• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2277-2288
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• 2021

To regulate the safety protocols in nuclear facilities, radioactive aerosols have been extensively researched to understand their health impacts. However, most measured particle-size distributions remain at low resolutions, with the particle sizes ranging from nanometer to micrometer. This study combines the high-resolution detection of 500 size classes, ranging from 6 nm to 10 ㎛, for aerodynamic diameter distributions, with a regional lung deposition calculation. We applied the new approach to characterize particle-size distributions of aerosols generated during the plasma arc cutting of simulated non-radioactive steel alloy wastes. The high-resolution measured data were used to calculate the deposition ratios of the aerosols in different lung regions. The deposition ratios in the alveolar sacs contained the dominant particle sizes ranging from 0.01 to 0.1 ㎛. We determined the distribution of various metals using different vapor pressures of the alloying components and analyzed the uncertainties of lung deposition calculations using the low-resolution aerodynamic diameter data simultaneously. In high-resolution data, the changes in aerosols that can penetrate the blood system were better captured, correcting their potential risks by a maximum of 42%. The combined calculations can aid the enhancement of high-resolution measuring equipment to effectively manage radiation safety in nuclear facilities.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2003년도 가을 학술논문집
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• pp.117-123
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• 2003

지난 논문에 이어서 삼중수소 취급시설의 일부인 삼중수소 주입계통과 재생계통을 소개하였다. 두 계통은 모두 삼중수소의 유출이 가능한 계통들로서 GB안에 설치되어야 하는 계통들이다. 삼중수소 주입계통은 삼중수소 취급시설을 사용하여 목적하는 제품을 생산하게 되는 주 계통으로서 삼중수소의 관리를 위하여 정확히 삼중수소의 주입/분배량을 계량할 수 있어야 하고, 주입 후 계통내 잔여 삼중수소를 최대한 회수할 수 있도록 하여 방사성 물질의 환경방출을 최소화 할 뿐만 아니라 귀한 자원의 손실을 최소화하도록 설계되었다. MS, Ni catalyst bed, metal getter 등 재생이 필요한 TRS 내부의 장치들은 별도의 재생계통을 사용하여 재생한다. 다른 장치들의 재생은 장치를 가열하면서 적절한 purge gas를 흘려주는 비교적 간단한 방법으로 재생이 가능하나 삼중수소를 흡착한 metal getter의 삼중수소를 회수해야 하기 때문에 복잡한 공정을 거쳐야 한다.

• 한국기계가공학회지
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• 제19권1호
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• pp.121-133
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• 2020

Underwater cutting has a different mechanism than dry cutting, and there are more restrictions than benefits. Due to these constraints, research and development of underwater cutting has been very limited. At present, reactor dismantling is emerging as an important task worldwide, and reactor pressure containers, a key part of the reactor, are decommissioned based on underwater cutting. Reactor pressure containers are high-level radioactive waste, which is one of the main goals of today, such as to bridge the gap between environmental, safety, and cutting performance; hence, a process suitable for cutting should be applied. Therefore, many studies are being conducted on underwater cutting in connection with the dismantling of nuclear reactors in various areas in order to find appropriate processes. This paper first introduces the core technology of underwater cutting processes and discusses various processes. The emphasis is then placed on the adequacy of the reactor dismantling application. More specifically, we examine the suitability for the mechanical and thermal cutting processes, respectively, to find a solution suitable for dismantling a reactor. We discuss how each solution can sufficiently perform the specified functions at each stage of reactor dismantling and suggest that these processes can perform all of the work of underwater cutting.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2018년도 추계학술논문요약집
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• pp.379-379
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• 2018

MXenes are a new family of 2D transition metal carbide nanosheets analogous to graphene (Lv et al., 2017; Sun et al., 2018). Due to the easy availability, hydrophilic behavior, and tunable chemistry of MXenes, their use in applications for environmental pollution remediation such as heavy metal adsorption has recently been explored (Li et al., 2017). In this study, three-dimensional (3D) MXene ($Ti_3C_2T_x$) films with high adsorption capacity, good mechanical strength, and high selectivity for specific radionuclide from aquose solution were successfully fabricated by a polymeric precursor method using vacuum-assisted filtration. The highest removal efficiency on the films was 99.54%, 95.61%, and 82.79% for $Sr^{2+}$, $Co^{2+}$, and $Cs^+$, respectively, using a film dosage of 0.06 g/ L in the initial radionuclide solution (each radionuclide concentration = 1 mg/L and pH = 7.0). Especially, the adsorption process reached an equilibrium within 30 min. The expanded interlayer spacing of $Ti_3C_2T_x$ sheets in MXene films showed excellent radionuclide selectivity ($Cs^+$ and/or $Sr^{2+}/Co^{2+}$) (Simon, 2017). Besides, the MXene films was not only able to be easily retrieved from an aqueous solution by filtration after decontamination processes, but also to selectively separate desired target radionuclides in the solutions. Therefore, the newly developed MXene ($Ti_3C_2T_x$) films has a great potential for radionuclide removal from aqueous solution.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3293-3298
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• 2022

Removing radioactive contaminated metal materials is a vital task during the decommissioning of nuclear power plants to reduce the cost of the post-dismantling process. The laser decontamination technique has been recognized as a key tool for a successful dismantling process as it enables a remote operation in radioactive facilities. It also minimizes exposure of workers to hazardous materials and reduces secondary waste, increasing the environmental friendless of the post-dismantling processing. In this work, we present a thorough and efficient laser decontamination approach using a single-mode continuous-wave (CW) laser. We subjected stainless steels to a surface-removal process that repetitively exposes the laser to a confined region of ~75 ㎛ at a high scanning rate of 10 m/s. We evaluate the decontamination performance by measuring the removal depth with a 3D scanning microscope and further investigate optimal removal conditions given practical parameters such as the laser power and scan properties. We successfully removed the metal surface to a depth of more than 40 ㎛ with laser power of 300 W and ten scans, showing the potential to achieve an extremely high DF more than 1000 by simply increasing the number of scans and the laser power for the decontamination of primary circuits.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2004년도 Proceedings of the 4th Korea-China Joint Workshop on Nuclear Waste Management
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• pp.165-169
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• 2004

It was studied on the reductive extraction between the eutectic salt and Bi metal phases. The solutes were zirconium and the rare earth elements, where zirconium was used as the surrogate for the transuranic(TRU) elements. All the experiments were performed in a glove box filled with argon gas. Two types of experimental conditions were used -high and low initial solute concentrations in salt. Li-Bi alloy was used as a reducing agent to reduce the high chemical activity of Li. The reductive extraction characteristics were examined using ICP, XRD and EPMA analysis. Zirconium was successfully separated from the rare earth elements by the reductive extraction method. The LiF-NaF-KF system was favorable among the fluoride salt systems, whereas the LiCl-KCl system was favorable among the chloride salt systems. When the solute concentrations were high, intermetallic compounds were found near the salt-metal interface.

• 방사성폐기물학회지
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• 제18권4호
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• pp.481-496
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• 2020

After nuclear power plants are permanently shut down and decommissioned, the remaining irradiated metal components such as stainless steel, carbon steel, and Inconel can be used as neutron absorber. This study investigates the possibility of reusing these metal components as neutron absorber materials, that is burnable poison. The absorption cross section of the irradiated metals did not lose their chemical properties and performance even if they were irradiated over 40-50 years in the NPPs. To examine the absorption capability of the waste metals, the lattice calculations of WH 17×17 fuel assembly were analyzed. From the results, Inconel-718 significantly hold-down fuel assembly excess reactivity compared to stainless steel 304 and carbon steel because Inconel-718 contains a small amount of boron nuclide. From the results, a 20wt% impurity of boron in irradiated Inconel-718 enhances the excess reactivity suppression. The application of irradiated Inconel-718 as a burnable absorber for SMR core was investigated. The irradiated Inconel-718 impurity with 20wt% of boron content can maintain and suppress the whole core reactivity. We emphasize that the irradiated metal components can be used as burnable absorber materials to control the reactivity of commercial reactor power and small modular reactors.

• 동아시아식생활학회지
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• 제25권4호
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• pp.691-702
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• 2015

This study examined the levels of risk perception of food risk elements by adopting a psychometric paradigm and analyzed factors affecting concerns about food risk elements to obtain basic materials for food safety policy. The data were collected from 296 housewives in Daegu, Korea, by a self-administered questionnaire. Frequency distributions, Pearson's correlation coefficient analysis, factor analysis, Cronbach's ${alpha}$, and multiple regression analyses were conducted by SPSS 21.0. The mean level of concern for food safety was 3.75/5.00 points, and the mean percentage of correct answers about heavy metal contamination was highest among food risk elements. The respondents perceived radioactive contaminated foods, GM foods, and endocrine disruptors as a new, delayed, scientifically unknown, involuntary, serious, and uncontrollable risk in risk perception. According to the result of factor analysis for risk perception, two factors such as non-controllability and dread were categorized. In the risk perception map, radioactive contaminated foods and GM foods were considered as an uncontrollable and dreaded risk, heavy metal contamination, endocrine disruptors, and pesticide residues as a controllable and dreaded risk, and foodborne illness and food additives as a controllable and less dreaded risk. On the other hand, the levels of concerns about food risk elements were higher in order of radioactive contaminated foods, GM foods, and endocrine disruptors. The results of multiple regression analysis showed that age, concern for food safety, percentage of correct answers about food risk elements, non-controllability, and dread influenced the concerns about food risk elements. These results imply that food safety policies should consider differences in consumer's risk perception of food risk elements.

• Nuclear Engineering and Technology
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• 제28권1호
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• pp.79-92
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• 1996

방사성폐기물 처분후 처분장내에서는 금속의 부식과 셀룰로스 물질의 미생물 분해에 의한 기체가 발생하게 된다. 이 논문에서는 금속부식과 미생물 분해에 의해 발생되는 기체의 발생률을 예측하는 수학적 모델을 검토하고, 그로부터 저준위 방사성폐기물 처분장에 대한 기체 발생률을 예측하여 보았다. 금속성 물질의 부식은 3단계로 일어나며 그중 마지막 단계에서 H$_2$가 발생하게 된다. 셀룰로스 물질의 미생물 분해는 8가지 형태의 박테리아에 의해 일어나는 화학반응에 따라H$_2$, $CO_2$, CH$_4$등이 발생하게 되는데 이는 처분장내의 pH 및 몇몇 화학종의 농도에 따라 반응률이 결정되게 된다. 이 논문에서는 처분후 약10,000년 동안 발생되는 주요 기체의 발생률 및 누적발생 량을 예측하여 보았다. 평가 결과, 중저준위 방사성폐기물 처분장내에서 발생되는 기체는 H$_2$가 가장 많이 발생되는 것을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제46권4호
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• pp.547-556
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• 2014

Korea expects a shortage in storage capacity for spent fuels at reactor sites. Therefore, a need for more metal and/or concrete casks for storage systems is anticipated for either the reactor site or away from the reactor for interim storage. For the purpose of interim storage and transportation, a dual purpose metal cask that can load 21 spent fuel assemblies is being developed by Korea Radioactive Waste Management Corporation (KRMC) in Korea. At first the gamma and neutron flux for the design basis fuel were determined assuming in-core environment (the temperature, pressure, etc. of the moderator, boron, cladding, $UO_2$ pellets) in which the design basis fuel is loaded, as input data. The evaluation simulated burnup up to 45,000 MWD/MTU and decay during ten years of cooling using the SAS2H/OGIGEN-S module of the SCALE5.1 system. The results from the source term evaluation were used as input data for the final shielding evaluation utilizing the MCNP Code, which yielded the effective dose rate. The design of the cask is based on the safety requirements for normal storage conditions under 10 CFR Part 72. A radiation shielding analysis of the metal storage cask optimized for loading 21 design basis fuels was performed for two cases; one for a single cask and the other for a $2{\times}10$ cask array. For the single cask, dose rates at the external surface of the metal cask, 1m and 2m away from the cask surface, were evaluated. For the $2{\times}10$ cask array, dose rates at the center point of the array and at the center of the casks' height were evaluated. The results of the shielding analysis for the single cask show that dose rates were considerably higher at the lower side (from the bottom of the cask to the bottom of the neutron shielding) of the cask, at over 2mSv/hr at the external surface of the cask. However, this is not considered to be a significant issue since additional shielding will be installed at the storage facility. The shielding analysis results for the $2{\times}10$ cask array showed exponential decrease with distance off the sources. The controlled area boundary was calculated to be approximately 280m from the array, with a dose rate of 25mrem/yr. Actual dose rates within the controlled area boundary will be lower than 25mrem/yr, due to the decay of radioactivity of spent fuel in storage.