Institute for Radiation Protection and Nuclear Safety (IRSN)
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Nouvelle approche pour étudier le phénomène d'hydruration secondaire sur les gaines M5Framatome dans des conditions d'APRP
No full textInternational audienceThe focus of this study is about a new experimental approach for a separate effects study of the secondary hydriding phenomenon under LOCA conditions. Many nuclear institutes perform semi–integrals tests to study the cladding behaviour during a LOCA transient. Those tests combined several phenomena and performing a detailed analysis of the secondary hydriding phenomenon using these tests can be challenging. A dedicated experimental protocol aiming at simulating secondary hydriding has been set up. Separate effects tests (SETs) were then carried out using this protocol to study the effects of both oxidation duration and temperature, on the hydrogen absorption during the oxidation stage of the LOCA transient on M5Framatome1 cladding. The effects of gap size were also investigated. Metallographic analysis has been used to characterise the M5Framatome clad metallurgical transformation after the high–temperature (HT) oxidation
An Analysis of a Coarse-Group Subgroup Method Based on the Physical Probability Tables in APOLLO3®
No full textM&C 2023 special issueInternational audienceThe legacy subgroup method of the APOLLO3® code, denoted the SG-GR-383g method in this paper, relies on the fine structure equation solved by the means of the General Resonance model and of the mathematical probability tables (MPTs) that are computed on the fly for the resonant mixture. Because of the use of these MPTs, a fine energy structure of 383 groups has to be employed.In our recent work, with the intention of decreasing computational time, a subgroup method adapted to coarse-group calculations has been implemented in APOLLO3. It is based on the use of physical probability tables (PPTs), taking into account the mixture treatment, and on the Intermediate Resonance model to derive the subgroup equations, as well as the application of the Superhomogenization correction to ensure the preservation of the reaction rates in a multigroup calculation. This method, denoted SG-IR-69g in this paper, uses a 69-coarse-group energy mesh. This paper presents a comparison of the SG-IR-69g method with the legacy SG-GR-383g method, taking as reference the continuous-energy Monte Carlo TRIPOLI-4® calculations on test cases of 3 × 3 pin cells, with a central cell being either a water hole or a Gd-UO2 pin cell surrounded by UO2 pin cells. Similar accuracy on the multiplication factor was obtained for both the SG-GR -383g and SG-IR-69g methods, although more error compensations were found in the multigroup reaction rates of the latter. Even though the calculation of PPTs is more expensive than that of the mathematical ones, overall the SG-IR-69g method is more time efficient thanks to the decrease in the number of energy groups
Computational homogenization of a physically-based crystal plasticity law for irradiated bainitic steels
No full textInternational audienceThe elasto-viscoplastic response of irradiated bainitic steels for pressure vessels of light water reactors is described by a multiscale micromechanical model. The model relies on a simplified set of complex constitutive equations describing intragranular flow under a wide range of temperatures, strain rates, and irradiation levels. These equations were themselves partially calibrated by multiscale analyses based on dislocation dynamics calculations, atomistic calculations, and experimental measurements. They include the contribution of jog drag, lattice friction, evolution of dislocation microstructures, and irradiation hardening. The scaling up of these intragranular laws to polycrystalline samples relies on a computational homogenization method which solves the field equations within periodic representative volume elements by means of Fast Fourier Transforms. This computational method proves advantageous relative to the finite element method in handling the complex microstructural morphology of the model required to achieve overall constitutive isotropy. Macroscopic simulations for uniaxial curves under different irradiation levels are first confronted to experimental curves to identify certain microscopic material parameters employed to describe the evolution of the mean-free path of dislocations with deformation. Subsequent comparisons for the evolution of the yield stress, irradiation hardening and the response to sudden strain-rate variations are then reported for a class of steels with various chemical compositions under wide ranges of temperature, loading rate and irradiation level. Good agreement is obtained in all cases. Finally, simulations are employed to explore the influence of the initial dislocation density on the intragranular stress and strain fields. An appreciable influence on the fields is observed during the elasto-viscoplastic transition but not deep in the plastic range
Analyse des particules produites par explosion au contact d'éprouvettes en béton
No full textNational audienceThe physical protection of nuclear facilities requires taking into account malicious acts, in particular explosions that could lead to radiological consequences. These scenarios are poorly documented in terms of aerosol release, and to date we have no precise knowledge of the mass of dust generated by explosions in contact with specimens containing radioelements. The aim of this work is to gain a better knowledge of generated dusts, particularly those with an aerodynamic diameter of less than 10 µm, by developing an experimental protocol for analysing the particles dispersed by explosions in contact with concrete specimens: weighing, sieving and optical counting are used.La protection physique des installations nucléaires impose la prise en compte des actes de malveillance, notamment les explosions pouvant engendrer des conséquences radiologiques. Ces scénarios sont peu documentés sur le plan des aérosols émis et nous ne connaissons pas, à ce jour, de manière précise, la masse des poussières dispersées par des explosions au contact de cibles incluant des radioéléments. Ce travail cherche à apporter des connaissances sur les poussières générées, notamment celles dont le diamètre aérodynamique est inférieur à 10 µm, en développant un protocole expérimental d'analyse des particules dispersées par des explosions au contact d'éprouvettes de béton : pesée, tamisage et comptage optique sont utilisés
Effects of salinity on the water retention properties and microstructure of the Opalinus Clay from the lower sandy facies (LSF) of Mont Terri
No full textInternational audienceIn this study, the impact of salinity on the water retention properties and microstructure of the Opalinus Clay from the lower sandy facies (LSF) of Mont Terri site was investigated by exposing a series of unsaturated Opalinus Clay samples to two sodium nitrate NaNO3 solutions of controlled osmotic suctions ( p ¼ 15 and 34MPa) nd to a synthetic water (same salinity as the natural pore water) p ¼ 1MPaÞ at different water contents. The water retention curves were determined along wetting path for the three osmotic suctions, and microstructural analyses were conducted at different saturation states. While the total suction increased with salinity, the porosity decreased, suggesting the decrease in the swelling potential. Exposing the Opalinus Clay to a highly saline solution at low water contents increased the specific surface area and the peak of the dominant mesopore population. This is due to the dispersion of the Na-clay fraction and to the swelling of the initially unsaturated clay fraction. At higher water content, the water transfer from the meso to the macropores prevails and a decrease in specific surface area, peak and density of the mesopores were observed. The higher the osmotic suction, the lower the water content at which the shrinkage of the mesopores is initiate
Active faulting of the southern segment of the Rhine River Fault, southern Germany: Geomorphological and paleoseismological evidence
No full textInternational audienceOur study focuses on the southern segment of the Rhine River Fault, located in one of the most seismically active regions in intraplate Europe, at the southern end of the Upper Rhine Graben and forming part of the eastern Rhine Graben Boundary Fault. It stands out due to its impressive geomorphological expression in the landscape near the village of Tunsel, in southwestern Germany. We present details about the timing of fault activity and the contribution of earthquakes to the morphology, as this information is crucial for seismic hazard assessment, considering its location 8 km from the Fessenheim Nuclear Power Plant. Through the integration of the sedimentary sequences, morphotectonic observations, shallow geophysics, and paleoseismological trenching, our findings demonstrate that several earthquakes along the RRF have ruptured the surface (M6.7 ± 0.5). The youngest surface rupturing earthquake occurred during medieval times (EZ) and the penultimate event (EY) is constrained by stratigraphic correlation with reworked Loess deposits dated to the Younger Dryas (ca. 13 kyr BP). Three older earthquake events have also been unearthed (EX, EW and EV) occurring prior to the Late Glacial Maximum, where event EX led to considerable lateral spread at the banks of the Pleistocene Rhine river. Vertical displacements reach up to 0.5 m and lateral offsets up to max. 1.5 m per earthquake event, consistently with a 15 - 30 km-long rupture of this segment of the Rhine River Fault
A step toward flow simulation through cracks in beam-particle models
No full textInternational audienceCrack characterization in reinforced concrete structures, such as the containment walls of 1300 MWe nuclear power plants, is critical for accurately estimating air leakage. Traditional modeling strategies, such as Poiseuille's law applied to a simplified geometry, rely on indirect parameters like a tortuosity coefficient, which is difficult to predict and has limited validity, leading to increased uncertainty. This study presents a novel post-processing tool based on the Beam-Particle simulation approach, capable of detecting micro-crack paths and constructing macro-crack geometries using graph theory. The generated macro-crack geometry can be integrated into computational fluid dynamics (CFD) simulations for more accurate airflow predictions or by calibrating simplified approaches like Poiseuille's law based on numerically obtained crack characteristics. Validation against optical measurements from Brazilian splitting tests demonstrates the tool's potential to advance simplified modeling and enhance detailed crack characterization, opening new possibilities for improved air leakage predictions
Results of a Geant4 benchmarking study for bio‐medical applications, performed with the G4‐Med system
No full textInternational audienceBackgroundGeant4, a Monte Carlo Simulation Toolkit extensively used in bio‐medical physics, is in continuous evolution to include newest research findings to improve its accuracy and to respond to the evolving needs of a very diverse user community. In 2014, the G4‐Med benchmarking system was born from the effort of the Geant4 Medical Simulation Benchmarking Group, to benchmark and monitor the evolution of Geant4 for medical physics applications. The G4‐Med system was first described in our Medical Physics Special Report published in 2021. Results of the tests were reported for Geant4 10.5. PurposeIn this work, we describe the evolution of the G4‐Med benchmarking system.Methods The G4‐Med benchmarking suite currently includes 23 tests, which benchmark Geant4 from the calculation of basic physical quantities to the simulation of more clinically relevant set‐ups. New tests concern the benchmarking of Geant4‐DNA physics and chemistry components for regression testing purposes, dosimetry for brachytherapy with a source, dosimetry for external x‐ray and electron FLASH radiotherapy, experimental microdosimetry for proton therapy, and in vivo PET for carbon and oxygen beams. Regression testing has been performed between Geant4 10.5 and 11.1. Finally, a simple Geant4 simulation has been developed and used to compare Geant4 EM physics constructors and physics lists in terms of execution times. ResultsIn summary, our EM tests show that the parameters of the multiple scattering in the Geant4 EM constructor G4EmStandardPhysics_option3 in Geant4 11.1, while improving the modeling of the electron backscattering in high atomic number targets, are not adequate for dosimetry for clinical x‐ray and electron beams. Therefore, these parameters have been reverted back to those of Geant4 10.5 in Geant4 11.2.1. The x‐ray radiotherapy test shows significant differences in the modeling of the bremsstrahlung process, especially between G4EmPenelopePhysics and the other constructors under study ( G4EmLivermorePhysics , G4EmStandardPhysics_option3 , and G4EmStandardPhysics_option4 ). These differences will be studied in an in‐depth investigation within our Group. Improvement in Geant4 11.1 has been observed for the modeling of the proton and carbon ion Bragg peak with energies of clinical interest, thanks to the adoption of ICRU90 to calculate the low energy proton stopping powers in water and of the Linhard–Sorensen ion model, available in Geant4 since version 11.0. Nuclear fragmentation tests of interest for carbon ion therapy show differences between Geant4 10.5 and 11.1 in terms of fragment yields. In particular, a higher production of boron fragments is observed with Geant4 11.1, leading to a better agreement with reference data for this fragment.ConclusionsBased on the overall results of our tests, we recommend to use G4EmStandardPhysics_option4 as EM constructor and QGSP_BIC_HP with G4EmStandardPhysics_option4 , for hadrontherapy applications. The Geant4‐DNA physics lists report differences in modeling electron interactions in water, however, the tests have a pure regression testing purpose so no recommendation can be formulated
Short internal open reading frames repress the translation of N-terminally truncated proteoforms
No full textInternational audienceInternal translation initiation sites, as revealed by ribosome profiling experiments can potentially drive the translation of many N-terminally truncated proteoforms. We report that internal short open reading frame (sORF) within coding sequences regulate their translation. nTRIP6 represents a short nuclear proteoform of the cytoplasmic protein TRIP6. We have previously reported that nTRIP6 regulates the dynamics of skeletal muscle progenitor differentiation. Here we show that nTRIP6 is generated by translation initiation at an internal AUG after leaky scanning at the canonical TRIP6 AUG. The translation of nTRIP6 is repressed by an internal sORF immediately upstream of the nTRIP6 AUG. Consistent with this representing a more general regulatory feature, we have identified other internal sORFs which repress the translation of N-terminally truncated proteoforms. In an in vitro model of myogenic differentiation, the expression of nTRIP6 is transiently upregulated through a mechanistic Target of Rapamycin Complex 1-dependent increase in translation initiation at the internal AUG. Thus, the translation of N-terminally truncated proteoforms can be regulated independently of the canonical ORF
Modélisation des courbes d’évolution des mesures nucléaires dégradées par des aérosols.
No full textInternational audienceIn nuclear facilities, the mandatory airborne contamination surveillance is operated by dedicated Continuous Air Monitors (CAM) that collect all airborne aerosol on a filter, measure the radioactivity and trig an alarm when a predetermined activity concentration is exceeded. This measurement and therefore the alarms are very integrated by the variations in size and concentration of the aerosols. A new adjustment process can be used to establish a relationship between the mass deposited on a sampling filter and the evolution of the nuclear measurement, based on a previously assembled data set. This relationship has been established for one aerosol dimension and requires extension to the other aerosol dimensions in the database. This represents the first explicit relationship between changes in nuclear measurements and changes in aerosols.Dans les installations nucléaires, la surveillance obligatoire de la contamination aéroportée est opérée par des instruments dédiés (CAM - Continuous Air Monitor) qui collectent les aérosols sur un filtre, mesurent la radioactivité déposée et déclenchent une alarme lorsqu'un seuil prédéterminé en activité est dépassé. Cette mesure et donc les alarmes sont très influencées par les variations en taille et concentration des aérosols. Sur la base d'un ensemble de données préalablement constitué, un processus d'ajustement nouveau permet de chercher à mettre en relation la masse déposée sur un filtre de prélèvement et l'évolution de la mesure nucléaire. Cette relation a pu être établie pour une dimension d'aérosol et doit être étendue aux autres dimensions d'aérosols de la base de données. Il s'agit ici de la première relation explicite entre les évolutions des mesures nucléaires et celle des aérosols