Effective construction management involves real-time decisions regarding the progress of specific activities, the location of materials and equipment, and the construction site safety. The decision making process can be improved using real-time positioning technologies such as Radio Frequency Identification Device (RFID) systems, Global Positioning System (GPS), and Ultra Wide Band (UWB) sensors. While the GPS is not applicable to indoor positioning and RFID tags cannot provide a fully automated system for position location, the characteristics of UWB systems make this technology a strong candidate for a fully automated positioning system in an indoor construction environment. This thesis presents a comprehensive study of the performance of UWB systems in a controlled laboratory environment and in an institutional construction site in Waterloo, Canada as well as for a particular safety application. A primary objective of the research was to establish the accuracy of real-time position location under various conditions, including the effect of different construction materials (e.g., wood and metal), and to analyze changes in the accuracy of position location as construction progresses and the indoor environment physically evolves. Different challenges faced in implementing such a system in an active construction environment are addressed. Based on a statistical analysis of laboratory data, and considering the construction site experience, the reliability of the UWB positioning system for the aforementioned environments is discussed. Furthermore, an automated safety system is proposed using the real-time UWB positioning technology. Based on the error modeling of the UWB position location, an optimum alarming algorithm is designed for the proposed safety system and the reliability of such system is evaluated through a statistical analysis.

The safety performance of nuclear power reactors is a very important factor in evaluating nuclear energy sustainability. Improving the safety performance of nuclear reactors can enhance nuclear energy sustainability as it will improve the environmental indicator used to evaluate the overall sustainability of nuclear energy. Great interest is given now to advanced nuclear reactors especially those using passive safety components. Investigation of the improvement in nuclear safety using advanced reactors was done by comparing the safety performance of a conventional reactor which uses active safety systems, such as Pressurized Water Reactor (PWR), with an advanced reactor which uses passive safety systems, such as AP1000, during a design basis accident, such as Loss of Coolant Accident (LOCA), using the PCTran as a simulation code. To assess the safety performance of PWR and AP1000, the “Global Safety Index” GSI model was developed by introducing three indicators: probability of accident occurrence, performance of safety system in case of an accident occurrence, and the consequences of the accident. Only the second indicator was considered in this work. A more detailed model for studying the performance of passive safety systems in AP1000 was developed. That was done using SCDAPSIM/RELAP5 code as it is capable of modelling design basis accidents (DBAs) in advanced nuclear reactors.

The master thesis deals with security in the energy sector. As it is historically clear that the vast majority of accidents, incidents, injuries and other negative occasions were caused by the human factor. Therefore, the first goal of this work was to find a solution for the purpose of reducing the possibility of arising these problems. Therefore, attention was focused on the investigation and subsequent determination of a working safe climate within the researched company, which aims to prevent the emergence of serious situations, as this method is based on behavioural theories that take into account the study of human factors. The second partial goal of this diploma thesis was to determine the degree of security required for the production area of the company so that the basic safety requirements are met, and last but not least, the model situation of securing the production power unit is shown too.

Safe and reliable operation of nuclear power plants is the basic requirement for the utilization of nuclear energy since accidents can release radioactivity and with that cause irreversible damage to human beings. Reliability and safety of nuclear reactors are highly dependent on the stability of thermal hydraulic processes occurring in them. Nucleate boiling occurs in Pressurized Water Reactors (PWRs) and Boiling Water Reactors (BWRs) as well as in their passive safety systems during an accident. Passive safety systems are solely driven by thermal gradients and gravitational force removing residual heat from the reactor core independent of any external power supply in the case of accidents. Instability of flow boiling in these passive circuits can cause flow oscillations. These oscillations may induce insufficient local cooling and mechanical loads, which threatens the reactors’ safety. Analysis of boiling two-phase flow and associated heat and mass transfer requires an accurate modeling of flow regime transitions and prediction of boiling parameters such as void fraction, steam bubble sizes, heat transfer coefficient, etc. Flow boiling has been intensively investigated through experiments, one-dimensional codes, and Computational Fluid Dynamics (CFD) methods. Costly hardware and no accessibility to all locations in complex geometries restrict the experimental investigation of flow boiling. Since one-dimensional codes such as ATHLET, RELAP and TRACE are ”lumped parameter” codes, they are unable to simulate complex flow boiling transition patterns. In the last decades, with the development of supercomputers, CFD has been considered as a useful tool to model heat and mass transfer occurring in flow boiling regimes. In many industrial applications and system designs, CFD codes and particularly the Eulerian-Eulerian (E-E) two-fluid model are quickly replacing the experimental and analytical methods. However, the application of this approach for flow boiling modelling poses a challenge for the development of bubble dynamics and wall boiling models to predict heat and mass transfer at the heating wall as well as phase-change mechanism. Many empirical and mechanistic models have been proposed for bubble dynamics modelling. Nevertheless, the validity of these models for only a narrow range of operating conditions and their uncertainties limit their applicability and consequently presently necessitate us to calibrate them for a given boundary condition via calibration factors. For that reason, the first aim of this thesis is the development of a bubble dynamics model for subcooled boiling flow, which needs no calibration factor to predict the bubble growth and detachment. This mechanistic model is formulated based on the force balance approach, physics of a single nucleated bubble and several well-developed models to cover the whole bubble life cycle including formation, growth and departure. This model considers dynamic inclination angle and contact angles between the bubble and the heating wall as well as the contribution of microlayer evaporation, thermal diffusion and condensation around the bubble cap. Validation against four experimental flow boiling data sets was conducted with no case-dependent recalibration and yielded good agreement. The second goal is the implementation of the developed bubble dynamics model in the E-E two-fluid model as a sub-model to improve the accuracy of boiling flow simulation and reduce the case dependency. This implementation requires an extension of the nucleation site activation and wall heat-partitioning models. The bubble dynamics and heat-partitioning models were coupled with the Population Balance Model (PBM) to handle bubble interactions and predict the Bubble Size Distribution (BSD). In addition, the contribution of bubble sliding to wall heat transfer, which has been rarely considered in other modelling approaches, is considered. Validation for model implementation in the E-E two-fluid model was made with ten experimental cases including R12 and R134a flow boiling in a pipe and an annulus. These test cases cover a wide range of operating parameters such as wall heat flux, fluid velocity, subcooling temperature and pressure. The validated parameters were the bubble diameter, void fraction, bubble velocity, Interfacial Area Density (IAD), bubble passing frequency, liquid and wall temperatures. Two-phase flow morphologies for an upward flow in a vertical heating pipe may change from bubbly to slug, plug, and annular flow. Since these flow patterns have a great impact on the heat and mass transfer rates, an accurate prediction of them is critical. The aim of this thesis is the implementation of the developed bubble dynamics and heat-partitioning models in the recently developed GENeralized TwO-Phase flow (GENTOP) framework for the modelling of these flow patterns transition as well. An adopted wall heat-partitioning model for high void fractions is presented and for a generic test case, flow boiling regimes of water in a vertical heating pipe were modelled using ANSYS CFX 18.2. Moreover, the impacts of wall superheat, subcooling temperature and fluid velocity on the flow boiling transition patterns and the effects of these patterns on the wall heat transfer coefficient were evaluated.:Nomenclature xi 1 Introduction 1 1.1 Background and motivation . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3 Outline of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2 State-of-the-art in modelling of subcooled flow boiling 11 2.1 Physics of boiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.2 Bubble growth modelling . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3 CFD simulation of boiling flows . . . . . . . . . . . . . . . . . . . . . 21 2.3.1 The Eulerian-Eulerian two-fluid model . . . . . . . . . . . . . 21 2.3.2 The Population Balance Model (PBM) . . . . . . . . . . . . . 22 2.3.3 Governing equations of the two-fluid model . . . . . . . . . . 25 2.3.4 Closure models for adiabatic bubbly flow . . . . . . . . . . . . 28 2.3.5 Phase transfer models . . . . . . . . . . . . . . . . . . . . . . 37 2.3.6 The Rensselaer Polytechnic Institute (RPI) wall boiling model 37 2.4 Flow boiling transition patterns in vertical pipes . . . . . . . . . . . . 42 2.5 The GENeralized TwO-Phase flow (GENTOP) concept . . . . . . . . . 45 2.5.1 Treatment of the continuous gas . . . . . . . . . . . . . . . . 46 2.5.2 The Algebraic Interfacial Area Density (AIAD) model . . . . . 46 2.6 Interfacial transfers of continuous gas . . . . . . . . . . . . . . . . . 47 2.6.1 Drag and lift forces . . . . . . . . . . . . . . . . . . . . . . . . 48 2.6.2 Cluster and surface tension forces . . . . . . . . . . . . . . . . 49 2.6.3 Complete coalescence . . . . . . . . . . . . . . . . . . . . . . 50 2.6.4 Entrainment modelling . . . . . . . . . . . . . . . . . . . . . . 51 2.6.5 Turbulence modelling . . . . . . . . . . . . . . . . . . . . . . 51 2.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3 An improved bubble dynamics model for flow boiling 55 3.1 Modelling of the bubble formation . . . . . . . . . . . . . . . . . . . 55 3.1.1 Bubble growth rate . . . . . . . . . . . . . . . . . . . . . . . . 57 3.1.2 Force balance . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 ix 3.1.3 Detachment criteria . . . . . . . . . . . . . . . . . . . . . . . 63 3.1.4 Wall heat flux model . . . . . . . . . . . . . . . . . . . . . . . 69 3.1.5 Heat transfer in the heating wall . . . . . . . . . . . . . . . . 70 3.2 Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . 72 3.2.1 Discretization dependency study . . . . . . . . . . . . . . . . 72 3.2.2 Model validation . . . . . . . . . . . . . . . . . . . . . . . . . 72 3.2.3 Sensitivity analysis . . . . . . . . . . . . . . . . . . . . . . . . 79 3.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4 An improved wall heat-partitioning model 85 4.1 The cavity group activation model . . . . . . . . . . . . . . . . . . . . 85 4.1.1 Bubble sliding length and influence area . . . . . . . . . . . . 88 4.1.2 Model implementation in the Eulerian-Eulerian framework . . 89 4.2 Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . 90 4.2.1 DEBORA experiments . . . . . . . . . . . . . . . . . . . . . . 90 4.2.2 Subcooled flow boiling of R134a in an annulus . . . . . . . . 102 4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 5 Modelling of flow boiling patterns in vertical pipes 115 5.1 Adopted wall heat-partitioning model for high void fractions . . . . . 115 5.2 Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5.2.1 Effect of wall superheat on the flow boiling transition patterns 118 5.2.2 Effect of flow morphologies on the wall heat transfer coefficient124 5.2.3 Comparison of GENTOP and Eulerian-Eulerian two-fluid models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 5.2.4 Effect of subcooling on the flow boiling transition patterns . . 129 5.2.5 Effect of inlet fluid velocity on the flow boiling transition patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 5.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 6 Conclusions and outlook 133 6.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 6.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 References 137 Declaration 155

[EN] The international debate on the environmental crisis, known since the 70's, pushes to review priorities in light of today's time to safeguard the future. In this regard, the problem of waste disposal takes on a great importance, especially from the construction sector. At the same time, it is necessary to revamp the Italian architectural heritage. The research identifies the implementation of regeneration building through the transformation of waste into resources for the area. The study of regulatory laws and best practices in the field of construction make it possible to identify effective ways of reusing components. In addition, the methods, tools, and techniques of demolition are analysed to ensure the uniformity of the merceologic fraction and the integrity of the elements. In the goal to promote the exploitation of the residual performances of materials that derive from selective demolitions, such as wood and steel, methodological and operational processes aimed at maximizing their reuse are further explained. The developed theories have been tested in the territory of L'Aquila, Italy. The city was severely damaged by the earthquake on the 6th of April, 2009. The reconstruction is an opportunity for the regeneration and development of the whole territory; however, it has many logistical, environmental, and economical problems. The restoration of the roads and the preservation of buildings necessitated the construction of safety systems. When reconstruction operations of a building begin, safety systems should be gradually dismantled. At present, end-life scenarios are not programmed, and the materials that constitute the safety systems are temporarily stored or transported to the landfill. The enormous quantity of waste results in economic and environmental damage, along with logistical disruptions. The research defines methodological-operative lines to reuse and recycle the materials that make up the safety systems, identify ways to pursue the optimization and sustainability of the rebuilding process. It has defined a process for the specific reuse in the seismic crater. Two lines of research developed from the data, and they are detailed below. Endogenous reuse: the materials that are derived from the dismantling of safety systems are immediately reused in sites for the construction of temporary buildings, i.e., construction site offices, changing rooms, refectories, toilets, etc. Temporary endogenous reuse is included in the reconstruction project with the matching function of structural or technological adjustment. Endogenous permanent reuse occurs through the improvement for the installations or redefinition of the internal space. Exogenous reuse: the materials that are derived from the dismantling of safety systems, are reused in neighbouring reconstruction sites within a radius of 100 km. The materials can also be used for the construction of temporary structures designed to accommodate the functions related to the community, such as school, offices, residences, etc. Finally, through the use of the prices present in the Region Abruzzo 2014 Price List, and by using the data previously obtained, a spread sheet for the assessment of the economic and environmental gain resulting from the reuse by businesses and public administrations was created. The research was used to define and develop sustainable methods for regeneration building, which also apply to the reconstruction of L'Aquila, to promote local resources and to resolve logistical, economical, and environmental issues related to this process. / [ES] El debate internacional sobre la crisis ambiental, desarrollada desde los años setenta, anima a revisar las prioridades de la época actual para salvaguardar el futuro. En este sentido tiene una gran importancia el problema de la eliminación de residuos, especialmente cuando provienen del sector de la construcción. Paralelamente existe la necesidad de renovar el patrimonio arquitectónico italiano. La investigación identifica las modalidades de ejecución en cuanto a la regeneración de las construcciones a través de la transformación de los residuos en recursos medioambientales o sostenibles. El estudio de las normas y de las buenas prácticas en el campo de la construcción, ha hecho posible determinar modalidades de actuación para la reutilización de componentes. Además, se han analizado los métodos, herramientas y técnicas para la demolición garantizando la uniformidad de los materiales y la integridad de los elementos. Con el objetivo de promover la explotación de las prestaciones residuales de los materiales resultantes de la demolición selectiva, en el caso de la madera y el acero fueron elaborados procesos metodológicos-operativos para la optimización de su reutilización. Las teorías desarrolladas han sido experimentadas en el territorio de L'Aquila (Italia), severamente dañado por el terremoto ocurrido el día 6 de abril de 2009. La reconstrucción es, de hecho, una oportunidad para la regeneración y el desarrollo de todo el territorio, pero en la actualidad tiene muchos problemas de orden logístico, ambiental y económico. La recuperación de la viabilidad y la preservación de los edificios han necesitado operaciones de consolidación de los edificios. Cuando comiencen las operaciones de reconstrucción del edificio, estos sistemas deben ser desmantelados. En la actualidad no han sido programados escenarios contemplen la viabilidad del final del ciclo de vida y los materiales que componen los sistemas de seguridad, por lo tanto, van a confluir en el almacenamiento o el vertedero temporal. Resulta un daño muy importante tanto a nivel económico, como ambiental y logístico. El proyecto de investigación define líneas metodológico-operativas para la reutilización/recuperación de los materiales que componen los sistemas de seguridad de los edificios e identifica maneras de conseguir la optimización y la sostenibilidad del proceso de reconstrucción. Se ha definido un proceso de reutilización específico para el territorio de L'Aquila, desarrollando dos líneas de investigación: reutilización endógena: los materiales provenientes del desmantelamiento de los sistemas de seguridad que son inmediatamente reutilizados dentro de la obra para la edificación de construcciones temporales o servicios, como oficinas, vestuarios, aseos, etc. (reutilización endógena temporal) o se insertan en el proyecto de reconstrucción con función de ajuste/mejoría de las estructuras, de las instalaciones o de los aspectos o la redefinición del espacio interno (reutilización endógena permanente); reutilización exógena: los materiales que derivan del desmantelamiento de los sistemas de seguridad se reutilizan en las obras de reconstrucción vecinas (en un radio de 100 km), o para la construcción de estructuras temporales que albergan las funciones relacionadas con la comunidad (escuelas, oficinas, residencias , etc.). Por último, a través de la utilización de la lista de precios de la Regione Abruzzo 2014 y el uso de los datos obtenidos previamente, ha sido elaborada una hoja de cálculo para evaluar el beneficio ambiental y económico resultante de la reutilización para las empresas y para las administraciones públicas. La investigación ha permitido desarrollar métodos de regeneración de la construcción sostenible, que pueden ser aplicados también a la reconstrucción en curso en la zona de L'Aquila, para promover los recursos locales y al mismo tiempo para resolver los problemas logístic / [CA] El debat internacional sobre la crisi ambiental, desenvolupada des dels anys setanta, anima a revisar les prioritats de l'època actual per salvaguardar el futur. En aquest sentit té una gran importància el problema de l'eliminació de residus, especialment quan provenen del sector de la construcció. Parallelament existeix la necessitat de renovar el patrimoni arquitectònic italià. La investigació identifica les modalitats d'execució quant a la regeneració de les construccions a través de la transformació dels residus en recursos mediambientals o sostenibles. L'estudi de les normes i de les bones pràctiques en el camp de la construcció, ha fet possible determinar modalitats d'actuació per a la reutilització de components. A més, s'han analitzat els mètodes, eines i tècniques per a la demolició garantint la uniformitat dels materials i la integritat dels elements. Amb l'objectiu de promoure l'explotació de les prestacions residuals dels materials resultants de la demolició selectiva, en el cas de la fusta i l'acer van ser elaborats processos metodològics-operatius per a l'optimització de la seva reutilització. Les teories desenvolupades han estat experimentades al territori de L'Aquila (Itàlia), severament danyat pel terratrèmol ocorregut el dia 6 d'abril de 2009. La reconstrucció és, de fet, una oportunitat per a la regeneració i el desenvolupament de tot el territori, però en l'actualitat té molts problemes d'ordre logístic, ambiental i econòmic.. La recuperació de la viabilitat i la preservació dels edificis han necessitat operacions de consolidació dels edificis. Quan comencin les operacions de reconstrucció de l'edifici, aquests sistemes han de ser desmantellats. En l'actualitat no han estat programats escenaris que contemplen la viavilitat de la fi del cicle de vida i els materials que composen els sistemes de seguretat, per tant, van a confluir en l'emmagatzematge o l'abocador temporal. Resulta un dany molt important tant a nivell econòmic, com ambiental i logístic. El projecte de recerca defineix línies metodològic-operatives per a la reutilització/recuperació dels materials que composen els sistemes de seguretat dels edificis i identifica maneres d'aconseguir l'optimització i la sostenibilitat del procés de reconstrucció. S'ha definit un procés de reutilització específic per al territori de L'Aquila, desenvolupant dues línies de recerca: reutilització endogena: els materials provinents del desmantellament dels sistemes de seguretat que són immediatament reutilitzats dins de l'obra per a l'edificació de construccions temporals o serveis, com a oficines, vestuaris, banys, etc. (reutilització endogena temporal) o s'insereixen en el projecte de reconstrucció amb funció d'ajust/millora de les estructures, de les instal·lacions o dels aspectes o la redefinició de l'espai intern (reutilització endogena permanent); reutilització exògena: els materials que deriven del desmantellament dels sistemes de seguretat es reutilitzen en les obres de reconstrucció veïnes (en un radi de 100 km), o per a la construcció d'estructures temporals que alberguen les funcions relacionades amb la comunitat (escoles, oficines, residències, etc.). Finalment, a través de la utilització de la llista de preus de la Regione Abruzzo 2014 i l'ús de les dades obtingudes prèviament, ha estat elaborat un full de càlcul per avaluar el benefici ambiental i econòmic resultant de la reutilització per a les empreses i per a les administracions públiques. La investigació ha permès desenvolupar mètodes de regeneració de la construcció sostenible, que poden ser aplicats també a la reconstrucció en curs a la zona de L'Aquila, per promoure els recursos locals i al mateix temps per resoldre els problemes logístics, econòmics i ambientals relacionats amb aquest procés. / De Gregorio, S. (2016). FROM POST-EARTHQUAKE WASTE TO RESOURCE [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/64872

Esta tese objetiva propor uma metodologia de especificação de requisitos de usabilidade e segurança orientada para arquitetura (MERUSA) aplicável a sistemas digitais de automação distribuídos e abertos. A estratégia utilizada para atingir esse objetivo consiste no desenvolvimento de uma metodologia focalizada nos processos de elicitação e análise dos requisitos de usabilidade e segurança, sincronizada com a evolução da arquitetura do sistema computacional. O modelo de referência ODP (Open Distributed Process) é utilizado como uma referência básica desse processo, fornecendo conceitos, procedimentos e modelos adequados à especificação e ao desenvolvimento de sistemas distribuídos e abertos de automação (orientados a objeto ou não), permitindo obter uma infra-estrutura coerente e gerenciável, com exigentes requisitos de integração. A eficácia da metodologia é verificada com a sua aplicação a um meta-modelo de especificação de projeto para sistemas digitais de controle distribuído de transmissão de energia para o sistema elétrico brasileiro. / This thesis purposes one new architecture oriented safety and usability requirements specification methodology (MERUSA) applied to open and distributed automation digital systems. The strategy used to achieve this goal consists on the development of a methodology centered on safety and usability requirement elicitation and analysis processes, synchronized with computational system architectural evolution. The RM-ODP (Reference Model of Open Distributed Process) is used as basic reference of this process. This pattern. supplies concepts, procedures and models appropriated to open and distributed system specification and development (object oriented or not), providing one coherent and manageable framework, with strong integration requirements. The methodology effectiveness is verified with its application to a project specification meta-model for energy transmission distributed control digital systems of Brazilian electrical system.

Esta tese objetiva propor uma metodologia de especificação de requisitos de usabilidade e segurança orientada para arquitetura (MERUSA) aplicável a sistemas digitais de automação distribuídos e abertos. A estratégia utilizada para atingir esse objetivo consiste no desenvolvimento de uma metodologia focalizada nos processos de elicitação e análise dos requisitos de usabilidade e segurança, sincronizada com a evolução da arquitetura do sistema computacional. O modelo de referência ODP (Open Distributed Process) é utilizado como uma referência básica desse processo, fornecendo conceitos, procedimentos e modelos adequados à especificação e ao desenvolvimento de sistemas distribuídos e abertos de automação (orientados a objeto ou não), permitindo obter uma infra-estrutura coerente e gerenciável, com exigentes requisitos de integração. A eficácia da metodologia é verificada com a sua aplicação a um meta-modelo de especificação de projeto para sistemas digitais de controle distribuído de transmissão de energia para o sistema elétrico brasileiro. / This thesis purposes one new architecture oriented safety and usability requirements specification methodology (MERUSA) applied to open and distributed automation digital systems. The strategy used to achieve this goal consists on the development of a methodology centered on safety and usability requirement elicitation and analysis processes, synchronized with computational system architectural evolution. The RM-ODP (Reference Model of Open Distributed Process) is used as basic reference of this process. This pattern. supplies concepts, procedures and models appropriated to open and distributed system specification and development (object oriented or not), providing one coherent and manageable framework, with strong integration requirements. The methodology effectiveness is verified with its application to a project specification meta-model for energy transmission distributed control digital systems of Brazilian electrical system.

The main target of the master´s thesis is reviewing the generation III nuclear reactors in term of the nuclear safety. At first we have to learn some theory of the nuclear safety in order to understand safety systems of the generation III nuclear reactors. Therefore the thesis is divided into two parts. Legislative and technical approaches to nuclear safety are mentioned in the first part. Regulatory bodies, whose task is to supervise nuclear safety in the nuclear power plants, belongs to the legislative approaches. There are defined terms such as defence in depth, redundancy, diversity, etc. There are mentioned methods to assessing nuclear safety – deterministic and probabilistic methods, especially probabilistic methods, for which a simple example is provided. There are also mentioned active and passive safety systems and their significance for nuclear safety and inherent safety too. There is an example of the function of the active and passive safety systems of the EDU nuclear power plant in conclusion of this issue. The second part deals with description of the selected nuclear reactors in context of the construction of the new units of nuclear power plant in Temelín. The nuclear reactors from companies, which applied for the public tender opened by ČEZ, a. s., for the construction of the ETE 3+4. Thus, the nuclear reactor MIR-1200 by ATOMSTROYEXPORT (Russian Federation), the nuclear reactor AP1000 by WESTINGHOUSE (USA) and the nuclear reactor EPR by AREVA (France) are taken into account . Comparison of the generation II and these generation III+ nuclear reactors necessarily belongs to this master´s thesis. These the generation III+ nuclear reactors are compared with the nuclear reactor VVER 440 (EDU) and in particular with the nuclear reactor VVER 1000, which is operated in the nuclear power plant Temelín. The final chapter contains generally appraisal of the whole problem.