Effects of process-generated hydrogen on RPV walls

5.3. Corrosion of the RPV wall

upper limit

lower limit:

. 1 · 10 − 6 1 · 96485 mol cm 2 s = 1 . 0364 · 10 − 12

10 − 6 1 · 96485 mol cm 2 s = 1 . 0364 · 10 − 11

˙ n H = 1 ·

˙ n H = 0

(5.8)

mol cm 2 s

mol cm 2 s

This can be recalculated to the total hydrogen production on the entire inner surface of the RPV over a period of one year. The inner surface of the RPV is about 200 m 2 and 31536000 seconds in a year. lower limit: ˙ n H = 1 . 0364 · 10 − 12 ∗ 200 · 10 4 ∗ 31536000 mol H yr ≈ 65 mol H yr (5.9) The lower limit of 0.1 µ A/cm -2 , corresponds to 65 mol H/yr. Similarly, the upper limit of 1 µ A/cm -2 results in a generation of 650 mol H/yr. Furthermore, Bogaerts [27] calculated that for a corrosion rate of 0.1 to 1 µ m/yr, which is a realistic value, there is a total hydrogen generation of approximately 60 mol H/yr. The atomic density of SS304 is about 14 10 4 mol/m 3 and it is assumed that each atom will release 2 electrons in the anodic oxidation reaction, which is true for the major elements like Fe and Ni, while Cr is oxidized to Cr 3+ . For a total inner surface of 200 m 2 , the hydrogen production is: Finally, Wanklyn and Jones [63] reviewed corrosion rate data of reactor metals. They found that “the vast number of reported values range between 5 and 20 mg/dm 2 /month (mdm)” for stainless steels. Using a molar weight for typical 300- type stainless steel of 56 g/mol a total surface area of 200 m 2 and again a release of 2 electrons per atom, a corrosion rate of 5 mdm in the complete reactor corresponds to: ˙ n H = 5 · 10 − 3 g dm 2 month ∗ 20000dm 2 ∗ 12months ∗ 2 e − atom 56 g mol ≈ 43 mol H yr (5.11) A corrosion rate of 5 mdm results in a atomic hydrogen generation of 43 mol/yr or 21 mol H 2 /yr. Equivalently, 20 mdm produces 170 mol H/yr or 85 mol H 2 /yr. Although the exact value of hydrogen production due to corrosion of the RPV wall differs for each of the calculations, the order of magnitude is the same for each 45 ˙ n H = 1 µ m yr ∗ 200m 2 ∗ 14 · 10 4 mol m 3 ∗ 2 e − atom = 56 mol H yr (5.10)