• 한국지진공학회논문집
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• 제25권5호
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• pp.223-232
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• 2021

The spatial variation characteristics of seismic motions at the nuclear power plant's site and structures were analyzed using earthquake records obtained at the Fukushima nuclear power plant during the Great East Japan Earthquake. The ground responses amplified as they approached the soil surface from the lower rock surface, and the amplification occurred intensively at about 50 m near the ground. Due to the soil layer's nonlinear characteristics caused by the strong seismic motion, the ground's natural frequency derived from the response spectrum ratio appeared to be smaller than that calculated from the shear wave velocity profile. The spatial variation of the peak ground acceleration at the ground surface of the power plant site showed a significant difference of about 0.6 g at the maximum. As a result of comparing the response spectrums at the basement of the structure with the design response spectrum, there was a large variability by each power plant unit. The difference was more significant in the Fukushima Daiichi site record, which showed larger peak ground acceleration at the surface. The earthquake motions input to the basement of the structure amplified according to the structure's height. The natural frequency obtained from the recorded results was lower than that indicated in the previous research. Also, the floor response spectrum change according to the location at the same height was investigated. The vertical response on the foundation surface showed a significant difference in spectral acceleration depending on the location. The amplified response in the structure showed a different variability depending on the type of structure and the target frequency.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4066-4076
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• 2023

Pressure resistance welding is usually used to seal the connection between the cladding tube and the end plug made of zirconium alloy. The seal welded joint has a direct effect on the service performance of the fuel rod cladding structure. In this paper, the pressure resistance welded joints of zirconium alloy tube-plug structure were obtained by thermal-mechanical simulation experiments. The microstructure and microhardness of the joints were both analyzed. The effect of processing parameters on the microstructure was studied in detail. The results showed that there was no β-Zr phase observed in the joint, and no obvious element segregation. There were different types of Widmanstätten structure in the thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) of the cladding tube and the end plug joint because of the low cooling rate. Some part of the grains in the joint grew up due to overheating. Its size was about 2.8 times that of the base metal grains. Due to the high dislocation density and texture evolution, the microhardnesses of TMAZ and HAZ were both significantly higher than that of the base metal, and the microhardness of the TMAZ was the highest. With the increasing of welding temperature, the proportion of recrystallization in TMAZ decreased, which was caused by the increasing of strain rate and dislocation annihilation.

• Nuclear Engineering and Technology
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• 제54권4호
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• pp.1355-1362
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• 2022

Nuclear fuel, including its fresh state, must be handled safely due to its critical and hazardous nature. Under normal transport conditions, several interactions take place among different components, such as transport cask used for loading the nuclear fuel and tie-down structure to attach with the vehicle. To ensure structural integrity of the nuclear fuel, vibrations and impacts transmitted from the vehicle must be sufficiently reduced. Therefore, in this study, we conducted two transportation tests from Daejeon to Kijang in Korea to verify the vehicle-induced vibrational characteristics of the KJRR-F fresh nuclear fuel when transported under normal transport conditions. The speed and location of the vehicle were obtained via GPS, and the accelerations between the vehicle and the KJRR-F fresh nuclear fuel were measured. Additionally, using the acceleration results, a structural analysis was conducted to confirm the structural integrity of the nuclear fuel under the most severe conditions during normal transport.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1556-1568
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• 2021

The plate-type fuel assembly adopted in nuclear research reactor suffers from complicated effect induced by non-uniform irradiation, which might affect stress conditions, mechanical behaviors and thermal-hydraulic performance of the fuel assembly. This paper is the Part II work of a two-part study devoted to analyzing the complex unique mechanical deformation and thermal-hydraulic characteristics for the typical plate-type fuel assembly under irradiation effect, which is on the basis of developed and verified numerical thermal-fluid-structure coupling methodology under irradiation in Part I of this work. The mechanical deformation, thermal-hydraulic performance and Mises stress have been analyzed for the typical plate-type fuel assembly consisting of support plates under non-uniform irradiation. It was interesting to observe that: the plate-type fuel assembly including the fuel plates and support plates tended to bend towards the location with maximum fission rate; the hot spots in the fuel foil appeared at the location with maximum thickness increment; the maximum Mises stress of fuel foil was located at the adjacent location with the maximum plate thickness increment et al.

• Nuclear Engineering and Technology
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• 제45권7호
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• pp.951-960
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• 2013

Energy group structure has a significant effect on the results of multigroup transport calculations. It is known that $UO_2-PuO_2$ (MOX) is a recently developed fuel which consumes recycled plutonium. For such fuel which contains various resonant nuclides, the selection of energy group structure is more crucial comparing to the $UO_2$ fuels. In this paper, in order to improve the accuracy of the integral results in MOX thermal lattices calculated by WIMSD-5B code, a swarm intelligence method is employed to optimize the energy group structure of WIMS library. In this process, the NJOY code system is used to generate the 69 group cross sections of WIMS code for the specified energy structure. In addition, the multiplication factor and spectral indices are compared against the results of continuous energy MCNP-4C code for evaluating the energy group structure. Calculations performed in four different types of $H_2O$ moderated $UO_2-PuO_2$ (MOX) lattices show that the optimized energy structure obtains more accurate results in comparison with the WIMS original structure.

• Nuclear Engineering and Technology
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• 제41권8호
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• pp.1109-1114
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• 2009

The evolution of a high burnup structure (HBS) in a light water reactor (LWR) $UO_2$ fuel was simulated using the Potts model. A simulation system for the Potts model was defined as a two-dimensional triangular lattice, for which the stored energy was calculated from both the irradiation damage of the $UO_2$ matrix and the formation of a grain boundary in the newly recrystallized small HBS grains. In the simulation, the evolution probability of the HBS is calculated by the system energy difference between before and after the Monte Carlo simulation step. The simulated local threshold burnup for the HBS formation was 62 MWd/kgU, consistent with the observed threshold burnup range of 60-80 MWd/kgU. The simulation revealed that the HBS was heterogeneously nucleated on the intergranular bubbles in the proximity of the threshold burnup and then additionally on the intragranular bubbles for a burnup above 86 MWd/kgU. In addition, the simulation carried out under a condition of no bubbles indicated that the bubbles played an important role in lowering the threshold burnup for the HBS formation, thereby enabling the HBS to be observed in the burnup range of conventional high burnup fuels.

• Bulletin of the Korean Chemical Society
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• 제32권7호
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• pp.2358-2368
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• 2011

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations, employing the B3LYP method and the LANL2DZ, 6-31G$^*$(LANL2DZ for Tc), 6-31G$^*$(cc-pVDZ-pp for Tc) and DGDZVP basis sets, have been performed to investigate the electronic structures and absorption spectra of the technetium-99m-labeled methylenediphosphonate ($^{99m}Tc$-MDP) complex of the simplest diphosphonate ligand. The bonding situations and natural bond orbital compositions were studied by the Mulliken population analysis (MPA) and natural bond orbital (NBO) analysis. The results indicate that the ${\sigma}$ and ${\pi}$ contributions to the Tc-O bonds are strongly polarized towards the oxygen atoms and the ionic contribution to the Tc-O bonding is larger than the covalent contribution. The electronic transitions investigated by TDDFT calculations and molecular orbital analyses show that the origin of all absorption bands is ascribed to the ligand-to-metal charge transfer (LMCT) character. The solvent effect on the electronic structures and absorption spectra has also been studied by performing DFT and TDDFT calculations at the B3LYP/6-31G$^*$(cc-pVDZ-pp for Tc) level with the integral equation formalism polarized continuum model (IEFPCM) in different media. It is found that the absorption spectra display blue shift in different extents with the increase of solvent polarity.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1390-1397
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• 2019

SiC coating and SiC/glassy carbon composite coating were prepared on IG-110 nuclear graphite (Toyo Tanso Co., Ltd., Japan) to strengthen its inertness to molten fluoride salt used in molten salt reactor (MSR). Two kinds of modified graphite were obtained and correspondingly named as IG-110-1 and IG-110-2, which referred to modified IG-110 with a single SiC coating and a SiC/glassy carbon composite coating, respectively. Both structure and property of modified graphite were carefully researched and contrasted with virgin IG-110. Results indicated that modified graphite presented better comprehensive properties such as more compact structure and higher resistance to molten salt infiltration. With the protection of coatings, the infiltration amounts of fluoride salt into modified graphite were much less than that into virgin IG-110 at the same circumstance. Especially, the infiltration amount of fluoride salt into IG-110-2 under 5 atm was merely 0.26 wt%, which was much less than that into virgin IG-110 under 1.5 atm (13.5 wt%) and the critical index proposed for nuclear graphite used in MSR (0.5 wt%). The SiC/glassy carbon composite coating gave rise to highest resistance to molten salt infiltration into IG-110-2, and thus demonstrated it could be a promising protective coating for nuclear graphite used in MSR.

• 한국전산구조공학회논문집
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• 제24권3호
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• pp.343-351
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• 2011

원자로 격납건물은 원자력발전소에서 발생가능한 모든 비상사태에 대한 최후의 방벽 역할을 하고 있다. 따라서 사고발생시 원자로 격납건물의 극한능력을 판단하는 것은 매우 중요하다. 대표적인 고려사항 가운데 하나인 LOCA사고 발생시 CANDU형 원자로 격납건물의 극한능력을 파악하기 위해서는 구조적 안전성 평가를 위한 구조해석이 필요하다. CANDU형 원자로 격납건물은 돔과 원통형벽체로 구성된 프리스트레스 콘크리트 쉘 구조물로서 부착식 텐돈을 사용하고 있다. 본 논문에서는 극한내압능력의 평가를 위하여 3차원 구조해석시스템을 사용한 프리스트레스 콘크리트 격납건물의 비선형해석을 수행하였다.

• 방사성폐기물학회지
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• 제7권1호
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• pp.49-62
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• 2009

사용후핵 연료 관리 정책 결정 에 있어 사회적 수용성은 중요한 의미를 갖는다. 본고에서는 그 역동적 과정을 담아낼 그릇으로서 공론장을 제안한다. 즉, 사용후핵 연료 관리 정책에 대한 공론장은 무엇이고, 공론장의 주체인 이해관계자들은 누구이며 또 공론장에 내재된 갈등구조는 어떠한지에 대해 살펴보고, 바람직한 공론장의 조건에 대해 논의한다. 공론장은 다양한 이해관계자와 시민이 스스로의 의지를 바탕으로 정책의 결정과정에 영향을 미칠 수 있는 기제와 제도를 의미한다. 현실성 있고 효과적인 공론장을 구축하고 운영하기 위해서는 사용후핵 연료 관리를 둘러싼, 정치, 외교안보, 경제, 사회문화, 법과 제도에 관한 면밀한 분석과 대응방안 마련이 필요하다.