between plant traits and plot-level soil parameters, mediated by species abundances. Only below ground traits were significantly linked to soil variables. Specific root length and ericoid mycorrhizal associations were negatively linked to total soil nitrogen, available ammonium, and pH. Post-fire heath soils favour a specific suite of species traits. Only a portion of the regional species pool possesses the above-mentioned traits, and when they are favoured by habitat conditions, they assemble into a community with low FD. The novelty of our study is here we show how the relationship between traits and soil chemistry can act as a secondary filter and exert community-level trait changes responsible for the low functional diversity observed in heaths.

Bayesian Evaluation of Solana HSV 1+2/VZV Assay Compared to Viral Culture and Commercial PCR Assay for Cutaneous or Mucocutaneous Specimens.

Results from the Solana HSV 1+2/VZV assay for the detection of herpes simplex virus 1 (HSV-1), HSV-2, and varicella-zoster virus (VZV) in cutaneous or mucocutaneous specimens were compared with that of viral culture and a commercial PCR assay (RealStar alpha herpesvirus PCR kit). Three hundred two mucocutaneous specimens, for which HSV-1, HSV-2, or VZV viral culture or PCR detection have been requested, were randomly selected and prospectively processed on the Solana assay and viral culture or the RealStar assay. Discordant results between culture and the Solana assay were further analyzed using the RealStar assay. A Bayesian latent class model was developed to estimate the performance of each method. Viral culture detected 123 positive specimens (85 HSV-1, 36 HSV-2, and 2 VZV), while the Solana assay detected 27 additional positive specimens (4 HSV-1, 11 HSV-2, and 12 VZV), in agreement with the RealStar PCR assay. The estimated sensitivity of the Solana assay according to our model was 92.7% to 98.7%, 87.1% to 97.8%, and 94.9% to 98.8% (95% confidence interval [CI]) for HSV-1 HSV-2, and VZV, respectively, while the estimated sensitivity of viral culture was 85.2% to 95.0%, 73.6% to 89.6%, and 30.9% to 45.8% (95% CI), respectively. A nonsignificant tendency toward increased sensitivity was noted for the Solana assay compared with culture for HSV-1 and HSV-2, and the Solana assay was significantly more sensitive than culture for the detection of VZV. The Solana assay performed comparably to the RealStar assay. Processing time was reduced with the Solana assay compared with viral culture.

Hydrothermal Conversion of Thorium Oxalate into ThO2·nH2O Oxide.

Hydrothermal conversion of thorium oxalate, Th(C2O4)2·nH2O, into thorium dioxide was explored through a multiparametric study, leading to some guidelines for the preparation of crystallized samples with the minimum amount of impurities. As the formation of the oxide appeared to be operated through the hydrolysis of Th4+ after decomposition of oxalate fractions, pH values typically above 1 must be considered to recover a solid phase. Also, because of the high stability of the thorium oxalate precursor, hydrothermal treatments of more than 5 h at a temperature above 220 °C were required. All the ThO2·nH2O samples prepared presented amounts of residual carbon and water in the range 0.2-0.3 wt % and n ≈ 0.5, respectively. A combined FTIR, PXRD, and EXAFS study showed that these impurities mainly consisted of carbonates trapped between elementary nanosized crystallites, rather than substituted directly in the lattice, which generated a tensile effect over the crystal lattice. The presence of carbonates at the surface of the elementary crystallites could also explain their tendency to self-assembly, leading to the formation of spherical aggregates. Hydrothermal conversion of oxalates could then find its place in different processes of the nuclear fuel cycle, where it will provide an interesting opportunity to set up dustless routes leading from ions in solution to dioxide powders in a limited number of steps.

Structural and Thermodynamic Investigation of the Perovskite Ba2NaMoO5.5.

Neutron diffraction, X-ray absorption spectroscopy (XAS), and Raman spectroscopy measurements of the quaternary perovskite phase Ba2NaMoO5.5 have been performed in this work. The cubic crystal structure in space group Fm3̅m has been refined using the Rietveld method. X-ray absorption near-edge structure spectroscopy (XANES) measurements at the Mo K-edge have confirmed the hexavalent state of molybdenum. The local structure of the molybdenum octahedra has been studied in detail using extended X-ray absorption fine structure (EXAFS) spectroscopy. The Mo-O and Mo-Ba distances have been compared to the neutron diffraction data with good agreement. The coefficient of thermal expansion measured in the temperature range of 303-923 K, using high temperature X-ray diffraction (HT-XRD) (αV = 55.8 × 10-6 K), has been determined to be ∼2 times higher than that of the barium molybdates BaMoO3 and BaMoO4. Moreover, no phase transition nor melting have been observed, neither by HT-XRD nor Raman spectroscopy nor differential scanning calorimetry, up to 1473 K. Furthermore, the standard enthalpy of formation (ΔfHm°) for Ba2NaMoO5.5(cr) has been determined to be -(2524.75 ± 4.15) kJ mol-1 at 298.15 K, using solution calorimetry. Finally, the margin for safe operation of sodium-cooled fast reactors (SFRs) has been assessed by calculating the threshold oxygen potential needed, in liquid sodium, to form the quaternary compound, following an interaction between irradiated mixed oxide (U,Pu)O2 fuel and sodium coolant.

Investigation of the Cs2(Mo,Te)O4 Solid Solution and Implications on the Joint Oxyde-Gaine System in Fast Neutron Reactors.

The formation of a thin layer, the so-called Joint Oxyde-Gaine (JOG), between the (U,Pu)O2 fuel pellets and the cladding has been observed in fast neutron reactors, due to the accumulation of volatile fission products. Cs2MoO4 is known to be one of the major components of the JOG, but other elements are also present, in particular tellurium and palladium. In this work, an investigation of the structural and thermodynamic properties of Cs2TeO4 and Cs2Mo1-xTexO4 solid solution is reported. The existence of a complete solubility between Cs2MoO4 and Cs2TeO4 is demonstrated, combining X-ray diffraction (XRD), neutron diffraction (ND), and X-ray absorption spectroscopy (XAS) results. High-temperature XRD measurements were moreover performed on Cs2TeO4, which revealed the existence of a α-ß phase transition around 712 K. Thermal expansion coefficients were also obtained from these data. Finally, phase equilibra points in the Cs2MoO4-Cs2TeO4 pseudobinary phase diagram were collected using differential scanning calorimetry and used to develop a thermodynamic model for this system using a regular solution formalism.

Oxidation as an Early Stage in the Multistep Thermal Decomposition of Uranium(IV) Oxalate into U3O8.

The thermal decomposition of actinide oxalates is greatly dependent on the oxidation state of the cation, the gas involved, and the physical characteristics of the precursor. In the actinides series, uranium(IV) oxalate U(C2O4)2·6H2O can be viewed as a peculiar case, as its sensibility toward oxidation leads to a specific series of reactions when heating under an oxygen atmosphere. In order to clarify the disagreements existing in the literature, particularly concerning potential carbonate intermediates and the possible transitory existence of UO3, we show here an extended characterization of the different intermediates through a combination of X-ray diffraction, vibrational spectroscopies and X-ray absorption near-edge spectroscopy. In this frame, uranium oxidation was found to occur at low temperature (200 °C) concomitantly to the onset of oxalate groups decomposition, leading to an amorphous oxo-oxalato compound. Pursuing the thermal conversion up to 350 °C led to complete oxidation of U(IV) into U(VI), then to the formation of amorphous UO3 still bearing adsorbed carbonates. The first pure oxide formed during the thermal conversion was further identified to substoichiometric UO3-δ after heating at 550 °C. Finally, U3O8 was obtained as the final stable phase after heating above 660 °C. The mechanism of thermal conversion of uranium(IV) oxalate into oxide under oxygen is then driven by a complex interplay between redox reactions and decomposition of the organic fractions. Such chemical reactions were also found to significantly modify the morphology of the powder through high-temperature environmental scanning electron microscopy observations: decomposition led to a 20% reduction in the size of the aggregates, while uranium oxidation clearly promoted growth within the agglomerates.

Size Dependence of Lattice Parameter and Electronic Structure in CeO2 Nanoparticles.

Intrinsic properties of a compound (e.g., electronic structure, crystallographic structure, optical and magnetic properties) define notably its chemical and physical behavior. In the case of nanomaterials, these fundamental properties depend on the occurrence of quantum mechanical size effects and on the considerable increase of the surface to bulk ratio. Here, we explore the size dependence of both crystal and electronic properties of CeO2 nanoparticles (NPs) with different sizes by state-of-the art spectroscopic techniques. X-ray diffraction, X-ray photoelectron spectroscopy, and high-energy resolution fluorescence-detection hard X-ray absorption near-edge structure (HERFD-XANES) spectroscopy demonstrate that the as-synthesized NPs crystallize in the fluorite structure and they are predominantly composed of CeIV ions. The strong dependence of the lattice parameter with the NPs size was attributed to the presence of adsorbed species at the NPs surface thanks to Fourier transform infrared spectroscopy and thermogravimetric analysis measurements. In addition, the size dependence of the t2g states in the Ce LIII XANES spectra was experimentally observed by HERFD-XANES and confirmed by theoretical calculations.