• Journal of Radiation Protection and Research
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• v.45 no.3
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• pp.130-141
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• 2020

Background: Concrete activation in cyclotron vaults is a major concern associated with their decommissioning because a considerable amount of activated concrete is generated by secondary neutrons during the operation of cyclotrons. Reducing the amount of activated concrete is important because of the high cost associated with radioactive waste management. This study aims to investigate the capability of the neutron absorbing materials to reduce concrete activation. Materials and Methods: The Particle and Heavy Ion Transport code System (PHITS) code was used to simulate a cyclotron target and room. The dimensions of the room were 457 cm (length), 470 cm (width), and 320 cm (height). Gd₂O₃, B₄C, polyethylene (PE), and borated (5 wt% ^natB) PE with thicknesses of 5, 10, and 15 cm and their different combinations were selected as neutron absorbing materials. They were placed on the concrete walls to determine their effects on thermal neutrons. Thin B₄C and Gd₂O₃ were placed between the concrete wall and additional PE shield separately to decrease the required thickness of the additional shield, and the thermal neutron flux at certain depths inside the concrete was calculated for each condition. Subsequently, the optimum combination was determined with respect to radioactive waste reduction, price, and availability, and the total reduced radioactive concrete waste was estimated. Results and Discussion: In the specific conditions considered in this study, the front wall with respect to the proton beam contained radioactive waste with a depth of up to 64 cm without any additional shield. A single layer of additional shield was inefficient because a thick shield was required. Two-layer combinations comprising 0.1- or 0.4-cm-thick B₄C or Gd₂O₃ behind 10 cm-thick PE were studied to verify whether the appropriate thickness of the additional shield could be maintained. The number of transmitted thermal neutrons reduced to 30% in case of 0.1 cm-thick Gd₂O₃+10 cm-thick PE or 0.1 cm-thick B₄C+10 cm-thick PE. Thus, the thickness of the radioactive waste in the front wall was reduced from 64 to 48 cm. Conclusion: Based on price and availability, the combination of the 10 cm-thick PE+0.1 cmthick B₄C was reasonable and could effectively reduce the number of thermal neutrons. The amount of radioactive concrete waste was reduced by factor of two when considering whole concrete walls of the PET cyclotron vault.

• Journal of the korean Society of Automotive Engineers
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• v.10 no.2
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• pp.61-69
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• 1988

The finite-difference three-dimensional boundary layer procedure of Chang and Patel is modified and applied to solve the boundary layer development on the automobile surface. The inviscid pressure distribution needed to solve the boundary layer equations is obtained by using a low order panel method. The plane of symmetry boundary layer exhibits the strong streamline divergence up to the midbody and convergence thereafter. The streamline divergence in front of the windshield helps the boundary layer to overcome the sever adverse pressure gradient and avoid the separation. The relaxation of the pressure right after the top of the wind-shield, on the other hand, makes the overly thinned boundary layer to readjust and prompts the streamlines to converge into the symmetry plane before the external streamlines do. The three-dimensional characteristics are less apparent after the midbody and the boundary layer is similar to that of the two-dimensional flow. The results of the off-plane-of-symmetry boundary layer are also presented.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2018.11a
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• pp.103-103
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• 2018

The liquid cathode processing is necessary to separate cadmium from the actinide elements in the pyroprocessing since the actinide deposits are dissolved or precipitated in a liquid cathode. Distillation process was employed for the cathode processing owing to the compactness. It is very important to avoid a splattering of cadmium during evaporation due to the high vapor pressure. Several methods have been proposed to lower the splattering of cadmium during distillation. A multi-layer porous round cover was proposed to avoid a cadmium splattering in our previous study. In this study, distillation behavior of $Cd-ZrO_2$ and Cd - Bi systems were investigated to examine a multi-layer porous round cover for the development of the cadmium splatter shield of distillation crucible. It was designed that the cadmium vapor can be released through the holes of the shield, whereas liquid drops can be collected in the multiple hemisphere. The cover was made with three stainless steel round plates with a diameter of 33.50 mm. The distance between the hemispheres and the diameter of the holes are 10 and 1 mm, respectively. Bismuth or zirconium oxide powder was used as a surrogate for the actinide elements. About 40 grams of Cd was distilled at a reduced pressure for two hours at various temperatures. The mixture of the cadmium and the surrogate was distilled at 470, 570 and $620^{\circ}C$ in the crucible with the cover. Most of the bismuth or zirconia remained in the crucible after distillation at 470 and $570^{\circ}C$ for two hours. It was considered that the crucible cover hindered the splattering of the liquid cadmium from the distillation crucible. A considerable amount of the surrogate material reduced after distillation at $620^{\circ}C$ due to the splattering of the liquid cadmium. The low temperature is favorable to avoid a liquid cadmium splattering during distillation. However, the optimum temperature for the cadmium distillation should be decided further, since the evaporation rate decreases with a decreasing temperature.

• Journal of the Korean Electrochemical Society
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• v.25 no.2
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• pp.51-68
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• 2022

Although lithium metal batteries have a high energy density, experimental skills capable of solving lots of problems induced by dendrite such as short circuit, low coulomb efficiency, capacity loss, and cycle performance are still only in academic research stage. In this paper, research cases for dendrite growth inhibition on lithium metal electrode were classified into four types: flexible SEI (solid electrolyte interface) layer responding to volume expansion of lithium metal electrode, SEI supporting layer to inhibit dendrite growth physically, SHES (self-healing electrostatic shield) mechanism to adjust lithium growth by leading uniform diffusion of Li⁺ ions, and finally micro-patterning to induce uniform deposition of lithium. We hope to advance the practical use of lithium metal electrode by analyzing pros and cons of this classification.

• Progress in Superconductivity and Cryogenics
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• v.16 no.2
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• pp.59-63
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• 2014

HTS power cable bypass the fault current through the former to protect superconducting tapes. On the other hand, the fault current limiting (FCL) power cable can be considered to mitigate the fault current using its increased inductance and resistance. Using the increased resistance of the cable is similar to the conventional resistive fault current limiter. In case of HTS power cable, the magnetic field of HTS power cable is mostly shielded by the induced current on the shield layer during normal operation. However, quench occurs at the shield layer and its current is kept below its critical current at the fault condition. Consequently, the magnetic field starts to spread out and it generates additional inductive impedance of the cable. The inductive impedance can be enhanced more by installing materials of high magnetic susceptibility around the HTS power cable. It is a concept of SFCL power cable. In this paper, a sample SFCL power cable is suggested and experimental results are presented to investigate the effect of iron cover on the impedance generation. The tests results are analyzed to verify the generation of the inductive and resistive impedance. The analysis results suggest the possible applications of the SFCL power cable to reduce the fault current in a real grid.

• Progress in Superconductivity and Cryogenics
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• v.12 no.1
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• pp.42-46
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• 2010

The HTS power cable is composed of 2 layers for transmission and 1 layer for shield. The superconducting tapes of transmission layers and shield layer are wound in a cylindrical shape with a winding pitch. The radius of cylinder and the number of superconducting tapes are decided considering to the transmission current capacity and the critical current of superconducting tapes. The increasement of transmission current capacity will increase in volume of HTS cable system. In this paper, the composition method of supercondcuting power cable using the multi-cable is presented. The coated conductor tape can be wound on the smaller cylinder because it has the smaller critical bending diameter than the BSCCO tape. A small-scale cable was composed using the coated conductor tapes and a multi-cable is composed using a small-scale cable considering to transmission current capacity. Even increase of transmission current capacity, this method has advantage that the HTS superconducting power cable can be composed easily. The 22.9 kV and 154 kV superconducting power cable was composed using the presented method.

• Journal of the Korean Magnetics Society
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• v.21 no.3
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• pp.99-103
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• 2011

In this study, we have performed systematical FEM analysis for design of open-ended 3-layer magnetic shield. For the simulation to calculated shielding factors, the relative permeability was varied in the range of $2{\times}10^3\sim1{\times}10^5$, and the length of the magnetic cylinders and length difference between layers were changed. We found that the shielding factor of -60 dB were obtained with the relative permeability of over 20000 and the lengths of magnetic layers of 40 cm, 45 cm and 50 cm, and the uniform magnetic field could be obtained in the range of $10cm{\times}10cm-\phi$.

• Nuclear Engineering and Technology
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• v.3 no.4
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• pp.185-197
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• 1971

Korea's TRIGA Mark-Ⅱ reactor was primarily designed in 1950's and was constructed in 1962 for 100 kw thermal output, but it was upgraded to 250 kw in July 1969. Nevertheless, the shield remains unchanged, although the radiation level has increased. The result of computation On this paper shows that, with the existing shield, it is safe for the fast neutrons even after the power upgrading by 2.5 times. It is, however, somewhat dangerous for the gamma rays which are comprised of primary and secondary. For the analysis of the reactor shielding design, an attempt is made for the computation toward the horizontal direction. From theoretical point of view, it can be concluded that some layer of additional shield must be reinforced to the existing concrete in order to be radiologically safe in the reactor hall.

• Journal of the Microelectronics and Packaging Society
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• v.16 no.4
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• pp.55-60
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• 2009

Porous silicon film is fabricated by electrochemical etching in a chemical mixture of HF and ethanol. Effects of Si type, Si resistivity, ultrasonic frequency, current density and etching time on surface morphology of PS film were studied. Electrochemical etching in ultrasonic bath promotes the uniformity of porous layer of Si. Frequency of ultrasonic was increased from 40 kHz to 130 kHz to obtain uniform pores on the Si surface. When current density was higher, the sizes of pores were larger. The new etching cell using back contact metal and current shield help to overcome nonhomogeneity and current crowding effect, and then leads to fabricate uniform pores on the Si surface. The distribution of pore size shows no notable tendency with etching time.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.2
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• pp.115-119
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• 2006

Electromagnetic shielding, transparent ITO coating layers have deposited on ocular lens substrate by magnetron sputtering. We investigated the effect induced by the substrate temperature on coating layer. The characteristics of the coating layers were analyzed using surface profiler, four-point probe, XRD, spectrophotometer and Auger Electron spectroscopy. As substrate temperature became higher, carrier concentration was increased and transmittance in the visible region was increased, too.