Consequences of the ion beam irradiation on the chemical durability of thorium phosphate diphosphate – kinetics study

RADIOCHIn the field of the long-term specific immobilization of actinides, thorium phosphate diphosphate (β-TPD), as potential candidate, must respond to several criteria. Among them, the material must present a good resistance to irradiation and keep its initial good properties such as resistance to aqueous alteration. In order to check this later point, sintered samples of β-TUPD solid solutions were pre-irradiated with ion beams with various conditions (fluence, stopping power) then submitted to leaching tests in different media (pH, temperature, complexing reagents, flow rate, ...). The normalized dissolution rates depend significantly on the amorphous fraction (increase by a factor of 10–100 between unirradiated and fully amorphized materials). On the contrary, the pre-irradiation of the samples does not affect the kinetic parameters of the dissolution such as the partial order relative to the proton concentration (n = 0.37 ± 0.01 and n = 0.34 ± 0.01 for unirradiated and fully amorphized samples, respectively) and the activation energy of the reaction of dissolution (Eapp = 49 ± 4 kJ mol−1 and Eapp = 42 ± 4 kJ mol−1 for unirradiated and partly amorphized samples (fA < 1), respectively)

SARS-CoV-2 specific immune responses in overweight and obese COVID-19 patients

Obesity is a known risk factor for severe respiratory tract infections. In this prospective study, we assessed the impact of being obese or overweight on longitudinal SARS-CoV-2 humoral and cellular responses up to 18 months after infection. 274 patients provided blood samples at regular time intervals up to 18 months including obese (BMI ≥30, n=32), overweight (BMI 25-29.9, n=103) and normal body weight (BMI 18.5-24.9, n=134) SARS-CoV-2 patients. We determined SARS-CoV-2 spike-specific IgG, IgA, IgM levels by ELISA and neutralising antibody titres by neutralisation assay. RBD- and spike-specific memory B cells were investigated by ELISpot, spike- and non-spike-specific IFN-γ, IL-2 and IFN-γ/IL-2 secreting T cells by FluoroSpot and T cell receptor (TCR) sequencing was performed. Higher BMI correlated with increased COVID-19 severity. Humoral and cellular responses were stronger in overweight and obese patients than normal weight patients and associated with higher spike-specific IgG binding titres relative to neutralising antibody titres. Linear regression models demonstrated that BMI, age and COVID-19 severity correlated independently with higher SARS-CoV-2 immune responses. We found an increased proportion of unique SARS-CoV-2 specific T cell clonotypes after infection in overweight and obese patients. COVID-19 vaccination boosted humoral and cellular responses irrespective of BMI, although stronger immune boosting was observed in normal weight patients. Overall, our results highlight more severe disease and an over-reactivity of the immune system in overweight and obese patients after SARS-CoV-2 infection, underscoring the importance of recognizing overweight/obese individuals as a risk group for prioritisation for COVID-19 vaccination

Amorphization of β\beta-thorium phosphate diphosphate (β\beta-TPD) irradiated with high energy krypton ions

Expérience GANILAs potential actinide-bearing phase for geological deposit of nuclear wastes, the $\beta$-Thorium Phosphate Diphosphate ceramic ($\beta$-TPD), Th$_4$(PO$_4$)$_4$P$_2$O$_7$, must be resistant against radiation. A high-energy ion beam (840-MeV Kr) was used to check this property by simulating the electronic effects of radiation. The amorphization of the material was followed in situ by using the on line XRD analysis setup (CHEXPIR) of the GANIL accelerator. XRD measurements show a complete amorphization of the material with a kinetics which fits to a direct impact model. Thermal annealing of amorphized samples leads to a complete recrystallization of the structure at 1023 K

Consequences of external irradiation on the chemical durability of the β\beta-thorium phosphate-diphosphate during leaching tests

Expérience GANILThe effect of external irradiation on $\beta$-thorium phosphate-diphosphate (tetravalent actini des bearing storage matrix) and the influence on its dissolution in aqueous media were studied. Highly energetic heavy ions were used to get the amorphization of the crystalline structure of the ceramic. The ex-situ dissolution expenments showed an increase of the dissolution versus amorphous fraction in several pH and temperature conditions. The in-situ dissolution experiments highlighted the primordial importance of radiolytic produced free radical species. From these results, the ceramic presents a good resistance to aqueous alteration even in amorphous state

Mechanisms of uranyl sorption. In: Energy, Waste and the Environment: a Geochemical Perspective. Chapter IV: Waste-Waste Interaction. R. Gieré and P. Stille (eds.), pp. 545-560.

International audienc

Avancées dans la synthèse et la mise en forme de carbures d’uranium

International audienc

An off-line method to characterize the fission product release from uranium carbide-target prototypes developed for SPIRAL2 project

International audienceIn the context of radioactive ion beams, fission targets, often based on uranium compounds, have been used for more than 50 years at isotope separator on line facilities. The development of several projects of second generation facilities aiming at intensities two or three orders of magnitude higher than today puts an emphasis on the properties of the uranium fission targets. A study, driven by Institut de Physique Nucléaire d'Orsay (IPNO), has been started within the SPIRAL2 project to try and fully understand the behavior of these targets. In this paper, we have focused on five uranium carbide based targets. We present an off-line method to characterize their fission product release and the results are examined in conjunction with physical characteristics of each material such as the microstructure, the porosity and the chemical composition