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Crack Growth Through the Thickness of Thin-Sheet Hydrided Zircaloy-4 download pdf

Crack Growth Through the Thickness of Thin-Sheet Hydrided Zircaloy-4 download pdf

Crack Growth Through the Thickness of Thin-Sheet Hydrided Zircaloy-4.cPatrick Ac Raynaud
Crack Growth Through the Thickness of Thin-Sheet Hydrided Zircaloy-4
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Author: Patrick Ac Raynaud
Number of Pages: 234 pages
Published Date: 07 Sep 2011
Publisher: Proquest, Umi Dissertation Publishing
Publication Country: United States
Language: English
Type: PDF
ISBN: 9781243655745
File Name: Crack.Growth.Through.the.Thickness.of.Thin-Sheet.Hydrided.Zircaloy-4.pdf
Download Link: Crack Growth Through the Thickness of Thin-Sheet Hydrided Zircaloy-4
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In recent years, the limits on fuel burnup have been increased to allow an increase in the amount of energy produced by a nuclear fuel assembly thus reducing waste volume and allowing greater capacity factors. As a result, it is paramount to ensure safety after longer reactor exposure times in the case of design-basis accidents, such as reactivity-initiated accidents (RIA). Previously proposed failure criteria do not directly address the particular cladding failure mechanism during a RIA, in which crack initiation in brittle outer-layers is immediately followed by crack growth through the thickness of the thin-wall tubing. In such a case, the fracture toughness of hydrided thin-wall cladding material must be known for the conditions of through-thickness crack growth in order to predict the failure of high-burnup cladding. The fracture toughness of hydrided Zircaloy-4 in the form of thin-sheet has been examined for the condition of through-thickness crack growth as a function of hydride content and distribution at 25C, 300C, and 375C. To achieve this goal, an experimental procedure was developed in which a linear hydride blister formed across the width of a four-point bend specimen was used to inject a sharp crack that was subsequently extended by fatigue pre-cracking. The electrical potential drop method was used to monitor the crack length during fracture toughness testing, thus allowing for correlation of the load-displacement record with the crack length. Elastic-plastic fracture mechanics were used to interpret the experimental test results in terms of fracture toughness, and J-R crack growth resistance curves were generated. Finite element modeling was performed to adapt the classic theories of fracture mechanics applicable to thick-plate specimens to the case of through-thickness crack growth in thin-sheet materials, and to account for non-uniform crack fronts. Finally, the hydride microstructure was characterized in the vicinity of the crack tip by means of digital image processing, so as to understand the influence of the hydride microstructure on fracture toughness, at the various test temperatures. Crack growth occurred through a microstructure which varied within the thickness of the thin-sheet Zircaloy-4 such that the hydrogen concentration and the radial hydride content decreased with increasing distance from the hydride blister. At 25C, the fracture toughness was sensitive to the changes in hydride microstructure, such that the toughness KJi decreased from 39 MPa√m to 24 MPa√m with increasing hydrogen content and increasing the fraction of radial hydrides. The hydride particles present in the Zircaloy-4 substrate fractured ahead of the crack tip, and crack growth occurred by linking the crack-tip with the next hydride-induced primary void ahead of it. Unstable crack growth was observed at 25C prior to any stable crack growth in the specimens where the hydrogen content was the highest. At 375C as well as in most cases at 300C, the hydride particles were resistant to cracking and the resistance to crack-growth initiation was very high. As a result, for this bend test procedure, crack extension was solely due to crack-tip blunting instead of crack growth in all tests at 375C and in most cases at 300C. The lower bound for fracture toughness at these temperatures, the parameter KJPmax, had values of K JPmax∼54MPa√m at both 300C and 375C. For cases where stable crack growth occurred at 300C, the fracture toughness was K Ji∼58MPa√m and the tearing modulus was twice as high as that at 25C. It is believed that the failure of...

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