• 제목/요약/키워드: Delayed Hydride Cracking (DHC)

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DHC Characteristics of M11 Pressure Tube in Wolsong Unit 1

  • Kim, Sung-Soo;Kim, Young-Suk
    • Nuclear Engineering and Technology
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    • 제32권1호
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    • pp.1-9
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    • 2000
  • Delayed hydride cracking (DHC) velocity and threshold stress intensity factor for DHC ($K_{IH}$) tests in the radial direction on M11 pressure tube material in Wolsong unit 1 were carried out following the Atomic Energy Canada Limited (AECL) standard test procedure in order to identify the effect of undercooling on DHCV and to acquire the $K_{IH}$ data. The results showed that $K_{IH}$ 's were 8.8$\pm$0.8 MPa√m in the back offcut and 11.4$\pm$0.7 MPa√m in the front offcut. The fact that $K_{IH}$ in the front offcut is about 20% higher than that in the back offcut is attributed to the microstructural difference between the materials of the front and back ends. $K_{IH}$ 's in M11 pressure tube appeared to be higher than the values from the tubes made of double melted ingot reported earlier. This can be interpreted by the fact that very small amounts of Chlorine (Cl) and Phosphorus (P) are contained in the ingot and that the content of the harmful elements in the M11 pressure tube is equivalent to that made of a quadruple melting process. DHC velocities at 25$0^{\circ}C$ in the front offcut in the radial direction are measured to be 5~8$\times$10$^{-8}$ m/s. The results show that the prior thermal history change the DHC velocity significantly. This effect was confirmed by the experiment of undercooling prior to the DHC tests.DHC tests.

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Zr-2.5Nb 압력관에서 Striation Spacing과 DHCV의 관계 (A Correlation of Striation Spacing and DHC Velocity in Zr-2.5Nb Tubes)

  • 최승준;안상복;박순삼;김영석
    • 대한기계학회논문집A
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    • 제28권8호
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    • pp.1109-1115
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    • 2004
  • The objective of this study is to elucidate what governs delayed hydride cracking (DHC) in Zr-2.5Nb tubes by correlating the striation spacings with DHCV(DHC Velocity). To this end, DHC tests were conducted on the compact tension specimens taken from the Zr-2.5Nb tubes at different temperatures ranging from 100 to $300^{\circ}C$ with a 3 to 6 data set at each test conditions. The compact tension specimens were electrolytically charged with 27 to 87 ppm H before DHC tests. After DHC tests, the striation spacings and DHCV were determined with the increasing the test temperature and yield strength. The striation spacing and DHCV increased as a function of yield $strength^2$ and the temperature. Since the plastic zone size ahead of the crack tip can be represented by ${\sim}(K_{IH}/{\sigma}_{Y})^2$, we conclude that the striation spacing is governed by the plastic zone size which in turn determines a gradient of hydrogen concentration at the crack tip. The relationship between the plastic zone size and the striation spacing was validated through a complimentary experiment using double cantilever beam specimens. Two main factors to govern DHCV of Zr-2.5Nb tubes are concluded to be hydrogen diffusion and a hydrogen concentration gradient at the crack tip that are controlled by temperature and yield strength, respectively. The activation energy of DHCV in the Zr-2.5Nb tubes is discussed on the basis of temperature dependency of hydrogen diffusion and the striation spacing.

Delayed Hydride Cracking Velocity of CANDU Zr-2.5Nb Tubes in High Temperature Water

  • Kim Young Suk;Cho Sun Young;Im Kyung Soo;Cheong Yong Moo;Kim Sung Soo
    • Nuclear Engineering and Technology
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    • 제35권3호
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    • pp.206-213
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    • 2003
  • This study focuses on an understanding of the environmental effect on delayed hydride cracking velocity (DHCV) of CANDU Zr-2.5Nb tubes. To simulate DHC susceptibility of the Zr-2.5Nb tubes in reactor operating conditions, DHC tests were successfully carried out in pressurized water at 180 and $250^{\circ}C$ using a self-designed autoclave for the first time. Using 17 mm compact tension specimens electorlytically charged to 34 and 60 ppm H, 3 to 7 DHCV data were determined in water at both temperatures and compared to those determined in air that were already confirmed to be valid through a round robin test on DHCV of Zr-2.5Nb tubes sponsored by a IAEA coordinated research program. The pressurized water environment has little effect on DHCV of Zr-2.5Nb tube in water at both temperatures even though DHCV is slightly lower in water than that in air. The lower DHCV of the Zr-2.5Nb tube during short-term tests is discussed in viewpoint of the cooling rate from the peak temperature to the test temperature.

중수로 압력관 LBB 평가에서의 수소화물에 의한 취화거동 (Hydride Embrittlement Behavior at the LBB Evaluation of PHWR Pressure Tube)

  • 오동준;김영석
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2003년도 추계학술대회
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    • pp.1192-1197
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    • 2003
  • The aim of this study is to investigate the hydride embrittlement when the LBB evaluation is carried out for the integrity of PHWR Pressure Tubes. The transverse tensile and CCT tests were performed at three hydrogen concentrations while the test temperatures were changed (RT to $300^{\circ}C$). The specimens were directly machined from the pressure tube retaining original curvature. Both the transverse tensile and the fracture toughness tests showed the hydrogen embrittlement clearly at RT but this phenomenon was disappeared while the test temperature arrived over $250^{\circ}C$. Using the DHC test results, the CCL and LBB time were calculated and compared. The hydride embrittlement behavior at the LBB evaluation was definitely showed.

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중수로 압력관의 수화물이 LBB평가에 미치는 영향 (Effect of Hydride of the PHWR Pressure Tube on the LBB Evaluation)

  • 오동준;김영석
    • 대한기계학회논문집A
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    • 제28권5호
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    • pp.610-616
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    • 2004
  • The aim of this study was to investigate the hydride embrittlement when the LBB evaluation was carried out for the integrity of PHWR Pressure Tubes. The transverse tensile and CCT toughness tests were performed at three hydrogen concentrations while the test temperatures were changed (RT to 30$0^{\circ}C$). Both the transverse tensile and the fracture toughness tests showed the hydrogen embitterment clearly at RT but this phenomenon was disappeared while the test temperature arrived at 25$0^{\circ}C$. Using the DHC test results, the CCL and LBB time were calculated and compared. The hydride embrittlement at the LBB evaluation made the LBB time short definedly. If the operating temperature, DHCV and LBB deterministic parameters such as A and m were known, LBB time could be estimated without the calculation of CCL.

Three-dimensional numerical simulation of hydrogen-induced multi-field coupling behavior in cracked zircaloy cladding tubes

  • Xia, Zhongjia;Wang, Bingzhong;Zhang, Jingyu;Ding, Shurong;Chen, Liang;Pang, Hua;Song, Xiaoming
    • Nuclear Engineering and Technology
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    • 제51권1호
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    • pp.238-248
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    • 2019
  • In the high-temperature and high-pressure irradiation environments, the multi-field coupling processes of hydrogen diffusion, hydride precipitation and mechanical deformation in Zircaloy cladding tubes occur. To simulate this hydrogen-induced complex behavior, a multi-field coupling method is developed, with the irradiation hardening effects and hydride-precipitation-induced expansion and hardening effects involved in the mechanical constitutive relation. The out-pile tests for a cracked cladding tube after irradiation are simulated, and the numerical results of the multi-fields at different temperatures are obtained and analyzed. The results indicate that: (1) the hydrostatic stress gradient is the fundamental factor to activate the hydrogen-induced multi-field coupling behavior excluding the temperature gradient; (2) in the local crack-tip region, hydrides will precipitate faster at the considered higher temperatures, which can be fundamentally attributed to the sensitivity of TSSP and hydrogen diffusion coefficient to temperature. The mechanism is partly explained for the enlarged velocity values of delayed hydride cracking (DHC) at high temperatures before crack arrest. This work lays a foundation for the future research on DHC.

CANDU 압력관에 대한 건전성 평가 시스템 개발 (Development of Integrity Evaluation System for CANDU Pressure Tube)

  • 곽상록;이준성;김영진;박윤원
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2000년도 추계학술대회논문집A
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    • pp.843-848
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    • 2000
  • The pressure tube is a major component of the CANDU reactor, which supports nuclear fuel bundle and it's containment vessel. If a flaw is found during the periodic inspection from the pressure tubes, the integrity evaluation must be carried out, and the safety requirements must be satisfied for continued service. In order to complete the integrity evaluation, complicated and iterative calculation procedures are required. Besides, a lot of data and knowledge for the evaluation are required for the entire integrity evaluation process. For this reason, an integrity evaluation system, which provides efficient way of evaluation with the help of attached databases, was developed. The developed system was built on the basis of ASME Sec. XI and FFSG(Fitness For Service Guidelines for zirconium alloy pressure tubes in operating CANDU reactors) issued by the AECL, and covers the delayed hydride cracking(DHC). Various analysis methods are provided for the integrity evaluation of pressure tube. In order to verify the developed system, several case studies have been performed and the results were compared with those from AECL. A good agreement was observed between those two results.

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