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Chaehun Lee,Seonkwang Yoon,Sang-bum Hong,Bumkyung Seo 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2
Radiological characterization is important in decommissioning and dismantling of nuclear facilities, in order to assess the radioactivity concentration, classify the wastes, and secure workers’ safety. The Some components such as Reactor Pressure Vessel (RPV) in nuclear facilities has dose rate higher than Sv/hr, thus in-situ gamma spectroscopy systems suffer from a very high count rate which causes energy resolution degradation, photo-peak shift, and count loss by pile-up and dead-time. The system must be operated in a very high count rate, in order to measure spectra precisely and to quantify radionuclide contents. In order to apply in-situ measurement in high radiation dose rate environment, the sensor, front-end electronics, and data acquisition (DAQ) should be carefully selected and designed as well as precise design of collimators and radiation shield. In this paper, the components of the detector system were selected and performance was evaluated in a high count rate before design the collimator and shield. A LaBr3 coupled with a PMT having short decay time constant (16 nsec) was selected for high count rate application, and two different amplifiers (a conventional charge sensitive preamplifier with 50 usec decay time constant, and wide-band voltage amplifier) were tested. As DAQs, DT5781 (14 bit, 100 MS/s, CAEN) of Pulse Height Analysis (PHA) which is conventionally used signal processing method in the gamma spectroscopy, and DT5730 (14 bit, 500MS/s, CAEN) of Pulse Shape Discrimination (PSD) which is similar to Charge to Digital Convertor (QDC) were used. The number of photons incident to the detector was varied by changing the detector-source distance with Certificate Radiation Material (CRM), and compared to the output count rate. The count rate capability, and energy resolution with different amplifier and DAQ was evaluated. Additionally, the performance of DAQs in extremely high count rate was evaluated with signal data generated by the emulator which can simulate the detector signal waveforms fed into the DAQ based on the measured spectrum.
Chaehun Lim,Seo Gyeong Jeong,Seongmin Ha,Naeun Ha,Seongjae Myeong,Young Seak Lee 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.124 No.-
CO2 capture has become the world’s most urgent agenda nowadays. In this work, we induced functionalitytransition of heteroatom-rich pine needle biochar based activated carbon for CO2 adsorption bymodulating activation conditions. The surface functionalities and porosity of the activated carbon derivedfrom pine needles were investigated intensively according to the activation conditions. The transition ofsurface functional groups and development of porosity were observed as activation progressed. CO2adsorption performances were determined under various conditions, and the adsorption capacities,adsorption selectivities, and cyclabilities were evaluated. From these results, different CO2 adsorptionmechanisms based on the surface functionality and porosity were clearly defined. The pyridinic,pyrrolic(N- based), and Ca(OH)2(Ca-based) CO2 sorbing functional groups derived from mild activationenabled chemical sorption with great adsorption selectivity. The high porosity derived from the severeactivation conditions resulted in physical adsorption with excellent cyclability at 298 K but the chemicalsorption property was weakened by the shift of surface groups to graphitic-N and CaCO3 rich groups. Themodulation of functional groups and porosity enabled utilizing pine needles for effective CO2 removalunder various conditions.
Chaehun Lim,Cheol Hwan Kwak,Seo Gyeong Jeong,Daesup Kim,Young‑Seak Lee 한국탄소학회 2023 Carbon Letters Vol.33 No.1
Removing CO2 gas to address the global climate crisis is one of the most urgent agendas. To improve the CO2 adsorption ability of activated carbon, nitrogen plasma surface treatment was conducted. The effect of nitrogen plasma treatment on the surface chemistry and pore geometry of activated carbon was extensively analyzed. The porosity and surface groups of the activated carbon varied with the plasma treatment time. By plasma treatment for a few minutes, the microporosity and surface functionality could be simultaneously controlled. The changed microporosity and nitrogen groups affected the CO2 adsorption capacity and CO2 adsorption selectivity over N2. This simultaneous surface etching and functionalization effect could be achieved with a short operating time and low energy consumption.
Conceptual design of neutron measurement system for input accountancy in pyroprocessing
Lee, Chaehun,Seo, Hee,Menlove, Spencer H.,Menlove, Howard O. Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.5
One of the possible options for spent-fuel management in Korea is pyroprocessing, which is a process for electrochemical recycling of spent nuclear fuel. Nuclear material accountancy is considered to be a safeguards measure of fundamental importance, for the purposes of which, the amount of nuclear material in the input and output materials should be measured as accurately as possible by means of chemical analysis and/or non-destructive assay. In the present study, a neutron measurement system based on the fast-neutron energy multiplication (FNEM) and passive neutron albedo reactivity (PNAR) techniques was designed for nuclear material accountancy of a spent-fuel assembly (i.e., the input accountancy of a pyroprocessing facility). Various parameters including inter-detector distance, source-to-detector distance, neutron-reflector material, the structure of a cadmium sleeve around the close detectors, and an air cavity in the moderator were investigated by MCNP6 Monte Carlo simulations in order to maximize its performance. Then, the detector responses with the optimized geometry were estimated for the fresh-fuel assemblies with different <sup>235</sup>U enrichments and a spent-fuel assembly. It was found that the measurement technique investigated here has the potential to measure changes in neutron multiplication and, in turn, amount of fissile material.
한국어 학습자의 함축 해석 능력에 대한 연구 -한국어 모어 화자와의 비교,대조를 중심으로
임채훈 ( Chaehun Yim ) 이중언어학회 2016 이중언어학 Vol.63 No.-
The purpose of this research is to investigate the implicature comprehension ability of Korean language leaners. The implicature comprehension ability is the most important one of pragmatic competence irrespective of first language or second language. Nevertheless, there was little study on this ability of Korean language learners. So this study examined the ability to comprehend implicatures in L2 Korean. Participants were two groups: advanced-level second language learners (n=42) and Korean native speakers (n=36). The result of experiments show clearly that the difference between two groups was statistically significant, hence implicatures have become educational items of Korean.