• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2017년도 춘계 학술논문 발표대회
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• pp.26-27
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• 2017

In this study, the cracking characteristics of cured pastes at 800℃ were investigated by X-ray CT. The test specimens were fabricated with and without aggregate, and the heating rate condition was applied at rapid heating (10.0℃/min). It is considered that the rapid heating condition does not cause a temperature gradient phenomenon because the temperature difference between the surface and the center of the sample is small due to a low heating rate unlike an actual fire. The cracking condition of the specimens without aggregate was more severe than that of specimens with aggregate.

• 한국압력기기공학회 논문집
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• 제6권1호
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• pp.43-49
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• 2010

The piping failure probability of the reactor coolant system in Kori unit 1 was evaluated considering stress corrosion cracking. The P-PIE program (Probabilistic Piping Integrity Evaluation Program) developed in this study was used in the analysis. The effect of some variables such as oxygen concentration during start up and steady state operation, and operating temperature, which are related with stress corrosion cracking, on the piping failure probabilities was investigated. The effects of leak detection capability, the size of big leak, piping loops, and reactor types on the piping failure probability were also investigated. The results show that (1) LOCA (loss of coolant accident) probability of Kori unit 1 is extremely low, (2) leak probability is sensitive to oxygen concentration during steady state operation and operating temperature, while not sensitive to the oxygen concentration during start up, and (3) the piping thickness and operating temperature play important roles in the leak probabilities of the cold leg in 4 reactor types having same inner diameter.

• Computers and Concrete
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• 제26권5호
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• pp.429-438
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• 2020

To shorten the construction times of nuclear facility structures, three high-strength concrete mixtures were developed with specific consideration given to their curing temperatures, their economic efficiency, and the practicality of their quality control. This study was conducted to examine the temperature rise profiles of these three concrete mixtures and the potential for early-age thermal cracking in the primary containment vessel of a nuclear reactor with a wall thickness of 1200 mm. The one-layer placement height of the concrete for the primary containment vessel was increased from the conventional 3 m to 3.5 m. A nonlinear finite element analysis (FEA) was conducted using the thermal properties of concrete determined from the isothermal hydration and adiabatic hydration tests, and tuned through comparisons made with temperature rise profiles obtained for 1200-mm-thick mock-up wall specimens cured at temperatures of 5, 20, and 35℃. The hydration heat performance of the three concrete mixtures and their potential to produce thermal cracking in nuclear facilities indicate that the mixtures have considerable potential for practical application to the primary containment vessel of a nuclear reactor at various curing temperatures, fulfilling the minimum requirements of the ACI 301 and minimizing the likelihood of the occurrence of thermal cracks.

• Journal of Welding and Joining
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• 제22권5호
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• pp.65-72
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• 2004

The tendency and degree of hot cracking of high strength 5083, 6N01 and 7N01 Al alloy welds by using DCSP-GTAW through modified Varestraint test and autogenous butt welding were investigated. In hot cracking test, 6N01 alloy showed the highest susceptibility to hot cracking in the weld metal and HAZ. Cracking susceptibilities generally increased with increase of solidification temperature range of the base metal and bead penetration-to-width ratio of the weld metal. The cracks in welds of the alloys vertically formed to solid-liquid interface and propagated along with columnar grain boundaries. The fracture facets of cracks showed the typical morphology of solidification crack observed as dendritic structures. Especially, in 6N01 alloy, liquation cracks which were due to elements of Si, Fe and Mg also observed in HAZ near fusion boundary. In butt welding of different Al alloys, the bead crack was mainly occurred in the welds of 6N01, 7N01 and other Al alloys together with 6N01 or 7N01. In the butt welds of 7N01, it was found that the component of Cu had an effect on the higher susceptibility to the hot cracking.

• Nuclear Engineering and Technology
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• 제41권2호
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• pp.171-178
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• 2009

The rate of delayed hydride cracking (DHC), V, has been measured in cold-worked and stress-relieved Zircaloy-4 fuel cladding using the Pin-Loading Tension technique. At $250^{\circ}C$ the mean value of V from 69 specimens was $3.3({\pm}0.8)x10^{-8}$ m/s while the temperature dependence up to $275^{\circ}C$ was described by Aexp(-Q/RT), where Q is 48.3 kJ/mol. No cracking or cracking at very low rates was observed at higher temperatures. The fracture surface consisted of flat fracture with no striations. The results are compared with previous results on fuel cladding and pressure tubes.

• Corrosion Science and Technology
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• 제3권1호
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• pp.6-13
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• 2004

The effect of inhibitors on the electrochemical behavior and the stress corrosion cracking resistance of Alloy 600(UNS N06600) was evaluated in 10% sodium hydroxide solution at $315^{\circ}C$. The specimens of a C-ring type for stress corrosion cracking test were polarized at 150 mV above the corrosion potential for 120 hours with and without inhibitors such as titanium oxide, titanium boride and cerium boride. The chemical compositions of the films formed on the crack tip in the C-ring specimens were analyzed using a scanning Auger electron spectroscopy. The cerium boride, the most effective, was observed to decrease the crack propagation rate more than a factor of three compared with that obtained in no inhibitor solution. It was found that the changes of the active-passive transition potentials and the film compositions were related to the resistance to stress corrosion cracking in high temperature caustic solution.

• Tribology and Lubricants
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• 제11권5호
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• pp.172-176
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• 1995

This study deals with thermomechanical cracking between the friction surface and the interior of the brake disc. Analytical model considered in this study was a semi-infinite solid subjected to the thermal loading of an asperity moving with a high speed. The temperature field and the thermal stress state were obtained and discussed on the basis of Von Mises and Tresca Yielding Criterion. Analytical results showed that the dominant stress in cracking of friction brake is thermal stress and cracking location is dependent on the friction coefficient of contact and Peclet number. On the basis of analytical results thermomechanical cracking model is proposed.

• Corrosion Science and Technology
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• 제7권4호
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• pp.237-242
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• 2008

Physical properties of water, such as dielectric constant and ionic product, significantly vary with the density of water. In the supercritical conditions, since density of water widely varies with pressure, pressure has a strong influence on physical properties of water. Dielectric constant represents a character of water as a solvent, which determines solubility of an inorganic compound including metal oxides. Dissociation equilibrium of an acid is also strongly dependent on water density. Dissociation constant of acid rises with increased density of water, resulting in drop of pH. Density of water and the density-related physical properties of water, therefore, are the major governing factors of corrosion and environmentally assisted cracking of metals in supercritical aqueous solutions. This paper discusses importance of "physical properties of water" in understanding corrosion and cracking behavior of alloys in supercritical water environments, based on experimental data and estimated solubility of metal oxides. It has been pointed out that the water density can have significant effects on stress corrosion cracking (SCC) susceptibility of metals in supercritical water, when dissolution of metal plays the key role in the cracking phenomena.

• Corrosion Science and Technology
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• 제22권4호
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• pp.265-272
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• 2023

The aim of this study was to develop a new in-situ observation method and instrument in micro-scale to investigate the mechanism of stress corrosion cracking (SCC) initiation of Ni-base alloys in a high temperature water environment of pressurized water reactors (PWRs). A laser confocal microscope (LCM), an autoclave with diamond window view port, and a slow strain-rate tester with primary water circulation loop system were components of the instrument. Diamond window, one of the core components of the instrument, was selected based on its optical, chemical, and mechanical properties. LCM was used to observe the specimen in micro-scale, considering the experimental condition of a high-temperature primary water environment. Using in-situ method and instrument, it is possible to observe oxidation and deformation of specimen surface in micro-scale through the diamond window in a high-temperature primary water in real-time. The in-situ method and instrument developed in this work can be utilized to investigate effects of various factors on SCC initiation in a high-temperature water environment.

• 대한금속재료학회지
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• 제49권1호
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• pp.73-78
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• 2011

Weldability, especially HAZ cold cracking, weld metal solidification cracking, and HAZ liquation cracking susceptibilities, of ASTM A356 CA6NM martensitic stainless steel casting was investigated and compared with that of 9-12% Cr ferritic steel castings. Irrespective of the Cr and Ni content in the castings, the HAZ maximum hardness increased with an increase of carbon content. CA6NM steel, which has the lowest carbon content, had the lowest HAZ hardness and showed no cold cracking in y-slit cracking tests. CA6NM steel, meanwhile, showed the largest weld metal solidification cracking susceptibility in varestraint tests because of its higher amount of impurity elements, phosphorus, and sulfur. All castings investigated had good high temperature ductility in hot ductility tests and showed little difference in liquation cracking susceptibility.