Effects of process-generated hydrogen on RPV walls

7. Hydrogen pressure in PWR

(a) Zoom on time dependent concentra- tion profile close to the steel-water inter- face.

(b) Zoom on the time dependent concen- tration profile at the lining-base material interface in the RPV wall.

Figure 7.7: Concentration profile in 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 90% absorption coefficient and a hydrogen generation rate of 150 mol H/yr. The lines show the concentration profile for different moments after the start of cooling with an interval of 1 hour up to 50 hours. cases when the temperature in the base material has reached 298 K are calculated in Table 7.3. The hydrogen fugacity resulting form a hydrogen generation rate of 150 mol H/yr and an absorption coefficient of 90% is 1.30 10 5 . This is equal to 1.3 atm, this is of course not enough to result in a growth of the hydrogen flakes by itself. However, since these cases only considered corrosion, it is clear that this source is not negligible. Table 7.3: Maximum hydrogen fugacity in the base material of the RPV due to corrosion after cold shutdown.

Hydrogen production rate 50 mol H/yr 150 mol H/yr f H [Pa]

Absorption efficiency

1.60 10 3 1.30 10 5

10 % 90 %

166

1.38 10 4

Radiolysis generated hydrogen As for the corrosion generated hydrogen, a calculation for the hydrogen fugacity can be performed for the hydrogen generated by radiolysis. However, the concentrations used in these calculations are much too large to be physically relevant. This, as 86