• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1681-1688
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• 2019

In accordance with ASME Boiler and Pressure Vessel (B&PV) Code Sec.XI Appendix. G, a postulated crack is located at the beltline of a reactor pressure vessel because the neutron flux at the beltline is higher than elsewhere. This means that the distance between the core and the semi-spherical bottom head is longer than the distance between the core and the cylindrical beltline. However, several Small and Medium sized Reactors have bottom heads with diverse shapes, including dished or semi-elliptical shapes, to satisfy the requirement and performance. So, the aim of this paper is to evaluate the effect of crack location on Pressure-Temperature limit curve. To do this, two types of postulated crack location, such as beltline and semi-elliptical bottom head, were adopted to derive the Pressure-Temperature limit curve. Also, parametric studies for neutron flux, crack shape and so on were performed. As a result, core critical temperature of semi-elliptical bottom head is found to higher than that of beltline even when they have same values of thickness and neutron flux. This result will be useful to enhance the understanding of Pressure-Temperature limit curve.

• Journal of the Korean Applied Science and Technology
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• v.22 no.2
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• pp.96-105
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• 2005

Core-shell polymers of methyl methacrylate-styrene system were prepared by sequential emulsion polymerization in the presence of sodium dodecyl benzene sulfonate(SDBS) as an emulsifier using ammonium persulfate(APS) in an initiator and the characteristics of these core-shell polymers were evaluated. Core-shell composite latex has the both properties of core and shell components in a particle, whereas polymer blends or copolymers show a combined physical properties of two homopolymers. This unique behavior of core-shell composite latex can be used in various industrial fields. However, in preparation of core-shell composite latex, several unexpected matters are observed, for examples, particle coagulation, low degree of polymerization, and formation of new particles during shell polymerization. To solve this matters, we study the effects of surfactant concentrations, initiator concentrations, and reaction temperature on the core-shell structure of PMMA-PSt and PSt-PMMA. Particle size and particles distribution were measured by using particle size analyzer, and the morphology of the core-shell composite latex was observed by using transmission electron microscope. Glass temperature was also measured by using differential scanning calorimeter. To identify the core-shell structure, pH of the composite latex solutions was measured.

• Journal of Korean Traditional Oncology
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• v.12 no.1
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• pp.25-35
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• 2007

There are very necessary for three factors, that is sun(oxygen), temperature, nutritions to maintain life. when sun shines, skin temperature get up. after man eat food, core body temperature get higher. temperature is temperature. therefore, common characteristic of three factors is temperature. temperature is energy and qi(氣) in korean medicine. in addition to this one, pyretomedicine also insists that the key point of all disease development mechanism is also the overenough and poor of energy. In this aspects, writer submit this thesis about all disease development, neoplasia devolpment and metastasis as hypothesis.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.31.2-31.2
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• 2011

We studied a method of manufacturing an anode to restrict contraction in reducing NiO/YSZ by uniformly mixing. In order to mix Ni and YSZ, a sub-micron Ni core surface was coated at high-speed by a mixture of nano-sized YSZ and a spherical core-shell was subsequently formed. The micron-sized core-shell anode powder was then heat treated at $400{\sim}1,450^{\circ}C$ in an air atmosphere and Ni was extruded and synthesized in nano-size. Subsequently, when the nano-sized mixture of the anode was heat treated and maintained at a temperature of $1,450^{\circ}C$, the anode was manufactured, where Ni and YSZ were uniformly distributed with the nano-structure. According to the nano-sized anode powder synthesis process, Ni particles were oxidized at $400{\sim}500^{\circ}C$ and became spherical by surface tension. In the case of the spherical core Ni powder, the heat treatment temperature rose to $1,250^{\circ}C$ and then a gap between the internal and external pressures occurred due to thermal and tensile stresses. A crack subsequently appeared on the surface, and the heat treatment temperature was increased continuously to increase the pressure gap and then the core Ni extruded as a nano-sized powder, Ni and YSZ uniformly distributed. It was found that the anode of 50~200 nm with a consistent structure obtained in this study has electric conductivity that is approximately 3 times larger than that of a commercial anode.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.215-218
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• 2002

HTS motors and generators have some advantages over LTS machines because of higher operating temperature. Very low temperature nakes LTS machines need higher refrigeration cost and large facilities. However, HTS machines are expected to be comparable with conventional counterparts at smaller machine ratings than LTS generators in terms of efficiency and size. As the operating temperature increases, the magnetic flux density generated by HTS field coils decreases relatively. For example, 1000hp HTS synchronous motor developed in a few years ago has maximum field density of 1.5T. At this point, magnetic material used in conventional machines is able to pass magnetic flux easily with high permeability. In order to investigate the effect, we arranged magnetic core only inside of magnet vessel of a 100hp target machine. By way of FEM analysis, we concluded that the magnetic core can reduce amount of expensive BSCCO conductor so much.

• Nuclear Engineering and Technology
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• v.29 no.5
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• pp.406-416
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• 1997

A computational method is developed for predicting the steady-state temperature field in an LMR core. Detailed core-wide coolant temperature profiles are efficiently calculated using the simplified energy equation mixing model[1] and the subchannel analysis method. The $\theta$-method is employed for discretizing the energy equations in the axial direction. The interassembly coupling is achieved by interassembly gap flow. Cladding and fuel temperatures are calculated with the one-dimensional conduction model and temperature integrals of conductivities. The accuracy of the method is tested by performing several benchmark calculations for too LMR problems. The results indicate that the accuracy is comparable to the other methods based on ENERGY model. It is also shown that the implicit scheme for the axial discretization is more efficient than the explicit scheme.

• Bulletin of the Korean Chemical Society
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• v.26 no.11
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• pp.1776-1782
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• 2005

ZnSe/ZnS, UV-blue luminescent core shell quantum dots, were synthesized via a thermal decomposition reaction of organometallic zinc and solvent coordinated Selenium (TOPSe) in a hot solvent mixture. The synthetic conditions of the core (ZnSe) and the shell (ZnS) were independently studied at various reaction temperature conditions. The obtained colloidal nanocrystals at corresponding temperatures were characterized for their optical properties by UV-vis, room temperature solution photoluminescence (PL) spectroscopy, and further obtained powders were characterized by XRD, TEM, and EDXS analyses. The synthetic temperature condition to obtain the best PL emission intensity for the ZnSe core was 300 ${^{\circ}C}$, and for the optimum shell capping, the temperature was 135 ${^{\circ}C}$. At this temperature, solution PL spectrum showed a narrow emission peak at 427 nm with a PL efficiency of 15%. In addition, the measured particle sizes for the ZnSe/ZnS nanocomposite via TEM were in the range of 5 to 12 nm. Furthermore, we have synthesized water-soluble ZnSe/ZnS nanoparticles by capping the ZnSe/ZnS hydrophobic surface with mercaptoacetate (MAA) molecules. For the obtained aqueous colloidal solution, the UV-vis spectrum showed an absorption peak at 250 nm, and the solution PL emission spectrum showed a peak at 425 nm, which is similar to that for hydrophobic quantum dot ZnSe/ZnS. However, the calculated PL efficiency was relatively low (0.1%) due to the luminescence quenching by water and MAA molecules. The capping ligand was also characterized by FT-IR spectroscopy, with the carbonyl stretching peak in the mercaptoacetate molecule appearing at 1575 $cm ^{-1}$. Finally, the particle sizes of the MAA capped ZnSe/ZnS were measured by TEM, showing a range of 12 to 17 nm.

• Journal of Photoscience
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• v.9 no.2
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• pp.406-408
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• 2002

In order to know the characteristics of circadian rhythms in core temperature in tropical inhabitants, we measured rectal temperatures every 10 min for 24 hrs in 6 Vietnamese, 20 - 22 yrs (5 males and I females) under natural conditions. Average light intensity was 16000 lx. Ambient temperatures ranged from 33 to 36 oC. These data obtained were compared with those in Japanese setters and the Polish inhabitants. The participants were sitting mostly during wakefulness and lying in bed during sleep. The results obtained are summarized as follows: I) The average maximum value was 37.7 oC, which was significantly higher than in the Japanese and Polish as well. 2) The average minimum value was 36.4 oC, which was also lower. 3) A range of oscillation was 1.3 oC, which was clearly greater than in the people living in the temperate areas. The higher maximum value of core temperature, which was actively regulated under warm temperature, seemed of adaptive significance in order to reduce water consumption. A greater rage of oscillation in tropical Vietnamese people might have ecological significance for efficient acclimatization in the environment with strong light intensity and high ambient temperature, suggesting that the setpoint of core temperature could show a greater range of oscillation.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.292-295
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• 2008

In a SCWR (SuperCritical pressure Water cooled Reactor), the coolant temperature initially at below the pseudo-critical temperature at the bottom of a reactor core increases as the coolant flows upward through the sub-channels of the fuel assemblies, and it finally becomes higher than the pseudo-critical temperature when it leaves the reactor core. At certain conditions, heat transfer deterioration occurs near the pseudo-critical temperature and it may cause a drastic rise of the fuel surface temperature resulting a fuel failure. Therefore, an accurate estimation of the heat transfer coefficient is very important for the thermal-hydraulic design of a reactor core. An experiment on heat transfer to the vertically upward flowing $CO_2$ at a supercritical pressure in a circular tube were performed at KAERI. The internal diameter of the test section is 6.32 mm, which corresponds to the hydraulic diameter of a sub-channel in the conceptional design proposed by KAERI. The test range of the mass flux is 285 to 1200 kg/m$^2$s and the maximum heat flux is 170 kW/m$^2$. The inlet pressure is maintained at 8.12 MPa, which is 1.1 times the critical pressure. A new correlation, which covers both the normal and deterioration heat transfer regimes was proposed and compared with the estimations by exiting correlations.

• Nuclear Engineering and Technology
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• v.45 no.1
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• pp.21-28
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• 2013

The flow and heat transfer characteristics of the ex-vessel core melt (corium) were investigated using a commercial CFD code along with the experimental data on the spreading of corium available in the literature (VULCANO VE-U7 test). In the numerical simulation of the unsteady two-phase flow, the volume-of-fluid model was applied for the spreading and interfacial surface formation of corium with the surrounding air. The effects of the key parameters were evaluated for the corium spreading, including the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The results showed a reasonable trend of corium progression influenced by the changes in the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The modeling of the viscosity appropriate for corium and the radiative heat transfer was critical, since the front progression and temperature profiles were strongly dependent on the models. Further development is required for the code to consider the formation of crust on the surfaces of corium and the interaction with the substrate.