Leak Before Break procedure: Recent modification of RCC-MR A16 appendix and proposed improvements

This paper presents recent modifications of the Leak Before Break procedure of the A16 appendix from French RCC-MR nuclear code and the improvements that will be proposed. The first part of the study deals with the prediction of the crack size at penetration. In the case of small initial defect the validity of the Master Curve used in the A16 appendix is confirmed for pipes. For large initial defects, a correction to the A16 procedure is proposed to take into account the effect of large initial crack length on its size at penetration.The second part of this paper focuses on the crack shape evolution after penetration, which is characterized by two stages: first straightening of the crack shape and then crack growth at both inner and outer surfaces. This typical behaviour is confirmed by numerical and experimental works for which particular loading conditions have been investigated.