Date of Award

1991

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Engineering, Materials Science.

Rights

CC BY-NC-ND 4.0

Abstract

This research work was undertaken to extend the work of previous researchers and to clarify the influence of both environmental and metallurgical conditions on the corrosion/hydriding behaviour of Zr-2.5Nb nuclear reactor pressure tubing material. The service performance of the pressure tube is known to be influenced among other things by its metallurgical history and the LiOH content in the aqueous medium. In this study, the in-reactor corrosion/hydriding behavior of pressure tubing material in solutions of different LiOH concentrations (O(deionized water), 1.2, 4.8, 10, 25, and 50g/l) was simulated using stainless steel autoclaves at a temperature of 300$\sp\circ$C and $\sim$9.0MPa pressure. Four metallurgical conditions were investigated, namely: as currently fabricated (cold-worked & stress relieved), and as-fabricated plus a secondary heat treatment for 24 hours at a temperature of 400, 500, or 560$\sp\circ$C. The testing method was an interrupted one and was carried out for exposure times of approximately 200, 500, 2000, and 5000 hours. The degree of corrosion (loss-in-metal-thickness) was determined using metallographic techniques. The amount of hydriding was determined using chemical analysis. Optical microscopy was used to characterize the hydride morphology and distribution. It is shown that for all metallurgical conditions, the presence of LiOH in the aqueous medium causes a "breakaway" or "breakdown" of the initial corrosion/hydriding process (protective kinetics) to occur at an early stage, and linear post-transition stage to occur. In general, an increase in the secondary heat treatment temperature causes a decrease corrosion and hydriding rates, in the post-transitional stage. A heat treatment for 24 hours at 560$\sp\circ$C gives the highest corrosion/hydriding resistance, and is therefore recommended for pressure tubing fabricated by the current route. Metallographic studies of hydride morphology and distribution show that the hydride (plates) in the as-received material remain predominantly in the circumferential orientation. Some of the hydride (plates) in the heat-treated material are oriented in a direction at $\sim$45 degrees to both circumferential and radial directions, while the remaining plates remain circumferentially oriented. Source: Dissertation Abstracts International, Volume: 53-01, Section: B, page: 0500. Thesis (Ph.D.)--University of Windsor (Canada), 1991.

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