• Geomechanics and Engineering
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• v.38 no.5
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• pp.529-539
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• 2024

A high-level nuclear waste (HLW) repository is designed for the long-term disposal of high-level waste. Positioned at depths of 500-1000 meters, it offers an alternative to the insufficient storage space for spent fuels, providing a long-term solution. High-level waste emits heat and radiation, causing structural deterioration, including strength reduction and cracks. Therefore, the use of piezoelectric sensors for structural health monitoring is essential for evaluating the safety of the structure over time. Unlike other structures, the HLW repository restricts human access after the disposal of HLW, rendering sensor replacement impossible. Therefore, it is necessary to assess both the lifespan and suitability of sensors under the disposal conditions in the HLW repository. This study employed an accelerated life test (ALT) to assess the sensor's lifespan under disposal conditions. Failure modes, failure mechanisms, and operational limits were analyzed through accelerated stress test (AST). Additionally, the parameters of the Weibull life probability distribution and the Arrhenius accelerated life model were estimated through statistical methods, including the likelihood ratio test, maximum likelihood estimation, and hypothesis testing. Results confirmed that the sensor's lifespan decreases significantly with the increase in the temperature limit of the HLW repository. The findings of this study can be used for improving sensor lifespan through shielding, development of alternative sensors, or lifespan evaluation of alternative monitoring sensors.

• Corrosion Science and Technology
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• v.18 no.6
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• pp.267-276
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• 2019

The purpose of this study was to examine the influence of conditions for quenching and/or tempering on the corrosion and hydrogen diffusion behavior of ultra-strong automotive steel in terms of the localized plastic strain related to the dislocation density, and the precipitation of iron carbide. In this study, a range of analytical and experimental methods were deployed, such as field emission-scanning electron microscopy, electron back scatter diffraction, electrochemical permeation technique, slow-strain rate test (SSRT), and electrochemical polarization test. The results showed that the hydrogen diffusion parameters involving the diffusion kinetics and hydrogen solubility, obtained from the permeation experiment, could not be directly indicative of the resistance to hydrogen embrittlement (HE) occurring under the condition with low hydrogen concentration. The SSRT results showed that the partitioning process, leading to decrease in localized plastic strain and dislocation density in the sample, results in a high resistance to HE-induced by aqueous corrosion. Conversely, coarse iron carbide, precipitated during heat treatment, weakened the long-term corrosion resistance. This can also be a controlling factor for the development of ultra-strong steel with superior corrosion and HE resistance.

• Korean Journal of Biological Psychiatry
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• v.12 no.2
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• pp.136-142
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• 2005

Object:The intracellular action of the antidepressant, venlafaxine, was studied in C6-gliomas using heat shock protein 70(HSP70) immunocytochemistry and HSP70 Western blots because HSP70 is associated with stress and depression. Methods:To examine how the glucocorticoid affects the expression of HSP70 in nerve cells, the rat C6 glioma cell was treated with dexamethasone for 6 hours. In addition, venlafaxine was administered to the experimental groups of C6 glioma cells for 1, 6, 24, and 72 hours each, after which the expression of HSP70 was investigated. Finally, venlafaxine and dexamethasone were simultaneously administered to the experimental groups for 1, 6, 24, and 72 hours, followed by an investigation of the expression of HSP70. Results:The short term(1 hour) venlafaxine treatment significantly increased the level of HSP70 expression. The short term treatment of venlafaxine with dexamethasone also increased the level of HSP70 expression but this reduction was not statistically significant. The long term(72 hours) venlafaxine with dexamethasone treatment significantly reduced the level of HSP70 expression. The long term treatment of venlafaxine also reduced the level of HSP70 expression but this reduction was not statistically significant. Dexamethasone(10uM, 6hours) did not affect the level of HSP70 expression compared with controls. Conclusion:Venlafaxine increases the expression of HSP70 at short term treatment, but prolonged treatment with dexamethasone suppresses the expression of HSP70.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.4
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• pp.123-129
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• 1999

Although type 316 stainless steel is widely used such as in reactors of petrochemical plants and pipes of steam power plants and s attracting attention as potential basic material for the fast breeder reactor structure alloys in nuclear power plants and is attracting attention as potential basic material for the fast breeder reactor structure alloys in nuclear power plants the effect of precipitates which form during the long term exposure at service temperature on creep properties is not known sufficiently. In this study to investigate the creep properties and the influence of prior aging on the microstructure to form precipitates specimens were first solutionized at 113$0^{\circ}C$ for 20 minutes and then aged for different times of 0 hr, 100 hrs, 1000 hrs and 2200 hrs at 75$0^{\circ}C$ After heat treatments tensile tests both at room temperature and $650^{\circ}C$ and constant load creep ruptuere tests were carried out.

• Korean Journal of Ichthyology
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• v.18 no.2
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• pp.65-77
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• 2006

Gene transcripts potentially responsive to the heat stress were surveyed by cDNA microarray analysis in mud loach (Misgurnus mizolepis). Transcriptional profiles of hepatic tissue in the fish exposed to either $23^{\circ}C$ or $32^{\circ}C$ for 4 weeks were compared each other by 3 replicated hybridization assays using 1,124 unigene clones selected from mud loach liver expressed sequence tags (ESTs). A total of 93 clones showed the substantially increased mRNA levels (>2-fold) in $32^{\circ}C$-exposed group when compared in $23^{\circ}C$control group. It includes various enzymes and proteins involved in energy pathway, protease/protein metabolisms, immune/antioxidant functions, cytoskeleton/cell structure, transport and/or signal transduction. Maximum level of increase was up to 15-fold relative to $23^{\circ}C$ treatment. Heat exposure also resulted in the significant decrease (less than 50% relative to $23^{\circ}C$-exposed fish) of the transcriptional activities in 85 genes. Besides the above categories, yolk protein (vitellogenin) and ribosomal proteins were notably down regulated in the fish exposed to heat stress. A number of novel gene transcripts were also detected in both up-regulated and down-regulated groups.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.596-603
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• 2011

The very high temperature gas reactor (VHTR) is one of the next generation nuclear reactors for its safety, long-term stability, and proliferation-resistance. The high operating temperature of over 800$^{\circ}C$ enables various applications with high energy efficiency. Heat is transferred from the primary helium loop to the secondary helium loop through the intermediate heat exchanger (IHX). The IHX material requires creep resistance, oxidation resistance, and corrosion resistance in a helium environment at high operating temperatures. A Ni-based superalloy such as Alloy 617 is considered as a primary candidate material for the intermediate heat exchanger. In this study, the microstructures of Alloy 617 crept in pure helium and air environments at 950$^{\circ}C$ were observed. The rupture time in helium was shorter than that in air under small applied stresses. As the exposure time increased, the thickness of outer oxide layer of the specimens clearly increased but delaminated after a long creep time. The depth of the carbide-depleted zone was rather high in the specimens under high applied stress. The reason was elucidated by the comparison between the ruptured region and grip region of the samples. It is considered that decarburization caused by minor gas impurities in a helium environment caused the reduction in creep rupture time.

• Corrosion Science and Technology
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• v.10 no.4
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• pp.118-124
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• 2011

Alloy 600 (Ni 75 wt%, Cr 15 wt%, Fe 10 wt%) as a heat exchanger tube of the steam generator (SG) in nuclear power plants (NPP) has been degraded by various corrosion mechanism during the long-term operation. Especially lead (Pb) is known to be one of the most deleterious species in the secondary system causing outer diameter stress corrosion cracking (ODSCC). Oxide formation and breakdown is requisite for SCC initiation and propagation. Therefore it is expected that a property change of the oxide formed on SG tubing materials by lead addition into a solution is closely related to PbSCC. In the present work, the SCC susceptibility was assessed by using a slow strain rate test (SSRT) in caustic solutions with and without lead for Alloy 600 and Alloy 690 (Ni 60 wt%, Cr 30 wt%, Fe 10 wt%) used as an alternative of Alloy 600 because of outstanding superiority to SCC. The results were discussed in view of the oxide property formed on Alloy 600 and Alloy 690. The oxides formed on Alloy 600 and Alloy 690 in aqueous solutions with and without lead were examined by using a transmission electron microscopy (TEM), equipped with an energy dispersive x-ray spectroscopy (EDXS).

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.521-528
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• 2004

In general, polymer concrete has more excellent mechanical properties and durability than Portland cement concrete, but very sensitive to heat and has large deformations. In this study, the long-term creep behaviors was predicted by the short-term creep test, and then the characteristic of creep of recycled-PET polymer concrete was defined by material and experimental variables. The error in the predicted long-term creep values is less than 5 percent for all polymer concrete systems. The filler carry out an important role to restrict the creep strains of recycled PET Polymer concrete. The creep strain and specific on using the $CaCO_3$ were less than using fly-ash. The creep increases with an increase in the applied stress, but not proportional the rate of stress increase ratio. The creep behavior of polymer concrete using recycled polyester resin is not a linear viscoelastic behavior.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.471-480
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• 2002

In this paper, the thermal stress analysis of spent nuclear fuel disposal canister in a deep repository at 500 m underground is carried out for the basic design of the canister. Since the nuclear fuel disposal usually emits much heat, a long term safe repository at a deep bedrock is used. Under this situation, the canister experiences the thermal load due to the heat generation of spent nuclear fuels in the basket. Hence, in this paper the thermal stress analysis is executed using the finite element method. The finite clement code Eot the analysis Is not written directly, but a commercial code, NISA, is used because of the complexity of the structure and the large number of elements required for the analysis. The analysis result shows that even though the thermal stress is added to the stress generated by the hydrostatic underground water pressure and the swelling pressure of the bentonite buffer, the total stress is still smaller than the yield stress of the cast iron. Hence, the canister is still structurally safe when the thermal loads we included in the external loads applied on the canister.

• Applied Chemistry for Engineering
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• v.19 no.1
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• pp.86-91
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• 2008

The rubber was compounded with carbon black and silica series-filler to examine the effects of the various rubber fillers on a gasket material's suitability and fuel cell stack conclusion. The evaluation of a long term heat resistance and oil resistance of the mixed rubber material was performed considering at the drive environment of PEMFC. Test results of compression set for the most influencing property of gasket showed that it was about less than 15% at long term of up to 1000 h. In this experiment, FEM analysis is carried out about the rubber material's properties depending on each filler and the stress which is produced when a gasket is contracted by using various filler. Sealing force was expected to maximum 2.5 MPa from minimum 0.2 MPa by using FEM (finite element method) at stacking gasket to gasket.