Optimum in-core power sharing with multicycle coupling effect

Multicycle optimization was carried out by assuming power sharing of each fuel batch as an independent parameter; that is, the power sharing of each fuel batch was considered as an optimization variable. The steepest descent method was used to optimize the power sharing for multiple cycles. Two different optimizations were carried out, i.e., multicycle and successive single-cycle optimizations. In the former, the power sharing of each fuel batch in each cycle was simultaneously optimized for multiple cycles. In the latter, optimization of the power sharing in a cycle was carried out, and then optimization in the next cycle was carried out. Maximization of discharge burnup and minimization of the number of fresh fuel assemblies were considered as the objective functions. The calculation results qualitatively and quantitatively clarify the implicit adverse effect of the single-cycle optimization, which is usually used in current core designs. Under the calculation conditions of the present study, the difference in the number of fresh fuel assemblies between multicycle and successive single-cycle optimizations is 2–3 fuel assemblies per cycle. Comparison of the power sharing obtained by both methods would provide insights to correct the adverse effect of the single-cycle optimization.     

Multi‐agent‐based autonomous power distribution network restoration using contract net protocol

A novel multi‐agent‐based system based on the contract net protocol (CNP), intended to achieve a distributed approach to power distribution network restoration, is proposed. In the proposed system, agents are assigned to areas sectioned by switches and constantly exchange environmental information among themselves. The information is used to construct a CNP overlay network to guard against network accidents. The parameters of the CNP required for robustness and effectiveness are optimized by the genetic algorithm (GA) in the operation phase. When a network accident occurs, the agents restore power distribution service autonomously through the CNP overlay network constructed. Simulation experiments indicate that CNP allows an effective power distribution network restoration strategy to be created by cooperation among agents. ©2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 56–63, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20661     

Effect of bonding conditions on joints of 5052Al and 6063Al in pulsed electric current bonding

Recent reports on sintering and bonding using the pulsed electric current bonding process indicate that the metals are subjected to Joule heating due to the electrical resistance at the contact points. However, the influence of bonding conditions on local heating phenomena and joint quality remains unclear. In this study, the effects of bonding conditions (bonding temperature, pressure, surface roughness, interlayer, electric current wave and so on) on joint efficiency are investigated using 5052A1 and 6063A1 in pulsed electric current bonding.

The joint strength of 5052A1 and 6063A1 are improved using 2024A1 as the interlayer between the bonding interfaces. The joints with the 2024A1 powder as the interlayer are stronger than ones with 2024A1 plate, and are as strong as the base metal. The improvements of the joints depend on effective heat generation at the bonding interface due to the electrical resistance. It is 0.08 g (thickness: 0.04 mm), enough for the amount of powder between the bonding interfaces. The dispersion of the powder from the joints does not occur under various conditions.

The surface roughness and electric current wave (direct current, duty ratio, pulse frequency) have no effect on the joint strength. With the increase of bonding temperature and pressure, the deformation of the joints increases. Then bonding temperature and pressure have to be selected to prevent a big deformation of joint configuration.     

Polyethylene ionomer-based nano-composite foams prepared by a batch process and MuCell® injection molding

To understand the correlation between foamability and melt rheology of polyethylene-based ionomers having different degrees of the neutralization and corresponding nano-composites, we have conducted the foam processing via a batch process in an autoclave and microcellular foam injection molding (FIM) process using the MuCell^® technology. We have discussed the obtainable morphological properties in both foaming processes. All cellular structures were investigated by using field emission scanning electron microscopy. The competitive phenomenon between the cell nucleation and the cell growth including the coalescence of cell was discussed in light of the interfacial energy and the relaxation rate as revealed by the modified classical nucleation theory and rheological measurement, respectively. The FIM process led to the opposite behavior in the cell growth and coalescence of cell as compared with that of the batch process, where the ionic cross-linked structure has significant contribution to retard the cell growth and coalescence of cell. The mechanical properties of the structural foams obtained by FIM process were discussed.     

Single-Crystal Growth of Bi-Sb-Te Thermoelectric Materials by Halide Chemical Vapor Transport Technique

This report describes synthesis of binary Bi₂Te₃ and ternary Bi_0.5Sb_1.5Te₃ single crystals using the halide chemical vapor transport technique. For synthesis of ternary Bi_0.5Sb_1.5Te₃, BiBr₃ is a more effective transport agent compared with iodine I₂. The single crystal includes a few atomic percent of Br. The Bi_0.5Sb_1.5Te₃ crystal shows p-type conduction and has a comparatively large residual resistivity ratio. The crystal exhibits relatively high electrical resistivity and high Seebeck coefficient. These high values are attributed to decrease of the hole concentration p due to doping of the transport agent Br.     

Radiative transfer modeling of filter-based measurements of light absorption by particles: Importance of particle size dependent penetration depth

We present new physical models to interpret the response characteristics of filter-based measurements of aerosol light absorption. They were motivated by a recently found particle size dependence of a systematic bias in absorption measurements that cannot be interpreted by any models reported thus far. A theory of particle filtration by fibrous filter is applied to reproduce the penetration depth of particles into a filter matrix, and the light transmissivity of the matrix is calculated by the use of radiative transfer theory for plane-parallel layers. Optical properties of individual layers are calculated from microphysical properties and the number density of filter fibers and deposited particles. The size-dependent systematic bias in absorption measurement is successfully explained by the particle size dependence of penetration depth into a filter matrix. In practice the physical models developed here are useful for selecting operating conditions and filter matrices for instruments with fewer systematic biases.     

Thermal and electrochemical durability of carbonaceous composites used as a bipolar plate of proton exchange membrane fuel cell

Thermal and electrochemical durability of carbonaceous composite plates, which are made from graphite powders and a resin for use as bipolar plates of PEMFC (proton exchange membrane fuel cell), were investigated. The thermal durability was investigated by TG (thermal gravimetry) coupled with DTA (differential thermal analysis) technique under air up to 600 °C. A weight loss was significant over 300 °C, but the hydrophobicity was decreased after heated at 80 °C for 192 h.The electrochemical durability was investigated in 10 μmol dm⁻³ of hydrochloric acid solution under nitrogen or oxygen atmosphere by means of potential holding test from 0.8 to 1.5 V against RHE (reversible hydrogen electrode) at 80 °C. During the potential holding tests, CO₂ production due to the corrosion was quantified by a GC (gas-chromatography) and the production was detectable above 1.3 V irrespective with atmosphere; on the other hand, it was clarified from the contact angle measurements that the hydrophobicity was changed below 1.3 V. The results of this study showed that the carbonaceous composite plates were electrochemically degraded under PEMFC condition and were seriously degraded in URFC (unitized regenerative fuel cell) condition.     

Electricity demand in the Chinese urban household-sector

This paper presents the results of estimating how much electricity is currently used and would be used in future in China’s urban household-sector. Conclusions are derived from an analysis of data obtained from a questionnaire survey recently conducted in 13 cities in China. Electricity used for various purposes in China’s urban-households is evaluated, considering climate conditions specific to the target regions and the possession of end-use appliances. How much electricity could be saved in the future by improving the efficiency of end-use lighting equipment, room air-conditioners, refrigerators, and TV sets is estimated. It is demonstrated that about 28% reduction could be achieved in the year of 2020 by means of improving the efficiency of these end-use appliances.     

Foam processing of polyethylene ionomers with supercritical CO2

Via a batch process, the foam processing of polyethylene-based ionomers having two different degree of the neutralization has been conducted using supercritical CO₂. The cellular structures obtained from various ranges of foaming temperature-CO₂ pressure were investigated by using field emission scanning electron microscopy. For comparison, the corresponding nano-composite also has been examined. The ionic cross-linked structure in the ionomer exhibited significant contribution to retard the cell growth and coalescence of cell, especially in ionomer having higher degree of the neutralization. For nano-composite foaming, experimentally, nano-clay particles led to an increase in cell density after foaming. However, the dispersed nano-clay particles did not act as nucleating sites for cell formation. The competitive phenomenon between the cell nucleation and the cell growth including the coalescence of cell was discussed in the light of the interfacial energy and the relaxation rate as revealed by the modified classical nucleation theory and rheological measurement, respectively.     

Global Monitoring of Large Concrete Structures Using Acoustic Emission and Ultrasonic Techniques: Case Study

Global monitoring of civil structures is a demanding challenge for engineers. Acoustic emission (AE) is one of the techniques that have the potential to inspect large volumes with transducers placed in strategic locations of the structure. In this paper, the AE technique is used to characterize the structural condition of a concrete bridge. The evaluation of AE activity leads to information about any specific part of the structure that requires attention. Consequently, more detailed examinations can be conducted once the target area is selected. In this case, wave propagation velocity was used as a means to evaluate, in more detail, the condition of the region indicated by the AE analysis.