[en] The control rod drive mechanism (CRDM) in nuclear power plant is usually cooled by outside forced ventilation to make sure it works properly. The forced ventilation outside the CRDM will lead to thermosyphon phenomenon inside the CRDM which results in the temperature rising along the axial direction of the CRDM. It was reported that the location of the drive rod is one of the most important factors which affect the thermosyphon phenomenon. In this study, the effect of the drive rod's location on the axial heat transfer of CRDM is investigated experimentally through measuring the axial temperature distribution of the CRDM under various ventilation speeds when the drive rod locates at both full height and half height of the CRDM. The experimental results show that the thermosyphon phenomenon is intensified for the full height condition comparing with the half height condition and more cooling capacity is achieved under the same ventilation condition. (authors)

[en] Highlights: • Redox mechanism of FeS_2 is studied by galvanostatic cycling and impedance analysis. • FeS_2 cannot be re-constituted by recharge once being fully discharged. • Li/FeS_2 battery converts into a hybrid of a Li/FeS cell and a Li/S cell in the first discharge. • Li/FeS_2 battery faces the same problems with Li/S battery in relation to the dissolution of polysulfide. - Abstract: The redox mechanism of micro-sized FeS_2 particles in a rechargeable lithium battery is studied by galvanostatic cycling and ac-impedance analysis. It is shown that FeS_2 is irreversibly reduced on the first discharge, turning Li/FeS_2 cell into a combination of Li/FeS and Li/S chemistries, as suggested by two distinct discharge plateaus at ∼1.5 and 2.0 V, respectively. The first discharge consists of an irreversible conversion of FeS_2 to Li_2FeS_2 intermediate and its subsequent reduction to metallic Fe and Li_2S. The first discharge suffers an initial voltage delay, suggesting that the discharge progresses in a thermodynamic non-equilibrium condition. The initial voltage delay can be attributed to the large grain boundary resistance (GBR) of pristine FeS_2 particles, which impedes the nucleation of a new solid Li_2FeS_2 phase causing high polarization. Ac-impedance spectra of the FeS_2 cathode are composed of a semicircle and a straight sloping line, representative of an electrode reaction resistance (R_e_r) and a Li"+ adsorption impedance, respectively. The R_e_r is found to decrease progressively during the first discharge and reaches a plateau when the cell is charged above 2.5 V vs. Li/Li"+, being consistent with the model that FeS_2 is irreversibly reduced during the first discharge and that the Li_2S/Li_2S_n redox couple is formed in recharge. It is indicated that Li/FeS_2 batteries face the same problems as Li/S batteries, such as the dissolution of lithium polysulfide, the formation of a redox shuttle, and the loss of sulfur active material

[en] Highlights: •Conventional separator is coated with a 50PEO-50SiO₂ (wt.%) composite layer. •Composite coating increases tensile strength and electrolyte wettability. •Coated separator offers an alternative approach for making gel polymer Li/S battery. •Li/S battery takes benefits of gel polymer electrolyte at the expense of capacity. -- Abstract: Gel polymer electrolyte (GPE) and composite gel polymer electrolyte (CGPE) have been widely employed to improve the safety and cycling performance of rechargeable lithium and lithium-ion batteries. In order to determine whether this approach is applicable to lithium/sulfur (Li/S) battery, we examine the effect of CGPE on the cycling and storage performances of Li/S cells by comparing a 50PEO-50SiO₂ (wt.%) composite coated separator (C-separator) with a pristine separator (P-separator). Results show that the composite coating significantly enhances the wettability of liquid electrolyte on the separator and that resulting CGPE can tightly glue the separator and electrode together. In comparison with the P-separator, the C-separator offers Li/S cells similar capacity retention and rate capability; however it greatly affects the specific capacity of sulfur. The analysis on the impedance spectrum of a lithium polysulfide (PS) solution reveal that the reduction of sulfur specific capacity is due to the high viscosity of the CGPE and the strong adsorption of SiO₂ filler to the PS species, which trap PS species in the separator and hence reduce the utilization of sulfur active material. Therefore, the benefits of the GPE and CGPE to the Li/S batteries can be taken only at the expense of sulfur specific capacity

[en] Under investigation in this paper is the AB system, which is used to describe the propagation of the wave packets in a marginally stable or unstable baroclinic shear flow. Introducing an auxiliary function $\mathrm{\alpha <!--\; ??\; -->}(\mathrm{\tau <!--\; ??\; -->})$, we predict irregular solitons and construct the high-order irregular dark solitons for the AB system, which are different from those in the existing literature. Affected by $\mathrm{\alpha <!--\; ??\; -->}(\mathrm{\tau <!--\; ??\; -->})$, the dark solitons are classified into three types, i.e., Type-I, Type-II and Type-III solitons. Type-I solitons propagate with unchanged shapes and velocities, Type-II solitons are shape-changing in the evolution, and Type-III solitons propagate with not only the shape variations but the appearances, splits, combinations and disappearances of some pits. We reveal that two Type-I solitons interact with each other elastically when they possess different velocities, and degenerate into the first-order solitons when they possess the same velocity. For the interactions between Type-II–Type-II, Type-II–Type-III, Type-III–Type-III solitons, it is found that $\mathrm{\alpha <!--\; ??\; -->}(\mathrm{\tau <!--\; ??\; -->})$ changes the interaction behaviors of the two solitons during the propagation. (paper)

[en] Integral test plays a key role in assessing the feasibility of the passive containment cooling system (PCCS) and the accuracy of the calculation model. The scaling analysis for ; mixing in large stratified volumes of PCCS provides the primary theoretical basis for determining the key size of the integral test facility. Based on the mixing in large stratified volumes, the key parameters were obtained by scaling analysis based on the hierarchical two-tiered scaling method. The similarity criteria that ensure the integral test facility can well simulate mixing in the passive containment was obtained. (authors)

[en] The preventive maintenance program is the guidance document of nuclear power plant operation and maintenance project, and its rationality plays an important role in the safe, reliable and economic operation of nuclear power plant. In this paper, an improved RCM maintenance optimization technology is proposed, which is based on the practical experience of traditional RCM. It has been successfully applied to the optimization of preventive maintenance program of the main transformer of nuclear power plant. The analysis efficiency is improved. It also makes the preventive maintenance program of the main transformer more reasonable. The operation reliability is improved, and the operation and maintenance cost is reduced. And it also provides a reference for the implementation and application of reliability maintenance optimization technology in nuclear power plant or other fields. (authors)

[en] Fluorescent carbon nanoparticles (CNPs) with a broad size distribution were synthesized by the nitric acid oxidation of diesel soot. The CNPs were separated by size using a combination of a solvent mixture and high-speed centrifuging, and the properties of the CNPs were investigated by elemental analysis, scanning electron microscopy and fluorescence spectroscopy to evaluate whether CNPs with improved fluorescence properties could be obtained by this method. There were three distinct improvements in our modified method. First, a novel raw material was successfully used to synthesize the water-soluble particles, and a simple method to separate the small-size CNPs from the heterogeneous particle mixture was developed. Second, the fluorescence intensity and color of the small particles changed with the pH value, and the isolation of the small particles also improved the fluorescence quantum yield, which was approximately 5%. Third, the fluorescence intensity of the small particles without any further functionalization was quenched by the presence of Mn(II) with a Stern–Volmer constant of 1.79×10⁴ L/mol. The synthesis and application of a novel biocompatible nanosensor for measuring Mn(II) is presented. -- Highlights: • Combustion soot of diesel was first used to synthesize the CNPs. • A simple method to separate the small-size CNPs was developed. • The fluorescence intensity and color of small particles changed with the pH value. • The isolation of the small particles improved the fluorescence quantum yield. • Application of a novel biocompatible nanosensor for measuring Mn(II) is presented

[en] In this Letter, the Exp-function method is used to seek generalized solitonary solutions of Riccati equation. Based on the Riccati equation and its generalized solitonary solutions, new exact solutions with three arbitrary functions of the (2+1)-dimensional Broer-Kaup-Kupershmidt equations are obtained. It is shown that the Exp-function method provides a straightforward and important mathematical tool for nonlinear evolution equations in mathematical physics

[en] A generalized F-expansion method is proposed and applied to the KdV-Burgers-Kuramoto equation. As a result, many new and more general exact travelling wave solutions are obtained including combined non-degenerate Jacobi elliptic function solutions, solitary wave solutions and trigonometric function solutions. The method can be applied to other nonlinear partial differential equations in mathematical physics

[en] In this Letter, a generalized auxiliary equation method is used to construct exact solutions of the (2+1)-dimensional breaking soliton equations. As a result, many new and more general exact non-traveling wave and coefficient function solutions are obtained including soliton-like solutions, trigonometric function solutions, exponential solutions and rational solutions, each of which contains an arbitrary function of two variables. It is shown that the generalized auxiliary equation method provides a powerful mathematical tool for solving many nonlinear partial differential equations in mathematical physics