Critical Reflections about Doel3 & Tihange2

Integrity reactor vessels Doel 3 and Tihange 2

Page: 39

2. At which temperature did the flaking occur? As far as I could reconstruct, the temperature should be below 400 o C. At this temperature, 1.5ppm is the saturation point. However, the material is very though above 100 o C. The fracture toughness remains at 195MPa / p m until the temperature drops below 100 o C. Then the fracture toughness rapidly decreases until 40MPa / p m at room temperature. So I believe that flaking occurs below 100 o C when the material is more brittle. Is this reasoning correct? 3. You mention that residual stresses resulting from the forging process influence the cracking process. Any idea how large these stresses could be? Are these stresses mainly thermal stresses due to the cooling? Is it necessary to take these stresses into account when evaluating the acceptability of the flaws with the ASME code? 4. You mention the existence of an UT-report of the shell at delivery. Is it possible to see this report? 5. Walter Bogaerts mentions in his paper that during operation of the reactor hydrogen is gen- erated and that hydrogen dissolves into the vessel steel. Are there hydrogen solubility curves available on which the hydrogen solubility at 150 atm and 300 o C can be determined? 6. In the paper of Evy De Bruycker "Phenomenology of Hydrogen Flaking in Nuclear Reactor Pressure Vessels" which we have discussed, on page 4, it is mentioned that a martensite trans- formation takes place at 200 o C. Is this valid for the steel of the reactor shell? Is this a reversible transformation? I ask this because this temperature is within the operating temper- ature of the reactor. 7. Are the data from the UT-measurements of 2016 of DOEL3 available? (number of flakes, size distribution etc..., such as presented in the previous reports of ENGIE)

I realize these are a lot of questions, and it will take some effort to answer them. I’m looking forward to these answers. It would be a great help.

FANC answer to the list of questions (e-mail March 9, 2017)

FANC greatly appreciates your strong interest in the highly technical issue of the flaw indications in the reactor pressure vessels of Doel 3 and Tihange 2. These last months, FANC took carefully note of your reflections on this issue, summarized in your report. The primary mission of the FANC is to ensure the safety of the population and the environment. In this framework, FANC and Bel V have thoroughly assessed from 2012 to 2015 the safety cases introduced by Electrabel and all studies and documents supporting them in order to justify the structural integrity of the two reactor pressure vessels. Based on our assessment and supported by the peer review by several groups of independent international experts, FANC decided to allow the restart of the two reactors in November 2015. As a Safety Authority, it is also our duty to continuously assess any new insights or arguments on safety topics which could challenge our previous positions or decisions. After thorough analysis of your arguments and the discussions you had with our experts on January 26, FANC however

R.Boonen & J.Peirs

May 18, 2017