Sensitivity Analysis for Reactive Transport Model in Concrete Disposal System

Min Seok Kim,Chang Min Shin,Jong-il Yun 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

LILW disposal repository in Gyeongju, South Korea is considered with a concrete mixture that uses Ordinary Portland Cement (OPC) partially substituted with supplementary cementitious materials (SCMs). The degradation of cementitious materials that result from chemical and physical attacks is a major concern in the safety of radioactive waste disposal. We present a reactive transport model utilized as one of the geochemical simulation approaches for the timescales of concern that range from hundreds to thousands of years. The purpose of this study is to investigate the sensitivity of parameters in concrete disposal systems and to evaluate the influence of various assumptions on the chemical degradation of the systems using a reactive transport model. A reactive transport model in the concrete disposal vault was developed to evaluate the behavior of engineered barriers composed of cementitious materials. The sensitivity analysis was performed using reactive transport models through the coupling between COMSOL and PHREEQC. The databases selected for the analysis are the Thermochimie database presented by ANDRA. Among many variables considered, two variables that can highly affect chemical degradation were selected for detailed sensitivity analysis for dealing with uncertainties. This is important because the chemical degradation mechanism is generally sensitive to precipitation and diffusion coefficient. The first factor is precipitation, which might be the most important factor in chemical degradation because it acts as a calcium leaching of cementitious materials in a disposal system in a highly alkaline environment, increasing the porosity of the system. To predict the change in annual precipitation, the measurement of the precipitation observatory station in the nearest area of Gyeongju for the past 80 years was collected. The second factor is the diffusion coefficient, which plays an essential role in the durability of the concrete disposal system, promoting the decalcification of cementitious minerals, accelerating system degradation, and increasing the porosity of its system, thereby facilitating the migration of radionuclides. The diffusion coefficient values used in studies similar to this work were calculated and evaluated using the box-and-whisker method. The results of the sensitivity analyses for the reactive transport model in the concrete disposal system will be presented. The sensitivity cases show that the results obtained are much more sensitive to changes in transport parameters.

Nitrate reduction and its effects on trichloroethylene degradation by granular iron

Lu, Qiong,Jeen, Sung-Wook,Gui, Lai,Gillham, Robert W. Pergamon Press 2017 Water research Vol.112 No.-

<P><B>Abstract</B></P> <P>Laboratory column experiments and reactive transport modeling were performed to evaluate the reduction of nitrate and its effects on trichloroethylene (TCE) degradation by granular iron. In addition to determining degradation kinetics of TCE in the presence of nitrate, the columns used in this study were equipped with electrodes which allowed for in situ measurements of corrosion potentials of the iron material. Together with Raman spectroscopic measurements the mechanisms of decline in iron reactivity were examined. The experimental results showed that the presence of nitrate resulted in an increase in corrosion potential and the formation of thermodynamically stable passive films on the iron surface which impaired iron reactivity. The extent of the decline in iron reactivity was proportional to the nitrate concentration. Consequently, significant decreases in TCE and nitrate degradation rates and migration of degradation profiles for both compounds occurred. Furthermore, the TCE degradation kinetics deviated from the pseudo-first-order model. The results of reactive transport modeling, which related the amount of a passivating iron oxide, hematite (α-Fe<SUB>2</SUB>O<SUB>3</SUB>), to the reactivity of iron, were generally consistent with the patterns of migration of TCE and nitrate profiles observed in the column experiments. More encouragingly, the simulations successfully demonstrated the differences in performances of three columns without changing model parameters other than concentrations of nitrate in the influent. This study could be valuable in the design of iron permeable reactive barriers (PRBs) or in the development of effective maintenance procedures for PRBs treating TCE-contaminated groundwater with elevated nitrate concentrations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nitrate reduction impaired iron reactivity for trichloroethylene degradation. </LI> <LI> Nitrate reduction resulted in formation of passive films on iron surfaces. </LI> <LI> The iron reactivity decline was proportional to the nitrate concentration. </LI> <LI> Modeling can be valuable in designing of permeable reactive barriers. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of supplementary cementitious materials on the degradation of cement-based barriers in radioactive waste repository: A case study in Korea

김민석,한솔찬,윤종일 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.9

This study focuses on investigating the chemical degradation characteristics of cementitious barriers used in lowand intermediate-level radioactive waste repository by reactive transport modeling. The impact of the blending with supplementary cementitious materials (SCMs) in the barriers on the chemical degradation was evaluated to find the optimum barrier design. A number of different barrier designs were examined by replacing ordinary Portland cement (OPC) by SCMs (i.e., fly ash, silica fume, and blast-furnace slag). The simulation results showed that silica fume blended barrier has better durability against chemical degradation by rainwater compared to fly ash or blast-furnace slag blended barriers. In addition, the chemical durability of silica fume-based barrier increased with increasing replacement level up to about 20 %. It seems that the amount of formed calcium silicate hydrate (CSH) in the initial cement-based barrier highly affects the overall chemical durability. The newly developed reactive transport model demonstrated its capability for understanding the barrier performance and investigating the optimal design of the barrier system.

A 3D mathematical evaluation of the emission into the air of reactive BTEX compounds: A new approach for mechanism reduction

Nesarak Eslami,Esmaeil Fatehifar,Mohammad Ali Kaynejad 대한환경공학회 2022 Environmental Engineering Research Vol.27 No.6

BTEX species are abundant volatile organic compounds that are classified as main pollutants by several environmental protection agencies. In this study, a new 3D air pollution dispersion model with the capability of taking into account the BTEX"s reactions was developed and evaluated. The Toxchem model is employed to estimate the amount of emitted BTEX from several area sources, followed by simulating the transport of the reactive species through a 3D model. Also, reduced mechanisms were developed, based on Master Chemical Mechanism (MCM), for the simulation of the atmospheric chemistry of BTEX. The application of the mechanism reduction method yielded a mechanism of 43 species and 45 reactions. Based on findings, the deviation of the reduced mechanism from the whole mechanism was < 4% throughout the simulation. In addition, the result showed that, during a 12 h period of simulation, the effect of the atmospheric chemical reaction on reducing the final concentration of benzene, toluene, ethylbenzene, m-xylene, o-xylene, and p-xylene was about 0.3, 1, 1.4, 5, 3.1, and 3.2%, respectively. Lastly, it was indicated that the estimated emission rates by Toxchem and simulated concentrations by the dispersion model were in good agreement with the reported experimental values.

다성분 반응 이동 모델링을 이용한 트리클로로에틸렌(TCE)으로 오염된 지하수에서의 자연저감 평가

진성욱,전성천,김락현,황현태,Jeen, Sung-Wook,Jun, Seong-Chun,Kim, Rak-Hyeon,Hwang, Hyoun-Tae 한국지하수토양환경학회 2016 지하수토양환경 Vol.21 No.6

To properly manage and remediate groundwater contaminated with chlorinated hydrocarbons such as trichloroethylene (TCE), it is necessary to assess natural attenuation processes of contaminants in the aquifer along with investigation of contamination history and aquifer characterization. This study evaluated natural attenuation processes of TCE at an industrial site in Korea by delineating hydrogeochemical characteristics along the flow path of contaminated groundwater, by calculating reaction rate constants for TCE and its degradation products, and by using geochemical and reactive transport modeling. The monitoring data showed that TCE tended to be transformed to cis-1,2-dichloroethene (cis-1,2-DCE) and further to vinyl chloride (VC) via microbial reductive dechlorination, although the degree was not too significant. According to our modeling results, the temporal and spatial distribution of the TCE plume suggested the dominant role of biodegradation in attenuation processes. This study can provide a useful method for assessing natural attenuation processes in the aquifer contaminated with chlorinated hydrocarbons and can be applied to other sites with similar hydrological, microbiological, and geochemical settings.

지하수 내 질산성 질소 반응-이동 모델링을 위한 부지특이적 탈질화 계수 선정 방안에 대한 고찰

김상현,정재식,이승학,Kim, Sang Hyun,Chung, Jaeshik,Lee, Seunghak 한국지하수토양환경학회 2021 지하수토양환경 Vol.26 No.6

A simple and efficient scheme is presented that attempts to implement the site-specific denitrification rate in the reactive transport modeling for the nitrate in groundwater. A series of correlation analyses were conducted using 133 datasets obtained from different nitrate-contaminated sites to find the empirical relationships between denitrification rates and various subsurface properties. Based on Pearson's correlation analysis, the soil organic carbon concentrations showed a statistically significant correlation (r = 0.75, p < 0.05) with the denitrification rates. A linear regression was performed, which could be utilized to effectively determine the site-specific denitrification rate based on the soil organic carbon concentration of a site. The proposed method is expected to effectively replace the conventional methods which either were too complicated for practical application or impose large uncertainties that might end up with unreliable results.

Reactive transport modeling on the behavior of CO₂ and SO₂ injected into deep saline aquifer

최병영(Byoung-Young Choi),채기탁(Gi-Tak Chae),김경호(Kyoung-Ho Kim),윤성택(Seong-Taek Yun) 대한지질학회 2009 지질학회지 Vol.45 No.5

A Preliminary Study on the Applicability of Reactive Transport Model to Uranium Transport in Single-Well Push-Pull Test

In-Hee Cho,Suh-Ho Lee,In-Woo Park,Jaeyeon Kim,Kang-Kun Lee 한국방사성폐기물학회 2024 한국방사성폐기물학회 학술논문요약집 Vol.22 No.1

CO2 지중저장 주입정에서의 CO2-H2O-시멘트 반응 운송 모델링

조민기 ( Min Ki Jo ),채기탁 ( Gi Tak Chae ),최병영 ( Byoung Young Choi ),유순영 ( Soon Young Yu ),김태희 ( Tae Hee Kim ),김정찬 ( Jeong Chan Kim ) 대한지질공학회 2010 지질공학 Vol.20 No.4

CO2 지중저장에서는 대량의 CO2를 장기간 안전하게 저장하여야하기 때문에 CO2 누출이 발생할 경우 CO2 지중저장의 목적이 달성될 수 없을 뿐만 아니라 주변지역으로 CO2가 확산되어 보건/환경/생태에 큰 영향을 미칠 수 있다. CO2 주입시 주입정을 통한 누출의 가능성이 가장 높기 때문에, 본 연구에서는 관정 시멘트에 crack이 발생하였다는 가정 하에 crack으로 CO2가 누출될 경우 CO2-H2O-시멘트 간에 발생할 수 있는 화학 반응을 지구화학 모델링을 통하여 예측하였다. 모델링 결과 CO2-plume이 진행됨에 따라 시멘트 페이스트를 구성하는 portlandite와 CSH(Calcium Silicate Hydrate)가 용해되고, 2차적으로 CSH의 침전과 calcite의 침전이 발생하는 것으로 예상되었다. 약 3년 후에는 침전물의 대부분을 calcite가 차지하고 약 30년까지 침전물의 대부분을 이루게 된다. 본 연구 결과는 CO2 누출 시 주입관정 내 시멘트에서 발생할 수 있는 화학적인 변화를 이해하고, 반응 모델은 누출을 방지하기 위한 시멘트 관련 연구/개발에 응용될 수 있을 것으로 기대된다. CO2 leakage from a geological formation utilized for CO2 storage could result in failure of the facility and threaten the environment, as well as human safety and health. A reactive transport model of a CO2-H2O-cement reaction was constructed to understand chemical changes in the case of CO2 leakage through a cement crack in an injection well, which is the most probable leakage pathway during geological storage. The model results showed the dissolution of portlandite and CSH (calcium silicate hydrate) within the cement paste, and the precipitation of secondary CSH and calcite as the CO2 plume migrated along the crack. Calcite occupied most of the crack after 3 year of reaction, which could be maintained until 30 years after crack development. The present results could be applied in the development of technology to prevent CO2 leakage and to enhance the integrity of wells constructed for CO2 geological storage.

Application of reactive transport modeling to an in-situ test for the removal of groundwater iron and manganese in aquifer

한찬(Chan Hahn),이명재(Myeong-Jae Yi),장호준(Ho-June Jang) 대한지질학회 2016 지질학회지 Vol.52 No.3