Three-dimensional behaviors of the hydrogen and steam in the APR1400 containment during a hypothetical loss of feed water accident

During a hypothetical severe accident in a nuclear power plant (NPP), hydrogen is generated by an active reaction of the fuel-cladding and the steam in the reactor pressure vessel and released with the steam into the containment. In order to mitigate hydrogen hazards which could possibly occur in the NPP containment, a hydrogen mitigation system (HMS) is usually adopted. The design of the next generation NPP (APR1400) developed in Korea specifies that 26 passive autocatalytic recombiners and 10 igniters should be installed in the containment for a hydrogen mitigation. In this study, an analysis of the hydrogen and steam behavior during a total loss of feed water (LOFW) accident in the APR1400 containment has been conducted by using the computational fluid dynamics (CFD) code GASFLOW. During the accident, a huge amount of hot water, steam, and hydrogen is released into the in-containment refueling water storage tank (IRWST). The current design of the APR1400 includes flap-type openings at the IRWST vents which operate depending on the pressure difference between the inside and outside of the IRWST. It was found from this study that the flaps strongly affect the flow structure of the steam and hydrogen in the containment. The possibilities of a flame acceleration and a transition from deflagration to detonation (DDT) were evaluated by using the Sigma–Lambda criteria. Numerical results indicate that the DDT possibility was heavily reduced in the IRWST compartment by the effects of the flaps during the LOFW accident.     

Preparation of Polymer-stabilized Palladium–silver Bimetallic Nanoparticles by γ-irradiation and their Catalytic Properties for Hydrogenation of cis,cis-1,3-Cyclooctadiene

Polyvinypyrrolidone (PVP)-stabilized Pd-Ag bimetallic colloids were successfully prepared in an acetone:2-propanol solution mixture of palladium acetate and silver perchlorate, and in an aqueous solution of palladium nitrate and silver nitrate by γ-irradiation. The prepared PVP-stabilized bimetallic nanoparticles were characterized by UV, TEM, XRD, and XPS. In Pd–Ag bimetallic nanoparticles, the XPS data indicated that the constituent elements were in the metallic state, and the palladium atoms were concentrated on the surface of the alloy cluster. These PVP-stabilized bimetallic nanoparticles were used as catalysts for hydrogenation of cis,cis-1,3-cyclooctadiene (COD).     

Hydrogen passivation effects under negative bias temperature instability stress in metal/silicon-oxide/silicon-nitride/silicon-oxide/silicon capacitors for flash memories

The paper presents the passivation effect of post-annealing gases on the negative bias temperature instability of metal/silicon-oxide/silicon-nitride/silicon-oxide/silicon (MONOS) capacitors. MONOS samples annealed at 850 °C for 30 s by a rapid thermal annealing (RTA) are treated by additional annealing in a furnace, using annealing gases N₂ and N₂-H₂ (2% hydrogen and 98% nitrogen gas mixture) at 450 °C for 30 min. MONOS samples annealed in an N₂-H₂ environment are found to have lowest oxide trap charge density shift, ΔN_ot = 8.56 × 10¹¹ cm⁻², and the lowest interface-trap density increase, ΔN_it = 4.49 × 10¹¹ cm⁻² among the three samples as-deposited, annealed in N₂ and N₂-H₂ environments. It has also been confirmed that the same MONOS samples have the lowest interface-trap density, D_it = 0.834 × 10¹¹ eV⁻¹ cm⁻², using small pulse deep level transient spectroscopy. These results indicate that the density of interface traps between the silicon substrate and the tunneling oxide layer are significantly reduced by the additional furnace annealing in the N₂-H₂ environment after the RTA.     

Spray effect on the behavior of hydrogen during severe accidents by a loss-of-coolant in the APR1400 containment

In order to analyze the effects of the spray activation on the behavior of steam and hydrogen which are produced in the reactor vessel and released into the containment of the APR1400 nuclear power plant during hypothetical severe loss-of-coolant accidents (LOCA), the 3-dimensional CFD code GASFLOW was used. For the two-phase flow with a gas mixture and spray droplets, GASFLOW solves a homogeneous two-phase model which was validated in this study by simulating one of the TOSQAN experiments. The results of the GASFLOW analyses for the LOCAs in the APR1400 show that the spray system can affect the hydrogen distributions in the containment by condensing the steam and it is important to control the spray system carefully during an accident from a hydrogen safety aspect.     

A novel self-assembly approach to form tubular poly(diphenylamine) inside the mesoporous silica

MCM-41 materials were synthesized using alkyl(decosane, dodecyl)trimethyl ammonium bromide as structure directing surfactants. X-ray diffraction (XRD) analysis and nitrogen adsorption measurements reveal that the pores are hexagonal with tunable textural properties through the choice of surfactant and experimental condition. Poly(diphenylamine), PDPA was entrapped into the pores of MCM-41 by initial sorption of diphenylamine (DPA, monomer) in a medium (napthalein sulfonic acid) that provides self-assembling of DPA inside the pores and subsequent oxidative of polymerization with peroxydisulphate. Clear presence of an additional peak (around 9-10°) in XRD pattern for the DPA loaded MCM-41 provides evidence for self-assembled structure. Upon polymerization the self-assembly of DPA molecules resulted tubular PDPA inside the pores of MCM-41. PDPA thus formed shows different electronic property than the PDPA prepared by conventional method. XRD and FTIR spectroscopic analysis of PDPA loaded MCM-41 clearly informs that PDPA are entrapped in channels of MCM-41.     

Microbial synthesis of magnetite and Mn-substituted magnetite nanoparticles: influence of bacteria and incubation temperature

Microbial synthesis of magnetite and metal (Co, Cr, Ni)-substituted magnetites has only recently been reported. The objective of this study was to examine the influence of Mn ion on the microbial synthesis of magnetite nanoparticles. The reductive biotransformation of an akaganeite (beta-FeOOH) or a Mn-substituted (2-20 mol%) akaganeite (Fe(1-x)Mn(x)OOH) by Shewanella loiha (PV-4, 25 degrees C) and Thermoanaerobacter ethanolicus (TOR-39, 60 degrees C) was investigated under anaerobic conditions at circumneutral pH (pH = 7-8). Both bacteria formed magnetite nanoparticles using akaganeite as a magnetite precursor. By comparison of iron minerals formed by PV-4 and TOR-39 using Mn-mixed akaganeite as the precursor, it was shown that PV-4 formed siderite (FeCO3), green rust [Fe2+Fe3+(OH)16CO3 x 4H2O], and magnetite at 25 degrees C, whereas TOR-39 formed mainly nm-sized magnetite at 60 degrees C. The presence of Mn in the magnetite formed by TOR-39 was revealed by energy dispersive X-ray analysis (EDX) is indicative of Mn substitution into magnetite crystals. EDX analysis of iron minerals formed by PV-4 showed that Mn was preferentially concentrated in the siderite and green rust. These results demonstrate that coprecipitated/sorbed Mn induced microbial formation of siderite and green rust by PV-4 at 25 degrees C, but the synthesis of Mn-substituted magnetite nanoparticles proceeded by TOR-39 at 60 degrees C. These results indicate that the bacteria have the ability to synthesize magnetite and Mn-substituted magnetite nano-crystals. Microbially facilitated synthesis of magnetite and metal-substituted magnetites at near ambient temperatures may expand the possible use of specialized ferromagnetic nano-particles.     

The effect of Mo addition on the liquid-phase sintering of W heavy alloy

The morphological and compositional changes of grains have been investigated in the initial stage of liquid-phase sintering of W-Mo-Ni-Fe powder compacts. Both large (5.4-μm) and small (1.3-μm) W powders have been used to vary their time of dissolution in the liquid matrix. When 8OW-10M0-7Ni-3Fe (wt pct) compacts of fine (about 1- to 2-μm) Mo, Ni, and Fe and coarse (5.4-μm) W powders are liquid-phase sintered at 1500 °C, the Mo powder and a fraction of the W powder rapidly dissolve in the Ni-Fe liquid matrix. The W-Mo grains (containing small amounts of Ni and Fe) nucleate in the matrix and grow while the W particles slowly dissolve. In this transient initial stage of the liquid-phase sintering, duplex structures of coarse W-Mo grains and fine W particles are obtained. As the W particles dissolve in the liquid matrix during the sintering, the W content in the precipitated solid phase also increases. The dissolution of the small W particles is assessed to be driven partially by the coherency strain produced by Mo diffusion at the surface. During sintering, the W particles continuously dissolve while the W-Mo grains grow. When the compacts are prepared from a fine (1.3-μm) W powder, the W grains dissolve more rapidly, in about 1 hour, and only W-Mo grains remain. These observations show that the morphological evolution of grains during liquid-phase sintering can be strongly influenced by the chemical equilibrium process. formerly Graduate Student, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology     

Washout algorithm with fuzzy-based tuning for a motion simulator

In the virtual environment, reality can be enhanced by offering the motion based on a motion simulator in harmony with visual and auditory modalities. In this research the Stewart-Gough-platform-based motion simulator has been developed. Implementation of vehicle dynamics is necessary in the motion simulator for realistic sense of motion, so bicycle dynamics is adopted in this research. In order to compensate for the limited range of the motion simulator compared with the real vehicle motion, washout algorithm composed of high-pass filter, low-pass filter and tilt coordination is usually employed. Generally, the washout algorithm is used with fixed parameters. In this research a new approach is proposed to tune the filter parameters based on fuzzy logic in real-time. The cutoff frequencies of the filters are adjusted according to the workspace margins and driving conditions. It is shown that the washout filter with the fuzzy-based parameters presents better performance than that with the fixed ones.     

Fabrication of platinum coating on continuous porous SiC–Si3N4 composites by the electroless deposition process

Continuous porous SiC–Si₃N₄ composite fabricated by a multi-pass extrusion process was investigated using SEM, XRD and TEM techniques. In the continuous pore regions, many single crystalline Si₃N₄ whiskers with an average diameter of about 1 μm, which could increase the surface area of the porous composites, were observed. However, to make a platinum coating on the composite, the electroless deposition method was adapted. The spot-type platinum particles, with a diameter of about 50–500 nm, attached to the SiC–Si₃N₄ matrix as well as the surface of the Si₃N₄ whiskers, which can enhance the catalytic activity.     

Recovery of iron as a form of ferrous acetate precipitates from low-grade magnetite ore

This paper describes the recovery process of iron as a form of ferrous acetate from low-grade magnetite ore (Shinyemi Mine, Gangwon province, Korea). The magnetically separated magnetite powder was dissolved in aqueous oxalic acid solution. The dissolution fraction of magnetite concentrates was measured as a function of initial pH, reaction temperature and oxalic acid concentration. Optimum conditions for dissolution of magnetite ore were the temperature higher than 90 °C, pH 1 and oxalic acid concentration 0.5 M. Addition of aqueous H₂O₂ solution oxidized ferrous ion of iron-containing solution. And then, at pH 4, ferric hydroxide was precipitated from iron-containing solution by the addition of NaOH aqueous solution. Ferrous acetate was prepared from the reaction between ferric hydroxide and acetic acid/acetic anhydride mixture and quantitatively characterized by ICP-AES, XRD, SEM, FT-IR and XPS. Purity of ferrous acetate was found to be 91.88% with other impure elements such as Na, Ca, K, Mg and Al by ICP-AES and XPS analysis. XRD and SEM analysis showed that as-prepared ferrous acetate in the present experiments was in low crystalline state. FT-IR spectra confirmed the presence of free acetate ions and monoacetato bidentate structure in as-prepared ferrous acetate.