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나태형,이영오,김태현,이동희 한국방사성폐기물학회 2023 방사성폐기물학회지 Vol.21 No.4
The aim of this study is to ensure the structural integrity of a canister to be used in a dry storage system currently being developed in Korea. Based on burnup and cooling periods, the canister is designed with 24 bundles of spent nuclear fuel stored inside it. It is a cylindrical structure with a height of 4,890 mm, an internal diameter of 1,708 mm, and an inner length of 4,590 mm. The canister lid is fixed with multiple seals and welds to maintain its confinement boundary to prevent the leakage of radioactive waste. The canister is evaluated under different loads that may be generated under normal, off-normal, and accident conditions, and combinations of these loads are compared against the allowable stress thresholds to assess its structural integrity in accordance with NUREG-2215. The evaluation result shows that the stress intensities applied on the canister under normal, off-normal, and accident conditions are below the allowable stress thresholds, thus confirming its structural integrity.
나태형 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.8
The most important process in the manufacture of light-water reactor nuclear fuel rods is tube-cap welding, which serves to seal radioactive uranium materials. Tube-cap welding is a method commonly used in production by sealing various materials into tubes and caps, and is used in the manufacture of fuel rods in nuclear power plants. In this study, the simulation-based characterization of tube-cap welding was carried out to understand the underlying mechanisms that govern the welding process and to use a model that can predict the melted volume during the welding process. The simulation results were then used to analyze the effects of various welding parameters on the melted volume during welding process. To analyze the mechanism of welding phenomena in the tube-cap welding, various weld variables such as welding current, overlap length, and force were used. Those are the main variables in the tube-cap welding used in nuclear fuel rods manufacturing thought simulation. To predict the melted volume of the weld, a regression model and a neural network were used to predict the amount of melt using the process with the main process variables as input variables. The study quantitatively determined the effects of each welding variable on the melted volume and analyzed the correlation between two factors.
나태형,이영오,김태현,김용덕 한국방사성폐기물학회 2023 방사성폐기물학회지 Vol.21 No.4
A transfer cask serves as the container for transporting and handling canisters loaded with spent nuclear fuels from light water reactors. This study focuses on a cylindrical transfer cask, standing at 5,300 mm with an external diameter of 2,170 mm, featuring impact limiters on the top and bottom sides. The base of the cask body has an openable/closable lid for loading canisters with storage modules. The transfer cask houses a canister containing spent nuclear fuels from lightweight reactors, serving as the confinement boundary while the cask itself lacks the confinement structure. The objective of this study was to conduct a structural analysis evaluation of the transfer cask, currently under development in Korea, ensuring its safety. This evaluation encompasses analyses of loads under normal, off-normal, and accident conditions, adhering to NUREG-2215. Structural integrity was assessed by comparing combined results for each load against stress limits. The results confirm that the transfer cask meets stress limits across normal, off-normal, and accident conditions, establishing its structural safety.
Realistic thermal analysis of the CANDU spent fuel dry storage canister
이태강,김태현,나태형,윤병조,정재준 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.12
Thermal analysis of the CANDU spent fuel dry storage canister is very important to ensure the integrity of the spent fuel. The analyses have been conducted using a conservative approach, with a particular focus on the peak cladding temperature (PCT) of the fuel rods in the canister. In this study, we have performed a realistic thermal analysis using a computational fluid dynamics (CFD) code. The canister contains 9 fuel bundle baskets. A detailed analysis of even a single basket requires significant computational resources. To overcome this challenge, we replaced each basket with an equivalent heat conductor (EHC), of which effective thermal conductivity (ETC) is developed from the results of detailed CFD calculations of a fuel bundle basket. Then, we investigated the effects of some conservative models, ultimately aiming at a realistic analysis. The results revealed: (i) The influence of convective heat transfer in the basket cannot be ignored, but it’s less significant than expected. (ii) Modeling of the lifting rod is crucial, as it plays a decisive role in axial heat transfer at the center of the canister and significantly reduces the PCT. (iii) Convection within the canister is very important, as it not only reduces the PCT but also shifts its location upwards.
Review of Aging Management for Concrete Silo Dry Storage Systems
이동희,정성환,김용덕,나태형 한국방사성폐기물학회 2023 방사성폐기물학회지 Vol.21 No.4
The Wolsong Nuclear Power Plant (NPP) operates an on-site spent fuel dry storage facility using concrete silo and vertical module systems. This facility must be safely maintained until the spent nuclear fuel (SNF) is transferred to an external interim or final disposal facility, aligning with national policies on spent nuclear fuel management. The concrete silo system, operational since 1992, requires an aging management review for its long-term operation and potential license renewal. This involves comparing aging management programs of different dry storage systems against the U.S. NRC’s guidelines for license renewal of spent nuclear fuel dry storage facilities and the U.S. DOE’s program for long-term storage. Based on this comparison, a specific aging management program for the silo system was developed. Furthermore, the facility’s current practices—periodic checks of surface dose rate, contamination, weld integrity, leakage, surface and groundwater, cumulative dose, and concrete structure—were evaluated for their suitability in managing the silo system’s aging. Based on this review, several improvements were proposed.
CFD 코드를 활용한 CANDU 사용후핵연료 건식저장 사일로 열특성 예비 평가
이태강,정재준,김용덕,나태형 한국에너지학회 2023 에너지공학 Vol.32 No.1
본 연구에서는 상용 CFD 코드인 ANSYS FLUENT를 이용해 CANDU 원전 사용후핵연료 건식저장 사일로 시설에 대한 최적 열특성 해석모델을 개발하고, 예비 평가를 수행하였다. 사일로 시설은 CANDU 사용후핵연료 의 중간저장시설로 핵연료봉 다발을 저장하는 바스켓과 이를 감싸고 있는 라이너와 사일로로 구성되어 있다. 사 일로 해석에 앞서 저장 바스켓의 열전달 특성을 평가하였다. 평가 결과, 바스켓에서는 복사, 대류, 전도 순으로 열전달 영향력이 컸다. 복잡한 내부형상을 가진 사일로의 효율적인 계산을 위해 먼저 핵연료봉 다발 저장 바스 켓을 대치하기 위한 등가 열전도체 모델을 개발하였다. 이후 개발된 등가 열전도체 모델을 적용하고, 시설의 형 상을 최대한 반영하여 사일로 시설 전체 열해석 모델을 개발하였다. 도출된 모델을 이용하여 예비 평가를 수행 하고 이전 보수적인 해석연구과 비교하였다. 그 결과, 최대 피복재 온도는 보수적 해석결과보다 약 25.7℃ 낮게 평가되었다.