Chemical analysis of fuel crud obtained from Korean nuclear power plants

Crud samples were obtained from two different kinds of used fuels in PWRs. The constituent elements were analysed according to the shapes of crud particles by SEM and EPMA. The principal elements of octahedral crystal particles were identified as Ni and Fe, where the ratio (Fe/Ni) was approximately 2. The major element of the observed needle-like structures was determined to be Ni. In addition, Zr composed the main element of particles shaped like broken fragments sized at 10-50 μm in diameter. The round particles less than 20 μm in diameter were identified as Si-containing compounds. We also found the Zn element in a series of fuel crud samples obtained from a plant. Zn was mainly detected in the hard crud, inner layer of crud, but not on the surface of crud. It was observed that there is an inverse relationship between the Ni and Zn contents in the hard crud.     

Geometric parameter design of a cantilever probing needle used in epoxy ring probe card

In wafer probe card fabrication, contact force and forward displacement of needle tip are both important considerations affecting the probing results critically. This study establishes a finite element model of a cantilever probing needle used in epoxy ring probe card, to explore the effects of needle geometric parameters and probing overdrive upon the needle tip situation. Taguchi's methodology is used to derive the optimal parameter selection. Analytical results show that factors of taper length and needle diameter are the most influential in contact force, and the force can be controlled by the horizontal distance of cantilever measured from the needle tip to the epoxy fixed end. As for the forward displacement of the needle tip, both of taper length and cantilever horizontal distance are significant, and the probing displacement of the needle tips could be validly adjusted by the factors of bending angle and insert angle. A real experimental card has been made to verify the analytical results. Related materials can be provided as effective references in probe card design.     

Convective instabilities and transport properties in horizontal fluid layers

This paper concerns the analysis of convective instabilities and fully developed transport properties in Bénard convection. The onset of convective instabilities driven by surface-tension variations and buoyancy forces is analyzed theoretically by using the propagation theory we have developed. Based on these stability criteria, the subsequent transport correlations of fully developed buoyancy-driven convection in horizontal fluid layers are suggested. It is found that the present predictions are compared favorably with existing experimental results.     

Direct Physical Imaging and Chemical Probing of LiFePO4 for Lithium‐Ion Batteries

The control of unexpectedly rapid Li intercalation reactions without structural instability in olivine‐type LiFePO₄ nanocrystals is one of the notable scientific advances and new findings attained in materials physics and chemistry during the past decade. A variety of scientific studies and technological investigations have been carried out with LiFePO₄ to elucidate the origins of many peculiar physical aspects as well as to develop more effective synthetic processing techniques for better electrochemical performances. Among the several features of LiFePO₄ that have attracted much interest, in this article we address four important issues—regarding doping of aliovalent cations, distribution of Fe‐rich secondary metallic phases, nanoparticle formation during crystallization, and antisite Li/Fe partitioning—by means of straightforward atomic‐scale imaging and chemical probing. The direct observations in the present study provide significant insight into alternative efficient approaches to obtain conductive LiFePO₄ nanocrystals with controlled defect structures.     

Synthesis and electroluminescent properties of π-conjugated copolymer based on 10-hexylphenothiazine and aromatic 1,2,4-triazole

A new polymer, poly((10-hexyl-3,7-phenothiazine)-alt-(4-(4-butyl-phenyl)-3,5-diphenyl-4H-[1,2,4]triazole)-3,5-diyl) (PT-TAZ), has been synthesized. In order to improve electron injection/transporting ability, we introduce electronegative 1,2,4-triazole group in the backbone. We also synthesized poly(10-hexylphenothiazine-3,7-diyl) (PT) to compare the physical properties with PT-TAZ. The photoluminescence (PL) maximum wavelength, the band gap energy, and the HOMO energy level of PT-TAZ film were 509 nm, 2.67 eV, and −5.06 eV, respectively, which are very comparable to those of PT. The maximum efficiency and brightness of the electroluminescent (EL) device based on PT-TAZ were 0.247 cd/A and 771 cd/m², respectively, which were significantly higher than those of the device based on the polymer without 1,2,4-triazole (TAZ) as a repeat unit (PT) (1.05 × 10⁻⁴ cd/A and 4.4 cd/m²). This is because TAZ unit improves the electron transporting ability in the emissive layer. The turn-on voltage of brightness of the device based on PT-TAZ was 5.0 V, which was slightly higher than that of the based on PT (4.5 V). This is because the ionization potential of PT-TAZ is very similar to that of PT.     

Sliding mode control of a shear-mode type ER engine mount

This paper presents feedback control characteristics of a shear-mode type electro-rheological (ER) engine mount. The field-dependent yield stress of an arabic gum-based ER fluid is obtained using a couette type electroviscometer, and it is incorporated into the governing equation of motion of the ER engine mount, which is derived from a bond graph model. A sliding mode controller which directly represents the field-dependent damping force is formulated by taking into account the stiffness and damping properties of the systems as parameter uncertainties. The controller is then experimentally realized by imposing a semi-active actuating condition. The effectiveness of the proposed ER engine mount is demonstrated showing capabilities of isolating the vibrations due to sinusoidal and random excitations.     

A case study on detection and sizing of defects in steam generator tubes using eddy current testing

Eddy current testing (ECT) method is widely used to detect various types of defects occurring in nuclear steam generator tubes. Therefore, the reliability of its detection and sizing accuracy for defects should be validated. For this purpose, two tubes with defect signals were pulled from an operating steam generator and destructively examined. The defect type was a circumferential crack for one tube and an intergranular attack (IGA) for the other tube. The plus point coil probe showed a better capability to detect and size both a circumferential crack and a volumetric IGA than pancake and bobbin coil probe. The destructive results are correlated with the ECT results obtained during the in-service inspection.     

An experimental study of the mean effective strain in rod (or bar) rolling process

This paper presents an experimental study that investigates the validity of the analytical model [9] for predicting the mean effective strains associated with bar (or rod) rolling. Designed for this purpose were plate and bar rolling experiments which consist of a four-pass groove (oval and round) rolling sequences, which have material at each pass that experience the same amount of mean effective strain. The microstructure and mechanical behaviors of specimens acquired from two types of rolling experiments at 650°C were compared. A parallelism between the mechanical behaviors of a plate-rolled specimen and a bar-rolled specimen has been found at each pass. We therefore concluded that the analytical model has the underlying rationale to be used in the analysis of the rod (or bar) rolling process.