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Study on Applicability of Plasma Assisted Machining for Hard-Machining Materials
Mingyu Choi,Seoyong Choi,Sunghoon Hong,Jeongsu Jeong 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1
Many countries are developing various mechanical cutting technologies to dismantle nuclear facility. However, most of mechanical cutting technologies have a problem like the degradation of tool life due to the Hard-Machining materials. To solve this problem, lab-scale test was performed with a Plasma Assisted Machining (PAM) technology and 25 mm of thickness Inconel 600 plate. Commonly, the strength of metals decreases by exposure at high temperature. And, previous study reported that strength of Inconel 600 is degraded above 500°C. This softening effect was applied to Inconel 600 cutting test. The optimal conditions such as the plasma torch power and the feed rate were determined by this study. As a result, the surface temperature of Inconel 600 was reached up to 500°C under the conditions which is 8.4 kW of plasma torch power and 150–250 mm·min?1 of feed rate. And it was confirmed that the tool life was improved under the conditions. In order to apply PAM for various Hard- Machining materials, it is necessary to investigate the softening temperature of Hard-Machining materials, the plasma torch power and feed rate.
Evaluation on Applicability of New Milling Machine Assisted Plasma Torch
Mingyu Choi,Seoyong Choi,Sunghoon Hong,Jeongsu Jeong 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1
Various cutting technologies are being developed for dismantling nuclear power plants. these technologies are including mechanical and thermal methods. For example, mechanical cutting methods include sawing, drilling and milling. But, due to the strength of material, mechanical cutting methods have limits of cutting depth and tool life. Therefore, this milling machine assisted plasma torch was developed to improve the limits. And this machine has the principle of softening effect caused by the high temperature. In this work, this developed device was evaluated in view of the cutting depth and tool life in cutting process. For this process, a plasma torch was attached to the front of the endmill processing path to heat the Inconel 600. As results, compare to conventional milling, when the plasma torch power is 6.4 kW, the cutting depth was increased by 4 mm at condition (feed rate is 100 mm·min?1, tool diameter is 10 mm, rotating speed is 1,000 rpm). And cutting length increase 2 times from 300 mm to 600 mm at 16 mm of tool diameter.
A Study on Cutting Technology for Dismantling Metal Structures of Nuclear Power Plant
Mingyu Choi,Seoyong Choi,Sunghoon Hong,Jeongsu Jeong 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1
Currently, dismantling technology for decommissioning nuclear power plants is being developed around the world. This study describes the cutting technology and one of the technologies being considered for the RV/RVI cutting of Kori Unit 1. The dismantling technology for nuclear power plants include mechanical and thermal methods. Mechanical cutting methods include milling, drill saw, and wire cutting. The advantages of the mechanical method are less generating aerosol and less performance degradation in water. However, the cutting speed is slow and the reaction force is large. Thermal cutting methods use heat sources such as plasma arcs, oxygen, and lasers. The advantages of thermal method are fast cutting speed, low reaction force and thick material cutting. On the other hand, they have problems with fume and melt. Among them, the cutability of the oxygen cutting method is better in carbon steel than in stainless steel. In order to cut the RV/RVI of the Kori Unit 1, the applicability of fine plasma, arc saw, and band/ wheel saw is being reviewed. For RV cutting, the applicability of arc saw and oxy-propane is being considered Because RV is mostly made of carbon steel. However, since the flange is cladded with stainless steel, the use of mechanical methods such as wire saws should be considered. In the case of RVI, since it has a complicated shape and is made of stainless steel, it seems necessary to review various cutting methods. In addition, it will be necessary to minimize radiation exposure of workers by cutting underwater cutting.
최민규(MinGyu Choi),주성찬(Sung Chan Joo),김원건(Kim Won Geon),김진솔(Jinsol Kim),길동현(DongHyun Gill),강태원(TaeWon Gang) 한국정보기술학회 2021 Proceedings of KIIT Conference Vol.2021 No.11
KOSPI 지수에 영향을 줄 수 있는 경제 지표와 원자재의 날짜별 가격을 입력 특성으로 선정한 후 랜덤 포레스트 알고리즘을 적용하여 익일 변동을 예측하였다. 수집한 데이터의 모든 특성을 포함하여 모델을 학습한 후, 특성의 중요도를 평가한다. 중요도에 따라 입력 특성을 선별한 후 모델을 다시 학습하여 정확도가 더 높은 모델을 구축한다. 실험 결과 초기 모델의 AUC는 0.57, 입력 특성을 선별한 모델의 AUC는 0.59로 다소 개선 되었음을 알 수 있었다. After selecting economic indicators that can affect the KOSPI and the price of raw materials by date as input characteristics, a random forest algorithm was applied to predict the next day"s fluctuations. After training the model including all the features of the collected data, the importance of the features is evaluated. After selecting input features according to their importance, the model is trained again to build a model with higher accuracy. As a result of the experiment, it was found that the AUC of the initial model was 0.57, and the AUC of the model in which the input characteristics were selected was slightly improved to 0.59.
중대재해 처벌등에 관한 법률상 안전사고의 현황과 대응방안
최민규(Mingyu Choi) 한국중재학회 2023 중재연구 Vol.33 No.2
In this thesis, the domestic and foreign legislative background and legislative process of the Serious Accident Punishment Act were reviewed, and the Serious Accident Punishment Act in Korea was reviewed. In 2022, more safety accidents occurred in the construction industry than in other fields, and in particular, the most deaths occurred in the ‘fall’ type. In April 2023, regarding two criminal first-instance trial cases, the courts all sentenced guilty, and in one case, the representative of the company(CEO) was sentenced to imprisonment and was arrested. In response, the management side expresses the opinion that the punishment is excessive and there is a concern that corporate management will shrink, while the workers side(Union) argues that the responsibility of the business operator or manager should be strengthened by heavier punishment. As a countermeasure to overcome rationally, we present a plan in terms of legislation and resolution process. In other words, we present a review of the amendment to the Serious Accident Punishment Act and the Court Organization Act. In addition, guidelines for the a safety and health system must be implemented, and if an accident occurs, it must be dealt with reasonably. As a result, safety accidents in the construction industry should drastically decrease and safety culture should be properly established.
Je, Mingyu,Jung, Hyeon Jin,Koutavarapu, Ravindranadh,Lee, Seung Jun,Lee, Seung Heon,Kim, Sung Kuk,Choi, Hyun Chul,Choi, Myong Yong Elsevier 2018 Materials chemistry and physics Vol.217 No.-
<P><B>Abstract</B></P> <P><B>Hypothesis</B></P> <P>Semiconductor nanocrystals with response in the near-infrared region include lead chalcogenide quantum dots (QDs), and these materials show a strong quantum confinement effect due to their large Bohr radius compared with the group II–VI QDs. In the present study, a facile synthesis of lead selenide (PbSe) QDs using a pulsed laser irradiation in liquid (PLIL) is presented.</P> <P><B>Experiments</B></P> <P>PbSe QDs were produced using a pulsed Nd:YAG laser (532 nm, 10 Hz, 7 ns) irradiation of the Pb and Se mixed precursor solutions using the following three surfactants at various concentrations: cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polyvinylpyrrolidone (PVP).</P> <P><B>Findings</B></P> <P>Interestingly, it was observed that the synthesis and particle size of PbSe QDs obtained via the PLIL technique were strongly influenced by the type and concentration of the surfactants and by the varying wavelength and power of the laser. A secondary irradiation of the prepared sample in PVP solution resulted in the formation of rock salt crystalline PbSe QDs that were approximately 6.83 nm in size.</P> <P><B>Highlights</B></P> <P> <UL> <LI> PbSe QDs are prepared from Pb and Se salts by a PLIL technique. </LI> <LI> The formation of PbSe QDs are dependent on surfactants. </LI> <LI> Structural and morphology studies confirm the formation of PbSe QDs. </LI> <LI> CTAB is effective for the synthesis of PbSe QDs at various experimental conditions. </LI> <LI> PVP is effective for the formation of small PbSe QDs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>