Effects of process-generated hydrogen on RPV walls

6.3. In-service hydrogen generation

Figure 6.10: Top: Schematic representation of the RPV wall used to model the diffusion of hydrogen. Bottom: Solution to the diffusion model in the RPV wall.

where J c H is the hydrogen flux due to corrosion at the steel-water interface in mol/m 2 s, D H is the diffusion coefficient of hydrogen in the RPV wall in m 2 /s, δc H δx is the change in hydrogen concentration, c H , with position x. The RPV lining has to be differentiated from the RPV base metal. The diffusion coefficient in the base material has been determined in equation 6.18. At 300 ◦ C, this diffusion coefficient is equal to 2.1 10 -9 m 2 /s. Diffusion coefficients for hydrogen in stainless steel lining is much lower. San Marchi [83] found a temperature dependent relation for the diffusion coefficient in stainless steel: A schematic representation of the RPV wall used in the diffusion problem is shown in Figure 6.10, together with a typical solution. c 1 and c 2 represent the concentrations at the steel-water interface and the lining-base material interface, respectively. The exact solutions for c 1 and c 2 for each of the parameters in Table 6.4, are shown in Table 6.5. Table 6.5: Hydrogen charging rates in the RPV due to corrosion at the steel-water interface. D ss H = 8 . 9 · 10 − 7 exp( − 53900 RT ) (6.22)

Hydrogen production rate 50 mol H/yr 150 mol H/yr c 1 [ppm] c 2 [ppm] c 1 [ppm] c 2 [ppm]

Absorption efficiency

10 % 90 %

0.077 0.695

0.010 0.090

0.232 2.084

0.030 0.271

75