The interconnection of components of industrial automation and control systems (IACS) and enterprise systems involved in processes ranging from generation and transmission to billing within electric utilities poses challenges regarding cyber security as well as division of organisational responsibility. One means of organising these components and systems is to use a zone model in which they are segmented, offering layered defences as well as a logical grouping. One such zone model is the zone model under review, which was presented by Zerbst et al. in a CIRED paper from 2009. This master thesis reviews that zone model and compares it to other industry standard zone models which have been found to be able to be categorised into either functional based models or layered defence models. The outcome is a rough definition of what kind of content fits in the various zones of the reviewed model, as well as a normalised zone model to be used for comparison. A suggested method for dividing system components into zones is based on the 4R-method considering the response time, resolution, reliability and reparability of the system component, although its accuracy has not been empirically tested.

La probabilité et la causalité sont deux outils indispensables à la prise en compte des situations de risque social. Lesrelations causales sont le fondement des représentations à partir desquelles on peut évaluer le risque et concevoirdes actions de prévention, de mitigation ou d’indemnisation. La probabilité permet de quantifier cette évaluation et de calibrer ces actions. Dès lors, il semble non seulement naturel, mais nécessaire d’expliciter la place de la causalité et de la probabilité dans la définition d’un problème de décision en situation de risque social. C’est l’objet de cette thèse.Un tour d’horizon de la terminologie du risque et des logiques d’intervention publique dans différentes catégories de risque social nous permettent de mieux comprendre la notion et les problèmes soulevés par sa représentation. Nous approfondissons notre analyse dans le cas de la sûreté nucléaire, en examinant en détail les méthodes et doctrinesdéveloppées dans ce domaine et leur évolution au cours du temps, ce qui nous conduit à formuler différentesobservations au sujet des évaluations de risque et de sûreté.En généralisant la notion d’intervention dans les réseaux bayésiens, nous développons une forme de réseau bayésien causal qui répond à nos besoins. Nous parvenons, par son biais, à une définition du risque qui semble pertinente pour un grand nombre de situations. Nous proposons ensuite des applications simples de ce modèle à certains aspects de l’accident de Fukushima et d’autres problèmes de sûreté nucléaire. Outre certains enseignements spécifiques, ceci nous amène à souligner la nécessité d’une démarche systématique d’identification des incertitudes dans ce domaine.Étendu en direction de la théorie de la décision, notre outil débouche naturellement sur un modèle de décision dynamique dans lequel les actes causent les conséquences et sont causalement liés entre eux. Il apporte en outre une interprétation causale au cadre conceptuel de Savage et permet d’en résoudre certains paradoxes et clarifier certains aspects. Il conduit enfin à envisager la question de l’ambigüité comme incertitude concernant la structure causale d’un problème de décision, ce qui correspond à une vision courante du principe de précaution. / Probability and causality are two indispensable tools for addressing situations of social risk. Causal relations are the foundation for building risk assessment models and identifying risk prevention, mitigation and compensation measures. Probability enables us to quantify risk assessments and to calibrate intervention measures. It therefore seems not only natural, but also necessary to make the role of causality and probability explicit in the definition of decision problems in situations of social risk. Such is the aim of this thesis.By reviewing the terminology of risk and the logic of public interventions in various fields of social risk, we gain a better understanding of the notion and of the issues that one faces when trying to model it. We further elaborate our analysis in the case of nuclear safety, examining in detail how methods and policies have been developed in this field and how they have evolved through time. This leads to a number of observations concerning risk and safety assessments.Generalising the concept of intervention in a Bayesian network allows us to develop a variety of causal Bayesian networks adapted to our needs. In this framework, we propose a definition of risk which seems to be relevant for a broad range of issues. We then offer simple applications of our model to specific aspects of the Fukushima accident and other nuclear safety problems. In addition to specific lessons, the analysis leads to the conclusion that a systematic approach for identifying uncertainties is needed in this area.When applied to decision theory, our tool evolves into a dynamic decision model in which acts cause consequencesand are causally interconnected. The model provides a causal interpretation of Savage’s conceptual framework, solves some of its paradoxes and clarifies certain aspects. It leads us to considering uncertainty with regard to a problem’s causal structure as the source of ambiguity in decision-making, an interpretation which corresponds to a common understanding of the precautionary principle.

The present Master´s thesis aims at designing an evolutionary scheme of secured power supply at nuclear power plants with VVER 440 reactors during design basis accidents as well as design extension conditions. In the first part of this thesis, concepts relating to the defence in depth of nuclear reactors, operating modes of the blocks as well as types and possibilities of electrical power supply and electric circuits of the block are defined. Although the present thesis deals with PWR 440 in general, special emphasis is put on the Czech NPP in Dukovany, where there are four PWR 440 reactors in operation, and on the possibilities for enhancing the defence in depth in this area. The second part of the thesis deals with the difference in station blackout definitions before and after Fukushima; not only the differences in situation evaluation are dealt with, but a solution is also proposed to make the system of secured power supply system during design basis accidents as well as design extension conditions more robust. This option has been selected out of a number of possibilities based on the evaluation of reliability, availability and cost-effectiveness of the proposal.

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.