Critical Reflections about Doel3 & Tihange2

Integrity reactor vessels Doel 3 and Tihange 2

Page: 16

Size Number Content H 2 pressure H 2 Volume H 2 Total Volume (mm) – (ml) (bar) (Nml) (Nml) 10 2000 0.001373 4948.9 6.80 13590 15 4000 0.003829 4040.8 15.47 61887 20 2300 0.007970 3499.4 27.89 64145 25 1100 0.01400 3130.0 43.82 48202 30 800 0.02220 2857.3 63.42 50734 35 400 0.03291 2645.3 87.04 34818 40 200 0.04613 2474.5 114.14 22828 45 150 0.06218 2332.9 145.05 21758 50 100 0.08126 2213.2 179.85 17985 55 80 0.10362 2110.2 218.66 17493 60 50 0.12946 2020.4 261.56 13078 65 30 0.15903 1941.1 308.70 9261 Total 11210 – – – 375777

Table 2: Distribution of the cracks in the Doel3 lower shell, with the volumes and pressure of hydrogen to cause them.

was available for flaw generation. If the size distribution of the cracks is equal to the distribution over the complete lower shell, the result will be as follows. The lower shell contains 11607 indications ( [ 16 ] p27). The distribution to size in the Doel 3 lower shell has been reconstructed from the graph ( [ 16 ] p30) and is presented in table 2. The finite element analysis has been carried out for each different flaw diameter. The corresponding pressures and volumes of hydrogen necessary to form the flaws are tabulated in table 2. When it is assumed that the high density area has the same distribution as the whole lower shell presented in table 2, the volume of H 2 to cause the cracks will be 375777 11210 · 41 = 1374 ml / dm 3 steel, which is approximately 22 times the hydrogen available for flaw formation. This leads to the conclusion that there is not sufficient hydrogen dissolved in the steel to generate such high density of cracks. In the complete lower shell with a wall thickness of 200mm, a diameter of 4m and a height of 2.5m, 823 l H 2 is dissolved of which 383 l H 2 is available for cracking for the uniform case. This is slightly more than the 375 l H 2 necessary to cause all the cracks. Then this hydrogen has to diffuse several meters following the circumference of the reactor vessel to form flaws in the high density areas. It is more likely that a large part of the hydrogen diffuses out of the 200mm thick wall or being trapped in the metal than to travel a few meters to the high flaw density areas. In both calculations, the amount of dissolved hydrogen initially in the steel is far too small (13 to 22 times too small) to cause such high density of flakes. This leads to the conclusion 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.

R.Boonen & J.Peirs

May 18, 2017