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A printed circuit steam generator (PCSG) is being considered as the component for pressurized water reactor (PWR) type small modular reactor (SMR) that can further reduce the physical size of the system. Since a steam generator in many PWR-type SMR generates superheated steam, it is expected that dryout front oscillation can potentially cause thermal fatigue failure due to cyclic thermal stresses induced by the transition in boiling regimes between convective evaporation and film boiling. To investigate the fatigue issue of a PCSG, a reference PCSG is designed in this study first using an in-house PCSG design tool. For the stress analysis, a finite element method analysis model is developed to obtain the temperature and stress fields of the designed PCSG. Fatigue estimation is performed based on ASME Boiler and pressure vessel code to identify the major parameters influencing the fatigue life time originating from the dryout front oscillation. As a result of this study, the limit on the temperature difference between the hot side and cold side fluids is obtained. Moreover, it is found that the heat transfer coefficient of convective evaporation and film boiling regimes play an essential role in the fatigue life cycle as well as the temperature difference.

The lack of plant-side energy storage analysis to support nuclear power plants (NPP), has setup this research endeavor to understand the characteristics and role of specific storage technologies and the integration to an NPP. The paper provides a qualitative review of a wide range of configurations for integrating the energy storage system (ESS) to an operating NPP with pressurized water reactor (PWR). The role of ESS technologies most suitable for large-scale storage are evaluated, including thermal energy storage, compressed gas energy storage, and liquid air energy storage. The methods of integration to the NPP steam cycle are introduced and categorized as electrical, mechanical, and thermal, with a review on developments in the integration of ESS with an operating PWR. By adopting simplified off-design modeling for the steam turbines and heat exchangers, the results show the performance of the PWR steam cycle changes with respect to steam bypass rate for thermal and mechanical storage integration options. Analysis of the integrated system characteristics of proposed concepts for three different ESS suggests that certain storage technologies could support steady operation of an NPP. After having reviewed what have been accomplished through the years, the research team presents a list of possible future works.

From the very first time that graphene was used as a transparent electrode for OLED applications, the emergence of active-matrix (AM)-graphene OLED displays has been envisioned. Realizing this expectation, however, turned out to be difficult. Two obstacles are the growth and transfer of a large-area graphene film and the patterning of a graphene film into pixels. To solve these problems, a process of patterning a graphene film without surface contamination was developed. The fabrication of OLED panels by the patterned graphene anode on Gen 2(370 × 470 mm)-sized and flexible substrates was successfully demonstrated. In this work, oxide TFT arrays were combined as a switching backplane, and a pixelated graphene OLED was used as an emissive layer, to realize AM-graphene OLED displays. To explore the technical feasibility of flexible AM-graphene OLED displays, the aforementioned components were formed on a flexible substrate. For commercial-level production, all the processes that were used were chosen to be compatible with the conventional display processes.

A nuclear power plant is one of the power sources that shares a large portion of base-load. However, as the proportion of renewable energy increases, nuclear power plants will be required to generate power more flexibly due to the intermittency of the renewable energy sources. This paper reviews a layout thermally integrating the liquid air energy storage system with a nuclear power plant. To evaluate the performance realistically while optimizing the layout, operating nuclear power plant conditions are used. After revisiting the analysis, the optimized performance of the proposed system is predicted to achieve 59.96% of the round-trip efficiency. However, it is further shown that external environmental conditions could deteriorate the performance. For the design of liquid air energy storage-nuclear power plant integrated systems, both the steam properties of the linked plants and external factors should be considered.

To facilitate the energy transition, the conventional baseload nuclear power must be equipped with flexibility. By integrating grid-scale energy storage systems to the existing nuclear plants, they can curtail their load to avoid surplus generation. Liquid air energy storage (LAES) has been steadily investigated for their advantages, and this paper suggests an integrated layout using mechanical drive steam turbine and packed bed energy storage systems. Possible options for integration of LAES to the existing nuclear steam cycle are considered. The performance of packed bed storage systems is analyzed using transient modeling, and the results are fed into the overall cycle design using an in-house code. The results of the analysis suggests that the concept can reach up to 45.7–59.8% in round-trip efficiency, under much simplified cycle layout than the reference LAES layouts.

Air pollution sensors based on organic transistors have attracted much interest recently; however, the devices suffer from low responsivity and slow response and recovery rates for gas analytes. These shortcomings are attributed to the low charge-carrier mobility of organic semiconductors and to a structural limitation resulting from the use of a thick and continuous active layer. In the present work, we investigated the material properties of a multiscale porous zeolitic imidazolate framework, [Zn(2-methylimidazole)2]n (ZIF-8), and examined its potential as an analyte channel material inserted at an organic-transistor active layer. A series of carbonized zeolitic imidazolate frameworks (ZIFs) were prepared by thermal conversion of ZIF-8 and also studied for comparison. The microstructures, morphologies, and optical/electrical characteristics of polythiophene/ZIF-8 hybrid films were systematically investigated. Organic-transistor-type nitrogen dioxide sensors based on the polythiophene/ZIF-8 hybrid films showed substantially improved sensing properties, including responsivity, response rate, and recovery rate. The electrical conductivity of the carbonized ZIF-8s enhanced the field-effect mobility of the organic transistors; however, the sensing performance was not improved, because of the closed pore structures resulting from the carbonization. These results provide invaluable information and useful insights into the design of transistor-type gas sensors based on organic semiconductor/metal-organic framework hybrid films.

A supercritical CO2 (S-CO2)-cooled Brayton cycle is under development for distributed power applications for remote regions. In order to successfully develop it, issues of controlling shaft levitation with bearings have to be solved. From several studies, magnetic bearings have been suggested for reliable levitation performance with reduced cost and complexity. However, several studies on magnetic bearing show that instability issues under high-pressure fluid and high-speed operating conditions may exist. The purpose of this research is to provide background for understanding the instability of magnetic bearings under S-CO2 conditions and propose functional requirements of the magnetic bearing. Thus, the rotating shaft with magnetic bearings operating under high pressure fluid was first analyzed. To test the theory, a magnetic bearing test rig was constructed. By comparing experimental data to the analysis results, the analysis results were verified. Therefore, the analysis results can be used for predicting instability in the future and can contribute to the development of better magnetic bearing controllers.

Operation with reduced number of operators is considered as an important operational mode to improve economics of a nuclear power plant (NPP) in the future and it will be more important for the small modular reactors (SMRs). To control NPPs efficiently and safely with a reduced number of operators, an intelligent operation system can be very useful. However, reduced number of operators will result in larger consequence in human error due to simultaneous multi-unit failures are now more probable than the conventional operational mode. Thus, to decrease the probability of human error occurrence for the reduced number of operators, the development of an autonomous operation system with certain level of intelligence is inevitable. The prediction capability of system’s behavior as well as understanding the root cause for the current situation should be an essential function of the designed autonomous operation system. The authors propose to use the current system thermal–hydraulic (STH) analysis code platform to develop such intelligence. As a demonstration of the suggested method, the authors used the STH code to track the accident initiator of both large pressurized water reactor (PWR) and SMR. The discussions on how this method can be useful for future NPP operation and how generic differences in system design actually influence the system behavior are presented.

Reactive oxygen species levels in semen with low quality increased from 25% to about 40%. Resveratrol (Res) is a natural grape-derived phytoalexin, and epigallocatechin-3-gallate (EGCG) is the major polyphenol in green tea (Camellia sinensis); both molecules are known to have high levels of antioxidant activity. The aim of this study was to investigate the effects of this antioxidant's supplementation on cryopreservation of stallion semen with poor quality. Experiment 1: Experiment design to asses stallions semen quality (n = 3). Arabian stallions were managed for breeding with fresh, extended, or chilled semen during 2 years (in two breeding season) with a resulting per cycle pregnancy rate (103/41 estrus cycle/conception) of 39.80%. A total of 81 ejaculates were collected and evaluated in fresh condition (total and progressive motility, membrane integrity, acrosome defects, morphology, and abnormal DNA condensation). Evaluation of several ejaculates revealed that sperm production and semen quality mostly did not change during the breeding season, maintaining normal sperm production with poor quality. Experiment 2: 18 ejaculates, collected with Missouri model artificial vagina from Arabian stallion (n = 3). Extended semen was centrifuged at 600 × g for 10 minutes. To eliminate individual stallion variability, the resulting sperm pellets were pooled and divided in seven different treatments in a final concentration of 100 × 106 sperm/mL by using semiskimmed milk extender containing no supplements (control), and the following supplements with three different concentrations: Res 5, 10, and 20 μM (Res 1, Res 2, Res 3, respectively) and EGCG 25, 50, 100 μM (EGCG 1, EGCG 2, and EGCG 3, respectively). After thawing, all samples were maintained at 37°C for 10 minutes. Evaluation of motility, plasma membrane integrity, viability, mitochondria activity, DNA fragmentation, and lipid peroxidation was determined. For all semen parameters, the lower concentration of Res (5 μM) and EGCG (25 μM) did not show significant differences compared to control (P > .05). Relative to the control group, Res 2 had better (P

The significant increase of renewable energy source is expected to induce stability issue of electric grid due to the intermittency of renewable energy. The challenge of intermittency is making energy storage system more important. Among the grid-scale energy storage systems, a Liquid Air Energy Storage System is increasingly popular with its high energy density, long expected service lifetime, less operation and maintenance cost, and less geographical constraint. At the same time, flexibility of nuclear power plant is becoming more important with higher penetration of renewable energy sources. However, load-following operation not only causes safety issues on the fuel integrity, but also leads to economic deterioration of nuclear power plant. In this study, the new concept is suggested by mechanically integrating nuclear steam cycle and liquid air energy storage system to achieve high flexibility and economy of a nuclear power plant. At off peak hour, nuclear energy is stored by bypassing steam from nuclear steam cycle to external steam turbine which mechanically connected to air compressor in the liquid air energy storage system. Air is compressed by air compressor and liquefied by cold energy storage system. At peak hours, the stored energy is recovered by evaporating and expanding. The thermodynamic and economic analyses are conducted on standalone liquid air energy storage system and nuclear integrated liquid air energy storage system to further examine the benefits of the proposed system. The results show that the round-trip efficiency of the proposed system is around 51% and the energy density is 116 kWh/m3. The round-trip efficiency is competitive and the energy density is superior to other grid-scale energy storage system. Also, the integration improves the capacity factor of nuclear power plant by 3%p. The Levelized Cost of Electricity shows $219.8/MWh for standalone liquid air energy storage system and $182.6/MWh for nuclear integrated liquid air energy storage system, reducing 17% of the standalone systems’ cost. The results show that the proposed concept can achieve better economy than using standalone liquid air energy storage system as well as other energy storage systems. In conclusion, the proposed nuclear integrated liquid air energy storage system has very good potential to become a competitive energy storage option and can assist to stabilize the future electricity grid with high reliance on renewable energy.

The new application of phase change material for passively cooling the containment building of a nuclear power plant provides many benefits such as minimized wall penetration, low maintenance cost, and the possibility of installation in currently operating power plants with a minimal design change. In this study, the applicability of PCM as a passive containment cooling system is verified through design and evaluation of the PCM condenser. In addition, the effective heat capacity method is verified for simulating the melting process of PCM in the condition of a reactor accident. The PCM condenser design is optimized with five design parameters; melting point, volume, heat transfer area, effective thermal conductivity, and total heat absorbed. The performance of the PCM condenser is evaluated by containment safety analysis and is compared to that of an active containment cooling system. Although the PCM condenser had a limitation for absorbing only a fixed amount of thermal energy due to the absence of an external heat sink, the PCM condenser shows better performance in the early stage after the accident initiation compared to the single spray system and finally maintains the integrity of the containment building.

This chapter delineates the technical issues and integration scheme related to the use of graphene as a transparent electrode in organic light–emitting diode (OLED) applications. We address fundamental issues related to the use of graphene electrode in OLED. Later, we deal with patterning of graphene films into pixels on array scale and their integration into OLED panels. In this course, we emphasize the importance of strong adhesion of graphene film to its support and geometrically correct patterning. Finally, we demonstrate a fully operational two-color OLED module and a flexible OLED module. Our results signify the technical possibility of using graphene films as actual components in commercial OLED products.

A methodology is developed for thermal-hydraulic analysis and design of a breed-and-burn molten salt reactor (BBMSR). By using separate fuel and coolant molten salts, the BBMSR is proposed to overcome key materials limitations of traditional breed-and-burn and molten salt reactor designs. The BBMSR fuel concept includes an inner wall that divides the ascending and descending flows of naturally convecting fuel salt. A finite-difference model (FDM) is developed to iteratively solve for the temperature and velocity distributions in both sections of the concentric fuel. The FDM is used to perform parametric studies of the effect of fuel geometry and heat generation rate on the heat transfer performance of the fuel. The FDM is then integrated into a design search algorithm that identifies the operational limits for a given BBMSR fuel geometry, within a set of defined constraints. A range of thermal-hydraulic fuel design options are evaluated, and trade-off studies are performed to identify the most promising fuel design space for competitive power production and neutronic efficiency in the BBMSR.

After the Fukushima accident, the importance of an emergency power supply for a nuclear power plant has been emphasized more. In order to maximize the performance of the existing emergency power source in operating nuclear power plants, adding a waste heat recovery system for the emergency power source is suggested for the first time in this study. In order to explore the possibility of the idea, a comparison of six supercritical carbon dioxide (S-CO2) power cycle layouts recovering waste heat from a 7.2 MW alternate alternating current diesel generator (AAC DG) is first presented. The diesel engine can supply two heat sources to the waste heat recovery system: one from exhaust gas and the other from scavenged air. Moreover, a sensitivity study of the cycles for different design parameters is performed, and the thermodynamic performances of the various cycles were evaluated. The main components, including turbomachinery and heat exchangers, are designed with in-house codes which have been validated with experiment data. Based on the designed cycle and components, the bottoming S-CO2 cycle performance under part load operating condition of AAC DG is analyzed by using a quasi-steady state cycle analysis method. It was found that a partial heating cycle has relatively higher net produced work while enjoying the benefit of a simple layout and smaller number of components. This study also revealed that further waste heat can be recovered by adjusting the flow split merging point of the partial heating cycle.

With increasing demand for transparent conducting electrodes, graphene has attracted considerable attention, owing to its high electrical conductivity, high transmittance, low reflectance, flexibility, and tunable work function. Two faces of single-layer graphene are indistinguishable in its nature, and this idea has not been doubted even in multilayered graphene (MLG) because it is difficult to separately characterize the front (first-born) and the rear face (last-born) of MLG by using conventional analysis tools, such as Raman and ultraviolet spectroscopy, scanning probe microscopy, and sheet resistance. In this paper, we report the striking difference of the emission pattern and performance of transparent organic light-emitting diodes (OLEDs) depending on the adopted face of MLG and show the resolved chemical and physical states of both faces by using depth-selected absorption spectroscopy. Our results strongly support that the interface property between two different materials rules over the bulk property in the driving performance of OLEDs.

Although the number of meshes and their distribution are important parameters that affect both computation resources and the accuracy of the numerical results, meshing of most of all computational problems still depends highly on the users’ experiences. In this paper, a deterministic adjoint-based method of optimizing mesh distribution is proposed. The developed method is applied to a nuclear power plant safety analysis. The mesh optimization was performed with 1D steady state cylindrical nuclear fuel problem first. Radial and axial mesh distributions are optimized respectively. With no surprise, the optimized mesh system performs superior than the same number of uniformly meshed system. However, it was unexpected that the optimized mesh retains generality and therefore, the optimized mesh system can be still the best mesh system for given number of meshes under different condition or even during transient analysis. The authors applied the optimized mesh distribution to nuclear system safety analysis. A large pressurized water reactor cold leg guillotine break (LBLOCA) scenario was analyzed and the consequence of different mesh systems is investigated and discussed. From this preliminary study the usefulness and implication of the adjoint based mesh optimization method for the nuclear safety analysis is uncovered.

As the share of renewable energy will be increasing, there is a growing interest in flexible power sources and energy storage systems due to the intermittent nature of renewable energy. We propose the Energy Storage System (ESS) integrated Nuclear Power Plant (NPP) as a solution. The system operates on load-following by branching the mass flow from the steam cycle to the ESS without changing the reactor thermal output. However, the merging point can be different for heat storing ESS and work storing ESS because the outlet conditions of the ESS vary depending on the type of ESS. In this study, the merging points are categorized into two types, feedwater heater and condenser. At each merging point, cycle optimization is performed while increasing the branch flow into ESS. The optimization goal is to maintain the feedwater temperature at the inlet of a steam generator. The power output and energy delivered to the ESS according to the merging point are estimated. From this study, it was found that when 25% of the inlet mass flow rate to the low-pressure turbine is diverted to ESS, the overall output of the steam cycle is decreased by 44.17% for the heat conversion ESS and 49.95% for the work conversion ESS.

A Supercritical CO2 (S-CO2) power cycle is one of the next generation power conversion cycles, which has many advantages originate from unique fluid’s characteristics near the critical point. Recently, a concept of small modular nuclear reactor (SMR) coupled with an S-CO2 power cycle is proposed to target aggressively expanding SMR market. However, many components of S-CO2 power cycle were designed with the experiences from the conventional fluids such as air and water. In this paper, in order to harness the full potential of the S-CO2 power cycle by utilizing the fluid properties further, an S-CO2 compressor with different characteristics from air compressor is evaluated in the viewpoint of system level. The analyzed compressor has a larger backswept angle in the impeller than the conventional compressor and this can be done due to the unique properties of S-CO2. A 10 MW scale SMR is selected to demonstrate the compressor’s effect on the system performance and control. As a result, S-CO2 cycle with larger backswept angle compressor can be regulated by inventory control in a wider load variation because the system has low surging mass flow rate. Thus, the system with larger backswept angle compressor has 5.6% wider part-load performance range with inventory control alone than the system with conventional compressor.

In the event of a core meltdown in a high-power reactor, the integrity of the reactor pressure vessel is presumably protected by severe accident mitigation systems such as in-vessel retention external reactor vessel cooling (IVR-ERVC). However, in the late phase of the accident, two possible locations on the RPV are prone to failure: the location of the focusing effect and location of in-core instrument penetration. These two potential points of damage in the RPV are investigated in this study. A numerical model for the prediction of the natural convection, melting, and solidification processes for IVR-ERVC is presented. The model is based on the enthalpy-porosity approach with an extension for continuous liquid fraction function. The model is implemented in open-source field operation and manipulation (OpenFOAM) computational fluid dynamic code to produce a new solver which is based on the combination of conjugate heat transfer solver and buoyant-driven natural convection solver and the new solver is validated against the melting Gallium experimental test, in-core instrumentation failure experimental test, and BALI experimental test. This numerical model is applied for the investigation of the RPV rupture at the location of the focusing effect and in-core instrumentation penetrations. Severe ablations of the cladding and the weld materials are observed at a heat load of about ~1800 K which is expected to lead to the ejection of the penetration tubes if the force holding the penetration tube in place is lower than the force exerted by the system pressure. Subsequently, a two-layer IVR configuration is assessed and the integrity of the RPV is found not to be compromised under external reactor vessel cooling. However, in the case of a boiling crisis, the temperature of the ex-vessel wall is expected to rise quickly and this is simulated by increasing the ex-vessel wall temperature. The RPV is found to fail near the beltline due to a phenomenon known as focusing effect when the ex-vessel wall temperature rises above 1200 K.

In a sodium-cooled fast reactor, a sodium-water reaction (SWR) could be occurred at pressure boundaries between the two separated systems, the steam Rankine cycle and the sodium coolant system, which results in a serious problem in the system. Since it has been a design challenge for researchers, as an alternative system, the supercritical CO 2 (S-CO 2 ) Brayton cycle was suggested. To utilize the S-CO 2 Brayton cycle to a SFR, a series of studies on the coupled system have been conducted at Korea Atomic Energy Research Institute (KAERI). The studies were mainly focused on the pressure boundary failure events and their consequences including Na-CO 2 reactions. Prior to the experimental studies, the authors classified the reaction behaviors of Na-CO 2 reaction based on the possible scenarios that could take place at pressure boundaries. Through experimental studies, it was found that the reaction follows typical chemical formulas and it is essentially dependent on the reaction temperature. More importantly, the reaction rate changed drastically at the specific temperatures and the reaction became flammable exceeding a certain temperature. To specify the design conditions of the SFR system coupled with the S-CO 2 Brayton cycle, by means of a dedicated set-up the self-ignition temperature has been evaluated. Exceeding this threshold temperature a significant increase in the reaction speed is observed. We setup an experimental apparatus and a test matrix based on one of possible scenarios where the flammable Na-CO 2 reaction takes place and we installed a visualized chemical reactor to watch reaction phenomenon around the self-ignition temperature. The experimental apparatus was designed to be easy to control heaters, to regulate gas supply, and to measure reaction temperature. Through the experiment, it was found that the flammable temperature of Na-CO 2 reaction lies between 598.3˚C and 599.9˚C and how liquid sodium reacts with gaseous carbon dioxide at these temperatures. The results will be help to set design criteria for the pressure boundary and it will take long time but an appropriate safety system would be introduced.

Organic wrinkle structures are investigated as an internal scattering layer for the fabrication of highly efficient organic light-emitting diodes (OLEDs). The solution-processed wrinkle structures are planarized with a high-index layer, resulting in a reduced surface roughness and optical haze simultaneously. The OLED device including the wrinkle structures achieved external quantum efficiency (EQE) of 24.2%, corresponding to a 1.24 time enhancement with respect to that of a control device having no internal scattering layer. By attaching a micro lens array (MLA) or a half ball lens (HBL) on the external surface of the substrate, the proposed device exhibits an EQE of 30.5% (1.56 time enhancement) and 41.8% (2.14 time enhancement), respectively. Randomness of the distributed wrinkle structures is shown to provide additional benefits of reduced angular spectral distortion and Lambertian-like emission properties. Trans-scale optical simulation combining wave-optics and the geometrical effect are used for the quantitative analysis of the emission characteristics of the device.

To realize transparent organic light-emitting diodes (OLEDs), a top electrode should have excellent optical, electrical, and mechanical properties. Conventionally, transparent conductive oxides and semitransparent metal have been widely used for transparent top electrodes, but they have several fundamental drawbacks. We herein report efficient large-area inverted transparent OLEDs using a vacuum-laminated top electrode with an embedded metal mesh. The laminated device with 1 mm pitch exhibits superior optical properties including a high transmittance of 75.9% at 550 nm, a low reflectance of 12.0% at 550 nm, and spectrally flat characteristics over the entire visible region and shows nearly ideal Lambertian angular emission characteristics with little angular color shift in both directions. Moreover, the lowered sheet resistance of 4 Ω/sq originating from the embedded metal mesh (1 mm pitch) led to efficient and uniform emission characteristics. As a result, the device shows a relatively high maximum curre...

In this paper, a new light-adaptable display (LAD) structure with minimum power consumption is proposed for the future advertising service, and the demonstrated results are reported. An organic light-emitting diode with color reflection (colored OLED) was applied for the reflective- and emissive-mode device, and a guest-host liquid-crystal device (GH-LC) was adopted for the light shutter device. The current efficiency and reflectance of the colored OLED were 35.15 cd/A at 457 cd/m2 luminance and 63% for the yellow color, respectively. The measured contrast ratio of GH-LC was 15.5:1 at dark-room conditions, respectively. Transparent oxide thin-film transistors were used for the backplane, and their average mobility was 9.08 cm2/V s, with a 0.5 standard deviation. Through the optimization of the fabrication process and the structures of each device, the LAD adaptively operating according to the environmental illuminance from dark to 10,000 nits was successfully demonstrated. Moreover, a new LAD driv...

With the increasing emphasis on reducing the CO2 emission while improving power generation efficiency, new power cycles are being developed. One of those promising power cycles is a supercritical CO2 (S-CO2) power cycle. To generate over 10MW electricity with S-CO2 power cycle, a magnetic bearing can be a good option for the hermetic type turbomachinery. However, from several studies on the magnetic bearing, the instability issues under high density fluid and high speed operating conditions were repeatedly mentioned. The instability in the magnetic bearing was observed to be related to the fluid conditions, mostly pressure and density. Because of this issue, the magnetic bearing sometimes cannot maintain enough clearance for the rotor leading to physical contact and consequently damaging the system. Thus, these instability issues should be thoroughly studied and be resolved for the successful and steady operation of the power system. The instability due to fluid force around the rotating shaft can be modeled with the Reynolds lubrication equation. The steady lubrication force analysis model is developed based on this equation. The model results imply that the lubrication performance is quite sensitive to the thermal condition of the CO2 especially density gradient around the shaft. Based on the modeling results, an experimental system is designed to investigate the issue. To study the instability issues experimentally, an impeller of the operating S-CO2 compressor is removed and the discharge line is blocked. Therefore, the main instability factor in this experiment will be the interaction between the rotor and the bearing only. The shaft position can be measured with inductive sensors. The forces exerted from the electromagnet is calculated from the electric current data which is applied by the controller. From these experimental data, the lubrication force is calculated. These results are compared with the analytical lubrication model to verify the model. From this study, it is expected that it will be possible to define the unstable operating conditions and suggest the required magnetic bearing performance for S-CO2 conditions.

A switchable diffraction device capable of driving with segment electrodes has been proposed and its operating characteristics were analyzed. The switchable diffraction device is based on a variable cavity structure using reversible electrodeposition technology and two kinds of diffraction gratings are designed to be selectively switched according to the driving electrode. The fabricated device was able to switch the diffraction patterns without any interference between the electrodes, which means that the interference between the electrodes will not be a problem in further device integration with driving circuits. However, when the electrode isolation is not perfect due to parasitic resistance between the electrodes, a weak interference between the electrodes is observed in the diffraction pattern. Therefore, it is expected that ensuring complete insulation between the electrodes will be a very important in the integration of the device. The proposed device can be used as a light control device, an image switchable hologram, etc. Furthermore, it is expected to be applied to reconfigurable metasurfaces through integration with active matrix circuits in the future.

The Northern Sea Route is a new way to connect Asia and Europe. To utilize the sea route, merchant ships are required to have the icebreaking capability. Since conventional fossil fuel engines have limitations for the icebreaking merchant ship propulsion, nuclear power having a long refueling period for icebreaking merchant ship is proposed in this paper. To evaluate the technical feasibility of the nuclear power for the icebreaking ship’s engine, 330MWth SMART is selected for the reference reactor core. The power conversion system for the SMART core is substituted with the trans-critical CO2 recompression cycle that has advantageous in low-temperature heat sink as in Northern Sea Route and low-temperature heat source, Pressurized Water Reactor operating conditions. In this paper, the major components of the trans-critical CO2 cycle are designed. Then, CO2 PRHRS, which is driven by CO2 natural circulation loop, is designed to substitute steam-water based PRHRS.

Summary Most of the small modular reactor (SMR) concepts developed in the past have compact size and a longer life reactor core than the conventional nuclear power plants. However, these concepts have not achieved the full modularization including power conversion system. This study suggests an innovative concept of a reactor cooled by supercritical state carbon dioxide (S-CO2). A reactor core with uranium carbide fuel controlled by drum type control rods was designed. The core has long life (20 years) without refueling or reshuffling as well as inherent safety features. The reactor can be used as a distributed power source and replace outdated fossil fuel power plants for small cities. Moreover, the authors propose the S-CO2 Brayton cycle as a power conversion system to achieve compact and lightweight module. Because of compact core and power conversion system, the entire system can be contained in a single module. The target of the system is to be able to transport a single core and power conversion system module via ground transportation. In order to meet this target, single module's total weight is minimized in the order of 100 tons. The external size of a module is less than 7 m in length and 4 m in diameter. It produces 12MWe electricity from 36MWt reactor core. The S-CO2 Brayton cycle was optimized, and the cycle components such as turbomachineries and heat exchangers were designed preliminarily to observe the potential to maximize the performance while minimizing the weight. Moreover, a dry air-cooling option to reject waste heat for inland installation was selected for the suggested nuclear system. A concept of passive decay heat removal system was developed, and its performance was examined to determine the required heat removal capacity of the system to assure the system's safety under various anticipated accidents. Copyright © 2016 John Wiley & Sons, Ltd.

We have fabricated transparent inverted organic light-emitting diodes (OLEDs) using a metal mesh embedded conductive film (MEF) with a non-metal transparent conductor and a novel vacuum lamination method. The device with the proposed electrode exhibits higher transmittance, lower reflectance, and especially much more stable optical properties than those of the conventional OLEDs with thin metal top electrodes over an entire visible region. Moreover, lower driving voltage is also achieved due to the embedded metal mesh. We demonstrate its potential as a reliable transparent top electrode in various optoelectronic devices.

Graphene produced by chemical-vapor-deposition inevitably has defects such as grain boundaries, pinholes, wrinkles, and cracks, which are the most significant obstacles for the realization of superior properties of pristine graphene. Despite efforts to reduce these defects during synthesis, significant damages are further induced during integration and operation of flexible and stretchable applications. Therefore, defect healing is required in order to recover the ideal properties of graphene. Here, the electrical and mechanical properties of graphene are healed on the basis of selective electrochemical deposition on graphene defects. By exploiting the high current density on the defects during the electrodeposition, metal ions such as silver and gold can be selectively reduced. The process is universally applicable to conductive and insulating substrates because graphene can serve as a conducting channel of electrons. The physically filled metal on the defects improves the electrical conductivity and mechanical stretchability by means of reducing contact resistance and crack density. The healing of graphene defects is enabled by the solution-based room temperature electrodeposition process, which broadens the use of graphene as an engineering material.

White organic light-emitting diodes (WOLEDs) are one of the most promising technologies to realize future solid-state lighting with high power efficiency, broad and adjustable spectral coverage, and area emission for more effective and natural illumination. In this work, we report a new method of tuning the correlated color temperature (CCT) of WOLEDs via spatially controlling the degree of the micro-cavity effect in an OLED. Varying the width of thin Ag strips deposited on top of a transparent electrode leads to changes in both intensity and phase of reflection at the anode, hence significantly altering emission spectra of proposed WOLEDs. CCT of the implemented WOLEDs span a wide range, from 3000 K to 8000 K, demonstrating that our proposed approach helps to meet the need for lighting with various CCTs.

In this paper, recent advances in Ocean Nuclear Power Plants (ONPPs) are reviewed, including their general arrangement, design parameters, and safety features. The development of ONPP concepts have continued due to initiatives taking place in France, Russia, South Korea, and the United States. Russia’s first floating nuclear power stations utilizing the PWR technology (KLT-40S) and the spar-type offshore floating nuclear power plant designed by a research group in United States are considered herein. The APR1400 and SMART mounted Gravity Based Structure (GBS)-type ONPPs proposed by a research group in South Korea are also considered. In addition, a submerged-type ONPP designed by DCNS of France is taken into account. Last, issues and challenges related to ONPPs are discussed and summarized.

In a reactor, various reactor instruments inform the operator of changes in the operating conditions. However, until now, the identification of the reactor state from interpretations of the instrumentation reading has been mostly left to the human operators, which sometimes can be flawed depending on circumstances. Therefore, an artificial cognitive system that can recognize the nuclear reactor state is suggested in this paper to aid the operator under severe environmental stress. Two reactor operating states are preliminarily considered: Normal state and loss of coolant accident state. The artificial cognitive system predicts the state of the reactor in real time, and it determines the type of LOCA if the reactor state is determined to be in an accident state. The proposed system uses only reactor protection system monitoring parameters among various available measurements. The proposed system is composed of two dynamic Bayesian models: Reactor State Determination (RSD) Model, and Accident Type Categorization (ATC) Model. When an accident occurs, the RSD model took 0.3 s to recognize it with 100% accuracy. The average accuracy of the ATC model is about 88%. The average accuracy increased more when the model was refined which suggests the model can be further improved in the future.

The non-base load operation of nuclear power plants is expected to be unavoidable in future due to the increasing shares of the intermittent renewables. In this paper, the physics conditions required for a passively autonomous frequency control operation (PAFO) in a 3400 MWt conventional pressurized water reactor (PWR) design is investigated. The PAFO scheme allows a PWR to passively achieve the requested power maneuverability for primary and secondary frequency regulations on the electrical grid. This study is carried out for a conventional coolant system with a typical critical boron concentration, which yields a less negative coolant temperature coefficient (CTC) than that in a soluble-boron-free (SBF) core. The PAFO scheme is expected to be more challenging in the conventional PWRs than in an SBF small modular reactor, particularly for the secondary frequency regulation. This is mainly due to the weaker coolant reactivity feedback and the higher fuel temperature, which yields a stronger Doppler reactivity feedback during the passive power transients. Numerical simulations of PAFO are performed, for typical power ranges and power ramping rates required for frequency regulations, using a lumped PWR model that is solved by an in-house Fortran-95 computer code. In conventional PWRs, the progressive dilution of the soluble-boron throughout the cycle and the fuel depletion vary the reactivity coefficients. Therefore, we perform sensitivity analyses on CTC, FTC, and Xe worth to assess the feasibility of PAFO throughout the fuel cycle. In addition, sensitivity analysis on the fuel temperature is done to study its role in altering the reactor performance during PAFO.

With the increased role of intermittent renewables in the energy mix, it is important for the Nuclear Power Plants (NPPs) to develop flexible load-follow capabilities in order to be economically competitive. By combining NPP with external superheaters, there is possibility to increase power conversion cycle efficiency and reduce load to some extent while maintaining the nuclear reactor operation at 100% of its rated power and thus maximizing its economic value. In this paper, parametric study of a Small Modular Boiling Water Reactor (SMBWR) conceptual design combined with external superheaters is presented quantifying its performance at different system pressure. The first part of the work is focusing on how operating pressure will affect the SMBWR system as a whole, which includes neutronics, thermal hydraulics, and thermodynamics. WIMS-PANTHER package and COBRA-EN were used as the neutronic and thermal hydraulic tools. In addition, MATLAB models of the SMBWR natural circulation loop and balance of plant were developed for the study. The second part of the work examines the maneuvering capability of SMBWR. It is found that increasing the pressure from 6.5 to 10.0 MPa has no significant neutronic effects, while thermal efficiency is slightly improved. It is also found that SMBWR is able to reduce the load to 65% while maintaining the reactor power at 100% of its rated value.

Modification of multilayer graphene films was investigated for a cathode of organic light-emitting diodes (OLEDs). By doping the graphene/electron transport layer (ETL) interface with Li, the driving voltage of the OLED was reduced dramatically from 24.5 to 3.2 V at a luminance of 1000 cd/m2. The external quantum efficiency was also enhanced from 3.4 to 12.9%. Surface analyses showed that the Li doping significantly lowers the lowest unoccupied molecular orbital level of the ETL, thereby reducing the electron injection barrier and facilitating electron injection from the cathode. Impedance spectroscopy analyses performed on electron-only devices (EODs) revealed the existence of distributed trap states with a well-defined activation energy, which is successfully described by the Havriliak-Negami capacitance functions and the temperature-independent frequency dispersion parameters. In particular, the graphene EOD showed a unique high-frequency feature as compared to the indium tin oxide one, which could be explained by an additional parallel capacitance element.

For environmental reason, buildings increasingly install smart windows, which can dim incoming daylight based on active electrochromic devices (ECDs). In this work, multi-layered graphene (MLG) was investigated as an ECD window electrode, to minimize carbon dioxide (CO2) emissions by decreasing the electricity consumption for building space cooling and heating and as an alternative to the transparent conductor tin-doped indium oxide (ITO) in order to decrease dependence on it. Various MLG electrodes with different numbers of graphene layers were prepared with environmentally friendly poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) to produce ECD cells. Tests demonstrated the reproducibility and uniformity in optical performance, as well as the flexibility of the ECD fabrication. With the optimized MLG electrode, the ECD cells exhibited a very fast switching response for optical changes from transparent to dark states of a few hundred msec.

One of the most promising approaches to recover the waste heat from internal combustion engines is the Organic Rankine Cycle owing to its efficiency and reliability. The design optimization of ORC, however, is nontrivial because there exist many design variables and practical considerations. The present paper proposes a comprehensive design methodology to optimize the Organic Rankine Cycles (ORC) considering a wide range of design variables as well as practical aspects such as component limitations and costs. The design process is comprised of three steps: heat source selection, candidate fluid selection, and thermodynamic cycle optimization. In order to select the best waste heat source, the available energy and other practical considerations of various heat sources have been compared. Among others, the Exhaust Gas Recirculation (EGR) cooler is found to be the best heat source, and thus used for the rest of this study. Based on a systematic working fluid analysis, Ethanol, Pentane, and R245fa are selected as three candidate fluids. For the comprehensive ORC optimization, four types of cycle layouts are considered; 1) subcritical cycle without a recuperator, 2) subcritical cycle with a recuperator, 3) supercritical without a recuperator, and 4) supercritical cycle with a recuperator. Four cycle layouts coupled with three candidate fluids give a total of twelve cycle analyses. Results show that the best performance is provided by the regenerative subcritical cycle with Ethanol, while the solution with minimum capital cost is the subcritical cycles with Ethanol but without a recuperator.

Optical, interfacial and patterning issues of anode graphene films in organic light emitting diode (OLED) applications were investigated. In the optical part, the microcavities of graphene and indium tin oxide (ITO) anode OLEDs were contrasted. With the use of graphene one may avoid spectral and organic stack design problems related to microcavity problems. However, due to the weak microcavity, emission enhancement using interference designs is practically impossible. By inserting an electron acceptor insert at the graphene/hole transport layer (HTL) interface, it was possible to enhance the current density by factor of three. Based on in situ ultraviolet photoelectron spectroscopy (UPS) results, the insert was interpreted as being a charge generation layer. Graphene patterning using laser or plasma methods turned out to be problematic. None of those methods could offer acceptable dimension accuracy and preserved graphene quality.

We report on a novel fabrication method for organic lightemitting diodes (OLEDs) by using a multilayered graphene (MLG) film and a lamination technique. The OLED structure with the MLG top electrode has higher transmittance and lower reflectance than the OLED structure with the conventional thin metal electrode. Moreover, higher luminous current efficiency of the device with the MLG top electrode has been achieved compared with that of the conventional bottom-emission OLEDs with aluminum metal electrode.

In this paper, we suggest the conceptual design of a water-cooled reactor system for a low-pressure inherent heat sink nuclear desalination plant (LIND) that applies the safety-related design concepts of high temperature gas-cooled reactors to a water-cooled reactor for inherent and passive safety features. Through a scoping analysis, we found that the current LIND design satisfied several essential thermal–hydraulic and neutronic design requirements. In a thermal–hydraulic analysis using an analytical method based on the Wooton–Epstein correlation, we checked the possibility of safely removing decay heat through the steel containment even if all the active safety systems failed. In a neutronic analysis using the Monte Carlo N-particle transport code, we estimated a cycle length of approximately 6 years under 200 MWth and 4.5% enrichment. The very long cycle length and simple safety features minimize the burdens from the operation, maintenance, and spent-fuel management, with a positive impact on the economic feasibility. Finally, because a nuclear reactor should not be directly coupled to a desalination system to prevent the leakage of radioactive material into the desalinated water, three types of intermediate systems were studied: a steam producing system, a hot water system, and an organic Rankine cycle system.

Various supercritical carbon dioxide (S–CO 2 ) cycles for a power conversion system of a Molten Carbonate Fuel Cell (MCFC) hybrid system are studied in this paper. Re-Compressing Brayton (RCB) cycle, Simple Recuperated Brayton (SRB) cycle and Simple Recuperated Transcritical (SRT) cycle layouts were selected as candidates for this study. In addition, a novel concept of S–CO 2 cycle which combines Brayton cycle and Rankine cycle is proposed and intensively studied with other S–CO 2 layouts. A parametric study is performed to optimize the total system to be compact and to achieve wider operating range. Performances of each S–CO 2 cycle are compared in terms of the thermal efficiency, net electricity of the MCFC hybrid system and approximate total volumes of each S–CO 2 cycle. As a result, performance and total physical size of S–CO 2 cycle can be better understood for MCFC S–CO 2 hybrid system and especially, newly suggested S–CO 2 cycle shows some success.

The carrier injection efficiencies of organic light-emitting diodes with a multilayer graphene (MLG) anode were compared for different hole injection layers (HIL). The energy level alignments at the hole injecting interface were also studied by using the ultraviolet photoelectron spectroscopy (UPS). We employed 1,1-bis[4-[N,N′-di(p-tolyl)amino]phenyl]cyclohexane (TAPC) as the hole transporting materials, while N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) or 1,4,5,8,9,12-hexaaza-triphenylene-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) was used as the HIL. The current–voltage characteristics of hole-only devices showed that the MLG anode was only slightly inferior to the indium-tin oxide (ITO) anode in hole injection performance for all the HIL layers. The best efficiency was observed for both MLG and ITO anodes with HAT-CN HIL. We compared UPS-measured energy level alignment of TAPC/HIL/MLG interface for different HILs and concluded that the unique charge generation interface at TAPC/HAT-CN played a crucial role for the improved performance of HAT-CN HIL.

From the Fukushima accident, protection of NPPs from any imaginable natural disasters became very important. In this study, the authors suggest a new concept of ocean nuclear power plant (ONPP) by using SMART as a reference reactor, which is the most recent Small Modular Reactor (SMR) developed by Korea, to demonstrate that the proposed concept can improve the safety of NPP from earthquake and tsunami. The proposed concept utilizes Gravity Based Structure (GBS), which is a widely spread construction technique of offshore plants. Because, floating type or submerged type NPPs can be easily affected by severe ocean environments such as tsunamis and storms, additional safety features have to be added to the existing land based plant. In contrast, the newly proposed GBS-type ONPP does not require going through significant design modifications due to inherent characteristics of the construction method. The authors have demonstrated this concept can be applied to the large nuclear power plant in the previous work and will expand this concept for SMRs in this paper. The authors discuss the new concept by presenting design parameters, design requirements, and the new total general arrangement. Furthermore, due to the unique configuration of ONPP SMART, innovative passive safety features can be added to the existing SMART design. The performance of proposed concept to resist earthquake as well as newly added passive safety feature will be discussed by presenting simplified analysis results.

As a part of Sodium-cooled Fast Reactor (SFR) development, the supercritical CO2 (S-CO2) Brayton cycle is considered as an alternative power conversion system to eliminate sodium-water reaction (SWR) from the current conventional steam Rankine cycle is utilized with SFR. The leakage flow of S-CO2 from turbo-machinery via seal becomes one of important issues since not only it influences the cycle efficiency due to parasitic loss but also it is important for evaluating the system safety under various operating conditions. Thus, a transient simulation for estimating the critical flow in a turbo-machinery seal is essential to predict the leakage flow rate and calculate the required total mass of working fluid in a S-CO2 power system. This paper briefly reviews the advantages of supercritical CO2 Brayton cycle relative to a typical steam Rankine cycle used in the Sodium-cooled Fast Reactor. In addition, this paper describes the test data using a CO2 critical flow experimental facility with three orifice configurations to model the flow resistance of a rotating shaft labyrinth seal. This data is used for validation of an existing transient analytical tool developed for transient hydraulic system analysis. Contained within this code is the analysis approach of Henry/Fauske from 1971 for two phase critical flow of one-component mixtures. This paper presents prediction of transient pressure, temperature, and flow profiles for critical and sub-critical flows of CO2 relative to blowdown test data to show that reasonable results are obtained. Similar analyses relative to test results of three orifice configurations are conducted and it shows that multiple orifices increase the time to equalize pressure in the blowdown system and therefore equates to higher flow resistance and lower leakage.

Semi-transparent, colored organic light-emitting diodes (OLEDs) were demonstrated by comprising a microcavity-embedded structure that uses an organic layer sandwiched between thin metal layers as the cathode. Without bias, the colored OLEDs exhibited various colors depending on the metal/organic/metal cathode configuration, by means of internal interference effects under ambient illumination. By varying the thickness of the organic layer, the transmittance and reflectance of the colored OLEDs could be controlled. The influence of the microcavity cathode on the light-emitting performances of OLEDs, such as the efficiencies and the electroluminescence spectra, was also studied.