Effect of oxygen partial pressure on the high-temperature oxidation of CVD SiC

The oxidation behavior of chemically vapor-deposited silicon carbide (CVD SiC) was studied at 1670-2010 K in O₂-Ar and CO₂-Ar. The oxidation kinetics in O₂-Ar was parabolic or linear parabolic, and was parabolic in CO₂-Ar. The activation energy for the parabolic rate constants (k_p) was 210-220 kJ/mol in O₂-Ar, and was 290-300 kJ/mol in CO₂-Ar. The oxygen partial pressure (P_O2) dependence of k_p was expressed as k_p∝ (P_O2)ⁿ, where n=0.08-0.13 and 0.37-0.53 in O₂-Ar and CO₂-Ar, respectively. Bubbles were formed at more than 1985 K and P_O2>5 kPa. The bubble formation temperature decreased with decreasing P_O2 at P_O2<5 kPa.     

Specific activity and activity ratios of radionuclides in soil collected about 20 km from the Fukushima Daiichi Nuclear Power Plant: Radionuclide release to the south and southwest

Soil samples at different depths (0-2, 5-7 and 10-12 cm) were collected from J Village, about 20 km south of Fukushima Daiichi Nuclear Power Plant (FNPP) to determine their radionuclide specific activities and activity ratios. The concentrations and activity ratios of ¹³¹I, ^{134, 136, 137}Cs and ^129mTe were obtained, but only trace amounts of ⁹⁵Nb, ^110mAg and ¹⁴⁰La were detected which were too low to provide accurate concentrations. Radionuclides such as ⁹⁵Zr, ^{103, 106}Ru and ¹⁴⁰Ba that were found in Chernobyl fallout, were not found in these soil samples. This suggests that noble gasses and volatile radionuclides predominated in the releases from FNPP to the terrestrial environment. The average activity ratios of ¹³¹I/¹³⁷Cs, ¹³⁴Cs/¹³⁷Cs, ¹³⁶Cs/¹³⁷Cs and ^129mTe/¹³⁷Cs were 55, 0.90, 0.22 and 4.0 (corrected to March 11, 2011) in the 0-2 cm soil samples of April 20 and 28, 2011.     

Bioconcentration and elimination of bis(tributyltin)oxide (TBTO) and triphenyltin chloride (TPTC) in several marine fish species

Pagrus major, Mugil cephalus and Rudarius ercodes were exposed to bis(tributyltin)oxide (TBTO) and triphenyltin chloride (TPTC) for 8 weeks in a flow-through aquarium system. The bioconcentration factors (BCFs) of TBTO and TPTC and the elimination rate constant of TBTO for these fish were determined. The BCF of TBTO ranged from 2400 to 11,000 depending on the fish species and the concentration in the rearing seawater. Out of the three, P. major had the smallest elimination rate constant (0.024 day⁻¹) and bioconcentrated the largest amount of TBTO (BCF: 9400–11,000). On the other hand, the BCF of TPTC of the two fish species examined was similar: 3100–3300 for P. major and 4100 for R. ercodes. These BCFs of TBTO and TPTC of P. major were larger than the values previously reported. TBTO and TPTC were the least accumulated in muscle among the tissues and organs of P. major examined, and no correlation was found between the lipid content and the accumulated TBT or TPT content.     

A numerical study on turbulence attenuation model for liquid droplet impingement erosion

The bent pipe wall thinning has been often found at the elbow of the drain line and the high-pressure secondary feed-water bent pipe in the nuclear reactors. The liquid droplet impingement (LDI) erosion could be regarded to be one of the major causes and is a significant issue of the thermal hydraulics and structural integrity in aging and life extension for nuclear power plants safety. In this paper two-phase numerical simulations are conducted for standard elbow geometry, typically the pipe diameter is 170 mm. The turbulence attenuation in vapor-droplets flow is analysed by a damping function on the energy spectrum basis of single phase flow. Considering the vapor turbulent kinetic energy attenuation due to the involved droplets, a computational fluid dynamic (CFD) tool has been adopted by using two-way vapor-droplet coupled system. This computational fluid model is built up by incompressible Reynolds Averaged Navier–Stoke equations using standard k–ε model and the SIMPLE algorithm, and the numerical droplet model adopts the Lagrangian approach, a general LDI erosion prediction procedure for bent pipe geometry has been performed to supplement the CFD code. The liquid droplets diameter, velocity, volume concentration are evaluated for the effects of carrier turbulence attenuation. The result shows that carrier turbulence kinetic energy attenuation is proved to be an important effect for LDI erosion rate when investigating the bent pipe wall thinning phenomena.     

Feasibility study of the application of exotic pin for tight-lattice fuel assembly

A tight-lattice fuel assembly having less space for the coolant is more feasibly applied in Liquid Metal Fast Breeder Reactor (LMFBR). The thermal hydraulic constraint due to smaller coolant space can be compensated by the high heat capacity of the liquid metal coolant. A tight pin configuration provides high fuel volume fraction which eventually gives better neutronic performance for longer core lifetime. A cylindrical pin array provides less flexible arrangement for tight-lattice assembly, which results in very narrow coolant gaps connecting its neighboring subchannels. Therefore, the so-called exotic pin shape is introduced, which enable to distribute the coolant flow more uniformly, to be applied in tight-lattice bundles with sodium coolant. As Nusselt number and wall friction correlation are absent for this type of geometry, CFD calculations are performed by employing k-ε turbulent model.     

Repair Priority Effect on Availability of a 2-unit System

This paper is concerned with a 2-unit parallel system with priority repair. The priority rule is a mixture of several disciplines. The optimal priority rule minimizes the s-expected total discounted time in which the system is failed. The optimality of Late Preemption Rule is shown and the effect of the rule on the availability of the system is investigated.     

A study of living plant specimens by low-temperature scanning electron microscopy

Young fresh Tradescantia reflexa stamen hair cells were used to clarify the optimal conditions for direct viewing and taking photographs with a scanning electron microscope (SEM) equipped with a cryo-system. The rate of protoplasmic streaming in the cells was measured under an optical microscope after examining and photographing them in the SEM over a period of a few minutes. Almost the same rate of streaming (5.5 μm/second, 20°C) was observed in nonirradiated control cells and irradiated cells photographed in the SEM using an accelerating voltage of 10 kV with the cryo-stage at a temperature of – 15°C. (The specimen holder and specimen were not at this temperature, but, rather, probably somewhat higher.) Fresh plant organs, tissues, and cells were also tested under the same conditions. The fine structure was well preserved in detail. The procedures were as follows: (1) prompt attachment of fresh plant materials on an aluminum specimen holder with double-faced adhesive Scotch tape or a small amount of plastic adhesive for woodcraft; (2) setting the holder on the cryo-stage cooled to –15°C in advance and rapid evacuation; and (3) quick SEM examination and photography (within several minutes). The advantages of this method are summarized as follows: (1) high possibility of viewing living materials; (2) minimal artifacts: freedom from chemical fixation and additional procedures utilized in ordinary SEM specimen preparation; and (3) simplicity, speediness, and economy in preparation for viewing. Since the specimens were not likely to be frozen during quick examination and photography, this method might well be called “low-temperature SEM” (LT-SEM) as distinguished from “cryo-SEM”.     

Analysis of thermal stability of acrylonitrile-acrylic elastomer-styrene terpolymer in injection molding

Acrylonitrile-acrylic elastomer-styrene terpolymer (AAS resin) was developed to improve weatherability of acrylonitrile-butadiene-styrene terpolymer (ABS resin). To compare thermal stability of both resins, test parts of AAS and ABS resins were injection molded at various temperatures and the Izod impact value of the resulting moldings was measured. A study was then made to find the relationship between this value and deterioration of the resins. AAS resin was molded at temperatures from 180°C to 280°C. The impact value of the resulting moldings was almost constant for temperatures up to 260°C, with the first major decrease occurring at 280°C. In contrast, the impact value of conventional ABS resin moldings constantly decreased as the molding temperature was elevated. To explain this phenomenon in both resins, two types of test program steps were undertaken: (1) The cause of the change in characteristics of the AAS resin was determined by obtaining its stress-strain curve in a high-speed flexural strength test; measuring its infrared absorption spectrum; and determining its flow properties with a constant-pressure extrusion type rheometer; (2) the distribution of elastomer in the resin was observed with an electron microscope. It was found that the decrease of impact values of both resins at high temperatures is caused by deterionration of the elastomer. Also, it was found that the different relationships between the impact value and molding temperatures for AAS and ABS resins are due to the difference between the rates of thermal degradation of the acrylic elastomer and butadiene elastomer.     

Two-photon excited states in charge-transfer type conjugated polymers

We have investigated two-photon excited states of charge-transfer (CT) conjugated copolymers, poly(aryleneethynylene) (PAE) and poly(thiophene-alt-thiazole) (PThTz), using two-photon absorption and electroabsorption methods. The fitting analysis of the experimental spectra reveals that the two-photon excited states are located 0.5–0.6 eV above the one-photon excited states. These results are compared with nonlinear optical spectra of another CT polymer and a non-CT polymer.