Institute for Radiation Protection and Nuclear Safety (IRSN)
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Characterization of Aerosols Emitted during Core Boring of Prototypic Fukushima Daiichi Fuel Debris Simulants
No full textInternational audienceOne of the important challenges for the decommissioning of the damaged reactors of the Fukushima Daiichi Nuclear Power Station (1F) is the fuel debris retrieval. In this context, the URASOL project (acronym coined from URAnium and aeroSOL) has been undertaken. It aims at acquiring basic data on the generation and characteristics of radioactive aerosols from the thermal or mechanical processing of fuel debris simulant blocks. Prototypic fuel debris blocks were fabricated at VULCANO facility. Here, we focus on blocks based on the average value computed for the lower head compositions in the OECD/BSAF benchmark for Fukushima Daiichi unit 2. Core boring of these blocks were carried out in a dedicated test section (FUJISAN for Fukushima Daiichi Uranium-containing sample Joint Investigations of the Source term of Aerosols and their Nature) at CEA Cadarache. Aerosols were sampled, collected and characterized. Particle size distribution determined from impactors show a bimodal distribution with a major mode around 4 µm and a minor around 0.4 µm. STEM-EDS and ICP-MS/OCP-AES have been carried out on the collected aerosols. Zirconium, uranium and iron are the major elements in the aerosols as well as in the fuel debris prototypes but in significantly different proportions. Boron concentration in the aerosols is larger than that in the blocks, suggesting a preferred aerosolization of borides. Fission product prototypes such as tellurium and yttrium have also a higher concentration in the collected aerosols than that in the block. Chemical composition is also significantly varying with the size of aerosols. From these tests, it is assumed that some of the phases of the fuel debris blocks are more likely to become aerosols than others. Knowing the estimated isotopic composition of each element in the Fukushima Daiichi unit 2 fuel 10 years after shutdown, it is possible to estimate the aerosol activity from its composition. More than 85% of the radioactivity is carried by Am, Cm and U which are represented by depleted uranium in these tests. Tin-121m is the most active non-actinide isotope in these aerosols
Numerical simulations for site effect estimation in a complex sedimentary basin: a comparison between different approaches for designing 3D seismic models of the subsurface
No full textInternational audienceEstimating site effects is important for seismic hazard assessment but can be difficult due to the scarcity of data in time and space, especially in low-to-moderate seismicity regions. Numerical simulations are helpful for understanding the physical parameters controlling site effects and for modelling their spatial variability, but simulations need detailed seismic models of the subsurface in input, as well as empirical measurements of amplification for calibrating their outputs. In this study, we perform 3D numerical simulations of seismic wave propagation and amplification in the Tricastin basin (Rhône valley, France) based on a range of models built with different sources of information. A first type of models consists of layers separated by interfaces interpreted from active seismic profiles and interpolated over the area of interest. A second type of models is obtained by Ambient Noise Surface-Wave Tomography (ANSWT) applied on a dense array of 400 3C sensors and resulting in a 3D model of shear-wave velocities. Array analysis of the seismic noise recorded by this network also provides us with an estimation of attenuation parameters (Qs) within the basin. We compare our numerical results with empirical amplification measurements based on earthquake and ambient noise recordings. Our results highlight the characteristics of the input models in terms of seismic amplification. Layered models generate significant 3D wave propagation effects consistent with the observations but, if over-simplified (e.g. sediments vs. bedrock) do not fully explain the measurements in complex areas of the basin. On the other hand, preliminary models based on purely data-driven ANSWT suffer from the resolution limits of the tomographic process, especially in terms of lateral variations, and do not reproduce expected 3D wave propagation effects, but seem to provide a satisfying estimation of the subsurface velocity structure in complex areas of the basin. This study sheds light into how to acquire and combine information to design and calibrate numerical simulations for site effect estimation
Implementation of dihydroxamate-based binding gels in DGT devices for uranium(VI) sampling in freshwater. An intercomparison study
No full textInternational audienceMining activities, production and use of nuclear fuel (65 kt/year), processing of spent fuel and storage of nuclear wastes may lead to the release of uranium into the environment, its transfer between the different compartments of the biosphere, and the ultimate contamination of trophic chains [1].Nowadays, the monitoring of contaminated sites requires new breakthroughs in analytical techniques in order to assess in detail the impact and bioavailability of actinides discharged into aquatic environments. In that respect, Diffusive Gradient in Thin-films (DGT) devices are particularly attractive tools for the passive sampling of various contaminants in aquatic environments.Unfortunately, the most frequently used and commercially available binding gels for uranium, namely the Chelex-100 ion-exchange resin or the TiO2-based Metsorb adsorbing material, behave poorly in carbonate-rich, hard freshwater and seawaters [2-3]. To overcome these limitations, we relied on a biomimetic approach for designing efficient pincer-like UO22+ chelators, bearing two terminal hydroxamate bidentate groups, which are able to coordinate the uranyl cation in its equatorial plane [4]. Equilibrium constants for complex formation with UO22+, Ca2+ and Mg2+ were determined by potentiometry. High affinity for the former and selectivity with respect to the two latter interfering species prompt us to graft covalently one of these binders on a hydrophilic organic resin, which was then incorporated in an agarose binding gel. Performances of the DGT samplers made thereof to accumulate uranium(VI) in natural freshwaters will be presented and compared to the experimental results obtained for a series of other binding resins, including Chelex-100 and Metsorb. These validation tests were performed both in the laboratory, using mineral water spiked with uranium, and in field by deploying the DGT samplers directly in a river
Toward a better understanding of radium lability in wetland soils
No full textInternational audienceRadium is a naturally occurring radioactive element and could in certain cases poses environmental and health risks due to its involvement in biological processes and subsequent release of radon gas from its radioactive decay. Interest in the environmental behavior of radium follows from its ubiquitous presence in the context of TE-NORM (Technologically Enhanced Naturally Occurring Radioactive Material) related activities, which mainly originate from uranium mining/milling, fossil fuels, etc… As such, the main scientific challenge calls for identifying its mobility, transport and bioavailability in the environment. The former uranium mining site of Rophin (Lachaux, France) is characterized at the downstream by a wetland area with high concentrations of 238U and its decay products, such as 226Ra [1]. In particular, an inherited layer of soil found at a depth of approximately 15 cm is recording radium concentrations up to 74 kBq.kg-1 of dry mass of soil. The overall adopted scientific approach is then to propose a mechanistic description of the mobility of radium in Rophin wetland soils by coupling laboratory experiments and field investigations with DET (Diffusive Equilibrium in Thin-Films) samplers. The objective was to determine which fraction is labile, i.e. the fraction that is adsorbed on soils and whose resupply in solution is rapid. This was assessed by desorption experiments under representative site conditions by an original methodology involving different solid/liquid ratios. This extensive lab methodology is based on a distribution coefficient (Kd) model allowing to assess the labile fraction of radium and Kd values in soils. DET probes field deployment followed to monitor radium concentrations in pore waters down to a depth of 50 cm. A centimetric-scale Ra profile was obtained from an original analytical strategy developed in Boudias (2022) [2] (see Boudias et al.’s abstract to this conference). Field data were then implemented into the Kd model to evaluate and improve the representativeness of the laboratory results on labile parameters of radium compared to the in natura equilibrium between soils and pore waters [3]. Overall, the labile fraction of radium was found to be very low (from 5 to 12 % for the inherited layer) and was characterized by Kd values of the order of 100 L.kg-1.This study provides access to valuable data essentials for a more detailed description of radium behavior and interactions in wetland soils. To go a step further, a combined DET-DGT (Diffusive Gradients in Thin-Films) approach will be implemented in the Rophin site in order to determine both labile and dissolved fractions from large soil profiles [3]. The ambition of this work will therefore be to directly access to in natura Kd values and associated kinetic parameters for a more accurate characterization of Ra lability and fate in soil layers
Confiance entre société et science – Quelles évolutions dans leurs relations de réciprocité dans les prochaines décennies ?: Rapport du groupe de travail PROSPER
No full textLa confiance mutuelle entre la communauté scientifique et la société est cruciale pour résoudre les défis contemporains, comprendre le monde et préparer l'avenir. Cependant, cette confiance est mise à l'épreuve dans un monde en constante évolution, où les résultats scientifiques suscitent à la fois admiration et doutes. Face à ce constat, le réseau PROSPER, réseau des responsables de prospective de la recherche publique française, a examiné les fondements de cette confiance, soulignant son importance pour la collaboration entre scientifiques et non-scientifiques.Au cœur de cette relation se trouve la notion de « vérité scientifique », caractérisée par l'exactitude des faits, le respect des normes de véracité, la tolérance au doute et l'authenticité des acteurs impliqués. Cette confiance repose sur la satisfaction des attentes légitimes des parties concernées et le respect de leurs engagements envers cette vérité scientifique. Pour anticiper l'évolution de cette relation jusqu'en 2040, le groupe de travail « Confiance entre société et science » a identifié des futurs possibles, souhaitables ou non, afin de déterminer les leviers d'action nécessaires pour renforcer la confiance et atténuer les risques de sa détérioration. Cela a permis au groupe d’émettre des recommandations en direction des différents acteurs. Ce processus de réflexion s'est déroulé en sept étapes, comprenant la clarification des termes clés, l'identification des attentes réciproques, l'analyse du système et de ses variables, la collecte de données, la construction de scénarios, l'évaluation de l'état de la confiance dans ces scénarios, et enfin, l'élaboration de pistes d'action pour favoriser la confiance entre société et science
Modelling the Influence of the Tube Support Plate on the Eddy CurrentTesting of the Steam Generator: Numerical Tools
No full textInternational audienceEddy current testing (ECT) of Steam Generator (SG) tubes is part of the maintenance program of Nuclear Power Plants. Tube Support Plates (TSP) are usually only considered as extraneous signals for tube inspection. However, for long-term operation of SGs, there is a safety concern related to the build-up of deposits in the TSPs flow holes.The clogging-up of the TSPs flow holes affect the safe thermal-hydraulic operation of SGs. The deposits come from the feedwater train and are mostly iron oxides (magnetite) with a weak electrical conductivity and magnetic permeability.The ability of ECT probes to detect and characterize TSPs deposits is therefore of great interest. The most common and industrial ECT technique, the bobbin coil, averages the surrounding electromagnetic field over 360°, whereas the geometry of tri-foiled and quadri-foiled TSPs, and thus of clogging, is rather complex and non-axisymmetric, hence motivating the evaluation of the performance of conventional ECT rotating probes used for SGs tubesinspection. Although simulation is a powerful tool to support such a study, it requires dedicated models to be made available to NDT experts, and CEA develops ECT physical models in CIVA for this purpose. In addition to standard fast CIVA modules based on 3D semi-analytical or 2D numerical calculations restricted to canonical or axisymmetric parts, respectively, CEA develops a module dedicated to the simulation of SG tube inspection basedon a 3D numerical simulation. This module allows tube deformation such as ovalization, bending or tube expansion. It also allows the addition of external objects such as anti-vibration bars, different geometries of tube support plates and now their clogging by deposits. This model is used to study various influent parameters and to perform benchmarks in the framework of a scientific collaboration between the CEA and the IRSN, related for example to the inspection of the U-bend tubes or of a friction wear under the anti-vibration bars. Here, the specificity of the TSPs and their clogging justifies further investigations between CEA and IRSN to qualify the simulation model before evaluating the influence of material and geometry properties of the deposit as well as the performance of the inspection techniques. We present the main characteristics of the simulation module in CIVA
Impact of initial air and subsequent H2 gas migration in a radioactive waste repository
No full textInternational audienceIn a geological repository for high-level radioactive waste, corrosion of steel and water radiolysis leadsto generation and accumulation of hydrogen gas which may significantly affect long-term safety of therepository. Numerical modeling can be used to predict the hydraulic and hydromechanical evolution ofsuch a disposal facility and to estimate the influence of excavation and generated gas on host clay rockand sealings. While several modelling teams have studied gas migration [1], very few have considered theinitial presence of air and its impact on later hydrogen migration. Note that, during excavation, the COxaround the tunnels is disturbed, which creates an Excavation Disturbed Zone (EDZ), both hydraulically(rock desaturation) and mechanically (fracturing, redistribution of stresses, natural convergence).In our study, we have compared results obtained from TOUGH [2] modules (Equations Of States):EOS5 for modeling two-phase flow with only water and hydrogen, and EOS7R for modeling a more complex multi-component two-phase system with water, brine, air, and two radionuclides able to volatilizeand dissolve. This EOS7R model is tuned to attribute non-radioactive hydrogen gas properties to the1rst radionuclide (brine and the 2nd radionuclide are turned off). The van Genuchten (1980) relativepermeability and capillary pressure functions are used.The model is then run at the scale of a waste cell: Figure 1a. One challenge is to estimate thepeak gas pressure around the cell and check whether it exceeds lithostatic pressure at depth 630m. Ifthat is achieved, the mechanical stability of the engineered system and natural barriers may be affected.The results indicate that hydrogen gas plume migration is impeded by the bentonite seal around thecanister. However, the migration of dissolved H2 waway from the container is less impeded, as indicatedby Figure 1b. In future, this model will be extended to take into account hydromechanical coupling
Radiocarbon-based modeling of the reign of King Den (1st dynasty, Egypt) and the start of the Old Kingdom
No full textInternational audienceThis study focuses on the chronology of King Den’s reign, the fifth ruler of the 1st Egyptian dynasty. A series of radiocarbon (C) dates were established on archaeological material from several tombs at the Abu Rawash site, near Cairo, which comprises a complex of 12 monumental mud-brick mastabas. Modeling the C results enables us to estimate the date of King’s accession and to link this to the beginning of the 3rd Dynasty, i.e., to Egyptian state’s structuration. Through the application of OxCal software, sets of C results obtained from the same archaeological context have been summarized and compared with the precise state of our knowledge on the historical duration of this reign. These results place King Den’s accession between 3104 and 2913 BCE (2σ), with the more likely date being 3011–2921 BCE (1σ). The modeled temporal density thus obtained is based both on new contextualized C dates and on an updated reading of the historical information on his reign. This is a dynamic result, which can be refined as soon as we have more data to integrate into the model. Above all, this resulting model becomes a crucial chronological point to better determine the beginning of the Egyptian Old Kingdom
Risques de cancers : reconstitution de co-expositions sur la vie entière: Composante radiologique de l'exposome, polyexpositions et risques de cancers dans la cohorte Constances
No full textL’ensemble de la population est exposé tout au long de sa vie, à des niveaux variables, aux rayonnements ionisants et aux polluants chimiques via de multiples sources naturelles et anthropiques, que ce soit dans le cadre de l’environnement résidentiel ou de différentes activités (professionnelles ou autres). Si les effets cancérigènes des rayonnements ionisants et de certains polluants chimiques sont bien établis, les effets d’expositions à de faibles doses demandent à être mieux documentés, ainsi que les relations entre expositions à différents stades de la vie, notamment l’enfance et la puberté, et les risques de cancers à l’âge adulte
Risque de tumeur cérébrale chez les professionnels médicaux exposés aux rayonnements ionisants: Analyse du risque de décès par tumeur cérébrale chez des professionnels médicaux exposés professionnellement aux rayonnements ionisants à faible dose
No full textLe projet BECOME (Brain cancEr risk in joint COhort of MEdical workers exposed to ionizing radiation) vise à étudier le risque de décès par tumeur cérébrale dans une étude conjointe incluant trois cohortes nationales de professionnels médicaux exposés aux rayonnements ionisants, en France, en Corée et aux États-Unis