To thoroughly analyze the mechanical properties and surface conditions of HF50S carbon fibers, the tensile properties, surface morphology, surface chemical element, surface energy, sizing agent properties, and Naval Ordnance Laboratory (NOL) ring of their composites were characterized. Furthermore, the aforementioned properties were exhaustively compared with those of T1000G carbon fibers. The results showed that the tensile strength, modulus, and elongation of the HF50S carbon fibers were 6638 MPa, 297 GPa, and 2.2%, respectively, thus demonstrating that the mechanical properties of the HF50S carbon fibers were on par with those of the T1000G carbon fibers, in addition, the coefficient of variation (Cv) indices of HF50S carbon fiber were below 3%, indicating good stability. The HF50S carbon fibers have a smooth surface without grooves, which is analogous to that of the T1000G carbon fibers prepared by the typical dry jet–wet spinning process. The main component of the sizing agent of the HF50S carbon fibers is an epoxy resin, which is also used for the preparation of epoxy matrix composites. Because the HF50S carbon fiber surface has greater O and N contents than the T1000G carbon fiber surface, the HF50S carbon fibers have more active functional groups and higher surface activity. The surface energy of the HF50S carbon fibers is 30.13 mJ/m2, which is higher than that of the T1000G carbon fibers (28.42 mJ/m2). Owing to the higher strength and surface activity of the HF50S carbon fibers than those of the T1000G carbon fibers, the strength and strength conversion of NOL ring based on the former are slightly higher than those of that prepared using the latter.

Accurate understanding of structural integrity and chemical reactivity of UO2 disposed in deep underground sites is of importance. Owing to the specific condition of the site location, UO2 may have substantially different properties from the conventional prediction. In this study, we demonstrate that the oxidation resistivity of UO2 is considerably modified by gadolinium (Gd), which is the element of neutron absorber and a byproduct of nuclear decay of radioactive U-235. Using density functional theory calculations, we investigate how the oxidation mechanism of UO2 changes with Gd incorporation in U lattice. Our study indicates that Gd remarkably enhances the thermodynamic stability of pristine UO2 against surface oxidation via three underlying mechanisms: (i) weakens the chemical bonding of adsorbed oxygen atom (O) with U, (ii) reduces active sites (U) for oxygen adsorption, and (iii) suppresses the subsurface diffusion of adsorbed O delaying the growth of the oxide layers on the UO2. Electronic and lattice structure analyses for Gd-doped UO2 indicate that amount of charge transfer from U to O is critically reduced and the lattice of the UO2 surface is contracted. Our results provide useful information for understanding long-term stability and improving the structural integrity of UO2 through the chemical doping process.

Near-surface disposal facility is more susceptible to intrusion than underground repository, resulting in more possible pathways for contaminant release. Alike human intrusion, animals (e.g. Ants, Moles, etc.) could intrude into the disposal site to excavate burrows, which could cause direct release of contaminants to biosphere. In this paper, animal intrusion is demonstrated using GoldSim’s commercial contaminant transport module and impact on the integrity of the near-surface disposal facility is evaluated in terms of fractional release rate of the contaminants. In this study, the near-surface disposal facility is modelled with a single concrete vault to contain radionuclide according to LLW concentration limit stated in NSSC notice No.2020-6. The release of contaminants is modelled to occur directly after the institutional control period, and the contaminants are mostly transported from the concrete vault to cover layers via diffusion. To produce mathematical model of the release of the contaminants due to animal intrusion, firstly, the fraction of burrow volume for each cover layer is calculated separately for each animal species, based on their maximum possible intrusion depth. In this study, fractions of burrow volume for ants and moles are calculated based on their maximum possible intrusion depths, where for ants is 2–3 m, and for moles is 0.1–0.135 m. Then, assuming that the contaminants are distributed homogeneously throughout each cover layers by diffusion, fraction of contaminants transported into the uppermost layer via excavation of the burrow is calculated for each layer based on burrow volume, and fraction of contaminants removed from the uppermost layer to the layers below via collapse of the burrow is also calculated based on the burrow volume. Lastly, the net transportation of contaminants into and out of the burrow via excavation and collapse, respectively, is calculated and demonstrated using direct transfer rate function of the GoldSim. Based on the simulated result, the maximum mass flux is too minor to cause a meaningful impact on the safety. The peak mass flux of the most sensitive radionuclide, I-129, is witnessed at around year 1,470, with a flux value of 5.36×10−6 g·yr−1. This minor release of the contaminants could be due to cover layers being much thicker than the maximum possible intrusion depth of the animals, preventing the animal intrusion into the deeper layers of higher radionuclide concentration. In future, this study can be used to provide a guidance and fundamental data for scenario development and safety evaluation of the near-surface disposal facility.

It has been discovered that the isosaccharinic acid (ISA) formed in a cellulose degradation leachate were capable of forming soluble complexes with thorium, uranium (IV) and plutonium. Since 1993, the ISA has received particular attention in the literature due to its ability to complex a range of radionuclides, potentially affecting the migration of radionuclides. ISA is formed as a result of interactions between cellulosic materials within the waste inventory and the alkalinity resulting from the use of cementitious materials in the construction of the repository. In an alkaline cementitious environment, cellulose degrades mainly via a peeling-off reaction. The main degradation product is ISA, a polyhydroxy type of ligand forming stable complexes with tri- and tetravalent radionuclides. ISA can have an adverse effect on the sorption of radionuclides to an extent which depends on its concentration in the cement pore water and potentially enhance their mobility. The concentration of ISA is governed by several factors such as cellulose loading, cement porosity, extent of cellulose degradation, etc. The sorption of ISA on cement, however, is the process which governs the concentration of ISA in the pore water. According to the experimental result from a literature, the ISA concentration in facilities with a cellulose loading of 5% is calculated to be of the order of 10−4 M. At this level, the effect of cellulose degradation products on radionuclide sorption is negligibly small. Recently in Korea, cellulous limits as waste acceptance criteria is studying and planning to prepare the detailed requirement for near surface radioactive waste disposal facilities. It is desirable to suggest consideration on cellulose disposal limits around the time that the regulatory body and concern organizations establish the cellulose disposal limits as follows. Firstly, identify the cellulose effect on the sorption of the nuclides as cementitious disposal environments such as affected nuclides, threshold value and contribution to radiological risks under domestic disposal environment. Secondly, make sure and consider the difference between lab-scale experimental conditions and probability occurring in real disposal conditions such as probability for generation and persistence of pH in cellulosic material disposal conditions and cellulosic material disposal methods. Finally, consider characterization of cellulosic material such as polymerization, contents of cellulose in law material and time of degradation process. As a result, desirable cellulose limits are to set up for both safety and economic aspect.

The disposing method of the low-intermediate-level radioactive waste, near-surface disposal facilities are generally used. This disposal method refers to a method of constructing a concrete structure on the surface of the ground, putting radioactive waste in it, and covering it with an engineered barrier to isolate human life. Among these, engineered barriers mean covering multiple layers of heterogeneous materials such as sand, clay, and gravel. Engineering barriers have the purpose of delaying the release of radioactive materials into the natural environment as much as possible, and maintaining the isolation of radioactive waste and human life for as long as possible. In this study, the design and construction method of the facility to demonstrate the performance of the engineered barrier that isolates the surface disposal facility from nature was described. In addition, the design and construction method of monitoring technology that can monitor the safety of engineered barriers by measuring information such as moisture, temperature, and slope safety in real time was also explained.

The safety assessment of a geological disposal system is performed over a period of hundreds of thousands of years, during which the activity of radionuclides in spent nuclear fuel decreases to natural radioactivity levels. During this period, the biosphere also experiences the long-term evolution of the surface environment including climate, terrain, and ecosystem changes. These changes cause changes in the water balance, which in turn change the pathways of radionuclides in the subsurface. Therefore, it is essential to consider these long-term changes in the surface environment for a reasonable biosphere safety assessment. For this purpose, this study developed the biosphere assessment module considering the long-term evolution of the surface environment, as a sub-module of APro (Adaptive process-based total system performance assessment framework). As a preceding study, the biosphere assessment module was previously developed using COMSOL for hydraulic and radionuclide transport processes, to simulate the pathway of radionuclides traveling from the shallow aquifer to the surface water body and soil. To consider the long-term evolution of the surface environment, the previous module needed to be improved to apply different water balances as boundary conditions of the module at each snapshot, which is a sub-time period divided based on the surface evolution data. To this end, this study utilized SWAT (Soil and Water Assessment Tool) which calculates the water balance using the surface environmental data including climate, terrain, land cover, and soil type. Conceptually, SWAT calculated annual water balance considering surface environmental changes, and certain components (i.e., groundwater recharge and hydraulic head of water bodies) of water balance were transferred to COMSOL as external data to simulate the pathway of radionuclide transport and spatio-temporal variability of radionuclides. At the current stage, the biosphere computational module has been developed to correspond to its conceptual model, and we plan to further test the applicability of the module using different surface environmental data.

It can take hundreds of thousands of years for decreasing radiological effects of high-level radioactive wastes to those of natural background radiation. Therefore, long-term time scale should be considered in order to demonstrate performance and safety of deep geological disposal of the radioactive wastes. The changes of surface environment for these long-term time scale can have influence on safety analysis by changing transport path of radionuclides from the radioactive wastes. Changes in climate is considered as one of main factors causing the long-term changes of the surface environment. The own effects and interactions of climate with other components of the geological disposal system are organized in features, events, and processes (FEPs). In this study, some natural processes occurred by changes of climate were suggested and the connectivity between each process is proposed based on the relation of the FEPs concerned with the changes of climate and surface environment. The processes were classified into global and regional/local scales and was analyzed, respectively. Then, the influences of the processes on shallow groundwater and surface water body environment, which might be transport path of radioactive nuclides in local/site scales, were expected. As the proposed connection demonstrate the order or hierarchical relations of the natural processes, it can shows that some output by a certain process may be input of other process connected the former process in numerical simulations for interpreting the processes. If the connection may be considered to be suitable to represent longterm changes of the surface environment, it can be evaluated that the expected scenarios based on the connection is also proper. In addition, it can be helpful in selecting factors to be studied more detailed in terms of climate change for expecting long-term changes in the surface environment by analysis on the input and output data. The results of this study can be used as basic approaches to represent the long-term changes in the surface environment caused by specific natural processes from changes of climate. It will be also helpful for formulating scenarios related to long-term evolution in the surface environment required for performance and safety assessments of the deep geological disposal.

Various diffusion experiments using geologic media have been carried out and it is often assumed that aqueous diffusion is the dominant transport mechanism. However, in some cases diffusive migration has been much faster than predicted in the model simulation. To explain such results surface diffusion of sorbing species was invoked. Experimental results were generally open to interpretation but possible existence of surface diffusion, whereby sorbed radionuclides could potentially migrate at much enhanced rates, necessitated investigation. The potential for surface diffusion of some sorbing nuclides on through-diffusion experiments using domestic rocks was examined. The apparent diffusion coefficients for sorbing cations were determined from their steady-state diffusion flux through rocks disks, while effective and pore diffusion coefficients were obtained with non-sorbing tracers through the same rocks. Diffusive transport models through domestic granites and granodiorites based only on pore diffusion did not often described adequately for sorbing cations. Thus, surface diffusion should be considered. Then what was the most important measure to estimate surface diffusion? As far as we examine, the sorption reversibility provides a hint of surface diffusion. The reversible sorbing species, for example, Sr, has a remarkable surface diffusion contribution, whereas surface diffusion has a relatively small contribution for irreversibly sorbing species such as Cs and Am under domestic experimental conditions.

피마자 기반 수성 폴리우레탄(CPUD)을 얻기 위해 무 변성 피마자유 (CO) 와 투명 필름을 얻기 위해 이소포론 디이소시아네이트(IPDI)를 사용했다. 유연성을 증가시키기 위해 폴리프로필렌글리콜 (PPG)의 혼합 효과를 분석하였다. 또한, 사슬연장제로 에틸렌다이아민(EDA)을 사용했다. 각각 피마자유 함유에 따른 변화와 사슬연장제 변화에 따른 인장강도, 연신율 내마모성을 측정했다. 피마자유 함유가 많은 시료의 인장강도가 1.112kgf/㎟, 연신율 88%로 나타났으며, 사슬연장제 함유가 많은 시료의 인장 강도가 3.33kgf/㎟, 연신율 99%로 측정되었다. 표면강도는 SEM을 통해 육안으로 확인하였다.

PURPOSES : The surface distress of asphalt pavements is one of the major factors affecting the safety of road users. The aim of this study was to analyze the factors influencing the occurrence of surface distress and statistically predict its annual change to contribute to more reasonable asphalt pavement management using the data periodically collected by the national highway pavement data management system. METHODS : In this study, the factors that were expected to influence the surface distress were determined by reviewing the literature. The normality was secured by changing the forms of the variables to make the distribution of the variables got closer to normal distribution. In addition, min-max normalization was performed to minimize the effect of the unit and magnitude of the candidate independent variables on the dependent variable. The final candidate independent variables were determined by analyzing the correlation between the annual surface distress change and each candidate independent variable. In addition, a prediction model was developed by performing data grouping and multi-regression analysis. RESULTS : An annual surface distress change prediction model was developed using present surface distress, age, and below 0 ℃ days as the independent variables. As a result of sensitivity analysis, the surface distress affected the annual surface distress change the most. The positive correlation between the dependent variable and each independent variable demonstrated engineering and statistical meaningfulness of the prediction model. CONCLUSIONS : The surface distress in the future can be predicted by applying the annual surface distress prediction model to the national highway asphalt pavement sections with survey data. In addition, the prediction model can be applied to the national highway pavement condition index (NHPCI) evaluating the national highway asphalt pavement conditions to be used in the prediction of future NHPCI.

PURPOSES : Recently, air pollution caused by particulate matter has been worsening. Among the substances generating particulate matter, NOx is the main precursor of particulate matter and is widely distributed in areas with a high volume of traffic. TiO2 has been used as a material for removing NOx through a chemical reaction as a photocatalyst. In this context, the reduction of NOx through TiO2 concrete is proposed. However, the research on the surface deterioration on the performance of TiO2 concrete is not documented yet. Therefore, the objective of this study was to evaluate the long-term durability and NOx removal efficiency of TiO2 concrete by considering the concrete surface deterioration. METHODS : Freezing–thawing resistance test (KS F 2456) and scaling test (ASTM C 672) were performed to investigate the variation in the TiO2 penetration distribution and NOx removal efficiency of TiO2 concrete corresponding to surface deterioration. The long-term durability of TiO2 concrete was evaluated through an environmental resistance test and changes in TiO2 penetration depth and distribution characteristics. In addition, the NOx removal efficiency of TiO2 concrete was evaluated as surface deterioration occurs. RESULTS : As a result of the freeze–thawing resistance test, a relative dynamic elastic modulus of more than 80 % was detected. In addition, a TiO2 penetration depth of 0.3 mm, NOx removal efficiency of 11.2 %, and a 30 % of TiO2 surface prediction mass ratio were achieved after 300 cycles. As a result of visual observation of the scaling test, “0, no scaling” was secured. After 50 cycles of scaling test, the TiO2 penetration depth, NOx removal efficiency, and TiO2 surface prediction mass ratio were 0.3 mm, 36.3 %, and 63 %, respectively. Through the results of the environmental resistance test, the excellent long-term durability and NOx removal efficiency of TiO2 concrete were confirmed. CONCLUSIONS : As a result of the experiment, long-term durability and NOx removal efficiency of TiO2 concrete were secured. The application of TiO2 concrete can be a good alternative with long-term performance and durability.

Carbon fiber and its composites are increasingly used in many fields including defence, military, and allied industries. Also, surface quality is given due importance, as mating parts are used in machineries for their functioning. In this work, the turning process is considered for Carbon Fiber Reinforced Polymer (CFRP) composites by varying three important cutting variables: cutting speed, feed, and depth of cut. Correspondingly, the surface roughness is measured after the completion of turning operation. As well, a prediction model is created using different fuzzy logic membership function and Levenberg–Marquardt algorithm (LMA) in artificial intelligence. Later, the surface roughness values from the developed models are compared against the experimental values for its correlation and effectiveness in using different membership functions of fuzzy logic and ANN. Thus, the experimental results are analyzed using the effect graphs and it is presented in detail.