Effect of hydrogenation on the mechanical property of amorphous Ni90Al10 membranes

To investigate the mechanism of hydrogen embrittlement in amorphous membranes, changes in the stress-strain curves of an amorphous Ni₉₀Al₁₀ model membrane as a function of hydrogen concentration were examined using Molecular Dynamics (MD) simulations. In addition, the fractional change of short-range ordered (SRO) structures during uniaxial tensile deformation was scrutinized using the Voronoi tessellation method. By correlating these structural evolutions related to volume expansion with changes in the mechanical property, the hydrogen embrittlement phenomenon occurring in the amorphous membrane was discussed with respect to the abrupt increase in the degree of strain localization during deformation. The possibility, not only of hydrogen embrittlement, but also of hydrogen-induced ductility enhancement, was demonstrated by the decrease in the degree of strain localization. Finally, we proposed a fundamental mechanism that can explain these overall phenomena occurring in the amorphous membrane by the introduction of hydrogen.     

Japan's spent fuel and plutonium management challenge

Japan's commitment to plutonium recycling has been explicitly stated in its long-term program since 1956. Despite the clear cost disadvantage compared with direct disposal or storage of spent fuel, the Rokkasho reprocessing plant started active testing in 2006. Japan's cumulative consumption of plutonium has been only 5 tons to date and its future consumption rate is still uncertain. But once the Rokkasho reprocessing plant starts its full operation, Japan will separate about 8 tons of plutonium annually. Our analysis shows that, with optimum use of available at-reactor and away-from-reactor storage capacity, there would be no need for reprocessing until the mid-2020s. With an additional 30,000 tons of away-from-reactor (AFR) spent-fuel storage capacity reprocessing could be avoided until 2050. Deferring operation of the Rokkasho plant, at least until the plutonium stockpile had been worked down to the minimum required level, would also minimize international concern about Japan's plutonium stockpile. The authors are happy to acknowledge Frank von Hippel, Harold Feiveson, Jungming Kang, Zia Mian, M.V. Ramana, and other IPFM members, as well as the generous grant from the MacArthur Foundation for helping make this research possible.     

Future regional nuclear fuel cycle cooperation in East Asia: Energy security costs and benefits

Economic growth in East Asia has rapidly increased regional energy, and especially, electricity needs. Many of the countries of East Asia have sought or are seeking to diversify their energy sources and bolster their energy supply and/or environmental security by developing nuclear power. Rapid development of nuclear power in East Asia brings with it concerns regarding nuclear weapons proliferation associated with uranium enrichment and spent nuclear fuel management. This article summarizes the development and analysis of four different scenarios of nuclear fuel cycle management in East Asia, including a scenario where each major nuclear power user develops uranium enrichment and reprocessing of spent fuel individually, scenarios featuring cooperation in the full fuel cycle, and a scenario where reprocessing is avoided in favor of dry cask storage of spent fuel. The material inputs and outputs and costs of key fuel cycle elements under each scenario are summarized.     

Precursor monitoring approach for reliability assessment of cooling fans

Cooling fans are a critical part of the thermal management capability of commercial and military electronic equipment. Although accelerated testing by increasing operating temperatures has been commonly adopted in order to estimate the reliability of cooling fans in a short time frame, the testing time is usually more than 6  months due to the high reliability of ball bearings today. However, these fans are also prone to fail before 3 years. Prognostics and health management is a potential way to cost effectively and timely find low reliability fans. The first step for prognostics and health management is to identify precursor parameters. This article begins with the identification of precursor parameters. The health of cooling fans was estimated by monitoring three precursor parameters including acoustic noise emission, shaft rotational speed, and current consumption. Then the parameter value changes were compared to the failure criteria described in the IPC-9591 standard.     

Application of multiple γ-ray detection to long-lived radioactive nuclide determination in environmental samples

ABSTRACT

Gamma-gamma coincidence measurement utilized in γ-ray spectroscopy experiments is well known to be effective for the improvement of signal-to-noise ratio in a γ-ray spectrum. We study its applicability to the determination of long-lived radioactive nuclides in environmental samples. The γ-ray simulation code Geant 4.10.2 was used. A conventional and effective detector system comprising five Ge detectors was assumed. We took up 38 nuclides which need to be determined for the evaluation of fission product leakage at the nuclear accident in the Fukushima nuclear power plants in Japan. Among them 12 nuclides emit γ-rays and five nuclides of ⁶⁰Co, ⁹⁴Nb, ¹³⁴Cs, ¹⁵²Eu, and ¹⁵⁴Eu can be the objectives of the multiple γ-ray detection methods. The simulation results indicate that the signal-to-noise ratio can be improved by a factor between 9.84 and 283, and the detection limit by a factor between 2.71 and 8.53 relative to the singles measurement, implying that the method can be well applied to the determination of the long-lived radioactive nuclides and will provide a quick and non-destructive analysis method.     

Gas-particle concentrations of atmospheric polycyclic aromatic hydrocarbons at an urban and a residential site in Osaka, Japan: effect of the formation of atmospherically stable layer on their temporal change

A comparative study on atmospheric polycyclic aromatic hydrocarbons (PAHs) in particulate matter and the gaseous phase was performed at an urban and a residential site in Osaka, Japan, during 2005-2006. PAH concentrations at the urban site were found to be approximately twice higher than those at the residential site. At both sites, particulate PAH concentrations increased mainly in winter while the trends of temporal change in gaseous PAH concentrations were not clearly observed. The main sources of PAHs were estimated to be local traffic, e.g., diesel engines with catalytic converter. PAH concentrations did not significantly negatively correlate with ozone concentrations and meteorological parameters. Gas-particle partitioning coefficients of representative PAHs with low molecular weight (LMW) significantly negatively correlated with ambient temperature, showing that temporal change in the LMW PAH concentrations in PM could be attributable to the shift of their gas-particle distribution caused by the change in ambient temperature. For the first time, we studied the effect of the formation of atmospherically stable layer following an increase in PAH concentrations in Japan. At the urban site, PAHs showed a significant positive correlation with potential temperature gradients, indicating that temporal variability in PAH concentrations would be dominantly controlled by the formation of atmospherically stable layer in Osaka area.     

Effect of the diaphragm of free-air ionisation chamber for X-ray air-kerma measurements

Free-air ionisation chambers are widely used at standards laboratories as primary standards for absolute measurements of air kerma in X-ray fields. The area of the diaphragm aperture of a free-air ionisation chambers is an important factor for absolute measurements because it defines the size of the X-ray beam incident on the free-air chamber. In this study, correction factors for the contribution of X rays transmitted through the diaphragm of a free-air ionisation chamber and those scattered from the surface of the diaphragm aperture are obtained by Monte Carlo simulation for two different sized free-air ionisation chambers and for various diaphragm aperture sizes, X-ray energies and source-to-chamber distances.     

Reducing average number of turbo decoding iterations

The average number of decoding iterations in a turbo decoder is reduced by incorporating CRC error detection into the decoding iteration process. Turbo decoding iterations are stopped when CRC decoding determines that there is no error in the decoded data sequence. Computer simulations assuming a turbo-coded W-CDMA mobile radio reverse link under frequency selective Rayleigh fading demonstrate that when the maximum number of iterations is 8, the average number of decoding iterations can be reduced to 1/4 at BER=10^-6     

Surface melting technique of small diameter stainless steel pipe by means of yttrium aluminium garnet laser

A new method of surface melting by using a high power yttrium aluminium garnet laser was developed. This method is applicable to a long distance and narrow space, because of the good accessibility of the laser beam through optical fibre.A desensitization of sensitized type 304 stainless steel pipe was demonstrated by using this technique. A melted layer of thickness approximately 200 μm had a very finite solidification structure, which contained approximately 1.5% δ-ferrite. The average chemical composition of this layer was almost the same as that of type 304 stainless steel, and a band of 300 μm thickness under the melted layer underwent solution heat treatment (SHT).As a result of such surface melting, the melted layer exhibited superior resistance to intergranular stress corrosion cracking (IGSCC). Since the SHT layer is highly resistant to IGSCC generally, it may be possible to improve the IGSCC resistance of base metal to a comparatively deep extent (500 μm from the surface) by this technique.