• Nuclear Engineering and Technology
• /
• v.47 no.7
• /
• pp.907-914
• /
• 2015

The energetic steam explosion caused by contact between the high temperature molten core and water is one of the phenomena that may threaten the integrity of the containment vessel during severe accidents of light water reactors (LWRs). We examined the dependence of steam explosion loads in a typical reactor cavity geometry on selected model parameters and initial/boundary conditions by using a steam explosion simulation code, JASMINE, developed at Japan Atomic Energy Agency (JAEA). Among the parameters, we put an emphasis on the water pool depth that has significance in terms of accident mitigation strategies including cavity flooding. The results showed a strong correlation between the load and the premixed mass, defined as the mass of the molten material in low void zones (void fraction < 0.75). The jet diameter and velocity that comprise the flow rate were the primary factors to determine the premixed mass and the load. The water pool depth also showed a significant impact. The energy conversion ratio based on the enthalpy in the premixed mass was in a narrow range ~4%. Based on this observation, we proposed a simplified method for evaluation of the steam explosion load. The results showed fair agreement with JASMINE.

• Geomechanics and Engineering
• /
• v.37 no.2
• /
• pp.179-187
• /
• 2024

In this paper, a unified time-dependent constitutive model of Darcy flow and non-Darcy flow is proposed. The influencing factors of flow velocity are discussed, which demonstrates that permeability coefficient is the most significant factor. Based on this, the dynamic evolution characteristics of water inrush during tunneling through fault fracture zone is analyzed under the constant permeability coefficient condition (CPCC). It indicates that the curves of flow velocity and hydrostatic pressure can be divided into typical three stages: approximate high-velocity zone inside the fault fracture zone, velocity-rising zone near the tunnel excavation face and attenuation-low velocity zone in the tunnel. Furthermore, given the variation of permeability coefficient of the fault fracture zone with depth and time, the dynamic evolution of water flow in the fault fracture zone under the variable permeability coefficient condition (VPCC) is also studied. The results show that the time-related factor (α) affects the dynamic evolution distribution of flow velocity with time, the depth-related factor (A) is the key factor to the dynamic evolution of hydrostatic pressure.

• Journal of Advanced Marine Engineering and Technology
• /
• v.34 no.5
• /
• pp.725-734
• /
• 2010

This study conducted hydraulic testing to assess the stability of two types of pyramid-shaped artificial reefs (ARs) constructed to promote the growth of shellfish and seaweed. Previous theoretical and hydraulic experimental studies have clearly demonstrated Froude similitude. The results of this study revealed that some dimensionless design parameters affected the stability of both types of artificial reefs under various wave and current field conditions (e.g., surf similarity parameters, water particle velocity, wave pressure). In the fixed bed condition, the dimensionless water particle velocity based on the surf similarity parameter was large (about 0.4), and in the moveable bed condition, the relative water depth based on the dimensionless wave pressure was low (about 0.11). In addition, horizontal wave pressure and uplift pressure varied by relative water depth, demonstrating the tendency for wave pressure to decrease linearly with increased relative depth. These findings indicate that the development of more stable design technology forartificial reefs should be based on long-term data and additional study of sliding due to wave action. The findings also highlight the importance of hydraulic experiments in solving problems that have emerged in the design and construction of artificial reefs.

• The Journal of the Acoustical Society of Korea
• /
• v.32 no.1
• /
• pp.1-13
• /
• 2013

Salinity does not generally affect sound speed because it shows very small variations in the ocean. However, low salinity water appears in the Western Sea of Jeju Island every summer so that sound speed and sound propagation can change near sea surface. We calculated Sound Speed Profile (SSP) using vertical profiles of temperature and salinity, which were averaged over years of normal salinity and low salinity (<28 psu) from 30 years (1980~2009) at 3 sites of Korea Oceanographic Data Center (KODC). As a result, sound speed variation by low salinity alone was -5.36 m/s at sea surface and -1.35 m/s at 10m depth for low salinity environments. Gradient of SSP was positive down to 5 m depth due to decrease of sound speed near surface, leading formation of haline channel. Simulation of acoustic propagation using a ray model (Bellhop) confirmed the haline channel. Haline channel has formed 4 times while hydrostatic channel controlled by only pressure has formed 9 times for 30 years. The haline channel showed larger critical angles of rays than hydrostatic channel. Haline channel was also formed at some sites among 20 measurement sites in low salinity water mass which appeared on August $1^{st}$ 2010.

• Journal of Korean Society of Water and Wastewater
• /
• v.23 no.2
• /
• pp.181-187
• /
• 2009

In this study, a runoff hydrograph and runoff volume were calculated by using the kinetic wave theory for small urban watersheds based on the concept of low impact development(LID), and the effective imperviousness was estimated based on these calculations. The degree of sensitivity of the effective imperviousness of small watersheds to the impervious to pervious area ratio, infiltration capability, watershed slope, roughness coefficient and surface storage depth was then analyzed. From this analysis, the following conclusions were obtained: The effective imperviousness and paved area reduction factor decreased as the infiltration capability of pervious area increased. As the slope of watersheds becomes sharper, the effective imperviousness and the paved area reduction factor display an increasing trend. As the roughness coefficient of impervious areas increases, the effective imperviousness and the paved area reduction factor tend to increase. As the storage depth increases, the effective imperviousness and the paved area reduction factor show an upward trend, but the increase is minimal. Under the conditions of this study, it was found that the effective imperviousness is most sensitive to watershed slope, followed by infiltration capability and roughness coefficient, which affect the sensitivity of the effective imperviousness at a similar level, and the storage depth was found to have little influence on the effective imperviousness.

• Journal of the Korean earth science society
• /
• v.22 no.1
• /
• pp.47-64
• /
• 2001

Water mass classification was conducted using the data of 1985 and 1986 in the East China Sea and the Korea Strait. Kuroshio water (type K) and mixed water (type I) were broadly distributed at 50 m depth in winter and spring, and mixed waters (type I to IV) were distributed in summer and autumn. At 100 m depth of the East China Sea, and mixed water (type I) was broadly distributed in winter and spring, and mixed waters (type I to III) were in summer, and type I was in autumn. Water mass in summer is the most influenced from the Chinese coastal water. In the Korea Strait, the Kuroshio water (type K) was the main water mass in winter and spring, and mixed waters (type I to IV) were in summer and autumn. If temperatures are corrected to remove the cooling effect from the atmosphere, the Kuroshiowater region was diminished, however the mixed water region was expanded in winter and spring. This shows that although the Kuroshio water appears to be a main water mass of the East China Sea and the Korea Strait in winter andspring, in reality the mixed water (type I) which is slightly changed from the Kuroshio water (type K) widely distributed. The tongue-shaped distribution of low density surface water indicates that the water mixed with the Chinese coastal water flows to the Korea Strait and the Okinawa in summer.

• The Journal of Korean Academy of Prosthodontics
• /
• v.41 no.4
• /
• pp.476-492
• /
• 2003

Purpose : The purpose of this study was to compare HEMA and TEGDMA as diluents for the composite resin. Material and methods : Eight kinds of experimental light curable composite resins were prepared and used. Concentrations of monomer and filler were same for all experimental composites, except, the diluent's ratios to the monomer. The ratio of diluents to Bis-GMA were 15%, 20%, 25%, and 30%, and two kinds of diluents were used, so total experimental groups were eight including one control group of 25% TEGDMA. Results : Depth of cure, flexural strength, shear bond strength to bovine enamel, shear bond strength to bovine dentin, water absorption and solubility of composites in water were measured. Sample size for each groups were 10. Arithmetic means were used as each groups representative values, and regression test for two diluents and low concentrations, Duncan's multiple range test, and Two-way ANOVA test were done for kinds of diluents and its concentrations at level of 0.05. Conclusion : Following results were obtained ; 1. There were not significant differences in effects of HEMA and TEGDMA to depth of cure, flexural strength of composites and shear bond strength to bovine enamel (p>0.05). 2. Increase of the concentrations of the diluents made the depth of cure (p<0.001) and flexural strength (p<0.05) a little higher. 3. Shear bond strength to dentin was higher on HEMA containing composites than TEGDMA containing composites (p<0.001). 4. Water absorption was higher on HEMA containing composites than TEGDMA containing composites (p<0.01).

• Applied Biological Chemistry
• /
• v.41 no.8
• /
• pp.583-586
• /
• 1998

Porous ceramic cups are used for monitoring ion concentration in soil solutions in various time course and depth. A soil solution sampler was constructed in laboratory by inserting pliable perfluoroalkoxy(PFA) tubings into porous cup through holes in PVC rod segment which plugged top opening of the porous cup. The system was installed in drip irrigated soil in a vertical position, and nitrogen movement below the drip basin was monitored. To collect soil solution, vacuum in the cup was applied with a hand vacuum pump. The samples obtained were sufficient enough to run quantitative analyses for a number of chemicals. Nitrogen transformation and movement could be well defined, and the system seemed to be relevant to the other soil solution samplers in monitoring chemical movement in soil. Although this system has general deficiencies found in the other samplers using ceramic cup, it could be easily constructed at a low cost. Since the tubing was pliable, the cups could be installed in horizontal position, and this allows installations of the cups at more precise depth increments and also more precise samplings of soil solution at each depth.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.4 no.1
• /
• pp.18-25
• /
• 1992

A discrete spectral model for generation, propagation and dissipation of wind waves for arbitrary depth and current is presented. This model incorporates wave current interaction, including changes of absolute frequencies due to unsteadiness of depth and currents. The numerical scheme for propagation if basically second-order accurate, and effects of refraction and frequency shills due to unsteadiness of depth and current are calculated on a fixed grid, also using second-order scheme.

• The Journal of the Acoustical Society of Korea
• /
• v.6 no.2
• /
• pp.48-53
• /
• 1987

The depth dependent sound fields have been calculated for a single frequency source to reveal the fluctuating sound energy at both near the surface and the bottom of the water layer. Those fluctuation are mainly due to the mode function behavior along the depth where the sound-speed gradient acts like trapping lower mode sound energy in those medium.