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Vol.60, No.5, 341 ~ 350, 2022
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| Title |
| Analysis of Dimensional Change in Zr-2.5%Nb CANDU Pressure Tube Material aged at 300-400°C using Neutron Diffraction |
| 정종엽 Jung Jong Yeob , 김형섭 Hyung Sub Kim , 김성수 Sung Soo Kim , 김영석 Young Suk Kim |
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| Abstract |
| The primary boundary of the CANDU reactor consists of Zr-2.5%Nb alloy pressure tubes and SA106 alloy feeder pipes. The pressure tubes are exposed to fast neutron (E>1Mev) irradiation during reactor operation, and experience dimensional changes. The actual dimensional change in the pressure tube during in-service operation is greater than the design estimate. It is not fully understood what is responsible for the dimensional changes in the pressure tubes. In this study, to accelerate the aging effect on the pressure tube material, aging was performed at 300-400℃ for up to 20,000 hours and neutron diffraction was used to track variation in lattice spacing, thereby identifying the reason for the dimensional change. The analysis result showed that α-Zr, the main phase of Zr-2.5%Nb, had little dimensional change at 350℃ or lower. On the other hand, the aging treatment at 400℃ resulted in anisotropic expansion in the α-Zr of the HCP crystal, of 0.02% and 0.08% in the (1010) and (0002) directions, respectively. It was confirmed that above 350℃ the β-phase in the Zr-2.5%Nb alloy was decomposed to precipitate β-Nb . The driving force of the lattice expansion may be due to the diffusing out tendency of the super saturated Nb in α-Zr and due to the residual cold working effect applied during the manufacturing process. The enhancing effects of fast neutron irradiation on lattice diffusion are discussed in detail.
(Received 6 October, 2021; Accepted 28 December, 2021) |
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| Key Words |
| Zr-2.5%Nb, aging, lattice variation, neutron diffraction, entropy |
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