Effects of process-generated hydrogen on RPV walls

6.3. In-service hydrogen generation

Figure 6.4: Relation between the temperature, where the maximum Henry coefficient is reached, and the Van der Waals radii of the noble gases. The linear correlation results in a R 2 -value of 0.98. This temperature for atomic hydrogen is estimated to be 287 K. [70, 72, 75]

120 pm, one can find a H max H correlation is found: T max i

equal to 18.6 GPa. Similarly, for T

, the following

max i

= 166 . 8 − 1 . 005 ∗ R V dW . Again, for a hydrogen atom, this results in a T max equal to 287 K. Using these estimated values for the hydrogen atom as the parameters necessary in equation 6.3, one can find a curve for the Henry coefficient of atomic hydrogen in water as a function of temperature (Figure 6.5). As now the evolution of the Henry coefficient in GPa of atomic hydrogen as a function of temperature is known, one can convert it to mol/m 3 Pa. This allows to use the initial form of Henry’s law, equation 6.1, and will result in easier calculations for the following part of this text. The conversion of the Henry constant can be done as follows: ( c i = H cf i · f i f i = H fxi · x i H cf i = 1 H fxi · c i x i (6.6) where H cf i is the Henry coefficient in mol/m 3 Pa relating the concentration, c i , in mol/m 3 to the fugacity, f i , in Pa. H fxi is the Henry coefficient in Pa relating the fugacity, f i , in Pa to the molfraction, x i . This last one, H fxi , is the Henry coefficient found above, expressed in Pa in stead of GPa. To complete the conversion of Henry 65