Critical Reflections about Doel3 & Tihange2

Integrity reactor vessels Doel 3 and Tihange 2

Page: 37

A temperature difference between ingot wall and molten core of about 500 o C is estimated to let solidify the melt in 24 hours. Also a FEM simulation with an isolated ingot wall leads to a similar temperature drop. 3. Hydrogen concentration in terms of temperature. As data for subsaturated hydrogen diffusion are not available, the hydrogen concentration is estimated from the solubility curve presented in figure 19. This should be a worst case assumption. The largest drop in solubility of hydrogen in solid material is taken for a temperature difference of 500 o C on the solubility curve of 1 atm presented in figure 19. Then, the same ratio of hydrogen concentration on the solubility curve is used for the hydrogen concentration in the subsaturated steel. The largest drop in solubility occurs on the curve between 900 o C and 1400 o C, including the α - γ -transformation, is from 8ppm to 3ppm, so a concentration ratio of 8 / 3 is used to calculate the hydrogen concentration gradient between the outer ingot wall and the inner radius of of the future shell. 4. Hydrogen concentration in the cracked zone and in the non-cracked zone. The total amount of hydrogen present in the ingot with a level of 1.5ppm is redistributed over the ingot, such that the total amount of hydrogen is conserved. The hydrogen concentration in the solidified part follows the temperature gradient and remains constant in the liquid part. A linear function is used to approximate the hydrogen concentration in terms of the radius for the solidified part of the ingot.

2.2

liquid

solid

2

1.8

1.6

1.4

1.2

1

hydrogen concentration (ppm)

0.8

0.6

0

0.2

0.4

0.6

0.8

1

1.2

ingot radius (m)

Figure 21: Hydrogen concentration in terms of ingot radius using a linearized model.

The result is presented in figure 21. At the outer wall, the hydrogen concentration has decreased until 0.75 ppm. At the radius which will become the inner wall of the future shell, the hydrogen concentration has increased until 2 ppm. The mean hydrogen concentration drops from 1.5 ppm to 1.31 ppm in the metal of the future shell (Zone A plus zone B in figure 20) as the central part of the ingot which is the most enriched with hydrogen will be machined out during manufacturing. The mean hydrogen concentration in the part of the ingot which will become zone A in figure 20

R.Boonen & J.Peirs

May 18, 2017