Energetically favorable sites of iodine atoms in zirconium crystal : an ab-initio approach

Théorie, AC

Helium precipitation study in UO2 by Transmission Electron Microscopy

International audienc

Crustose coralline algae can contribute more than corals to coral reef carbonate production

This is the final version. Available on open access from Nature Research via the DOI in this recordData availability: Data are available at https://github.com/JayCrlt/CCA_MethodsCode availability: Codes are available at https://github.com/JayCrlt/CCA_MethodsUnderstanding the drivers of net coral reef calcium carbonate production is increasingly important as ocean warming, acidification, and other anthropogenic stressors threaten the maintenance of coral reef structures and the services these ecosystems provide. Despite intense research effort on coral reef calcium carbonate production, the inclusion of a key reef forming/accreting calcifying group, the crustose coralline algae, remains challenging both from a theoretical and practical standpoint. While corals are typically the primary reef builders of contemporary reefs, crustose coralline algae can contribute equally. Here, we combine several sets of data with numerical and theoretical modelling to demonstrate that crustose coralline algae carbonate production can match or even exceed the contribution of corals to reef carbonate production. Despite their importance, crustose coralline algae are often inaccurately recorded in benthic surveys or even entirely missing from coral reef carbonate budgets. We outline several recommendations to improve the inclusion of crustose coralline algae into such carbonate budgets under the ongoing climate crisis.French Embassy - French Related Research Projects (F2RP)Agence Nationale de la Recherche (ANR)Royal Society of New Zealand Te Apārang

Release of fission products (Xe, Kr, I, Cs) implanted in polycrystalline UO2

International audienceUnder irradiations in nuclear reactors, the microstructure of oxide nuclear fuel changes. To improve the modeling of the UO2 fuel behavior under irradiation, it is necessary to understand the elementary mechanisms of fission products diffusion. Among them, rare gas Xenon and Krypton represent 30% of created elements and fission products such as Iodine and Caesium are corrosive for the clad. Our experimental work consists in the measurement of the fission products release kinetics by Knudsen cell mass spectrometry. For that, 8mm diameter-1 mm height fresh polycrystalline UO2 pellets are implanted with different concentrations in 129Xe, 83Kr, 127I, 133Cs to understand the effect of the fission products density on the diffusion. The release kinetics is studied either during the heating at a given rate from room temperature to about 2050DC (Figure) or during isothermal annealing every 100 DC from 100 to 1600 DC

Diffusion of Xe and Kr implanted at low concentrations in UO2_2 as a function of temperature – An experimental study

International audienceFission gases production and release have a large impact on uranium dioxide fuel performance. To predict fuel properties in pile, a better understanding of the fission gas behaviour in uranium dioxide is needed. UO2 samples were implanted with Xe or Kr at low doses to avoid trapping by irradiation defects and/or gas clusters. The release rates of Xe and Kr were studied at temperatures ranging up to 1400°C. Results show an excellent agreement with the substantial literature on xenon diffusion in irradiated UO2

Experimental study of the diffusion of Xe and Kr implanted at low concentrations in UO2 and determination of their trapping mechanisms

The fission of uranium dioxide produces gaseous elements degrading nuclear fuel properties. A thorough understanding of the transport and release of gaseous products is thus essential. The present work focuses on xenon and krypton migration mechanism in uranium dioxide. Desorption experiments on ion implanted UO2 were performed at 1300°C. Xe and Kr releases were simulated using a mesoscale model that was developed taking into account single gas atom diffusion and defect traps. We showed that the defects have a high influence on Xe and Kr migration mechanisms and therefore have to be considered to accurately determine diffusion coefficients. We evaluated the diffusion coefficient of Xe and Kr at (1.73 ± 0.15)x10−20 m2/s at 1300°C and we showed that the diffusion of rare gases is subjected to two trapping mechanisms. The first occurs during the ion implantation and the second during high-temperature annealings. The nature of the trapping sites is discussed in the light of the literature on radiation induced defects. This study also consolidates the use of non activated UO2 implanted with heavy ions as a less-hazardeous substitute for irradiated UO2