Ionic Diffusion Oxidation Model of Uranium - A Revisit Study

Myungjin Kang,Kunok Chang,Kwangheon Park 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

After the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) was signed, Korea is undergoing nuclear inspection by the International Atomic Energy Agency (IAEA) as a non-nuclear-armed state. By the inspection, nuclear material measurement and management have been carried out according to safety measures. Uranium dioxide, a major component of nuclear fuel, is a material that naturally oxidizes at room temperature, yielding a volume change. In this case, it will have an impact on the management of nuclear material measurement, and a model for predicting this will be required. At room temperature, an oxide film is grown by oxygen diffusion on the surface of uranium dioxide, and if the thickness of the oxide film is predicted based on this, the volume change of uranium dioxide can also be predicted. In relation to this, Ghargozloo’s ionic diffusion oxidation model exists. Therefore, in this paper, an modified oxidation model based on Ghargozloo’s oxygen diffusion in uranium dioxide is presented and the volume change of uranium dioxide due to oxidation is predicted.

A phase-field modeling of void swelling in the Austenitic stainless steel

Chang, Kunok,Lee, Gyeong-Geun,Kwon, Junhyun GORDON & BREACH / HARWOOD ACADEMIC PUBLISHING 2016 RADIATION EFFECTS AND DEFECTS IN SOLIDS Vol.171 No.3

<P>Two-dimensional phase-field simulations of void swelling in the Austenitic stainless steel were performed for irradiated materials. A numerical model was established for void swelling with an implementation of the elasticity effect, and we examined the roles of the applied stress and grain boundary sink strength and Frenkel defect recombination in determining the void swelling rate. The obtained results were compared with the existing experimental observations.</P>

Role of second-phase particle morphology on 3D grain growth: A phase-field approach

Chang, Kunok,Kwon, Junhyun,Rhee, Chang-Kyu Elsevier 2016 Computational materials science Vol.124 No.-

<P><B>Abstract</B></P> <P>The incorporation of second-phase particles in polycrystalline materials is one of the most efficient and practical methods for the retardation of grain growth during high-temperature heat treatment. To obtain a more systematic understanding of the related pinning effect, we employ a multi-order-parameter phase-field grain-growth model to simulate 3D grain growth in the presence of inert second-phase particles. We compare the pinning efficacy of the second-phase particles depending on the particle size, distribution, morphology, and the number of alignment directions. The dependence of the number of average neighboring grains on the spatial distributions of the inert second-phase particles is also evaluated.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Phase-field Modeling of Precipitate Behavior in RPV Steel Using CALPHAD Database

Chang, Kunok,Kwon, Junhyun,Lee, Gyeong-Geun The Korean Institute of Metals and Materials 2018 대한금속·재료학회지 Vol.56 No.6

중성자 조사재의 미세구조 설계와 모델링

장근옥 ( Kunok Chang ) 한국공업화학회 2020 공업화학 Vol.31 No.4

재료는 방사선과 상호작용을 통해 그 물리적, 화학적 특성이 변화하며 여러 방사선 중에서 전하를 띄고 있지 않아 침투깊이가 깊은 중성자 조사에 의한 금속소재의 조사손상은 원자력발전소의 안전과 관련해서 오랜 기간 동안 집중적인 연구대상이었다. 중성자 조사에 의한 조사손상은 초반 피코 초 스케일에서 벌어지는 원자단위의 점결함의 생성으로 시작되며 그 이후의 전개 양상은 전위 고리나 공극과 같은 미세구조상 결함으로 확인될 수 있다. 이러한 미세구조상 결함의 형상과 분포에 따라 소재의 특성에 미치는 효과는 상이하게 된다. 그러므로 중성자 조건에 따른 미세구조를 예측하는 것은 매우 중요한 일로, 본 논문에서는 중성자 조사에 의한 재료 내의 미세구조 발달에 대해 리뷰한 뒤 조사된 소재의 미세구조 변화 예측에 널리 사용될 수 있는 상장 모델에 대해 간략히 소개하였다. A material changes its physical and chemical properties through the interaction with radiation and also the neutrons, which is electronically neutral so that the penetration depth is relatively deeper than that of other radioactive way including alpha or beta ray. Therefore, the radiation damage by neutron irradiation has been intensively investigated for a long time with respect to the safety of nuclear power plants. The damage induced by neutron irradiation begins with the creation of point defects in atomic scale in the unit of picoseconds, and their progress pattern can be characterized by microstructural defects, such as dislocation loops and voids. Their morphological characteristics affect the properties of neutron-irradiated materials, therefore, it is very important to predict the microstructure at a given neutron irradiation condition. This paper briefly reviews the evolution of radiation damage induced by neutron irradiation and introduces a phase-field model that can be widely used in predicting the microstructure evolution of irradiated materials.

Effect of Inhomogeneous Nucleation of Hydride at α/β Phase Boundary on Microstructure Evolution of Zr–2.5 wt%Nb Pressure Tube

Sung‑Soo Kim,Sangyeob Lim,Dong‑Hyun Ahn,Gyeong‑Geun Lee,Kunok Chang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.4

We analyzed the microstructural characteristics such as number density and length and width of hydrides in Zr–2.5 wt%Nbpressure tube. The hydrogen was charged cathodically and the hydride-contained sample was evaluated using the advancedanalysis methodologies. We performed a diff erential scanning calorimetry analysis to more quantitatively understand thethermodynamics of the hydride formation/growth process. We characterized the micrograph of hydride-contained Zr samplesto estimate the microstructural characteristics of the matrix and hydrides. We investigated eff ects of hydrogen concentrationand microstructure of matrix on determining microstructural measures of the hydrides. Particularly, we found that β phasein the matrix becomes isolated during the heat treatment same or above 475 °C and this change increases the inhomogeneousnucleation sites signifi cantly. We claim that the microstructure change of this matrix phase greatly increases the numberdensity of hydride.

컴퓨터 시뮬레이션 기법을 이용한 입계면 - 이상 입자 간 상호작용 모사 연구 동향

장근옥,Chang, Kunok 한국분말야금학회 2020 한국분말재료학회지 (KPMI) Vol.27 No.4

Since the interaction between the second-phase particle and grain boundary was theoretically explained by Zener and Smith in the late 1940s, the interaction of the second-phase particle and grain boundary on the microstructure is commonly referred to as Zener pinning. It is known as one of the main mechanisms that can retard grain growth during heat treatment of metallic and ceramic polycrystalline systems. Computer simulation techniques have been applied to the study of microstructure changes since the 1980s, and accordingly, the second-phase particle-grain boundary interaction has been simulated by various simulation techniques, and further diverse developments have been made for more realistic and accurate simulations. In this study, we explore the existing development patterns and discuss future possible development directions.

Expert Opinion Collection Methodology and Integrated FEP List Development for High-level Radioactive Waste Disposal Site Establishment

Myeongjin Kang,Kunok Chang 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

Spent nuclear fuel temporary storage in South Korea is approximately 70% of total storage capacity as of the 4th quarter of 2022 amount is stored. In addition, according to the analysis of the Korean Radioactive Waste Society, saturation of nuclear power plant temporary storage is expected sequentially from 2031, and accordingly, the need for high-level radioactive waste disposal facilities has emerged. Globally, after the conclusion of the EU Taxonomy, for nuclear energy in order to become an ecofriendly energy, it is necessary to have a high-level radioactive waste disposal site and submit a detailed operation plan for high-level radioactive waste disposal site by 2050. Finland and Sweden have already received permission for the construction of high-level radioactive waste disposal facilities, and other countries, such as Switzerland, Japan, the United States, and Canada, are in the process of licensing disposal facilities. In order to establish a repository for high-level radioactive waste, the performance and safety analysis of the repository must be conducted in compliance with regulatory requirements. For safety analysis, it needs a collection of arguments and evidence. and IAEA defined it as ‘Safety case’. The Systematic method, which derives scenarios by systematizing and combining possible phenomena around the repository, is widely used for developing Safety case. Systematic methods make use of the concept of Features, Events and Processes (FEP). FEP identifies features that affect repository performance, events that can affect a short period of time, and processes that can have an impact over a long period of time. Since it is a characteristic of the Systematic method to compose a scenario by combining these FEP, the Systematic method is the basic premise for the development of FEP. Completeness is important for FEP, and comprehensiveness is important for scenarios. However, combining all the FEP into one scenario is time-consuming and difficult to ascertain the comprehensiveness of the scenario. Therefore, an Integrated FEP list is being developed to facilitate tracking between FEP and scenarios by integrating similar FEP. In this study, during the integrated FEP development process, a method for utilizing experts that can be used for difficult parts of quantitative evaluation and a quantitative evaluation process through the method were presented.

한국방사성폐기물학회

Jeongho An,Kunok Chang 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

Graphite is widely used as a reflector or moderator in nuclear reactors, and since it is exposed to high flux neutron irradiation, long-lived radioactive isotopes such as C-14 are formed. Therefore, quantitatively prediction of production amount is a very essential task for reliable radioactive waste management. In this study, considering nuclear reactions such as (?, ?) reaction by thermal neutrons and elastic scattering, various characteristics such as the rate of formation of C-14 and energy distribution of thermal neutrons according to the penetration depth from the graphite surface were numerically analyzed. The evaluation was carried out in consideration of the average energy of neutrons and reaction/collision cross-sectional area at given energy, and a comparative study was also performed when the thermal neutrons were in thermal equilibrium and when they were not. The numerically evaluated results were compared qualitatively with the experimental study, and methods to further increase the accuracy were also discussed.

Phase-field modeling 기반 Fe-Cr 시스템의 spinodal decomposition 모사 연구

이정환(Jeonghwan Lee),장근옥(Kunok Chang) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.4