Effects of process-generated hydrogen on RPV walls

6.3. In-service hydrogen generation

Figure 6.6: Henry coefficient in mol/m 3 Pa for atomic hydrogen as a function of temperature. It is calculated as H cpi = ρ H 2 O M H 2 O · H pxi .

Equivalent H and H 2 fugacity Knowing the Henry coefficient for atomic H in water as a function of temperature, one can calculate the equivalent atomic H pressure in equilibrium with the primary water. The concentration of atomic H in the primary water for typical conditions during a PWR fuel cycle are calculated to decrease from 8.7 10 -7 to 8.0 10 -7 mol/l between the beginning and end of cycle (see section 5.4.3). At a temperature of 300 ◦ C the equivalent atomic H pressure is found to be:

c H H H = 8 . 7 · 10 − 4 20 . 0 · 10 − 6

f H =

(6.8)

= 43 . 5 Pa

At the beginning of the fuel cycle, the equivalent H fugacity in the primary system is found to be 43 Pa. Similarly, it can be calculated that the equivalent H fugacity at the end of cycle is 40 Pa. The chemical equilibrium between H and H 2 is given by: H 2 ←−→ 2H (6.9) 67