Critical Reflections about Doel3 & Tihange2

Integrity reactor vessels Doel 3 and Tihange 2

Page: 38

wherein all the hydrogen flakes are found amounts 1.61 ppm. The mean hydrogen concentration in the part of the ingot which will become zone B in figure 20 wherein no hydrogen flakes are found amounts 1.0 ppm. By using a more refined analysis, the gradient will be probably smaller, but data lacks for such an analysis.

Total dissolved available H 2 volume

concentration H 2 volume

for cracking (Nml / dm 3 )

(Nml / dm 3 )

(ppm)

threshold concentration outer shell concentration

0.8 1.0

70 87

–

17 44 61 71

mean total shell concentration

1.31

114 131 141

uniform concentration inner shell concentration

1.5

1.61

Table 3: Volume of normal cm 3 H

3 steel for different concentrations in the shell.

2 in 1 dm

Table 3 presents the amounts of hydrogen in the steel for different hydrogen concentrations in the different cases. The maximum concentration of hydrogen amounts 1.61ppm, which is slightly higher than the 1.5 ppm in the uniform case. This implies that significant enrichment of hydrogen in the inner 100 mm of the shell did not occur. The conclusion remains that hydrogen flaking cannot be the only cause of the flaws, but that another cause has resulted in flaking or that the flaws have been growing during time.

Communication of the list of questions to FANC. (e-mail February 16, 2017)

First, I want to thank you for the opportunity to have a meeting with the FANC experts on January 26. The information you provided me was very useful. The most important point we have discussed was the hydrogen balance and the amount of hydrogen which could be present in the ingot. As far as I understood from your side, the process of concentration of hydrogen in the segregated zones was as follows: In the melt, hydrogen was dissolved. After pouring the ingot, the ingot starts to cool down. First, the outside of the ingot solidifies and impurities and alloy elements are diffusing to the molten part inside the ingot. Once the inside part of the ingot solidifies, these impurities and alloy elements segregate in segregation zones where they form ghost lines, which are sensitive to hydrogen cracking. Also the hydrogen diffuses to the high temperature zones, where the hydrogen segregates as the ingot further cools down, and in the ghost line areas, they cause hydrogen flaking. My viewpoint is that there is not sufficient hydrogen dissolved in the melt to cause such high density of flakes, a fraction of 10So, I’m still puzzled and I’m looking for answers of the following questions: 1. The melt contains 1.5ppm H according to a measurement of KRUPP, and samples from the solidified ingot also contain 1.5ppm H. The level of H-concentration was very low compared to the solubility of H in the steel. What could be the maximum concentration of H in the centre of the ingot after cooling down to room temperature?

R.Boonen & J.Peirs

May 18, 2017