Pour évaluer la gravité d'un accident de feu de boîte à gants dans une installation nucléaire, il est important de connaitre le terme source, qui est la quantité de matière radioactive mise en jeu. On cherche à identifier les phénomènes à l'origine de la libération de contaminants particulaires lors de la dégradation thermique de ces boîtes à gants. Deux matériaux (alumine et carbure de tungstène) ont été retenus pour simuler le comportement du contaminant considéré, le dioxyde de Plutonium. Deux dispositifs expérimentaux ont été conçus afin de contaminer et de dégrader thermiquement des plaques de Plexiglas (PMMA). Un ensemble d'essais à petite échelle a également permis de mieux comprendre les phénomènes à l'origine de la libération ou du piégeage des particules. La masse volumique du matériau utilisé a un impact direct sur l'émission des particules, la granulométrie des particules a un impact lorsque la dégradation thermique est rapide (flux thermique élevé). Ceci s'explique par l'interaction entre les particules émises et l'écoulement en proche paroi, phénomène qui a pu être observé expérimentalement. Une modélisation numérique de la situation étudiée a été réalisée et a permis de reproduire partiellement les résultats expérimentaux. Des améliorations peuvent encore être apportées, notamment sur la représentation du phénomène de piégeage des particules dans la matrice polymère. Cette étude pourra également donner des éclaircissements sur la problématique de l'émission des nanoparticules lors de la combustion de polymères nanochargés. / In order to assess the consequences of a glove box fire occurring in a nuclear facility, it is important to gather information on the source term, the amount of radioactive material that can be emitted to the environment. The objective is to identify the different phenomenon contributing to the release of radioactive particles from the surface of glove box materials undergoing pyrolysis. Two materials (alumina and tungsten carbide) were chosen as possible surrogates of the considered radioactive material, which is Plutonium dioxide. Two experimental facilities were designed to generate deposit on Plexiglas (PMMA) plates and burn them. Several small-scale experiments were also conducted to obtain knowledge of the phenomenon causing the release or trapping of the particles. Material density was found to have a direct impact on the release of particles, while particle size distribution had an impact only for fast thermal degradation (corresponding to high external heat flux). The reason is the strong interaction between the particles and the air flow close to the sample surface, which has been observed experimentally. A theoretical model of the problem was constructed, it was able to reproduce the experimental results, albeit partially. Improvements can be made, especially on the modelling of the trapping of particle by the polymer matrix. This study could help in understanding the problematic of nanoparticle emission from burning nanomaterials.

Graduation theses deals with problems of nuclear energetics and its impact on the environment. It presents the progress of nuclear power station in all contexts and tries to demostrate that the nuclear energetics is unavoidable progression. The work further describes the influence of Nuclear power station Dukovany on its close environment, especially on animals, plants and the health of inhabitants.

Nuclear law in the Czech Republic Abstract Nuclear law can be defined as a set of legal rules designed to regulate legal or natural persons engaged in activities related to fissile materials, ionizing radiation, and radiation from natural sources of radiation, with the aim of ensuring the protection of persons, property, and the environment. The topic of the thesis Nuclear law in the Czech Republic is the legal regulation of peaceful use of nuclear energy and ionizing radiation in the context of Czech legislation within the framework of public law, including its links and connections to the legal regulation of this issue at the international (European, global) level. After a brief introduction of nuclear law and its basic terminology, the thesis presents in a comprehensive summary the legal regulation at the international, European and national level, together with the legal principles that are manifested within the legal norms of nuclear law. Within the framework of the Czech legal framework, the main focus is on Act No. 263/2016 Coll., the Atomic Act, and its relation to individual areas of nuclear law. In terms of institutional arrangements for the administration of the use of nuclear energy in the Czech Republic, the institutions with significant competencies within the framework of nuclear law are...

At the beginning of 2011, the former Forschungszentrum Dresden-Rossendorf (FZD) was fully integrated into the Helmholtz Association, as Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Therefore, the present Annual Report 2010 of the Institute of Radiochemistry (IRC) is published as the first HZDR-Report. The Institute of Radiochemistry is one of the six Research Institutes of this centre. IRC contributes to the research program “Nuclear Safety Research” in the “Research Field of Energy” and performs basic and applied research in radiochemistry and radioecology. Motivation and background of our research are environmental processes relevant for the installation of nuclear waste repositories, for remediation of uranium mining and milling sites, and for radioactive contaminations caused by nuclear accidents and fallout. Because of their high radiotoxicity and long half-life the actinides are of special interest.

<p dir="ltr">Risk assessment involves analyzing potential accident scenarios to identify hazards and assess associated risk factors. Nuclear safety and security share the common goal of protecting against radiation exposure. However, they have developed separately, each with their own distinct risk assessment methodologies. As a result, there is a need for a comprehensive risk assessment method that covers both safety and security aspects. This thesis proposes a methodology that integrates risk assessment approaches for nuclear safety and security to address the gap in the current development of their risk assessment methodologies.</p><p dir="ltr">The proposed methodology applies the existing probabilistic risk assessment (PRA) methodology to the PFRI (Potential Facility Risk Index), originally developed to evaluate quantitative nuclear security risks, to enable the inclusion of safety risks in the assessment. The PFRI framework and methodology are modified to ensure that the PFRI score accurately reflects the overall risk of the facility for both nuclear safety and security. The facility-based approach of the existing PFRI is maintained to ensure a comprehensive assessment of the research reactor.</p><p dir="ltr">To achieve the goal of developing a comprehensive risk assessment method, the traditional PRA tools, such as event tree analysis (ETA) and fault tree analysis (FTA), are utilized in combination with the modified PFRI methodology. In addition, the consequence analysis method of PFRI is changed using the MACCS, which is commonly used for consequence analysis in PRA. The modified methodology is then used to conduct a risk assessment for the PFRI by setting safety and security scenarios at a hypothetical nuclear facility. The results demonstrate that the modified PFRI can provide a reasonable traditional risk unit and enable the comparison of risks from both safety and security aspects.</p><p dir="ltr">The final goal of this study is to develop the PFRI to determine the overall risk of the facility, considering both nuclear safety and security aspects. The PFRI score is utilized as a quantitative measure to show the total risk associated with hypothetical nuclear facility, providing a comprehensive understanding of its safety and security. By developing a methodology that integrates risk assessment approaches for nuclear safety and security, this thesis contributes to the improvement of the risk assessment methodology for nuclear facilities.</p>

<p>Flow pulsations in subchannel geometries play an important role in homogenization of fluid temperatures within a fuel rod bundle cross-section. As such, there is a strong need to develop accurate integral models that incorporate the underlying physics of these flows for inclusion in the broader safety analysis codes. This research is concerned with using computational fluid dynamics to investigate the flow pulsations in order to develop an enhanced understanding of the flow physics. The vast majority of previous experimental work has been in the turbulent regime, with varying degrees of geometric complexity. Previous numerical work has focused on steady or unsteady simulation of the turbulent experimental results, with the requirement that an appropriate turbulence model must be selected.</p> <p>Recent experimental work by Gosset and Tavoularis in 2006 has indicated that flow pulsations can occur under laminar conditions. Computational modeling of laminar flow pulsations provides an ideal framework for studying the physical mechanisms or instabilities that promote formation of the pulsations. Simulations of their experimental domain were run for a gap height normalized by the rod diameter (δ/D) of 0.3 and Reynolds numbers of 718, 900 and 955. These simulations found frequencies in the same range as Gosset and Tavoularis, as well as qualitatively similar particle tracks to their dye streaks. Analysis of the numerical pulsations showed them to be fluid rotations around the rod. These rotations were shown to be strongly correlated with the axial velocity gradient, which acted to transfer momentum from axial flow to the crossplane rotational pulsatile flow. The pulsations were shown to develop from a purely axial flow through disturbances in the axial velocity gradient, which initially arose near inflection points in the axial velocity profile in the spanwise direction. Under the influence of the axial velocity gradient and fluctuating pressure, these disturbances evolve into a sustained quasi-periodic flow.</p> / Master of Applied Science (MASc)

<p>The reprocessing of spent fuel is a key component in reducing the end waste from nuclear power plant operations and creating a sustainable closed fuel cycle. Central to this effort is the extraction and reprocessing of actinide materials to be recycled into fast or thermal reactors. Reprocessed actinides can contribute additional energy and may be partially transmuted in current thermal systems using mixed oxide fuels before being sent to fast reactors. The use of current thermal reactors as an intermediary step significantly reduces the fast reactor infrastructure needed to handle the spent fuel inventory in the long term, and also provides a source of additional energy from existing mined resources in the short term. An optimization of the fast and thermal systems in a closed fuel cycle reduces the end cycle waste to primarily fission products which have little residual value and manageable disposal and monitoring demands. The dissertation explores the design and analysis of an actinide transmutation solution utilizing a current thermal reactor design. The TRUMOX-30 CANDU-900 system defined herein uses a mixed oxide fuel containing 3.1% transuranic actinides extracted from 30 year cooled spent fuel from a prototypical Pressurized Water Reactor (PWR) and mixed with natural uranium. A significant constraint imposed on the design is that the actinide burning is to occur in an existing CANDU design without major changes or infrastructure replacement. Hence the standard CANDU design and analysis methodology was employed to produce and evaluate the system. The phased approach includes extensive neutron transport modeling of the lattice and control device super-cell configurations, which feed forward in to a detailed full core diffusion model of the TRUMOX-30 CANDU-900 design. Suitable fuel burnup and significant actinide conversion was achieved while remaining within the prescribed operational envelope of the CANDU reactor. The design was evaluated against existing operational constraints and limits, performing well and achieving the goal of actinide transmutation with no changes to the reactor design. This effort demonstrated the adaptation of a current CANDU-900 reactor as a platform for intermediary actinide transmutation which may form part of a sustainable and efficient fuel cycle.</p> / Doctor of Philosophy (PhD)

In a nuclear reactor, in case of a severe accident occurs, backup circuits are usedlike SIS and CSS, flooding the reactor with water. This might lead to many liquidleakages outside the reactor containment building. These leakages contain a lot offission products and especially iodine that is dangerous in terms of radiotoxicity oncereleased into the environment. Therefore, it is necessary to model correctly the liquidleakage in a reactor to size their impact properly. Their re-injection with a newpump implemented as part of the safety review for the extension lifetime of reactorsbeyond 40 years constitutes also a safety improvement to reduce the source term inthe environment.Modelling the transfer of fission products through liquid leakage and the re-injectionof said leakages is performed at IRSN with the ASTEC code. This thesis focuses onthe optimization of this model, and the consequences of modification in the code forfission products. Indeed, the model of pump used for leakages and re-injection hadsome issues that had to be circumvented.Also, the efficiency of re-injection will be tested with the new model, knowing thatthis implementation has already been proven to be effective in reducing releases tothe environment. Besides, this thesis studies the failure of the reinjection of liquidleaks that can lead to an accumulation of fission products in the auxiliary safeguardingbuilding. Other pH sensitivities in different areas are also studied. / Om en allvarlig olycka inträffar i en kärnreaktor används reservkretsar som SISoch CSS för att översvämma reaktorn med vatten. Detta kan leda till mångavätskeläckage utanför reaktorns inneslutningsbyggnad. Dessa läckage innehållermycket fissionsprodukter och särskilt jod som är farligt i form av radiotoxicitet när detsläpps ut i miljön. Det är därför nödvändigt att modellera vätskeläckage i en reaktorpå ett korrekt sätt för att kunna bedöma konsekvenserna. Återinsprutning med en nypump som genomförs som en del av säkerhetsöversynen för att förlänga reaktorernaslivslängd till mer än 40 år utgör också en säkerhetsförbättring för att minska källan imiljön.Modellering av överföringen av fissionsprodukter genomvätskeutsläpp och återinjektion av dessa läckage utförs vid IRSN med ASTEC-koden.Denna avhandling är inriktad på optimering av denna modell och konsekvenserna avändringar i koden för fissionsprodukter. Den pumpmodell som används för läckageoch återinjektion hade nämligen vissa problem som måste kringgås.Effektiviteten av återinsprutningen kommer också att testas med den nya modellen,eftersom det redan har visat sig att denna implementering är effektiv när detgäller att minska utsläppen till miljön. Dessutom studeras i denna avhandlingmisslyckandet med återinjektion av vätskeläckage som kan leda till en ackumuleringav fissionsprodukter i den extra säkerhetsbyggnaden. Andra pH-känsligheter i olikaområden studeras också.

<p dir="ltr">Protecting workers, the public, and the environment from the potential hazards associated with radiation exposure relies on two disciplines: safety and security. Historically, these two disciplines operate in isolation, but new emerging threats have exploited weaknesses in the disciplines’ isolated practices. A method for overcoming weakness in isolation and strengthening protection is the integration of nuclear safety and security. Integration can provide increased protection for nuclear facilities and operations. This research identifies and fills gaps within integration research that promotes the active practice of integration. </p><p dir="ltr">Eight integration points were identified across the overlap of nuclear safety and security. Definitions for the points of overlap were determined using qualitative research methodologies. These definitions provided measurable aspects of practiced integration among the eight points. The eight integration points were also analyzed for importance using a quantitative methodology known as an analytical hierarchy process with an assisted Monte Carlo simulation. This study found that reactor staff placed access control and transportation of materials as the highest points of importance. However, a 10-year review of United States Nuclear Regulatory Commission violations and citations revealed culture as the most common issue for research reactors. This supports the need for a shift in perspective regarding nuclear safety and security practices.</p><p dir="ltr">An integration assessment tool was designed to measure the active practice of integrative techniques among research reactor staff. When applied to a research reactor, specific integration points were assessed, and an overall integration score for the facility was provided. The results of the integration assessment tool were applied to a newly developed integrated risk model that determined the facility’s vulnerability, consequences, and integrated risk score. </p><p dir="ltr">Through the efforts of this research, the eight points of integration have clearly and concisely identified how integration can be exercised at a facility level—this is something that has not yet been done. This research identified trends in safety and security practices that indicated strengths and weaknesses and how integration can improve those strengths and address the weaknesses. This research also provided a novel risk analysis model focused on actively applied integrative techniques instead of simulated hypothetical probabilities. Through this adjusted focus on integration, this research has found a new method for increasing the safety and security of nuclear operations.</p><p><br></p>

The topic of this diploma thesis is Czech Nuclear Law. The nuclear law is a set of legal norms concerned with the ways and conditions of usage of nuclear energy and ionising radiation, the systems used to protect people and the environment against the damaging effects of ionising radiation, protocols to be followed in the case of accidents, radioactive waste disposal as well as the role of the state administration in supervising usage of nuclear energy and ionising radiation. A short historical review of the usage of nuclear energy and ionising radiation is followed by 2 chapters dedicated to international and EU nuclear law. The aims and content of international and EU collaboration concerning non-military usage of nuclear energy and ionising radiation are defined in these chapters. The other chapters of this thesis are concerned with Czech Nuclear Law. The constitutional foundation of this Law is described as well as nuclear law as a legal subject and the rules forming the base of Czech Nuclear Law. The following section deals with the power characteristics of the individual state authorities in the field of non-military usage of nuclear energy. Attention is paid to the classification of ionising radiation sources and characteristics of the tools used by the legal norm for environmental...