NPP Life Management_vs02

remedy is to use vacuum ladle degassing methods to decrease the content of hydrogen to 2 ppm, which should avoid or mitigate flake formation.

Hydrogen and NPP Life Management: Doel 3 and Tihange 2

Figure 5: Typical “ hydrogen flake ” cracking in carbon or low-alloy steel. Specific features of hydrogen- induced brittle fracture are: micro-quasi-cleavage fracture, pores and fine hair-lines (indicating ductile fracture on a micro-scale). Not all forged components of the Doel 3 and Tihange 2 RPVs contain the same amount of flaws. Based on an analysis of the ingot size and the combined sulfur and hydrogen content, there appears to be a good correlation with the intrinsic susceptibility to hydrogen flaking and the amount of flakes found in each forged component. The key question remaining is about the possible evolution over time of these so-called “hydrogen flakes” . The position of the regulatory authorities and the operator, so far, has been that the defects found in the Doel and Tihange RPV “are usually associated with manufacturing and are not due to aging” and that it is “improbable” that the flaws have evolved since their

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