Tesi sul tema "Accident grave de réacteur"
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Lacoue-Nègre, Marion. "Chimie de l’iode dans le circuit primaire d’un réacteur nucléaire en situation d’accident grave : étude de mélanges CsI/MoO3 sous vapeur d’eau". Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10163/document.
Iodine and cesium radio nuclides constitute important fission products (FP) of 235U. If the volatile forms (gas, aerosol) of FP would be released into the environment during a hypothetical severe accident of pressurized water reactor (PWR), a potential health hazard would be the ensue. Understanding their behaviors is an important prerequisite for planning appropriate mitigation measures. Severe reactor accident simulations are conducted in several tests of the international PHEBUS-FP program. The suspected connection existing between FP such as Cs, Mo and I, hydrothermal chemistry and its role on the iodine speciation in the primary circuit of reactor coolant system are highlighted. An experimental setup was developed to study the chemical behavior of CsI/MoO3 mixtures at 1600°C under steam and then during the steam cooling to 150 °C. These hydrothermal conditions are representative of the primary circuit of PWR. The analyses using ICP-MS, powder XRD, MEBE-EDX and Raman microspectrometry identify submicrometric aerosol particles as CsI, MoO3.xH2O and Cs2MonO3n+1 (n=1, 2, 3, 5, 7) according to the starting CsI/MoO3 ratio. The formation of Cs2MonO3n+1 induces the generation of gaseous iodine. This later result is in agreement with PHEBUS-FP experiments. The simulations of vapor phase chemistry and aerosol phenomena of the {I, Cs, Mo, O, H} system in the experimental setup were carried out using the SOPHAEROS code based on the thermodynamic chemical equilibriums. Some discrepancies were observed between experimental and simulated results, particularly for Mo rich particles and the volatile iodine species release
Sanchez-Brusset, Mathieu. "Mécanismes d'oxydation de l'acier liquide lors de l'Interaction Corium-Béton à haute température en cas d'accident grave de réacteur nucléaire". Thesis, Perpignan, 2015. http://www.theses.fr/2015PERP0015/document.
In case of severe nuclear accident, the loss of coolant leads to the formation of a high temperature liquid mixture (T>2500K) of nuclear fuel and structural materials inside the vessel. After the vessel failure, the corium could interact with the concrete of the reactor pit. The metallic phase inside the corium during corium-concrete interaction, changes the ablation processes and release H2 and CO. The aim of the PhD thesis was to study the kinetics and mechanisms of the liquid steel oxidation during corium-concrete interaction. In this way, the study was divided in three parts: with calculations at the thermodynamic equilibrium, with analytical experiments and with prototypical experiments. The results of oxidation analyses during prototypical experiments show that gases inside the concrete are not the only one source of oxidation and that another source outside the concrete have to participate to the oxidation mechanism. The analytical experiments and the thermodynamic approach show that the corium can oxidize the metallic phase whereas the concrete oxides cannot. The oxidation mechanism of liquid steel is based on high chromium and iron oxidation leading to their depletion. Oxidation of nickel does not occur, it would be mainly evaporated according to the thermodynamic calculations. Thanks to the kinetic study, the rates of the liquid steel oxidation by O2 et CO2 have been found and a phenomenological model have been proposed to estimate the steel oxidation during the prototypical experiments
Belloni, Julien. "Modélisation des phénomènes de dissolution lors des phases précoces et avancées d'un accident grave de réacteur nucléaire". Phd thesis, Ecole Centrale Paris, 2009. http://tel.archives-ouvertes.fr/tel-00453295.
Garnier, Nadine. "Modélisation des lits de débris pouvant apparaître lors d'un accident grave survenant sur un réacteur à eau pressurisée". Aix-Marseille 2, 1994. http://www.theses.fr/1994AIX22008.
Martin, Franck. "La nucléation homogène : étude des intéractions vapeurs-aérosols dans le circuit primaire d'un réacteur nucléaire lors d'un accident grave". Aix-Marseille 1, 1997. http://www.theses.fr/1997AIX11007.
Pieraccini, Michel. "Contribution à la vérification et à l'amélioration des modèles d'oxydation d'un coeur de réacteur à eau pressurisée lors d'un accident grave". Aix-Marseille 1, 1996. http://www.theses.fr/1996AIX11005.
Pometko, Serguei͏̈. "Modélisation, dans un logiciel de sûrete, du comportement d'un bain liquide de matériaux fondus au cours d'un accident grave dans un coeur de réacteur". Aix-Marseille 1, 1996. http://www.theses.fr/1996AIX11004.
Mouly, Aude. "Modélisation de la formation et de la détente rapide d'une bulle polyphasique pour l'évaluation des conséquences d'un accident grave de RNR_Na". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0362.
A new generation of nuclear reactor is nowadays developed in order to take into account the economic, environmental and societal stakes of the 21th century. Among the different concepts taking part of the fourth generation, the sodium fast reactors (SFR) are studied in this PhD thesis. These reactors are the only ones of the fourth generation already having a considerable operating feedback in France.To achieve the safety objective of this new generation, the safety approach has to be adapted as soon as the reactor preconceptual and conceptual phases in order to integrate severe accidents, identify and define limitation ways as well as their consequences. This work, dedicated to the study and to the modelling of the expansion phase of a severe accident in SFR, is positioned in the CEA's work dynamic by contributing to the development of the safety approach. The goal of this PhD is to create a tool modelling the important physical phenomena induced by a power excursion in a molten material pool. This involves the formation of a vaporized sodium and molten material bubble and its subsequent expansion.After conducting detailed state of art of the different phenomena involved in the expansion phase, dimensional analysis of the physical processes is performed in order to identify the important ones. Based on this analysis, a model is developed and integrated into a tool, aiming at determining and prioritising the total phenomenon contributions to mechanical loadings on SFR vessel depending on the studied severe accident scenario. A validation step of the tool is then realised in two parts; Separate effect tests and global tests, using experimental results and calculation results obtained with other validated tools. Finally, preconceptual parametrical studies are performed to quantify the results variability due to modelling, scenarios and physical data uncertainties
Lacour, Vincent. "Modélisation de la production d'hydrogène lors de la phase de renoyage des coeurs de réacteurs nucléaires en situation d'accidents graves". Paris, ENMP, 2001. http://www.theses.fr/2001ENMP1011.
Zhang, Shaoliang. "Etudes cinétiques de l'oxydation radicalaire en phase gazeuse d'iodures organiques et de la formation de particules d'oxydes d'iode sous conditions simulées de l'enceinte d'un réacteur nucléaire en situation d'accident grave". Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4820/document.
Within the framework of the research in the nuclear reactor safety field, the iodine oxides formation by organic iodides destruction in the containment has been studied with the means of the atmospheric chemistry field. The destruction kinetics and their activation energy of organic iodides by OH and O radical has been quantified by a Flash Photolysis system able to monitor the oxidant radicals by resonance fluorescence. Those results have been published and some of them for the first time in the literature. The mechanisms leading to the organic iodides destruction are either by a hydrogen atom abstraction, either by the formation of a complex, depending on the organic iodide involved. Then, certain kinetics reactions have been updated in the IODAIR code. Other reactions have been added based on the recent literature available. A comparison of the kinetics destruction of CH3I by OH and O with IODAIR and the global kinetics of destruction in ASTEC/IODE showed a difference of about 2 which shows the importance of these two radicals (and mainly O) in those destruction processes. The other main path of destruction would be by electron radiation. Other radicals like H and N would not contribute significantly to organic iodides destruction. A sensitivity analysis highlighted that organic iodides would mostly be destroyed into iodine oxides with a almost complete conversion within a few hours. Finally, an atmospheric chamber has been used to quantify iodine oxides growth, density and composition. Under the conditions studied, their formation is fast. Particles sizes of about 200- 400 nm are formed within a few hours
Monfort, Marguerite. "Influence du milieu aqueux récepteur sur le devenir de produits de fission dans l'environnement : cas d'aérosols susceptibles d'être émis lors d'un accident grave survenant sur un réacteur à eau pressurisée". Montpellier 2, 1989. http://www.theses.fr/1989MON20100.
Singh, Shifali. "Radioscopie X pour les interactions corium-sodium lors d'un scénario d'accident grave". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS114.
In Sodium-cooled Fast Reactors (SFR), hypothetical failure of the core cooling system or the plant protection system may lead to a severe accident scenario. In such a scenario, core materials (fuel and cladding) melt down generating a hot molten mixture called corium. This corium may interact with the coolant (liquid sodium) leading to Fuel Coolant Interaction (FCI) which can generate energetic events and hence jeopardize the reactor structures. The yield of these energetic events strongly depends on the state of the corium-sodium mixture prior to the energetic event. Therefore, the knowledge of the features of the mixture composed of three-phases (i.e., corium, liquid sodium, and sodium vapor) is crucial. The lack of knowledge on the phenomenology of the interaction emphasizes the need to study it with the help of experiments. PLINIUS-2, the future large-mass experimental platform of CEA Cadarache, will be dedicated to experiments aiming at understanding the interaction phenomenology of prototypic corium with coolant (sodium and water). The present research aims to develop a high-energy X-Ray imaging system for this facility, to visualize and better understand the corium-sodium interaction. An image-processing algorithm to analyze the three-phase repartition is also developed to contribute to the improvement of numerical modeling. This Ph.D. research has been executed in three steps. In the first step, a bibliographic study of the past experiments was carried out to better understand the physics of the interaction and the mechanism of fragmentation during corium-sodium interaction. This bibliographic study, along with a statistical analysis of the particle size distribution data of various experiments conducted in the past, revealed that the particles formed in these tests are extremely fine fragments with characteristic diameters smaller than 1 mm. Due to the small particle size and the detection limitations of corium fragments in sodium with our X-Ray system, clouds of particles were detected instead of individual particles. In the second phase, the simulation of clouds of corium particles followed by the designing of phantoms (3D mock-ups) representing the 3-phase medium was carried out. Simulations of clouds of corium fragments in liquid sodium and vapor were performed using the CEA Cadarache in-house tool MODHERATO. Based on the results obtained from the simulations, certain phantoms were designed to conduct some physical experiments. These phantoms representative of the FCI interaction zone were manufactured to experimentally evaluate the performance of the radioscopy system and to facilitate the development and calibration of the image processing software. The third step of this work was dedicated to performing experiments with the phantoms and analyzing the radiographic images by developing an image processing algorithm. Experiments were carried out with phantoms in several configurations with the X-Ray radiography system at the CEA Cadarache KROTOS facility. The radioscopic images obtained were treated by developing a new comprehensive image processing and analysis code called PICSEL to identify the three phases composing the medium. Further verification and validation of the PICSEL software were carried out on a test conducted between corium and water at the KROTOS facility under the Euro-Chinese project “ALISA”. Thus, in this Ph.D. research, an X-Ray imaging system was qualified to visualize the corium-sodium interaction in the future PLINIUS-2-FR facility. A qualitative analysis of the images produced by this system was also performed using the PICSEL software to better characterize the evolution of the three-phase mixture and understand the FCI phenomenon, knowledge of which is deemed essential to improve the safety and designs of future sodium-cooled fast reactors
Tyrpekl, Vaclav. "Effet matériaux lors de l'interaction corium-eau : analyse structurale des débris d'une explosition vapeur et mécanismes de solidification". Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00758983.
Obada, Dorel. "Evaluation de rejets moyen-terme en situation accidentelle grave d’un réacteur à eau pressurisée : étude expérimentale de la re-vaporisation de dépôts de produits de fission (Cs, I)". Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10148/document.
In case of a severe nuclear accident on a Pressurized Water Reactor, radioactive fission products can be released in the environment and represent a hazard for the human. In order to better predict the progress of the accident and the release of fission products with the use of dedicated simulation tools, the knowledge of all physicochemical phenomena is necessary. This research is focused on the re-vaporisation, up to 750°C, of iodine-containing fission products’ deposits, particularly CsI and AgI, from the surface of the primary circuit, composed of partially oxidized 304L, 316L steels and Inconel 600 alloy. The results have revealed a strong influence of the re-vaporisation atmosphere composition on the quantities and the chemical species nature of re-vaporized caesium and iodine. In steam atmosphere, iodine and caesium are released integrally from the surface, mainly as CsI. In presence of air, iodine is released integrally, mainly as I2(g), whereas caesium is partially retained on the surface of the steel as caesium chromate, resulting from the interaction between caesium and chromium (III) oxide present in the oxide layer. The use of an online optical spectroscopic technique such as IBB-CEAS allowed to follow the I2(g) re-vaporisation kinetics. The latter exhibits two release peaks, suggesting several mechanisms leading to I2(g) formation. A similar result has been observed during the re-vaporisation of AgI in presence of air. Finally, thermodynamic equilibrium computations have been performed in order to identify the main reaction pathways leading to the formation of gaseous molecular iodine in presence of air
Guyot, Maxime. "Neutronics and thermal-hydraulics coupling : some contributions toward an improved methodology to simulate the initiating phase of a severe accident in a sodium fast reactor". Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4345.
This project is dedicated to the analysis and the quantification of bias corresponding to the computational methodology for simulating the initiating phase of severe accidents on Sodium Fast Reactors. A deterministic approach is carried out to assess the consequences of a severe accident by adopting best estimate design evaluations. An objective of this deterministic approach is to provide guidance to mitigate severe accident developments and recriticalities through the implementation of adequate design measures. These studies are generally based on modern simulation techniques to test and verify a given design. The new approach developed in this project aims to improve the safety assessment of Sodium Fast Reactors by decreasing the bias related to the deterministic analysis of severe accident scenarios.During the initiating phase, the subassembly wrapper tubes keep their mechanical integrity. Material disruption and dispersal is primarily one-dimensional. For this reason, evaluation methodology for the initiating phase relies on a multiple-channel approach. Typically a channel represents an average pin in a subassembly or a group of similar subassemblies. Inthe multiple-channel approach, the core thermal-hydraulics model is composed of 1 or 2 D channels. The thermal-hydraulics model is coupled to a neutronics module to provide an estimate of the reactor power level.In this project, a new computational model has been developed to extend the initiating phase modeling. This new model is based on a multi-physics coupling. This model has been applied to obtain information unavailable up to now in regards to neutronics and thermal-hydraulics models and their coupling
Kauric, Guilhem. "Contribution to the investigation of the chemical interaction between sodium and irradiated MOX fuel for the safety of Sodium-cooled Fast Reactors". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASF027.
In case of a severe accident in Sodium-cooled Fast Reactors, interactions between partly molten fuel and sodium could happen at high temperature. Therefore, to predict the degradation evolution of fuel pins and phase formation in the different systems existing in the irradiated fuel, a thorough study of the Na-FP-Pu-U-O with FP= Ba, Cs, I, Mo, Te has to be performed. For such multicomponent system and large temperature and composition range, the Calphad method is a suitable way for developing a thermodynamic database to predict the phase formation depending on the temperature, pressure and composition of the system. Compositions with four Pu/(U+Pu) ratio in the Na-O-Pu-U system were synthesised by solid state synthesis method using nanoparticules of MOX fuel and characterised by XRD, ²³Na-NMR and HR-XANES techniques. The oxidation state of plutonium and uranium in the different structures was systematiquely investigated. When the measured oxidation state of actinides was different from the theoretical one, charge compensation mechanisms were suggested either by adding sodium in the structure or oxygen vacancies. Then, the structure of quaternary compounds in the Ba-Mo-Na-O and Cs-Mo-Na-O systems were also investigated by several structural techniques (XRD, neutron diffraction, HT-XRD, HT-Raman spectroscopy, XAS). Thermodynamic properties such as standard enthalpy of formation or enthalpy of decomposition were also determined. Finally, the Cs₂MoO₄-Na₂MoO₄ pseudo-binary section was re-investigated experimentally by DSC and a Calphad model for this system was developed
Viot, Louis. "Couplage et synchronisation de modèles dans un code scénario d’accidents graves dans les réacteurs nucléaires". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLN033/document.
This thesis focuses on solving coupled problems of models of interest for the simulation of severe accidents in nuclear reactors~: these coarse-grained models allow for fast calculations for statistical analysis used for risk assessment and solutions of large problems when considering the whole severe accident scenario. However, this modeling approach has several numerical flaws. Besides, in this industrial context, computational efficiency is of great importance leading to various numerical constraints. The objective of this research is to analyze the applicability of explicit coupling strategies to solve such coupled problems and to design implicit coupling schemes allowing stable and accurate computations. The proposed schemes are theoretically analyzed and tested within CEA's procor{} platform on a problem of heat conduction solved with coupled lumped parameter models and coupled 1D models. Numerical results are discussed and allow us to emphasize the benefits of using the designed coupling schemes instead of the usual explicit coupling schemes
Aujollet, Yvan. "Etude des interactions chimiques iode-peinture dans un réacteur nucléaire (réacteur à eau pressurisée) en situation d'accident grave". Aix-Marseille 3, 1999. http://www.theses.fr/1999AIX30085.
Ryckwaert, Yves. "Strangulation aigue͏̈ grave accidentelle de l'enfant". Montpellier 1, 1990. http://www.theses.fr/1990MON11279.
Lainault, Franck. "Modélisation de la libération d'énergie liée aux accidents graves dans les réacteurs nucléaires à neutrons rapides". Poitiers, 1997. http://www.theses.fr/1997POIT2308.
Frolov, Kirill. "Diffusion chimique à l'état liquide dans des bains silicatés : application aux accidents graves de réacteurs nucléaires". Université Joseph Fourier (Grenoble), 2004. http://www.theses.fr/2004GRE10062.
In this work, one of the aspects of the late phase of a hypothetic water reactor severe accident long-term of an artificial magma called corium within the nuclear power plant (NPP) containement has been investigated. It is shown in this study that plane-front solidification of multicomponent oxide mixtures can be described in terms of the series of interfacial stability criterai wich incorporate the ionic constituents self-diffusion coefficients as key parameteres. For the current chemical diffusion models, their application to such criteria would require either experimental or theoretical knowledge of these coefficients. An advanced modification of the square wave voltametric technique alowwing a higher precision determination of self-diffusion coefficients is thus proposed and validated on the molten concrete simulants at 1200-1700°C. On the other hand, it is shown that the current self-diffusion models of STOKES-EINSTEIN and EYRING among others are poorly applicable to corium type mixtures. We have come up thus in this work with a novel type of correlation employing the self-diffusion and viscosity coefficients which we have lalidated using some published data on these coefficients for silicate oxide mixture. Finally, we present conclusions on the limit of silica concentration in corium melts that would allow plane-front solidification obtained with the use of data on corium slow solidification together with the semi-empirical self-diffusion models of MUNGALL
Journeau, Christophe. "Contribution des essais en matériaux prototypiques sur la plate-forme PLINIUS à l'étude des accidents graves de réacteurs nucléaires". Habilitation à diriger des recherches, Université d'Orléans, 2008. http://tel.archives-ouvertes.fr/tel-00343657.
Peeters, Agnes. "Application of the Stimulus-Driven Theory of Probabilistic Dynamics to the hydrogen issue in level-2 PSA". Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210641.
Ces accidents sévères dépendent non seulement de défaillances matérielles ou d’erreurs humaines, mais également de l’occurrence de phénomènes physiques, tels que des explosions vapeur ou hydrogène. La prise en compte de tels phénomènes dans le cadre booléen des arbres d’événements s’avère difficile, et les méthodologies dynamiques de réalisation des EPS sont censées fournir une manière plus cohérente d’intégrer l’évolution du processus physique dans les changements de configuration discrète de la centrale au long d’un transitoire accidentel.
Cette thèse décrit l’application d’une des plus récentes approches dynamiques des EPS – la Théorie de la Dynamique Probabiliste basée sur les Stimuli (SDTPD) – à différents modèles de déflagration d'hydrogène ainsi que les développements qui ont permis cette applications et les diverses améliorations et techniques qui ont été mises en oeuvre.
Level-2 Probabilistic Safety Analyses (PSA) of nuclear power plants aims to identify the possible sequences of events corresponding to an accident propagation from a core damage to a potential loss of integrity of the containment, and to assess the frequency of occurrence of the different scenarios.
These so-called severe accidents depend not only on hardware failures and human errors, but also on the occurrence of physical phenomena such as e.g. steam or hydrogen explosions. Handling these phenomena in the classical Boolean framework of event trees is not convenient, and dynamic methodologies to perform PSA studies are expected to provide a more consistent way of integrating the physical process evolution with the discrete changes of plant configuration along an accidental transient.
This PhD Thesis presents the application of one of the most recently proposed dynamic PSA methodologies, i.e. the Stimulus-Driven Theory of Probabilistic Dynamics (SDTPD), to several models of hydrogen explosion in the containment of a plant, as well as the developed methods and improvements.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
Andriolo, Lena. "Impact des combustibles sphere-pac innovants sur les performances de sûreté des réacteurs à neutrons rapides refroidis au sodium". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI067/document.
Future sodium cooled fast reactors (SFRs) have to fulfill the GEN-IV requirements of enhanced safety, minimal waste production, increased proliferation resistance and high economical potential. This PhD project is dedicated to the evaluation of the impact of innovative fuels (especially minor actinides bearing oxide sphere-pac fuels) on the safety performance of advanced SFRs with transmutation option. The SIMMER-III code, originally tailored to mechanistically analyze later phases of core disruptive accidents, is employed for accident simulations. During the PhD project, the code has been extended for a better simulation of the early accident phase introducing the treatment of thermal expansion reactivity effects and for taking into account the specifics of sphere-pac fuels (thermal conductivity and gap conditions). The entire transients (from the initiating event to later accident phases) have been modeled with this extended SIMMER version. Within this PhD work, first the thermo-physical properties of sphere-pac fuel have been modeled and casted into SIMMER-III. Then, a new computational method to account for thermal expansion feedbacks has been developed to improve the initiation phase modeling of the code. The technique has the potential to evaluate these reactivity feedbacks for a fixed Eulerian mesh and in a spatial kinetics framework. At each time step, cell-wise expanded dimensions and densities are calculated based on temperature variations. Density factors are applied to the expanded densities to get an equivalent configuration (in reactivity) with original dimensions and modified densities. New cross sections are calculated with these densities and the reactivity of the equivalent configuration is computed. The developed methods show promising results for uniform and non-uniform expansions. For non-uniform expansions, model improvement needs have been identified and neutronics simulations have been carried out to support future SIMMER extensions. Preliminary results are encouraging. In the third part of the PhD, two core designs with conventional and sphere pac fuels are compared with respect to their transient behavior. These designs were established in the former CP-ESFR project: the working horse core and the optimized CONF2 core (with a large sodium plenum above the core for coolant void worth reduction). The two fuel design options are compared for steady state and transient conditions (Unprotected Loss of Flow accident, ULOF) either at beginning of life (BOL) or under irradiated conditions. Analyses for sphere-pac fuel reveal two main phases to consider at BOL. At start-up, the non-restructured sphere-pac fuel shows a low thermal conductivity compared to pellet fuel of same density. However, the fuel restructures quickly (in a few hours) due to the high thermal gradients and its thermal conductivity recovers. The fuel then shows a behavior close to the pellet one. The study also shows that the CONF2 core leads to a very mild transient for a ULOF accident at BOL. The large upper sodium plenum seems to effectively prevent large positive reactivity insertions. However, stronger reactivity and power peaks are observed under irradiated conditions or when americium is loaded in the core and lower axial blanket. This PhD work demonstrates, under current simulation conditions, that sphere-pac fuels do not seem to cause specific safety issues compared to standard pellet fuels, when loaded in SFRs. The accurate simulation of core thermal expansion reactivity feedbacks by means of the extended SIMMER version plays an important role in the accident timing (simulations confirm the expected delay in the first power peak) and on the energetic potential compared to the case where these feedbacks are omitted. The analyses also confirm the mitigating impact of a large sodium plenum on transients with voiding potential. The behavior of sphere-pac fuel in these conditions opens a perspective to its practical application in SFRs
Gouello, Mélany. "Chimie de l'iode et composition des aérosols dans le circuit primaire d'un réacteur nucléaire en situation d'accident grave". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00832204.
Chesnel, Alain. "Étude paramétrique d'un accident de réactivité dans un réacteur à eau pressurisée : éjection d'une grappe de contrôle". Paris 11, 1985. http://www.theses.fr/1985PA112391.
Clamens, Olivier. "Analyse et propagation des incertitudes associées à la dépressurisation de l’Hélium 3 sur les transitoires de puissance du réacteur CABRI". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI061/document.
CABRI is a pool type pulsed reactor designed for studying pre-irradiated nuclear fuel behavior under RIA (Reactivity Initiated Accident) conditions.The helium-3 depressurization from the transient rods system allows the insertion of up to 4 $ reactivity mainly countered by the Doppler effect when the power reaches in few milliseconds up to 200,000 times the initial 100~kW power.This thesis presents the improvements added to the power transients prediction and the associated uncertainties studies.The point kinetics calculation coupled with 1D thermal-hydraulics and heat transfer has been improved by the addition of surrogate models based on experimental analysis and Best-Estimate calculations of the helium-3 depressurization and of the reactivity effects and of the kinetics parameters.The power transients modeling improvements have a positiv impact on the CABRI tests prediction.The propagation of the experimental and of the modeling uncertainties was realized with the SPARTE code and the URANIE uncertainty platform.Finally, the power transients characteristics optimization is approached in order to improve the CABRI experiments designing
Belloni, Julien Goyeau Benoît. "Modélisation des phénomènes de dissolution lors des phases précoces et avancées d'un accident grave de réacteur nucléaire". S. l. : Ecole centrale de Paris, 2009. http://theses.abes.fr/2009ECAP0008.
Beuzet, Emilie. "Modélisation des conséquences d'une entrée d'air en cuve sur le calcul du terme source en accident grave". Paris 11, 2010. http://www.theses.fr/2010PA112240.
This work deals with severe accidents in nuclear power plants with an air ingress in the vesse!. Air, which is very oxidizing, enhances noticeably ruthenium release, due to a high fuel oxidation. Oxygen affinity is decreasing between zircaloy cladding, fuel and ruthenium which is released from fuel as volatile and radiotoxic oxides. The main objective was to develop models for cladding and fuel oxidation and ruthenium release and implement them in the severe accident code MAAP. For each phenomenon, the literature study contributes to establish numerical models, validated against specific experiments. Cladding oxidation by air leads to a dense zirconia layer and, after cracking, a porous zirconia. Its modelling was validated against QUENCH-10 (KIT) and PARAMETER-SF4 (LUCH) experiments and 'NUREG' oxide mass gain law was selected as the best current compromise. Ruthenium release is modelled as an instantaneous oxide volatilisation at the fuel surface, controlled by fuel oxidation, which is itself based on a surface reaction assumption. These models were validated against a selected set of VERCORS (CEA) experiments. Ruthenium release is well-reproduced, particularly for air and steam atmospheres. To finish, an accidental scenario with air ingress in the vessel was simulated : a first value was given for the time needed to completely release ruthenium still present in core and was compared to the other studies. This simulation underlines the high ruthenium release under air conditions
Mun, Christian. "Etude du comportement du produit de fission ruthénium dans l'enceinte de confinement d'un réacteur nucléaire, en cas d'accident grave". Paris 11, 2007. http://www.theses.fr/2007PA112032.
Ruthenium tetroxide is an extremely volatile and highly radiotoxic species. During a severe accident with air ingress in the reactor vessel, ruthenium oxides may reach the reactor containment building in significant quantities. Therefore, a better understanding of the RuO4(g) behaviour in the containment atmosphere is of primary importance for the assessment of radiological consequences, in the case of potential releases of this species into the environment. A RuO4(g) decomposition kinetic law was determined. Steam seems to play a catalytic role, as well as the presence of ruthenium dioxide deposits. The temperature is also a key parameter. The nature of the substrate, stainless steel or paint, did not exhibit any chemical affinities with RuO4(g). This absence of reactivity was confirmed by XPS analyses, which indicate the presence of the same species in the Ru deposits surface layer whatever the substrates considered. It has been concluded that RuO4(g) decomposition corresponds to a bulk gas phase decomposition. The ruthenium revolatilisation phenomenon under irradiation from Ru deposits was also highlighted. An oxidation kinetic law was determined. The increase of the temperature and the steam concentration promote significantly the oxidation reaction. The establishment of Ru behavioural laws allowed making a modelling of the Ru source term. The results of the reactor calculations indicate that the values obtained for 106Ru source term are closed to the reference value considered currently by the IRSN, for 900 MWe PWR safety analysis
Beloeil, Laurent. "Etude d'un accident de criticité mettant en présence des crayons combustibles et de l'eau hors réacteur de puissance". Aix-Marseille 1, 2000. http://www.theses.fr/2000AIX11017.
Chebbi, Mouheb. "Piégeage d’espèces iodées volatiles sur des adsorbants poreux de type zéolithique dans le contexte d’un accident nucléaire grave". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0340/document.
A severe nuclear accident (as Fukushima) may induce dramatic consequences in terms of radiological releases into the environment. The combination of current filtration devices (such as aqueous scrubbers and sand bed filters) with an additional filtration stage made of inorganic porous adsorbent (zeolite) constitute a promising solution in order to avoid the release of radioactive iodine species. The present study aims to establish some correlations between chemical and structural parameters of porous adsorbents mainly silver-zeolites, on the one hand, and adsorption properties towards I2 and CH3I on the other hand. The role played by various zeolitic parameters was assessed by combining adsorption data in gaseous phase (adsorption capacity, decontamination factors, trapping stability) together with physico-chemical data obtained from characterization studies (XRD, ATR/IR, DRIFTS of adsorbed CO, SEM, TEM and DR-UV-Vis). Then, the effect of adsorption temperatures, potential inhibitors and irradiation was also discussed for the most interesting adsorbents in order to extrapolate to severe accidental conditions. The trapping mechanism was also investigated using in-situ spectroscopic accessories as well as theoretical calculations by DFT. It was shown that CH3I adsorption capacities are mainly dependent on the amount of silver that could be deposited in dispersed form (as Ag+, and small clusters) within the internal framework, as well as structural parameters such as pore size. On the other hand, a specific methodology was applied in order to quantify the different forms of stored iodine and therefore to better assess the influence of structural parameters on the trapping thermal stability. It was found that the trapping stability is mainly dependent on silver exchange level and on the nature of zeolitic structure. For the first time, the combination of several spectroscopic techniques was also implemented. On the one hand, in situ Diffuse Reflectance UV-Vis Spectroscopy (DRS-UV-Vis) was employed in order to monitor the evolution of silver species during exposure to gaseous methyl iodide. On the other hand, the time- and temperature-evolution of organic species was investigated using in situ Diffuse Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS) combined with gas-phase reactor measurements. The first step is the dissociation of some CH3I molecules, which is catalyzed by the acidic and silver sites of the zeolite. The dissociated I is then captured by silver to form molecular and clustered AgI entities within the zeolite supercages, which can coalesce and sinter on the external surface upon prolonged exposure to humidity to form silver iodide precipitates (detected by XRD). On the other hand, the carbonaceous part of the CH3I molecules undergo successive catalytic transformations at medium temperatures with zeolite active sites, to yield different by-products (MeOH, DME, higher alkanes, alkenes…). Among all the investigated sorbents for iodine species retention, Ag/Y zeolites have displayed the best retention performances. Promising results were also found in the presence of inhibitors, under irradiation and for low concentrations. The obtained results allow to consider using some of the tested formulations for a nuclear severe accident application, but also to give insights about the behavior of other new adsorbents (Metal Organic Framework MOF and silver-impregnated or functionalized mesoporous silica)
Cintra, Eliane de Araujo. "Niveis de arginina vasopressina e disturbios de sodio e agua em pacientes com lesão cerebral grave". [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/313566.
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas
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Resumo: Antecedentes. Desordens do balanço de sódio e água, especialmente aqueles secundários ao diabete insípido (DI), à síndrome da secreção inapropriada do hormônio anti-diurético (SIHAD) e à síndrome cerebral perdedora de sal (SCPS), são freqüentemente vistas em pacientes com lesão cerebral grave (LCG), tanto traumática quanto não-traumática, podendo comprometer seus prognósticos. Diversos autores têm sugerido que um aumento na secreção de vasopressina (AVP) pode ser responsável pela piora da lesão cerebral primária uma vez que ela afeta os mecanismos cerebrais de formação de edema. Contudo, as alterações fisiopatológicas anteriormente citadas continuam sendo focos de debates na literatura. Objetivo. Avaliar o comportamento dos níveis plasmáticos de vasopressina e a presença de desordens do balanço de sódio e água em pacientes com LCG. Desenho. Estudo prospectivo, observacional e aberto. Local. Unidade de terapia intensiva geral de adultos do Hospital das Clínicas da Universidade Estadual de Campinas. Pacientes e Métodos. Trinta e sete pacientes adultos, de ambos os sexos, com LCG (pontuação inicial na escala de coma de Glasgow ? 8) e tempo estimado de lesão ? 72 horas foram estudados. Dados clínicos e laboratoriais de interesse foram registrados e a AVP foi mensurada em amostras de sangue venoso colhidas no 1o, 2o, 3o e 5o dias após a inclusão. Dados laboratoriais de 29 voluntários adultos sadios, previamente relatados, serviram de controle (CTRL). Resultados. Os níveis plasmáticos médios de AVP permaneceram dentro da faixa de normalidade nos pacientes com LCG, sem diferenças significativas em relação ao grupo controle, mas mostraram-se proporcionalmente menores no 5o dia comparado ao 1o dia após a inclusão (1,5 ± 1,6pg/ml vs 2,3 ± 2,8pg/ml; p = 0,035). Os níveis plasmáticos de AVP foram ligeiramente maiores nos pacientes que evoluíram para o óbito em relação aos sobreviventes (p = 0,062), e mostraram uma queda do 1o em relação ao 5o dia de observação em ambos os grupos (p = 0,049). O sódio sérico e a osmolalidade plasmática, assim como suas variações em relação à faixa de normalidade, foram maiores nos pacientes que evoluíram para o óbito em relação aos sobreviventes (p < 0,05). Conclusão. Os níveis plasmáticos de AVP permaneceram dentro da faixa de normalidade nos pacientes com LCG, e estes tenderam a diminuir com o tempo de evolução, tanto nos sobreviventes quanto nos que evoluíram para o óbito. Contudo, o sódio sérico e a osmolalidade plasmática mostraram grandes variações nos pacientes com LCG, e os não sobreviventes apresentaram desvios mais amplos e mais significativos em relação à faixa de normalidade que os sobreviventes, especialmente hipernatremia e hiperosmolalidade, compatíveis com a presença de disfunção do eixo hipotálamo-hipófisário posterior, principalmente diabete insípido. Contudo, estes resultados não nos permitem afirmar com segurança se esses distúrbios atuaram como agravantes da lesão primária ou se meramente foram um reflexo da gravidade da injúria cerebral
Abstract: Background. Disorders of sodium and water balance, especially those secondary to diabetes insipidus (DI), syndrome of inappropriate anti-diuretic hormone (SIADH) and cerebral salt wasting syndrome (CSWS), are frequently seen in patients with severe brain injury (SBI), either traumatic or non-traumatic, and may jeopardize their prognosis. Many authors have suggested that an increase in vasopressin (AVP) secretion may be responsible for the worsening of primary brain lesion as long as it affects the brain mechanisms of edema formation. However, this remains a focus of debate in the literature. Objective. To evaluate vasopressin plasma levels and sodium and water balance disorders in patients with SBI. Design. Prospective, observational, open label study. Setting. General adult intensive care unit, Hospital de Clínicas, Campinas State University. Patients and Methods. Thirty-seven adult patients, both sexes, with SBI (admission Glasgow Coma Scale score ? 8) and an estimated time of injury ? 72 hours were studied. Clinical and laboratory data were recorded and AVP was measured in venous blood samples collected on the 1st, 2nd, 3rd and 5th days following inclusion. Laboratory data from 29 healthy adult volunteers previously reported served as control. Results. Mean AVP serum levels remained inside the normal range in SBI patients, without significant differences in relation to control group, and were proportionally lower at 5th day compared to 1st day following inclusion (1.5 ± 1.6 pg/ml vs 2.3 ± 2.8 pg/ml; p = 0.035). AVP serum levels were slightly higher in patients who died compared to survivors, but this difference was not significant (p = 0.062), and have shown a decrease from the 1st to 5th day of observation in both groups (p = 0.049). Serum sodium and plasma osmolality, and long as their variability, were greater in non-survivor than in survivor patients (p < 0.05). Conclusion. AVP plasma levels remained within normal range in SBI patients, and these levels tended to decrease over time, both in survivor and non-survivors. However, serum sodium and plasma osmolality have shown great variations in SBI patients, and non-survivor ones have shown greater and more significant deviations from normal values than those who survived, especially hypernatremia and hyperosmolality, consistent with the presence of posterior hypothalamus-hypophysial axis dysfunction, mainly diabetes insipidus. Nevertheless, these results do not allow us to clearly define whether these disturbances aggravate the primary lesion or if they are merely a reflex of the cerebral injury severity
Doutorado
Ciencias Biomedicas
Doutor em Ciências Médicas
Mabrouk, Ahmed. "Developpements d'outils d'aide au diagnostic en contexte incertain". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066449.
The diagnosis of severe nuclear accident scenarios represents a major challenge for nuclear safety and crisis management. The problem is complex and remains until now one of the main research topics due to the complexity of the physical and chemical phenomena underlying severe accidents, the difficulty in understanding the different correlations between them, and in addition the unavailability of efficient public datasets. Thus, the purpose of this thesis is to propose a dedicated tool for modeling and diagnosis of accident scenarios based on Bayesian networks. The learning process of the Bayesian networks is based on the use of databases created with the ASTEC severe accident software. It should be emphasized that the use of Bayesian networks in this context has faced many challenges, notably the learning process from the accidental data which, after numerous studies, has been doomed to be ineffective to address efficiently this task. These difficulties arise mainly because the used data contains on the one hand, many continuous variables and on the other hand a set of both deterministic and probabilistic relationships between variables. These two constraints present a serious problem for the learning algorithms of Bayesian networks because these latter assume that all relationships between variables are probabilistic and all the used variables in the datasets are factorial (or discrete). Concerning the first point, we proposed of a new structure learning algorithm based on the use of a set of new rules (whose effectiveness has been proven theoretically and experimentally). Regarding discretization step, we proposed a multivariate approach which, according to a detailed experimental study, has enabled us to overcome the drawbacks of these latter while minimizing the information loss during the data transformation
Villermaux, Clotilde. "Modélisation physique et numérique de la convection naturelle dans une couche de fluide de faible rapport d'aspect dans le cadre des études d'accidents graves de réacteurs à eau sous pression". Grenoble INPG, 1999. http://www.theses.fr/1999INPG0028.
Sestier, Karine. "Evolution microstructurale et comportement mécanique à haute température de l'acier de cuve 16MND5 en situation d'accident grave". Grenoble INPG, 1998. http://www.theses.fr/1998INPG0153.
Manchon, Xavier. "Contribution à la prédiction du déroulement de scénarios d'accidents graves dans un RNR-Na". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC047/document.
Severe accidents’ modeling is required for the design and safety analysis of ASTRID, a Generation IV Sodium-cooled Fast Reactor under development in France. This thesis aims at contributing to identify the driving processes of ASTRID’s severe accidents scenarios. First, a stability criterion is developed to analyze the beginning of an unprotected loss of flow accident. This stability criterion assesses whether the decreasing flow is stable or unstable, leading to the core disassembly. This criterion also considers power variations during the loss of flow, which former stability criteria do not take into account. Then, the driving processes of a transient involving a fuel vaporisation followed by its vapor expansion are identified using a dimensional analysis. The simplifications justified by this dimensional analysis are considered further to develop a numerical tool that computes the mechanical energy transmitted to the core vessel in case of fuel vaporisation. The thermal exchange between the expanding fuel vapor and the sodium coolant is especially analyzed. The tool is validated by comparing its results to experimental measures and to another tool’s computations. In the end, parametric studies are done in order to assess the tool computations’ variability induced by physical uncertainties or modeling options
Mabrouk, Ahmed. "Developpements d'outils d'aide au diagnostic en contexte incertain". Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066449.
The diagnosis of severe nuclear accident scenarios represents a major challenge for nuclear safety and crisis management. The problem is complex and remains until now one of the main research topics due to the complexity of the physical and chemical phenomena underlying severe accidents, the difficulty in understanding the different correlations between them, and in addition the unavailability of efficient public datasets. Thus, the purpose of this thesis is to propose a dedicated tool for modeling and diagnosis of accident scenarios based on Bayesian networks. The learning process of the Bayesian networks is based on the use of databases created with the ASTEC severe accident software. It should be emphasized that the use of Bayesian networks in this context has faced many challenges, notably the learning process from the accidental data which, after numerous studies, has been doomed to be ineffective to address efficiently this task. These difficulties arise mainly because the used data contains on the one hand, many continuous variables and on the other hand a set of both deterministic and probabilistic relationships between variables. These two constraints present a serious problem for the learning algorithms of Bayesian networks because these latter assume that all relationships between variables are probabilistic and all the used variables in the datasets are factorial (or discrete). Concerning the first point, we proposed of a new structure learning algorithm based on the use of a set of new rules (whose effectiveness has been proven theoretically and experimentally). Regarding discretization step, we proposed a multivariate approach which, according to a detailed experimental study, has enabled us to overcome the drawbacks of these latter while minimizing the information loss during the data transformation
Gerardin, Jonathan. "Évaluation du transfert radiatif dans le coeur d'un Réacteur à Eau Pressurisée (REP) lors de la phase de renoyage d'un Accident de Perte de Réfrigérant Primaire (APRP)". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0145/document.
We developped a method of resolution of radiative transfer inside a medium of vapor-droplets surrounded by hot walls, in order to couple it with a simulation of the flow at the CFD scale. The scope is the study of the cooling of the core of nuclear reactor following a Loss Of Coolant Accident (LOCA). The problem of radiative transfer can be cut into two sub problems, one concerning the evaluation of the radiative properties of the medium and a second concerning the solution of the radiative transfer equation. The radiative properties of the droplets have been computed with the use of the Mie Theory and those of the vapor have been computed with a Ck model. The medium made of vapor and droplets is an absorbing, anisotropically scattering, emissive, non grey, non homogeneous medium. Hence, owing to the possible variations of the flow properties (diameter and volumetric fraction of the droplets, temperature and pressure of the vapor), the medium can be optically thin or thick. Consequently, a method is required which solves the radiative transfer accurately, with a moderate calculation time for all of these prerequisites. The IDA has been chosen, derived from the well-known P1-approximation. Its accuracy has been checked on academical cases found in the literature and by comparison with experimental data. Simulations of LOCA flows have been conducted taking account of the radiative transfer, evaluating the radiative fluxes and showing that radiative transfer influence cannot be neglected
Delipei, Gregory. "Développement d'une méthodologie de Quantification d'Incertitudes pour une analyse Mutli-Physique Best Estimate et application sur un Accident d’Éjection de Grappe dans un Réacteur à Eau Pressurisée". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX078/document.
The computational advancements of the last decades lead to the development of numerical codes for simulating the reactor physics with increa-sing predictivity allowing the modeling of the beha-vior of a nuclear reactor under both normal and acci-dental conditions. An uncertainty analysis framework consistent with Best Estimate (BE) codes was develo-ped in order to take into account the different sources of uncertainties. This framework is called Best Esti-mate Plus Uncertainties (BEPU) and is currently a field of increasing research internationally. In this the-sis we study the multi-physics uncertainty quantifi-cation for Rod Ejection Accident (REA) in Pressuri-zed Water Reactors (PWR). The BE modeling avai-lable in CEA is used with a coupling of APOLLO3 (neutronics) and FLICA4 (thermal-hydraulics and fuel-thermal) in the framework of SALOME/CORPUS tool. In the first part of the thesis, we explore different statistical tools available in the scientific literature including: dimension reduction, global sensitivity analy-sis, surrogate modeling and design of experiments. We then use them in order to develop an uncer-tainty quantification methodology. In the second part of the thesis, we improve the BE modeling in terms of its uncertainty representation. A Best Effort coupling scheme for REA analysis is available at CEA. This in-cludes ALCYONE V1.4 code for a detailed modeling of fuel-thermomechanics behavior. However, the use of such modeling increases significantly the compu-tational cost for a REA transient rendering the uncer-tainty analysis prohibited. To this purpose, we deve-lop a methodology for calibrating a simplified analytic gap heat transfer model using decoupled ALCYONE V1.4 REA calculations. The calibrated model is finally used to improve the previous BE modeling. Both de-veloped methodologies are tested initially on a small scale core representative of a PWR and then applied on a large scale PWR core
Morfin, Franck. "Combustion catalytique de l'hydrogène comme parade au rique de déflagration dans l'enceinte de confinement d'un réacteur nucléaire en situation d'accident grave : étude de l'empoisonnement des catalyseurs en atmosphère représentative". Lyon 1, 2000. http://www.theses.fr/2000LYO10116.
Le, Gall Claire. "Contribution à l'étude du relâchement des produits de fission hors de combustibles nucléaires en situation d'accident grave : effet de la pO2 sur la spéciation du Cs, Mo et Ba". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY053/document.
In the nuclear community, it is a top priority to gain in-depth understanding of fission product (FP) speciation mechanisms occurring in nuclear fuel in order to precisely estimate the source term of a severe accident. Among the FP produced, some are highly reactive and may have a strong radiological impact if released into the environment. This is particularly the case of cesium (Cs), molybdenum (Mo) and barium (Ba). In this context, the objective of this study is to provide experimental data on the effect of the oxygen potential on Cs, Mo and Ba speciation in nuclear fuels at different stages of a severe accident.A thermodynamic approach was coupled with the experimental work to support the interpretation of experimental data. Two types of samples were studied in detail: irradiated MOX fuels and simulated high burn-up UO2 fuels produced through sintering at high temperature (SIMFuel). The samples were submitted to thermal treatments in conditions representative of a pressurised water reactor (PWR) severe accident. This approach made it possible to cover a temperature range from 400°C up to 2530°C and oxygen potentials from -470 kJ.mol(O2)-1 to -100 kJ.mol(O2)-1. The samples were characterized before and after each test using complementary techniques like OM, SEM, EPMA and SIMS in the case of irradiated fuels. XANES measurements using synchrotron radiation facilities were performed on SIMFuels and provided valuable results on FP speciation. Moreover, spark plasma sintering (SPS) was successfully investigated for the production of SIMFuel samples containing Cs, Mo and Ba in a chemical state representative of PWR fuel in normal operating conditions.This work highlighted the effect of oxidizing severe accident conditions on the fuel and FP behavior. Oxidation of Mo initially contained in the fuel’s metallic inclusions into MoO2 was observed to take place around 1000°C in oxidizing conditions. An interaction between MoO2 and the oxide phase containing Ba took place in the same conditions, leading to the formation of BaMoO4. The oxygen potential also plays an important role in fuel-cladding interactions, enhancing the diffusion of species in oxidizing conditions and lowering the temperature at which fuel melting occurs
Javouhey, E. "Enfants victimes de l'insécurité routière : épidémiologie des traumatismes et séquelles". Phd thesis, Université Claude Bernard - Lyon I, 2007. http://tel.archives-ouvertes.fr/tel-00544001.
Nandan, Shambhavi. "Modélisation de la dissolution d'une phase solide (UO2-ZrO2-Zr) par une phase liquide (Fe) par une approche macroscopique diphasique". Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0663.
With regards to the safety of the Nuclear Power Plants (NPP) in case of a severe nuclear accident, one of the main challenges associated is the retention of the molten nuclear fuel and reactor internals, called corium, within the Reactor Pressure Vessel (RPV). One of the ways of cooling corium with in the RPV is by cooling the vessel from outside. This strategy is termed as In-Vessel Retention (IVR). In case of the In-Vessel Retention (IVR) strategy, it is expected that the corium pool will be surrounded by an oxide crust, which will be in contact with molten steel from top of the pool as well as from sides of the vessel. It has been observed in CORDEB experiments (funded by IRSN, CEA and EDF), that this crust becomes permeable due to dissolution by molten steel, affecting the flux associated with the RPV. Consequently, the dissolution has been studied by deriving an up-scaled model consist of volume averaged transport equations — Mass, Momentum, Species and Energy transport — over a Representative Elementary Volume (REV). The final system of Partial Differential Equations (PDEs) has been closed by deriving several empirical relations for effective species diffusivity, mass transfer coefficients, permeability and effective conductivity. Further, the model has been solved to study dissolution in crust for different cases with and without convection
Duplat, Françoise. "Refroidissement et dispersion du corium lors de sa chute dans l'eau pendant un accident sévère de réacteur nucléaire à eau pressurisée : description des interactions mécaniques et thermiques en écoulement triphasique lors de la dispersion de sphères solides froides ou chaudes dans un bain liquide". Grenoble INPG, 1998. http://www.theses.fr/1998INPG0106.
Haurais, Florian. "Evaluate the contribution of the fuel cladding oxidation process on the hydrogen production from the reflooding during a potential severe accident in a nuclear reactor". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS375/document.
In nuclear power plants, a severe accident is a very unlikely sequence of events during which components of the reactor core get significantly damaged, through chemical interactions and/or melting, because of very high temperatures. This may potentially lead to radiotoxic releases in the containment building and to air ingress in the reactor core. In that context, this thesis work led at EDF R&D aimed at modeling the deterioration of the nuclear fuel cladding, made of zirconium alloys, in accidental conditions: high temperature and either pure steam or air-steam mixture. The final objective was to improve the simulation by the MAAP code of the cladding oxidation and of the hydrogen production, in particular during a core reflooding with water. Due to the progressive thickening of a dense and protective ZrO2 layer, the oxidation kinetics of Zr in steam at high temperatures is generally (sub-)parabolic. However, at certain temperatures, this oxide layer may crack, becoming porous and not protective anymore. By this “breakaway” process, the oxidation kinetics becomes rather linear. Additionally, the temperature increase can lead core materials to melt and to relocate down to the vessel lower head whose failure may induce air ingress into the reactor core. In this event, oxygen and nitrogen both react with the pre-oxidized claddings, successively through oxidation of Zr (thickening the ZrO2 layer), nitriding of Zr (forming ZrN particles) and oxidation of ZrN (creating oxide and releasing nitrogen). These self-sustained reactions enhance the cracking of the cladding and of its ZrO2 layer, inducing a rise of its open porosity.In order to quantify this cladding porosity, an innovative two-step experimental protocol was defined and applied: it consisted in submitting ZIRLO® cladding samples first to various accidental conditions during several time periods and then to measurements of the open porosity through porosimetry by mercury intrusion. The tested corrosion conditions included numerous temperatures ranging from 1100 up to 1500 K as well as both pure steam and a 50-50 mol% air-steam mixture. For the ZIRLO® samples oxidized in pure steam, except at 1200 and 1250 K, the “breakaway” kinetic transitions do not occur and the open porosity remains negligible along the oxidation process. However, for all other samples, corroded in air-steam or oxidized in pure steam at 1200 or 1250 K, “breakaway” transitions are observed and the porosimetry results show that the open porosity increases along the corrosion process, proportionally to the mass gain. Moreover, it was evidenced that the pore size distribution of ZIRLO® samples significantly extends during corrosion, especially after “breakaway” transitions. Indeed, the detected pore sizes ranged from 60 μm down to around: 2 μm before the transition, 50 nm just after and 2 nm longer after. Finally, a two-step numerical model was developed in the MAAP code to improve its simulation of the cladding oxidation. First, thanks to the proportionality between open porosity and mass gain of cladding samples, porosity correlations were implemented for each tested corrosion condition. Second, the calculated porosity values are used to proportionally enhance the cladding oxidation rate. This improved model thus simulates not only chemical reactions of Zr-based claddings (oxidation and nitriding) but also their mechanical degradation and its impact on their oxidation rate. It was validated by simulating QUENCH tests (-06, -08, -10 and -16), conducted at KIT to study the behavior of claddings in accidental conditions with a final reflooding. These simulations show a better cladding thermal behavior and a hydrogen production significantly higher and so closer to experimental values, in particular during the reflooding
Peña, Carrillo Juan David. "Étude expérimentale du transfert paroi/fluide dans le cas d’un écoulement vertical vapeur/gouttes dans une géométrie tubulaire". Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0193/document.
During a Loss of Coolant Accident (LOCA) in a Pressurized Water Reactor (PWR), caused by a break or a leakage on the primary circuit, partial or even complete drying of the fuel assemblies may occur. In these conditions, the fuel temperature increases, leading to a significant deformation and rupture of the fuel rod cladding. The cooling flow might be impaired, according to the size and distribution of the deformed zones within the fuel assemblies during the emergency cooling phase (Reflooding phase). To contribute to the thermalhydraulic study of the reflooding phase, this study aims to characterize experimentally the coolability of a representative deformed sub-channel by a steam-droplets flow under LOCA conditions. In order to reproduce such a scenario, the experimental thermal-hydraulic set-up COLIBRI was designed. Several geometrical blockage configurations are analyzed (Blockage ratios and axial lengths). Three measurement techniques are set up to follow the cooling transient phase of each experience: Phase Doppler Anemometry (PDA) in order to obtain both velocity and diameter of droplets, Laser Induced Fluorescence (LIF) to measure the mean droplet temperature and Infrared thermography to estimate the heat flux removed by the two-phase flow. Additionally, a one-dimensional mechanistic model, taking into account of the heat transfers mechanisms in the post-dry out region, is developed in order to analyze the experimental data and identify each one of the wall-to-fluid heat transfers (radiation with vapor and droplets, convection with vapor, evaporation, and droplet impact)
Peña, Carrillo Juan David. "Étude expérimentale du transfert paroi/fluide dans le cas d’un écoulement vertical vapeur/gouttes dans une géométrie tubulaire". Electronic Thesis or Diss., Université de Lorraine, 2018. http://www.theses.fr/2018LORR0193.
During a Loss of Coolant Accident (LOCA) in a Pressurized Water Reactor (PWR), caused by a break or a leakage on the primary circuit, partial or even complete drying of the fuel assemblies may occur. In these conditions, the fuel temperature increases, leading to a significant deformation and rupture of the fuel rod cladding. The cooling flow might be impaired, according to the size and distribution of the deformed zones within the fuel assemblies during the emergency cooling phase (Reflooding phase). To contribute to the thermalhydraulic study of the reflooding phase, this study aims to characterize experimentally the coolability of a representative deformed sub-channel by a steam-droplets flow under LOCA conditions. In order to reproduce such a scenario, the experimental thermal-hydraulic set-up COLIBRI was designed. Several geometrical blockage configurations are analyzed (Blockage ratios and axial lengths). Three measurement techniques are set up to follow the cooling transient phase of each experience: Phase Doppler Anemometry (PDA) in order to obtain both velocity and diameter of droplets, Laser Induced Fluorescence (LIF) to measure the mean droplet temperature and Infrared thermography to estimate the heat flux removed by the two-phase flow. Additionally, a one-dimensional mechanistic model, taking into account of the heat transfers mechanisms in the post-dry out region, is developed in order to analyze the experimental data and identify each one of the wall-to-fluid heat transfers (radiation with vapor and droplets, convection with vapor, evaporation, and droplet impact)
Roki, Fatima-Zahra. "ETUDE DE LA CINETIQUE ET DE LA THERMODYNAMIQUE DES SYSTEMES REACTIONNELS (X-I-O-H) PAR SPECTROMETRIE DE MASSE HAUTE TEMPERATURE". Phd thesis, 2009. http://tel.archives-ouvertes.fr/tel-00367690.
Mestre, Luis. "Plano Setorial de Apoio Psicossocial à População". Master's thesis, 2019. http://hdl.handle.net/10400.26/31302.
The assessment of the civil protection emergency plan of Portimão allowed to understand how is organized the operations to help the population in a disaster scenario. It is clear that the plan does not include a detailed procedure regarding the psychosocial support for the population. The bibliographic research developed for this academic work was focused on this theme, with the purpose to find information on how the concentration and population support zones (ZCAP) work in other countries. For the creation of a specific plan to support the population, it is necessary to have a deep knowledge of it, like its size and other characteristics, as well as the identification of the adequate sites where ZCAP can be installed. For this purpose, checklists were built to define the best place and the best infrastructure to implement a ZCAP. It is still necessary, in this organizational process, to define who does what, how will be the constitution of the ZCAP teams, and what will be its framework and role, to guarantee their autonomy, despite their dependency on the Municipal Civil Protection Service (SMPC). It was possible to conclude that a lot of things are already done in Portimão, and they are different from what is being done in the rest of the country, especially in how ZCAP are planned and organized, where nothing is left to chance and everyone knows what it is role within the structure. It is therefore essential to create a Sectoral Plan of Psychosocial Support to Populations (ZCAP) so that the response in psychosocial support to populations can be as organized as the response on the relief side.