The demand for fossil-free energy production is rising due to electrification and increased consumption in the energy system. There are also multiple climate goals to reach, to preserve the possibilities of a sustainable future. A response to this is the BWRX-300, a natural circulation boiling water small modular reactor (SMR) concept developed by GE Hitachi Nuclear Energy. It is currently at the forefront of study for many power utility companies around the world. For decision making it is of interest to investigate the capabilities of new facilities. This Master Thesis work's aim is to study the BWRX-300 reactor's feasibility together with evaluating and optimizing its performance using the core simulation softwares Casmo5 and Simulate5. This is carried out by first verifying Simulate5's natural circulation capabilities by modifying an existing forced-circulation reactor to natural circulation, then comparing simulation results to real world data.  Next a comprehensive model of the BWRX-300 reactor pressure vessel is modelled and validated. Equilibrium cores for 12- and 24-month cycle lengths are then simulated where key reactor performance metrics such as fuel economy, safety margins, axial profiles (of voids and pressure drop) and reactor characteristics are extracted. The effect of different fuel assembly designs in the BWRX-300 reactor core is investigated to find first core design optimums. Furthermore the decay heat removal system in the BWRX-300 is investigated. Lastly the results are used to evaluate the optimal operating mode given the current and future more dynamic projected state of the energy system.  The results show that there are no real technical difficulties while operating the BWRX-300 reactor for 12 or 24 months. The decay heat removal system and core flow characteristics provide abundant coolant flow to maintain long term fuel integrity during both normal and abnormal operation modes. More or less routine core design optimization work is required to obtain sufficient safety margins and improve fuel economy. It is observed that the smaller reactor core requires an increase in average fuel enrichment to maintain criticality throughout the cycle, potentially creating an incentive to raise the current licensing limit. However it is deemed possible to avoid this by conducting further fuel design optimization work.

High-Pressure Partial Oxidation (HP-POX) of natural gas is one of the techniques in the synthesis gas production by non-catalytic reforming. On the path to emissions reduction, all operating facilities must be optimized to satisfy environmental regulations. In a rapidly changing economic and political environment, technological development from lab-scale to demo-scale, and industrial-scale is no longer feasible. Therefore, new research and design methods must be applied. One of such methods commonly used in science and industry is numerical modeling, which utilizes Computational Fluid Dynamics (CFD), Reduce Order Models (ROMs), kinetic, and equilibrium models. The CFD models provide details about flow field, temperature distribution, and species conversion. However, the computational effort required to conduct such calculations is significant. The computationally expensive CFD models cannot be effectively used in the reactor optimization. Herewith, other modeling techniques utilizing kinetic and equilibrium models do not provide necessary details for process optimization and can only be used for adjustments of boundary conditions, investigation of specific processes occurring in the reactor, or development of sub-models for CFD. A numerical investigation was conducted to validate existing CFD models against benchmark experiments. The results reveled that the CFD model is sensitive to modeling parameters, when simulating complex flows where turbulence-chemistry interaction occurs. Moreover, it was shown that the results sensitivity increases along with the oxidizer/fuel inlet velocities ratio. Based on the conducted experiments, the CFD model validation resulted in definition of the modeling parameters suitable for modeling of HP-POX of natural gas. Based on the validated CFD model, a ROM for HP-POX of natural gas was developed. The model assumes that the reactor consists of several zones characterized by specific conversion processes. Moreover, the model considers inlet streams dissipation upon the injection, and includes several optimization stages that allows model adjustments for any reactor geometry and boundary conditions. It was shown that the developed ROM can reproduce global reactor characteristics at non-equilibrium conditions unlike other ROMs, kinetic, or equilibrium models. Moreover, the validation against CFD results showed that the ROM can correctly account for the \gls{rtd} in the reactors of different geometries and volumes without extensive additional optimization. Finally, new experiments were designed and conduced at semi-industrial HP-POX facility at TU Bergakademie Freiberg. The experiments aimed to study the influence of different oxidizer/fuel velocities ratios on the reactants mixing and process characteristics at high operating pressures. The high velocity difference between oxidizer and fuel was achieved by injection of High-Velocity Oxidizer (HVO). The experiments showed no significant influence of the HVO on the global reactor characteristics and overall species conversion process. However, the numerical analysis of the experimental results demonstrated that the oxidation zone is affected by the oxidizer inlet velocity, and becomes less efficient in the fuel conversion when the oxidizer/fuel inlet velocities ratio is increased. In summary, a sophisticated numerical model validation was conducted and sensitivity of the numerical results to the modeling parameters was carefully studied. The novel natural gas conversion technique was experimentally studied. Based on the conducted experiments and numerical evaluation a ROM was developed. The ROM is capable of producing high accuracy results and greatly decreases the computational effort and time needed for reactor development and optimization.

Hydrering är en viktig process för att producera produkter med önskade egenskaper samt att uppfylla de lagliga krav som existerar med avseende på miljö och hälsa. Reaktionerna som sker vid hydreringen är katalytiska vilket innebär att förstå sam utnyttja de mest lämpliga katalysatorerna är av yttersta vikt. Avsvavling (HDS) är en av de mest studerade reaktionerna medan avaromatisering (HDA) samt borttagandet av kväve (HDN) är diskuterade samt förstådda i lägre grad. Trots det är aromatiska samt kväverika föreningar naturligt förekommande i matningar till hydreringsreaktorerna där de organiska kväveföreningarna är inhibitorer. I detta arbete är målet att tillverka samt utvärdera några hydreringskatalysatorer med fokus på deras prestanda för HDA och HDN reaktionerna. Den bästa möjliga tekniken idag för tillverkningen av hydreringskatalysatorer utnyttjar kelateringsreagens vid beredningen. Detta har visat sig ha en positiv inverkan på egenskaperna och aktivteten vid hydrering för NiMo-katalysatorer. För att undersöka detta närmare har två typer av katalysatorer tillverkats, en med kelateringsreagens (typ II) och en utan (typ I). Dessa var sedan utvärderade i dess HDA och HDN aktiveter. Katalysatorerna var tillverkade samt karaktäriserade vid KTH och sedan aktiverade via sulfidering samt utvärderade vid Nynas AB. Aktiviteten för de sulfiderade katalysatorerna var utvärderade i ett surrogatsystem bestående av fenantren (PHE) som modell för aromatiska föreningar samt karbazol (CBZ) eller akridin (ACR) som modell för icke-basiskt samt basiskt organisk-kväve. Aktivitetsutvärderingen utfördes i en porlbäddreaktor där aktiviteten undersöktes vid närvarandet samt avsaknandet av de organiska kväveföreningarna. När matningen byttes, en så kallad modeswitch, ändras aktiviteten beroende på de betingelser som undersöktes. Reaktortemperaturen varierade mellan 300 °C och 320 °C vid ett konstant systemtryck på 120 barg. Katalysatornsaktivitet var positivt korrelerad med reaktortemperaturen där en lägre aktivtetuppmättes vid 300 °C jämfört med 320 °C. Det visade sig även att båda typerna av organiskt kväve påverkade aktivteten negativt vid båda undersökta temperaturerna. Utöver det så var de basiska kväveföreningarna mer inhiberande jämfört med de icke-basiska föreningarna för båda katalysatorerna. Inhiberingen orsakad av karbazol visade sig vara helt reversibel medan akridininhiberingen antydde på mer permanenta effekter för typ II katalsatorn. Dessa resultat antyder, trots de preliminära antagandena, att typ I katalysatorn var bättre än typ II katalysatorn. / Hydrotreating processes are of high importance in helping to obtain the desired characteristics of products as well as to comply with the legislation regarding health hazards and environmental pollution. Hydrotreating reactions are catalytic reactions which imply that the understanding and utilization of the most suitable catalysts is crucial. While hydrodesulfurization is a vastly studied branch of hydrotreating, hydrodearomatization (HDA), and hydrodenitrogenation (HDN) processes are less discussed and understood. However, aromatic compounds along with nitrogen-containing inhibitors are naturally present in the hydrotreater feeds. Therefore, the aim of this study was the preparation and evaluation of hydrotreating catalysts with the main focus on HDA and HDN reactions. According to the current state of the art, the utilization of chelating agents during preparation has a positive impact on the characteristics and activity of hydrotreating catalysts therefore NiMo catalysts with (Type II) and without (Type I) a chelating agent were prepared and evaluated towards HDA and HDN reactions. The catalysts were prepared and characterized at KTH and then activated (sulfided) and evaluated at Nynas AB. The activity of the sulfided catalysts was evaluated using surrogate mixture models containing phenanthrene (PHE) as an aromatic compound, and carbazole (CBZ) or acridine (ACR). The latter ones were representing two types of nitrogen-containing inhibitors, non-basic and basic. The activity testing was carried out in a trickle-bed microreactor during three-step experiments in the presence and absence of the organic nitrogen compounds (mode switches). During the mode switches the activity of the catalysts under varying conditions was investigated. The operating temperature of the reactor varied between 300 and 320°C under constant H2 pressure of 120 barg. The catalytic activity was positively correlated with temperature with the catalysts exhibiting lower activities at 300°C than at 320°C. It is noteworthy that the activity of all the catalysts was hindered by the presence of both nitrogen compounds at all temperatures with the basic nitrogen (ACR) being more inhibitory for both catalysts. CBZ inhibition to the HDA reactions showed reversibility, while ACR had a more permanent inhibiting effect in the case of the Type II catalyst. The results indicated that despite the preliminary assumptions, the Type I catalyst outperformed the Type II.

Under de senaste 30 åren så har antalet massa- och pappersbruk minskat medan den totala produktionen av massa och papper har ökat. En högre produktion per bruk tillsammans med en hårdare miljölagstiftning, sätter ett högre tryck på vattenreningen på varje bruk. I flera massa- och pappersbruk så är vattenreningen en av faktorerna som begränsar produktionen av massa och papper. Dessutom så renas oftast restvattnet från massa- och pappersbruken med aerob rening som kräver mycket elektricitet och som producerar slam. För att minska kostnaden av vattenreningen och för att öka kapaciteten, så kan en anaerob vattenrening användas före den aeroba reningen. Fördelar med att ha en anaerob rening före den aeroba reningen är att den minskar belastningen av organiskt material på den aeroba reningen, värdefull biogas produceras, anaerob rening producerar mindre slam och kräver mindre elektricitet. Däremot så innehåller restvattnet från massa- och pappersbruk en hög halt av sulfat, vilket har orsakat en instabil biogasproduktion på flera existerande anläggningar. En potentiell lösning på detta är att använda en ytterligare anaerob reaktor före den biogasproducerande reaktorn, med syftet att reducera sulfat. Syftet med detta projekt var att optimera en anaerob två-stegs process för att få en effektiv biogasproduktion och för en stabil process. I projektet har två upp-flöde anaerob packad bädd (UAPB) reaktorer använts. Den första reaktorn var anrikad med sulfatreducerande bakterier före starten av projektet och den andra reaktorn innehöll metanogener. Processvatten från ett massa- och pappersbruk som använder barrträd som råmaterial och gör termomekanisk massa, användes i projektet. Den anaeroba två-stegs processen optimerades genom att minska retentionstiden i båda reaktorerna; genom att undersöka alternativ för att minska sulfidkoncentrationen i inflödet till biogasreaktorn; och genom att minska tillsatsen av näringsämnen till processvattnet. Stabiliteten av två-stegsprocessen mättes genom att analysera sulfat, sulfid och COD innehållet med spektrofotometri; genom att analysera pH; genom att analysera innehållet av metan i biogasen med gaskromatografi; och genom att analysera flyktiga fettsyror i utflödet med högtrycksvätskekromatografi. Resultaten visade att processen var stabil när retentionstiden för den sulfatreducerande reaktorn och biogasreaktorn var 0.3 dagar respektive 1.5 dagar. Effektiviteten av borttagningen av sulfat och COD i den sulfatreducerande reaktorn var 82% respektive 31%. Innehållet av metan i biogasen i den sulfatreducerande reaktorn var 53% i genomsnitt. I biogasreaktorn var borttagningen av COD 32% och metanhalten i biogasen var 31% i genomsnitt. Den totala borttagningen av COD för tvåstegsprocessen var 61%, när reaktorerna var kopplade via en uppsamlingsflaska. Biometanpotentialen i processvattnet och i utflödet från den sulfatreducerande reaktorn var 147 NmL CH4/g VS respektive 47 NmL CH4/g VS. Slutsatsen av projektet är att processen var stabil när retentionstiden för den sulfatreducerande reaktorn och biogasreaktorn var 0.3 dagar respektive 1.5 dagar, motiverat med stabiliteten av borttagning av sulfat och COD. Däremot var metanpotentialen för utflödet från den sulfatreducerande reaktorn bara 32% jämfört med processvattnet och nedbrytbarheten av COD var lägre i utflödet än i processvattnet. Eftersom den sulfatreducerande reaktorn var stabil vid de testade förhållandena så skulle det vara intressant att testa en enstegsprocess i en UAPB reaktorpilot i framtiden. Det skulle även vara intressant att minska retentionstiden i biogasreaktorn för att se om metanhalten i biogasen ökar. / In the past 30 years, the number of P&P mills have decreased while the total production of pulp and paper have increased. A higher production per mill together with a stringent environmental legislation puts a high pressure on the wastewater treatment of P&P mills. In several P&P mills the wastewater treatment is one of the factors limiting the production of pulp and paper. In addition, the wastewater is usually treated with aerobic treatment that consumes a high amount of electricity and produces sludge. To decrease the cost of the wastewater treatment and to increase the treatment efficiency, an anaerobic treatment can be used before the aerobic treatment. Advantages of having an anaerobic treatment before the aerobic treatment is that it reduces the organic loading of the aerobic treatment, valuable biogas is produced, anaerobic treatment produce less sludge and requires less electricity. However, the wastewater of P&P mills is rich in sulphate, which have resulted in an unstable biogas production. A potential solution for this to have another anaerobic reactor before the biogas producing reactor, with the purpose to remove sulphate. The aim of this project was to optimize a two-step anaerobic treatment for an effective biogas production and for a stable process. In the project, two UAPB reactors were used. The first bioreactor (hereafter pretreatment reactor) was enriched with sulphate reducing bacteria before the start of the project while the second reactor contained methanogens (hereafter biogas reactor). Wastewater from a P&P mill using the TMP process and soft wood as raw material was used in this project. The anaerobic two-step process was optimized by decreasing the HRT of both reactors, by investing alternatives to decrease the sulphide in the influent to the biogas reactor and by decreasing the addition of nutrients to the process water. The stability of the two-step process was measured by analysing the sulphate, sulphide and COD content spectrophotometrically; by analysing pH; by analysing the methane content in the headspace of the reactors with GC and by analysing the VFA content in the effluents using HPLC. The results showed that the process was stable when the HRT of the pretreatment reactor and biogas reactor was 0.3 days and 1.5 days, respectively. The removal efficiency of sulphate and COD in the pretreatment reactor was 82% and 31%, respectively. The methane content in the biogas of the PT reactor was 53% in average. The COD removal efficiency of the biogas reactor was 32% and there was in average 31% methane in the biogas. The average total COD removal efficiency of the two-step process was 61% when the reactors were coupled via a collection tank. The biomethane potential of the process water and the effluent of the pretreatment reactor was 147 NmL CH4/g VS and 47 NmL CH4/g VS, respectively. The process was stable when the HRT of the pretreatment reactor and biogas reactor was 0.3 days and 1.5 days, respectively, considering the stability of the sulphate and COD removal efficiency. However, the BMP of the effluent of the PT reactor was only 32% of the BMP of the process water and the degradability of the COD was lower in the effluent. Since the PT reactor exhibited stability at the tested conditions, it would be interesting to try it as a one-step process in a pilot UAPB reactor in the future. In the future, research is needed to investigate if the methane content in the headspace of the biogas reactor can be increased by decreasing the HRT of the reactor.

Bei der Behandlung organische Abfälle werden zunehmend Feststoff-Vergärungsverfahren mit Perkolation eingesetzt. Sie werden bevorzugt, wenn eine Vorab-Zerstörung der Feststoffstruktur nachteilig für die Gärrest-Verwendung oder sich daraus keine ökonomischen Vorteile ergeben. Das trifft auch bei strohartiger Biomasse zu. Zur satzweisen Vergärung wurden zahlreiche Erkenntnisse publiziert. Zeitgleich wurde das Sauter-Verfahren für den kontinuierlichen Betrieb zur Anwendungsreife entwickelt sowie am Leibniz-Institut für Agrartechnik und Bioökonomie e.V. (ATB) Forschungen einer zweistufigen Variante publiziert. Erstmalig erfolgt unter Verwendung von Silagen ein Vergleich der Varianten. Einflüsse der Perkolationsintensität auf Zusammensetzung und Eigenschaften der Feststoffe und der Prozessflüssigkeit sowie auf die Kinetik der Gasbildung werden untersucht. Die Perkolatzusammensetzung variiert variantenabhängig. OTS-Belastungs-Grenzen lassen sich in erster Näherung bestimmen. Geeignete Vergleichsparameter werden dargestellt. Betreiberbefragungen und messtechnische Begleitung einer Sauter-Anlage ergänzen die Arbeit. Eine differenzierte Beurteilung der Perkolationsverfahren ist nun möglich. Betrachtet werden die Feststoffdichte im Fermenter, die TS-Gehalte im Gärstock sowie der Schwimmschicht. Die Verweilzeit der partikulären Biomasse im Fermenter ist erheblich kürzer als bisher angenommen. Das beeinflusst direkt die Hydrolyserate und mittelbar die Mikroflora im Fermenter. Nähere Untersuchungen sind erforderlich. Auch bei Perkolationsverfahren beeinflusse Substratzusammensetzung und Mahlgrad die Kinetik der Gasbildung. Die Methanausbeuten unterscheiden sich nur unwesentlich von Rührkessel-Systemen. Die Erweiterung der perkolierten Vergärung durch eine Perkolat-Methanisierungsstufe sind höhere Raum-Zeit-Ausbeuten möglich. Das erlaubt eine zeitlich gesteuerte Methanerzeugung, wobei Ausmaß und Leistungsgradient weiterer Forschung bedürfen. / Numerous research findings and experience on the batchwise fermentation of stacked biomass are available. At the same time, the percolated and continuously operated Sauter-process was developed to market maturity. Research on a two-stage variant has been carried out and published by the Leibnitz Institute for Agricultural Engineering and Bioeconomics e.V. (ATB). This paper provides for the first time a direct comparison of the above-mentioned percolated process variants using maize and sedge silages. The effects of percolation intensity on composition and properties of the solids and the process fluid as well as on the gas formation kinetics are investigated in particular. Furthermore, suitable benchmarks of the variants are identified and evaluated. The link to practice is a operators questioning and a one year lasting monitoring of a Sauter plant. The findings allow a differentiated assessment of percolation processes. Findings on solid matter density as well as on dry matter content in the fermenting stock or floating layer are presented in detail. During continuous operation, particulate biomass retention time is considerably shorter than would result from usual calculation of hydraulic retention time. It is indicated that the microflora in the fermenter is also indirectly affected. This requires further research work. It is shown that in percolation processes substrate composition and extent of grinding also dominate the gas formation kinetics, albeit to different extents. Methane yields differ under comparable load and operating parameters only marginally from yields of stirred tank systems. Composition of percolate also varies variant-specific. Findings can be used to define in a first approximation limits of volatile solid load. It has been proven that percolated solid-state fermentation with an additional percolate methanization stage allows higher space-time yields. This extra stage suits also for controlled flexible methane production.

Die Dissertation setzt sich mit den fotografischen Repräsentationen der Atombombenabwürfe auf Hiroshima und Nagasaki sowie der Havarie des Kernkraftwerks Tschernobyl auseinander. Dabei werden künstlerische, dokumentarische und touristische Bilder analysiert, die sich der jeweiligen Strahlenkatastrophe oftmals erst Jahre nach dem Ereignis annehmen und ikonografische oder medial-materielle Bezüge zu ihr aufweisen. Es zeigen sich zentrale Strategien, atomare Katastrophen, seien sie militärischer oder ziviler Natur, in fotografische Bilder überzuführen. Gerade das eigentliche Unvermögen, die visuell nicht sichtbaren Strahlenemissionen oder die Komplexität der Vorgänge auf atomarer Ebene zu visualisieren, hat sich als prägend erwiesen und bestimmt als Paradigma der Unsichtbarkeit die kulturelle Rezeption der Ereignisse. Es ist dieser Umgang mit den Abstraktionspotentialen der nuklearen Technologie, die im aktuellen Spannungsfeld ökologischer, sozialer und energietechnologischer Bildpolitik ihre Relevanz stets von neuem unter Beweis stellt. / The dissertation project seeks to analyse the photographic positions that deal with the atomic bomb attacks on Hiroshima and Nagasaki and the accident of the nuclear power plant in Chernobyl. This focus includes press photographs of the events as well as artistic, documentary and touristic images that take an approach towards the disasters often years after and hereby form iconographic or material references to the events. The study reveals central strategies for photographic images of atomic catastrophes, be they of military or civil nature. It is the inability to visualize non-visible nuclear rays or the complexity of processes on an atomic level that has turned out to be crucial. This incapacity of making images, a paradigm of invisibility, substantially coins the cultural role of the events. The question of how a society deals with these abstract potentials of nuclear technology has turned out to be always anew of high relevance in regard to ecological, social and technological policies of images.

Analyses of nuclear reactor safety have increasingly required coupling of full three dimensional neutron kinetics (NK) core models with system transient thermal–hydraulics (TH) codes.  In order to produce results within a reasonable computing time, the coupled codes use two different spatial description of the reactor core.  The TH code uses few, typically 5 to 20 TH channels, which represent the core.  The NK code uses explicit one node for each fuel assembly.  Therefore, a spatial mapping of a coarse grid TH and a fine grid NK domain is necessary.  However, improper mappings may result in loss of valuable information, thus causing inaccurate prediction of safety parameters. The purpose of this thesis is to study the effectiveness of spatial coupling (channel refinement and spatial mapping) and develop recommendations for NK/TH mapping in simulation of safety transients.  Additionally, sensitivity of stability (measured by Decay Ratio and Frequency) to the different types of mapping schemes, is analyzed against OECD/NEA Ringhals–1 Stability Benchmark data. The research methodology consists of spatial coupling convergence study, by increasing the number of TH channels and varying mapping approaches, up to and including the reference case.  The reference case consists of one-to-one mapping: one TH channel per one fuel assembly.  The comparisons of the results are done for steady–state and transient results.  In this thesis mapping (spatial coupling) definition is formed and all the existing mapping approaches were gathered, analyzed and presented.  Additionally, to increase the efficiency and applicability of spatial mapping convergence, a new mapping methodology has been proposed.  The new mapping approach is based on hierarchical clustering method; the method of unsupervised learning that is adopted by many researchers in many different scientific fields, thanks to its flexibility and robustness.  The proposed new mapping method turns out to be very successful for spatial coupling problem and can be fully automatized allowing for significant time reduction in mapping convergence study. The steady–state results obtained from three different plant models for all the investigated cases are presented.  All models achieved well converged steady–state and local parameters were compared and it was concluded that solid basis for further transient analysis was found.  Analyzing the mapping performance, the best predictions for steady–state conditions are the mappings that include the power peaking factor feature alone or with any combination of other features.  Additionally it is of value to keep the core symmetry (symmetry feature).  The big part of this research is devoted to transient analysis.  The selection of transients was done such that it covers a wide range of transients and gathered knowledge may be used for other types of transients.  As a representative of a local perturbation, Control Rod Drop Accident was chosen.  A specially prepared Feedwater Transient was investigated as a regional perturbation and a Turbine Trip is an example of a global one.  In the case of local perturbation, it has been found that a number of TH channels is less important than the type of mapping, so a high number of TH channels does not guarantee improved results.  To avoid unnecessary averaging and to obtain the best prediction, hot channel and core zone where accident happens should be always separated from the rest.  The best performance is achieved with mapping according power peaking factors, and therefore this one is recommended for such type of perturbation. The regional perturbation has been found to be more challenging than the others.  This kind of perturbation is strongly dependent on mapping type that affects the power increase rate, SCRAM time, onset of instability, development of limit cycle, etc.  It has been also concluded that a special effort is needed for input model preparation.   In contrast to the regional perturbation, the global perturbation is found to be the least demanding transient.  Here, the number of TH channels and type of mapping do not have significant impact on average plant behaviour – general plant response is always well recreated.  A special effort has also been paid to investigate the core stability performance, in both global and regional mode.  It has been found that in case of unstable cores, a low number of TH channels significantly suppresses the instability.  For these cases number of TH channels is very important and therefore at least half of the core has to be modeled to have a confidence in predicted DR and FR.  In case of regional instability in order to get correct performance of out-of-phase oscillations, it is recommended to use full-scale model.  If this is not possible, the mapping which is a mixture of 1st power mode and power peaking factors, should be used. The general conclusions and recommendations are summarized at the end of this thesis.  Development of these recommendations was one of the purposes of this investigation and they should be taken into consideration while designing new coupled TH/NK models and choosing mapping strategy for a new transient analysis. / <p>QC 20130516</p>

The main goal of this dissertation was to show that the principle of atomic layer deposition (ALD) can be applied to “endless” fibers. A reactor of atomic layer deposition has been designed, especially for coating depositions onto meter long bundles of fibers. Aluminum oxide (alumina), titanium oxide (titania), double layers of alumina and titania, as well as aluminium phosphate have been deposited onto bundles of carbon fibers using the home-built reactor. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images indicate that the coatings were uniform and conformal onto fiber surface. There was a good adhesion of the coatings to the fibers. Alumina has been deposited using two separate aluminum sources (aluminum trichloride and trimethylaluminum), and water as a source of oxygen. In case of alumina deposition using aluminum trichloride and water, initial deposition temperature was 500 °C. In these conditions, a part of the fiber bundle has been damaged. Thus, the deposition temperature was decreased to 300 °C and the fibers were unaffected. In addition, during this process hydrochloric acid is formed as a byproduct which is a corrosive substance and affects the reactor and there was a chloride impurity in the coatings. Thus, aluminum trichloride precursor was replaced by trimethylalumium. Alumina deposition onto carbon fibers using trimethylaluminum and water was carried out at a temperature of 77 °C. SEM images revealed that the fibers were unaffected and the coatings were uniform and conformal. Oxidation resistance of the carbon fibers was improved slightly after alumina deposition. Oxidation onset temperature of the uncoated fibers was about 630 °C. The resistance was linearly increased with the coating thickness (up to 660 °C) and getting saturated over a thickness of 120 nm. Titania coatings have been deposited using titanium tetrachloride and water. The physical appearances of the titania coatings were similar to the alumina coatings. The oxidation onset temperature of the titania coated carbon fibers was similar to the uncoated fibers but the rate of oxidation was decreased than the uncoated fibers. Two double layer coatings were deposited, alumina followed by titania (alumina/titania), and titania followed by alumina (titania/alumina). If the fibers were coated with the double layer of alumina/titania, they had almost same oxidation onset as alumina coated fibers but the rate of oxidation was decreased significantly compared to alumina coated fibers. This feature is independent of the thickness of the titania layers, at least in the regime investigated (50 nm alumina followed by 13 nm and 40 nm titania). On the other hand, the oxidation onset temperature of fibers coated with titania/alumina (20 nm titania /30 nm alumina) was approximately 750 °C. The fibers were burned completely when temperature was further increased to 900 °C and held another 60 minutes at 900 °C. This is significantly better than any other coating used in this dissertation. ALD of titania and alumina in principle was known beforehand, this dissertation here applies this knowledge for the first time to endless fibers. Furthermore, this dissertation shows for the first time that one can deposit aluminum phosphate via ALD (planar surface as well as fibers). Aluminum phosphate might be special interest in the fiber coating because it is a rather soft material and thus might be used to obtain a weak coupling between fiber and matrix in composites. Aluminum phosphate was deposited using trimethylaluminum and triethylphosphate as precursors. Energy dispersive X-ray spectroscopy and solid state nuclear magnetic resonance spectra confirmed that the coating comprises aluminum phosphate (orthophosphate as well as other stoichiometries). Scanning electron microscopic images revealed that coatings are uniform and conformal. In cases of alumina and titania, it was observed that the coatings were delaminated from the ends of cut fibers and thus formed of clear steps. On the other hand, for aluminum phosphate coating it was observed that the border between coating and underlying fiber often being smeared out and thus formed an irregular line. It seems in case aluminum phosphate cohesion is weaker than adhesion, thus it might be act a weak interface between fiber and matrix. Alumina, titania, and double layer microtubes have been obtained after selective removal of the underlying carbon fibers. The carbon fibers were selectively removed via thermal oxidation in air at temperatures exceeding 550 °C. SEM and TEM images indicate that the inner side of the tube wall has the same morphology like the fibers. In addition, it was observed that the individual microtubes were separated from their neighbors and they had almost uniform wall thicknesses. The longest tubes had a length of 30 cm. / Das Hauptziel dieser Dissertation bestand darin nachzuweisen, dass die Atomlagenabscheidung (engl. atomic layer deposition (ALD)) auf „endlose“ Fasern angewendet werden kann. Es wurde ein Reaktor zur Atomlagenabscheidung gestaltet, der speziell für die Beschichtung meterlanger Faserbündel geeignet ist. Aluminiumoxid, Titanoxid, Doppelschichten aus Aluminiumoxid und Titanoxid sowie Aluminiumphosphat wurden mit Hilfe des selbstgebauten Reaktors auf Kohlefaserbündel abgeschieden. Rasterelektronenmikroskopische (REM) und transmissionselektronenmikroskopische (TEM) Aufnahmen zeigten, dass die Beschichtung auf den Fasern einheitlich und oberflächentreu war. Des Weiteren wurde eine gute Adhäsion zwischen Beschichtung und Fasern beobachtet. Das Prinzip der Beschichtung mit Titanoxid und Aluminiumoxid mit Hilfe der ALD war bereits vorher bekannt und im Rahmen dieser Dissertation jedoch erstmals auf "endlose" Fasern angewendet. Des Weiteren wird in dieser Dissertation erstmals gezeigt, dass es möglich ist, Aluminiumphosphat mittels ALD abzuscheiden (sowohl auf planaren Oberflächen als auch auf Fasern). Aluminiumphosphat könnte von besonderem Interesse in der Faserbeschichtung sein, da es ein relativ weiches Material ist und könnte daher als eine Art „schwacher“ Verbindung zwischen Faser und Matrix in Kompositen dienen. Die Oxidationsbeständigkeit von beschichten Kohlefasern wurde im Vergleich zu unbeschichteten Fasern bis zu einem gewissen Grad erhöht. Monoschichten von Aluminiumoxid und Titanoxid waren dafür wenig effektiv. Aluminiumphosphatbeschichtete Fasern waren deutlich besser geeignet als die beiden anderen. Eine Doppelschicht aus Titanoxid gefolgt von Aluminiumoxid verbesserte die Oxidationsbeständigkeit nochmals deutlich gegenüber allen anderen Beschichtungen, die in dieser Dissertation verwendet wurden. Mikroröhren aus Aluminiumoxid, Titanoxid und Doppelschichten wurden durch die selektive Entfernung der zugrunde liegenden Kohlefasern erhalten. Einzelne Mikroröhren waren von benachbarten Röhren getrennt und sie weisen eine nahezu einheitliche Wanddicke auf.

This diploma thesis deals with the validation of spectral average cross-sections (SACS) of 55 Mn(n,2n)54 Mn, 90 Zr(n,2n)89 Zr, 127 I(n,2n)126 I reactions in well-defined LR-0 reactor spectrum. The measurement of SACS for selected reactions is of high interest because they are used for the practical reactor dosimetry. Various experiments for description of neutron field in reactor and detector characterization, which are necessary for validation, are described. The spectral average cross-sections are derived from Net Peak Areas of irradiated samples measured using a semiconductor high purity germanium detector. Obtained result were compared with MCNP6 calculations using ENDF/B-VII.0, ENDF/B-VII.1, JEFF-3.1, JEFF-3.2, JENDL-3.3, JENDL-4, ROSFOND-2010, CENDL-3.1 and IRDFF nuclear data libraries. Notable discrepancies were found in 90 Zr(n,2n)89 Zr and 127 I(n,2n)126 I reactions. This thesis also contains a theoretical basis for the interaction of neutrons with matter.

Diploma thesis will be dealt with the utilization of ozone wastewater treatment. Experimental part will be focused on study of ozone utilization in two different reactors (bubble column, jet loop reactor). Reactors will be compared by overall mass transfer coefficient and saturation concentration. Ozonization will be applied because of biological resistent and toxic compound 2-mercaptobenzothiazole disposal. Changes of biological decomposition will be measured and assessed by respirometric measurements.