Institute for Radiation Protection and Nuclear Safety (IRSN)
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Propriétés thermiques du béton armé des enceintes de confinement de réacteurs nucléaires pour les études de pressurisation enceinte : état de l'art et proposition pour des valeurs enveloppe et "best-estimate"
No full textInternational audienceIn case of loss of coolant accident or severe accident in a nuclear pressurised water reactor, the containment pressure must remain below the design pressure to prevent radioactive releases. The evolution of containment pressure can be estimated by computer codes such ASTEC or MAAP. However, especially for severe accident, the pressurisation kinetics during the first 24 hours is very sensitive to the thermal properties of the containment concrete, which stores most of the decay heat. A wide range of thermal properties (thermal conductivity, specific heat and density) of concrete and reinforced concrete can be found in the literature, depending on the concrete temperature, composition and relative humidity. This paper presents a review of available thermal properties for concrete and reinforced concrete and makes some proposals for best estimate and conservative properties to calculate the evolution of the containment pressure during the first 24 hours after the accident initiator.En cas d'accident de perte de réfrigérant ou d'accident grave dans un réacteur nucléaire à eau pressurisée, la pression dans l'enceinte de confinement doit rester inférieure à la pression de dimensionnement afin de minimiser les rejets radioactifs. L'évolution de la pression dans l'enceinte de confinement peut être estimée à l'aide de codes informatiques tels que ASTEC ou MAAP. Cependant, en particulier dans le cas d'un accident grave, la cinétique de pressurisation au cours des premières 24 heures est très sensible aux propriétés thermiques du béton de l'enceinte de confinement, qui stocke la majeure partie de la chaleur résiduelle. La littérature scientifique fait état d'une grande variété de propriétés thermiques (conductivité thermique, chaleur spécifique et densité) du béton et du béton armé, qui dépendent de la température, de la composition et de l'humidité relative du béton. Cet article présente une revue des propriétés thermiques disponibles pour le béton et le béton armé et formule quelques propositions pour une estimation "best-estimate" et des propriétés enveloppes permettant de calculer l'évolution de la pression dans l'enceinte de confinement pendant les premières 24 heures suivant le déclenchement de l'accident
Cross Section Doppler Broadening prediction using Physically Informed Deep Neural Networks
No full textTemperature dependence of the neutron-nucleus interaction is known as the Doppler broadening of the cross-sections. This is a well-known effect due to the thermal motion of the target nuclei that occurs in the neutron-nucleus interaction. The fast computation of such effects is crucial for any nuclear application. Mechanisms have been developed that allow determining the Doppler effects in the cross-section, most of them based on the numerical resolution of the equation known as Solbrig's kernel, which is a cross-section Doppler broadening formalism derived from a free gas atoms distribution hypothesis. This paper explores a novel non-linear approach based on deep learning techniques. Deep neural networks are trained on synthetic and experimental data, serving as an alternative to the cross-section Doppler Broadening (DB). This paper explores the possibility of using physically informed neural networks, where the network is physically regularized to be the solution of a partial derivative equation, inferred from Solbrig's kernel. The learning process is demonstrated by using the fission, capture, and scattering cross sections for in the energy range from thermal to 2250 eV
Iron Metallurgy in Ancient Cambodia: Production Dynamics, Traditions and Chronologies in a Southeast Asian Context (9th–14th centuries CE)
No full textInternational audienceCollaborative studies in iron archaeometallurgy in Cambodia over the past decade, particularly through the IRANGKOR project, have advanced our understanding of iron production dynamics during the Angkorian period (9th–15th centuries CE). This research examines metallurgical remains and artifacts within a systemic framework, linking them to production sites, geological contexts, and usage settings, such as iron clamps in monumental constructions. Studied diachronically and across multiple spatial scales, these remains provide insights into production practices and “recipes,” production dynamics, and the circulation and supply of iron, particularly within the central production territory of Phnom Dek, historically recognized for its metallurgical tradition.The study explores the relationships between resources, production processes, metallurgical practices, and iron circulation. Central to the research is the use of provenance analyses, direct dating of the metal itself, and the examination of comparative patterns, providing precise chronological and spatial benchmarks. Combining historical and archaeological sources with material analysis of artifacts and smelting debris establishes a framework for interpreting these dynamics across the Angkorian territory.The resulting datasets reveal changes in metallurgical “recipes” as well as in supply strategies and demands over more than 1,400 years. This presentation synthesizes recent results, highlighting the contribution of compositional and chronological data to frameworks for understanding continuities and changes in ancient metallurgical practices. Situating these findings within a broader Asian context highlights similarities in practices and recipes and their implications for regional technical dynamics
CFD validations of ballooning effects during LOCA against MASCARA experiments
No full textInternational audienceThis study investigates the thermal–hydraulic behavior through deformed fuel assemblies during LOCAs using CFD simulations. The MASCARA experiments uses a dedicated mock-up and Magnetic Resonance Velocimetry (MRV) to study how ballooned nuclear fuel rods affect coolant flow. We consider CFD validation against MASCARA experimental data. Employing the Code_Saturne solver, we reproduce flow redistribution and extrapolate thermal behavior in a 7x7 fuel rod bundle with different blockage configurations of 4x4 balloons. The chosen turbulence models with carefully designed meshes capture critical flow phenomena, including intense transverse velocities upstream and recirculation zones downstream of blocked regions. Validation against MRV data confirms the reliability of Code_Saturne in replicating experimental observations across various blockage conditions. Thermal simulations reveal the recirculation-driven heat accumulation and evacuation based on different geometry of deformed subchannels. The study is dedicated to improving sub-channel code predictions in ballooning effects and demonstrating the potential of high-fidelity CFD for multiscale nuclear safety assessments
Local-scale experimental investigation of a two-phase cross-flow in a tube bundle and flow-induced vibration: Intermittent/Churn flow
No full textInternational audienceTwo-phase cross-flows in tube bundle can induce vibrations. This occurs in many industrial situations, such as nuclear power plant U-tube Steam Generator (SG). With the purpose of gathering high quality data for the validation of multiphase CFD simulation tools, a new experimental apparatus was designed and put in operation. The facility is instrumented for the two-phase air-water flow and tube vibration characterization. This article deals with experimental results in the churn/intermittent two-phase flow conditions. The experimental study was achieved by means of three measurement techniques: high-speed camera, optical dual-tip probe and wire mesh sensor. The behavior of the two-phase flow upstream of the tube bundle, characterized by the continuous generation of large gas structures, is detailed: highspeed camera and wire mesh sensor data reveal the prevalence of dispersed bubbles near the wall and large gas structures in the core region. The rising frequency of the large gas structures could be determined. Profiles of void fraction and gas velocity were measured within the tube bundle.The flow regime map of the experiment is proposed and is correlated with the study of flow-induced tube vibration. It highlights the role played by gas structure size distribution, thus flow pattern in the structural response in intermittent flow regimes with a local-scale characterization of the flow. Finally, the present work is a major contribution to improve and validate local-scale numerical simulation
Continuing to work in the nuclear industry or in ports during the first lockdown of the COVID-19 Pandemic
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Ageing of activated carbons in the nuclear context
No full textInternational audienceActivated carbons (AC) co-impregnated with triethylenediamine (TEDA, ~ 5 wt. %) and potassiumiodide (KI, 1 wt. %) are employed within the ventilation networks of French nuclear power plants (NPP)to avoid the dissemination of radiotoxic volatile iodine species (namely I2 and CH3I) into theenvironment. A decrease of adsorption performances is known to occur for these materials as a functionof time due to ageing, oxidation and poisoning phenomena [1]. However, uncertainties remain about theinvolved degradation mechanisms as well as the kinetics of AC alteration. The present paper aims toinvestigate the effect of experimental conditions on the AC degradation kinetics. In addition, insightsabout the involved ageing mechanisms are presented and compared with realistic conditions by exploringthe performances of on-site used materials
Unraveling the complex rupture of the 2020 Mw 6.4 Petrinja Earthquake (Croatia): insights from joint inversion of geodetic benchmarks, InSAR and optical correlation data.
No full textInternational audienceThe Mw 6.4 Petrinja earthquake, which struck Croatia on December 29, 2020, is among the most powerful earthquakes recorded in the slowly deforming region of Eastern Europe. In areas of low tectonic strain, limited seismic monitoring and the sporadic occurrence of strong earthquakes often hinder detailed analyses of coseismic ruptures preventing the scientific community to fully understand the processes governing these moderate and destructive events. In particular, it's not clear whether those continental earthquakes follow the same scaling laws than the ones occurring on mature faults, hence the need to better understand the source of these events.Seismic source inversions and InSAR-based models from multiple studies indicate that the coseismic rupture of the Petrinja earthquake results from a single patch of right-lateral slip. On the other hand, we showed in a previous study that discontinuous surface ruptures and slip inversions of near-field geodetic benchmarks suggest rather along-strike complexities of the fault slip (Henriquet et al., 2023). To better constrain the slip distribution of the Petrinja earthquake, we leverage dense near field measurements from optical image correlation and numerous geodetic benchmarks together with InSAR data. We first assess the sensitivity of the model to each dataset to show that slip patterns are overall consistent to first order, although significant differences appear along dip, mainly depending on the distance between the fault trace and the considered measurements. We then jointly invert all the displacement data to provide a robust solution of the coseismic slip. The results confirm that the coseismic slip occurred on a near-vertical strike-slip fault at shallow depths, less than 10 km, with significant slip extending to the surface locally. It also indicates that fault bending near Kriz influenced the rupture propagation, as the largest slip, exceeding 3 meters, was concentrated in the northwestern section at depths of less than 5 km and that a deeper slip of smaller amplitude is required by the data to the southeast. This along-strike variation in slip depth and amplitude also correlates with changes in aftershocks rate and average depth (Herak et al., 2023), which confirms that the Petrinja fault is not a straight, mature fault system. This complexity in the slip distribution is in agreement with the large stress drop values obtained by seismological studies (Lončar et al., 2024). In conclusion, this study offers new insights into the seismogenic source of the Petrinja earthquake and highlights the value of combined displacement fields in improving source models of moderate intracontinental earthquakes
Worker studies and their interpretation
No full textInternational audienceA recent commentary on epidemiological studies of nuclear workers notes that these studies can provide radiation risk estimates that complement those derived from the study of Japanese atomic bomb survivors. The author asserts that the results from some nuclear worker studies are difficult to interpret due to the fact that ERR/Gy estimates vary across subcohorts, and subcohort-specific estimates are not always equal to estimates obtained in the overall study population. We discuss settings in which it is reasonable to expect that an estimate of association in a subcohort should be similar to an estimate obtained in the full cohort and settings in which a subcohort analysis may differ from the estimate obtained in a full cohort analysis. Focusing on the INWORKS study, we describe some of the steps taken to understand variation in estimates of ERR/Gy between subgroups and upon restrictions, as well as interpretation of estimates of external dose-mortality associations in the total study population
Modélisation de radon atmosphérique et des débits de dose gamma à l’échelle continentale
No full textInternational audienceLe lessivage (dépôt humide) des descendants du radon atmosphérique cause une augmentation du débit de dose gamma ambiant observable sur les stations de surveillance. Plus de 10 000 événements significatifs par an attribuables à ce lessivage sont ainsi observés sur le réseau Téléray opéré par l’ASNR.Le modèle de dispersion atmosphérique LdX permet de prévoir ces pics en utilisant les prévisions météorologiques de Météo-France et des cartes d’exhalation du radon. Ces simulations permettent de 1) fournir une validation statistique des modèles de dispersion de la radioactivité 2) travailler sur la représentativité de la mesure 3) fournir des métriques des performances à grande échelles des cartes d’exhalation du radon 4) prédire les fausses alertes sur le réseau de surveillance causées par ce phénomène.Nous proposons un résumé des travaux des six dernières années de l’ASNR portant sur la modélisation du radon atmosphérique, ainsi que les perspectives à court et moyen terme