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[en] The reasons for the renewed interest in fast reactors and an overview of the progress in sodium cooled fast reactor operation in the last ten years are given. The excellent operational performance of sodium cooled fast reactors in this period is highlighted as a sound basis for the development of new fast reactors. The operational performance of the BN-600 is compared and evaluated against the performance of German light water reactors to assess the reliability. The relevance of feedback effects for safe reactor design is described, and a new method for the enhancement of feedback effects in fast reactors is proposed. Experimental reactors demonstrating the inherent safety of advanced sodium cooled fast reactor designs are described and the potential safety improvements resulting from the use of fine distributed moderating material are discussed.
[en] This article proposes a system-wide optimal resource dispatch strategy that enables a shift from a primarily energy cost-based approach, to a strategy using simultaneous price signals for energy, power and ramping behavior. A formal method to compute the optimal sub-hourly power trajectory is derived for a system when the price of energy and ramping are both significant. Optimal control functions are obtained in both time and frequency domains, and a discrete-time solution suitable for periodic feedback control systems is presented. The method is applied to North America Western Interconnection for the planning year 2024, and it is shown that an optimal dispatch strategy that simultaneously considers both the cost of energy and the cost of ramping leads to significant cost savings in systems with high levels of renewable generation: the savings exceed 25% of the total system operating cost for a 50% renewables scenario.
[en] One of the main technical hurdles associated with adsorbent based hydrogen storage systems is relative to their ability to discharge hydrogen effectively, as dictated by fuel cell requirements. In this study, a new honeycomb finned heat exchanger concept was examined to evaluate its potential as a heat transfer system for hydrogen desorption. A bench scale 0.5 L vessel was equipped with the proposed heat exchanger, filled with MOF-5® adsorbent material. The heating power, required to desorb hydrogen, was provided by a 100 W electric heater placed in the center of the honeycomb structure. Two desorption tests, at room temperature and under cryogenic temperatures, were carried out to evaluate the hydrogen desorption performance of the proposed system under different operating conditions. The bench scale vessel performance was verified from both an experimental and a modeling point of view, demonstrating the ability to desorb about 45% of the adsorbed hydrogen in reduced time and applying low heating power. Further modeling analyses were also carried out showing the potential of the proposed system to reach high hydrogen discharging rates at cryogenic temperature conditions and operating pressures between 100 bar and 5 bar. The proposed adsorption system also demonstrated to be able to discharge all the available hydrogen in less than 500 s operating at cryogenic conditions and with a nominal heating power of 100 W.
[en] This paper reviews the supply of small nuclear power plants (200 to 500 MWe electrical generating capacity) available on today's market, including the pre-fabricated designs of the United Kingdom's Rolls Royce Ltd and the French Alsthom-Atlantique Company. Also, the Russian VVER-440 conventionally built light-water reactor design is reviewed, including information on the Soviet Union's plans for expansion of its reactor-building capacity. A section of the paper also explores the characteristics of LDC electricity grids, reviewing methods available for incorporating larger plants into smaller grids as the Israelis are planning. Future trends in reactor supply and effects on proliferation rates are also discussed, reviewing the potential of the Indian 220 MWe pressurised heavy-water reactor, South Korean and Jananese potential for reactor exports in the Far East, and the Argentine-Brazilian nuclear programme in Latin America. This study suggests that small reactor designs for electrical power production and other applications, such as seawater desalination, can be made economical relative to diesel technology if traditional scaling laws can be altered by adopting and standardising a pre-fabricated nuclear power plant design. Also, economy can be gained if sufficient attention is concentrated on the design, construction and operating experience of suitably sized conventionally built reactor systems. (author)
[en] Coordinated operation of distributed thermostatic loads such as heat pumps and air conditioners can reduce energy costs and prevents grid congestion, while maintaining room temperatures in the comfort range set by consumers. This paper furthers efforts towards enabling thermostatically controlled loads (TCLs) to participate in real-time retail electricity markets under a transactive control paradigm. An agent-based approach is used to develop an effective and low complexity demand response control scheme for TCLs. The proposed scheme adjusts aggregated thermostatic loads according to real-time grid conditions under both heating and cooling modes. Here, a case study is presented showing the method reduces consumer electricity costs by over 10% compared to uncoordinated operation.
[en] Operating conditions of the laser uranium enrichment plant to obtain cheaper enriched uranium are optimised by using the standard optimisation procedure. A simple kinetic model is given to obtain the ion production rate as a function of the laser energy density, ultraviolet light energy density, atomic density and depth and height of the reaction region. The unit cost of enriched uranium is chosen as a value function instead of the unit cost of the separative work. The construction cost is expressed by means of an exponential function to take the scale merit into account. Two numerical results are given. In case 1, the laser power and efficiency are subject to the restraints determined by the present technical levels and in case 2, they are free. The unit cost of the enriched uranium is higher than those of the gaseous diffusion and gas centrifuge methods by a factor of 2 approximately 11. Results indicate that laser uranium enrichment is probably competitive with the other uranium enrichment methods, provided that the laser efficiency is improved by up to 1% and the laser lifetime is extended several times. (author)
[en] Effective removal of nitrogen oxides (NOx) from flue gas allows more fossil fuels to be produced and utilized with less negative impact on the environment. It would be more cost-effective, however, if nitric oxide (NO) is oxidized to soluble nitrate and nitrite and then removed from the air by existing desulfurization wet scrubbers. This paper compares the effectiveness of three different oxidants for this purpose, namely, ethylenediaminetetraacetic acid; iron (2+) (Fe(II)–EDTA), hexamminecobalt(II) chloride ([Co(NH3)6]Cl2), and hydrogen peroxide (H2O2). Experimental results using column reactors showed that [Co(NH3)6]Cl2 was more effective over the same period of time. The best initial NO removal efficiency of about 96.45% was measured at the inlet flow rate of 500 ml/min; the temperature of approximately 19 °C; the pH value of around 10.5; and the concentrations of [Co(NH3)6]Cl2 , NO and O2 of 0.06 mol/L, 500 ppm and 5.0%, respectively.
[en] Highlights: ► A performance benchmarking exercise is conducted for diesel combustion simulations. ► The reduced chemical mechanism shows its advantages over base and skeletal models. ► High efficiency and great reduction of CPU runtime are achieved through 4-node solver. ► Increasing ISAT memory from 0.1 to 2 GB reduces the CPU runtime by almost 35%. ► Combustion and soot processes are predicted well with minimal computational cost. - Abstract: In the present study, in-cylinder diesel combustion simulation was performed with parallel processing on an Intel Xeon Quad-Core platform to allow both fluid dynamics and chemical kinetics of the surrogate diesel fuel model to be solved simultaneously on multiple processors. Here, Cartesian Z-Coordinate was selected as the most appropriate partitioning algorithm since it computationally bisects the domain such that the dynamic load associated with fuel particle tracking was evenly distributed during parallel computations. Other variables examined included number of compute nodes, chemistry sizes and in situ adaptive tabulation (ISAT) parameters. Based on the performance benchmarking test conducted, parallel configuration of 4-compute node was found to reduce the computational runtime most efficiently whereby a parallel efficiency of up to 75.4% was achieved. The simulation results also indicated that accuracy level was insensitive to the number of partitions or the partitioning algorithms. The effect of reducing the number of species on computational runtime was observed to be more significant than reducing the number of reactions. Besides, the study showed that an increase in the ISAT maximum storage of up to 2 GB reduced the computational runtime by 50%. Also, the ISAT error tolerance of 10−3 was chosen to strike a balance between results accuracy and computational runtime. The optimised parameters in parallel processing and ISAT, as well as the use of the in-house reduced chemistry model allowed accurate results to be produced with reduced computational runtime, especially in simulating in-cylinder reacting spray jet and soot characteristics on standard computing platforms.
[en] Highlights: ► We evaluate the suitability of 11 empirically performance models for centrifugal water chillers. ► The prediction accuracy of each model is based on CV values. ► The evaluation for model suitability is based on five indexes. ► The BQ, MP, SMP, and MDOE-2 models have good prediction accuracy. ► The BQ, MP, and SMP models have the best suitability. - Abstract: This study evaluates the performance prediction ability and model suitability of eleven empirically-based performance models for centrifugal water chillers. Specifically, this study uses over 2000 datasets with a constant or variable chilled water flow rate for fixed or variable speed drive centrifugal liquid chillers. The best regression coefficients for each empirical-based model were obtained using the ordinary least squares (OLSs) method. The model prediction accuracy of each empirical-based model is based on the coefficient of variation of root-mean-square error (CV). The evaluation for model suitability is based on the considerations of prediction ability, the complexity in training datasets, the effort needed to calibrate, the generality of the model, and its ability to physically interpret the model regression coefficients in this study. Results show that among the eleven empirical-based models, the BQ (CV = 0.54%), MP (CV = 0.61%), SMP (CV = 0.70%), and MDOE-2 (CV = 0.63%) models have overall prediction CV values under 1% for all kinds of datasets and achieve extremely good prediction accuracy. Because the MDOE-2 model has a more complicated datasets training process than the BQ, MP, and SMP models, and it has no ability to physically interpret the model regression coefficients, the BQ, MP, and SMP models have the best suitability. The results of this study provide important reference values for selecting empirically-based performance models for energy analysis, optimal operating control, energy efficiency measurement and verification (M and V), and the development of fault detection and diagnosis (FDD) systems in centrifugal water chillers.
[en] A two-dimensional, non-isothermal model of a proton exchange membrane fuel cell was implemented to elucidate heat balance through the membrane electrode assembly (MEA). To take local utilization of platinum catalyst into account, the model was presented by considering the formation of agglomerated catalyst structure in the electrodes. To estimate energy balance through the MEA, various modes of heat generation and depletion by reversible/irreversible heat release, ohmic heating and phase change of water were included in the present model. In addition, dual-pathway kinetics, that is a combination of Heyrovsky–Volmer and Tafel–Volmer kinetics, were employed to precisely describe the hydrogen oxidation reaction. The proposed model was validated with experimental cell polarization, resulting in excellent fit. The temperature distribution inside the MEA was analyzed by the model. Consequently, a thorough investigation was made of the relation between membrane thickness and the temperature distribution inside the MEA.