Effects of process-generated hydrogen on RPV walls

5.4. Radiolysis in the primary water

The values for the parameters used in the simulation of these extreme conditions are shown in Table 5.3. These values are based on typical conditions in a PWR with some extra margin. The radiation values have a margin around the typical radiations for a PWR at full power. The α -radiation is related to the concentration of boron in the primary water, as explained earlier. This is seen in the table, as the absorbed α -radiation is a function of the boron concentration in ppm and the absorbed neutron-radiation in R/s. Table 5.3: Values for the extreme conditions used for the stability test of the model, based on typical values in a PWR. [53]

Value

Unit

Temperature

290–330

◦ C

Pressure

150

bar

Boron

4000 – 0

ppm ppm

Lithium

5 – 0

3 /kg

H 2 O 2

50 – 25 0.01 – 0 0.01 – 0

STP cm

ppm ppm R/s R/s R/s

H 2 O 2

5 10 4 – 5 10 5

γ -radiation

neutron-radiation 5 10 4 – 5 10 5 α -radiation 7.34 10 -5 *[B]*Γ n

Specific combinations of these parameter limits are simulated with the code. As a result the time dependency of the concentration of each of the species is found. Figure 5.7 gives an overview of these findings. From all the different graphs in Figure 5.7, it is clear that a steady state condition is reached after about 10 -4 s. This is valid for all different combinations of conditions. As typical flow rates for the primary water in a PWR are 1 m/s, it is clear that the chemical equilibrium in the reactor is reached much faster than the water flows through the reactor. Therefore, the concentration can be considered to be homogeneous over the complete height of the reactor and no position dependency must be taken into account. Furthermore, it can be seen in the graphs that the temperature does not have a big influence on the steady state concentrations. This is especially clear when one compares figures 5.7a and 5.7b, where exactly the same conditions are simulated for a different temperature, being at 330 and 290 ◦ C, respectively. 5.4.3 Hydrogen concentration during typical fuel cycle As the stability of the system is proven and the influence of the temperature, between 290 and 330 ◦ C, on the chemical equilibrium in the primary water is negligible, one can start to simulate the conditions in a typical fuel cycle for a PWR. As, for this 53