The large copper butterfly Lycaena dispar (Haworth, 1803; Lepidoptera: Lycaenidae) has been categorized as a near-threatened species (NT) in South Korea from 2012 mainly due to limited distribution. In this study, we visited 36 sites spread across all South Korean provinces to verify the distributional range of the species and sequenced mitochondrial COI for 53 individuals from nine sites. We observed L. dispar at 15 sites in six provinces, including the two previously known provinces, indicating a southward range expansion. The in-field monitoring and genetic data collectively suggested that L. dispar does not have a limited distribution nor is it isolated, indicating that it should be reclassified as less vulnerable. Our study demonstrates that the combination of field and genetic data can provide a more reliable assessment of the stability of a species.

To ensure the safety of disposal facilities for radioactive waste, it is essential to quantitatively evaluate the performance of the waste disposal facilities by using safety assessment models. This paper addresses the development of the safety assessment model for the underground silo of Wolseong Low-and Immediate-Level Waste (LILW) disposal facility in Korea. As the simulated result, the nuclides diffused from the waste were kept inside the silo without the leakage of those while the integrity of the concrete is maintained. After the degradation of concrete, radionuclides migrate in the same direction as the groundwater flow by mainly advection mechanism. The release of radionuclides has a positive linear relationship with a half-life in the range of medium half-life. Additionally, the solidified waste form delays and reduces the migration of radionuclides through the interaction between the nuclides and the solidified medium. Herein, the phenomenon of this delay was implemented with the mass transfer coefficient of the flux node at numerical modeling. The solidification effects, which are delaying and reducing the leakage of nuclides, were maintained the integrity of the nuclides. This effect was decreased by increasing the half-life and the mass transfer coefficient of radionuclides.

Over the years, in the field of safety assessment of geological disposal system, system-level models have been widely employed, primarily due to considerations of computational efficiency and convenience. However, system-level models have their limitations when it comes to phenomenologically simulating the complex processes occurring within disposal systems, particularly when attempting to account for the coupled processes in the near-field. Therefore, this study investigates a machine learning-based methodology for incorporating phenomenological insights into system-level safety assessment models without compromising computational efficiency. The machine learning application targeted the calculation of waste degradation rates and the estimation of radionuclide flux around the deposition holes. To develop machine learning models for both degradation rates and radionuclide flux, key influencing factors or input parameters need to be identified. Subsequently, process models capable of computing degradation rates and radionuclide flux will be established. To facilitate the generation of machine learning data encompassing a wide range of input parameter combinations, Latin-hypercube sampling will be applied. Based on the predefined scenarios and input parameters, the machine learning models will generate time-series data for the degradation rates and radionuclide flux. The time-series data can subsequently be applied to the system-level safety assessment model as a time table format. The methodology presented in this study is expected to contribute to the enhancement of system-level safety assessment models when applied.

Coupled thermo-hydraulic-mechanical (THM) processes are essential for the long-term performance of deep geological disposal of high-level radioactive waste. In this study, a numerical sensitivity analysis was performed to analyze the effect of rock properties on THM responses after the execution of the heater test at the Kamaishi mine in Japan. The TOUGHFLAC simulator was applied for the numerical simulation assuming a continuum model for coupled THM analysis. The rock properties included in the sensitivity study were the Young’s modulus, permeability, thermal conductivity, and thermal expansion coefficients of crystalline rock, rock salt, and clay. The responses, i.e., temperature, water content, displacement, and stress, were measured at monitoring points in the buffer and near-field rock mass during the simulations. The thermal conductivity had an overarching impact on THM responses. The influence of Young’s modulus was evident in the mechanical behavior, whereas that of permeability was noticed through the change in the temperature and water content. The difference in the THM responses of the three rock type models implies the importance of the appropriate characterization of rock mass properties with regard to the performance assessment of the deep geological disposal of high-level radioactive waste.

경험식에 기반한 폭발 해석방법은 폭압-시간 이력곡선을 하중으로 적용하여 해석하는 방법이다. 이 방법은 모델링이 간단하고 해 석시간이 짧아 효율적이지만, 일부 연구에 따르면 근거리 폭발 해석에는 적합하지 않음이 보고되고 있다. 본 연구에서는 예로써 환산 거리 0.4~1.0의 근거리 폭발조건에 있는 RC 보에 대해 해석방법에 따른 결과의 차이 및 원인을 분석하였고, 이를 통해 경험식 방법을 이용한 해석의 적용 범위를 구체적으로 검토 및 확인할 수 있었다. 사용된 유한요소해석 프로그램은 LS-DYNA이다. 해석결과에 따르 면, 원거리 폭발 실험 데이터를 근거로 하는 경험식 해석방법은 충격량을 과소평가하고 있었다. 이로 인해 RC 보의 처짐은 측정된 처 짐 또는 ALE(Arbitrary Lagrangian Eulerian) 해석결과에 비해 작게 계산되었다. 구조체의 응답이 크게 나타나는 근거리 폭발에 대해 서는 ALE 해석방법을 사용하는 것이 더 적합할 것으로 사료된다.

The “shadow zone” is defined as a region below a flow obstacle, such as a vault, in unsaturated soils. Due to the capillary discontinuity of the cavity, water saturation on the top and side of the cavity is higher than the ambient saturation. On the bottom of the cavity, however, there is a region where water saturation is lower than ambient saturation. Undoubtedly, a shadow zone may also exist below a LILW disposal vault built in subsurface soils above the water table before the vault is fully degraded. During the degradation, flow in the shadow zone is controlled by the rate of water infiltrating the degrading vault. In this study, as one of the efforts to be made for enhancing safety margin by a realistic safety assessment of the engineered vault type LILW disposal facility, the shadow zone effect is investigated by a numerical parametric study using AMBER code. The conceptual model and data were excerpted from IAEA, ISAM Vault Test Case for the liquid release design scenario. It is assumed that the nearfield barriers degrade with time. In order to compare a visible shadow zone effect, the vault degradation period is assumed to be both 500 and 1,000 years, and the shadow zone depth to be varied according to unsaturated zone lithology. It can be seen that with a shorter shadow zone (2.7 m), radionuclides arrive at the water table earlier than with a full shadow zone (55 m) due to increased advection rate in the unsaturated zone. This effect tends to be more visible in the case of a longer degradation period. For radionuclides with short residence time relative to their half-lives in the unsaturated zone, such as Tc-99 and I-129, the radionuclides are shown to come out because they will arrive sooner, thereby allowing less peak release rate, when the shadow zone effect is considered. Once the vault is completely degraded and the infiltration rate of water flowing through the vault is equal to the ambient rate, the shadow zone effect disappears. In this example calculations using IAEA ISAM Vault Test Case input parameters, it might not be shown a significant shadow zone effect. Nevertheless, when the extent of the shadow zone is determined through more sophisticated hydraulic studies in the unsaturated soils surrounding the vault, the shadow zone effect would be checked up on the realistic near-field radionuclide transport modeling in order to contribute to gaining safety margins for post-closure safety assessment of the Wolsong 2nd phase LILW disposal facility.

Organic complexing agents which are contained in the radioactive waste can form the complex with radionuclides and enhance the solubility of radionuclides. The mobility of radionuclides to the far-field from the repository will be increased by radionuclide-ligand complex formation. Therefore, the assessment of the radionuclides’ solubility should be performed in the presence of organic complexing agents. In this study, five radionuclides (cobalt, strontium, iodine, cesium, and uranium) and three organic complexing agents (ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and isosaccharinic acid (ISA)) were selected as model radionuclides and organic complexing agents, respectively. For simulating the in-situ condition, the groundwater near the repository was collected and applied in solubility experiments and the solubility was measured in various environmental conditions such as different pHs (7, 9, 11, and 13), temperatures (10°C, 20°C, and 40°C), and a range of organic complexing agent concentrations (10-5, 10-4, 10-3, and 10-2 M). In cases of cesium and iodine, they were very soluble in all conditions, and the effect on their solubilities was not observed. However, at high pHs, cobalt and strontium showed lower solubilities than at neutral pH and the solubility enhancement by the organic complexing agents was significant. Moreover, the effects of each organic ligand showed obvious differences and were in the order of EDTA > NTA > ISA. The solubility of uranium was increased with increasing the organic ligand concentration at lower pHs, but the organic complexing agents did not cause a remarkable difference at high pHs. According to these results, the presence of complexing agents could enhance the radionuclides’ solubility and increase the potential to release the radionuclides to the far-field from the repository. Solubility experiments of other major radionuclides in the repository are in progress.

국내 중·저준위 방사성폐기물 처분시설로 고려되고 있는 표층처분시설의 불포화대에서 핵종 이동을 야기하는 지하수 유동을 평가하기 위하여 유한요소법 기반의 COMSOL Multiphysics을 이용한 수치모델을 개발하였다. 그리고, 처분장 가장자리 를 대상으로 처분고, 뒤채움재, 처분덮개로 구성되는 표층처분시설과 그 아래에 위치한 불포화대를 포함한 수직 2차원의 모델 영역을 구성하여, 시나리오 별 모델링을 수행하였다. 지속적 강수 유입 조건과 간헐적 강수 유입 조건 비교에서 포화도의 파동 현상을 제외하고는 뚜렷한 차이점을 보이지 않는 것으로 판단되었다. 불포화대의 공극률이나 잔류함수비와 같은 입력 자료는 전반적으로 불포화대 지하수 유동에 큰 영향도가 없는 것으로 판단되었다. 하지만, 불포화대의 수리전도도는 지하수 유동에 큰 영향을 미치는 것으로 판단되었다. 즉, 처분고로의 지하수 유입 속도를 판단하기 위해서는 불포화대의 수리전도도 특성이 신중하게 고려되어야 할 것으로 판단되었다.

Metam-sodium has been generally applied to control Pinus koraiensis, P. densiflora and P. thunbergii infected by pine wilt disease in the forest field of Korea. We determined the atmospheric concentration of nematocidal and insecticidal gaseous methyl isothiocyanate (MITC) and more volatile and toxic gaseous methyl isocyanate (MIC) in the metam-sodium fumigated fields depending on the distance from metam-sodium treated site, time and season by OSHA No. 52 method. Determined atmospheric MIC was below acute exposure limit (50 ㎍/㎥) and chronic exposure limit (1.0 ㎍/㎥) of EPA regulation in all detection point. In summer, the maximum of MITC and MIC was observed to 105.2 ㎍/㎥ in the 1st day and 0.41 ㎍/㎥ in the 4th day after metam-sodium treatment, respectively. On the other hand, in winter, the maximum of MITC and MIC was observed to 4.6 ㎍/㎥ in the 4th day and 0.52 ㎍/㎥ in the 5th day after metam-sodium treatment, respectively. Atmospheric concentrations of MITC and MIC were higher the closer to the metam-sodium treated site, but decreased below LOQ with distance (~ 50 m). This result showed that the reaction rate of metam-sodium to MITC is more affected by temperature and the translation rate of MITC to MIC is generally very low, regardless of season.