Institute for Radiation Protection and Nuclear Safety (IRSN)
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Design of TEX-MOX critical experiments varying neutron spectrum
No full textInternational audienceIn the International Criticality Safety Benchmark Evaluation Project (ICSBEP) only a limited amount of critical experiments representative of MOX fuel with low moderation is present. This paper aims at describing the design of a set of critical experiments with varying neutron spectra that should contribute to nuclear data validation for this kind of configurations.Complementary to the few existing experiments in the ICSBEP, a series of independent experiments can be performed on the PLANET machine at NCERC (National Criticality Experiments Research Center) using the uranium-plutonium fuel plates. Due to the decay heat emitted by the fuel plates, a dedicated thermal-mechanical design of the assembly has been defined to fit all the experimental constraints: weight, limited temperature and temperature gradient within the assembly, minimal effect on neutronics and others. The 5 critical configurations designs are described in this paper
Dating the end of the Egyptian Old Kingdom: new contextualized dates from the reign of King Pepy II
No full textInternational audienceIn this study, the temporal accession date of king Pepy II is modeled by using a series of C dates based on samples from the burial of Djau at Deir el-Gebrawi in Middle Egypt. Djau was one of Pepy II’s officials—overseer of Upper Egypt and nomarch of the 8th and 12th provinces. Five samples of Djau’s wrapping as well as his wooden coffin were analyzed. ATR-FTIR (Attenuated Total Reflection–Fourier Transform InfraRed spectroscopy) analyses were carried out on textile samples to ensure they were not contaminated by organic chemicals due to the embalming process, prior to being dated using the conventional radiocarbon method at the IFAO Laboratory (Cairo). Based on archaeological evidence, the temporal density associated with Djau’s death is then used as a chronological marker for the death date of king Pepy II. Taking into account the possibility of either biennial, annual or irregular censuses to assess the duration of his reign, the accession date of Pepy II is thus modeled using OxCal software. The results place king Pepy II’s accession date between 2492 to 2256 BCE with 95.4% probability, and between 2422 to 2297 BCE with68.3
Towards simulations of fuel rod behaviour during severe accidents by coupling TRANSURANUS with SCIANTIX and MFPR-F
No full textInternational audienceAmong the applications of the multiscale modelling approach in nuclear fuel rod performance, the coupling of integral thermo-mechanical fuel performance codes with lower-length meso-scale modules is of great interest. This strategy allows to overcome correlation-based approaches with mechanistic ones and test their application in accidental conditions. In this work, we explore the coupling between the TRANSURANUS fuel performance code and two meso-scale modules for fission gas/product behaviour: MFPR-F and SCIANTIX. These modules, coupled within TRANSURANUS, are assessed against the IFA-650.10 loss-of-coolant accident test to analyse their overall impact and highlight future developments toward mechanistic modelling of fission gas during accident scenarios
The EURADOS CR-39 Quality task for the optimisation and harmonisation of personal neutron dosimetry with CR-39 (PADC)
No full textInternational audienceAbstract CR-39 (PADC) nuclear track detectors are among the most widespread devices used for personal neutron dosimetry; however, some issues related to the variable material quality of the CR-39 polymer hinder the performance of CR-39-based dosemeters. For this reason, the Working Group 2 (WG2) of the European Radiation Dosimetry Group (EURADOS) has recently launched the CR-39 Quality task, a project aimed at improving and harmonising personal neutron dosimetry with CR-39 in Europe. Whitin this task, a close collaboration among researchers, individual monitoring services and dosemeter grade CR-39 manufacturers is achieved, thus facilitating the direct dialog between producer and consumer to reach an optimised material for personal neutron dosimetry applications
Interaction between forced and natural convection in a thin cylindrical fluid layer at low Prandtl number
No full textInternational audienceMotivated by nuclear safety issues, we study the heat transfers in a thin cylindrical fluid layer with imposed fluxes at the bottom and top surfaces (not necessarily equal) and a fixed temperature on the sides. We combine direct numerical simulations and a theoretical approach to derive scaling laws for the mean temperature and for the temperature difference between the top and bottom of the system. We find two asymptotic scaling laws depending on the flux ratio between the upper and lower boundaries. The first one is controlled by heat transfer to the side, for which we recover scaling laws characteristic of natural convection (Batchelor, Q. Appl. Maths , vol. 12, 1954, pp. 209–233). The second one is driven by vertical heat transfers analogous to Rayleigh–Bénard convection (Grossmann & Lohse, J. Fluid Mech. , vol. 407, 2000, pp. 27–56). We show that the system is inherently inhomogeneous, and that the heat transfer results from a superposition of both asymptotic regimes. Keeping in mind nuclear safety models, we also derive a one-dimensional model of the radial temperature profile based on a detailed analysis of the flow structure, hence providing a way to relate this profile to the imposed boundary conditions
Fondements scientifiques de l’utilisation du modèle linéaire sans seuil (LNT) aux faibles doses et débits de dose en radioprotection
No full textInternational audienceLe modèle linéaire sans seuil (LNT) a été introduit dans le système de radioprotection il y a environ 60 ans, mais ce modèle et son utilisation en radioprotection sont encore débattus aujourd'hui. Cet article résume les résultats en radiobiologie et en épidémiologie accumulés au cours de la dernière décennie sur les effets d'une exposition aux rayonnements ionisants à faible Transfert d'Énergie Linéique (TEL) et discute de leur impact sur l'utilisation du modèle LNT dans l'évaluation des risques de cancer par rayonnement à faibles doses. Les connaissances acquises au cours des 10 dernières années, tant en radiobiologie qu'en épidémiologie, ont renforcé les fondements scientifiques sur les risques de cancer à faibles doses. En radiobiologie, bien que certains mécanismes ne soient pas linéaires avec la dose, les premiers stades de la cancérogenèse composés d'événements mutationnels, qui jouent un rôle clé dans la cancérogenèse, montrent des réponses linéaires à des doses aussi faibles que 10 mGy. L'impact des mécanismes non mutationnels sur le risque de cancer associé aux rayonnements à faibles doses est actuellement difficile à évaluer. En épidémiologie, les résultats montrent un excès de risques de cancer à des niveaux de dose de 100 mGy ou moins. Bien que certains résultats récents indiquent des relations non linéaires avec la dose pour certains types de cancers, le modèle LNT ne surestime pas substantiellement globalement les risques à faibles doses. Les résultats actuels, en radiobiologie ou en épidémiologie, ne démontrent pas l'existence d'un seuil de dose en dessous duquel le risque de cancer associé aux rayonnements serait nul. Des incertitudes persistent mais un tel seuil de dose, s'il existe, ne pourrait être supérieur à quelques dizaines de mGy. L'IRSN considère que les connaissances scientifiques actuellement disponibles ne remettent pas en cause l'utilisation du modèle LNT pour l'évaluation des risques de cancers radio-induits en appui au système de radioprotection. L'utilisation de ce modèle semble raisonnable d'un point de vue scientifique, et aucune autre relation dose-réponse ne semble plus adaptée ou justifiée à des fins de radioprotection
Étude expérimentale des effets chimiques sur le colmatage des filtres dans l’industrie nucléaire
No full textDuring a LOCA accident (Loss Of Coolant Accident) occurring to a nuclear Pressurized Water Reactor (PWR), debris are generated and can be partially transported to the RIS-EAS filter in the sumps located in the bottom of the nuclear reactor containment. These debris can contribute to the « physical » clogging of the filters. Another effect called « chemical effects » corresponds to the presence of cations in solution resulting from the debris' corrosion and the possible corrosion of the metal surface present in the reactor containment vessel. In the case of a severe accident with core fuel meltdown, additional loads debris are to be considered as presence of particles formed of structural materials, control rod material, fission products and concrete particles resulting from corium-concrete interaction. To ensure the long term liquid recirculation functionality, the chemical effect have to be understood: nature of these chemical effects, conditioning parameters and potential effect on the clogging. The thesis aims at studying the chemical effects after designing a dedicated experimental loop: a parametric approach , coupled with several chemical and pressure drop measurements. Chemical speciation in solution and precipitate characterizations will/can be respectively performed by ICP and MEB-EDX, DRX and XPS techniques.Lors d'un accident de type APRP (Accident de Perte du Réfrigérant Primaire) survenant dans réacteur nucléaire à eau pressurisé (REP), des débris sont générés et ils peuvent être partiellement transportés jusqu'aux filtres des systèmes de secours RIS-EAS des puisards situés dans le fond de l'enceinte de confinement du réacteur. Ces débris peuvent contribuer au colmatage « physique » des filtres. Un autre effet dit « effet chimique » correspond à l'apport de cations en solution de par la corrosion des débris (fibres d'isolant) et la possible corrosion de surfaces métalliques présentes dans le bâtiment réacteur. Ces cations métalliques peuvent former des précipités au sein du lit fibreux formés et accentuer le colmatage physique. En cas d'accident grave avec fusion du cœur, des charges additionnelles de débris sont à considérer comme la présence de particules formées de matériaux de structure, des barres de commande et de produits de fission et des particules de béton résultant d'un interaction corium-béton. Il a été clairement identifié dans la littérature que ces effets chimiques sont à prendre en compte pour s'assurer de la fonction recirculation sur une longue période. La question de recherche est d'être en mesure de comprendre la nature de ces effets chimiques, les paramètres les conditionnant et leurs ampleurs. Le sujet de thèse porte sur l'étude de ces effets chimiques, pour cela une approche paramétrique sera suivie en couplant plusieurs mesures chimiques et en corrélant ces mesures à une perte de charge. Les mesures chimiques en solution se feront principalement par ICP et la caractérisation des précipités potentiellement formés pourra se faire par des analyses type MEB-EDX, DRX et XPS. La boucle de filtration est à concevoir
Managing nursing shortages in the hospital: a distributed view of personnel management
No full textInternational audienceThis paper explores how nursing teams of a hospital department manage constraints and resources to ensure quality of care in the context of staff shortages. Specifically, the study seeks to understand how these teams address decisions (imposed by the organization to compensate for staff shortages) and their subsequent impact on daily operations. To this end, an on-site study was conducted in seven neurology inpatient units at a Parisian hospital affected by a significant shortage of nursing staff. This qualitative study employed three different data collection techniques-analysis of organizational documents, systematic observations, and simulated case interviews, adopting an activity-centered ergonomics approach. The results reveal that nurses do not merely implement managerial decisions regarding personnel management. Instead, they contribute to formulating these organizational solutions (such as substitution, working time regulation, and mobility) and facilitate their execution through various regulatory actions and reorganization of resources (workload redistribution, competency balancing, task rescheduling). These findings propose a distributed perspective of workforce management, where it is not solely seen as a top-down process, or the mechanical fallout of managerial decisions to allocate resources. Rather, it is understood as the evolution and enactment of choices made at all levels of the organization, with the aim to optimize work quality, secure operational safety, and protect existing resources
Exposition des personnels navigants aux rayonnements cosmiques en france sur la période 2015-2019
No full textInternational audienceCosmic particle flux increases with latitude and altitude and is significantly higher on-board aircraft than at ground level. Furthermore, its intensity depends on solar activity and eruptions. Due to their professional activity, flight crews (FCs) may receive an annual dose of some millisieverts. Therefore, the European directive adopted in 1996 requires the aircraft operators to assess the dose. The effective dose is to be estimated using various experimental and calculation means. In France, it is carried out by the computerized system for flight assessment of exposure to cosmic radiation SIEVERTPN, which sends to SISERI, the national dose registry, the monthly effective dose of each crew member. The average annual effective dose of French FCs was 2.19 mSv in 2019, i.e. between the standard permissible limits set for the public and the limit set for occupationally exposed persons. The effective dose received by the most exposed French FCs increased during the period 2015–2019 and that could be due to the solar cycle effect, changes in the staff flight time or the aircraft model. It can also be noted that more technical flight crews (TFCs) received a dose greater than 5 mSv over the 2016 to 2019 period than commercial flight crew (CFCs). Our study indicates that the number of FCs having received a dose greater than 5 mSv also increased over the period 2016 to 2019. Some parameters, that may affect the assessment of the aircrew effective dose, are not considered in SIEVERTPN calculations, as for example the Forbush decreases and the location in the plane. Lastly, several factors lead us to expect a decrease in the doses received by French aircrew staff in the coming years, such as the peak activity of the 25th eleven-year solar cycle expected in July 2025. However, some unexpected events, as for instance the war in Ukraine, can alter this prediction.Le flux de particules cosmiques augmente avec la latitude et l'altitude et est significativement plus élevé à bord des avions qu'au niveau du sol. De plus, son intensité dépend de l'activité solaire et des éruptions. Du fait de leur activité professionnelle, les personnels navigants (PN) peuvent recevoir une dose annuelle de quelques millisieverts. Ainsi, la directive européenne adoptée en 1996 impose aux compagnies aériennes d'évaluer la dose. La dose efficace est estimée à l'aide de différents moyens expérimentaux et de calcul. En France, elle est réalisée par le système informatisé d'évaluation en vol de l'exposition aux rayonnements cosmiques SIEVERTPN, qui transmet à SISERI, le registre national des doses, la dose efficace mensuelle de chaque PN. La dose efficace annuelle moyenne des PN français est de 2,19 mSv en 2019, soit entre les limites standards admissibles fixées pour le public et la limite fixée pour les personnes exposées professionnellement. La dose efficace reçue par les PN français les plus exposés a augmenté au cours de la période 2015-2019 et cela pourrait être dû à l'effet du cycle solaire, à des changements de temps de vol du personnel ou au modèle d'avion. On peut également noter que davantage d'équipages techniques (PNT) que commerciaux (PNC) ont reçu une dose supérieure à 5 mSv sur la période 2016 à 2019. Notre étude indique que le nombre de PN ayant reçu une dose supérieure à 5 mSv a également augmenté sur la période 2016-2019. Certains paramètres, pouvant affecter l'évaluation de la dose efficace des PN, ne sont pas pris en compte dans les calculs de SIEVERTPN, comme l'effet Forbush ou l'emplacement dans l'avion. Enfin, plusieurs facteurs laissent présager une diminution des doses reçues par les PN français dans les années à venir, comme le pic d'activité du 25ème cycle solaire attendu en juillet 2025. Cependant, certains événements inattendus, comme la guerre en Ukraine, peuvent modifier cette prédiction
Spectral unmixing of multi-temporal data in gamma-ray spectrometry
No full textInternational audienceA challenging problem in gamma-ray spectrum analysis is the rapid detection of artificial radionuclides at low activity levels. Until now, traditional methods focus on activity estimation based on single spectra, obtained by integrating over time the measured disintegration events. However, accounting for the wellconstrained radionuclides decay should allow for a more accurate and sensitive activity estimation. For that purpose, we investigate a novel approach to estimate radionuclides' activity, which is i) first based on multi-temporal data, obtained from several short measurements rather than a single one, and ii) built upon a dedicated spectral unmixing, which allows processing multi-temporal data. The proposed algorithm allows accounting for both the full spectrum of each radionuclide (i.e. peaks and Compton continuum) and their activity decay in time. To that purpose, different approaches are investigated to model the temporal dependencies of the radionuclides' activities, and specifically to account for potentially out of equilibrium radionuclides' decay chains. Experimental results on both simulated spectra and real measurements are presented and compared to standard methods, it is shown that the proposed approach leads to more accurate estimations and faster detection of artificial radionuclides