월성 1호기 중수로 압력관의 조사후 인장거동 특성

안상복(Sang-Bok AHN),오동준(Dong-Jun OH),권상철(Sang-Chul Kwon),김영석(Young-Suk KIM),김정규(Jung-Kyu KIM) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3

The tensile test of irradiated and un irradiated Zr-2.5Nb CANDU pressure tube materials in the temperature range of room to 300℃ have been conducted to investigate the degradations of mechanical properties induced mainly by neutron irradiations. The irradiated longitudinal and transverse specimens which had a different operation temperatures and irradiation amounts are fabricated at coolant inlet, middle, and outlet part rings from M-11 tube operated in Wolsung Unit-1. A different tensile behaviors are showed with the specimen directions in the irradiated and un irradiated ones. The transverse have higher strength and lower elongation than the longitudinal specimens. It is believed to the effect of the microstructure anisotropy caused by extrusion fabrication process. The increased strength hardening and the decreased elongation embrittlement are showed in the irradiated ones compared to those of the un irradiated. The strength and elongation in the inlet part are higher and smaller compared to the outlet part. Specially in the same ring, the upper postion specimen have higher strength than the lower. Considering the operation temperature and irradiation amount distributions in tube, it is proposed that the irradiation temperature in tensile properties degradation can be more sensitive factor.

Zr-2.5Nb 압력관의 온도변화에 따른 수소취화 파괴거동

오동준(Dong Joon Oh),안상복(Sang Bok Ahn),김영석(Young Suk Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4

The aim of this study is to inveslingate the effect of hydrogen embriltlement of Zr-2.5Nb CANDU pressure tube. The were performed at three hydrogen contents for transverse tensile and CCT specimens while the test temperatures were changed (RT to 300℃). The specimens were directly machined from the tube retaining original curvature using electric discharge machine, Both the transverse tensile and the fracture toughness tests showed the hydrogen embrittlement elearly at RT but this phenomenon was disappeared<br/> while the test temperature arrived over 250℃. From the fracture toughness test, it was found that fracture toughness allda was increased up to 200℃ and then decreased.

Zircaloy-4 피복관의 DCPD 파괴언성시험법 개발

오동준(Dong Joan Oh),안상복(Sang Bok Ahn),정양홍(Yang Hong Cheong),주용선(Yong Sun Choo),홍권표(Kwon Pya Hong) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8

To define the causes of cladding degradation which can take place during an operation of nuclear power plants, it is required to develop the new fracture toughness test of fuel cladding. The fracture toughness of Zircaloy-4 cladding has been estimated using the recently developed KAERI embedded Charpy (KEC) specimen. Axially notched KEC specimens which were cut directly from fuel claddings, have been tested in a way similar to the standard toughness test method for a Single Edge Bending (SEB) specimen using DCPD method. The results of KEC fracture toughness test at room temperatures using single specimen were compared with the test data of the previous studis such as multiple specimen method and discussed. In conclusions, even though the KEC fracture toughness test using single specimen DCPD method for fuel claddings was easier and more reliable than those developed earlier, the results from the cladding fracture tests were not the material characteristics but the specific fracture parameters which was deeply related to the specification of claddings. In addition, the phenomenon of a thickness yielding was not observed from the fracture surface. It was closely related to the fact that the plane strain condition of the KEC specimen was changed to the plane stress condition during crack advancing.

Zr-2.5Nb 압력관의 연성-취성 천이 거동

김영석(Young Suk Kim),안상복(Sang Bok Ahn),김강수(Kang Soo Kim),오동준(Dong Joon Oh) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11

Fracture toughness tests were carried out at temperatures ranging from RT to 300 ℃ on compact tension specimens of the Zr-2.5Nb containing up to 200 ppm H. Hydrides drastically decreased fracture toughness resistance, dJ/da of the Zr-2.5Nb pressure tube at RT along with the formation of fissures. However at higher temperatures larger than 200 ℃, little decrease in fracture toughness of the Zr-2.5Nb tube showed up along with no formation of the fissures. Thus, a ductile-brittle transition temperature lay in the temperature range of 130-180 ℃. Fissures are suggested to occur by fracture of hydrides by deformation twins accompanied during a crack growth in the Zr-2.5Nb tubes. The amount of deformation twins was determined though textural changes before and after tensile tests where the tensile stress was applied in the circumferential direction of the tubes. The ductile-to-brittle transition behavior of the Zr-2.5Nb tube with hydrogen concentration and heat treatment conditions is discussed in association with interaction of deformation twins and the γ- to δ-hydride phase transition, which causes the maximum fracture toughness of the as-received Zr-2.5Nb tube at 180 ℃.

Zircaloy-4 피복관의 KEC 파괴인성시험법 개발

오동준(Dong Joon Oh),안상복(Sang Bok Ahn),김도식(Do Sik Kim),주용선(Yong Sun Choo),홍권표(Kwon Pyo Hong) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3

To define the causes of cladding degradation which can take place during an operation of nuclear power plants, it is required to develop the new fracture toughness test of fuel cladding. The fracture toughness of Zircaloy-4 cladding has been estimated using the recently developed KAERI embedded Charpy (KEC) specimen. Axially notched KEC specimens which were cut directly from fuel claddings, have been tested in a way similar to the standard toughness test method for a Single Edge Bending (SEB) specimen. The results of KEC fracture toughness test at room temperatures were compared with the test data of the previous studis and discussed. In conclusions, even though the KEC fracture toughness test for fuel claddings was easier and more reliable than those developed earlier, the results from the cladding fracture tests were not the material characteristics but the specific fracture parameters which was deeply related to the specification of claddings. In addition, the phenomenon of a thickness yielding was not observed from the fracture surface. It was closely related to the fact that the plane strain condition of the KEC specimen was changed to the plane stress condition during crack advancing. It was also supported by the fractographic evidence that the formation of ductile dimple at the crack initiation became the similar state such as a quasi-cleavage.

혼합 모드(Ⅰ/Ⅱ) 하중의 AS4P 시험편의 균열진전각도의 영향

오동준(Dong-Joon Oh),안상복(Sang-Bok Ahn),홍권표(Kwon-Pyo Hong) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8

The aim of this study is to investigate the ductile fracture behavior under mixed mode (I/II) loading using A533B pressure vessel steel. Anti-symmetric 4-point (AS4P) bending tests were performed to obtain the J-R curves under two different mixed mode (I/II) loadings. In addition, the crack profile observation such as a linear roughness parameter and a crack path angle was carried out to compare with those of pure Mode I and Mode II. In conclusions, the J-R curves under Mixed Mode (I/II) loading were located between those of Mode I and Mode II loadings. When the mixity of mixed mode (I/II) loading was high, the J-R curve of mixed mode (I/II) loading approached that of pure mode I loading after some amount of crack propagation In contrast with the above fact, if the mixity was low, the J-R curve looked after that of pure mode II loading. Using RDDT, the finite element analyses were performed and the predicted J-R curves under mixed mode (I/II) loading were compared with those from AS4P tests. Finally, the effect of the crack path angle on J-R curves under mixed mode (I/II) loading was discussed.

Zr-2.5Nb 압력관에서의 Striation Spacing과 DHCV의 관계

최승준(Seung Jun Choi),안상복(Sang Bok Ahn),김성수(Sung Soo Kim),임경수(Kyoung Soo Im),김영석(Young Suk Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8

The objective of this study is to elucidate a relationship between striation spacing and DHCV in Zr-2.5Nb tubes. To this end, DHC tests were conducted at different temperatures ranging from 100 to 300 oC with 3 to 6 data set at each test conditions for data confidence. Hydrogen charging amount was determined with testing temperature, from 27 to 87 ppm. Before applying load, specimens were heated up in order to dissolve hydrogen into matrix, and cooled down to testing temperature. From the results, DHCV and striation spacing increased with increased testing temperature, leading to a apparent relation that striation spacing became larger with increased DHCV. However, through a normalization of DHCV by diffusivity and solubility of hydrogen, it is found that the DHCV decreased with increased striation spacing. This correlation of the striation spacing and the DHCV was confirm through DHC tests on irradiated Zr-2.5Nb tubes with higher yield strength demonstrating the higher DHCV with the smaller striation spacing.

가동 시간에 따른 Zr-2.5Nb 압력관의 크립속도

김영석(Kim Young Suk),서용찬(Suh Yong Chan),안상복(Sang Bok Ahn),정용무(Cheong Yong Moo),임경수(Im Kyung Soo) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3

With a view to assessing a change in the creep rate of the Zr-2.5Nb pressure tubes operating in the reactor with the operation time, Zr-2.5Nb sheets were made with four different kinds of manufacturing process to simulate a microstructural change of the pressure tubes with time. The creep tests were conducted on the Zr-2.5Nb sheets at temperatures ranging from 623 to 673 K and constant stress of 120 ㎫. As an indirect evaluation of the Nb content dissolved in the α-Zr grains, the Nb content in the β-Zr phase of Zr-2.5Nb sheets made with 4 different processes was measured using a replica method. Zr-2.5Nb made with process P1 had the lowest creep rate while that made with process P3 or P4 had the highest creep rate. By correlating the Nb content in the α-Zr grains with the creep rate and strength of the Zr-2.5Nb sheets, we conclude that the Nb contents dissolved in the the c-Zr grains governs the creep rate and strength of Zr-2.5Nb alloy. A change in the creep rate of the Zr-2.5Nb pressure tubes was discussed on the basis of a fact that α-Zr grains in the Zr-2.5Nb pressure tubes have the Nb content decreasing with the operation time increasing.

Zr-2.5Nb 압력관에서 Hydride 파괴해석

김강수(Kang Soo Kim),김영석(Young Suk Kim),정용무(Yong Moo Cheong),안상복(Sang Bok Ahn),임경수(Kyoung Soo Im) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.8

The objective of this study is to suggest the new mechanism of DHC. At the stage Ⅰ of DHC, DHC velocity increase quickly and that is constant at the stage Ⅱ even if the stress intensity factor(K) increase. Also, the striation spacing on the fractured surface of DHC CT specimen is firstly wide and becomes gradually narrow according to increasing K value. Finally, that becomes constant at the stage Ⅱ. The new DHC model suggested can explain the above situation. To this end, CT specimen is modelled using FEM and the behavior of the elements near the crack tip is examined. Also, the direction of the principal stress, the maximum shear stress and the plastic zone size near the crack tip is calculated.

Zr-2.5Nb 압력관 크랙선단에서 수소화물의 응력해석

김강수(Kang Soo Kim),김영석(Young Suk Kim),정용무(Yong Moo Cheong),안상복(Sang Bok Ahn),임경수(Kyoung Soo Im) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3

Delayed Hydride Cracking (DHC) tests are conducted by using CT specimens of Zr-2.5Nb at 250℃. The test data is inputed for the FEM model. The stresses of the hydride and Zr-2.5Nb elements near the crack tip of the FEM model are examined. Also, the plastic zone size and average stresses near the crack tip are calculated for checking the effects of the plastic constraint. The material behavior of the elements near a crack tip, the hydride expansion stress, the hydride fracture strength and the size of the plastic zone according to each K are found. Also, Stage Ⅰ and Stage Ⅱ of the unique DHC phenomenon can be explained through an analysis of the plastic constraint force in the plastic zone.