• Nuclear Engineering and Technology
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• v.44 no.7
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• pp.767-772
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• 2012

In support of optimizing electrorefining technology for treating spent nuclear fuel, lithium drawdown has been investigated for separating actinides from molten salt electrolyte. Drawdown reaction selectivity is a major issue that requires investigation, since the goal is to remove actinides while leaving the fission products and other components in the salt. A series of lithium drawdown tests with surrogate fission product chlorides was run to obtain selectivity data with non-radioactive salts, develop a predictive model, and draw conclusions about the viability of using this process with actinide-loaded salt. Results of tests with CsCl, $LaCl_3$, $CeCl_3$, and $NdCl_3$ are reported here. Equilibrium was typically achieved in less than 10 hours of contact between lithium metal and molten salt under well-stirred conditions. Maintaining low oxygen and water impurity concentrations (<10 ppm) in the atmosphere was observed to be critical to minimize side reactions and maintain stable salt compositions. An equilibrium model has been formulated and fit to the experimental data. Good fits to the data were achieved. Based on analysis and results obtained to date, it is concluded that clean separation between minor actinides and lanthanides will be difficult to achieve using lithium drawdown.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1426-1433
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• 2005

In this paper, reliability analysis of surface settlement by ground water drawdown is performed using a reliability-groundwater flow numerical model. The result is compared with that of the deterministic model to evaluate the influence of the uncertainty from hydraulic conductivity in the soft ground as well as to determine the range of hydraulic conductivity of grouted ground. From the analyses, it was found that probability of failure to exceed the tolerable settlement was very high, if the hydraulic conductivity of grouted ground is decided from the deterministic flow model only. Reliability analysis which evaluates variance of hydraulic conductivity should be used together with the deterministic model for grouting design of tunnels to prevent ground water drawdown.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.635-642
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• 2018

Braced excavation systems are commonly required to ensure stability in construction of basements for shopping malls, underground transportation and other habitation facilities. For excavations in deposits of soft clays or residual soils, stiff retaining wall systems such as diaphragm walls are commonly adopted to restrain the ground movements and wall deflections in order to prevent damage to surrounding buildings and utilities. The ground surface settlement behind the excavation is closely associated with the magnitude of basal heave and the wall deflections and is also greatly influenced by the possible groundwater drawdown caused by potential wall leakage, flow from beneath the wall, flow from perched water and along the wall interface or poor panel connections due to the less satisfactory quality. This paper numerically investigates the influences of excavation geometries, the system stiffness, the soil properties and the groundwater drawdown on ground surface settlement and develops a simplified maximum surface settlement Logarithm Regression model for the maximum ground surface settlement estimation. The settlements estimated by this model compare favorably with a number of published and instrumented records.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.487-491
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• 2004

For tile hydrogeological data of the National Groundwater Monitoring Wells(NGMW), a statistical analysis is made to reveal aquifer characteristics of the country. Results of the pumping and recovery test are classified into 4～5 types by the pattern of drawdown and residual drawdown curves. The analysis of aquifer characteristics shows that the hydraulic conductivity of alluvial aquifers is greater than that of fractured-rock aquifers. The hydraulic conductivity of alluvial aquifers slightly increases as the distance to the discharge area decreases. 77.5% of the NGMWs, where the distance to the discharge area is more than 100m, shows the constant head boundary. This result suggests that the fractured and the alluvial aquifers are fairly interconnected, and water can be supplied from one aquifer to tile other where pumping tests are performed. It is analyzed that the wells showing the impermeable boundary are influenced by small scale of aquifers, poor aquifer transmissivities, and impermeable layers.

• Journal of the Korean Geotechnical Society
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• v.39 no.10
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• pp.27-39
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• 2023

To effectively manage flood risk, it is crucial to assess the stability of flood defense structures like levees under extreme flood conditions. This study focuses on the time-dependent probabilistic assessment of embankment slope stability when subjected to rapid water level drops. We integrate seepage analysis results from finite element analysis with slope stability analysis and employ Monte Carlo simulations to investigate the time-dependent behavior of the slope during rapid drawdown. The resulting probability of failure is used to develop fragility curves for the levee slope. Notably, the probability of slope failure remains low up to a specific water level, sharply increasing beyond that threshold. Furthermore, the fragility curves are strongly influenced by the rate of drawdown, which is determined through hydraulic analysis based on flood scenarios. Climate change has a significant impact on the stability of the water-side slope of the embankment due to water level fluctuations.

• Korean Journal of Agricultural Science
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• v.39 no.3
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• pp.427-439
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• 2012

In this study, an experiment with large-scale model was performed according to raising embankment in order to investigate the behaviour of failure due to overtopping. The pore water pressure, earth pressure and settlement by high water level, a rapid drawdown and overtopping were compared and analyzed. Also, seepage analysis and slope stability analysis were performed for steady state and transient conditions. The pore water pressure and earth pressure for inclined core type showed high value at the base of the core, but they showed no infiltration by leakage. The pore water pressure and earth pressure by overtopping increased at the upstream slope and core, it is considered a useful data that can accurately estimate the possibility of failure of the reservoir. The behavior of failure due to overtopping was gradually enlarged towards the downstream slope from reservoir crest, and the inclined core after the raising embankment was influenced significantly to prevent the reservoir failure. The pore water pressure distribution for steady state and transient condition showed positive (+) pore water pressure on the upstream slope, it was gradually changed negative (-) pore water pressure on the downstream slope. The pore water pressure by overtopping showed a larger than the high water level at the downstream slope, it was likely to be the piping phenomenon because the hydraulic gradients showed largely at the inclined core and reservoir crest. The safety factor showed high at the steady state, and transient conditions did not show differences depending on the rapid drawdown.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.4
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• pp.1-8
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• 1985

Stability analysis of the embankment as to water level varation is the most important problem in the safety of the slope because the stress of embankment inside varies as to drawdown of seepage line. Especially when the water level is rapidly drawdown, because the flow direction of the free surface changes the toe of embankment, the factor of safety comes to small, therefore the embankment is dangered. For the purpose of studing these phenomena, the experimental models are built with sand in the laboratory. In the experimental consideration, the falling seepage line and the shape of failure are measured. This paper intends to study the failure slip surface, the relationship between the factor of safety and drawdown velocity, and hydraulic gradient. The results of the experimental study are summarized as follows; 1. Owing to the drawdown of free surface, sliding failure occurred in the upstream fill, the height of failure is 5~10, 9~15, and 13~21(cm) in each model. 2. In consideration of the distribution of pore water pressure Table-5 shows each factor of safety. In the relationship between the drawdown velocity and the factor of factor it's velocity should be limited to 0.21~0.28 (cm/sec), according to each models. In the relationship between the factor of safety and the hydraulic gradient within the upstream slope, it's gradient must be below 0.36~0.43.

• Korean Journal of Ecology and Environment
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• v.50 no.3
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• pp.337-354
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• 2017

Cyanobacteria Aphanizomenon population is widely distributed in the world, and well known as harmful algae by producing toxins and off-flavor materials, thus belonging to one of the taxa that became more interested in the field of limnoecology. In this study, the frequency, intensity, and duration of Aphanizomenon occurrence were increased with the abnormal drawdown of water level in the winter in Boryeong Reservoir, and the spatial and temporal characteristics of them are compared with each other in the perspective of hydrometeorology (1998 to 2017) and limnology (2010 to 2017). In Korea, Aphanizomenon flourished mainly in high temperature, and the appearance in the low temperature was rare in total five times. The harmful cyanobacteria Aphanizomenon was observed in the low temperature (December to February) in Boryeong Reservoir from 2014, and then reached a maximum value of $2,160cells\;mL^{-1}$ in January 2017. In addition, the period exceeding $1,000cells\;mL^{-1}$ at this time was more than 3 months. This was simultaneously associated with abnormal water level fluctuation in the low temperature ($<10^{\circ}C$). The large drawdown of water level in the winter season has the potential to promote or amplify the germination and development of harmful algae. Also, subsequent water quality and ecological impacts(e.g., algal toxins and off-flavor substances) need to be considered carefully.

• Journal of the Korean Society of Groundwater Environment
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• v.6 no.4
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• pp.188-193
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• 1999

Transport of pollutants in aquifer largely depends on groundwater flow which is governed by aquifer hydraulic parameters. Determination of these parameters and associated groundwater modeling become essential for adequate remediation of contaminate groundwater. The objective of this paper is to analyze groundwater flow and determine the optimum hydraulic parameters by performing groundwater modeling based on sensitivity analysis for unconfined sandy gavel aquifer constructed in a laboratory scale under various boundary condition. Results revealed that the simulated drawdown was lower than the observed drawdown irrespective of boundary conditions. and specific yield (S$_{y}$) had less effect on the grondwater flow than permeability (K) in the aquifer. Water balance analysis showed that the measured drawdown in neighboring observation wells during pumping was higher than either simulated or recovered water table. The indicated that a difference might exist in the water tables between aquifer and wells. The difference was investigated by time domain reflectometry (TDR) measurements on water contents in the region of water table and capillary fringe, and explained by a delayed response of water table during gravitational drainage as the water table was lowered as a result of pumping.g.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.09a
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• pp.168-171
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• 2001

It is a common practice to extract water from the ground for domestic, agricultural or industrial uses or to lower the groundwater level for construction work. An accurate prediction of ground settlement Is sometimes crucial when groundwater is pumped. This case study have shown that drawdown of the groundwater table may cause ground subsidence. Many settlement gauges was installed in the vicinity of a pumped well to measure the surface settlement. The relationships between the level of groundwater drop and surface settlement is investigated In this research.