SYMPOSIA PAPER Published: 28 July 2021
STP162220190015

Full-Scale Fracture Toughness Behavior of Zr-2.5Nb Pressure Tubes with High Hydrogen Concentrations and Different Hydride Morphologies

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Fracture toughness is required for fracture initiation and leak-before-break evaluation of Zr-2.5Nb pressure tubes in Canadian Deuterium Uranium, or CANDU, reactors. The effects of high hydrogen concentration ([H]) and associated hydride morphology on fracture toughness need to be better characterized to support continued operation and reactor life extension. This paper summarizes results from 16 rising pressure burst tests performed on Zr-2.5Nb pressure tubes. Test variables include: material variability, hydrogen concentration, hydride orientation, and test temperature. Hydride orientation was characterized by the hydride continuity coefficient (HCC). The tests were performed over a range of temperatures to characterize the fracture toughness behavior in the lower-shelf, transition, and upper-shelf fracture regimes. Test results indicate that, under essentially the same hydride reorientation conditions, there was large variation in hydride reorientation between the two tubes tested. At room temperature, the fracture toughness of the hydrided specimens was significantly lower than that of the specimens containing as-fabricated [H]. Increasing [H] from 60 ppm to 100 ppm led to more reoriented hydrides and a further reduction in fracture toughness, and increasing from 100 ppm to 130 ppm did not lead to a further increase in reoriented hydrides or a reduction in fracture toughness. Hydrided specimens with relatively low HCC exhibited a gradual transition behavior from lower shelf to upper shelf. Hydrided specimens with high HCC exhibited a relatively steep transition behavior. Increasing HCC led to a reduction in fracture toughness in the lower-shelf regime and an increase in transition temperature from lower shelf to upper shelf. Examinations of hydride morphologies and fracture surfaces suggested that the crack growth behavior was dominated by hydride fracture in the lower-shelf regime and mainly governed by matrix failure in the upper-shelf regime. A combination of both fracture mechanisms occurred in the transition region. All test specimens with different [H] and hydride morphologies approached the upper-shelf toughness at 150°C.

Author Information

Cui, Jun
Kinectrics Inc., Toronto, CA
Shek, Gordon, K.
Kinectrics Inc., Toronto, CA
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Pages: 262–293
DOI: 10.1520/STP162220190015
ISBN-EB: 978-0-8031-7691-1
ISBN-13: 978-0-8031-7690-4