The thesis deals with the analysis of the grid node operation after the connection the nuclear unit. The aim of the master´s thesis is to describe the influence of network´s faults to a nuclear unit. Thesis is dealing with three fundamental problems. An influence of short circuits and power imbalance on the synchronous generator of nuclear power plant and its operation of the island network. The thesis is focused especially on the nuclear unit. However, in the case of any failure in the network, it´s necessary to check other units and their protections in the test system because unit failure could cause the disintegration of the power network. For the purposes of the simulation a test system of the power network has been developed. The test system was optimized in the LUG software, which is used to calculate the power network. Transient simulations are performed in the MODES software. Single faults are configured with scenarios. Results are generated into output files. Analysis of influence network´s faults on the synchronous generator of nuclear power plants. The ability of the synchronous generator to restore the primary steady state or hold the new steady state during changes in operating parameters of the network is one of the important parts of the safe and reliable operation of the power network. During the short circuit the damped transient actions occur. With the extension of the short circuit duration, the amplitude of the transient action increases. The risk of the stability loss of a synchronous generator increases. Therefore, the critical clearing time of a short circuit is being defined, which is the time when there is not any loss of stability. Critical clearing time of research generator is sufficient to turn off the short circuit with the help of its protection (the worst case is 0,8 s). For example, by comparison with the hydroelectric power plant, the critical clearing time is much longer. Models of other power plants have been designed with high reliability so in the case of these faults, it doesn’t cause the disintegration of the power network. Creation of island grid is characterized by strong current surges. Units must be resistant to these surges. In the island grid fast changes of the electrical parameters often occurs. Therefore, units must respond to these changes as quickly as possible and in the broadest limits. For this purpose an island operation regulator is being used. In the case of surplus island grid in steam power plants a dump condenser can be used. This is an important ability of steam power plants because the units are able to react quickly to changes of electrical parameters in island grid. The main result of this thesis is the behavior of the nuclear power plant during various faults in the power network. Researched generator of the nuclear power plant is highly stable against faults in the power network based on the findings. The results allow to continue in this topic with real network and real unit of nuclear power plant.

This Master’s thesis focuses on calculation of power and temperature distribution in fuel assemblies of VVER-440 reactor at Dukovany Nuclear Power Plant. Theoretical section contains a brief description of VVER-440 technology, fuel and its development at Dukovany Nuclear Power Plant, basics of heat generation in nuclear reactors as well as an overview and categorization of computer codes, used for core calculations. Of these codes, the MOBY-DICK computer code is then described in depth, including its input and output files. The MOBY-DICK code is later on used for pinwise calculating power distribution of selected fuel cycles of defined units at Dukovany Nuclear Power Plant, with vizualization of output values for characteristic fuel assemblies. Results of this computation are then used for analysis, whether uneven power distribution in the core and heat generation gradient within fuel assemblies have any influence on measuring channel output temperatures, which is the pivotal part of this thesis.

This thesis deals with the analysis of warming and starting up the nuclear unit of Dukovany NPP after the outage. First part explains the various operating modes of nuclear power plants, specifically operating modes of Dukovany NPP. The following part contains the analysis of heat sources in the primary circuit and also the individual production and consumption of steam by the NPP. The next part deals with division into several points of the warming of the Dukovany NPP. The analysis of warming nuclear unit after a outage is made on the basis of the industry based data, measured in December 2015. The result of the analysis is determination the amount of steam passing from a another nuclear unit, which is following by the own proposal of the external steam source.

Avstängda kärnkraftverk berövar många människor av elektricitet och det skulle ha en negativ inverkan både på företagets framtoning och mänskliga aktiviteter. På grund av detta behöver tillgängligheten av utrustningen i alla byggnaderna som kärnkraftverken består ses till. HVAC-system (Heating, Ventilation and Air Conditioning) spelar en viktig roll när det gäller tillgänglighet av utrustning eftersom dessa system ser till pålitligheten är på topp genom att anpassade omgivningsförhållanden till utrustningen. Att designa ventilationssystemet rätt är därför mycket viktigt och måste göras noggrant. Denna rapport introducerar metodologin för att designa och optimera ett ventilationssystem för en av byggnaderna i ett kärnkraftverk. Utöver detta utvecklas och beskrivs en metodologi för att designa ett rökkontrollssystem för en byggnad som ingår i kärnkraftverket. Dessa metodologier har implementerats för en byggnad i en demineraliseringsstation, Hinkley Point C project. / During nuclear power plants shutdown many people could be deprived of electricity and it would have a negative impact both on the company’s image and on people activities. As a consequence, availability of equipments in the different buildings which compose the power plant needs to be assured. HVAC system (Heating, Ventilation and Air Conditioning) plays an important role on the reliability of these equipments as it makes sure that ambient conditions in the buildings fit the operating temperature range of the equipments. Consequently sizing a ventilation system is really important and it needs to be carried out seriously. This paper introduces the methodology to size and optimize a ventilation system for nuclear power plants’ building. This paper also develops the methodology used to size a smoke control system in a nuclear related building. Direct application of this methodology has been realised for a specific building which is the demineralization station of Hinkley Point C project.

This master thesis examines how the Fukushima accident has affected the French energy policy and the impact on the perception of nuclear energy by policymakers, the public and energy companies. Nuclear energy does comprises three-quarters of the total electricity production in the country and thus forms the backbone of the energy mix in France. The study uses comparative analysis as a main approach, to compare public discourse of state actors (in particular the President, the Ministry of Energy and Nuclear Safety Agency) and the French energy companies before and after the accident from March 11, 2011. At the beginning, the study refers on the position of nuclear energy in the world, historical development of nuclear energy in France and its importance for the energy security of the country. It also describes the Fukushima accident and its immediate consequences on nuclear energy worldwide. In a research section it presents a summary of France's energy policy before the Fukushima accident, in which emphasis was placed on maintaining a high share of nuclear energy in the energy mix of the country. In the next part of the research is described the French energy policy after the accident and subsequently the prospect of possible change of energy strategy of France.

The most important requirement for running a nuclear power plant safely is having a reliable safety system, especially during the emergency shutdown condition. For performing a scrutiny load flow and voltage drop study a detailed and comprehensive electrical model for the emergency electrical distribution system of the Trojan Nuclear Power Plant has been developed. This model includes the representation of the transformers, circuit breakers, motors, cables and load data from 4160 volts level down to the individual 480 volts loads.

Risk assessment is essential for nuclear power plants (NPPs) due to the complex dynamic nature of such systems-of-systems, as well as the devastating impacts of nuclear accidents on the environment, public health, and economy. Lessons learned from the Fukushima nuclear accident demonstrated the importance of enhancing current risk assessment methodologies and developing efficient early warning decision support tools. Static probabilistic risk assessment (PRA) techniques (e.g., event and fault tree analysis) have been extensively adopted in nuclear applications to ensure NPPs comply with safety regulations. However, numerous studies have highlighted the limitations of static PRA methods such as the lack of considering the dynamic hardware/software/operator interactions inside the NPP and the timing/sequence of events. In response, several dynamic probabilistic risk assessment (DPRA) methodologies have been developed and continuously evolved over the past four decades to overcome the limitations of static PRA methods. DPRA presents a comprehensive approach to assess the risks associated with complex, dynamic systems. However, current DPRA approaches are faced with challenges associated with the intra/interdependence within/between different NPP complex systems and the massive amount of data that needs to be analyzed and rapidly acted upon. In response to these limitations of previous work, the main objective of this dissertation is to develop a physics-based DPRA platform and an intelligent data-driven prediction tool for NPP safety enhancement under normal and abnormal operating conditions. The results of this dissertation demonstrate that the developed DPRA platform is capable of simulating the dynamic interaction between different NPP systems and estimating the temporal probability of core damage under different transients with significant analysis advantages from both the computational time and data storage perspectives. The developed platform can also explicitly account for uncertainties associated with the NPP's physical parameters and operating conditions on the plant's response and probability of its core damage. Furthermore, an intelligent decision support tool, developed based on artificial neural networks (ANN), can significantly improve the safety of NPPs by providing the plant operators with fast and accurate predictions that are specific to such NPP. Such rapid prediction will minimize the need to resort to idealized physics-based simulators to predict the underlying complex physical interactions. Moving forward, the developed ANN model can be trained under plant operational data, plants operating experience database, and data from rare event simulations to consider for example plant ageing with time, operational transients, and rare events in predicting the plant behavior. Such intelligent tool can be key for NPP operators and managers to take rapid and reliable actions under abnormal conditions. / Thesis / Doctor of Philosophy (PhD)

In this study, the current use of natural language processing in Swedish and international nuclear power plants has been investigated through semi-structured interviews. Furthermore, natural language processing techniques have been studied to find out how text data can be analyzed and utilized to aid operations and maintenance in the Swedish nuclear power plant industry. The state-of-the-art transformers model BERT was used to analyze text data from operations at a Swedish nuclear power plant.  This study has not managed to find any current implementations of natural language processing techniques for operations and maintenance in Swedish nuclear power plants. Natural language processing does exist in examples such as embedded search functionalities internally or chatbots on the customer side, but it does not relate to the scope of this project. Some international actors have successfully implemented natural language processing for the classification of text data such as corrective action programs. Furthermore, it was observed that the lingo and jargon in the nuclear power plant industry differ between utilities as well as from the native language. To tackle this, models further trained on domain-specific data could be beneficial to better analyze the text data and solve natural language processing tasks. As the data used in this study was unlabeled, expert input from the nuclear domain is required for a proper analysis of the results. Working for a more data-driven industry would be valuable for the implementation of natural language processing. / I denna studie har den nuvarande användningen av Natural language processing (NLP) i svenska och internationella kärnkraftverk undersökts genom semistrukturerade intervjuer. Vidare har NLP studerats för att ta reda på hur textdata kan analyseras och användas för att underlätta drift och underhåll i den svenska kärnkraftsindustrin. Transformersmodellen BERT användes för att analysera textdata från driften vid ett svenskt kärnkraftverk. Denna studie har inte lyckats hitta några aktuella implementeringar av NLP för drift och underhåll i svenska kärnkraftverk. NLP finns som inbäddade sökfunktioner internt eller chatbottar på kundsidan, men dessa omfattas inte av detta projekt. Vissa internationella aktörer har framgångsrikt implementerat NLP för klassificering av textdata som t.ex. avhjälpande underhåll (Corrective action programs). Vidare observerades att språket och jargongen inom kärnkraftsindustrin skiljer sig mellan olika kraftverk och från det vanliga språket. Genom att träna modellerna på domänspecifik data skulle modellerna kunna prestera bättre. Eftersom data som användes i denna studie var omärkt (unlabeled), krävs expertinput från kärnkraftsområdet för en korrekt analys av resultaten. Att arbeta för en mer datadriven industri skulle vara värdefullt för implementeringen av NLP / Feasibility Study on Artificial Intelligence Technologies in Nuclear Applications

[pt] Enfoca-se a análise sísmica de usinas termonucleares sob metodologia no domínio da frequência utilizando-se como modelo, o do prédio do reator da usina Angra 3 e como principal ferramenta o programa de análise de problemas com interação solo-estrutura, SASSI. São avaliadas alternativas para três fases distintas do projeto: geração de sismos artificiais, análise do sistema principal e desenvolvimento de espectros para análise do sistema secundário. Na geração de sismos artificiais, a introdução de critérios de compatibilização complementares ao do espectro de resposta é avaliada considerando-se as consequências sobre as respostas em um ponto da estrutura. No sistema principal, sujeito a excitações sísmicas nas direções horizontal e vertical, comparam-se soluções no domínio do tempo e da freqüência e se reconhece a metodologia na frequência como uma alternativa conveniente à análise no tempo para cálculo de respostas em termos de acelerações , deslocamentos e tensões máximas e de espectros de acelerações. São ainda, desenvolvidos espectros de resposta acoplados para a análise de sistemas secundários segundo sistemática já proposta, para cálculo no domínio do tempo, que comparados com estes, alcançam amplitudes da mesma ordem, porém com tempo de processamento inferior. A metodologia de análise no domínio da frequência apresenta- se como um recurso mais preciso, pois permite a consideração de parâmetros do solo não constantes com a frequência; no que diz respeito ao programa utilizado, mostra-se flexível e acessível. / [en] The seismic analysis of nuclear power plant structures and components is considered to evaluate the convenience to update the brazilian design routine through the use of frequency domain techniques provided by codes such as SASSI. For this purpose one uses a FEM model of a reactor building which has been already analyzed by current techniques in time domain, and comparisons are made with results obtained in the frequency domain, with special attention to the following points: - analysis of the main structures using foundation impedance functions variable with the excitation frequency; - generation of coupled floor response spectra and their application to the analysis of secondary systems; - consideration of complementary criteria based on a minimum seismic spectral density function to generate artificial ground motion accelerograms compatible with a prescribed design response spectrum. As a first step, an exploratory work on the usage of SASSI program is made running a couple of simple examples. In the continuation of the work, a series of runs is made using the above-mentioned structural model under currently prescribed ground motions in the design of brazilian NPP structures. The results are compared with those from previous analyses using different methodologies and some interesting conclusions are brought up. / [es] En el presente trabajo se enfoca el análisis sísmico de plantas termonucleares bajo la metodología en el dominio de la frecuencia utilizando como modelo, el del edificio del reactor de la planta Angra 3 y como principal herramienta el programa de análisis de problemas con interacción suelo-extructura, SASI. Son evaluadas alternativas para tres fases distintas del proyecto: generación de sismos artificiales, análisis del sistema principal y desarrollo de espectros para análisis del sistema secundario. En la generación de sismos artificiales, se evalúa la introducción de criterios de compatibilización complementares al del espectro de respuesta. En el sistema principal, sujeto a excitaciones sísmicas en las direcciones horizontal y vertical, se compararon soluciones en el dominio del tiempo y de la frecuencia. Se reconoce la metodología en la frecuencia como una alternativa conveniente para cálculo de respuestas en términos de aceleraciones, deslocamientos y tensiones máximas y de espectros de aceleraciones. Se desarrollan, además, espectros de respuesta acoplados para el análisis de sistemas secundarios según sistemática ya propuesta, para cálculo en el dominio del tiempo, que comparados con éstes, alcanzan amplitudes de la misma orden, pero con tiempo de procesamiento inferior. La metodología de análisis en el dominio de la frecuencia se presenta como un recurso más preciso, pués permite la consideración de parámetros del suelo no constantes con la frequencia; con respecto al programa utilizado, éste se muestra flexible y accesible.

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