• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.385-390
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• 1998

방사성 페이온교환수지 아스팔트고화체를 처분장 등지에서 장기간 저장시 안전성 확보를 위하여 물리적 강도가 높고 고화체내에서 방사성핵종의 침출저항성 및 처리시 감용의 효과가 우수한 고화체 연구가 필요하게 되었다. 실험에 사용된 이온교환수지는 입상형 양이온 교환수지를 대상으로 하였으며 고화매질로서는 도로포장용으로 생산되는 직류아스팔트 60/70을 사용하였다. 고화보조제는 방사성 고체패기물 포장시 사용되어 폐기물로 발생되는 페폴리에틸렌(폐PE) 필름을 사용하였다. 실험결과 고화체의 형태안정성은 PE 함유량이 10 wt% 이상일 때 고화체 형태를 그대로 유지할 수 있으며 압축강도는 414 kPa(60 psi) 이상을 나타내었다. 최적의 운전조건은 이온교환수지, PE 함유량이 건조기준으로 각각 30~50 wt%, 10~25 wt% 이며, 고화온도는 170~20$0^{\circ}C$이다. 고화체의 침출특성은 확산 (diffusion) 으로 해석이 가능하며, 유효확산계수(De)는 Cs, Co의 경우 각각 1.621$\times$$10^{-7}$, 1.186$\times$$10^{-9}$ $\textrm{cm}^2$/day로 나타나고, Leachablity index는 각각 11.7, 13.8로 미국 원자력위원회 (NRC)가 요구하는 기준값 6보다 훨씬 높게 나타났다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.46-52
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• 2017

Recently durability design based on deterministic or probabilistic method has been attempted since service life evaluation in RC(Reinforced Concrete) structure exposed to chloride attack is important. The deterministic durability design contains a reasonable method with time effect on surface chloride content and diffusion coefficient, however the probabilistic design procedure has no consideration of time effect on both. In the paper, a technique on PDF(Probability of Durability Failure) evaluation is proposed considering time effect on diffusion and surface chloride content through equivalent surface chloride content which has same induced chloride content within a given period and cover depth. With varying period to built-up from 10 to 30 years and maximum surface chloride content from $5.0kg/m^3$ to $10.0kg/m^3$, the changing PDF and the related service life are derived. The proposed method can be reasonably applied to actual durability design with preventing conservative design parameters and considering the same analysis conditions of the deterministic method.

• Applied Chemistry for Engineering
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• v.31 no.2
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• pp.208-214
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• 2020

In this study, the characteristics and mechanism of microwave-assisted drying were investigated to improve the efficiency of the storage and extraction of biomass through the removal of moisture from plant cell Taxus chinensis. The efficiency of microwave-assisted drying increased with increasing microwave power. When the experimental data were fitted to typical drying kinetic models, the page and modified Page models were the most appropriate. The microwave-assisted drying was determined to be a spontaneous endothermic process, and randomness increased during the drying process. The effective diffusion coefficient (3.445 × 10^-9~7.163 × 10^-7 ㎡/s) and mass transfer coefficient (3.1529 × 10^-5~1.2895 × 10^-2 m/s) increased with increasing microwave power. The small Biot number (0.3890~0.7198) indicated that the mass transfer process was externally controlled.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.5
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• pp.241-246
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• 2015

Cellular foamed insulation such as polyurethane foam ages and degrades the thermal conductivity. Aging of foam is a result from the diffusion of gases, initially consisting of $CO_2$ but eventually replaced by air from the environment. The variation of the cell gas content with time is primarily influenced by the increase of thermal conductivity of the cellular foam. The weight of foam also changes as the gas diffuses and exchanges. In this study, a weight measurement method has been proposed to evaluate the effective diffusion coefficients of $CO_2$ and Air, $D_{CO2}=7.08504E-11$ and $D_{air}=4.86086E-12$, respectively and are compared with the gas analysis method.

• Korean Journal of Optics and Photonics
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• v.23 no.3
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• pp.113-118
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• 2012

The concentration and hydrodynamic radius of nano-sized fluorescence particles diffusing in solution were compared by using fluorescence correlation spectroscopy (FCS), which can measure the variation of the correlation function of a fluorescence signal by size and number of particles. The used nano-sized fluorescence particles are Alex Fluor 647, quantum dots, and fluorescence beads, and three kinds of sample solutions with different concentrations were prepared by dilution to 1/10 and 1/100 with distilled water for each kind of particles. The effective focal volumes were calculated by using the known diffusion coefficient of Alexa Fluor 647 particles, and the diffusion time, number of particles in focal volume, and variation of concentration according to the dilution could be measured by the FCS system. Through this study, we determined that the concentrations of arbitrarily diluted sample solutions can be measured by a home-built FCS setup in the range of 0.1 nM ~ 10 nM and that the diffusion coefficient of the quantum dot was $27{\pm}1{\mu}m^2/s$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.157-163
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• 2010

Solid oxide fuel cells (SOFCs) are commonly composed of ceramic compartments, and it is known that the physical properties of the ceramic materials can be changed according to the operating temperature. Thus, the physical properties of the ceramic materials have to be properly predicted to develop a highly reliable simulation model. In this study, several physical properties that can affect the performance of SOFCs were selected, and simulation models for those physical properties were developed using our own code. The Gibbs free energy for the open circuit voltage, exchange current densities for the activation polarization, and electrical conductivity for the electrolyte were calculated. In addition, the diffusion coefficient-including the binary and Knudsen diffusion mechanisms-was calculated for mass transport analysis at the porous electrode. The physical property and electrochemical reaction models were then simulated simultaneously. The numerical results were compared with the experimental results and previous works studied by Chan et al. for code validation.

• Nuclear Engineering and Technology
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• v.27 no.6
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• pp.870-876
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• 1995

In this paper, a new three-dimensional nodal diffusion code which is based on the AFEN methodology is described and tested. The method expands the homogeneous flux within a node in ter-ms of eighteen analytic basis functions satisfying the diffusion equation at any point of the node. And the nodal coupling equations are derived such that nodal balance, current continuity and leakage balance within an infinitesimally small box around the edge are satisfied. To verify its accuracy, the code was applied to the well-known static LMW benchmark problem and a small core benchmark problem that has the same material properties as the three-dimensional IAEA benchmark problem and compared with two other codes (QUANDRY, VENTURE). The results show that the code provides good accuracy both in the power distribution and in the effective multiplication factor.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.606-614
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• 2003

The major cause of deterioration for the concrete bridge decks exposed to de-icing chemicals would be chloride-induced reinforcement corrosion. Thus, in this paper, in order to predict time to corrosion for concrete bridge decks in the urban area, chloride concentration was measured with depth from the surface. A frequency analysis on surface chloride concentration and chloride diffusion coefficient of concrete bridge deck equals 0.192, 29.828 in the scale parameter and 7.899, 1.983 in the shape parameter of gamma distribution. The average value of surface chloride concentration equals 1.5 kg/㎥ and condenses from 1 to 2 kg/㎥ in the level of probability 70%. From the probabilistic results, it is confirmed that 26mm of minimum cover depth in order to target 20 years over is calculated. The countermeasure strategy to extend the service life of concrete bridge deck exposed to de-icing chemicals would be an effective method to increase cover depth and to place high performance concrete, which could lead to reduce the chloride diffusion coefficient and distribution range.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4664-4670
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• 2010

Comparison of the classical mobile-immobile zone (MIM) model to the derived model led to several conclusions. If the MIM model is to be applied, the initial concentration in the immobile zone has to be down-scaled by a correction factor that is a function of pore geometry. The MIM model was valid only after sufficiently long time has passed, i.e., only after the diffusion front reaches the deepest pore wall in the immobile zone. The MIM mass-transfer coefficient $\alpha$, was inversely proportional to the square of the pore depth. Also it did not depend on the mobile-zone flow velocity, contrary to the number of laboratory and field observations. The classical MIM model displayed a rapid exponential decay of immobile-zone concentration. Meanwhile at large times, the newly derived model displayed similar exponential decay. This was contrary to the mounting evidence of power-law BTC tails observed in laboratory and field settings.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.667-673
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• 2017

We investigated the temperature uniformity in an anode-supported solid oxide fuel cell, using the open source computational fluid dynamics (CFD) toolbox, OpenFOAM. Numerical simulation was performed in three different flow paths, i.e., co-flow, counter-flow, and cross-flow paths. Gas flow in a porous electrode was calculated using effective diffusivity while considering the effect of interconnect rib. A lumped internal resistance model derived from a semi-empirical correlation was implemented for the calculation of electrochemical reaction. The result showed that the counter-flow path displayed the most uniform temperature distribution.