Root Cause Analysis of Cracking in Alloy 182 BWR Core Shroud Support Leg Cracks
Cracks were found in the Alloy 182 weld and buttering of two core shroud support legs in the Forsmark BWR Unit 1. This paper presents the root cause analysis based on mechanical and metallurgical analysis by Microscopy, Electron Backscatter Diffraction, and micro- and nano-indentation analysis along the crack path. The High Resolution Analytical Transmission Electron Microscopy examinations on the oxides are presented in detail in another paper at this conference. The morphology of the cracks, local hardness, crystallographic orientations and compositions along the crack path and crack tip regions were examined. The crack penetrated the boat keel surface into the A182 Low Alloy Steel mixing zone. Cracking was identified as IGSCC and signs of grinding and elevated micro-hardness near the boat top surface region were detected. Plastic deformation was observed in a crack tip region in a sample section with the largest crack depth, while not at the crack periphery.
KeywordsCrack Alloy 182 Failure analysis BWR Core shroud Support leg SEM
The authors wish to express their sincere gratitude to Mr. Roger Lundström and Mr. Michael Jakobsson at Studsvik Nuclear AB who performed light optical microscopy work, Prof. Esteban Broitman at, formerly Linköping University who helped with nano-indentation measurement and scientific discussion about the result, and to Dr. J. Öijerholm at Studsvik Nuclear AB for his technical and administrative support.
- 1.J. Chen et al., Microstructure of Oxide Films Formed in Alloy 182 BWR Core Shroud Support Leg Cracks, in Paper Presented in this Conference Google Scholar
- 2.A. Jenssen et al., Assessment of Cracking in Dissimilar Metal Welds, in 10th International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors (NACE International, Houston, TX, USA, 2002)Google Scholar
- 3.T. Cassagne et al., Stress Corrosion Crack Growth Rate Measurements in Alloys 600 and 182 in Primary Water Loops under Constant Load, in Proceedings of the 9th International Symposium on Environmental Degradation of Materials in Nuclear Systems-Water Reactors (The Minerals, Metals & Materials Society, Warrendale, PA, 1999), pp. 217–224Google Scholar
- 4.W.J. Mills, C.M. Brown, Stress Corrosion Crack Growth Rates or Alloy 82H Welds in High Temperature Water, in Proceedings of I1th International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors (ANS, 2003), pp. 1240–1254Google Scholar