Reliability of Steam Generator Tubes With Axial Cracks

[+] Author and Article Information
L. Cizelj, B. Mavko

Reactor Engineering Division, “Jožef Stefan” Institute, P. O. B. 3000, 1001 Ljubljana, Slovenia

P. Vencelj

University of Ljubljana, Jadranska 21, 1000 Ljubljana, Slovenia

J. Pressure Vessel Technol 118(4), 441-446 (Nov 01, 1996) (6 pages) doi:10.1115/1.2842211 History: Received January 30, 1995; Revised February 15, 1996; Online February 11, 2008


An approach for estimating the failure probability of tubes containing through-wall axial cracks has already been proposed by the authors. It is based on probabilistic fracture mechanics and accounts for scatter in tube geometry and material properties, scatter in residual and operational stresses responsible for crack propagation, and characteristics of nondestructive examination and plugging procedures (e.g., detection probability, sizing accuracy, human errors). Results of preliminary tests demonstrated wide applicability of this approach and triggered some improvements. The additions to the model are extensively discussed in this paper. Capabilities are demonstrated by results of analysis of steam generator no. 1 in Slovenian nuclear power plant located in Krško after the 1992 inspection and plugging campaign. First, the number of cracked tubes and the crack length distribution were estimated using data obtained by the 100-percent motorized pancake coil inspection. The inspection and plugging activities were simulated in the second step to estimate the efficiency of maintenance in terms of single and multiple-tube rupture probabilities. They were calculated as a function of maximum allowable crack length. The importance of human errors and some limitations of present nondestructive examination techniques were identified. The traditional wall thickness and crack-length-based plugging criteria are compared. The crack-length-based criterion is shown to be more efficient and more safe, especially because of strong suppression effect on probability of multiple-tube rupture. The results are considered to be important for safety and maintenance of existing plants and for further research.

Copyright © 1996 by The American Society of Mechanical Engineers
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