Determination of the pressure in micrometric bubbles in irradiated nuclear fuels

In oxide nuclear fuels, at high burn-up or during high temperature periods such as ramp tests, out-of- pile heating tests, or any irradiations at high linear heat rates, fission gases can form micrometric or quasi-micrometric bubbles. During nominal operations, these bubbles participate to the pellet swelling, to the decrease of the fuel thermal conductivity and are involved in the mechanisms leading to fission gas release. During events involving a temperature increase, the resulting increase in the internal pres- sure of the bubbles might play a role in fuel fragmentation and in the opening of grain boundaries. The gas densities inside these bubbles are therefore one of the useful experimental information for the un- derstanding of the fuel behaviour, and for the fuel behaviour code progress and validation. Two methods were developed to evaluate the gas density in the quasi-micrometric bubbles, using electron probe micro analyser, secondary ion mass spectrometry and focused ion beam scanning electron microscope together. The first method provides a mean gas density for all quasi-micrometric bubbles in a given area. The sec- ond method provides a gas density in a single selected bubble. In addition to the gas density, the 3D size and shape of the selected bubble is measured and can be related to the gas density result. In this work, these methods were applied to the bubbles formed in the centre of a PWR Cr doped UO 2 at 38.8 GWd/t U after a ramp test in the Osiris reactor, with a 12 h plateau at 470 W/cm, and to the bubbles formed in a PWR Cr doped UO 2 at 62.8 GWd/t U in the centre of the pellet and on the bubbles of the high burn-up structure on the rim. Both show the high pressures reached in these bubbles.CEA-DES, EDF and Framatom

Fission products behaviour during a power transient: Their inventory in an intragranular bubble

International audienceThe behavior of fission products is a key issue during incidental or accidental sequence for nuclear fuel. Here we characterized how fission products behaved inside a UO$_2$ pellet during a power ramp. In the pellet center fission products have left the UO$_2$ ceramic and can be found in bubbles. The composition of the bubble was determined using an original experimental methodology. The existence of separated precipitates made of metallic, for the one, and volatile, for the other, fission products was evidenced. This result is discussed with regards to the behavior of fission products during a power ramp

Dynamic SIMS for Materials Analysis in Nuclear Science

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Dynamic SIMS for materials analysis in nuclear science

International audienceOffering high sensitivity, depth profiling and ion imaging capabilities together with high throughput, dynamic secondary ion mass spectrometry (SIMS) proves extremely useful for a wide range of nuclear science applications. The CAMECA IMS 7f/7f-Auto is a versatile magnetic sector SIMS well suited for such applications. In this work, various examples of material analyses that are of interest for nuclear science are presented: depth profiling of the xenon and mapping of contaminants in CeO2, in-depth distribution of iodine in SiC using the energy filtering technique for improving the I detection limit, and depth profiling analysis of molybdenum in UO2 using eucentric sample rotation for minimizing surface roughness development (thus improving data quality)

Experimental determination of cesium and iodine speciation in UO2 as a function of temperature and oxygen partial pressure

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Experimental determination of cesium and iodine speciation in UO2 as a function of temperature and oxygen partial pressure

International audienc

Behaviour of fission products in UO2: Experimental characterization of the Cs-I-UO2 model system at high temperature

International audienceThe interactions of iodine and caesium in UO2 have been investigated. For this purpose, implanted UO2 samples were thermally treated (4h at 900°C or 1h at 1200°C) under controlled atmosphere (0.03% H2O/H2) and then characterized by several experimental techniques for their structural and chemical studies. Thermodynamic calculations were also performed in order to optimize heat treatment conditions before performing tests, and to help in the interpretation of results afterwards. The sample characterizations after thermal treatments reveal the presence of bubbles and precipitates (mean diameter around 10 - 20 nm) and have allowed to clearly identify the presence of CsI in these bubbles which is in agreement with the calculations. The chemical form of the observed precipitates is not well defined yet, due to the lack of experimental reference spectra, but they consist very likely of caesium uranates, as predicted by the thermodynamic calculations

Type 1 Diabetes in People Hospitalized for COVID-19: New Insights From the CORONADO Study

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The association between macrovascular complications and intensive care admission, invasive mechanical ventilation, and mortality in people with diabetes hospitalized for coronavirus disease-2019 (COVID-19)

International audienceAbstract Background It is not clear whether pre-existing macrovascular complications (ischemic heart disease, stroke or peripheral artery disease) are associated with health outcomes in people with diabetes mellitus hospitalized for COVID-19. Methods We conducted cohort studies of adults with pre-existing diabetes hospitalized for COVID-19 infection in the UK, France, and Spain during the early phase of the pandemic (between March 2020—October 2020). Logistic regression models adjusted for demographic factors and other comorbidities were used to determine associations between previous macrovascular disease and relevant clinical outcomes: mortality, intensive care unit (ICU) admission and use of invasive mechanical ventilation (IMV) during the hospitalization. Output from individual logistic regression models for each cohort was combined in a meta-analysis. Results Complete data were available for 4,106 (60.4%) individuals. Of these, 1,652 (40.2%) had any prior macrovascular disease of whom 28.5% of patients died. Mortality was higher for people with compared to those without previous macrovascular disease (37.7% vs 22.4%). The combined crude odds ratio (OR) for previous macrovascular disease and mortality for all four cohorts was 2.12 (95% CI 1.83–2.45 with an I 2 of 60%, reduced after adjustments for age, sex, type of diabetes, hypertension, microvascular disease, ethnicity, and BMI to adjusted OR 1.53 [95% CI 1.29–1.81]) for the three cohorts. Further analysis revealed that ischemic heart disease and cerebrovascular disease were the main contributors of adverse outcomes. However, proportions of people admitted to ICU (adjOR 0.48 [95% CI 0.31–0.75], I 2 60%) and the use of IMV during hospitalization (adjOR 0.52 [95% CI 0.40–0.68], I 2 37%) were significantly lower for people with previous macrovascular disease. Conclusions This large multinational study of people with diabetes mellitus hospitalized for COVID-19 demonstrates that previous macrovascular disease is associated with higher mortality and lower proportions admitted to ICU and treated with IMV during hospitalization suggesting selective admission criteria. Our findings highlight the importance correctly assess the prognosis and intensive monitoring in this high-risk group of patients and emphasize the need to design specific public health programs aimed to prevent SARS-CoV-2 infection in this subgroup