The need for the development of sustainable, efficient, and green radioactive waste disposal methods is emerging with the saturation of spent nuclear waste storage facilities in the Republic of Korea. Conventional radioactive waste management methods like using cement or glass have drawbacks such as high porosity, less chemical stability, high energy consumption, carbon dioxide production, and the generation of secondary wastes, etc. To address this gigantic issue of the planet, we have designed a study to explore the potential of alternative materials having easy processability, low carbon emissions and more chemical stability such as ceramic (hydroxyapatite, HAP) and alkali-activated materials (geopolymers, GP) to capture the simulated radioactive cobalt ions from the contaminated water and directly solidify them at low temperatures. Physical and mechanical properties of HAP alone and 15wt% GP incorporated HAP (HAP-GP- 15) composite were studied and compared. The surface of both materials was fully sorbed with an excess amount of Co(II) ions in the aqueous system. Co(II) sorbed powders were separated from aqueous media using a centrifuge machine operating at 5,000 RPM for 10 minutes and dried at 100°C for 8 hours. The dried powders were then placed in stainless steel molds, and shaped into cylindrical pellets using a uniaxial press at a pressure of 1 metric ton for 1 minute. The pellets were sintered at 1,100°C for 2 hours at a heating rate of 10°C/min. Following this, the water absorption, density, porosity, and compressive strength of the polished pellets were measured using standard methods. Results showed that HAP has a greater potential for decontamination and solidification of Co(II) due to its higher density (2.65 g/cm3 > 1.90 g/cm3), less open porosity (16.2±2.9% < 42.4 ±0.9%) and high compressive strength (82.1±10.2 MPa > 6.9±0.8 MPa) values at 1,100°C compared to that of HAP-GP-15. Nevertheless, further study with different constituent ratio of HAP and GP at various temperatures is required to fully optimize the HAP-GP matrix for waste solidifications.

The ultimate objective of deep geological repositories is to achieve complete segregation of hazardous radioactive waste from the biosphere. Thus, given the possibility of leaks in the distant future, it is crucial to evaluate the capability of clay minerals to fulfill their promising role as both engineered and natural barriers. Selenium-79, a long-lived fission product originating from uranium- 235, holds significant importance due to its high mobility resulting from the predominant anionic form of selenium. To investigate the retardation behaviors of Se(IV) in clay media by sorption, a series of batch sorption experiments were conducted. The batch samples consisted of Se(IV) ions dissolved in 0.1 M NaCl solutions, along with clay minerals including kaolinite, montmorillonite, and illite-smectite mixed layers. The pH of the samples was also varied, reflecting the shift in the predominant selenium species from selenious acid to selenite ion as the environment can shift from slightly acidic to alkaline conditions. This alteration in pH concurrently promotes the competition of hydroxide ions for Se(IV) sorption on the mineral surface as the pH increases and impedes the selective attachment of selenium. The acquired experimental data were fitted through Langmuir and Freundlich sorption isotherms. From the Freundlich fit data, the distribution coefficient values of Se(IV) for kaolinite, montmorillonite, and illite-smectite mixed layer were derived, which exhibited a clear decrease from 91, 110, 62 L/kg at a pH of 3.2 to 16, 6.3, 12 L/kg at a pH of 7.5, respectively. These values derived over the pH range provide quantitative guidance essential for the safety assessment of clay mineral barriers, contributing to a more informed site selection process for deep geological repositories.

This program aims to build a specialized and converged educational platform for the training of students in the back-end nuclear fuel cycle and cultivate integrated human resources encompassing majors, generations, and fields. To achieve this, we have established an infrastructure for integrated education and training in the radiochemistry and back-end nuclear fuel cycle and operated specialized educational courses linked with special lectures, experimental practices, and field trips. Firstly, to construct an integrated educational and training infrastructure for the back-end nuclear fuel cycle, we formed a committee of experts from both inside and outside the institution and built an advanced radiochemistry laboratory equipped with physical and chemical analysis instruments. Through a comprehensive educational program involving theory, experiments, and discussions, we have established an integrated curriculum across adjacent majors and interdisciplinary studies. We also operate short-term education and experimental training programs (e.g., summer and winter schools for the back-end nuclear fuel cycle). Secondly, the program has connected leading researchers domestically and internationally, as well as the next generation of scholars. The program offers long-term educational opportunities and internships targeting both undergraduate and graduate students. To support this, we continuously offer expert colloquiums and individual research internships. Through regular committee meetings and workshops, we focus on nurturing the integrated talents necessary for the back-end nuclear fuel cycle. Through this program, students from various fields are being trained as competent integrated human resources capable of addressing various issues in the back-end nuclear fuel cycle. It is expected that this will enable us to supply specialized technical personnel in the back-end nuclear field in line with mid-to-long-term demands.

The domestic Pressurized Heavy Water Reactor (PWHR) nuclear power plant, Wolsong Unit 1, was permanently shut down on December 24, 2019. However, research on decommissioning has mainly focused on Pressurized Water Reactors (PWRs), with a notable absence of both domestic and international experience in the decommissioning of PHWRs. If proper business management such as radiation safety and waste is not performed, it can lead to increased business risks and costs in decommissioning. Therefore, the assessment of waste volume and cost, which provide fundamental data for the nuclear decommissioning process, is a crucial technical requirement before initiating the actual decommissioning of Wolsong Unit 1. Decommissioning radiation-contaminated structures and facilities presents significant challenges due to high radiation levels, making it difficult for workers to access these areas. Therefore, technology development should precede decommissioning process assessments and safety evaluations, facilitating the derivation of optimal decommissioning procedures and ensuring worker safety while enhancing the efficiency of decommissioning operations. In this study, we have developed a program to estimate decommissioning waste amounts for PHWRs, building upon prior research on PWR decommissioning projects while accounting for the specific design characteristics of PHWRs. To evaluate the amount of radioactive waste generated during decommissioning, we considered the characteristics of radioactive waste, disposal methods, packaging container specifications, and the criteria for the transfer of radioactive waste to disposal operators. Based on the derived algorithm, we conducted a detailed design and implemented the program. The proposed program is based on 3D modeling of the decommissioning components and the calculation of the Work Difficulty Factor (WDF), which is used to determine the time weighting factors for each task. Program users can select the cutting and packaging conditions for decommissioning components, estimate waste amount based on the chosen decommissioning method, and calculate costs using time weighting factors. It can be applied not only to PHWRs, but also to PWRs and non-nuclear fields, providing a flexible tool for optimizing decommissioning process.

금번 연구를 통해 외래산림해충 확산 분석 플랫폼 K-SDM (K-SDM)의 해충 분포 기능이 개발되었다. 해충 분포를 보여주는 기능은 2가지로 구현되며, 조사 자료를 바탕으로 현재 국내의 해충 분포를 나타내는 “외래산림 해충분포”기능과 데이터를 분석하여 예측되는 미래의 해충 분포를 제공하는 “외래산림해충예측”기능이 있다. “외래산림해충분포”는 조사자에 의해 현장에서 구축된 DB 현황을 지도상에 수치로 나타내며, 입력 기간, 해충 종 별로 구분이 가능하여 원하는 해충종의 분포를 선택하여 볼 수 있다. 지도 좌측에는 각 도별로 조사된 해충 개체수의 통계를 도표로 제공하여 수치상으로도 해충 분포를 파악할 수 있다. “외래산림해충예측”은 DB를 분석 하고 미래 기후 시나리오를 적용하여 도출한 미래의 해충 예측 분포도를 사용자에게 제공되며, 미리보기 이미지 와 함께 원본자료가 첨부되어 좀 더 자세한 정보를 열람할 수 있다. 본 플랫폼의 해충 분포 기능은 최근 기후변화 등으로 외래산림해충의 발생이 증가하는 추세에 맞춰 이들의 현재 분포와 미래의 분포양상을 조기 파악하여 이를 통한 추후 조기 방제 및 대응책 마련 등에 크게 기여할 것으로 기대된다.

최근 국내에서는 꿀벌 대량소실 현상이 2022년부터 전국적으로 발생하고 있다. 우리나라 뿐 만 아니라, 전세계 적으로 양봉산업에 큰 위협이 되고 있는 봉군붕괴현상은 2016년 미국에서 세계 최초로 보고되었다. 국내에서는 2022년 민관 합동조사 결과, 이상기온, 응애, 말벌 등이 주요 원인으로 지목되었다. 대량소실 현상을 보인 양봉농 가와 정상 농가의 병원체 검출 비교 결과, 유의성있게 검출이 증가되는 병원체는 발견되지 않았다. 그러나, Tyrophagus mite, Trypanosome, Lake Sinai virus, Apis mellifera filamentous virus 등의 신종 응애, 원충 및 바이러 스 감염이 추가로 확인되었다. 국내에서 새롭게 감염이 확인된 기생충과 병원체가 대량소실, 나아가 봉군붕괴현 상에 직간접적으로 영향을 주었을 것으로 사료되며, 지속적인 조사와 연구개발을 통해 기후등 환경변화에 따른 신종 질병 검색과 대책을 마련해야 할 것이다.

Studies on automatic scoring systems in writing assessments have also evaluated the relationship between human and machine scores for the reliability of automated essay scoring systems. This study investigated the magnitudes of indices for inter-rater agreement and discrepancy, especially regarding human and machine scoring, in writing assessment. The mean of the overall population correlation between automated and human scoring in essay writing was .78. The overall common d effect size was 0.001. Results from this meta-analysis indicated a strong relationship with no discrepancies between automated and human scoring. Both the I2 and Q values suggested that the population correlation values studied seemed to be heterogeneous, in contrast to homogenous d effect sizes. Therefore, it is necessary to investigate the sources of the between-studies variations for r correlations. Practical implications for ways of reporting results of automatic-scoring systems research and limitations of the study are also discussed.

To ensure radiological safety margin in the transport and storage of spent nuclear fuel, it is crucial to perform source term and shielding analyses in advance from the perspective of conservation. When performing source term analysis on UO2 fuel, which is mostly used in commercial nuclear power plants, uranium and oxygen are basically considered to be the initial materials of the new fuel. However, the presence of impurities in the fuel and structural materials of the fuel assembly may influence the source term and shielding analyses. The impurities could be radioactive materials or the stable materials that are activated by irradiation during reactor power operation. As measuring the impurity concentration levels in the fuel and structural materials can be challenging, publicly available information on impurity concentration levels is used as a reference in this evaluation. To assess the effect of impurities, the results of the source term and shielding analyses were compared depending on whether the assumed impurity concentration is considered. For the shielding analysis, generic cask design data developed by KEPCO-E&C was utilized.

주방세제의 진딧물 살충효과와 분국화 생육에 미치는 영향 을 알아보기 위해 실험을 수행하였다. 복숭아혹진딧물과 목화 진딧물을 대상으로 주방세제 100, 200, 400배액 단용처리와 주방세제 400배액 100mL에 소주 10mL 또는 20mL를 혼용 하여 분무 처리하였다. 그 결과 주방세제 400배 이하의 모든 농도에서 복숭아혹진딧물은 85%, 목화진딧물은 90%의 살충 률을 보였다. 주방세제와 소주 혼용처리에 의한 살충효과 상 승은 보이지 않았다. 하우스안에서 진딧물이 많이 발생한 분 국화 잎에 400배액 이하의 농도로 3일 간격으로 2회 처리함 으로써 90% 이상의 진딧물이 감소되는 효과를 얻을 수 있었 다. 또한 분국화를 재배하면서 3~4일 간격으로 5주간 지속적 으로 주방세제를 처리했을 때, 대조구에서는 90% 잎에서 진 딧물이 발생한데 비해, 모든 주방세제 단독 처리구에서는 발 생율이 15% 이하로 낮게 유지되었다. 또한 국화의 생체중, 초 장, 엽수는 주방세제 농도가 높아질수록 조금씩 낮아지는 경 향이었으나, 초폭이나 분지수에서는 차이가 없었다. 그러나 주방세제 200배 이하의 농도에서는 국화의 잎이 갈변되거나 꽃잎 끝이 백화되는 약해가 관찰되었다.

Th(IV) is a stable actinide that can act as a chemical analogue of U(IV) and Pu(IV), which are important radionuclides in safety assessments of deep geological repositories (DGR). Therefore, to understand the geochemical behaviour of U(IV) and Pu(IV), batch sorption of Th(IV) onto crystalline rocks were performed in oxidising conditions. The distribution coefficients (Kd) of Th(IV) were of particular interest. Gyeongju fresh groundwater (GF) and Gyeongju brackish groundwater (GB) were obtained at the Gyeongju Low and Intermediate Level Radioactive Waste (LILW) Disposal Facility. Crystalline granite (gr) and biotite gneiss (bg) were collected in Gyeongju and Gwacheon respectively and were grounded to a particle size smaller than 150 μm. Sorption samples were continuously shaken for 7 days under 200 rpm at 25°C. The liquid-to-solid ratio (V/m) was 200 L·kg-1. Th(IV) concentrations of the sorption samples were determined by UV-Vis-NIR absorption colorimetry from the formation of Th(IV)-arsenazo III complexes. Although the method allowed the initial Th(IV) concentrations to be determined, the final Th(IV) concentrations fell below the limit of detection (LOD), 6.27×10-9 mol·L-1. Taking the LOD as the final concentrations, conservative Kd were calculated to be 4,410 L·kg-1 for GF-gr and GF-bg, and 7,830 L·kg-1 for GB-gr and GB-bg. The result indicates a strong sorption affinity of Th(IV) onto granite and biotite gneiss within Gyeongju groundwater, suggesting a similar behaviour for U(IV) and Pu(IV). Furthermore, comparison of the conservative Kd obtained from the experiment were compared with existing Kd values of Th(IV). Such analysis and comparison of Th(IV) Kd in various types of groundwater could help locate the optimal site for a DGR in South Korea.

The safe disposal of high-level radioactive waste is a critical concern in many countries, especially in the context of the increasing use of nuclear power to overcome climate change. To provide a comprehensive understanding of the behavior of the radionuclides in the crystalline natural barrier, sorption of the artificially synthesized high-level radioactive waste (HLW) leachate was conducted. Granite (-1,000 m from ground level) and biotite gneiss (-100 m from ground level) rock cores were collected from Gyeongju and Gwacheon, respectively. The rock cores were milled with a jaw crusher and steel disk mill and then sieved. The crushed rocks with a diameter of 0.6 – 1.0 mm were selected, washed three times with deionized water, and then dried. To synthesize the simulated HLW leachate, representative elements (U(VI), Se(IV), Mo(VI), and Ni(II)) were added to natural groundwater collected from Gyeongju. The kinetic sorption experiment was performed in a polypropylene bottle with a solid-to-liquid ratio of 100 g/L in the orbital shaking incubator (200 rotations per min, 25.0°C). After the sorption, the supernatants were filtered by a 0.2-μm polytetrafluoroethylene syringe filter and subsequently analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). Through the kinetic change of aqueous concentration, the contact time has been determined to be 7 days. Ni(II) showed the highest distribution coefficients (Kd = 0.81 L/m2 for granite and 8 – 16 L/m2 for biotite gneiss), followed by U(VI) (Kd = 0.03 – 0.04 L/m2 for granite and 0.04 – 0.05 L/m2 for biotite gneiss). Highly mobile nuclides such as Se(IV) (Kd = 0.02 L/m2 for granite and 0.03 L/m2 for biotite gneiss) and Mo(VI) (Kd = 0.01 – 0.02 L/m2 for granite and 0.01 L/m2 for biotite gneiss) showed the lowest distribution coefficient. Our study provides insights into the migration-retention behaviors of the HLW leachate with granite and biotite gneiss in geological systems and verifies the sorption parameters, e.g., distribution coefficients, experimentally produced by other groups to ensure the safe disposal of HLW.

With the aging of nuclear power plants (NPPs) in 37 countries around the world, 207 out of 437 NPPs have been permanently shutdown as of August 2022 according to the IAEA. In Korea, the decommissioning of NPPs is emerging as a challenge due to the permanent shutdown of Kori Unit 1 and Wolsong Unit 1. However, there are no cases of decommissioning activities for Heavy Water Reactor (HWR) such as Wolsong Unit 1 although most of the decommissioning technologies for Light Water Reactor (LWR) such as Kori Unit 1 have been developed and there are cases of overseas decommissioning activities. This study shows the development of a decommissioning waste amount/cost/process linkage program for decommissioning Pressurized Heavy Water Reactor (PHWR), i.e. CANDU NPPs. The proposed program is an integrated management program that can derive optimal processes from an economic and safety perspective when decommissioning PHWR based on 3D modeling of the structures and digital mock-up system that links the characteristic data of PHWR, equipment and construction methods. This program can be used to simulate the nuclear decommissioning activities in a virtual space in three dimensions, and to evaluate the decommissioning operation characteristics, waste amount, cost, and exposure dose to worker. In order to verify the results, our methods for calculating optimal decommissioning quantity, which are closely related to radiological impact on workers and cost reduction during decommissioning, were compared with the methods of the foreign specialized institution (NAGRA). The optimal decommissioning quantity can be calculated by classifying the radioactivity level through MCNP modeling of waste, investigating domestic disposal containers, and selecting cutting sizes, so that costs can be reduced according to the final disposal waste reduction. As the target waste to be decommissioning for comparative study with NAGRA, the calandria in PHWR was modeled using MCNP. For packaging waste container, NAGRA selected three (P2A, P3, MOSAIK), and we selected two (P2A, P3) and compared them. It is intended to develop an integrated management program to derive the optimal process for decommissioning PHWR by linking the optimal decommissioning quantity calculation methodology with the detailed studies on exposure dose to worker, decommissioning order, difficulty of work, and cost evaluation. As a result, it is considered that it can be used not only for PHWR but also for other types of NPPs decommissioning in the future to derive optimal results such as worker safety and cost reduction.

The sorption behavior of Se(IV) on montmorillonite clay, a promising buffer and backfill material, was investigated in the presence of aquatic fulvic acid. Selenium-79 is one of the major radioactive nuclides which are long-lived and highly mobile in subsurface environments. Moreover, it is highly toxic even in small amounts, so the selenium quantity in soil and groundwater should be assessed. Although natural organic matters such as humic and fulvic acids are present in the environment, the influence of natural organic matters on Se(IV) migration has not yet been extensively studied. The batch sorption experiments were performed under oxic conditions. Suwannee River III standard aquatic fulvic acid (International Humic Substances Society) was used to build an organicrich environment. The N2 – BET surface area of the montmorillonite (Clay Minerals Society) was 97 ± 5 m2·g−1. The montmorillonite suspensions with/without fulvic acid were equilibrated with air before adding Na2SeO3. The solid-to-liquid ratio was 5 g·L−1, the ionic medium was 0.1 M NaCl, fulvic acid concentration was 50 mg·L−1, and the final pH was 3. The horizontal vial roller was used to prevent the clay from sinking. After 7 days of sorption at room temperature, the suspensions were centrifuged at 10,600 g for 15 min and filtered through 0.2 μm PTFE filters. The colloidal fulvic selenide and free Se(IV) concentrations were entirely measured by inductively coupled plasma–mass spectrometry (ICP-MS). The sorption results were fitted with Langmuir and Freundlich models. At concentrations lower than 20 μM, the distribution coefficients (Kd) were 50 ± 9 L·kg−1 without fulvic acid, and 36 ± 5 L·kg−1 with 50 mg·L−1 fulvic acid. For the concentrations between 20 and 100 μM, the Kd values without and with fulvic acid were 16 ± 7 L·kg−1 and 10 ± 1 L·kg−1, respectively. As a result, it turned out that fulvic acid interferes with the sorption of Se(IV) on montmorillonite in competition with the selenite anion. This indicates that such organic matter may facilitate the migration of selenium in deep geological groundwaters.