Diffusivity in metallic beryllium: The case of the H, C, N and O species

International audienceThe insertion and diffusivity of interstitial species in metallic beryllium are discussed in this work using a multi-scale methodology, coupling first-principles calculations and a multi-site approach. Emphasis is placed on the main interstitial species, i.e., H, C, N and O atoms. The results show that the most stable site is strongly dependent on the nature of the interstitial atom. Indeed, carbon is most stable in octahedral sites and hydrogen tetrahedral sites, while oxygen and nitrogen are most stable in basal tetrahedral sites. From the stable insertion sites and symmetrical saddle points identified, a number of migration pathways were mapped. The diffusion pathways were then completed using nudged elastic band (NEB) calculations. The diffusivity of the atoms shows an isotropic behavior as expected for carbon, which shows a strong anisotropic behavior with faster diffusivity along the basal plane. These theoretical results are in agreement with known experimental data, especially for hydrogen diffusion. The discrepancy between theory and experiment is corrected by the vacancy trapping effect. Finally, this paper theoretically determines the Arrhenius parameters of each diffusing species, in particular carbon and oxygen, for which no data were available

Intercomparison Exercise on Electron Paramagnetic Resonance Dosimetry in Sorbitol

International audienceThis paper presents the results of the first intercomparison exercise on Electron Paramagnetic Resonance (EPR) dosimetry using sorbitol, where the performance parameters of sorbitol as dosimetric material were evaluated by three independent participants. Each participant was asked to determine a calibration curve using a set of sorbitol powder samples irradiated to four different doses (1.00, 2.50, 5.00, and 10.00 Gy of air kerma). The calibration doses were known to the participants, who were asked to measure each sample three times, and to report the EPR signal response, the mass of aliquots measured, and the parameters of EPR signal acquisition and signal evaluation. Critical dose and detection limit were calculated based on the calibration-curve parameters obtained by each participant. The mean values of the detection limit and average critical dose were found to be 802 ± 148 mGy and 411 ± 77 mGy, respectively. These values were compared with those of for alanine, glass and tooth enamel. The participants were also provided with four blind samples irradiated to four unknown doses, and their reported doses were compared with the delivered doses and performance quotient was calculated for each participant. The findings indicate that sorbitol is a promising candidate for accidental and retrospective dosimetry

First wheat certified reference material for organically bound tritium measurement in the environment

International audienceMeasuring the radioactivity of organically bound tritium in environmental samples is difficult. For the past twenty years, many laboratories have been working on the development of reliable tritium measurement methods. In this context, several interlaboratory comparisons have been organised to develop these methods and enable laboratories to compare themselves. However, the trueness of the measurement methods has never been estimated due to the lack of certified reference materials available for use during the analyses. This document presents the production of the first certified reference material for the measurement of organically bound tritium radioactivity in environmental samples

Towards real-time calibration-free LIBS supported by machine learning

International audienceCalibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) enables multi-elemental quantification without needing standards. This type of approach can be used to analyze complex samples containing traces or gradients of species. This type of diagnosis requires a high level of expertise, and is cumbersome to set up. These constraints limit its application to field diagnostics. Using the MERLIN generalized radiative transfer code, we are able to generate a diversified emission database with no dimensioning limitations. We show that training a convolutional residual network with such a database enables the quantification of 9 species, as well as evaluation of electron density and temperature, without any prior expertise at a rate greater than 10 Hz. The accuracy of this innovative method depends solely on the basic spectroscopic data (emission probabilities and Stark parameters), regardless of the thermodynamic conditions of the laser-induced plasma, as long as it is in Local Thermodynamic Equilibrium (LTE)

Metabolomics identifies plasma biomarkers of localized radiation injury

International audienceA radiological accident may result in the development of a local skin radiation injury (LRI) which may evolve, depending on the dose, from dry desquamation to deep ulceration and necrosis through unpredictable inflammatory waves. Therefore, early diagnosis of victims of LRI is crucial for improving medical care efficiency. This preclinical study aims to identify circulating metabolites as biomarkers associated with LRI using a C57BL/6J mouse model of hind limb irradiation. More precisely, two independent mice cohorts were used to conduct a broad-spectrum profiling study followed by a suspect screening analysis performed on plasma metabolites by mass spectrometry. An integrative analysis was conducted through a multi-block sparse partial least square discriminant analysis (sPLS-DA) to establish multi-scale correlations between specific metabolites levels and biological, physiological (injury severity), and functional parameters (skin perfusion). The identified biomarker signature consists in a 6-metabolite panel including putrescine, uracil, 2,3-dihydroxybenzoate, 3-hydroxybenzoate, L-alanine and pyroglutamate, that can discriminate mice according to radiation dose and injury severity. Our results demonstrate relevant molecular signature associated with LRI in mice and support the use of plasma metabolites as suitable molecular biomarkers for LRI prognosis and diagnosis

One-dimensional oscillatory flows in partially saturated media with moving multi-front

International audienceThe moving multi-front (MMF) methods are used to analyze the response of partially saturated flow due to tidal periodic forcing imposed at the bottom of a vertical porous column comprising a saturated zone, a water table, and an unsaturated zone above it. The MMF is a Lagrangian semi-analytical method for solving the nonlinear Richards equation, based on a non-linear ordinary differential equations system, which is compared in this paper to a Eulerian finite volume solution. The MMF is used here to analyze the water table fluctuations Zs(t), the bottom flux fluctuations q0(t), as well as the vertical profiles of total head H(z,t), and finally, the complex behavior of the zero-flux planes Z0(t), during the cyclic motion. Additionally, the MMF is used to develop a parametric study of the mean water table height vs frequency. A systematic error analysis is developed for MMF vs the number of moving fronts (N), leading to a characterization of error norm for the space–time water content profiles (with second order accuracy) and for the temporal water table elevation (with order of accuracy 4/3). The MMF method is a generalization of the Green–Ampt piston flow approximation, which corresponds to a single moving front (N=1). The errors of the N-front MMF are rapidly reduced as the number of fronts increases. In many cases, 20 moving fronts are sufficient to capture most features. For sandy soils (fine sand), even the 2-front solution (N= 2) is satisfactory in terms of water table response Zs(t). Overall, the MMF method is a useful and efficient tool for exploring the frequency response of the water table and the unsaturated zone to tidal forcing

Induced polarization of clay-rich materials - Part 4 : Water content and temperature effects in bentonites

International audienceDeep Geological Disposals (DGDs) are widely seen to be the best solution to safely contain high-level radioactive wastes. Compacted bentonite and bentonite-sand mixtures are considered as the most appropriate buffers or sealing materials for access drifts, ramps, and shafts due to their favorable physicochemical and hydro-mechanical properties.Bentonite-sand mixtures are expected to swell and seal all voids when in contact with water, forming an impermeable barrier to radioactive elements. The parameters that will most affect the hydraulic performance of these seals are their water content, dry density, water salinity and temperature. Monitoring and assessing these parameters are therefore crucial to confirm that the seals safety functions are fulfilled during the life of a DGD. Induced polarization is a non-intrusive geophysical method able to perform this task. However, its underlying physics for bentonite sand mixtures has not been checked. The complex conductivity spectra of 42 compacted bentonite-sand mixtures were measured in the frequency range 1 Hz -45 kHz in order to develop relationships between in-phase and quadrature conductivities versus water content and saturation, pore water conductivity, bentonite-sand ratio (10% to 90%), temperature (10-60°C), and dry density (0.97 to 1.64 g cm -3 ). We observe that conductivity is mostly dominated by surface conductivity associated with the Stern layer coating the surface of smectite, the main component of bentonite. At a given salinity and temperature, the inphase and quadrature conductivities obey power law relationships with water content and saturation. The in-phase and quadrature conductivities depend on temperature according to a classical linear relationship with the same temperature coefficient. A Stern layer-based model is used to explain the dependence of the complex conductivity with water content, dry density, water salinity and temperature. It could be used to interpret induced polarization field data to monitor the efficiency of the seal of DGD facilities.</p

Outcomes of the Experimental and Numerical Work on the Operational Behavior of Passive Autocatalytic Recombiners in the Late Phase of a Severe Accident in the Framework of the AMHYCO Project

International audienceThe molten corium-concrete interaction in the ex-vessel phase of a severe accident ina light water reactor is a source of significant amounts of gaseous products includingcarbon monoxide. The European project AMHYCO addresses open issues related tothe understanding of the impact of carbon monoxide on safety-relevant accidentphenomena like combustion and on hydrogen mitigation measures. In order to supportthe simulation of accident sequences and the assessment of safety measures, Task3.2 aimed to provide realistic models considering the influence of carbon monoxide onthe operating behavior of passive auto-catalytic recombiners. The work programincluded conducting new experiments, analyzing existing experimental data, andfurther developing numerical models.The experimental program performed within Task 3.2 involved the REKO facilities atResearch Center Jülich (FZJ) to study the impact of predicted accident atmospheresincluding oxygen-lean mixtures and the presence of carbon monoxide on the hydrogenrecombination efficiency of different generic catalysts. More specifically, criteria werederived to predict the atmospheric conditions leading to catalyst poisoning. At thesame time, a unified database including selected datasets from the variousOECD/NEA-THAI projects was developed. The available experimental data were usedto further advance numerical models such as the manufacturer’s engineeringcorrelation for Framatome PARs as well as the scientific codes SPARK (IRSN),PARUPM (UPM), and REKO-DIREKT (FZJ)

Radionuclide sorption dynamics in the Rhone River: Experimental and modelling approach

International audienceThe transfer of radionuclides discharged into rivers by nuclear facilities are conditioned by their solid/liquid fractionation, commonly represented by an equilibrium approach using the distribution coefficient K_d. This coefficient, largely used in modeling, assumes an instantaneous and completely reversible reaction. However, such assumptions are rarely verified. Compared to instantaneous adsorption of radionuclides onto particles, slower reactions may lead to an underestimation of the dissolved fraction, and modifications of environmental conditions (e.g. at confluences, dams…) may induce a change in solid/liquid partition. Considering this background, this study aims to assess whether models incorporating one or more kinetics to describe this fractionation allow more accurate estimations than the equilibrium approach. A large dataset has been obtained experimentally to compare and test fractionation models. The exchanges of four radionuclides (137Cs, 60Co, 54Mn, and 110mAg) between solution and riverine suspended particulate matter (from the Rhone River, France) were followed in laboratory. Adsorption kinetics were monitored starting from 30 minutes up to 2 months. They stabilized only after several days and up to 2 weeks. Dilutions of the contaminated suspension were carried out after 1 hour, 3 days, 10, 21 and 31 days of prior adsorption, to simulate a change in environmental conditions, such as the input of uncontaminated water from a tributary. The dilution induced a quick release from solid to liquid at first, followed by a non-expected re-adsorption for all four radionuclides. 31-days sorption data were used to fit the parameters of a Kd model and derived models involving one (EK) or two fractionation kinetics (KK). Predictions were then carried out to evaluate the model capacities to react to a dilution of the contamination. Unlike the Kd model, which is a constant, the kinetic models predicted a variation in the solid/liquid activity ratio over time and when environmental conditions changed. However, models developed on one-step sorption showed limitations to reproduce the adsorption kinetics observed after a dilution, especially when a previous steady-state was reache

Impact of Alkali-Silica Reaction and Delayed Ettringite Formation-induced cracking on air permeability and water diffusivity in concrete

International audienceManaging the effects of Internal Swelling Reactions (ISR), Delayed Ettringite Formation (DEF), and Alkali-Silica Reaction (ASR) on the integrity of concrete structures with containment functions, such as nuclear facilities and dams, remains a major challenge for both long-term operation and maintenance. However, the effect of cracking caused by ISR on the mass transport properties of concrete has not been extensively investigated. To date, there is limited characterization of water diffusive phenomena and permeability in concretes affected by ISR. To address these gaps, a comprehensive and complete characterization of mass transport properties evaluating water porosity, pore distribution, diffusivity, and apparent air permeability in concrete affected by ASR and DEF is conducted hereafter. This experimental work points out the impact of cracking induced byexpansion on these parameters. Water diffusivity is multiplied by a maximum of 2.8 for 0.22% expansion in DEF, while permeability can be multiplied by 44 for ASR concrete after expansion to 0.22%. The cracking patterns induced by ASR and DEF are different, leading to differences in the evolution of transport properties. Overall, crucial experimental insights to enhance existing models are thus highlighted, particularly concerning the intricate relationship between expansion advancement, cracking, and mass transport properties in concrete