<p>The effect of pressure transients on the onset of intermittent dryout in upward annular flow was experimentally investigated in order to resolve the conflict between the observations drawn from two major data sets in the literature. A delay in time to the onset of dryout at the test section exit relative to the time predicted based on steady-state data was observed in the R-12 experiments of Celata et al (1988; 1991). Steady-state prediction methods were sufficient to predict the upstream progression of a pre-existing dryout front in the water experiments of Lyons and Swinnerton (1983). Steady state and pressure transient dryout experiments were performed using water with outlet pressures of 2 to 6 MPa and mass fluxes of 1000 to 2500 kg/m2/s in an electrically heated 1.32 m long 4.6 mm ID vertical Inconel 600 tube with depressurisation rates of up to 1.0 MPa/s. Transient experiments were performed with a small margin to dryout and with post-dryout initial conditions in order to test the hypothesis that these initial conditions influenced the onset of dryout during transients. The results of a comparison between the steady dryout data and two dryout prediction methods---the Biasi et al (1967) correlation and the 2006 CHF look-up table (Groeneveld et al, 2007)---were used to develop correction factor correlations to reduce systematic error when these methods were used to predict the transient time to dryout. These modified methods yielded mean predicted dryout delays of -0.1 and 1.5 s respectively with standard deviations of approximately 3 s. There was no statistically significant variation between the pre- and post-dryout initial conditions. Based on this result it was concluded that the initial conditions did not affect the observed time to dryout. The mean wall temperature exhibited a discontinuous decrease as the heat flux approached 92 to 95% of the dryout value. It was postulated that this was caused by a heat transfer regime change from liquid film evaporation to droplet evaporation based on the observations of Hewitt (1970), Doroschuk et al (1970) and Groeneveld (2011). For the range of conditions of the present work the onset of intermittent dryout (Groeneveld, 1986) was caused by deterioration of droplet evaporation heat transfer. Celata et al (1988) noted that in their pressure transient experiments the decrease in saturation temperature drove a rapid increase in the heat flux to the fluid. This was caused by the release of stored thermal energy as the test section wall cooled. Celata et al (1991) stated that the systematic dryout delay was observed for depressurisation rates greater than 0.2 MPa/s. Using Celata et al's (1988) pressure transient data it was concluded that the stored thermal energy transient did not influence the onset of intermittent dryout when rho_w c_pw L_w *(dT_sat/dt)<0.3*q''_a.</p> / Doctor of Philosophy (PhD)

South Africa is in the critical process of determining the profile of its power composition for the next 30 years and beyond. From the IRP2010 it seems that too much emphasis is placed on renewable energy, coal and other technologies and too little on nuclear power. In the revision of the IRP2010, the renewable portion of the energy composition has been increased substantially from 11.4 to 17.8GW, where nuclear remains on 9.6GW (DME, 2011). The purpose of this research is to investigate and compare power-generating technologies. The investigation of the different technologies is corroborated through modelling the IRP2010 planned energy mix efficiency, as well as a proposed energy mix. These models will be built using Microsoft Excel. Topics not investigated are socio-economic impacts and politics around nuclear energy in South Africa. The main finding of the research is that nuclear power is the best option for base load energy in order to meet South Africa‟s growing demand for electricity. It has the highest load factor, longest economic life, best safety record, adheres to the Kyoto protocol, uses the least fresh water and is economically competitive. It addresses all the concerns stipulated in the IRP2010 and the technology also offers benefits outside the electricity industry, such as the mining, medical, agriculture and research sectors. This versatile, reliable and powerful technology holds great benefits and has the potential to uplift the quality of life for the whole South African nation. / MSc (Nuclear Engineering), North-West University, Potchefstroom Campus, 2015

South Africa is in the critical process of determining the profile of its power composition for the next 30 years and beyond. From the IRP2010 it seems that too much emphasis is placed on renewable energy, coal and other technologies and too little on nuclear power. In the revision of the IRP2010, the renewable portion of the energy composition has been increased substantially from 11.4 to 17.8GW, where nuclear remains on 9.6GW (DME, 2011). The purpose of this research is to investigate and compare power-generating technologies. The investigation of the different technologies is corroborated through modelling the IRP2010 planned energy mix efficiency, as well as a proposed energy mix. These models will be built using Microsoft Excel. Topics not investigated are socio-economic impacts and politics around nuclear energy in South Africa. The main finding of the research is that nuclear power is the best option for base load energy in order to meet South Africa‟s growing demand for electricity. It has the highest load factor, longest economic life, best safety record, adheres to the Kyoto protocol, uses the least fresh water and is economically competitive. It addresses all the concerns stipulated in the IRP2010 and the technology also offers benefits outside the electricity industry, such as the mining, medical, agriculture and research sectors. This versatile, reliable and powerful technology holds great benefits and has the potential to uplift the quality of life for the whole South African nation. / MSc (Nuclear Engineering), North-West University, Potchefstroom Campus, 2015

89 Abstract The topic of the thesis concerns Czech nuclear law. Nuclear law can be defined as a set of special legal norms adjusting the terms of the nuclear energy and ionizing radiation usage, protection of population and environment against ionizing radiation, radiation accidents solving and treatment of radioactive waste. As such, nuclear law fully adjust the behaviour of all the natural and legal persons who are concerned with activities connected to the nuclear materials, ionizing radiation and natural resources of ionizing radiation. The field of nuclear law is closely connected to the branches of science dealing with the nuclear energy and ionizing radiation usage; therefore, the factual issues of which at least the fundamental knowledge is necessary for the understanding of nuclear law are given space at the beginning of the thesis. In its provisions, Czech nuclear law adjustment also reflect a number of international treaties and European Union regulations. On account of this, the next part of the thesis deals briefly with the international and European nuclear law adjustment. Important international organizations of the field are mentioned as well. The core of the paper consists in the part concerning the outline and analysis of the present adjustment of Czech nuclear law. The taxonomy of this...

O trabalho apresenta um estudo com a finalidade de verificar a aplicabilidade do Modelo do Sistema Viável (VSM Viable System Model) no projeto de uma arquitetura robusta de um Sistema de Informação voltado à área naval nuclear. A ênfase do estudo está em avaliar uma modelagem alternativa para a especificação da arquitetura do Sistema de Informação, incorporando o conjunto de funcionalidades especificadas pelo VSM, com o objetivo de fortalecer esta arquitetura. A estratégia desta pesquisa baseia-se em uma revisão bibliográfica relacionada ao VSM, aos Sistemas de Informação e a sua arquitetura, e às influências destes elementos na sobrevivência das organizações diante das mudanças constantes no ambiente. É apresentado um estudo de caso onde são mostrados os elementos teóricos do VSM e da arquitetura de SI aplicados na elaboração da arquitetura de um SI. O Sistema escolhido para esta aplicação é o Sistema de informação de incidentes nucleares (SIN) nas instalações onde são feitas pesquisas e desenvolvimento de tecnologia nuclear a ser aplicada na propulsão de um submarino. / The present work presents a study aiming to verify the applicability of the Viable System Model (VSM) in a robust architecture for an Information System targeting nuclear naval area. The emphasis of the study is in assessing an alternative modeling for the Information System (IS) architecture specification, incorporating a set of functionalities defined by the VSM, with the purpose of strengthening this architecture. The strategy of this research is based on a bibliographic revision on VSM, Information System and its architecture, and the influence of those elements in the survival of the organizations in a ever changing environment. It is presented one case study where it is showed the theoretical elements of the VSM and IS architecture applied on the development of a IS architecture. The selected system for this application is the IS for nuclear incidents (SIN) on the installations dedicated to research and development on nuclear technology applied to submarine propulsion system.

Cette thèse étudie la conception et l’évolution du régime de régulation de la sûreté nucléaire en France entre 1945 et 2017. En nous appuyant sur le concept de régime de régulation (Hood et al, 2001), nous avons proposé une modélisation qui permet d’identifier trois périodes, correspondant à trois « philosophies » : la première (19451969) voit la formation d’un embryon de régime de régulation au sein du CEA marqué par « l’expérimentation et l’autocontrôle ». La seconde, la « raisonnable souplesse » (19691986), est marquée par une réorganisation institutionnelle mais laisse de nombreuses marges de manœuvre aux experts et exploitants, dans un contexte de développement industriel intensif. Enfin, la troisième période (1986-2017) voit le développement d’un régime « en recherche d’auditabilité », produit d’une hybridation entre le régime de la « raisonnable souplesse » et un idéaltype standardisé répondant aux bonnes pratiques internationales (ouverture, transparence et indépendance du régulateur et de l’expert). Pour expliquer les évolutions du régime, nous nous sommes focalisés sur une de ses composantes, les règles, analysées comme des instruments de régulation, et avons qualifié de « travail de régulation », l’ensemble des activités et interactions d’un groupe d’acteurs qui agissent pour concevoir, transformer et implémenter ces instruments (pour notre cas, les règles et guides en matière d’inondation). Nous défendons l’idée que ce travail de régulation, à la fois cognitif, politique, social et organisationnel, a pour effet, au-delà de la production d’un instrument, d’explorer des évolutions du régime de régulation, tout en construisant les savoirs mobilisés dans les instruments de régulation, et simultanément, le collectif interorganisationnel qui les partage. Ce processus expliquerait la relative lenteur du processus d’hybridation en cours. / This thesis studies the design and evolution of the risk regulation regime of nuclear safety in France between 1945 and 2017. Based on the concept of “risk regulation regimes” (Hood et al, 2001), we propose a model that identifies three periods, corresponding to three types of "philosophies". During the first period (1945-1969), an embryonic regulatory regime developed within CEA is characterized by "experimentation and autocontrol". The second period of "reasonable flexibility" (1969-1986) is marked by an institutional reorganization but leaves many room for maneuver to experts and operators, in a context of intensive industrial development. Finally, during the third period (1986-2017), a regime "in search of auditability" is the product of hybridization between the regime of "reasonable flexibility" and a standardized regime responding to international good practice (openness, transparency, and regulator’s and expert’s independence). To explain the evolution of the regime, we focus on one of its components, the rules, which we analyze as regulatory instruments, and we describe as "regulatory work" all activities and interactions of a group of agents who act to design, transform and implement these instruments (for our case, flooding rules and guides). We argue that regulatory work is at the same time cognitive, political, social and organizational, and, beyond producing an instrument, it results in exploring evolutions of the regulation regime, while building both the knowledge mobilized in regulatory instruments and interorganizational collective that shares them. This process would explain the relative slowness of the ongoing hybridization process.

Branduolinės energetikos objektas – statybos teisinis reguliavimas – branduolinės saugos principai – specialusis teisinis reguliavimas Branduolinės energetikos objektų statybos teisinis reguliavimas yra unikalus, išsiskiriantis iš kitų statinių statybos padidintu dėmesiu branduolinės saugos priemonių įgyvendinimui. Šio objekto statybos teisinio reguliavimo srities svarba tampa vis aktualesne dabartinių branduolinės energetikos objektų statybos procesų aktyvėjimo kontekste. Nežiūrint į tai, jog Lietuva priklauso branduolinę energetiką vystančių šalių grupei, siekiančiai plėsti branduolinės energetikos pajėgumus, dabartinis branduolinės energetikos objektų statybos teisinis reguliavimas nėra tinkamai paruoštas įgyvendinti nuoseklią bei nepertraukiamą branduolinės energetikos objekto statybą. Branduolinės energetikos objektų statybos teisinio reguliavimo ypatumai bei skirtumai, lyginant su kitų objektų statybos teisiniu reguliavimu, yra akivaizdūs viso statybos proceso teisinio reguliavimo metu. Lietuvai tapus tarptautinės bendrijos nare, tarptautiniai teisės aktai tapo privaloma nacionalinės teisės sistemos dalimi. Branduolinės energetikos objektų statybos procesas yra glaudžiai susijęs su kitomis teisinio reguliavimo sritimis, tokiomis kaip teritorijų planavimu, žemės teisiniais santykiais, nuosavybės teisiniu reguliavimu ir kitomis, tačiau svarbiausias šio teisinio reguliavimo bruožas yra branduolinės saugos priemonių įgyvendinimas. Šis, objekto saugumo, tikslas... [toliau žr. visą tekstą] / Nuclear Facility – Legal Regulation of Construction – Nuclear Safety Principles – Special Regime of Legal Regulation Legal regulation of the construction of nuclear facilities is unique of its nature, varying from the construction of the other buildings in enhanced attention for the implementation of nuclear safety measures. The legal regulation of the construction of such an facility becomes more actual in the context of the construction of new nuclear facilities which, in nowadays, becomes more active despite the fact that Lithuania belongs to the group of countries enrolled in nuclear energy, having the goal to increase the capacity of nuclear energy, the present legal regulation of the construction of nuclear facilities is not arranged enough for the consistent and continuous implementation of the construction of new nuclear facilities. The peculiarities and differences of the legal regulation of the new nuclear facilities, in comparison of the legal regulation of other constructions, are obvious in the overall process of construction legal regulation. When Lithuania became a member of the international community, international legal acts became a part of national legal regulation. The construction process of nuclear facilities is closely related to other spheres of legal regulation, especially with territory planning, land law, regulation of the ownership right and others, however the most important feature of legal regulation is the implementation of nuclear safety... [to full text]

Cette thèse est motivée par le besoin de compléter les connaissances actuelles des phénomènes ayant lieu lors d’un renvoi d’eau dans un lit de débris radioactifs, opération appelée « renoyage » et qui intervient dans une séquence d’accident grave où un cœur de réacteur nucléaire est dégradé suite à une perte prolongée de refroidissement primaire. Notre étude, de nature expérimentale, vise à mieux caractériser la crise d’ébullition en convection forcée, dans un milieu poreux chauffant. Le cœur du dispositif expérimental est un milieu poreux modèle quasibidimensionnel, composé de 276 cylindres disposés entre deux plaques de céramique distantes de 3 mm, dont l’une, transparente, permet de visualiser les écoulements. Les cylindres, de 2 mm de diamètre, sont des sondes thermo-résistives qui ont une double fonction : elles sont utilisées comme éléments chauffants et comme capteurs de température. Une boucle fluide permet de contrôler le débit d’injection de liquide dans la section test, la température d’injection ainsi que la pression. La section test est placée verticalement, le liquide est injecté par le bas à une température proche de la saturation. Dans une première série d’expériences, la puissance thermique dissipée globalement par un ensemble de cylindres chauffants est augmentée de façon progressive jusqu’à atteindre l’assèchement d’une zone du milieu poreux. Les résultats montrent deux types de phénoménologies dans le déclenchement de la crise d’ébullition. Pour des débits d’injection faibles (densités de flux massique de l’ordre de 4 kg.m^-2.s^-1 maximum), l’atteinte de la puissance d’assèchement se traduit par un lent recul du front diphasique jusqu’à sa stabilisation en haut de la zone chauffée ; en aval de la zone chauffée, l’écoulement est monophasique vapeur. Pour des débits d’injection plus élevés, la crise d’ébullition apparaît autour d’un des éléments chauffants, conduisant à une ébullition en film localisée, tandis qu’un écoulement diphasique liquide-vapeur continue de parcourir l’aval de la section test. Les visualisations de ces expériences permettent d’identifier qualitativement la structure des écoulements. D’autres expériences consistent à mesurer le flux critique local autour d’un cylindre choisi, pour différentes configurations d’écoulements. Le débit d’injection est fixé. Une puissance de chauffe est imposée à une ligne horizontale de cylindres en amont du cylindre choisi. Les résultats montrent que le flux critique sur ce cylindre diminue en fonction de la puissance délivrée à la ligne chauffée. La distance du cylindre étudié à la ligne chauffée semble avoir peu d’influence sur le flux critique. Des visualisations expérimentales sont utilisées pour caractériser l’écoulement diphasique en aval de la ligne chauffée, dans le but de mettre en relation le flux critique local avec des paramètres hydrodynamiques (saturations, vitesses des phases). Les images obtenues sont difficiles à exploiter. Afin de calibrer les paramètres des algorithmes de traitement d’images, nous avons reproduit une cellule d’essai de géométrie identique à l’originale, mais où l’on injecte du gaz par une ligne de cylindres en amont de la section test dans une configuration d’écoulement diphasique isotherme. Dans ce dispositif, le débit d’injection de gaz est contrôlé et mesuré. Les visualisations obtenues servent alors de références auxquelles sont comparées les visualisations d’ébullition convective. / This work is motivated by the need to better understand the phenomena occurring while some water is injected into a heated porous debris bed. This reflooding operation is a part of the planned mitigation procedure used during a Loss Of Coolant Accident (LOCA) that may occur into a nuclear power plant and results into a severe core damage. Our experimental study aims to characterize the boiling crisis that can happen in a boiling flow taking place within a heatgenerating model porous medium. The test section is a two-dimensional model porous medium, composed of an array of 276 cylinders placed between two ceramic plates spaced from one another by 3 mm, one of which is transparent and allows visualizations of the flow. The 2 mm diameter cylinders are Pt100 resistance temperature detectors that perform a dual function: they act as heating elements (heated by Joule effect) and are also used as temperature probes. A fluid loop allows controlling the liquid injection flow rate, its inlet temperature as well as its pressure. The test section is held vertically, the liquid injected from bottom at a temperature close to the saturation temperature. In a first series of experiments, the thermal power applied to a bundle of heating cylinders is progressively increased until a dry zone is detected in the porous medium. Two kinds of phenomenology are observed during these “dryout experiments”. First, at low liquid injection rate (4 kg.m^-2.s^-1 maximum mass flux), reaching the dryout power results into a liquid front receding down to the upper limit of the heated zone, while downstream the heated zone, the porous medium is vapour-saturated. Second, at higher flow rate, the boiling crisis happens at the surface of a single heating element, resulting in a local film boiling, whereas a two-phase flow still go through the whole test section. High-speed visualizations allow characterizing the flow regimes. Other experiments focus on determining the local critical heat flux on a given cylinder, for different upstream flow configurations. The inlet liquid flow rate is fixed. A thermal power is uniformly applied to a line of heating cylinders, upstream the cylinder under study. Results show that the local critical heat flux decreases as the power applied to the heated line increases. The distance from the cylinder under study to the heated line seems not to have a significant effect on the critical heat flux. Visualizations are used to characterize the two-phase flow upstream the heated line, aiming at expressing the critical heat flux as a function of the hydrodynamic parameters (saturations, phase velocities). The image analysis is particularly challenging. In order to calibrate the image processing parameters, we use a second model porous medium with the same geometry as the heat generating one, but where an isothermal two-phase flow is obtained by injecting gas into the liquid flow rather than generated by boiling. The gas injection flow rate is controlled and measured. Isothermal two-phase flow visualizations provide a reference case and are compared to flow boiling visualizations.

Les travaux réalisés pendant cette thèse portent sur l’étude de la sûreté du Molten Salt Fast Reactor (MSFR) et incluent à la fois des méthodes d’analyse de risques et des calculs déterministes de sûreté et de design. Ce travail s’inscrit dans le cadre du projet européen SAMOFAR.Le MSFR est un réacteur régénérateur à spectre neutronique rapide qui fonctionne en cycle thorium dans sa configuration de référence, établie en début du projet SAMOFAR. Il a été sélectionné par le Forum International Génération IV pour son potentiel prometteur. Comme tout réacteur nucléaire de quatrième génération, il doit répondre à différentes contraintes dont une sûreté optimale. Celle-ci doit être étudiée dès le stade de conception afin d’être intégrée au design lors de sa définition plutôt qu’ajoutée a posteriori. En raison de ses spécificités, en particulier l’état liquide du combustible, et du stade préliminaire de son design, l’analyse de sûreté du MSFR nécessite l’utilisation de méthodologies d’analyse de sûreté adaptées et technologiquement neutres. Dans cette thèse, une telle méthodologie a été développée et une première application au MSFR réalisée. Elle a notamment permis d’identifier les évènements initiateurs d’accident de ce réacteur et d’élaborer une liste resserrée d’évènements à traiter dans la suite de l’analyse de sûreté.D’autre part, un nouveau code système a été développé pour les études de sûreté. Il est basé sur la diffusion neutronique, prend en compte le transport des précurseurs de neutrons retardés et la puissance résiduelle du combustible. Il a été utilisé pour simuler les transitoires associés à certains des évènements initiateurs et évaluer leurs conséquences pour définir, par la suite, des systèmes de protection adaptés. Ce travail a confirmé l’importance d’un dispositif spécifique au MSFR, le système de vidange d’urgence, permettant de vidanger le combustible en cas d’accident en cœur. Des études paramétriques ont été menées afin de dimensionner ce système avec pour objectif d'assurer l’évacuation de la chaleur résiduelle du combustible et sa sous-criticité en toutes circonstances.Enfin, une première ébauche de l’architecture de sûreté du réacteur a été proposée incluant l’identification des systèmes de protection et la définition des barrières de confinement. Les études de sûreté ont permis de faire des retours sur le design initialement défini. Ils incluent l’ajout de composants, des propositions de design alternatifs, et soulignent les manques de connaissances sur certains phénomènes ou procédures. L’analyse de sûreté réalisée remplit ainsi son objectif principal : guider le design du réacteur dès sa conception afin d’en améliorer la sûreté. / This PhD thesis focuses on the study of the Molten Salt Fast Reactor (MSFR) safety. It includes risk analysis methods and deterministic computations for the safety and the design of the reactor. This work was performed in the frame of the SAMOFAR European project.The MSFR is an is-breeder reactor with a fast neutron spectrum. In its reference configuration, defined at the beginning of the SAMOFAR project, it works with the thorium fuel cycle. The MSFR was selected by the Generation IV international forum for its promising features. As any fourth-generation reactor, it must fulfill several objectives including an improved safety. Thus, safety studies should be performed from the early design phases to achieve a safety that is built-in the design rather than added-on. Because of the unique characteristics of the MSFR, including a liquid circulating fuel, and its preliminary design phase, the safety assessment of the reactor should rely on adapted and technological neutral methodologies. In this PhD, such a methodology was developed and a first application to the MSFR was carried on. It allowed to identify the initiating events of the reactor and to elaborate a restricted list of events to be studied in the next steps of the safety analysis.Furthermore, a new code system was developed for the safety studies. It is based on neutronic diffusion and takes into account the movement of the delayed neutrons precursors and the production of the residual heat in the fuel. It was used to simulate the transients associated to some of the identified initiating events with the objective to evaluate their consequences and the need for adequate protection systems. This work confirmed the importance of a device that is specific to the MSFR: the emergency draining system (EDS). It allows to drain the fuel in case of accident in the core. Parametric studies were then carried on for the sizing of the EDS with the objective to ensure the evacuation of the residual heat and the sub-criticality of the system under any circumstances.Finally, a first version of the safety architecture was proposed with the identification of the protection systems and the definition of the confinement barriers. Thanks to the safety studies, feedbacks on the initial design were made to enhance the safety the reactor. They include the addition of new components, the modification of some systems and they highlight the lack of knowledge on some phenomena or procedure. In that respect, the safety analysis fulfil its main objective: to influence the design of the reactor since its conception in order to improve its safety.

O trabalho apresenta um estudo com a finalidade de verificar a aplicabilidade do Modelo do Sistema Viável (VSM Viable System Model) no projeto de uma arquitetura robusta de um Sistema de Informação voltado à área naval nuclear. A ênfase do estudo está em avaliar uma modelagem alternativa para a especificação da arquitetura do Sistema de Informação, incorporando o conjunto de funcionalidades especificadas pelo VSM, com o objetivo de fortalecer esta arquitetura. A estratégia desta pesquisa baseia-se em uma revisão bibliográfica relacionada ao VSM, aos Sistemas de Informação e a sua arquitetura, e às influências destes elementos na sobrevivência das organizações diante das mudanças constantes no ambiente. É apresentado um estudo de caso onde são mostrados os elementos teóricos do VSM e da arquitetura de SI aplicados na elaboração da arquitetura de um SI. O Sistema escolhido para esta aplicação é o Sistema de informação de incidentes nucleares (SIN) nas instalações onde são feitas pesquisas e desenvolvimento de tecnologia nuclear a ser aplicada na propulsão de um submarino. / The present work presents a study aiming to verify the applicability of the Viable System Model (VSM) in a robust architecture for an Information System targeting nuclear naval area. The emphasis of the study is in assessing an alternative modeling for the Information System (IS) architecture specification, incorporating a set of functionalities defined by the VSM, with the purpose of strengthening this architecture. The strategy of this research is based on a bibliographic revision on VSM, Information System and its architecture, and the influence of those elements in the survival of the organizations in a ever changing environment. It is presented one case study where it is showed the theoretical elements of the VSM and IS architecture applied on the development of a IS architecture. The selected system for this application is the IS for nuclear incidents (SIN) on the installations dedicated to research and development on nuclear technology applied to submarine propulsion system.