Effect of Dissolved Hydrogen on the Crack Growth Rate and Oxide Film Formation at the Crack Tip of Alloy 600 Exposed to Simulated PWR Primary Water
The effect of dissolved hydrogen (DH) on primary water stress corrosion cracking of nickel base alloys has been of intense interest for plant operators worldwide. In this study, crack growth rates of Alloy 600 were measured in simulated PWR primary coolant at 330 °C with DH levels of 5, 16, 45 and 75 cc H2/kg H2O, respectively. The oxide films formed in the crack tip regions were examined using transmission electron microscopy (TEM). The results show low and similar crack growth rates at all DH levels, without a maximum at 16 cc H2/kg H2O. The low DH content favors nickel oxide formation at the crack tip region, whereas the high DH level favors Me3O4 type spinel formation. Also, the oxide films were found to grow epitaxially on some metal grain surfaces in the cracks. The possible effects of alloy composition on the oxide films formed, and the effect of DH on the crack growth are briefly discussed.
KeywordsPWSCC Alloy 600 Dissolved hydrogen Oxide characterization High resolution microscopy
This work would not be possible without the contributions from several people and organizations. All their contributions are gratefully acknowledged. In particular, Dr. A. Riazanova and Professor L, Belova at Royal Institute of Technology, Sweden, prepared the TEM Lamellas for this work. Many colleagues at Studsvik Nuclear AB helped with daily experimental maintenance during the course of the experimental work. Financial support by Ringhals AB and Swedish Radiation Safety Authority is also gratefully acknowledged.
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