SuperCritical-Water-cooled Reactors (SCWRs) are being developed as one of the Generation-IV nuclear-reactor concepts. SuperCritical Water (SCW) Nuclear Power Plants (NPPs) are expected to have much higher operating parameters compared to current NPPs, i.e., pressure of about 25 MPa and outlet temperature up to 625 oC. This study presents the heat transfer analysis of an intermediate Heat exchanger (HX) design for indirect-cycle concepts of Pressure-Tube (PT) and Pressure-Vessel (PV) SCWRs. Thermodynamic configurations with an intermediate HX gives a possibility to have a single-reheat option for PT and PV SCWRs without introducing steam-reheat channels into a reactor. Similar to the current CANDU and Pressurized Water Reactor (PWR) NPPs, steam generators separate the primary loop from the secondary loop. In this way, the primary loop can be completely enclosed in a reactor containment building. This study analyzes the heat transfer from a SCW primary (reactor) loop to a SCW and Super-Heated Steam (SHS) secondary (turbine) loop using a double-pipe intermediate HX. The numerical model is developed with MATLAB and NIST REFPROP software. Water from the primary loop flows through the inner pipe, and water from the secondary loop flows through the annulus in the counter direction of the double-pipe HX. The analysis on the double-pipe HX shows temperature and profiles of thermophysical properties along the heated length of the HX. It was found that the pseudocritical region has a significant effect on the temperature profiles and heat-transfer area of the HX. An analysis shows the effect of variation in pressure, temperature, mass flow rate, and pipe size on the pseudocritical region and the heat-transfer area of the HX. The results from the numerical model can be used to optimize the heat-transfer area of the HX. The higher pressure difference on the hot side and higher temperature difference between the hot and cold sides reduces the pseudocritical-region length, thus decreases the heat-transfer surface area of the HX. / UOIT

Taking into account the expected increase in global energy demands and increasing climate change issues, there is a pressing need to develop new environmentally sustainable energy systems. Nuclear energy will play a major role in being part of the energy mix since it offers a relatively clean, safe and reliable source of electrical energy. However, opportunities for building new generation nuclear systems will depend on their economic and safety attractiveness as well as their flexibility in design to adapt in different countries and situations. Keeping these objectives in mind, a framework for international cooperation was set forth in a charter of Generation IV International Forum (GIF) (GIF Charter, 2002) and six design concepts were selected for further development. To achieve high thermal efficiencies of up to 45 ??? 50%, the use of SuperCritical Fluids (SCFs) as working fluids in heat transfer cycles is proposed Generation IV designs. An important aspect towards development of SCF applications in novel Gen IV Nuclear Power Plant (NPP) designs is to understand the thermodynamic behavior and prediction of Heat Transfer Coefficients (HTCs) at supercritical (SC) conditions. In addition to the nuclear power industry applications; SCFs are also expected to play a vital role in a number of other important technologies such as refrigeration systems, and geothermal systems, to name a few. Given the potential for vast number of applications of SCFs in industry, the objective of this work was to gain an understanding on the behavior of SCFs and to develop a fundamental knowledge of the heat-transfer processes and correlations for SC Water and SC CO2 flowing in bare circular tubes. Experimental datasets for SC Water and SC CO2 were compiled and used to obtain a basic 1-D empirical correlation that can predict HTC in bare circular tubes during the transient phases. The accuracy of these correlations was also analyzed using statistical techniques. Limitations and applications for 1-D correlations are discussed as well. The new correlations showed promising results for HTC and Tw calculations for the reference dataset with uncertainty of about ??25% for HTC values and about ??10-15% for the calculated wall temperature.

Previous studies have successfully used near and supercritical water (SCW) for cracking and desulfurization of heavy crude oil and bio-oil, suppressing coke formation as a low-value by-product. Some of these studies benefited from using zeolite catalysts to increase the activity and selectivity toward targeted products; however, in depth studies are required to identify the role of water on zeolite catalysis under supercritical condition. Using three common zeolites, ZSM-5, HY, and β for supercritical water cracking of dodecane at 400°C, 24±2 MPa (in a 100 ml batch reactor), we showed that ZSM-5 is the only catalyst that partially retains its crystalline structure and activity under hydrothermal conditions. Further characterization of the ZSM-5 (used under 50/50 wt% SCW/dodecane feed) revealed 95% decrease in Brønsted acid site (BAS) density and 80% decrease in microporous area after 2 h reaction time. However, compared to the runs where SCW was absent, the apparent dodecane cracking rate constant in SCW decreased only by a factor of 2.6. Examining catalytic activity of ZSM-5 degradation products and re-using ZSM-5 showed that the unexpected activity cannot be ascribed to ZSM-5 degradation products. Using a group-type model, we showed that SCW accelerated gas and suppressed coke formations. Additionally a coke gasification pathway was suggested to account for formation of CO and CO2 in the presence of SCW. Additional experiments with two different ZSM-5 particle sizes suggested that dodecane cracking reaction is diffusion-limited in the absence of SCW and reaction-limited in its presence. Zero length chromatography of calcined and hydrothermally treated ZSM-5 showed 10 times greater apparent diffusivity for un-treated catalyst. This, according to Weisz-Prater analysis, suggested a 250 times greater dodecane surface concentration in the absence of SCW. We successfully optimized the water content of feed (5-15 wt%) to decrease the destructive effects of SCW on the structure, increase the selectivity toward BTEX products and eliminate coke formation.

There has been an exponential increase of plastics being produced, used, and disposed of over the last 60 years. Most of plastic waste (76%) is consigned to landfills, 12% is incinerated, 3% ends up in the oceans while only 9% is recycled. If the current trend continues, more than 30 billion tons plastic waste will be generated on this planet and more plastic than fish will be in the oceans by 2050. Plastics take more than 100 years to degrade into plastic debris, microplastics, and toxic chemicals, which pose serious threats to the ecosystems, water and food supply, and eventually human health.<br>Polyolefins (Type 2 HDPE, Type 4 LDPE, and Type 5 PP), which are the majority (63%) of global plastic waste, are targeted in this study. Two methods, Hydrothermal Processing (HTP) and Sequential Selective Extraction and Adsorption (SSEA) were developed and tested. HDPE was converted into wax and oils using supercritical water under HTP at reaction temperature 400- 450 °C with reaction time 0.5- 3 hr. PP was converted into oils under supercritical water at 425 °C with reaction time 1- 3 hr. The oil products from HDPE and PP via HTP were composed of paraffins, olefins, cyclics, and aromatics with carbon numbers from C6 to C31. Reaction intermediates were analyzed using two-dimensional gas chromatography with a flame ionization detector (GC × GC-FID). The results were used to establish potential reaction pathways of HDPE and PP, respectively. PP was found to react faster than HDPE under the same HTP conditions while generating more olefins and cyclics than HDPE. Clean wax was obtained from PE waste via HTP. Its Fourier-Transform Infrared Spectroscopy (FT-IR) spectrum was almost identical to the one of commercial paraffin wax. Oils converted from PE waste via HTP was distilled into three fractions. The diesel-like fraction (170 °C≤ b.p. < 300 °C) has similar properties as No.1 ultra-low-sulfur diesel. It also can be used as a blendstock for No2. Ultra-low-sulfur diesel.<br>SSEA methods were developed to recover pristine polymers from polyolefin waste via extraction and adsorption. Mixed solvents with higher selectivity, reduced toxicity, and lower costs were found based on their Hansen Solubility Parameters. Extraction conditions were investigated using model polyolefins. Selective mixed solvents were found for the separation of LLDPE from LLDPE/PP blend. Pristine PE polymers were recovered from dark green PE waste pellets.<br>Preliminary analyses indicated HTP and SSEA have a higher energy efficiency and lower greenhouse gas (GHG) emissions than incineration, mechanical recycling, and pyrolysis. A combination of these two methods has the potential to convert 63% of the plastic waste into useful and profitable products. It also helps transform current linear path from crude oil to plastics to landfills, to a more sustainable circular path.<br>

Previous studies have successfully used near and supercritical water (SCW) for cracking and desulfurization of heavy crude oil and bio-oil, suppressing coke formation as a low-value by-product. Some of these studies benefited from using zeolite catalysts to increase the activity and selectivity toward targeted products; however, in depth studies are required to identify the role of water on zeolite catalysis under supercritical condition. Using three common zeolites, ZSM-5, HY, and β for supercritical water cracking of dodecane at 400°C, 24±2 MPa (in a 100 ml batch reactor), we showed that ZSM-5 is the only catalyst that partially retains its crystalline structure and activity under hydrothermal conditions. Further characterization of the ZSM-5 (used under 50/50 wt% SCW/dodecane feed) revealed 95% decrease in Brønsted acid site (BAS) density and 80% decrease in microporous area after 2 h reaction time. However, compared to the runs where SCW was absent, the apparent dodecane cracking rate constant in SCW decreased only by a factor of 2.6. Examining catalytic activity of ZSM-5 degradation products and re-using ZSM-5 showed that the unexpected activity cannot be ascribed to ZSM-5 degradation products. Using a group-type model, we showed that SCW accelerated gas and suppressed coke formations. Additionally a coke gasification pathway was suggested to account for formation of CO and CO2 in the presence of SCW. Additional experiments with two different ZSM-5 particle sizes suggested that dodecane cracking reaction is diffusion-limited in the absence of SCW and reaction-limited in its presence. Zero length chromatography of calcined and hydrothermally treated ZSM-5 showed 10 times greater apparent diffusivity for un-treated catalyst. This, according to Weisz-Prater analysis, suggested a 250 times greater dodecane surface concentration in the absence of SCW. We successfully optimized the water content of feed (5-15 wt%) to decrease the destructive effects of SCW on the structure, increase the selectivity toward BTEX products and eliminate coke formation.

No description available.

No description available.

<p>The supercritical water cooled reactor (SCWR) is a Generation IV reactor concept that features light water coolant in a supercritical state. Canada is developing a pressure tube variant of the supercritical water reactor as an evolution of the CANDU reactor. The main advantages of the pressure tube SCWR are an improved thermal efficiency over current reactors, enhanced safety through passive safety features, and plant simplifications. The objective of this thesis was to investigate current fuel and core designs for the Canadian SCWR concept.</p> <p>Simulations of 2-D lattice cells for fuel assemblies containing 43 and 54 fuel elements were performed using the neutron transport code WIMS-AECL. Safety parameters and fuel burnup performance were investigated here. Three dimensional full core simulations were performed using the diffusion code RFSP. These studies examined batch fueling, cycle length, radial and axial power profiles, linear element ratings, and reduction of axial power peaking through graded enrichment along the fuel channel. Finally, a study of reactivity transients was performed using the FUELPIN heat transfer/point kinetics code.</p> <p>The main results of the studies show that the coolant density change that occurs as water passes through the pseudocritical point strongly affects fuel performance. It is concluded that the 54 element assembly design is acceptable in terms of coolant void reactivity performance with lattice pitch smaller than 26 cm. To meet the burnup target, a fuel enrichment of about 5% is required. From the RFSP studies, this level of fuel enrichment will provide an operating period of 370 days between refueling. Relatively high axial power peaking is observed at the beginning of cycle conditions. A main finding is that the proposed reactor power level of 2540 MWth produces unacceptably high linear element ratings. This is confirmed using the FUELPIN code. A reduction in linear element rating is suggested for consideration.</p> / Master of Applied Science (MASc)

A gaseificação utiliza o conteúdo intrínseco de carbonos e hidrogênios das matérias primas sólidas ou líquidas na geração de uma mistura de hidrogênio (H2), monóxido de carbono (CO), dióxido de carbono (CO2) e metano (CH4). Tal mistura pode ser utilizada como matéria prima na síntese de novos produtos ou como combustível. A gaseificação pode ser utilizada no processamento de uma gama variada de produtos, independentemente de suas características ou estado físico. A utilização de biomassa como insumo da gaseificação vem sendo cada vez mais explorada e estudada, já que apresenta benefícios não somente na esfera ambiental, mas também em âmbitos econômicos e sociais. A vinhaça é um subproduto do processo de produção de álcool, que contém grandes concentrações de nutrientes e matéria orgânica em sua composição. A sua utilização hoje está limitada a fertirrigação e a aplicações isoladas em biodigestão e outros, que não são suficientes para o consumo da produção anual crescente do resíduo. Seu uso na gaseificação permitiria o aproveitamento do conteúdo orgânico da mesma e a produção de gases de alto valor agregado. Como a umidade do insumo interfere negativamente na eficiência da gaseificação clássica, a aplicação da mesma para matérias primas com alto teor de líquidos não é recomendada. Uma alternativa viável seria a utilização do meio gaseificante supercrítico, que resulta em rendimentos constantes, independentemente da umidade da corrente de entrada do reator. O presente trabalho consiste no projeto de um módulo de gaseificação de vinhaça em água supercrítica, a ser instalado como uma unidade anexa a usinas de açúcar e álcool. Ele compreende o projeto conceitual e análise de viabilidade deste módulo, incluindo estimativas de CAPEX (Capital Expenditure) e OPEX (Operation Expenditure) e uma análise de sensibilidade dos mesmos. O estudo apresenta ainda o estado da arte do conhecimento e da tecnologia de gaseificação com água supercrítica (SCWG), relacionando os gargalos a serem resolvidos, assim como os ganhos intrínsecos da definição conceitual do projeto. / The gasification process uses the carbon and hydrogen content in a given solid or liquid feedstock to produce a gaseous mixture of hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2) and methane (CH4). This mixture can be used as a precursor in the synthesis of new products or directly as a fuel. The gasification can be used in the processing of a wide range of materials, regardless of its characteristics or physical state. The use of vinasse as a gasification feedstock has been increasingly explored and studied, since its appeal lies not only on the environmental sphere, but as well on economic and social scope. Vinasse is a byproduct of the ethanol/ sugar producing process and contains large concentrations of nutrients and carbon organic matter in its protein-rich composition. The use of this fluid is limited today to fertirrigation and isolated applications, that are not enough for the consumption of its growing production. The possibility of gasifying the vinasse would allow a more profitable use of the fluid. In the classical gasification, the moisture content of the product being gasified impairs the yield of the reaction. So, for liquid feedstock its use is not recommended. One viable alternative for this case would be the use of the supercritical water as a reaction medium, which results in constant yields regardless of the moisture content of the raw material. This work consists on the design of module for vinasse gasification in supercritical water, to be installed as a unit, attached to an alcohol/ sugar plant. It comprises the conceptual design and feasibility study of the module, including CAPEX and OPEX estimates, plus a sensitivity analysis. The study also presents the state of the art of the knowledge associated to SCWG technology, relating bottlenecks to be solved, as well as the intrinsic gains from conceptual design definition.

The SuperCritical Water-cooled nuclear Reactor (SCWR) is one of six Generation-IV nuclear-reactor concepts currently being designed. It will operate at pressures of 25 MPa and temperatures up to 625°C. These operating conditions make a SuperCritical Water (SCW) Nuclear Power Plant (NPP) suitable to support thermochemical-based hydrogen production via co-generation. The Copper-Chlorine (Cu‒Cl) cycle is a prospective thermochemical cycle with a maximum temperature requirement of ~530°C and could be linked to an SCW NPP through a piping network. An intermediate Heat eXchanger (HX) is considered as a medium for heat transfer with operating fluids selected to be SCW and SuperHeated Steam (SHS). Thermalhydraulic calculations based on an iterative energy balance procedure are performed for counter-flow double-pipe design concept HXs integrated at several locations on an SCW NPP coolant loop. Using various test cases, design and operating parameters are recommended for detailed future research. In addition, predicted effects of heat transfer enhancement on HX parameters are evaluated considering theoretical improvements from helically-corrugated HX piping. The effects of operating fluid pressure drop are briefly discussed for applicability in future studies. / UOIT