Critical Reflections about Doel3 & Tihange2

Integrity reactor vessels Doel 3 and Tihange 2

Page: 18

6 Treatment of flaws by Electrabel

The absence of a consolidated theory about multiple cracks and interaction between cracks, and the absence of publications of other applications of such a theory on other cases such as aviation or other reactor vessels (chemical industry) is the main point of concern. Electrabel has conducted research to multiple cracks and has developed grouping rules for closely spaced flaws [ 18 ] ,p18. As far as the author could trace the method to group these flaws from their publications, one of the publications on which the grouping method Electrabel has developed is based on is the work of Kunio Hasegawa, Koichi Saito and Katsumasa Miyzaki [ 22 ] . A similar study has been carried out by Ali Abbaszadeh Bidokhti and Amir Reza Shahani which is published in the Latin American Journal of Solids and Structures [ 23 ] . Hasegawa et al. are searching for alignment rules to decide if cracks which are in close proximity to each other should be treated as non-aligned or as coplanar. The criteria for these alignment rules are defined in many fitness-for-service codes (AMSE, JSME, etc. . . ), however, these criteria are different in the different codes. Based on finite elements simulations and tensile tests on steel specimen with two parallel cracks in opening mode at different distances from each other, they propose new alignment rules for cracks for linear elastic fracture mechanics evaluation.

Figure 14: Illustration of flaw grouping [ 14 ] p74.

Based on the paper of Kunio Hasegawa, Koichi Saito and Katsumasa Miyzaki [ 22 ] , Electrabel de- veloped grouping rules for flaws which are published in two papers which are presented at two different conferences [ 24, 25 ] . This work has led to the proposal of an ASME code case N–848 "Alternative characterization rules for quasi-laminar flaws – Section XI, Division I" [ 26 ] , [ 27 ] . Using these newly developed rules, a part of the flaws will be grouped in rectangular boxes ( [ 14 ] p71-75) based on the proximity of the flaws to each other as presented in figure 14 (figure 4.37 in [ 14 ] p74). Then, the circle or ellipse with the largest dimension, as illustrated in figure 15 (figure 4.38 in [ 14 ] p75), will be taken as an ”equivalent flaw” which should be the worst case flaw and will then be evaluated as a single flaw using the ASME BPVC criteria. There is no proof found in the literature or in the reports available at the FANC website which

R.Boonen & J.Peirs

May 18, 2017