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Research Papers: Materials and Fabrication

# Initiation and Arrest of Delayed Hydride Cracking in Zr–2.5Nb Tubes

[+] Author and Article Information
Young S. Kim1

Zirconium Team, Korea Atomic Energy Research Institute, 150 Dukjin-dong, Yuseong, Daejeon 305-353, Koreayskim1@kaeri.re.kr

1

Corresponding author.

J. Pressure Vessel Technol 131(1), 011401 (Nov 11, 2008) (6 pages) doi:10.1115/1.3012264 History: Received January 11, 2007; Revised December 16, 2007; Published November 11, 2008

## Abstract

Using Kim’s delayed hydride cracking (DHC) model, this study reanalyzes the critical temperatures for DHC initiation and arrest in Zr–2.5Nb tubes that had previously been investigated with the previous DHC models. At the test temperatures above $180°C$, DHC initiation temperatures fell near the terminal solid solubility for precipitation temperatures, requiring some undercooling or $ΔT$ from the terminal solid solubility for dissolution (TSSD) temperatures, and increased toward TSSD with the number of thermal cycles. At the test temperatures below $180°C$, DHC initiation occurred at temperatures near TSSD with little $ΔT$. DHC arrest occurred on heating toward TSSD where the hydrogen concentration difference between the bulk region and a crack tip $ΔC$ decreased to a minimum $ΔCmin$, under which nucleation of the hydrides was restrained. $ΔCmin$ after the first thermal cycle increased with increasing temperature, demonstrating that nucleation of the hydrides becomes more difficult with increasing temperatures. Different DHC initiation and arrest temperatures with the test temperatures or hydrogen concentrations are discussed in view of a supersaturation of hydrogen $(ΔC)$ for nucleation of hydrides in the zirconium matrix.

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Copyright © 2009 by American Society of Mechanical Engineers
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## Figures

Figure 6

DHC arrest temperatures on heating with hydrogen concentrations in the Zr–2.5Nb tube. ΔC is equal to a difference between the initial hydrogen concentration or C0 and CTSSD for a given Th or the distance BC.

Figure 5

TSSP routes at a crack tip and in the bulk region of the Zr–2.5Nb tube when it was cooled from 50°C over the TSSD temperature: the route of A-B′-C′-C for the crack tip and the route of A-B′-B for the bulk region

Figure 4

An increase in DHC initiation (a) and arrest (b) temperatures toward the TSSD temperatures with the number of thermal cycles in the Zr–2.5Nb tube

Figure 3

DHC initiation temperatures with hydrogen concentrations of the unirradiated Zr–2.5Nb tube, which were determined only after the first thermal cycle shown in Fig. 2

Figure 2

Unratcheting thermal cycle applied for DHC initiation on a stepwise cooling to the unirradiated Zr–2.5Nb tube (4)

Figure 1

The ratios of the maximum hydrogen concentration at the crack tip Cmax over the hydrogen concentration C0 in the bulk region due to the applied tensile stresses in the Zr–2.5Nb tube (4) along with the measured ratios of CTSSP over CTSSD for the Zr–2.5Nb tube reported by Pan (5) and Slattery (6)

Figure 7

Temperature dependence of ΔCmin that is required for arresting DHC of the Zr–2.5Nb tube

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