Effects of process-generated hydrogen on RPV walls

7. Hydrogen pressure in PWR

ppm Pa -1/2 .

f H =

x H k S

2

(7.3)

7 . 447 · 10 − 4 ! 2

= 9 . 67 · 10 − 3

= 166 Pa

The corrosion conditions responsible in the lowest concentration of hydrogen in the RPV wall, 10% absorption efficiency and 50 mol H/yr, result in a hydrogen fugacity of maximum 166 Pa in the base material. Figure 7.4 shows that the highest hydrogen fugacity indeed is reached when the wall has cooled down. Since diffusion is very slow, the decrease in hydrogen fugacity after 28 hours is not noticeable in the curve. Similar calculations can be performed for the other conditions listed in Table 6.5. The graphs corresponding to these conditions are shown in Figures 7.5 to 7.7.

Figure 7.4: Hydrogen fugacity in the base material of the RPV wall as a result of the typical cooling path for the reactor coolant of a pressurized water reactor during a cold shutdown considering only corrosion generated hydrogen with a 10% absorption coefficient and a hydrogen generation rate of 150 mol H/yr. As expected, similar to the first case, the concentration of hydrogen in the base material does not decrease a lot over a time period of 50 hours after the start of the cold shutdown. The hydrogen fugacities corresponding to each of the considered 84