• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.16-22
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• 2006

Stainless steel has widely been used in various industrial fields because it has high corrosion resistance. But, we have little design data about the creep life prediction of SUS316L stainless steel. Therefore, in this study, a series of creep tests and study on them under 16 constant stress and temperature combined conditions have been performed to get the creep design data and life prediction of SUS316L stainless steels and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy is estimated about 10. And last, the creep rupture fractographs show the intergranular ductile fracture with many dimples.

• Nuclear Engineering and Technology
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• v.44 no.4
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• pp.415-420
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• 2012

It is important to understand the amount of time required to execute an emergency procedural task in a high-stress situation for managing human performance under emergencies in a nuclear power plant. However, the time to execute an emergency procedural task is highly dependent upon expert judgment due to the lack of actual data. This paper proposes an analytical method to estimate the operator's performance time (OPT) of a procedural task, which is based on a measure of the task complexity (TACOM). The proposed method for estimating an OPT is an equation that uses the TACOM as a variable, and the OPT of a procedural task can be calculated if its relevant TACOM score is available. The validity of the proposed equation is demonstrated by comparing the estimated OPTs with the observed OPTs for emergency procedural tasks in a steam generator tube rupture scenario.

• Journal of Korean Society for Atmospheric Environment
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• v.17 no.E1
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• pp.17-24
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• 2001

For the purpose of collecting fog droplets as a function of size a new sampling method was developed in this study. Formation of 100$\pm$10㎛ thickness of polymeric water absorbent film (PWAF) on a nuclepore filter could be successfully realized. Also applicability of particle induced X-ray emission (PIXE) method to the chemical analysis of size-segregated fog droplets collected on PWAF was examined experimentally with synthetic fog droplets generated from a nebulizer. Absorption capacity of S-PAAS polymeric water absorbent shows marked decreases in the range less than 1 wt% and slight decrease between 1 and 3.5 wt% of every salt concentration. Dependency of absorption capacity on pH shows the maximum at pH 7. No apparent peak which can influence the quantitative analysis of elements dissolved and suspended in fog droplets was found at PIXE spectrum of PWAF blank. PWAF kept the original shape without rupture under the PIXE analytical conditions of beam intensity for 10 to 60 nA and irradiation time of 4∼5 min. It should be said that the proposed new technique in the work is helpful to get more detailed information of fog droplets, to clarify the fog formation processes, and to develop a model of acid deposition process.

• Structural Engineering and Mechanics
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• v.34 no.6
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• pp.755-778
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• 2010

Near-fault ground motion with directivity or fling effects is significantly influenced by the rupture mechanism and substantially different from ordinary records. This class of ground motion has large amplitude and long period, exhibits unusual response spectra shapes, possesses high PGV/PGA and PGD/PGA ratios and is best characterized in the velocity and the displacement time-histories. Such ground motion is also characterized by its energy being contained in a single or very few pulses, thus capable of causing severe damage to the structures. This paper investigates the characteristics of near-fault pulse-like ground motions and their implications on the structural responses using new proposed measures, such as, the effective frequency range, the energy rate (in time and frequency domains) and the damage indices. The paper develops also simple mathematical expressions for modeling this class of ground motion and the associated structural responses, thus eliminating numerical integration of the equations of motion. An optimization technique is also developed by using energy concepts and damage indices for modeling this class of ground motion for inelastic structures at sites having limited earthquake data.

• Nuclear Engineering and Technology
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• v.20 no.1
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• pp.54-64
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• 1988

This paper assesses the models in the SCDAP code using the results of the FLHT-2 test. Calculations show that the SCDAP correctly predicts Ire temperatures, oxidation front movement, overall hydrogen generation and peak generation rate, internal fuel rod pressure, and cladding rupture due to ballooning. A comparison of the calculated results with measured data shows that two phase level is underpredicted, and that radiation heat transfer and auto-catalytic reaction temperature of zircaloy are overpredicted. These models are recommended to be modified. The analysis also shows that the simulation of the gap in a fuel rod improves the code prediction on core damage progression.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.13 no.2
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• pp.51-59
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• 2017

Steam jets ejected from a rupture zone of high energy pipes may cause damage to adjacent structures. This event could lead to more serious accidents in nuclear power plants. Therefore, to prevent serious accidents, high energy pipes of nuclear power plants are designed according to the ANSI / ANS 58.2 technical standard. However, the US Nuclear Regulatory Commission (USNRC) has recently pointed out non-conservatism in existing high energy pipe fracture evaluation methods, and required the assessment of the unsteady load of the jet caused by a potential feedback mechanism as well as the impact range of steam jet, the jet impact loads and the blast wave effects at the initial breakage stage. The potential feedback mechanism refers to a phenomenon in which a vortex formed by impingement jets amplifies vortex itself and induces jet vibration in a shear layer. In this study, CFD methodology using the LES turbulence model is established and numerical analysis is carried out to evaluate the dynamic behavior of impingement jets and the potential feedback mechanism during jet impingement. Obtained results have been compared with an empirical correlation and experiment.

• Nuclear Engineering and Technology
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• v.53 no.2
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• pp.572-582
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• 2021

This study investigated the creep and creep crack growth (CCG) behavior of the base metal (BM), weld metal (WM), and heat affected zone (HAZ) in a Gr. 91 weldment, which was made by a shield metal arc weld process. A series of tensile, creep, and CCG tests were performed for the BM, WM, and HAZ at 550 ℃. Creep behavior of the BM, WM, and HAZ was analyzed in terms of various creep laws; Norton's power-law, Monkman-Grant relation and damage tolerance factor (λ), and their constants were determined. In addition, each CCGR law for the BM, WM, and HAZ was proposed and compared in terms of a C^*-fracture parameter. The WM and HAZ revealed faster creep rate, lower rupture ductility, and faster CCGRs than the BM, but they showed a similar behavior in the creep and CCG. The CCGRs obtained in the present study exhibited a marginal difference when compared with those of RCC-MRx of currently elevated design code in France. A creep crack path in the HAZ plane progressed towards a weak fine-grained HAZ adjacent to the BM.

• Nuclear Engineering and Technology
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• v.55 no.10
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• pp.3571-3580
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• 2023

The application of the induction bending process to pipe systems in various industrial fields is increasing. Recently, efforts have also been made to apply this bending process to nuclear power plants because it can innovatively reduce welded parts of the curved pipes, such as elbows. However, there have been no cases of the application of induction bending to the piping of nuclear power plants. In this study, the applicability of the P91 induction bending piping for the sodium-cooled fast reactor PGSFR was validated through high temperature low cycle fatigue tests and creep tests using P91 induction bending pipe specimens. The tests confirmed that the materials sufficiently satisfied the fatigue life and the creep rupture life requirements for P91 steel at 550 ℃ in the ASME B&PV Code, Sec. III, Div. 5. The results show that the effects of heating and bending by the induction bending process on the material properties were not significant and the induction bending process could be applicable to piping system of PGSFR well.

• Journal of the Korean Institute of Gas
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• v.26 no.6
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• pp.9-15
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• 2022

In order to verify the durability of the high-pressure hydrogen tank in the operating pressure range, a hydraulic rupture test should be performed. However, if the bubbles generated by the initial injection process of water are attached to the inner wall of the tank and remain, a sudden pressure change of the bubbles during the rupture of the pressurized tank may cause shock and noise. Therefore, in this study, the flow velocity required to remove the bubbles remaining on the inner wall of the tank was predicted through simplified formulas, and the shape of the injection nozzle to maintain the flow velocity was determined based on the shape of the hydrogen tank for the hydrogen bus. In addition, a numerical model was developed to predict the change in flow velocity according to the inlet pressure, and an experiment was performed through a model tank to prove the validity of the prediction result. As a result of the experiment, the flow velocity near the tank wall was similar to the predicted value of the analysis model, and when the inlet pressure was 1.5 to 5.5 bar, the minimum size of the removable bubble was predicted to be about 2.2 to 4.6 mm.

• Clean Technology
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• v.19 no.4
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• pp.355-369
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• 2013

Economic feasibility is one of the most important factors in energy production from regenerative biomass. From the aspect, biogas from anaerobic digestion of wastewater sludge is regarded as the most economical because of its cheap substrate and additional income from the disposal of waste sludge. Sludge hydrolysis has been regarded as the rate limiting step of anaerobic digestion and many sludge pre-treatment technologies have been developed to accelerate anaerobic sludge digestion for enhanced biogas production. Various sludge pre-treatment technologies including biological, thermo hydrolysis, ultrasonic, and mechanical methods have been applied to full-scale systems. Sludge pre-treatment increased the efficiency of anaerobic digestion by enhancing hydrolysis, reducing residual soilds, and increasing biogas production. This paper introduces the characteristics of various sludge pre-treatment technologies and the energy balance and economic feasibility of each technology were compared to prepare a guideline for the selection of feasible pre-treatment technology. It was estimated that thermophilic digestion and thermal hydrolysis were most economical technology followed by Cell rupture$^{TM}$, OpenCEL$^{TM}$, MicroSludge$^{TM}$, and ultrasound. The cost for waste sludge disposal shares the biggest portion in the economic analysis, therefore, water content of the waste sludge was the most important factor to be controlled.