[en] The temporal and spatial characteristics of plasma ion currents produced from the laser irradiation (10⁹ - 10¹¹ W/cm² at 1.06 μm) on solid targets have been studied experimentally and compared to a simple theoretical model. The data collection and acquisition system includes a Faraday cup coupled with preamplifier circuit, a high speed waveform digitizer, and a computer system interfaced via CAMAC and a GPIB bus. The data obtained with this system proved to be highly reproducible, resulting in reliable and quantitative data analysis. A self-similar hydrodynamic expansion model has been adopted to analyze the laser plasma expansion into the vacuum. The plasma density, expansion velocity, temperature, and pressure in conjunction with the laser beam absorption and dissipation processes are considered as the governing parameters to describe the asymptotic behavior of the laser excited plasma. The numerical calculations demonstrate that the model well represents experimental observations. The results indicate that a substantial fraction of the input laser energy is transported to energetic ions expanding into the vacuum. The fast ions have keV kinetic energies and these energies tend to increase as the irradiation power density increases. At a laser intensity of approximately 10¹¹ W/cm², the ion current distribution begins to show strong directionality along a line normal to the target plane, while at an input beam intensity below 3 x 10⁹ W/cm², the plasma ion currents show more spherically uniform distributions

[en] The Regulatory Guide 1.82 recommends an analysis of hydraulic performance for sump of ECCS (Emergency Core Cooling System) when LOCA (loss of coolant accident) occurs in a nuclear power plant. The present study deals with 3-dimensional, unsteady, turbulent and two-phase flow simulation to examine the behavior of mixture of reactor coolant and debris near the floor of containment building in conjunction with appropriate assumptions. The dispersed solid model has been adjusted to the interfacial momentum transfer between reactor coolant and debris. According to the results, the counterclockwise recirculation zone had been formed in the region between sump and connection aisle about 376 second after LOCA occurs. The debris thickness accumulated ona sump screen periodically increases or decreases up to 2000 second, afterwards its peak decreases. (author)

[en] Polycrystalline BaTiO₃ ceramics were synthesized from Mn-coated semiconducting BaTiO₃ powders by hot-press sintering. The diffusion coefficients of the Mn, Ba, Ti ions near the grain boundary were estimated from the chemical distribution near the grain boundary of the ceramics; the chemical distribution was obtained by analytical transmission electron microscopy. The grain boundary potential barrier height was also estimated from the chemical distribution

[en] Nano-grained BaTiO₃ ceramics were synthesized by sintering BaTiO₃ nano-powders; these powders were coated with Mn-materials. The phase transition and physical features of the BaTiO₃ ceramics were investigated as a function of the sintering temperature and the amount of coating materials. With increasing the sintering temperature and/or the amount of the coating materials, the formation of a tetragonal phase was increased; this seems to be due to grain growth and grain boundary chemical features. The relation of the dielectric features of the nano-grained BaTiO₃ ceramics with the structural variation is discussed in terms of process parameters

[en] In order to understand the broad technology of nuclear energy, we have explored how our present knowledge of nuclear energy has been developed, and how some of this knowledge is applied. Techniques learned from nuclear physics are used the build fearsome weapons of mass destruction, whose proliferation is a constant threat to our future. To develop military applications of nuclear technology systematically, high level human resources and creative brains should be sufficiently trained and secured

[en] The effects of deposition parameters and post-deposition heat-treatment on the structural and magnetic characteristics of (Ce:) yttrium iron garnet (YIG) films, prepared by RF magnetron sputter techniques, have been investigated. The Ce ions of the Ce : YIG films are composed of Ce³⁺ and Ce⁴⁺, and the fraction of the Ce³⁺ in the films is at its maximum when the oxygen fraction in sputter gas (Ar+O₂) is 10%. The variation of the chemical stoichiometry as well as the oxidation state of the Ce ions with the oxygen fraction in sputter gas is discussed with the structural and magnetic features of the films. With raising the temperature of post-deposition heat-treatment from 900 deg. C to 1100 deg. C, the surface roughness of the films on gadolinium gallium garnet substrates increases, but the coercive force as well as the ferromagnetic resonance linewidth decreases

[en] In this work, we propose a method to measure the feedwater flow using multi-path ultrasonic flow meter (UFM). Since the UFM measures a path velocity at which the ultrasonic wave is propagated, the flow profile may be important to convey the path velocity to the velocity averaged over the entire cross section of the flowing medium. The conventional UFM has used the smooth-wall circular pipe model presented by Nikurades. However, this model covers a lower range which is less than 3.2 million while the Reynolds number of the feedwater flow in operating nuclear power plants (NPPs) is about 20 million. Therefore, we feedwater flow in operating nuclear power plants (NPPs) is about 20 million. Therefore, we proposed the non-linear correlation model that combines the ratio between the DP output and proposed the non-linear correlation model that combines the ratio between the DP output and UFM output. Experiments were performed using both computer simulation and newly constructed NPPs' test data. The uncertainty analysis result shows that the proposed method has reasonably lower uncertainty than conventional UFM

[en] A numerical analysis for RDT sparger of PWR is carried out. Computation is performed for flow characteristic as the change of design factor. As the result of this study, RDT sparger's flow resistance coefficient is K = 3.53 at the present design condition if engineering margin is considered with 20 percent, and flow ratio into branch pipe is Q_s/Q_i = 0.41. Velocity distribution at exit is not uniform because of separation in branch pipe. In the change of inlet flowrate and section area ratio of branch pipe for main pipe, flow resistance coefficient is increased as Q_s/Q_i decreasing, but in the change of branch angle and outlet nozzle diameter of main pipe, flow resistance coefficient is decreased as Q-s/Q_i decreasing. The change rate of Q_s/Q_i is the larger, the change rate of flow resistance coefficient is the larger. The change rate of pressure loss is the largest change as section area ratio changing. The optimal design condition of sparger is estimated as the outlet nozzle diameter ratio of main pipe is D_e/D_i = 0.333, the section area ratio is A_s/A_i = 0.2 and the branch angle is α = 55 ^o. (author)

[en] The thermohydraulic phenomena in the reactor vessel cavity of Korea Nuclear Power Plant has been studied by the numerical analysis. The heat transfer and flow analysis in reactor vessel cavity is important in determining the capacity of HVAC device as well as in the thermal design of the reactor power plant. To improve the insulation and RCCS design, the heat transfer characteristics and design requirements were examined in accordance with the reactor insulation wall conditions and the inlet temperature change in the reactor cavity with the reactor vessel insulation and HVAC design data of UCN 3 and 4. The result indicates the reactor cavity inlet air temperature should be lower than 40 deg C (104 deg F) in order to satisfy the design requirement of the outlet temperature of the reactor cavity. (author)

[en] It is necessary to collect data sets of local flow parameter for improving accuracy of interfacial area transfer equation that was proposed for interfacial transfer terms at the two fluid model. In this research, a measurement method using capacitive probe is proposed to measure local flow parameter. The electric field calculation was performed to quantify the capacitance between probes. The calculated value was well in agreement with the experimental data. For the capacitance measurement, a charge/discharge circuit was employed to measure up to Femto-Farad level. Though the work, the present capacitance local probe can be applicable for the microgravity two-phase flow, which is important to nuclear power for the space program