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

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

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

Numerical investigation of mechanisms affecting alkali-silica reaction advancement by reactive transport simulations

International audienceAlkali-Silica Reaction (ASR) is a long-term chemical degradation induced in concrete by the difference in pH between the aggregate and the cement paste. ASR advancement is thus driven by the combination of the ionic species diffusion and the dissolution of reactive silica. In this paper, the reactive transport model is based on the principal sequence of the ASR-mechanisms: hydroxide, alkali and calcium diffusion, silica dissolution and reaction products precipitation. First, the proposed model highlights the impact of the competition between diffusion and dissolution kinetic on the formation of products in the depth of the aggregate particles according to the calcium concentration. Secondly, the numerical study on the size effect of the aggregate particles highlights the efficacy of this approach to reproduce the dependence of the products type formed during precipitation, allowing for the competition between ASR and pozzolanic effect to be reproduced

Exploring the safety and performance of molten salt reactors for their deployment in the European Union: the MIMOSA and ENDURANCE projects

International audienceMolten Salt Reactors (MSR) are Generation IV nuclear systems in which the fuel is dissolved in a molten salt circulating through the primary system. There is growing interest in this advanced technology in Europe, but also in the US, China, South Korea, Japan and Russia, due to their inherently high safety level, flexibility, reliability, load-following capabilities, and potential for multi-recycling of materials contained in light-water reactors’ spent nuclear fuels. These advantages could position MSRs as ideal complements to other decarbonized energy sources in a future sustainable energy mix. In this respect, it is probably one of the most promising advanced technologies and, at the same time, the least mature and studied one. Two ongoing EURATOM-funded projects, MIMOSA and ENDURANCE projects are exploring molten salt reactors’ safety and performance features, as well as fuel cycle aspects, in order to assess and demonstrate their potential for future deployment in Europe. The MIMOSA and ENDURANCE projects have the common objective of improving the maturity of MSR technology. The MIMOSA project develops and analyses multi-recycling strategies for the European Union based on the use of MSR and demonstrates several key aspects of their technical feasibility and performance by both calculations and experimental investigations. The ENDURANCE project supports the safe operation and the development of Critical Technology Elements by connecting design developers and industry with universities and research centres while ensuring alignment with regulatory requirements. Whereas ENDURANCE is in its starting phase, MIMOSA has already delivered important results

Analyse paléosismologique des failles de la terminaison NE cévenole après le séisme du Teil : qu’avons-nous appris ?

National audienceLe séisme du Teil en 2019, dont l’épicentre est situé le long de la faille de la Rouvière à proximité des centrales nucléaires de Cruas et de Tricastin, est apparu comme un séisme sans précédent en France métropolitaine. Il a généré une rupture de surface inédite (4.5 km de long, 10 cm de déplacement du sol en moyenne avec un mouvement inverse), de fortesaccélérations du sol (1g le long de la faille) et est situé à une profondeur superficielle (~1 km).Cet événement a soulevé un ensemble d’interrogations auxquelles la communauté scientifique tente de répondre par le biais de nombreuses observations et recherches, notamment dans le cadre de l'axe Failles actives France de l'Action transverse sismicité d'Epos-France. Début 2025, toutes les failles de la terminaison NE cévenole n’ont pu être étudiées. Il est donc fondamental de poursuivre ces études paléosismologiques pour mieux contraindre l’aléa sismique associé aux réseau de failles situé dans une partie de la vallée du Rhône, fortement peuplée et industrialisée

Extreme skew surge estimation combining systematic skew surges and historical record sea levels on the English Channel and North Sea coasts

International audienceCoastal planning implies the estimation of extreme sea levels. As the distribution of astronomical high tides can be predicted, most recent publications suggest focusing on the estimation of extreme skew surges. Historical information, record sea levels observed before the beginning of systematic tide gauge recordings, can improve estimations. The corresponding skew surges can be estimated but are not necessarily exhaustive. Indeed, some historical extreme skew surges can remain unnoticed if they are combined with low or moderate tides, or for a variety of reasons. To deal with this exhaustiveness issue, a previous publication proposed an unbiased method for combining systematic period skew surges with historical period extreme sea levels. This method appeared more reliable than previously proposed approaches. The present study aims at presenting a broader evaluation of this method, based on its application to nine sites located on the English Channel and North Sea coasts. The method is also improved to consider several historical periods and various types of historical information. Results confirm the method to be reliable, useful, and relevant. A number of recommendations is also formulated for the selection and use of historical information for sea level frequency analyses

Radiation vulnerability of optical fiber cables for underground nuclear waste monitoring

International audienceThis work presents our evaluation of the radiation vulnerability of optical fiber cables candidate to monitor temperature and strain in nuclear waste repositories. For this, the cables have been both exposed to γ-1 MGy Total Ionizing Dose (TID) and to mixed-field neutron-γ-rays up to 150 Gy TID and neutron fluence of 2.8 × 10 13 n/cm 2 . The effect of hydrogen-rich atmospheres is also investigated as this constraint is associated with the targeted environments. The evolution of the properties of seven optical fiber cables, differing in their compositions and structures, were evaluated during these two irradiation campaigns. Radiation-Induced Attenuation (RIA), Brillouin Frequency Shift (BFS), and Rayleigh Frequency Shift (RFS) were measured online at room temperature. Additional post-irradiation assessments have been performed: thermo-mechanical properties of both Brillouin and Rayleigh scatterings were evaluated pre-and post-irradiation, along with carbon coating H 2blocking capabilities and radiation-induced degradation. Results demonstrated that radiation induces hydrogen diffusion from some of the cable structures, particularly from gel components. This, in addition to RIA, significantly increases the optical loss levels at infrared wavelengths under γ-rays (>1200 dB/km, at 1550 nm). The study explores the origins of these losses and the radiation-induced BFS and RFS levels. Post-mortem analyses, including spectral assessments, macroscopic cable degradation observations, and hydrogenation, provided further insights into cable behavior in such conditions. A PEEK-structured cable showed notable resilience, with minimal changes in its Brillouin/Rayleigh sensitivity, no visible degradation, and the lowest H 2 -blocking capability degradation under irradiation. This work offers a comprehensive qualification process for evaluating optical fiber cable performance for nuclear waste monitoring, and the findings exhibit broader implications for various nuclear industry applications

Godiva-IV leakage dose characterization

International audienceAs new nuclear accident dosimetrists are being trained by their respective institutions, there was a need for nuclear accident dosimeter (NAD) ntercomparison exercises. This required a reference neutron and photon dose for nuclear accident dosimetrists to test their dosimeters and analysis. The U.S. Department of Energy (DOE) Nuclear Criticality Safety Program (NCSP) supported an experimental campaign to characterize the Godiva-IV leakage dose in 2014 to support future exercises. A Passive Bonner Sphere Spectrometer (PBSS) was deployed by Atomic Weapons Establishment (AWE) to measure the neutron spectrum. CaF thermoluminescent dosimeters (TLDs) were used to measure the photon doses. The results were documented in a report at that time but this paper reanalyzed and updated those results with other measurements in the interim. This work established updated reference neutron and photon doses as a function of radial distance from the center of Godiva-IV, which will be used for future NAD intercomparison exercises

On the Development of a Self-Sealing Experimental Setup for Natural Claystones Considered as Potential Host Rocks for Radioactive Waste Disposal: Application to the Sandy Opalinus Clay

International audienceA new experimental device allowing the follow-up of the self-sealing of damaged claystone has been developed. This device consists of a constant volume cell with a displacement transducer tracking the closure of the artificially created diametric fracture. Two additional sensors were installed to obtain additional information: a total pressure sensor monitoring the radial swelling pressure and a mini-pressure sensor inserted within the diametric fracture that measure the pressure changes during the sealing process. To simulate in situ conditions, a series of three small-scale mock-up tests were performed on artificially fractured Opalinus Clay samples from the lower sandy facies of the Mont Terri site. The solutions used were synthetic water with the same salt concentration and pH as the natural neutral pore water, a sodium nitrate (NaNO3) saline solution, and an alkaline solution. Results showed that the end frictions, identified from the evolution of the radial swelling pressure, together with the mini-pressure sensor, control the fracture closing. The mini-pressure sensor that was installed in the first test immediately fell out of service because of hydration, and the radial swelling pressure was affected by the rigid-rigid contact between the sample and the total pressure sensor. This series of tests revealed the key points related to the designed cell for further improvement. In the second design, a cavity to house the mini-pressure sensor was engraved on the facet of one of the two half-samples, and the preparation of this sensor was improved to ensure its water tightness. A cylindrical wedge was fabricated to avoid the rigid-rigid contact. A second series of tests with the same three solutions and the same material were then conducted. This series has been running for 270 days and its results are more satisfactory