Critical Reflections about Doel3 & Tihange2

Integrity reactor vessels Doel 3 and Tihange 2

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the vessel walls, branched flaws are present. An example of a grouped box is presented in figure 16 (figure in [ 13 ] p16). This box has as dimen- sion 69 mm and is composed of 7 flaws of which 4 flaws with a dimension of 11 mm, 1 flaw of 13 mm, 1 flaw of 14 mm and 1 flaw of 42 mm. To what extend this boxed flaw behaves as a single flaw of 69 mm is not described in the FANC reports. As stated before, current research concerns the interaction of two or a few flaws [ 8 ] ,p361, but never in such flaw density as reported in de Electrabel reports about the reactor vessels. The Oak Ridge National Laboratory (ORNL) performed a detailed technical review of the 2015 Electrabel Safety Cases prepared for the Belgium reactor pressure vessels at Doel3 and Tihange2 [ 18 ] . The ORNL carried out an independent quantitative assessment of the entire flaw popula- tion in the two Belgian reactors according to the ASME Boiler and Pressure Vessel Code, Section XI, Appendix G, "Fracture Toughness Criteria for Protection Against Failure", New York (1992 and 2004) using ORNL tools, methodologies, and the ASME Code Case N-848, "Alternative Character- ization Rules for Quasi-Laminar Flaws". The ORNL also pointed to an internal Electrabel report CNT-KCD / 4NT / 20374 / 000 / 01, dd. 30 / 07 / 2014, wherein proximity rules for flaws are been inves- tigated [ 18 ] p18. In the investigation of the ORNL, the majority of the flaws are treated as single flaws according to the ASME BPVC criteria. The other flaws were grouped according to the code case N–848, the grouped flaws were treated as a single flaw with as dimension the largest circular dimension of the resulting box diagonal. For the flaw groups which were found non-compliant to the ASME BPVC acceptance criteria after screening, the circle is replaced by an ellipse fitting into the 3D-boxes (see figure 15, the ellipse in dashed line) and screened again. [ 18 ] p23. The grouped flaws which do not comply the ASME BPVC acceptance criteria are listed in tables 5.2, 5.3, 5.4, 5.5 and 5.6 in the ORNL report [ 18 ] p39-45. After the new screening of the elliptical equivalent flaws, the flaw groups which were found non- compliant to the ASME BPVC criteria, the flaws previously in a group are no longer treated as a group, but are modelled individually in a finite element multi-flaw model that should account for mechanical interactions among closely spaced flaws. Particularly for the latter group, the results are questionable as in these cases, there is no con- solidated fracture mechanics theory available for multiple closely spaced cracks with interaction between these cracks and no precedent cases have been published. It makes the nuclear reactor vessels of Doel3 and Tihange 2 an experimental case for a non- consolidated fracture mechanics theory.

7 Chronology of the events leading to the nuclear code case N-848

As the nuclear code case N–848 is of prime importance to the analysis of the flaws in the Doel 3 and Tihange 2 nuclear reactor vessels, the chronology of the events which led to this code case has been reconstructed as well as possible by the authors using internet information. In this section, the time sequence is represented with the internet addresses which lead to technical documents, which

R.Boonen & J.Peirs

May 18, 2017