NPP Life Management_vs02

the corrosion reaction at the metal/water interface alone. In terms of hydrogen gas volumes this would be 1.3 m 3 STP.

SCK data 42 even show higher corrosion-hydrogen productions, up to 65 or 200 mol H/yr (Figure 11).

Figure 11: Slide summarizing corrosion rate estimates and related hydrogen production volumes.

How much of this produced hydrogen will effectively enter into the steel wall is open to debate. Figures op to 90% have been mentioned 43 , but 50 to 20% or less could be a more realistic estimate. It should be remembered, however, that hydrogen evolution – i.e. the amount of molecular hydrogen that is released from the metal surface and not being absorbed into the base metal matrix – occurs as a result of the following reactions:

Hydrogen and NPP Life Management: Doel 3 and Tihange 2

H + + e - → H

ads

→ H

2 H ads

2

In these, the latter reaction step is known to be relatively slow, and its rate determines the overall production of hydrogen gas, the rest being absorbed into the base metal. The increased concentration of surface hydrogen favors entrance and absorption of hydrogen atoms into the

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