Nuclear Engineering and Design 235 (2005) 2099–2108 Optimum local failure model of steam generator tubes with multiple axial through-wall cracks Seong In Moon a , Young Jin Kim a,∗ , Jin Ho Lee b , Youn Won Park b , Myung Ho Song b a School of Mechanical Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Kyonggi-do 440-746, Republic of Korea b Korea Institute of Nuclear Safety, 19 Gusung-dong, Yusung-gu, Daejeon 305-338, Republic of Korea Received 18 November 2004; received in revised form 24 May 2005; accepted 30 May 2005 Abstract It is commonly required that steam generator tubes wall-thinned in excess of 40% should be plugged. However, the plugging criteria are known to be too conservative for some locations and types of defects and its application is confined to a single crack. In the previous study, a crack coalescence model applicable to steam generator tubes with two collinear axial through-wall cracks was proposed and a coalescence evaluation diagram was developed which can be used to determine whether the adjacent cracks detected by NDE coalesce or not. In this paper, a total of 9 local failure models including flow stress model, necking-based model, stress-based model, reaction force model and plastic zone contact model were introduced to determine the optimum local failure model. Plastic collapse tests and finite element analyses using thin plates with two collinear through-wall cracks were performed for the selection of the optimum local failure model. By comparing the test results with the prediction results obtained from local failure models, the reaction force model and plastic zone contact model were determined as the optimum local failure models. © 2005 Elsevier B.V. All rights reserved. 1. Introduction It is commonly requested that steam generator tubes with defects exceeding 40% of wall thickness in depth should be plugged (ASME, 1998; USNRC, 1976, 1996). However, this criterion is known to be too con- ∗ Corresponding author. E-mail address: yjkim50@skku.edu (Y.J. Kim). servative for some locations and types of defects. Many defects detected during in-service inspection show that the formation of multiple cracks at the top of tube sheet is typical but there is no reliable plugging criterion for the tubes with multiple cracks (Cochet and Flesch, 1987; Kim et al., 1999a,b,c; Kim et al., 1993; Lee et al., 2000, 2001; Yu et al., 1994). There have been stud- ies for multiple cracks but most of them are limited to elastic analyses and only few studies have been done 0029-5493/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2005.05.024