首页|Diffusion of H in Zircaloy-2 and Zr-2.5%Nb rolled plates between 250 degrees C and 350 degrees C by off-situ neutron imaging experiments
Diffusion of H in Zircaloy-2 and Zr-2.5%Nb rolled plates between 250 degrees C and 350 degrees C by off-situ neutron imaging experiments
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NSTL
Elsevier
Zirconium alloys in nuclear power plants operate in high-pressure water at temperatures between 250 and 350 degrees C. Hydrogen (or deuterium) ingress due to waterside corrosion and if the solubility is exceeded H precipitates as a brittle hydride phase. Degradation mechanisms involve the accumulation of these brittle hydrides at cold spots or crack tips, as a result of H redistribution in response to thermal and stress gradients, respectively. Knowledge of H diffusion coefficients at operating temperatures is central to evaluating the rate of hydride accumulation and crack growth velocity. We determine the diffusion coefficients of H in Zircaloy-2 and Zr-2.5%Nb rolled plates at 250 degrees C, 300 degrees C and 350 degrees C along the rolling and normal directions by neutron imaging experiments with sensitivity of 5 wt ppm H for a spatial resolution 0.04 mm x 2 mm. These values were evaluated from H concentration profiles measured at room temperature on specimens of dimensions 10 x 10 x 4 mm(3) containing a hydride layer on one face, after annealing treatments between 60 and 600 min. This allowed the identification of a transition zone of 200-300 mu m between the hydride layer and the Zr alloy material, composed by large, sparsely distributed hydrides. In Zircaloy-2 plates, no substantial differences were observed in H diffusion along different directions or metallurgical conditions, and diffusion coefficients (0.6 +/- 0.1 10(-10) m(2)/s at 300 degrees C). By contrast, in hot rolled Zr-2.5%Nb plates the diffusion along the rolling direction (5.5 +/- 0.5 x 10(-10) m(2)/s at 300 degrees C) was much faster than along the normal direction (2.5 +/- 0.7 10(-10) m(2)/s at 300 degrees C), very likely due to H diffusing along the continuous network of beta filaments. After a thermal treatment of 3 h at 860 degrees C the plate microstructure changed generating radically changed H diffusion coefficients, resulting in H diffusion being much faster along the normal direction (4.0 +/- 0.5 10(-10) m(2)/s at 300 degrees C) than along the rolling direction (1.4 +/- 0.5 10(-10) m(2)/s at 300 degrees C). (c) 2022 Elsevier B.V. All rights reserved.
NSTL
Elsevier
