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Probabilistic Integrity Assessment of Axial Flaw in CANDU Pressure Tube Due to the Diameter and Thickness Variation

[+] Author Affiliations
Sang-Log Kwak, Young-Jin Kim

University of Sungkyunkwan, Suwon, Korea

Joon-Seong Lee

University of Kyonggi, Suwon, Korea

Youn-Won Park

Korea Institute of Nuclear Safety, Daejon, Korea

Paper No. PVP2002-1316, pp. 111-118; 8 pages
  • ASME 2002 Pressure Vessels and Piping Conference
  • Fitness for Service Evaluations and Non-Linear Analysis
  • Vancouver, BC, Canada, August 5–9, 2002
  • Conference Sponsors: Pressure Vessels and Piping Division
  • ISBN: 0-7918-4653-9
  • Copyright © 2002 by ASME


In the CANDU nuclear reactor, pressure tubes of cold-worked Zr-2.5Nb material are used in the reactor core to contain the fuel bundles and heavy water coolant. The pressure tubes are installed horizontally inside the reactors and only selected samples are periodically examined during In-Service Inspection (ISI) due to numerous numbers of tubes. Also, these tubes gradually pick up deuterium, as such are susceptible to a crack initiation and propagation process called delayed hydride cracking (DHC). If undetected, such a cracking mechanism could lead to unstable rupture of the pressure tube. Up to this time, integrity evaluations are performed using conventional deterministic approaches. So it is expected that the results obtained are too conservative to perform a rational evaluation of lifetime. In this respect, a probabilistic safety assessment method is more appropriate for the assessment of overall pressure tube safety. This paper describes probabilistic fracture mechanics analyses of the pressure tubes in consideration of the diameter and thickness variation. Initial hydrogen concentration, the depth and aspect ratio of an initial surface crack, the DHC velocity and fracture toughness are considered as probabilistic variables. In all the analyses, failure probabilities are calculated using the Monte Carlo (MC) simulation. It is clearly demonstrated from these analyses that failure probabilities are somewhat sensitive in size change of the pressure tube and the hydride precipitation temperature.

Copyright © 2002 by ASME
Topics: Pressure , Thickness



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