NPP Life Management_vs02

content of steels. Old results 44 already indicated that at a given temperature the lattice hydrogen will be practically independent of the composition of the steel, which indicates that variations in hydrogen content of steels of different compositions and structures is due to hydrogen located at traps. Some models have been proposed to relate the overall diffusion to the number of trap sites and the probability of capture and release from the trap. Detailed interpretations of the available experimental data, however, often remain impossible due to limitations in the exact understanding of the trapping process(es) 45, 46 . The various data, however, show that retained hydrogen concentrations can be considerable. A Laborelec report to the operator 47 , based on calculations from SCK-CEN, mentions a maximum total hydrogen uptake concentration in the RPV of about 0.04 wppm H, and states that this is “in correspondence with values found in literature”. This again is erroneous . Actual values from the old source referred to (i.e. Harries and Broomfield, 1963 23 ] effectively correspond to 0.244 wppm H at 250°C, a factor of 6 higher (when corrosion rates are assumed to be very low). Other international sources show similar effective H-concentration values. Old data from Whitman 24 mention hydrogen concentrations in low-alloy steel RPV steel of 0.3 ppm under operational RCS conditions. Other data are shown in Figure 13. They are generally in line with each other.

Hydrogen and NPP Life Management: Doel 3 and Tihange 2

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Figure 13: Slide summarizing literature data on RPV hydrogen concentrations.