• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1887-1892
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• 2021

The effect of gadolinium and boron on the texture development and magnetic properties of the texture controlled 23Cr-10NiCu duplex stainless steels were studied to develop a high performance neutron and electromagnetic shielding material. The 23Cr-10NiCu base alloy is composed of 60% of austenite and 40% of ferrite, whereas, the 23Cr-10NiCu-0.5Gd-0.8B modified alloy is composed of 66% of austenite, 27% of ferrite and 7% of CrFeB intermetallic compounds. The gadolinium and boron addition to the 23Cr-10NiCu base alloy increased mechanical properties. Microstructure observation showed that the small addition of 0.5 wt% gadolinium and 0.8 wt% boron to the alloy retarded to form texture at the same hot rolling conditions, and improved the maximum magnetism, residual magnetism and coercive force about 3%, 122% and 120%, respectively.

• Fisheries and Aquatic Sciences
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• 제18권3호
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• pp.283-286
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• 2015

This is the first report of Pterygotrigla multiocellata from the family Triglidae, collected in Korea. The specimen (314 mm in standard length) was caught in a gill net in the coastal waters of Jeju Island on 11 February 2010. This species is characterized by the following morphological traits: head large and triangular, bony plates absent along the base of the second dorsal fin, antrorse rostral spine long, and cleithral spine long. We suggest a new Korean name, "Gin-ppul-mit-seong-dae" for P. multiocellata.

• The korean journal of orthodontics
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• 제37권3호
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• pp.231-240
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• 2007

Objective: The purpose of this study was to investigate the maxillary protraction effects of the Tandem Traction Bow Appliance (TTBA), a new appliance devised several years ago for the treatment of growing skeletal Class III patients. Methods: Participants were 88 Korean children (42 boys, 46 girls) with skeletal Class III malocclusion treated with TTBA at the orthodontic clinic of Ewha Womans University Mokdong Hospital. Mean age at the start of treatment was 7.5 years${\pm}$1.5 years. Mean treatment periods were $13{\pm}3$ months. Pretreatment and posttreatment lateral cephalograms were traced and superimposed by the same investigator and analyzed by modified McNamara analysis and pitchfork analysis. Changes were evaluated with paired t-tests at a significance level of p<0.05. Results: The maxilla and maxillary dentition moved forward. The mandible moved backward, although not significantly; and the mandibular dentition moved forward. The net dental changes combined with the apical base change resulted in a favorable total molar relationship correction. Net dental movement was 26% and the apical base change 74% of the total molar relationship correction. Conclusion: These results suggest that TTBA has a maxillary protraction effect that can be useful in the treatment of growing skeletal Class III malocclusion with maxillary deficiency.

• Nuclear Engineering and Technology
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• 제41권1호
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• pp.107-112
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• 2009

Corrosion of nickel-base alloys (Hastelloy C-276, Inconel 625, and Inconel X-750) in $500^{\circ}C$, 25MPa supercritical water (with 10 wppb oxygen) was investigated to evaluate the suitability of these alloys for use in supercritical water reactors. Oxide scales formed on the samples were characterized by gravimetry, scanning electron microscopy/energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results indicate that, during the 1000h exposure, a dense spinel oxide layer, mainly consisting of a fine Cr-rich inner layer ($NiCr_{2}O_{4}$) underneath a coarse Fe-rich outer layer ($NiFe_{2}O_{4}$), developed on each alloy. Besides general corrosion, nodular corrosion occurred on alloy 625 possibly resulting from local attack of ${\gamma}$" clusters in the matrix. The mass gains for all alloys were small, while alloy X -750 exhibited the highest oxidation rate, probably due to the absence of Mo.

• Nuclear Engineering and Technology
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• 제46권5호
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• pp.699-706
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• 2014

The probabilistic seismic performance of a standard Korean nuclear power plant (NPP) with an idealized isolation is investigated in the present work. A probabilistic seismic hazard analysis (PSHA) of the Wolsong site on the Korean peninsula is performed by considering peak ground acceleration (PGA) as an earthquake intensity measure. A procedure is reported on the categorization and selection of two sets of ground motions of the Tohoku earthquake, i.e. long-period and common as Set A and Set B respectively, for the nonlinear time history response analysis of the base-isolated NPP. Limit state values as multiples of the displacement responses of the NPP base isolation are considered for the fragility estimation. The seismic risk of the NPP is further assessed by incorporation of the rate of frequency exceedance and conditional failure probability curves. Furthermore, this framework attempts to show the unacceptable performance of the isolated NPP in terms of the probabilistic distribution and annual probability of limit states. The comparative results for long and common ground motions are discussed to contribute to the future safety of nuclear facilities against drastic events like Tohoku.

• Nuclear Engineering and Technology
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• 제47권1호
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• pp.102-114
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• 2015

Background: A technique developed to produce artificial intergranular stress corrosion cracks in structural components was applied to thick, forged alloy 600 base and alloy 182 weld metals for use in the qualification of nondestructive examination techniques for welded components in nuclear power plants. Methods: An externally controlled procedure was demonstrated to produce intergranular stress corrosion cracks that are comparable to service-induced cracks in both the base and weld metals. During the process of crack generation, an online direct current potential drop method using array probes was used to measure and monitor the sizes and shapes of the cracks. Results: A microstructural characterization of the produced cracks revealed realistic conformation of the crack faces unlike those in machined notches produced by an electrodischarge machine or simple fatigue loading using a universal testing machine. Conclusion: A comparison with a destructive metallographic examination showed that the characteristics, orientations, and sizes of the intergranular cracks produced in this study are highly reproducible.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.825-837
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• 2017

Due to the severe impacts of recent earthquakes, the use of seismic isolation is paramount for the safety of nuclear structures. The diversity observed in seismic events demands ongoing research to analyze the devastating attributes involved, and hence to enhance the sustainability of base-isolated nuclear power plants. This study reports the seismic performance of a seismically-isolated nuclear reactor containment building (NRCB) under strong short-period ground motions (SPGMs) and long-period ground motions (LPGMs). The United States Nuclear Regulatory Commission-based design response spectrum for the seismic design of nuclear power plants is stipulated as the reference spectrum for ground motion selection. Within the period range(s) of interest, the spectral matching of selected records with the target spectrum is ensured using the spectral-compatibility approach. NRC-compliant SPGMs and LPGMs from the mega-thrust Tohoku earthquake are used to obtain the structural response of the base-isolated NRCB. To account for the lack of earthquakes in low-to-moderate seismicity zones and the gap in the artificial synthesis of long-period records, wavelet-decomposition based autoregressive moving average modeling for artificial generation of real ground motions is performed. Based on analysis results from real and simulated SPGMs versus LPGMs, the performance of NRCBs is discussed with suggestions for future research and seismic provisions.

• Nuclear Engineering and Technology
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• 제50권8호
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• pp.1387-1401
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• 2018

An aircraft impact (AI) on a nuclear power plant (NPP) is considered to be a beyond-design-basis event that draws considerable attention in the nuclear field. As some NPPs have already adopted the seismic isolation technology, and there are relevant standards to guide the application of this technology in future NPPs, a new challenge is that nuclear power engineers have to determine a reasonable method for performing AI analysis of base-isolated NPPs. Hence, dynamic influences of the seismic isolation on the vibration and structural damage characteristics of the base-isolated CPR1000 containment are studied under various aircraft loads. Unlike the seismic case, the impact energy of AI is directly impacting on the superstructure. Under the coupled influence of the seismic isolation and the various AI load, the flexible isolation layer weakens the constraint function of the foundation on the superstructure, the results show that the seismic isolation bearings will produce a large horizontal deformation if the AI load is large enough, the acceleration response at the base-mat will also be significantly affected by the different horizontal stiffness of the isolation bearing. These concerns require consideration during the design of the seismic isolation system.

• Nuclear Engineering and Technology
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• 제53권1호
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• pp.304-313
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• 2021

Nickel base Alloy X-750, which is used as fastener parts in light-water reactor (LWR), has experienced many failures by environmentally assisted cracking (EAC). In order to improve the reliability of passive components for nuclear power plants (NPP's), it is necessary to study the failure mechanism and to predict crack growth behavior by developing a probabilistic failure model. In this study, The Bayesian inference was employed to reduce the uncertainties contained in EAC modeling parameters that have been established from experiments with Alloy X-750. Corrosion fatigue crack growth rate model (FCGR) was developed by fitting into Paris' Law of measured data from the several fatigue tests conducted either in constant load or constant ΔK mode. These parameters characterizing the corrosion fatigue crack growth behavior of X-750 were successfully updated to reduce the uncertainty in the model by using the Bayesian inference method. It is demonstrated that probabilistic failure models for passive components can be developed by updating a laboratory model with field-inspection data, when crack growth rates (CGRs) are low and multiple inspections can be made prior to the component failure.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1269-1279
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• 2023

Pool boiling experiments are performed within an isolated bubble regime at inclination angles of 0° and 45°. When a bubble grows and departs from the heating surface, the pressure, buoyancy, and surface tension force play important roles. The curvature and base diameter are required to calculate the pressure force, the bubble volume is required to calculate the buoyancy force, and the contact angle and base diameter are required to calculate the surface tension force. The contact angle, base diameter, and volume of the bubbles are evaluated using images captured via a high-speed camera. The surface tension force equation proposed by Fritz is modified with the contact angles obtained in this study. When the bubble grows, the contact angle decreases slowly. However, when the bubble departs, the contact angle rapidly increases owing to necking. At an inclination angle of 0°, the contact angle is calculated as 82.88° at departure. Additionally, the advancing and receding contact angles are calculated as 70.25° and 82.28° at departure, respectively, at an inclination angle of 45°. The dynamic behaviors of bubble growth and departure are discussed with forces by pressure, buoyancy, and surface tension.