Institute for Radiation Protection and Nuclear Safety (IRSN)
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Différences dans la distribution d'activité au cours de la journée entre garçons et filles âgés de 3 à 17 ans
No full textInternational audiencePhysical activity (PA) decreases from childhood to adolescence, with girls being less active than boys. The timing of these differences remains unknown. Using accelerometer data from three cross-sectional studies in Norway and Belgium (n=2507, age=3-17years), we assessed sex differences in sedentary behaviour (SB) and PA levels (light, moderate, vigorous) throughout the day and across the full spectrum of activity intensity distribution on weekdays and weekend days, using linear regression and functional data analyses. Across all age groups (preschoolers (3-5y), children (6-10y), adolescents (11-17y)), girls were less active than boys, particularly on weekdays (eg, vigorous PA (>1111 counts/15s) difference: -16.9minutes/day (95% Confidence interval: -19.3, -14.4; p-value <0.001) in children). It was the case throughout the day, particularly during school hours (8h30-15h29) in all age groups. Analysis of the full spectrum of activity intensity distribution (0 to 3000 counts) added to these findings that on weekend days, girls spent less time in zero-count SB than boys (difference=-21.0 minutes/day (-28.7, -13.4; p-value <0.001) in children), but higher (17.3 minutes/day (13.2,21.4; p-value <0.001)) in the "other SB", 1-180 counts/15s. The sex differences in PA during school hours suggest the need for targeted interventions promoting activities engaging girls. Additionally, the time spent in zero-count, particularly evident in boys on weekend days, deserves further investigation.L'activité physique (AP) décline de l'enfance à l'adolescence, les filles étant moins actives que les garçons. La temporalité de ces différences est toujours inconnue. À partir des données d'accéléromètres de trois études transversales menées en Norvège et en Belgique (n=2507, âge=3-17 ans), nous avons évalué les différences en temps sédentaire (TS) et différents niveaux d’activité physique (légère, modérée, intense) entre garçons et filles tout au long de la journée, ainsi que sur la distribution d’activité physique (de 0 à 3 000 counts/15s), en utilisant des analyses de régression linéaire et des analyses de données fonctionnelles. Dans tous les groupes d’âge (maternelle (3-5 ans), enfants (6-10 ans), adolescents (11-17 ans)), les filles étaient moins actives que les garçons (par exemple, différence en AP vigoureuse : -16.9 minutes/jour (intervalle de confiance (IC) à 95% : -19.3 à -14.4 ; p<0,001) chez les enfants), en particulier les jours de semaine pendant le temps scolaire (8h30-15h29). L’analyse utilisant la distribution d’activité physique a révélé des différences spécifiques entre garçons et filles quand l’accélération était proche de zéro (0 count/15s), les garçons étant plus susceptibles d'avoir ce comportement que les filles, en particulier pendant les jours de week-end (par exemple, différence = -21,0 minutes/jour (IC à 95 % : -28,7, -13,4 ; p-value<0,001) chez les enfants). Les différences d'AP entre les sexes pendant les heures d'école suggèrent la nécessité d'interventions spécifiques promouvant des activités engageant les filles. De plus, l’utilisation de la distribution d’activité physique a révélé des différences entre les garçons et filles, dans la partie inférieure de la distribution qui peuvent être masquées par l'utilisation de seuils pour différencier les niveaux d'activité
One-dimensional oscillatory flows in partially saturated media with moving multi-front
No full textInternational 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
Radionuclide sorption dynamics in the Rhone River: Experimental and modelling approach
No full textInternational 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
COAL Experiments Investigating the Reflooding of a 7 × 7 Rod Bundle During a Loss-of-Coolant Accident: Effect of a Partially Blocked Area with Ballooned Rods
No full textInternational audienceDuring a loss of coolant accident (LOCA) in a pressurized water reactor, the drying of the fuel assemblies leads to an increase in the fuel temperature and deformation of the fuel rod claddings. In addition to the restriction of the flow area, the relocation of the fragmented irradiated fuel within the ballooned area leads to an increase of the local residual power. The COAL experiments (COolability of a fuel Assembly during Loca) focus on the coolability issue of a partially deformed fuel assembly during water injection with the safety systems using a 7x7 bundle of electrically heated rods. These experiments are part of the PERFROI project (FRENCH acronym : PERte de reFROIdissement) launched by IRSN with the support of the FRENCH “Agence Nationale pour la Recherche” (ANR), EDF and the US-NRC. The effect of the flow blockage {intact geometry up to long ballooning (100 to 300 mm) with different blockage ratios (80 to 90%)} were evaluated for various powers, inlet water mass flow rates and different pressures representative to Large (LBLOCA at 0.3 MPa) and Medium break size (MBLOCA from 0.5 to 3 MPa) configurations. Relocation of fragmented fuel in the balloons are taken into account by a local increase of the power by a factor of 1.5. This paper presents the thermal hydraulics parameters and the main results of the experiments performed in a facility of the STERN Laboratories (Canada). We studied the effect of the inlet water flow rate which is the consequence of the amount of water entering the reactor core after the break of the primary circuit and the effect of the pressure. The presence of the balloons increases significantly the Peak Cladding Temperature according to the flow rate, the pressure and the power. These results are used to improve and validate the heat exchange models of thermal hydraulics codes dealing with the complex reflooding processes in such a configuration
Exploring the safety and performance of molten salt reactors for their deployment in the European Union: the MIMOSA and ENDURANCE projects
No full textInternational 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
Experimental and computational analysis of the DNA damage induced in zebrafish, Danio rerio, early life stages after exposure to tritiated thymidine
No full textInternational audienceTritium is an ubiquitous radioactive hydrogen isotope. It is found in all environmental compartments, in three different forms: tritiated water (HTO), gaseous tritium (HT) and organically bound tritium (OBT). Once internalized in the organism, it can either be found free in the tissues (TFWT) or bound to organic matter (OBT). This study aims to assess if tritiated thymidine, an organic form of tritium, induces DNA breaks once internalized in a model organism and its DNA. To do so, both experimental procedures and nanodosimetry simulations have been used. Zebrafish embryos (3.5 hpf, hours post fertilization) were exposed to three tritiated thymidine activity concentrations (7.5, 40, 110 kBq/mL, leading to internal dose rates of 22, 170 and 270 μGy/h) for four days. Individuals were sampled after 1 and 4 days of exposure and DNA break levels were assessed by the comet assay. Results showed that, even at the lowest activity concentration, tritiated thymidine induced DNA breaks in both embryos (1 dpf) and larvae (4 dpf). It was also highlighted that there was no increase nor decrease in DNA break level between 1 and 4 dpf, except in the case of the exposure to 170 μGy/h, where a slight decrease was observed. Geant4-DNA Monte Carlo simulations, performed on two spherical zebrafish nuclei of two different radii (2.5 and 5 μm), highlighted that organic tritium mainly induced single strand breaks (SSB). The results also showed that most of the damage was indirectly induced. Those results, combined with various experimentations, expose tritiated thymidine genotoxic pathways that could lead to both short- and long-term health effects
Measurement of the Prompt Neutron Decay Constant in a Zero-Power Reactor Using a Novel 3D Detector System
No full textInternational audienceAnalyzing neutron noise in zero-power reactors provides information about integral parameters, such as the prompt decay constant α. This information can be used to validate codes that predict said parameters, or time-dependent behavior, particularly reactor transients. The CROCUS zero-power research reactor has been widely used for conducting noise experiments and has recently been enhanced with a new neutron detection system SAFFRON. This system includes an array of about 150 miniature neutron detectors evenly dispersed throughout the core, allowing for three-dimensional (3D) spatial detection capabilities. We conducted a neutron noise experiment using the 3D array to test this new system to determine the prompt decay constant α. Our results, derived from the Rossi-α method, aligned with the predictions from the Serpent 2 Monte Carlo code, which utilized the Lawrence Livermore National Laboratory FREYA library for fission. The agreement was within 1σ of the estimated uncertainties. We notably observed that based on previous experiments, using all 150 detectors does not achieve the levels of detection efficiency (in counts per fission) expected to be necessary to observe the fission chain decay, yet we still observe the decay with comparatively high statistical significance. We therefore show experimentally that the spatial extent of the detection system is an important parameter in the prediction of the success of the neutron noise technique. We also explored the cross-spectral density method for different combinations of SAFFRON detectors, which gave consistent results with the Rossi-α method. In addition, uncertainty estimation methods, including the bootstrap method, were applied to SAFFRON, addressing both temporal and spatial aspects. We discuss the benefits of using bootstrap methods for estimating the uncertainty of the prompt decay constant, which we found often underestimated when using the covariance matrix from a standard nonlinear fit. The results also indicate that SAFFRON is a powerful measurement tool that can be expanded for use in active perturbation experiments, 3D flux maps, and other high-resolution reactor physics experiments
Effets sur la santé humaine des faibles doses de rayonnements ionisants : un bref état des connaissances issues des études épidémiologiques
No full textInternational audienceSi les effets des rayonnements ionisants sur la santé humaine à des doses modérées ou élevées (> 100 mGy) sont bien connus, les effets aux faibles doses (< 100 mGy) le sont moins. Les connaissances issues des études épidémiologiques confirment un risque de cancer associé à une exposition à de faibles doses de rayonnements ionisants, sans qu’il soit possible de confirmer ou non l’existence d’un seuil de dose à partir duquel ces effets apparaîtraient. Les risques de maladies du système circulatoire, du système nerveux central ou d’opacités cristalliniennes ne sont pas exclus aux faibles doses mais les résultats des études épidémiologiques restent contradictoires. Enfin, les effets héréditaires observés chez l’animal ne le sont pas chez l’humain, les études épidémiologiques restant cependant limitées
Radiation vulnerability of optical fiber cables for underground nuclear waste monitoring
No full textInternational 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
Uncertainty quantification for severe-accident reactor modelling: Results and conclusions of the MUSA reactor applications work package
No full textInternational audienceThe recently completed Horizon-2020 project “Management and Uncertainties of Severe Accidents (MUSA)” has reviewed uncertainty sources and Uncertainty Quantification methodology for assessing Severe Accidents (SA), and has made a substantial effort at stimulating uncertainty applications in predicting the radiological Source Term of reactor and Spent Fuel Pool accident scenarios.The key motivation of the project has been to bring the advantages of the Best Estimate Plus Uncertainty approach to the field of Severe Accident modelling. With respect to deterministic analyses, expected gains are avoiding adopting conservative assumptions, identifying uncertainty bands of estimates, and gaining insights into dominating uncertain parameters. Also, the benefits for understanding and improving Accident Management were to be explored.The reactor applications brought together a large group of participants that set out to apply uncertainty analysis (UA) within their field of SA modelling expertise – in particular reactor types, but also SA code used (ASTEC, MELCOR, MAAP, RELAP/SCDAPSIM), uncertainty quantification tools used (DAKOTA, SUSA, URANIE, self-developed tools based on Python code), detailed accident scenarios, and in some cases SAM actions. The setting up of the analyses, challenges faced during that phase, and solutions explored, are described in Brumm et al. ANE 191 (2023).This paper synthesizes the reactor-application work at the end of the project. Analyses of 23 partners are presented in different categories, depending on whether their main goal is/are (i) uncertainty bands of simulation results; (ii) the understanding of dominating uncertainties in specific sub-models of the SA code; (iii) improving the understanding of specific accident scenarios, with or without the application of SAM actions; or, (iv) a demonstration of the tools used and developed, and of the capability to carry out an uncertainty analysis in the presence of the challenges faced.A cross-section of the partners’ results is presented and briefly discussed, to provide an overview of the work done, and to encourage accessing and studying the project deliverables that are open to the public. Furthermore, the partners’ experiences made during the project have been evaluated and are presented as good practice recommendations.The paper ends with conclusions on the level of readiness of UA in SA modelling, on the determination of governing uncertainties, and on the analysis of SAM actions