Effects of process-generated hydrogen on RPV walls

7.2. Pressure during normal operating conditions

Figure 7.2: Temperature profile as a function of depth in the RPV wall, where 0 mm is its inner surface. The temperature profile is a result of the typical cooling path for the reactor coolant of a pressurized water reactor during a cold shutdown.The lines show the temperature profile for different moments after the start of cooling. The interval between the lines corresponds to 1 h. The equilibrium temperature of 298 K is reached in the whole thickness of the RPV wall after approximately 28 hours. The different lines in Figure 7.2 represent the temperature profiles in the RPV wall with a time interval of 1 hour. One can see that the temperature gradient in the RPV wall is relatively small over the complete cooling period. The maximum temperature difference between the coldest and hottest position during cooldown is limited to 30 ◦ C. The equilibrium temperature of 298 K is reached over the complete thickness of the RPV wall after approximately 28 hours. As the reactor cools down during a cold shutdown, the hydrogen production has dropped to a negligibly low value as the radiation has decreased towards zero. Furthermore, the temperature goes down and therefore, the hydrogen production due to corrosion will similarly decrease. To simulate the change in hydrogen concentration in the RPV wall during a cold shutdown, the time dependent temperature profiles calculated before can be used to calculate the diffusion of the hydrogen in the steel. Only diffusion and effusion of the hydrogen will be considered as the production of hydrogen has dropped to negligible values. Furthermore, to be conservative, diffusion will be considered to be the rate determining process and effusion is considered to be 81