• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.625-636
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• 2013

Pressing demands of economic competitiveness, the need for large-scale deployment, minimizing the need of human intervention, and experience from the past events and incidents at operating reactors have guided the evolution and innovations in reactor technologies. Indian innovative reactor 'AHWR' is a pressure-tube type natural circulation based boiling water reactor that is designed to meet such requirements, which essentially reflect the needs of next generation reactors. The reactor employs various passive features to prevent and mitigate accidental conditions, like a slightly negative void reactivity coefficient, passive poison injection to scram the reactor in event of failure of the wired shutdown systems, a large elevated pool of water as a heat sink inside the containment, passive decay heat removal based on natural circulation and passive valves, passive ECC injection, etc. It is designed to meet the fundamental safety requirements of safe shutdown, safe decay heat removal and confinement of activity with no impact in public domain, and hence, no need for emergency planning under all conceivable scenarios. This paper examines the role of the various passive safety systems in prevention and mitigation of severe plant conditions that may arise in event of multiple failures. For the purpose of demonstration of the effectiveness of its passive features, postulated scenarios on the lines of three major severe accidents in the history of nuclear power reactors are considered, namely; the Three Mile Island (TMI), Chernobyl and Fukushima accidents. Severe plant conditions along the lines of these scenarios are postulated to the extent conceivable in the reactor under consideration and analyzed using best estimate system thermal-hydraulics code RELAP5/Mod3.2. It is found that the various passive systems incorporated enable the reactor to tolerate the postulated accident conditions without causing severe plant conditions and core degradation.

• Korean Journal of Materials Research
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• v.17 no.9
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• pp.453-457
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• 2007

Interest in use of ink-jet printing for pattern-on-demand fabrication of metal interconnects without complicated and wasteful etching process has been on rapid increase. However, ink-jet printing is a wet process and needs an additional thermal treatment such as an annealing process. Since a metal ink is a suspension containing metal nanoparticles and organic capping molecules to prevent aggregation of them, the microstructure of an ink-jet printed metal interconnect 'as dried' can be characterized as a stack of loosely packed nanoparticles. Therefore, during being treated thermally, an inkjet-printed interconnect is likely to evolve a characteristic microstructure, different from that of the conventionally vacuum-deposited metal films. Microstructure characteristics can significantly affect the corresponding electrical and mechanical properties. The characteristics of change in microstructure and electrical resistivity of inkjet-printed silver (Ag) films when annealed isothermally at a temperature between 170 and $240^{\circ}C$ were analyzed. The change in electrical resistivity was described using the first-order exponential decay kinetics. The corresponding activation energy of 0.44 eV was explained in terms of a thermally-activated mechanism, i.e., migration of point defects such as vacancy-oxygen pairs, rather than microstructure evolution such as grain growth or change in porosity.

• Journal of the Korean Magnetics Society
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• v.15 no.6
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• pp.311-314
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• 2005

We investigated the composition dependence of the tunneling magnetoresistance (TMR) behavior and the stability of the magnetic tunnel junctions (MTJs) with TiAlOx barrier and the microstructural evolution of TiAl alloy films. The TMR ratio increased up to $49\%$ at $5.33\;at\%$ Ti. In addition, a significant tunneling magnetoresistance (TMR) value of $20\%$ was maintained after annealing at $450^{\circ}C$, and the breakdown voltage ($V_B$) of and 1.35 V were obtained in the MTJ with $5.33\;at\%$ Ti-alloyed AlOx barrier. These results were closely related to the enhanced quality of the barrier material microstructure in the pre-oxidation state. Ti alloying enhanced the barrier/electrode interface uniformity and reduced microstructural defects. These structural improvements enhanced not only the TMR effect but also the thermal and electrical stability of the MTJs.

• Economic and Environmental Geology
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• v.29 no.6
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• pp.753-765
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• 1996

It is a well known fact that the remanent magnetization direction of the Tertiary rocks is deflected significantly clockwise (about $50^{\circ}$) in the Tertiary basins of the southeastern part of Korean peninsula. This fact has been interpreted as an evidence of north-south spreading of the East Sea (Sea of Japan) and dextral strike-slip motion of the Yangsan fault. As deflection (rotation) of remanent magnetizations is frequently reported from various regions of the world in the vicinities of strike-slip fault, such phenomena are to be expected in the Yangsan fault region also. It was the purpose of this study to clarify whether such premise is right or not. A total of 445 independently oriented core samples were collected from Cretaceous rocks of various lithology (sedimentary rocks, andesites and I-type granites) in the Yangsan fault area. In spite of through AF and thermal demagnetization experiments, no sign of remanent magnetization deflection was found. Instead, palaeomagnetic poles calculated from formation-mean ChRM directions are very similar to those of contemporary (Barremian, and late Cretaceous-Tertiary) sedimentary and plutonic rocks in the other parts of $Ky{\check{o}}ngsang$ basin as well as those of China. Therefore, possibility of tilting of granite plutons and horizontal block rotation of study area is excluded. It is also concluded that the Yangsan fault did not take any significant role in the Cenozoic tectonic evolution of southeast Korea and the East Sea region. The boundary between rotated and unrotated region of remanent magnetization is not the Yangsan fault line, but must lie further east of it.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.45-50
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• 2008

Microstructural evolution and the intermetallic compound (IMC) growth kinetics in an Au stud bump were studied via isothermal aging at 120, 150, and $180^{\circ}C$ for 300hrs. The $AlAu_4$ phase was observed in an Al pad/Au stud interface, and its thickness was kept constant during the aging treatment. AuSn, $AuSn_2,\;and\;AuSn_4$ phases formed at interface between the Au stud and Sn. $AuSn_2,\;AuSn_2/AuSn_4$, and AuSn phases dominantly grew as the aging time increased at $120^{\circ}C,\;150^{\circ}C,\;and\;180^{\circ}C$, respectively, while $(Au,Cu)_6Sn_5/Cu_3Sn$ phases formed at Sn/Cu interface with a negligible growth rate. Kirkendall voids formed at $AlAu_4/Au$, Au/Au-Sn IMC, and $Cu_3Sn/Cu$ interfaces and propagated continuously as the time increased. The apparent activation energy for the overall growth of the Au-Sn IMC was estimated to be 1.04 eV.

• Metals and materials international
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• v.24 no.6
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• pp.1346-1358
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• 2018

A novel additive manufacturing method with TIG-MIG hybrid heat source was applied for fabricating 5356 aluminum alloy component. In this paper the microstructure evolution, mechanical properties and fracture morphologies of both as-deposited and heat-treated component were investigated, and how these were affected by different heat-treated temperature. The as-deposited microstructure showed dominant equiaxed grains with second phase, and the size of them is coarse in the bottom region, medium in the middle region and fine in the top region owing to different thermal cycling conditions. Compared with as-deposited microstructure, the size of grain becomes large and second phases gradually dissolve in the matrix as heat-treated temperature increase. Different microstructures determine the mechanical properties of component. Results show that average ultimate tensile strength enhances from 226 to 270 MPa and average microhardness increases from 64.2 to 75.3 HV0.1 but ductility decreases from 33 to 6.5% with heat-treated temperature increasing. For all components, the tensile properties are almost the same in the vertical direction (Z) and horizontal direction (Y) due to equiaxed grains, which exhibits isotropy, and the mechanisms of these are analyzed in detailed. In general, the results demonstrate that hybrid arc heat source has the potential to fabricate aluminum alloy component.

• Journal of Electrochemical Science and Technology
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• v.12 no.1
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• pp.112-125
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• 2021

The new emerging "High entropy materials" attract the attention of the scientific society because of their simpler structure and spectacular applications in many fields. A novel nanocrystalline high entropy (Be,Mg,Ca,Sr,Zn,Ni)3O4 oxide has been successfully synthesized through mechanochemical treatment followed by sintering and air quenching. The present research work focuses on the possibility of single-phase formation in the aforementioned high entropy oxide despite the great difference in the atomic sizes of reactant alkaline earth and 3d transition metal oxides. Structural properties of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide were explored by confirmation of its single-phase Fd-3m spinel structure by x-ray diffraction (XRD). Further, nanocrystalline nature and morphology were analyzed by scanning electron microscopy (SEM). Among thermal properties, thermogravimetric analysis (TGA) revealed that the (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is thermally stable up to a temperature of 1200℃. Whereas phase evolution in (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide before and after sintering was analyzed through differential scanning calorimetry (DSC). Electrochemical studies of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide consists of a comparison of thermodynamic and kinetic parameters of water and hydrazine hydrate oxidation. Values of activation energy for water oxidation (9.31 kJ mol-1) and hydrazine hydrate oxidation (13.93 kJ mol-1) reveal that (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is catalytically more active towards water oxidation as compared to that of hydrazine hydrate oxidation. Electrochemical impedance spectroscopy is also performed to get insight into the kinetics of both types of reactions.

• Journal of Microbiology and Biotechnology
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• v.32 no.8
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• pp.1041-1046
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• 2022

Nucleoside deoxyribosyltransferase (NDT) is an enzyme that replaces the purine or pyrimidine base of 2'-deoxyribonucleoside. This enzyme is generally used in the nucleotide salvage pathway in vivo and synthesizes many nucleoside analogs in vitro for various biotechnological purposes. Since NDT is known to exhibit relatively low reactivity toward nucleoside analogs such as 2'-fluoro-2'-deoxynucleoside, it is necessary to develop an enhanced NDT mutant enzyme suitable for nucleoside analogs. In this study, molecular evolution strategy via error-prone PCR was performed with ndt gene derived from Lactobacillus leichmannii as a template to obtain an engineered NDT with higher substrate specificity to 2FDU (2'-fluoro-2'-deoxyuridine). A mutant library of 214 ndt genes with different sequences was obtained and performed for the conversion of 2FDU to 2FDA (2'-fluoro-2'-deoxyadenosine). The E. coli containing a mutant NDT, named NDT^L59Q, showed 1.7-fold (at 40℃) and 4.4-fold (at 50℃) higher 2FDU-to-2FDA conversions compared to the NDT^WT, respectively. Subsequently, both NDT^WT and NDT^L59Q enzymes were over-expressed and purified using a His-tag system in E. coli. Characterization and enzyme kinetics revealed that the NDT^L59Q mutant enzyme containing a single point mutation of leucine to glutamine at the 59^th position exhibited superior thermal stability with enhanced substrate specificity to 2FDU.

• International Journal of Industrial Entomology and Biomaterials
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• v.45 no.2
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• pp.56-69
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• 2022

Silk is a unique natural biopolymer with outstanding biocompatibility, high mechanical strength, and superior optical transparency. Due to its excellent properties, silk has been widely reported as an ideal biomaterial for several biomedical applications. Recently, fluorescent silk protein, a variant of native silk, has been reported as a biophotonic material with the potential for bioimaging and biosensing. Despite the realization of fluorescent silk, the traditional degumming process of fluorescence silk is crude and often results in fluorescence loss. The loss of fluorescent properties is attributed to the sensitivity of silk fibroin to temperature and solvent concentration during degumming. However, there is no comprehensive information on the influence of these processing parameters on fluorescence evolution and decay during fluorescent silk processing. Therefore, we conducted a spectroscopic study on fluorescence decay as a function of temperature, concentration, and duration for fluorescent silk cocoon degumming. Sodium carbonate solution was tested for degumming the fluorescent silk cocoons with different concentrations and temperatures; also, sodium carbonate solution is combined with Alcalase enzyme and triton x-100 to find optimal degumming conditions. Additionally, we conducted a molecular dynamics study to investigate the fundamental effect of temperature on the stability of the fluorescent protein. We observed degumming temperature as the prime source of fluorescent intensity reduction. From the MD study, fluorescence degradation originated from the thermal agitation of fluorescent protein Cα atoms and fluctuations of amino acid residues located in the chromophore region. Overall, degumming fluorescent silk with sodium carbonate and Alcalase enzyme solution at 25 ℃ preserved fluorescence.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.884-894
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• 2023

Design and safety assessment of fuel pins for application in innovative Generation IV fast reactors calls for a dedicated nuclear fuel modelling and for the extension of the fuel performance code capabilities to the envisaged materials and irradiation conditions. In the INSPYRE Project, comprehensive and physics-based models for the thermal-mechanical properties of U-Pu mixed-oxide (MOX) fuels and for fission gas behaviour were developed and implemented in the European fuel performance codes GERMINAL, MACROS and TRANSURANUS. As a follow-up to the assessment of the reference code versions ("pre-INSPYRE", NET 53 (2021) 3367-3378), this work presents the integral validation and benchmark of the code versions extended in INSPYRE ("post-INSPYRE") against two pins from the SUPERFACT-1 fast reactor irradiation experiment. The post-INSPYRE simulation results are compared to the available integral and local data from post-irradiation examinations, and benchmarked on the evolution during irradiation of quantities of engineering interest (e.g., fuel central temperature, fission gas release). The comparison with the pre-INSPYRE results is reported to evaluate the impact of the novel models on the predicted pin performance. The outcome represents a step forward towards the description of fuel behaviour in fast reactor irradiation conditions, and allows the identification of the main remaining gaps.