Institute for Radiation Protection and Nuclear Safety (IRSN)
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Modelling the influence of the Tube Support Plate on the Eddy Current Testing of the steam generator: sensitivity study and validation
No full textNDT.net Issue: 2024-06Proceedings of the 20th World Conference on Non-Destructive Testing (WCNDT 2024), 27-31 May 2024 in Incheon, South Korea (WCNDT 2024)Special Issue of e-Journal of Nondestructive Testing (eJNDT)International 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 magnetite 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 tubes inspection. 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 based on 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. Here, the specificity of the TSPs and their clogging justifies qualifying 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 features of the simulation module in CIVA, its experimental validation, and the main trends in the distortion of the simulated signal as a function of variation in the clogging description
Characterization of Stilbene scintillator for neutron metrology and spectrometry from 100 keV to 22 MeV
No full textInternational audienceThanks to new crystal growth method, pure stilbene scintillators can now detect neutrons from 100 keV. For neutron metrology purposes, two 2”x2” stilbene scintillators were characterized as secondary reference detectors for neutron field measurements in the energy range from 100 keV to 22 MeV. Photon sources were used to determine the electron calibration and resolution. Calibration was performed using the “second derivative” method to determine the Compton edges, assimilated to the inflection point. Resolution function was determined using adjustments at each Compton edge between a broadened MCNP simulation and the measurement. For neutron characterization, due to the anisotropic response, only a full experimental characterisation is possible for now. The neutron response function in the energy range of scintillators was determined using a white neutron spectrum and the Time-of-Flight technique. Reference neutron fluence measurements were used to adjust the scintillator fluence response at calibration point. This method leads to a complete characterization of these scintillators for neutrons field from 100 keV up to 22 MeV
Quand il n’y a plus d’os… la datation 14C des carbonates de plomb des ampoules de Grandmont
No full textInternational audienceRecent years have seen the development of absolute dating of lead carbonates – cerussite (PbCO3) and hydrocerussite (2PbCO3.Pb(OH)2) – using the radiocarbon method. Cosmetics, pigments, and paints based on lead white have been successfully dated (Beck et al., 2018-2020; Hendriks et al., 2019; Messager et al., 2021, 2022). The dating has been made possible by the synthesis method of lead white, which uses horse manure as a source of CO2 to form the carbonates. It has thus been demonstrated that organic carbon marked with 14C was incorporated during this synthesis, which has been attested since the 4th century BC. In the study presented here, a similar approach was attempted on lead carbonates formed by in situ corrosion of lead ampoules found in graves in the cemetery area of the Grandmont Abbey. Since 2013, a multidisciplinary team from the University of Picardie has been conducting research in Limousin at Saint-Sylvestre, on the site of the Grandmontine order’s mother house. Lead was a material widely used in the abbey’s architecture, notably thanks to the patronage of Henry II Plantagenet, who provided a large quantity of lead from England in the second half of the 12th century. This material was chosen from the founding of the monastery around 1124 to make ampoules for eulogy, placed in contact with the body in graves located to the east of the abbey church. With more than forty ampoules recorded to date, Grandmont provides a unique corpus for Western medieval studies. The study of the distribution of the graves and the five types of ampoules partly outlines the topochronological evolution of the cemetery in the 12th-13th centuries, despite the poor preservation of human bones in the granite environment. The lead carbonates collected during the restoration of the ampoules represent, for a significant portion of the graves, the only opportunity to obtain an absolute date. Fifteen samples were prepared by thermal decomposition at LMC14 and measured on the SMA ARTEMIS. Four results from lead carbonates show remarkable consistency, with dates all between 899 and 1157 AD. Four other grouped results are slightly later, between 1043 and 1209 AD. These dates are consistent with those obtained on the bones of two nearby graves, which range from 1028 to 1162 AD. For the other results, the dates are later. Three of them fall in the middle of the 13th century (1220-1280 AD). These dates may correspond to a later phase of use of the cemetery, while the two others may reflect disturbed areas from the modern period. The consistency of the results obtained from both the lead carbonates and the bones suggests that the formation of the lead carbonates is indeed the product of the corrosion of the metal by an organic substance, probably related to the decomposition of the bodies. This hypothesis remains to be demonstrated, but it can be suggested that the dates obtained from the lead carbonates, in the context of the Grandmont burials, correspond to the months following the interment. Thus, radiocarbon dating of lead corrosion provides access to the burial date and opens new perspectives when bones are no longer present or poorly preserved.Ces dernières années ont vu le développement de la datation absolue des carbonates de plomb – cérusite (PbCO3) et hydrocérusite (2PbCO3.Pb(OH)2 – par la méthode du radiocarbone. Cosmétiques, pigments et peintures à base de blanc de plomb ont ainsi été datés avec succès (Beck et al., 2018- 2020 ; Hendriks et al., 2019 ; Messager et al., 2021, 2022). La datation a été rendue possible par le mode de synthèse du blanc de plomb qui utilise du fumier de cheval comme source de CO2 pour former les carbonates. Il a été ainsi été démontré que du carbone d’origine organique marqué en 14C avait été incorporé lors de cette synthèse attestée depuis le IVe siècle avant J.-C. Dans le cadre de l’étude présentée ici, une approche similaire a été tentée sur des carbonates de plomb formés par la corrosion in situ d’ampoules en plomb retrouvées dans des sépultures d’une zone cémétériale de l’abbaye de Grandmont. Depuis 2013, une équipe pluridisciplinaire de l’université de Picardie mène des recherches en Limousin à Saint-Sylvestre, sur le site de la maison mère de l’ordre Grandmontain. Le plomb est un matériau très utilisé dans l’architecture de l’abbatiale, notamment grâce au patronage d’Henri II Plantagenêt qui fournira une quantité importante de plomb provenant d’Angleterre dans la seconde moitié du XIIe siècle. Ce matériau est choisi dès la fondation du monastère vers 1124 pour fabriquer des ampoules à eulogie déposées au contact du corps dans les sépultures situées à l’est de l’abbatiale. Avec plus d’une quarantaine d’ampoules répertoriées à ce jour, Grandmont livre un corpus unique pour le Moyen Âge occidental. L’étude de la répartition des tombes et des cinq types d’ampoules permet en partie d’esquisser l’évolution topochronologique du cimetière aux XIIe-XIIIe siècles, malgré une mauvaise conservation des ossements humains en milieu granitique. Les carbones de plomb prélevés lors de la restauration des ampoules constituent, pour une part importante des tombes, la seule opportunité d’obtenir une datation absolue. Quinze échantillons ont été préparés par décomposition thermique au LMC14 et mesuré sur le SMA ARTEMIS. Quatre résultats sur carbonates de plomb offrent une remarquable identité, les dates étant toutes comprises entre 899 et 1157 AD. Quatre autres résultats groupés sont légèrement plus tardifs, entre 1043 et 1209 AD. Ces dates sont cohérentes avec celles obtenues sur les ossements de deux sépultures proches, comprises entre 1028 et 1162 AD. Pour les autres résultats les dates sont plus tardives. Trois d’entre elles se situent au milieu du XIIIe s. (1220-1280 AD). Ces dates pourraient correspondre à une phase tardive d’utilisation du cimetière et les deux autres à des secteurs perturbés à l’époque moderne. La cohérence des résultats obtenus à la fois sur les carbonates de plomb et les ossements suggère que la formation des carbonates de plomb est bien le produit de la corrosion du métal par une substance organique, probablement liée à la décomposition des corps. Cette hypothèse reste à démontrer mais on peut cependant avancer que les dates obtenues sur les carbonates de plomb, dans le contexte des sépultures de Grandmont, correspondent aux mois qui ont suivis l’inhumation. Ainsi, la datation 14C de la corrosion du plomb donne accès à la date des sépultures et ouvre de nouvelles perspectives dans le cas où les ossements ne sont plus présents ou mal conservés
Understanding the stress field at the lateral termination of a thrust fold using generic geomechanical models and clustering methods
No full textInternational audienceThis study employs numerical simulations based on the limit analysis (LA) method to calculate the stress distribution in a model that includes a basal detachment, featuring the lateral termination of a generic fault under compression. We conduct 2500 2D and 500 3D simulations with varying basement and fault friction angles to analyze and classify the results into clusters representing similar failure patterns to understand the stress fields. Automatic fault detection methods are employed to identify the number and positions of fault lines in 2D and fault surfaces in 3D. Clustering approaches are utilized to group the models based on the detected failure patterns. For the 2D models, the analysis reveals three primary clusters and five transitional ones, qualitatively consistent with the critical Coulomb wedge theory and the influence of inherited structural and geometric aspects over rupture localization. In the 3D models, four different clusters portray the lateral prolongation of the inherited fault. High stress magnitudes are detected between the compressive boundary and the activated or created faults and at the root of the inherited active fault. Tension zones appear near the outcropping surface relief, while stress decreases with depth at the footwall of the created back thrusts. A statistical cluster-based stress field analysis indicates that for a given cluster, the stress field mainly conserves the same orientations, while the magnitude varies with changes in friction angles and compressive field intensity, except in failure zones where variations are sparse. Small parametric variations could lead to significantly different stress fields, while larger deviations might result in similar configurations. The comparison between 2D and 3D models shows the importance of lateral stresses and their influence on rupture patterns, distinguishing between 3D analysis and 2D cross-sections. Lastly, despite using small-scale models, stress field variations over a span of a couple of kilometers are quite large
Bayes-based methodology to update seismic response of RC nuclear buildings
No full textInternational audienceThe numerical prediction of the nonlinear behavior of structures under a given seismic load remains a very complex task regarding many aspects: the choice of the modeling strategy, the description of the soil behavior, the description of the soil-structure-interaction, the induced structural effects, the description of the reinforced concrete behavior under cyclic loadings, etc. Such complexity, coupled with the inherent and intrinsic randomness of material properties, usually induces a gap between the blindly modeled quantities of interest and the ones measured or observed (when measurements are available). To reduce such gap, one might increase the accuracy of the used physical models (using different models, adding more physical phenomena, etc.) and/or improve this knowledge of the model’s inputs leading to the observed responses. In this work, we assume that the used model is sufficiently complex to be considered physically representative (main physical phenomena are accounted for already). Therefore, we consider that the lack of knowledge concerns mainly the used inputs and that is the issue that needs to be addressed. Eventually, this work focuses mainly on available tools and methods to solve the issue of updating the inputs of seismic behaviour models based on the acquired data (experimental observations preferably or in situ data from post-earthquake survey if experimental evidence is not available) expressed in terms of displacements, strains, forces, etc. The Bayesian approach is one of the most relevant and widely used technique. In this paper, it is applied to adjust material properties in the model of SMART2013 mock-up (3-story reinforced concrete structure at the scale 1/4) leading to a better quantification of the median properties of concrete at the structural level and a clear reduction of epistemic uncertainties based on the feedback provided by experimental measurements during successive seismic loads
Major achievements of the EC MUSA project
No full textInternational audienceMaturity of severe accident (SA) codes, progress in the computational methods, and computer infrastructures were considered a sound platform to conduct, for the first time in SA modelling, a systematic and broad application of Uncertainty and Sensitivity Analysis (UaSA) in this domain. The overall objective of the HORIZON-2020 project on "Management and Uncertainties of Severe Accidents (MUSA)" was to quantify the uncertainties of SA integral codes when modelling reactor and spent fuel pool (SFP) accident scenarios of Gen II and Gen III reactor designs for the prediction of the radiological source term. This paper presents the major achievements accomplished by MUSA. To name a few: a database on input parameter uncertainties has been assembled; SA codes and statistical tools, either in-house built or existing ones, have been properly coupled by scripting or interfaces; major specific challenges have been identified and different solutions have been worked out; and, applications to several reactor types and SFP scenarios have shown interesting insights of this simulation approach, particularly when dealing with Source Term variables as figures of merit. No less important, major challenges were found and are here discussed as needs to be addressed before achieving an effective implementation of UaSA in the SA domain
Flux de tritium à l'interface air mer dans la Manche, Mesures expérimentales et modélisation
No full textInternational audienceTritium is a radionuclide released to the atmosphere and in river or sea by nuclear industries in various forms, mainly HTO. Generally in impact studies leading to population dose estimates, for tritium, only atmospheric releases are considered. However, tritium discharged into liquid media can under certain conditions be transferred to the atmosphere by evaporation phenomena and then transported to terrestrial ecosystems by winds. Our study was conducted in the northwest of France, near the fuel reprocessing plant in La Hague (Orano), which releases tritium into the Western English. The objective was to check if a coastal water mass with high tritium concentrations compared to tritium activities in the water vapour of the nearby air, could contribute to increase air water vapour activities in nearby land areas after evaporation from sea (sea-air exchange) and atmospheric transport
Influence of steam deviation, droplets mass flow rate and residual power on dispersed flow film boiling at sub-channel scale in LOCA conditions
No full textInternational audienceAfter a hypothetical loss of primary coolant accident (LOCA) in a pressurized water reactor (PWR), the reactor safety systems inject water into the core to cool it. During this re-flooding process, a flow of steam and dispersed droplets (DFFB — Dispersed Flow Film Boiling) is formed downstream of the quench front. This two-phase flow serves to cool the section of the nuclear fuel rods that are not yet in contact with water. On the other hand, depending on the severity of the accident, the rods may deform, causing the reduction in the passage area of the coolant fluid. In addition, these deformations cause the steam flow (formed in the quench front) to be partially deviated to less deformed sub-channels, a phenomenon known as steam flow redistribution. Because of this, the cooling capacity of these partially blocked sub-channels may be compromised. During the present work, different tests were performed with the COLIBRI experimental bench in order to evaluate the influence of steam deviation on the cooling of a partially blocked sub-channel. The COLIBRI experimental bench allows the evaluation of the heat flux extracted by a typical steam and droplet flow of a LOCA in different blockage configurations. In this study two blockage configurations were considered: an intact configuration (0%) and a severely blocked configuration (90%). Given that steam convection is presumed to be the primary heat transfer mechanism in DFFB, we aim to assess the impact of reduced vapor mass flow rates in blocked sub-channels resulting from vapor redistribution on internal two-phase flow heat dissipation. The results show that steam deviation negatively impacts the heat flux extracted by the internal steam and droplet flow (heat flux could degrade by up to 43%). However, it was observed that the decrease in heat flux between the steam and the wall could be partially compensated by the droplets. In addition, the influence of the residual power on the heat flux extracted by the DFFB was also investigated, but no significant effect of this parameter on the heat flux value was revealed
Achieving Consistent Reporting of Radiation Dosimetry by Adoption of Compatibility in Irradiation Research Protocols Expert Roundtable (CIRPER) Recommendations
No full textInternational audienceIn radiobiology, radiation physics, and related areas, there is growing interest in transitioning from cesium-based irradiators to X-ray technologies. Therefore, it makes it imperative for reproducibility purposes, for researchers to provide specifications regarding device parameters, machine calibration details, and experimental setup when innovative X-ray technology is being employed
Updated findings on temporal variation in radiation-effects on cancer mortality in an international cohort of nuclear workers (INWORKS)
No full textInternational audienceThe International Nuclear Workers Study (INWORKS) contributes knowledge on the dose-response association between predominantly low dose, low dose rate occupational exposures to penetrating forms of ionizing radiation and cause-specific mortality. By extending follow-up of 309,932 radiation workers from France (1968–2014), the United Kingdom (1955–2012), and the United States (1944–2016) we increased support for analyses of temporal variation in radiation-cancer mortality associations. Here, we examine whether age at exposure, time since exposure, or attained age separately modify associations between radiation and mortality from all solid cancers, solid cancers excluding lung cancer, lung cancer, and lymphohematopoietic cancers. Multivariable Poisson regression was used to fit general relative rate models that describe modification of the linear excess relative rate per unit organ absorbed dose. Given indication of greater risk per unit dose for solid cancer mortality among workers hired in more recent calendar years, sensitivity analyses considering the impact of year of hire on results were performed. Findings were reasonably compatible with those from previous pooled and country-specific analyses within INWORKS showing temporal patterns of effect measure modification that varied among cancers, with evidence of persistent radiation-associated excess cancer risk decades after exposure, although statistically significant temporal modification of the radiation effect was not observed. Analyses stratified by hire period (< 1958, 1958+) showed temporal patterns that varied; however, these analyses did not suggest that this was due to differences in distribution of these effect measure modifiers by hire year