Stability of uranium inventory under dynamic redox condition in highly eroded granites, demonstrated by long-lived radioactive isotopes in uranyl carbonates

YeoJin Ju,Ji-Hun Ryu,Hun Suk Im,Min Hoon Baik 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10

Mobility of uranium (U) in subsurface is highly related to the redox processes. This implies that the safety of the geological disposal of nuclear waste is dependent on the redox condition around the U inventory. KAERI Underground Research Tunnel (KURT) is located in an active groundwater recharge area where, oxic meteoric water infiltrating down to the subsurface through highly weathered zones of granite, forming a complex redox system. Uranyl carbonate minerals, known for its high solubility in groundwater, were investigated as a fracture filling materials (FFMs) in granites, considered as a source of high U concentration in groundwater of KURT (up to 3 ppm). In this study, we examined the long-lived radioactive isotopes such as <SUP>230</SUP>Th, <SUP>234</SUP>U, <SUP>235</SUP>U and <SUP>238</SUP>U in uranyl carbonate minerals to understand the stability of the U precipitation in fractured granites, under dynamic redox conditions. In the redox front zone, the U minerals occurred from 53–203 m depth of highly eroded granites that were infiltrated by meteoric water to dissolve U and, precipitated by reducing condition during 144–164 Ka. According to the occurrence of uranyl carbonate minerals (144~164 Ka) in the redox front zone from 53~203 m depths indicated the stability of reducing condition below the redox front zone were reserved for the geological time scales.

Investigation on the Safety of Boeun U Ore Using Multiple Environmental Tracers

YeoJin Ju,Min Hoon Baik,Seung Yeop Lee,Kang-Kun Lee,Dugin Kaown,Dongbok Shin,Ji-Hun Ryu 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

Uranium inventory in Boeun aquifer is facing the artificial reservoir that intended for supplying water to nearby cities (40-70 m apart) where, toxic radionuclides might mobile and enter the reservoir. In order to understand U mobility in the system, groundwater and fracture filling materials (FFMs) were analyzed for microbial signatures, C, O, Fe, S and U-series isotopes. The δ18O-H2O and 14C signatures suggested groundwater was originated from upland recharges dominantly and not affected by mixing with the surface water. However, the 234U/238U activity ratios (ARs) and 230Th/234U ARs in FFMs ranged from 0.93 to 1.67 and from 0.22 to 1.97, respectively, indicating that U was mobile along the fractures. In shallow FFMs, the U accumulations (~157 mg/kg) were found with Fe enrichments (~226798 mg/kg) and anomalies of δ56Fe and δ57Fe, implied U mobility in shallow depths was associated with Fe-rich environment. Also, in the shallow depths, Fe-oxidizers, Gallionella was prevailing in groundwater while Acidovorax was abundant near U ore depth. The Fe-rich environment in shallow depths was formed by pyrite dissolution, demonstrated using δ34S-SO4 and δ18O-SO4 distribution. Conclusively, the Fe-rich aquifer was capable of immobilizing the dissolved U through biotic and abiotic processes, without significant discharge into the nearby reservoir.

Hydrogeochemical Factors Related to Uranium Concentration Levels in Granitic Aquifers in Korea

YeoJin Ju,Sanghoon Lee,Min-Hoon Baik,Ji-Hun Ryu 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

Uranium (U) is a hazardous material that can lead to both chemical and radiological toxicity, including kidney damage and health issues associated with radiation exposure. In South Korea. In Korea, where shallow weathered granitic aquifers are widespread, several previous studies have reported high levels of radioactivity in shallow groundwater. This ultimately led to the closure of 60 out of 4,140 groundwater production wells in South Korea. In this study, we examined aquifers currently dedicated to drinking water supply and investigated a dataset of 11,225 records encompassing 103 environmental parameters, based on the random forest classifier. This dataset comprises 80 physical parameters associated with the hydraulic system and 23 chemical parameters linked to water-rock interactions. Among the hydraulic parameters, the presence of a coarse loamy texture in the subsoil displayed a notable positive relationship with the concentration of uranium, implying that it plays a significant role in forming redox conditions for the leaching of uranium from host rocks. Fluorine (F), a major product of water-rock interaction in granitic aquifers, exhibited a positive correlation with the distribution of uranium concentrations. The positive relationship between F concentration and uranium levels suggests that the dissolved uranium originates from groundwater interacting with granites. In conclusion, our findings indicate that two key factors, namely the infiltration capacity of soil layers and the aqueous speciation in groundwater resulting from interactions with local solids, play important roles in determining uranium concentrations in granitic aquifers.

Factors Controlling Uranium Level in Granitic Aquifer

YeoJin Ju,Vikram Thapar,Ji-hun Ryu 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2

Uranium (U) is hazardous material can cause chemical and radiological toxicity, e.g., kidney toxicity and health effects associated with radiation. In Korea, where shallow weathered granitic aquifers are ubiquitous, several previous studies have reported high level of radioactivity in shallow groundwater. This eventually led to the closure of 60 out of 4,140 groundwater production wells in South Korea. Here, we examined aquifers currently dedicated for drinking water supply and investigated the 11,225 dataset of 103 environmental parameters. This dataset includes 80 physical parameters associated with the hydraulic system and 23 chemical parameters associated with waterrock interactions. Among hydraulic parameters, coarse loamy texture in subsoil displayed a notable relation with U concentration level, implied it is controlling the leaching of U from host rocks. Fluorine (F), is one of major products from water-rock interaction in granitic aquifer, exhibited high correlation with U concentration distribution. Positive relation of F concentration with uranium level suggested the dissolved U originated from groundwater interacted with granites. Conclusively, we found that infiltration capacity of soil layers and (2) aqueous speciation in groundwater formulated by interaction of groundwater with local solids, played important role for U concentration in granitic aquifer.

Application of multiple environmental tracers to understand the N nutrient cycle in river-side granitic aquifers

YeoJin Ju,Dong-Chan Koh,Hong-Il Kwon,Dong-Hun Kim 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10

The quality of river-side groundwater is dependent on the complicated hydrodynamic conditions, such as the convergent flow setting and stream-aquifer interactions. To understand the water mass balance and the nutrient dynamics in agricultural riparian zones, we used water and nitrate stable isotopes, inert gas tracers, 16S rRNA gene analysis and land use information with the aid of regional scale chemical data. Water samples were collected from the river-side granitic aquifers, which recently shows significant water level drawdown (-0.8 m/y). Heterogeneous river water infiltration into granitic aquifer was identified using the Bayesian mixing model (7.1% to 48.6%) considering uncertainties of SiO₂(aq) and d<SUP>18</SUP>O in regional groundwater. The stream-aquifer interaction was also demonstrated by the spatial distribution of He tracer. The major source of the N-nutrient was manure/sewage from dry farmland and residential area, with their land use (area, %) explained the majority of NO₃ distribution in groundwater (R²=0.935). δ<SUP>15</SUP>N, δ<SUP>18</SUP>O and NO₃<SUP>-</SUP> distributions revealed that the denitrification process was dominant in the river-side groundwater, generating N2(g). The correlation between N2(g) and paddy field (area, %), implied the importance of low permeable layers for natural attenuation. Anammox bacteria were present in multiple locations of the river-side groundwater, implying the efficient attenuation of nitrate in the site. Distribution of He and Ar indicated the aquifers were not closed for the N transformation process with loss of the generated N2(g) up to 21%. The N2(g) loss in the riverside aquifers is likely to be related to the pressure reduction induced by heavy groundwater pumping in this area.

U-series Disequilibrium and Stability of Uranium Minerals: Natural Analogue for High-level Radioactive Repository in Granite

YeoJin Ju,,Ji-Hun Ryu,Hun Suk Im,Min Hoon Baik 한국방사성폐기물학회 2021 한국방사성폐기물학회 학술논문요약집 Vol.2021 No.11

Uncertainty assessment of groundwater age-dating for monitoring wells located in a fractured rock aquifer system

YeoJin Ju,Arash Massoudieh,Dugin Kaown,Yoon-Yeol Yoon,Kang-Kun Lee 대한지질학회 2019 대한지질학회 학술대회 Vol.2019 No.10

Application of inert gas tracers to evaluate mass balance of the leaking CO₂ budget at EIT site, Eumseong, Korea

YeoJin Ju,Seong-Sun Lee,Dugin Kaown,Kang-Kun Lee 대한지질학회 2017 대한지질학회 학술대회 Vol.2017 No.10

THE EFFECT OF CATHETER-DIRECTED ETHANOL SCLEROTHERAPY ON OVARIAN RESERVE IN PATIENTS WITH RECURRENT ENDOMETRIOSIS: COMPARATIVE ANALYSIS WITH PRIMARY ENDOMETRIOSIS

( Yeojin Lee ),( Jae Kyung Lee ),( Sanghwa Kim ),( Yeon Ju Lee ),( Kichang Han ),( Man-deuk Kim ),( Heeyon Kim ),( Seok Kyo Seo ) 대한산부인과학회 2022 대한산부인과학회 학술대회 Vol.108 No.-

Objective: Although the surgical treatment remains gold standared in endometrioma, ovarian reserve is injured after the hemostasis and excision of the cyst. Catheter-directed ethanol sclerotherpy is known to affect the ovarian function less, increase efficacy, and reduce complications. This study aims to investigate the changes in ovarian reserve after catheter-directed ethanol sclerotherpy in recurrent endometrioma. Methods: Electronic medical records and pictures in patients with endometrioma who underwent catheter-directed ethanol sclerotherpy were obtainted in single institution from August 2014 to April 2022. Patient with aged >18 years old and AMH level >1.0 and <5.0 were enrolled in the study and age, BMI, cyst diameter, unilaterality, number of loculation and AMH level and CA-125 level before and after 1month, 6month, 1year and 2year of sclerotherapy were obtained. Results: 139 patients were enrolled in the study under IRB. There was significant differnece in AMH level before sclerotherapy in primary and recurrent endometrioma(2.68 vs. 2.04, p-value=0.011). However, there was no statistically significant difference in delta value of AMH after sclerotherapy in primary and recurrent endometrioma in 1month, 6month, 1year and 2year after sclerotherpy(91.78% vs. 96.14%, 74.75% vs. 81.58%, 83.98% vs. 65.79%, 97.08% vs. 52.52%, with p-value=0.593, 0.695, 0.217, 0.069, respectively). Also, this results were consistent regardless of unilaterality and loculation and CA-125 level showed no differerence between primary and recurrent endometrioma on every 1month, 6month, 1year and 2year after sclerotherpy. Conclusion: The effect of Catheter-directed ethanol sclerotherpy on ovarian reserve is not inferior in recurrent endometrioma compared to primary endometrima. Since sclerotherapy is known to less deteriorate the ovarian function than surgical removal of endometrioma, clinician could consider this as the first-line therapy in patient with recurrent endometrioma.

커널 밀도 추정치를 이용한 유한혼합모형의 초기화 방법과 모형기반 군집분석에의 응용

조현주(Hyun-ju Cho),정여진(Yeojin Chung),김영민(Youngmin Kim) 한국데이터정보과학회 2018 한국데이터정보과학회지 Vol.29 No.2

유한 혼합 모형은 확률 모형에 기반한 군집분석을 위해 다양하게 활용되고 있다. EM 알고리즘은 유한혼합모형과 같이 숨겨진 구조의 모형의 최대우도추정량을 계산하는데 널리 쓰인다. 하지만 EM 알고리즘은 초기 값에 따라 그 성능이 좌우되어 우도함수의 최대값이 아닌 고정점으로 수렴하거나 수렴 속도가 느려질 가능성이 있다. 본 연구에서는 커널 밀도 추정치의 정점의 위치를 사용하여 유한 혼합모형의 모수 추정을 위한 EM 알고리즘을 초기화 하는 방법을 제안한다. 기존의 무작위 초기화에 기반한 방법들과 비교하여 모의실험을 통해 본 연구에서 제안하는 초기화 방법이 우도함수의 최대값을 찾는데 더 우월함을 확인한다. 또한 추정된 유한확률모형을 기반으로 한 군집분석을 기업부도 데이터에 적용하여 보다 나은 군집 결과를 가져옴을 보여준다. The finite mixture model is widely used for model-based cluster analysis. The EM algorithm finds the maximum likelihood estimates of the finite mixture model. Since the performance of the EM algorithm is largely influenced by its initial value, the choice of the initial value has been regarded as an important factor for EM. This study proposes a new initialization method for the EM algorithm using the kernel density estimator. The location of modes of the kernel density estimate is calculated by the MEM algorithm and set as an initial value for component means for Gaussian mixture model. Simulation study and application on corporate default data show that the proposed method gives parameter estimates higher than the exising methods. In addition, we apply the model-based clustering based on the estimated mixture model and compare the performance of clustering.