A Correlation of Striation Spacing and DHC Velocity in Zr-2.5Nb Tubes

Zr-2.5Nb 압력관에서 Striation Spacing과 DHCV의 관계

  • 최승준 (한국원자력연구소, 지르코늄팀) ;
  • 안상복 (한국원자력연구소, 지르코늄팀) ;
  • 박순삼 (한국원자력연구소, 지르코늄팀) ;
  • 김영석 (한국원자력연구소, 지르코늄팀)
  • Published : 2004.08.01


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.


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