Effects of process-generated hydrogen on RPV walls

6. Hydrogen concentration in PWR wall

The equilibrium concentrations at the steel-water interface are found to vary between 0.077 and 2 ppm, while the concentrations at the interface between the lining and the base material varies between 0.01 and 0.271 ppm, depending on the absorption efficiency and the hydrogen production rate from corrosion. A big gradient for the hydrogen concentration in the RPV lining is the result of the low diffusion coefficient in the material compared to the ferritic base material. Therefore, a much higher gradient is necessary in order to maintain the same flux of hydrogen. 6.4 Conclusion The process generated hydrogen results in an increased hydrogen concentration in the RPV wall. It has been calculated that the radiolytic hydrogen generation results in a very large activity of hydrogen in the steel, 3.16 10 15 ppm. The hydrogen charging due to corrosion results in an equilibrium concentration between 0.010 and 0.271 ppm at the lining-base material interface, depending on the assumed value for the absorption efficiency and the hydrogen production rate from corrosion.

76