Effects of process-generated hydrogen on RPV walls

6.3. In-service hydrogen generation

the error between the experimental values and the equation by Himmelblau is limited. The error increases for higher temperatures, smaller (1 /T ) ∗ values, up to 50 %. This error can however be accepted for this simple correlation.

0,2 0,3 0,4 0,5 0,6 0 0 , , 7 8 0,9 1 1,1

Himmelblau function (1960) He (Krause and Benson) He (Potter and Clynne) Ne (Krause and Benson) Ne (Crovetto) Ar (Krause and Benson) Ar (Crovetto) Kr (Krause and Benson) Kr (Crovetto) Xe (Krause and Benson) Xe (Crovetto)

H* (/)

0,1

0,0

0,5

1,0

1,5

2,0

(1/T)* (/)

Figure 6.2: Experimental values by by Krause and Benson [71], Crovetto and Fernandez-Prini [72] and Potter and Clynne [73] for Henry coefficient of noble gases as function of temperature, together with the equation found by Himmelblau [70]. Both parameters, H max H and T max H , for atomic hydrogen can be estimated using the Henry coefficients of the noble gases. One can imagine that the size of a particle will determine its solubility. The size of an atom can be defined in multiple ways. The covalent radius is defined as the radius of an atom when it forms a covalent bond with another atom. [74] The Van der Waals radius is half the distance that atoms from neighbouring molecules can approach. [74] As the dissolved atoms are not bonded, the best approach is to use the Van der Waals radius of the element. Therefore, a reasonable estimation of the H max H and T max H for atomic hydrogen can be based on the values of the noble gases, where the Van der Waals radii of the elements is used as a weighting factor. Table 6.2 gives these parameters for the noble gases. A linear correlation for H max i and T max i with the Van der Waals radius is shown in Figures 6.3 and 6.4, respectively. The corresponding R 2 -value for the respective correlations is 0.97 and 0.98, which is very reasonable for this first order correlation. The correlation found between the H max i and the Van der Waals radius is H max i = 36 . 9 − 0 . 153 ∗ R V dW . Using the Van der Waals radius of a hydrogen atom, 63