• Nuclear Engineering and Technology
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• v.35 no.5
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• pp.426-441
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• 2003

A reactor inlet header break experiment, B9401, performed in the RD-14M multi channel test facility was analyzed using RELAP5/MOD3.2 and RELAP5/CANDU[1]. The RELAP5 has been developed for the use in the analysis of the transient behavior of the pressurized water reactor. A recent study showed that the RELAP5 could be feasible even for the simulation of the thermal hydraulic behavior of CANDU reactors. However, some deficiencies in the prediction of fuel sheath temperature and transient behavior in athe headers were identified in the RELAP5 assessments. The RELAP5/CANDU has been developing to resolve the deficiencies in the RELAP5 and to improve the predictability of the thermal-hydraulic behaviors of the CANDU reactors. In the RELAP5/CANDU, critical heat flux model, horizontal flow regime map, heat transfer model in horizontal channel, etc. were modified or added to the RELAP5/MOD3.2. This study aims to identify the applicability of both codes, in particular, in the multi-channel simulation of the CANDU reactors. The RELAP5/MOD3.2 and the RELAP5/CANDU analyses demonstrate the code's capability to predict reasonably the major phenomena occurred during the transient. The thermal-hydraulic behaviors of both codes are almost identical, however, the RELAP5/CANDU predicts better the heater sheath temperature than the RELAP5/MOD3.2. Pressure differences between headers govern the flow characteristics through the heated sections, particularly after the ECI. In determining header pressure, there are many uncertainties arisen from the complicated effects including steady state pressure distribution. Therefore, it would be concluded that further works are required to reduce these uncertainties, and consequently predict appropriately thermal-hydraulic behaviors in the reactor coolant system during LOCA analyses.

• Journal of Magnetics
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• v.20 no.3
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• pp.308-311
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• 2015

We design a crisscrossed double-layer birdcage (DLBC) coil by modifying the coil geometry of a standard single-layer BC (SLBC) coil to enhance the homogeneity of transmitting magnetic flux density ($B_1{^+}$) along the main magnetic field ($B_0$)-direction for small-animal magnetic resonance imaging (MRI) at 300 MHz. The performance assessment of the crisscrossed DLBC coil is conducted by computational analysis with the finite-difference time domain method (FDTD) and compared with SLBC coil in terms of the $B_1$ and the $B_1{^+}$ distribution. As per the computational calculation studies, the mean value in the two-dimensional $B_1{^+}$ map obtained at the mid-axial slice with the proposed DLBC coil is slightly lower than that obtained with the SLBC coil, but the $B_1{^+}$ value of the DLBC coil in the outermost plane (40 mm away from the central plane) shows improvements of 19.3% and 24.8% over the SLBC coil $B_1{^+}$ value when simulating a spherical phantom and realistic mouse body modeling. These simulation results indicate that, the $B_1{^+}$ homogeneity along the z-direction was improved by using DLBC configuration. Our approach enables $B_1{^+}$ homogeneity improvement along the zdirection, and it can also be applied to ultra-high field (UHF) MRI systems.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.57.2-57.2
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• 2018

We present the preliminary result from our KVN single-dish observations of the MALATANG sample. The MALATANG (Mapping the dense molecular gas in the strongest star-forming Galaxies) is one of the JCMT legacy surveys on the nearest 23 IR-brightest galaxies beyond the Local Group. The goal of the MALATANG survey is to map the sample in the dense gas tracers (HCN and HCO+J=4-3), and probe the relationships between the dense molecular gas and star formation activities. As a complementary study, we recently launched a KVN/KaVA program on the same sample, in order to measure their flux densities and parsec-scale jet/outflows in the millimeter regime, which will be greatly useful in understanding the initial conditions of the feedback process. In this work, we present the preliminary result from our pilot KVN single-dish program on a sub-sample, which will be used to select the future VLBI imaging study under plan. We investigate the KVN spectral energy distributions (SED) of the sample as a function of the power source of the luminous IR brightness of each target (starburst? AGN? or hybrid?). We also discuss the technical challenges that we experienced during our KVN observations due to the large size of the sample in the sky.

• Journal of Korean Society of Rural Planning
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• v.16 no.4
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• pp.109-116
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• 2010

Climate change is known to affect both natural and managed ecosystems, and will likely impact on the terrestrail carbon balance. This paper reports the effects of climate change on spatial-temporal changes in carbon reductions in South Korea's during 2000-2100. Future carbon (C) stock distributions are simulated for the same period using various spatial data sets including land cover, net primary production(NPP) and leaf area index (LAI) obtained from MODIS(Moderate Resolution Imaging Spectroradiometer), and climate data from Data Assimilation Office(DAO) and Korea Meteorological Administration(KMA). This study attempts to predict future NPP using multiple linear regression and to model dependence of soil respiration on soil temperature. Plants store large amounts of carbon during the growing periods. During 2030-2100, Carbon accumulation in vegetation was increased to $566{\sim}610gC/m^2$/year owing to climate change. On the other hand, soil respiration is a key ecosystem process that releases carbon from the soil in the form of carbon dioxide. The estimated soil respiration spatially ranged from $49gC/m^2$/year to $231gC/m^2$/year in the year of 2010, and correlating well with the reference value. This results include Spatial-Temporal C reduction variation caused by climate change. Therefore this results is more comprehensive than previous results. The uncertainty in this study is still large, but it can be reduced if a detailed map becomes available.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.107.1-107.1
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• 2012

We present the results of far-ultraviolet (FUV) observations of comet C/2001 Q4 (NEAT) obtained with Far-ultraviolet Imaging Spectrograph (FIMS) on board the Korean microsatellite STSAT-1, which operated at an altitude of 700 km in a sun-synchronous orbit. FIMS is a dual-channel imaging spectrograph (S channel 900-1150 ${\AA}$, L channel 1350-1750 ${\AA}$, ${\lambda}/{\Delta}{\lambda}$ ~ 550) with large image fields of view (S: $4^{\circ}.0{\times}4^{\prime}.6$, L: $7^{\circ}.5{\times}4^{\prime}.3$, angular resolution 5'-10') optimized for the observation of diffuse emission of astrophysical radiation. Comet C/2001 Q4 (NEAT) was observed with a scanning survey mode when it was located around the perihelion between 8 and 15 May 2004. Several important emission lines were detected including S I (1425, 1474 ${\AA}$), C I (1561, 1657 ${\AA}$) and several emission lines of CO $A^1{\Pi}-X^1{\Sigma}^+$ system in the L channel. Production rates of the notable molecules, such as C I, S I and CO, were estimated from the photon fluxes of these spectral lines and compared with previous observations. We compare the flux and the production rates in the radius of $3{\times}10^5$ km with $20{\times}10^5$ km from the central coma. We obtained L-channel image which have map size $5^{\circ}{\times}5^{\circ}$ The image was constructed for the wavelength band of L-channel (1350 - 1710 ${\AA}$. We also present the radial profiles of S I, C I, CO obtained from the spectral images of the central coma. The radial profiles of $2{\times}10^6$ km region are compared with the Haser model.

• Economic and Environmental Geology
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• v.3 no.1
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• pp.17-24
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• 1970

The purpose of this report is to prepare a data for the economic evaluation on the Goobong Limestone Mine which is located at the south-eastern corner of the Yongchun Quadrangle scaled in 1:50,000. The accessibility from the mine to railroad was considered in two ways. One is to Dodam Station on Central Railway Line and the other is to reach Songjung-ni village which is near Sangyong Station on Hamback Railway Line. The distance of the former way is 26.7km and the later is 24.2km. Geologically the mine is situated near the base of the Greast Limestone Series which strikes generally $N25^{\circ}{\sim}30^{\circ}E$. The series comprises six different formations from older to younger; Pungchon Limestone Formation and Whajol Formation of Cambrian age, and Dongjum Quartzite Formation, Dumudong Formation, Maggol Limestone Formation and Goseong Formation of lower to middle Ordovician age. 82 samples; 48 from Pungchon Limestone Formation, 11 from Dumudong Formation, 15 from Maggol Limestone Formation and 8 from Goseong Formation, were taken from the series in the crossed direction to the general trend of the series as shown in geological map. They were chemically analyzed on the components of CaO, MgO, $SiO_2$, $R_2O_3(Al_2O_3+Fe_2O_3)$ and ignition loss as shown in table 2, table 3, table 4, and table 5. As seen from the tables, among the formations of the series, middle to upper parts of the Pungchon Limestone Formation and middle and upper parts of the Dumudong Formation have chemical composition as available source for the raw material of cement industry, not only that but also the part of the Pungchon Formation was highly evaluated as source for the flux of iron smelting and the raw material of carbide manufacturing because of its high purity of calcium carbonate.

• Nuclear Engineering and Technology
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• v.52 no.1
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• pp.37-50
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• 2020

A passive containment cooling system (PCCS) has been developed as advanced safety feature for innovative power reactor (iPOWER). Passive systems are inherently less stable than active systems and the PCCS encountered the flashing-induced instability previously identified. The objective of this study is to develop stability maps for flashing-induced instability using MARS (Multi-dimensional Analysis of Reactor Safety) code. Firstly, we conducted a series of sensitivity analysis to see the effects of time step size, nodalization, and alternative MARS user options on the onset of flashing-induced instability. The riser nodalization strongly affects the prediction of flashing in a long riser of the PCCS, while time step size and alternative user options do not. Based on the sensitivity analysis, a standard input and an analysis methodology were set up to develop the stability maps of PCCS. We found out that the calculated equilibrium quality at the exit of the riser as a stability boundary above 5 kW/㎡ was approximately 1.2%, which was in good agreement with Furuya's results. However, in case of a very low heat flux condition, the onset of instability occurred at the lower equilibrium quality. In addition, it was confirmed that inlet throttling reduces the unstable region.

• Nuclear Engineering and Technology
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• v.41 no.9
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• pp.1143-1156
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• 2009

The SPACE code that is based on a multi-dimensional two-fluid, three-field model is under development for licensing purposes of pressurized water reactors in Korea. Among the participating research and industrial organizations, KAERI is in charge of developing the physical models and correlation packages for the constitutive equations. This paper introduces a developed wall-to-fluid heat transfer package for the SPACE code. The wall-to-fluid heat transfer package consists of twelve heat transfer subregions. For each sub-region, the models in the existing safety analysis codes and the leading models in literature have been peer reviewed in order to determine the best models which can easily be applicable to the SPACE code. Hence a wall-to-fluid heat transfer region selection map has been developed according to the non-condensable gas quality, void fraction, degree of subcooling, and wall temperature. Furthermore, a partitioning methodology which can take into account the split heat flux to the continuous liquid, entrained droplet, and vapor fields is proposed to comply fully with the three-field formulation of the SPACE code. The developed wall-to-fluid heat transfer package has been pre-tested by varying the independent parameters within the application range of the selected correlations. The smoothness between two adjacent heat transfer regimes has also been investigated. More detailed verification work on the developed wall-to-fluid heat transfer package will be carried out when the coupling of a hydraulic solver with the constitutive equations is brought to completion.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.21 no.1
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• pp.1-10
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• 2016

Currently available surface seawater partial pressure carbon dioxide ($pCO_2$) data sets in the East Sea are not enough to quantify statistically the carbon dioxide flux through the air-sea interface. To complement the scarcity of the $pCO_2$ measurements, we construct a neural network (NN) model based on satellite data to map $pCO_2$ for the areas, which were not observed. The NN model is constructed for the Ulleung Basin, where $pCO_2$ data are best available, to map and estimate the variability of $pCO_2$ based on in situ $pCO_2$ for the years from 2003 to 2012, and the sea surface temperature (SST) and chlorophyll data from the MODIS (Moderate-resolution Imaging Spectroradiometer) sensor of the Aqua satellite along with geographic information. The NN model was trained to achieve higher than 95% of a correlation between in situ and predicted $pCO_2$ values. The RMSE (root mean square error) of the NN model output was $19.2{\mu}atm$ and much less than the variability of in situ $pCO_2$. The variability of $pCO_2$ with respect to SST and chlorophyll shows a strong negative correlation with SST than chlorophyll. As SST decreases the variability of $pCO_2$ increases. When SST is lower than $15^{\circ}C$, $pCO_2$ variability is clearly affected by both SST and chlorophyll. In contrast when SST is higher than $15^{\circ}C$, the variability of $pCO_2$ is less sensitive to changes in SST and chlorophyll. The mean rate of the annual $pCO_2$ increase estimated by the NN model output in the Ulleung Basin is $0.8{\mu}atm\;yr^{-1}$ from 2003 to 2014. As NN model can successfully map $pCO_2$ data for the whole study area with a higher resolution and less RMSE compared to the previous studies, the NN model can be a potentially useful tool for the understanding of the carbon cycle in the East Sea, where accessibility is limited by the international affairs.

• Korean Journal of Agricultural and Forest Meteorology
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• v.13 no.2
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• pp.69-78
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• 2011

Rice is one of the world's staple foods. Paddy rice fields have unique biophysical characteristics that the rice is grown on flooded soils unlike other crops. Information on the spatial distribution of paddy fields and the timing of irrigation are of importance to determine hydrological balance and efficiency of water resource management. In this paper, we detected the timing of irrigation and spatial distribution of paddy fields using the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard the NASA EOS Aqua satellite. The timing of irrigation was detected by the combined use of MODIS-based vegetation index and Land Surface Water Index (LSWI). The detected timing of irrigation showed good agreement with field observations from two flux sites in Korea and Japan. Based on the irrigation detection, a land cover map of paddy fields was generated with subsidiary information on seasonal patterns of MODIS enhanced vegetation index (EVI). When the MODISbased paddy field map was compared with a land cover map from the Ministry of Environment, Korea, it overestimated the regions with large paddies but underestimated those with small and fragmented paddies. Potential reasons for such spatial discrepancies may be attributed to coarse pixel resolution (500 m) of MODIS images, uncertainty in parameterization of threshold values for discarding forest and water pixels, and the application of LSWI threshold value developed for paddy fields in China. Nevertheless, this study showed that an improved utilization of seasonal patterns of MODIS vegetation and water-related indices could be applied in water resource management and enhanced estimation of evapotranspiration from paddy fields.