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Research Papers: Materials and Fabrication

A Risk-Informed Approach to Leak-Before-Break Assessment of Pressure Tubes in CANDU Reactors

[+] Author and Article Information
M. D. Pandey1

Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, ON, N2L 3G1, Canadamdpandey@uwaterloo.ca

A. K. Sahoo

Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, ON, N2L 3G1, Canadaasahoo.uw@gmail.com

1

Corresponding author.

J. Pressure Vessel Technol 132(2), 021403 (Feb 03, 2010) (8 pages) doi:10.1115/1.3148087 History: Received October 09, 2008; Revised April 03, 2009; Published February 03, 2010; Online February 03, 2010

The leak-before-break (LBB) assessment of pressure tubes is intended to demonstrate that in the event of through-wall cracking of the tube, there will be sufficient time followed by the leak detection, for a controlled shutdown of the reactor prior to the rupture of the pressure tube. CSA Standard N285.8 (2005, “Technical Requirements for In-Service Evaluation of Zirconium Alloy Pressure Tubes in CANDU Reactors,” Canadian Standards Association) has specified deterministic and probabilistic methods for LBB assessment. Although the deterministic method is simple, the associated degree of conservatism is not quantified and it does not provide a risk-informed basis for the fitness for service assessment. On the other hand, full probabilistic methods based on simulations require excessive amount of information and computation time, making them impractical for routine LBB assessment work. This paper presents an innovative, semiprobabilistic method that bridges the gap between a simple deterministic analysis and complex simulations. In the proposed method, a deterministic criterion of CSA Standard N285.8 is calibrated to specified target probabilities of pressure tube rupture based on the concept of partial factors. This paper also highlights the conservatism associated with the current CSA Standard. The main advantage of the proposed approach is that it retains the simplicity of the deterministic method, yet it provides a practical, risk-informed basis for LBB assessment.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

A schematic of the CANDU fuel channel

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Figure 2

A typical reactor shutdown transient

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Figure 3

Variation of lower-bound Kc and upper-bound V during the RSDT

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Figure 4

Actual and critical crack lengths versus time after leak

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Figure 5

Partial factors versus reliability index for δR=0.1 and δS=0.2

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Figure 6

Probability distribution of fracture toughness and DHC growth rate at full power

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Figure 7

Distributions of actual and critical crack lengths during RSDT

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Figure 8

Mean and 95% bounds for actual and critical crack lengths during the RSDT cycle

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Figure 9

Calibrated partial factors versus target reliability index

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