• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2005.10a
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• pp.283-288
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• 2005

Application of semiconductor sensors has widely spreaded into various industries because those have several merits like easy miniaturization and batch production comparison with previous mechanical sensors. But external conditions such as thermal and repetitive load have a bad effect on sensors's lifetime. Especially, this paper was focused on fatigue life of a interconnect made by various materials. Firstly we implemented the stress analysis for interconnect under thermal load and wording pressure. And the fatigue lifetime of each material was induced by Manson & Coffin Equation using the plastic stress-strain curve obtained by the plastic-elastic Finite Element Analysis.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.126-131
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• 2010

The purpose of this study is to assess the condition of composites used in aircraft under varying temperature environment with ultrasound guided wave technique. Investigation of crucial influential factor on the composite health monitoring related to aircraft operational environments such as the number of thermal cycles and temperature deviation between ground level and flight altitude has been of a great concern for aircraft safety issue. In this study, ultrasonic guided wave health monitoring scheme is proposed to evaluate composite specimens damaged with the thermal fatigue simulating aircraft operational condition. Guided wave dispersion curves are used to select right modes which show a promising sensitivity to each different thermal fatigue damage level. The present approach can be also implemented as one of on-lines health monitoring tools for aircraft.

• Nuclear Engineering and Technology
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• v.22 no.1
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• pp.12-19
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• 1990

The Loss of Offsite Power Transient at 77.5% power which occurred on June 9, 1981 at the Kori Unit 1 PWR (Pressurized Water Reactor) is simulated using the RELAP5/MOD2 system thermal-hydraulics computer code. Major thermal-hydraulic parameters are compared with the available plant data. The comparison of the analysis results with the plant data demonstrates that the RELAP5/MOD2 code has the capability to simulate the thermal-hydraulic behaviour of PWRs under accident conditions of this type with accuracy, except the pressurizer pressure and level. The pressurizer pressure increase is sensitive to the in surge now it is believed that the interracial heat transfer in a horizontal stratified flow regime may be estimated low and the compression effect due to insurge flow may be high. In the nodalization sensitivity study it is found that S/G noding with junctions between bypass plenum and steam dome is preferred to simulate the S/G water level decreasing and avoid the spurious level peak at trubine trip.

• Nuclear Engineering and Technology
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• v.22 no.1
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• pp.66-74
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• 1990

The thermal-hydraulic characteristics of the 17$\times$17 OFA (Optimized Fuel Assembly) used in the KNU 7&8 are analyzed and compared with that of the 17$\times$17 SFA (Standard Fuel Assembly) loaded in the KNU 5&6. The thermal-hydraulic characteristics analyzed are minimum DNBR, fuel centerline temperature and exit void fraction at normal operation and design over power transient. Additionally, local linear rod power, which will cause fuel centerline melting, is calculated. The DNBR sensitivity calculations are performed with respect to the reactor operating parameters. COBRA-IV-I code is used for these calculations. The modified W-3 correltion and the drift-flux model are applied for the critical heat flux calculation and the void fraction calculation, respectively. From the calculated results, it has been found that the possibility of DNB occurrence is higher in the OFA than in the SFA. The other hand, the local linear power resulting in fuel centerline moiling of the OFA is nearly equal to that of the SFA.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.3
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• pp.89-99
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• 2019

The project to utilize kenaf as thermal power plant fuel has a positive effect on the unused energy utilization, greenhouse gas reduction, and farm income. However, it is analyzed that it is difficult to secure economical efficiency because the fuel cost of kenaf is higher than that of power by thermal power plant and Renewable Energy Certification (REC). The project of power generation using kenaf is meet the government's major policies, while government support is essential for securing economical efficiency. As a result of the sensitivity analysis on the ratio of the government subsidies, to secure economical efficiency, the power generation prices using kenaf through the direct financial support of the government indicate that 47% and 76% of kenaf fuel cost are supported by government in case of the Saemangeum reclamation and Gangneung-si, respectively. In the case of the government indirect policy support, if kenaf is included as a renewable energy source of Renewable Energy Portfolio Standard and REC is granted, the economic efficiency of Saemangeum reclamation and Gangneung-si is obtained when REC secured at 1.05 or more and 2.43 or more, respectively. The results of this study are meaningful in that the direct and indirect effects of the government on the development of the herbaceous energy crop, kenaf, were evaluated economically. These results are to suggest the need for demonstration study, but economics analyze and evaluate are necessary based on operational data through the demonstration phase in the future.

• Nuclear Engineering and Technology
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• v.50 no.7
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• pp.1138-1147
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• 2018

Delayed hydride cracking (DHC) is an important failure mechanism for Zircaloy tubes in the demanding environment of nuclear reactors. The threshold stress intensity factor, $K_{IH}$, and critical hydride length, $l_C$, are important parameters to evaluate DHC. Theoretical models of them are developed for Zircaloy tubes undergoing non-homogenous temperature loading, with new stress distributions ahead of the crack tip and thermal stresses involved. A new stress distribution in the plastic zone ahead of the crack tip is proposed according to the fracture mechanics theory of second-order estimate of plastic zone size. The developed models with fewer fitting parameters are validated with the experimental results for $K_{IH}$ and $l_C$. The research results for radial cracking cases indicate that a better agreement for $K_{IH}$ can be achieved; the negative axial thermal stresses can lessen $K_{IH}$ and enlarge the critical hydride length, so its effect should be considered in the safety evaluation and constraint design for fuel rods; the critical hydride length $l_C$ changes slightly in a certain range of stress intensity factors, which interprets the phenomenon that the DHC velocity varies slowly in the steady crack growth stage. Besides, the sensitivity analysis of model parameters demonstrates that an increase in yield strength of zircaloy will result in a decrease in the critical hydride length $l_C$, and $K_{IH}$ will firstly decrease and then have a trend to increase with the yield strength of Zircaloy; higher fracture strength of hydrided zircaloy will lead to very high values of threshold stress intensity factor and critical hydride length at higher temperatures, which might be the main mechanism of crack arrest for some Zircaloy materials.

• Nuclear Engineering and Technology
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• v.56 no.2
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• pp.575-600
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• 2024

During an earthquake on December 29th 2020, the Krško NPP automatically shutdown due to the trigger of the negative neutron flux rate signal on the power range nuclear instrumentation. From the time course of the detector signal, it can be concluded that the fluctuation in the detector signal may have been caused by the mechanical movement of the ex-core neutron detectors or the pressure vessel components rather than the actual change in reactor power. The objective of the analysis was to evaluate the sensitivity of the neutron flux at the ex-core detector position, if the detector is moved in the radial or axial direction. In addition, the effect of the core barrel movement and core inside the baffle movement in the radial direction were analysed. The analysis is complemented by the calculation of the thermal and total neutron flux gradient in radial, axial and azimuthal directions. The Monte Carlo particle transport code MCNP was used to study the changes in the response of the ex-core detector for the above-mentioned scenarios. Power and intermediate-range detectors were analysed separately, because they are designed differently, positioned at different locations, and have different response characteristics. It was found that the movement of the power range ex-core detector has a negligible effect on the value of the thermal neutron flux in the active part of the detector. However, the radial movement of the intermediate-range detector by 5 cm results in 7%-8% change in the thermal neutron flux in the active part of the intermediate-range detector. The analysis continued with an evaluation of the effects of moving the entire core barrel on the ex-core detector response. It was estimated that the 2 mm core barrel radial oscillation results in ~4% deviation in the power and intermediate-range detector signal. The movement of the reactor core inside baffle can contribute ~6% deviation in the ex-core neutron detector signal. The analysis showed that the mechanical movement of ex-core neutron detectors cannot explain the fluctuations in the ex-core detector signal. However, combined core barrel and reactor core inside baffle oscillations could be a probable reason for the observed fluctuations in the ex-core detector signal during an earthquake.

• Economic and Environmental Geology
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• v.49 no.6
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• pp.459-467
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• 2016

Due to the limited areal space for installation, borehole heat exchangers (BHEs) at depths deeper than 300 m are considered for geothermal heating and cooling in the urban area. The deep vertical closed-loop BHEs are unconventional due to the depth and the range of the typical installation depth is between 100 and 200 m in Korea. The BHE in the study consists of 50A (outer diameter 50 mm, SDR 11) PE U-tube pipe in a 150 mm diameter borehole with the depth of 300 m. In order to compensate the buoyancy caused by the low density of PE pipe ($0.94{\sim}0.96g/cm^3$) in the borehole filled with ground water, 10 weight band sets (4.6 kg/set) were attached to the bottom of U-tube. A thermal response test (TRT) and fundamental basic surveys on the thermophysical characteristics of the ground were conducted. Ground temperature measures around $15^{\circ}C$ from the surface to 100 m, and the geothermal gradient represents $1.9^{\circ}C/100m$ below 100 m. The TRT was conducted for 48 hours with 17.5 kW heat injection, 28.65 l/min at a circulation fluid flow rate indicates an average temperature difference $8.9^{\circ}C$ between inlet and outlet circulation fluid. The estimated thermophysical parameters are 3.0 W/mk of ground thermal conductivity and 0.104 mk/W of borehole thermal resistance. In the stepwise evaluation of TRT, the ground thermal conductivity was calculated at the standard deviation of 0.16 after the initial 13 hours. The sensitivity analysis on the borehole thermal resistance was also conducted with respect to the PE pipe diameter and the thermal conductivity of backfill material. The borehole thermal resistivity slightly decreased with the increase of the two parameters.

• Journal of the Korean Vacuum Society
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• v.10 no.3
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• pp.289-297
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• 2001

Highly-porous $SnO_2$thin films were prepared for recognizing and detecting of the inflammable gases, like butane, propane, LPG, carbon monoxide. To obtain sensing films, Sn, Pt/Sn, Au/Sn, and Pt,Au/Sn films were deposited employing a thermal evaporator for Sn film and a sputter for novel metals of Pt or/and Au. These films were annealed for 2 h at $700^{\circ}C$ to form $SnO_2$-based thin films. The films showed the tetragonal structure and also exhibited many defects and porosity, which could give high sensitivity to thin films. The thin films showed high sensitivity and reproductivity to the tested gases(butane, propane, LPG, and carbon monoxide) to even to low gas concentrations in range of workplace environmental standards. Especially, Pt/$SnO_2$film showed the highest sensitivity to butane, LPG, and carbon monoxide. And pure $SnO_2$ film manifested the highest sensitivity to propane. By using the sensing patterns from the films, we could reliably recognize the kinds and the quantities of the tested inflammable gases within the range of the threshold limit values(TLV) and the lower explosion limit(LEL) through the principal component analysis(PCA).

• Tunnel and Underground Space
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• v.19 no.3
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• pp.203-212
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• 2009

The prediction of near field behavior around an underground high-level radioactive waste repository is important for the repository design as well as the safety assessment. In this study, a sensitivity analysis for seven parameters consisted of design parameters and material properties was carried out using a three-dimensional finite difference code. From the sensitivity analysis, it was found that the effects of borehole spacing, tunnel spacing, cooling time and rock thermal conductivity were more significant than the other parameters. For getting a statistical distribution of buffer and rock temperatures around the repository, an artificial neural network, backpropagation, was applied. The reliability of the trained neural network was tested with the cases with randomly chosen input parameters. When the parameter variation is within ${\pm}10%$, the prediction from the network was found to be reliable with about a 1% error. It was possible to calculate the temperature distribution for many cases quickly with the trained neural network. The buffer and rock temperatures showed a normal distribution with means of $98^{\circ}C$ and $83.9^{\circ}C$ standard deviations of $3.82^{\circ}C$ and $3.67^{\circ}C$, respectively. Using the neural network, it was also possible to estimate the required change in design parameters for reducing the buffer and rock temperatures for $1^{\circ}C$.