[en] Bottom-up type in-core instruments (ICIs) are used for the pressurized water reactors of OPR-1000, APR- 1400 in order to measure neutron flux and temperature in the reactor. It is a well-known technique and a proven design using years in the nuclear field. ICI consists of one pair of K-type thermocouple, five self-powered neutron detectors (SPNDs) and one back ground detector. K-type thermocouple's purpose is to measure the core exit temperature (CET) in the reactor. The CET is a very important factor for operating nuclear power plants and it is 327 .deg. C when generally operating the reactor in the nuclear power plant(NPP) in case of OPR- 1000. If the CET will exceed 650 .deg. C, Operators in the main control room should be considered to be an accident situation in accordance with a severe accident management guidance(SAMG). The Multi Thermocouple ICI is a new designed ICI assuming severe accident conditions. It consists of four more thermocouples than the existing design, so it has five Ktype thermocouples besides the thermocouple measuring CET is located in the same elevation as the ICI. Each thermocouple is able to be located in the desired location as required. The Multi Thermocouple ICI helps to measure the temperature distribution of the entire reactor. In addition, it will measure certain point of melted core because of the in-vessel debris of nuclear fuel when an accident occurs more seriously. In this paper, to simulate a circumstance such as a nuclear reactor severe accident was examined. In this study, the K-type thermocouples of Multi Thermocouple ICI was confirmed experimentally to be able to measure up to 1370 .deg. C before the thermocouples have been melted. And after the thermocouples were melted by debris, it was able to be monitored that the signal of EMF directed the infinite value of voltage. Therefore through the results of the test, it can be assumed that if any EMF data among the Multi Thermocouple ICI will direct the infinite value, the reactor core will be damaged as to the position of installed that thermocouple. Also, It is able to know that if the temperature data of the thermocouple will be decreased below 1300 .deg. C by properly controlled after a severe accident, it can be confirmed to re-make a new thermocouple junction at a withdrawal point. In that case, the operators of nuclear power plant can make sure that the severe accident mitigation action is effective. In this study, it is confirmed that the Multi Thermocouple ICI can be importantly applied as a detector to be monitored from entry to mitigation during the nuclear reactor severe accident

[en] Highlights: • A study on Mo⁶⁺-doped TiO₂ as a high performance anode material. • Mo⁶⁺ doping significantly influence the crystal structure and particle sizes. • The electrical conductivity is significantly improved by Mo⁶⁺ doping. • Mo-doped TiO₂ exhibits better electrochemical performances than undoped sample. • Mo doping creates the Ti⁴⁺ vacancies in the lattice and generates more free holes. - Abstract: The effects of molybdenum (Mo⁶⁺) doping on the electrochemical properties of anatase-type titanium dioxide (TiO₂) were investigated. The Mo⁶⁺-doped TiO₂ samples were prepared using a simple and cost-effective solvothermal method with the doping levels of 1, 3, and 5 wt%, followed by annealing at a low temperature of 300 °C for 5 h. High-resolution synchrotron X-ray diffraction and electron microscopy were conducted to know the structural and morphological properties of doped TiO₂ samples. The dopant significantly suppresses the growth of TiO₂ grains and reduces the particles sizes, which can also improve markedly the performance and stability of charge/discharge cycles. The particles sizes are in the range of 115–250 nm and 5–10 nm for undoped and Mo-doped TiO₂ nanoparticle samples, respectively. Electrochemical results show that the Mo⁶⁺-doped TiO₂ nanoparticle samples display a significantly lower charge transfer resistance, higher rate capability and excellent reversibility. Author’s believed that the high rate performance offered by Mo-doped TiO₂ nanoparticle electrodes may be attributed to the enhanced electronic and ionic conductivity, which are achieved by increasing the number of Ti⁴⁺ vacancies in the lattice via Mo⁶⁺ doping, which may lead to the generation of more free holes in the doped p-type semiconductor. The increased hole concentration in the valence band can contribute to the electrical conductivity of the doped sample

[en] An application using coupled kinetics and thermal hydraulics analysis is presented, which supports constructing and confirming the reactor design to maneuver the power operation in a research reactor. Whether the design can essentially cover the required stable and safe operation of power in an acceptable manner is confirmed by analyzing the behavior of the power during a transient state from inserted reactivity coming from the movement of the control absorber rod using a certain type of control logic. A simulation tool capable of handling transient behavior with coupled kinetics and thermal-hydraulics is a must-have kit through all design processes, especially at the starting phase of the design. Herein, a code able to catch the very physics with point kinetics and simplified thermal hydraulics within the incorporated core has been developed and programmed in modern MATLAB/SIMULINK, but originally written in FORTRAN. The tool was verified and tested through numerical experiments using the PARET/ANL code. A set of calculated results suggests the possibility of the code for its extension to a tool to prepare the guidelines for safe operation

[en] Highlights: • Factors controlling temporal change of CO₂ NAF in a stratified reservoir is studied. • Buoyant turbulence strongly affects CO₂ NAF under thermally unstable conditions. • Surface renewal gas exchange models yield twice the CO₂ NAF of the empirical models. • Data-driven models elucidated water quality factors determining temporal variability of CO₂ NAF. • RF model explained 84.4% of the temporal change in CO₂ NAF using EC, DO, and TOC. The temporal variations in CO₂ net atmospheric flux (NAF) in stratified reservoirs are controlled by both physical and biological factors. However, research on the factors and processes affecting CO₂ NAF variability over time is insufficient, and as a result, there is considerable uncertainty in present estimations of global reservoir CO₂ emissions. In the present study, we analyzed the effects of hydrodynamic and water quality factors on CO₂ NAF variability in a stratified reservoir based on field studies and data modeling. Three empirical and four surface renewal gas transfer models were used to characterize the effects of hydrodynamic factors on gas transfer rate and CO₂ NAF at the air–water interface. Buoyant turbulence notably affected CO₂ NAF when the stratification strength was reduced. As a result, the CO₂ NAF (1485 mg-CO₂ m⁻² day⁻¹) estimated using surface renewal models that considered the effects of buoyant turbulence were twice greater than the NAFs estimated using empirical models that only considered wind force (724 mg-CO₂ m⁻² day⁻¹). The best linear regression model explained 81.6% of the temporal variation in CO₂ NAF using water temperature (Tw), electrical conductivity (EC), pH, chlorophyll a, total organic C (TOC), and alkalinity. The nonlinear parsimonious random forest model explained 84.4% of the temporal change in CO₂ NAF using only three independent variables (EC, dissolved oxygen, and TOC). Principal component analysis revealed that the CO₂ NAF tended to be large under low Tw, weak stratification, and low pH. These results indicate that the temporal variability of CO₂ NAF in the stratified reservoir can be predicted using data-driven modeling with minimal water quality variables and selection of an appropriate gas exchange model. The findings improve the accuracy of estimates of CO₂ emissions and monitoring activities in stratified reservoirs.

[en] We investigated the surface atomic structure of a graphene layer grown on a single-crystal Cu(111) surface by using a chemical vapor deposition method. The low-energy electron diffraction pattern shows a clear ring structure, which indicates the existence of multiple domains with different in-plane orientations. In the scanning tunneling microscopy experiment, two domains showing different Moire patterns and a domain boundary between them are observed. The misorientation angle between the domains could be estimated from the quantum interference pattern around the domain boundary and the atom-resolved image of each domain.

[en] Nanostructured thermoelectric bismuth telluride (Bi₂Te₃) powders with various morphologies, such as nanoplates, nanorods, and nanotubes, were prepared by a hydrothermal method based on the reaction between BiCl₃, Te, and sodium ethylenediaminetetraacetate (Na₂-EDTA) at 150, 180, and 210 .deg. C. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). The effect of reaction temperature on the morphology of the Bi₂Te₃ particles was investigated, and the possible mechanism of morphology control was proposed

[en] Highlights: • LiNi_1/3Co_1/3Mn_1/3O₂ cathode synthesis via an ambient temperature redox reaction. • The stoichiometric elemental composition is controlled by the redox synthesis. • The cathode exhibits ordered layer-type structure with minimal cation mixing. • The cathode exhibited reasonable electrochemical properties versus lithium. - Abstract: The present work reports on the development of layered-type Li_x(Ni_1/3Co_1/3Mn_1/3)O₂ (x = 1.05 and 1.1) cathodes by a simple ambient temperature redox synthesis followed by post-heat treatments with added lithium source. The intermediate precursor (Ni_1/3Co_1/3Mn_1/3O_y) was synthesized through redox reaction between KMnO₄, CoCl₂ and NiCl₂ in aqueous KOH medium. Synchrotron XANES and ICP measurements were performed to confirm the changes in the oxidation states and successful control in stoichiometric ratio of ternary transition metal oxide (Ni²⁺_0.33Co³⁺_0.35Mn⁴⁺_0.32O_y) during the redox reaction. Synchrotron X-ray diffraction studies of post lithiation confirmed the formation of a well-developed layer-type hexagonal phase of α-NaFeO₂ with least cation mixing, as observed from the estimated lattice parameters (a = 2.858 Å and c = 14.228 Å), integrated intensity ratio (I₀₀₃/I₁₀₄ = 1.79), and c/3a ratio (∼1.659) values. FE-SEM images revealed loosely agglomerated particles with average diameters of 60 nm in the intermediate product while the particle-size grows to a few hundred nanometers after lithiation at elevated temperatures. The electrochemical performances in the potential range of 3.0–4.3 V vs. Li/Li⁺ at 14 mAg⁻¹ indicated that reasonable specific capacities and cycle performances are registered for all the prepared cathodes. In particular, the Li_1.05(Ni_1/3Co_1/3Mn_1/3)O₂ composition demonstrated the highest capacity retention value (∼99%) after 50 cycles and better rate performances (104, 91, 76, and 67 mAhg⁻¹) at high current densities (229, 457, 914, and 1429 mAg⁻¹ respectively).

[en] We have observed relaxation oscillations in an argon capacitive discharge connected to a peripheral grounded chamber through a slot with dielectric spacers. The oscillations, observed from time-varying optical emission of the main discharge chamber, show, for example, a high frequency (∼40 kHz) relaxation oscillation at 100 mTorr, with absorbed power near that for peripheral breakdown, and a low frequency (∼3 Hz) oscillation, at higher absorbed power. The high frequency oscillation is found to ignite a plasma in the slot, but usually not in the periphery. We interpret the high frequency oscillations using an electromagnetic model of the slot impedance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations and indicate a variety of behaviors dependent on the matching conditions

[en] Highlights: • The V-doped MnO_2 was prepared by a simple ambient redox reaction. • The V-doped MnO_2 was tested as a cathode in aqueous zinc-ion batteries (ZIBs). • The doped cathode showed better zinc-storage properties than the bare cathode. • The present study facilitates the development of safe and reliable aqueous ZIBs. - Abstract: In this work, we demonstrate the first use of a V-doped MnO_2 nanoparticle electrode for zinc-ion battery (ZIB) applications. The V-doped MnO_2 was prepared via a simple redox reaction and the X-ray diffraction studies confirmed the formation of pure MnO_2, accompanied by an anisotropic expansion of MnO_2 lattice, suggesting the incorporation of V-ions into the MnO_2 framework. V doping of MnO_2 not only increased the specific surface area but also improved the electronic conductivity. When Zn-storage properties were tested, the V-doped MnO_2 electrode registered a higher discharge capacity of 266 mAh g"−"1 compared to 213 mAh g"−"1 for the pure MnO_2 electrode. On prolonged cycling, the doped electrode retained 31% higher capacity than that of the bare MnO_2 electrode and thereby demonstrated superior cycling performance. This study may pave the way towards understanding the enhancement of the energy storage properties via doping in electrodes of aqueous ZIB applications and also furthers the efforts for the practical realization of a potential eco-friendly battery system.

[en] K-type thermocouple is widely used in nuclear power plants (NPP) and they provide reliable service. Generally, the thermocouple assembly is the finished product and usually only nondestructive tests are performed on the assembly, whereas destructive tests are confined to selected bulk cable specimens. This K-type thermocouple has been used representatively in the In-Core Instrument Assembly (ICI) in the nuclear power plants. The ICI consists of five rhodium emitter detectors that provide information on the thermal power for the core and one K-type thermocouple made with two cables (Chromel-Alumel) that provides the temperature of core exit (CET). Generally, the quantity of the ICI is absolutely different according to the number of fuel assemblies in the NPP. In the case of SKN 3 and 4, they were designed to the 61 ICI to provide information on the core cooling to the inadequate core cooling monitoring system (ICCMS). This measured temperature could be also used to check the entry condition of severe accidents. The technology of the TFDR is a generic skill to detect the fault position of the cable. In-core Instruments (ICIs) were used to detect the Core Exit Temperature (CET) in a reactor. This measured temperature was also used to check the entry condition of severe accidents. However, if a serious accident occurs, the upper portion of the core is damaged. This instrument has not been available. This paper illustrates the estimation possibility for the status of molten core through the high-temperature characteristics test of k-type thermocouple. It turns out that it is possible to measure the k-type thermocouple up to 1350 .deg. C degrees before melting during insertion into the melting furnace. Additionally, in order to measure a high temperature of 2000 .deg. C or more, the replacement possibility of k-type thermocouple was evaluated. However the tungsten-rhenium thermocouple is impossible to use in the detection of temperature at the in-core because of the change of elements