The Effect of Microstructure on the Corrosion Behavior of Zircaloy-2 in BWRs

Although the complete mechanisms are not yet fully understood, it is well established that the secondary phase particle ͑SPP͒ size distribution and chemical composition have a crucial affects in the reactor corrosion rate and hydrogen uptake in boiling water reactor ͑BWR͒ cladding. To further study these effects, different selected fuel rod assemblies with standard LK3 cladding materials that have been irradiated in KernKraftwerk Leibstadt ͑KKL͒ for three, five, six, seven, and nine annual cycles were investigated using transmission electron microscopy ͑TEM͒. TEM analysis of the samples showed that the average size of SPPs increases as the small SPPs are dissolved during irradiation. After three cycles the Fe-Cr bearing SPPs have been identified as completely amorphous over the whole range of examined samples and the Fe-Ni bearing SPPs remained crystalline. The EDX analyses of several Fe-Ni bearing precipitates show that the Fe/Ni ratio stays more or less constant for the irradiated material at 1.5 to 1.6 and drops to about 1 after fast fluence of 17.9ϫ10 21 n/cm 2 ͑Ͼ1 MeV͒ for nine cycles sample. Results from this study confirms that the increased oxide thickness, the higher hydrogen content, and the accelerated growth of the rods at rod average burnup of 78 MWd/kgU goes along with a change in the appearance of SPPs by TEM.

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The Correlation Between Microstructures and in-BWR Corrosion Behavior of Highly Irradiated Zr-based Alloys

Takagawa¹,

Ishimoto²,

Etoh³

et al. 2005

Journal of ASTM International

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The microstructures of four kinds of Zircaloy-2-type materials with neutron exposure up to about 15 × 1025 n/m2 (E>1MeV) were examined to investigate the microstructural evolution and to correlate it with the in-reactor corrosion behavior at very high fluences. The materials examined in this study included two advanced Zr-based alloys with good corrosion resistance, namely High Fe Zry and High FeNi Zry, and two other kinds of Zry-2 materials with slightly different elemental compositions and fabrication processes producing differing second phase particle sizes. All alloys showed good corrosion behavior and low hydrogen pickup when irradiated up to four cycles in dummy neutron source holders located outside of channel boxes. After six irradiation cycles, all four of the alloys had an increase in the rate of uniform corrosion and hydrogen pickup. The results of the microstructure examinations after six-cycle irradiation indicated two interesting points: (1) increased insight into the dissolution process for Zr-Fe-Cr particles, and (2) a correlation between the number density of Zr-Fe-Cr particles surviving through irradiation and the corrosion behavior at high fluences. From these results, it is suggested that increasing the initial particle size and/or controlling the alloy chemistry would be beneficial to improve the uniform corrosion performance and to lower hydrogen pickup, especially at very high fluences.

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The Effect of Microstructure on the Corrosion Behavior of Zircaloy-2 in BWRs

Cited by 10 publications

References 25 publications

Evolution of Zr(Fe,Cr)2 second phase particles in Zircaloy-2 under heavy ion irradiation

Evolution of Zr(Fe,Cr)2 second phase particles in Zircaloy-2 under heavy ion irradiation

Effects of Secondary Phase Particle Dissolution on the In-Reactor Performance of BWR Cladding

The Correlation Between Microstructures and in-BWR Corrosion Behavior of Highly Irradiated Zr-based Alloys

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