• Journal of Food Hygiene and Safety
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• v.34 no.6
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• pp.583-590
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• 2019

As the consumption of fresh fruits and vegetables increases, food poisoning caused by foodborne pathogen contamination is not decreasing. To prevent the contamination of produce, a quick and easy, low-cost, environmentally-safe disinfection method that does not affect produce freshness or quality is needed. This study demonstrates a new-concept, circulating-water disinfection system that purifies water by using newly developed 'LED-PS (photosensitizer)-induced ROS generation unit'. Using various types of LED-PS induced ROS generation units, we investigated the conditions for reducing the density of various pathogenic bacteria by more than 3 log CFU / mL in 1 hour. The major operational factors affecting the density reduction of the LED-PS-induced ROS generation unit were analyzed. Depending on bacteria species, the density reduction rate was varied. The effect of the units on reducing the density of Bacillus cereus and Pectobacterium carotovorum subsp. carotovorum was high, but the effect on foodborne bacteria such as Escherichia coli was relatively low. In this circulating water disinfection system, the density reduction effect tended to increase as the flow rate increased and the initial bacterial density decreased. As the amount of PS absorbed beads increased, the density reduction effect increased exponentially in some bacteria. Model 3280, a double cylindrical unit connecting two single cylindrical units, could completely sterilize more than 3 log CFU/mL of B. cereus and P. carotovorum subsp. carotovorum in 30 minutes of LED irradiation.

• Journal of Radiation Protection and Research
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• v.23 no.1
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• pp.33-47
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• 1998

Using a combination of an X-ray generator Installed in radiation calibration laboratory of Korea Atomic Energy Research Institute (KAERI) and a series of 8 radiators and filters described in ISO-4037, monoenergetic fluorescent X-rays from 8.6 keV to 75 keV were produced. This fluorescent X-rays generated by primary X-rays from radiator were discriminated $K_{\beta}$ lines with the aid of filter material and the only $K_{\alpha}$ X-rays were analyzed with the high purity Ge detector and portable MCA. The air kerma rates were measured with the 35 co ionization chamber and compared with the calculational results, and the beam uniformity and the scattered effects of radiation fields were also measured. The beam purities were more than 90 % for the energy range of 8.6 keV to 75 keV and the air kerma rates were from 1.91 mGy/h (radiator : Au, filter : W) to 54.2 mGy (radiator : Mo, filter : Zr) at 43 cm from center of the radiator. The effective area of beam at the measurement point of air kerma rates was 12 cm ${\times}$ 12 cm and the influence of scattered radiation was less than 3 %. The fluorescent X-rays established in this study could be used for the determination of energy response of the radiation measurement devices and the personal dosemeters in low photon energy regions.

• Journal of Radiation Protection and Research
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• v.38 no.4
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• pp.228-233
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• 2013

It has been continuously generated the requirement for the replacement of the main components such as a steam generator due to the deterioration of the nuclear power plant all around the world. Also, a large amount of radioactive metal was generated during the decommissioning in a short period. It is required to make an accurate measurement of the residual radioactivity for recycling the metal waste for releasing from regulatory control. In planning the measurement procedures, the influence of geometry, self-absorption, density and other relevant factors on the representativeness of the measurements should be considered for the decommissioning metal waste. In this study, the method for measurement procedures, the source term evaluation, the ways to secure representative samples, the measurement device for wide area and the self-absorption correction factors for different density were evaluated. The metal samples for measurement were prepared for securing the simple geometry and representative by melting process. The developed correction method for measuring the radioactivity a variety density of metal waste could improve the reliability of the evaluation results for clearance.

• Journal of Radiation Protection and Research
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• v.29 no.3
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• pp.187-196
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• 2004

The health effects resulting from severe accidents of typical 1,000MWe KSNP(Korea Standard Nuclear Plant) PWR and typical 600MWe CANDU(CANada Deuterium Uranium) plants were estimated and compared. The population distribution of the site extending to 80km for both site were considered. The releaese fraction for various source term categories(STC) and core inventories were used in the estimation of the health effects risks by using the MACCS2(MELCOR Accident Consequence Code System2) code. Individuals are assumed to evacuate beyond 16km from the site. The health effects considered in this comparative study are early and cancer fatality risk, and the results are presented as CCDF(Complementary Cumulative Distribution Function) curves considering the occurrence probability of each STC's. According to the results, the early and cancer fatality risks of PHWR plants we lower than those of PWR plants. This is attributed the fact that the amount of radioactive mateials that released to the atmosphere resulting from the postulated severe accidents of PHWR plants are smaller than that of PWR plants. And, the dominating initiating event of STC that shows maximum early and cancer fatality risk is SGTR(Steam Generator Tube Rupture) for both plants. Therefore, the appropriated actions must be taken to reduce the occurrence probability and the amounts of radioactive materials released to the environment in order to protect the public for both PWR and PHWR plants.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.21-26
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• 2016

This paper presents a step-down DC-DC buck converter with a CCM/DCM dual-mode function for the internal power stage of portable electronic device. The proposed converter that is operated with a high frequency of 1 MHz consists of a power stage and a control block. The power stage has a power MOS transistor, inductor, capacitor, and feedback resistors for the control loop. The control part has a pulse width modulation (PWM) block, error amplifier, ramp generator, and oscillator. In this paper, an external capacitor for compensation has been replaced with a multiplier equivalent CMOS circuit for area reduction of integrated circuits. In addition, the circuit includes protection block, such as over voltage protection (OVP), under voltage lock out (UVLO), and thermal shutdown (TSD) block. The proposed circuit was designed and verified using a $0.18{\mu}m$ CMOS process parameter by Cadence Spectra circuit design program. The SPICE simulation results showed a peak efficiency of 94.8 %, a ripple voltage of 3.29 mV ripple, and a 1.8 V output voltage with supply voltages ranging from 2.7 to 3.3 V.

• KSBB Journal
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• v.13 no.5
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• pp.502-510
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• 1998

Stabilization of antibody, which is specific to Salmonella typhimurium antigens, present in dry states on membranes was accomplished, and its shelf-life, i.e., duration for maintaining minimum 90% of the initial activity, under optimal conditions was determined. To prepare two major components of an immuno-strip, the antibody was not only immobilized on nitrocellulose membrane surfaces but also placed within the pores of glass fiber membrane after conjugating it with old colloids as signal generator. Among potential stabilizers of the immuno-components, a disaccharide, trehalose, showed a significant protection effect of immunoglobulin structure from thermal energy. Optimal concentrations of trehalose for the respective component were significantly different (8-fold higher for the antibody-gold conjugate than for the immobilized antibody), which probably resulted from distinct densities and configurations of antibody present on the membranes. An additional requirement for the gold conjugate was freeze-drying of this substance such that the conjugate can be readily resolubilized upon contact with aqueous medium. By using the components prepared under optimal conditions, immuno-strips were constructed and exposed to thermal energy. Signals with less than 10% decrease in the intensity were maintained for approximately 21 days at 60$^{\circ}C$. Compared to previous reports, this result represented a 2-year shelf-life at room temperature. it was, however, two times longer if determined from thermal acceleration tests based on the theory of inactivation rate of protein. Such discrepancy between the two estimates could be mainly attributed to errors in accurately controlling temperatures and also to changes in the physical properties of membranes due to a high thermal energy.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.4
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• pp.271-277
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• 2016

For a stable electric power supply in the space, nuclear batteries have been used as the main power source in a spacecraft owing to their long lifetime and high reliability. In accordance with the plan for lunar mission in Korea, nuclear batteries will supply electricity to the rover that needs to be developed. According to the information about the estimated payload, Korea Atomic Energy Research Institute started with the conceptual design based on the previous studies in USA and Russia. Because a nuclear battery converts the decay heat of the radioisotope into electricity, thermal design, radiation shield, and shock protection need to be considered. In this study, two types of nuclear batteries, radial type and axial type, were designed according to the alignment of the thermoelectric module. Heat transfer analyses were performed to compare their thermoelectric efficiency, and test mockups were fabricated to evaluate their performances.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.1
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• pp.133-143
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• 2001

This paper describes the correlation of the transient impedance and its parameters with the stationary resistance of a grounding system to a square pulse current and a lightning impulse current. In the experiment, the grounding system consists of a single grounding rod$(\Psi10[mm], 1[m])$and/or a triple-grounding rods of equilateral triangles with 5[m] spacing for operation. To analyze the transient impedance characteristics of the grounding system, a pulse generator which can produce square wave of a 30[ns] rise-time and a $20[\mus] $pulse duration is designed and fabricated. The injected content in the grounding system and the developed potential were recorded, and the time variation of the transient impedance were calculated as the ratio of the potential rising to the injected current at each time. The transient impedance and the effective surge impedance Z3 which defines economic protection level in power system were quite higher than the stationary resistance. The grounding impedance is decreased by the application of the triple-rods grounding system, and its effect is decreased as the frequency of the current is increased due to the inductance of the grounding leads.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2001.05b
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• pp.85-91
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• 2001

This paper provides a case study of landfill gas (LFG) utilization fer direct use as process fuel, and for electrical power generation at restored landfills in the Hong Kong Special Administrative Region of China (HKSAR). The paper specifically covers the LFG utilization schemes, which are required under landfill restoration contracts at the Shuen Wan and Urban Landfills. These contracts provide for the restoration and aftercare of six landfills, and are administered by the Environmental Protection Department (EPD) of the Hong Kong Government. The LFG utilization scheme at the Shuen Wan Landfill incorporates the direct use of LFG by compressing and dehumidifying the LFG prior to conveyance through a 1.6-kilometer (1-mile) pipeline. The pipeline provides an alternate fuel source to naphtha during process heating for gas production at the Tai Po Gas Production Plant of the Hong Kong and China Gas Limited (HKCC). The LFG utilization scheme at the Jordan Valley Landfill (one of the Urban Landfills) beneficially uses the LFG as fuel for electrical power generation with reciprocating internal combustion engines. The LFG is compressed, cooled, and filtered prior to delivery to two engine/generator sets. This system provides power to operate the leachate pre-treatment plant, which processes leachate from all of the Urban Landfill sites. The case study will examine the technical and non-technical considerations, including harriers, for developing, designing and implementing the LFG utilization projects in Hong Kong. Specific regulatory considerations and external governmental agency approvals are discussed, including the requirement to register as a gas-producing utility. While the paper focuses on LFG utilization applications in Hong Kong, many of the considerations discussed are also applicable to development of LFG utilization in other regions of Asia.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1034-1035
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• 2015

Watertight 25.8 kV/600 A/12.5 kA fault current limiters (FCLs) have successfully installed in five areas (Incheon, Seoul, Gyeong-gi, Daejeon, Suwon) on KEPCO power distribution line for the purpose of commercial demonstrations. The fault current limiting operation of this FCL, which includes functions of sensing, commutation, and reduction of fault currents, is perfectly completed within 1 cycle immediately after fault occurs. The performance of FCL was verified by short circuit test, impedance test, insulation test, temperature-rise test, and control test, etc at PT&T in LS industrial systems, which is the official certification institute in Korea. In 2013, and also the FCL field test was performed in order to test the protection coordination between conventional relays and FCL, on the 1.5 kA and 5.0 kA faults, which were made by connecting the Artificial Fault Generator (AFG) to the distribution line in test grid at KEPCO Power Testing Center. The next step of this project is to check the FCL conditions caused by real external environment, and acquire the various data from five regions installed with FCL. In this paper, we intend to explain the FCL specifications and performance characteristics, and check the expected effect by application of FCL to power distribution line based on the power system analysis of an application site.