• Nuclear Engineering and Technology
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• 제52권3호
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• pp.621-625
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• 2020

Cast austenitic stainless steel (CASS) is used for fabricating different components of the primary reactor coolant system of pressurized water reactors. However, the thermal embrittlement of CASS resulting from long-term operation causes structural safety problems. Ultrasonic testing for flaw detection has been used to assess the thermal embrittlement of CASS; however, the high scattering and attenuation of the ultrasonic wave propagating through CASS make it difficult to accurately quantify the flaw size. In this paper, we present a different approach for evaluating the thermal embrittlement of CASS by assessing changes in the material properties of CASS using a nonlinear ultrasonic technique, which is a potential nondestructive method. For the evaluation, we prepared CF8M specimens that were thermally aged under four different heating conditions. Nonlinear ultrasonic measurements were performed using a contact piezoelectric method to obtain the relative ultrasonic nonlinearity parameter, and a mini-sized tensile test was performed to investigate the correlation of the parameter with material properties. Experimental results showed that the ultrasonic nonlinearity parameter had a correlation with tensile properties such as the tensile strength and elongation. Consequently, we could confirm the applicability of the nonlinear ultrasonic technique to the evaluation of the thermal embrittlement of CASS.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.17-22
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• 2007

Low-cycle environmental fatigue tests of cast austenitic stainless steel CF8M at the condition of fatigue strain rate 0.04%/sec were conducted at the pressure and temperature, 15MPa, $315^{\circ}C$ of a operating pressurized water reactor. The used test rig was limited to install an extensometer at the gauge length of the cylindrical fatigue specimen inside the small autoclave. So the magnet type LVDT's were used to measure the fatigue displacement at the specimen shoulders inside the high temperature and high pressure water autoclave. However, the displacement and strain measured at the specimen shoulders is different from the one at the gauge length for the geometry and the cyclic strain hardening effect. FEM calculated the displacement and the strain of the gauge length from the data measured at the shoulders. Tensile test properties in elastic and plastic behavior of CF8M material were used in the FEM analysis. A series of low cycle fatigue tests simulating the cyclic strain hardening effect verified that the FEM calculation was well agreed with the simulated tests. The process and method developed in this study would be so useful to produce reliable environmental fatigue curves of CF8M stainless steel in pressurized water reactors.

• 대한기계학회논문집A
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• 제32권2호
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• pp.177-185
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• 2008

Low-cycle environmental fatigue tests of cast austenitic stainless steel CF8M at the condition of fatigue strain rate 0.04%/sec were conducted at the pressure and temperature, 15MPa, $315^{\circ}C$ of a operating pressurized water reactor (PWR). The used test rig was limited to install an extensometer at the gauge length of the cylindrical fatigue specimen inside a small autoclave. So the magnet type LVDT#s were used to measure the fatigue displacement at the specimen shoulders inside the high temperature and high pressure water autoclave. However, the displacement and strain measured at the specimen shoulders is different from the one at the gauge length for the geometry and the cyclic strain hardening effect. Displacement of the fatigue specimen gauge length calculated by FEM (finite element method) used to modify the measured displacement and fatigue life at the shoulders. A series of low cycle fatigue life tests in air and PWR conditions simulating the cyclic strain hardening effect verified that the FEM modified fatigue life was well agreed with the simulating test results. The process and method developed in this study for the environmental fatigue test inside the small sized autoclave would be so useful to produce reliable environmental fatigue curves of CF8M stainless steel in pressurized water reactors.

• 해양환경안전학회지
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• 제13권1호
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• pp.1-7
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• 2007

동해의 해양 심층수 자원 기반 환경 연구의 일부로 청결기술을 적용하여 해수 중의 용존 미량금속(Cd, Co, Cu, Ni, Pb, Zn) 농도 분포와 변화를 조사하였다. 강원과 경북 지역에 총 6개 정점을 선정하고, 각 지역마다 최대 채수 수심 각각 200-300m와 500m까지 시료를 채취하였다. 본 연구의 미량금속을 위한 연안해수 표준물질(CASS-4)의 분석 결과 각 원소 평균 회수율은 Co의 89.4%에서 Cd의 99.8%의 범위였다. 용존 미량원소의 분포는 해역 및 시기적인 변화가 다양하게 나타났다. Cd, Ni, Zn의 경우는 영양염 의존형으로 표층에서 낮고 저층으로 갈수록 증가하는 경향이 뚜렷하였다. 그러나 Co, Cu, Pb은 수직적으로 불규칙적인 분포를 나타내었다. 본 연구의 동해 심층수 원수의 중금속 농도는 해역별 수질 기준과 먹는 물 기준을 만족하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.368-371
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• 2008

An extensometer system to measure strain and displacement of cylindrical fatigue specimen in a autoclave of high temperature and high pressure environment has been developed by KEPRI. The extensometer reads the displacement caused by fatigue loads at the target length of the specimen installed inside the autoclave. The performance of the extensometer were tested at 15MPa, $315^{\circ}C$ of a operating pressurized water reactor. Two LVDT's of magnet type were connected to the extensometer and used for converting the fatigue displacement to electronic signal. The device is being used for developing environmental fatigue curve of CF8M cast austenitic stainless steel (CASS) in the test condition of low cycle and low strain. This paper introduces the background and results of the development.