M.A.Sc candidateDep. of Mechanical and Materials Engineering, Nicol Hall, 60 Union Street, Kingston, K7L 3N6, Ontario, Canada Tel: (613) 533-3236 Email: cochranec[at]me[dot]queensu[dot]ca |
Current Research Field
- Effect of interstitial oxygen on deformation on pressure tube alloy
- Anisotropic strain of formation of zirconium hydrides
Biography:
- BSc Engineering Physics, Materials Option (First Class)
Queen's University
Current Research
An alloy of zirconium (Zr-2.5Nb) is used in pressure
tubes within the Canadian-designed CANDU (CANada Deuterium Uranium) nuclear
reactors. The zirconium components absorb hydrogen during normal reactor
operation, which leads to the eventual formation of zirconium hydride
precipitates. The incidence of these hydrides has been associated with a
phenomenon known as delayed hydride cracking, or DHC. This phenomenon can lead
to premature and unpredicted failure of components in the reactor. The
likelihood of failure by this mode increases as the reactor lifetime increases
because more hydrogen is present in the zirconium components and thus more
hydrides are able to form.
Hydrides tend to form in cornflake-like structures called platelets. This shape is anisotropic, and the orientation of the platelet is affected by the direction of the applied loads when the hydride forms. Sub-features in the platelets, referred to as micro-platelets, tend to be oriented in specific directions relative to the crystallography of the zirconium matrix in which they form. When these micro-platelets form, they strain the surrounding zirconium. Studies have shown that the nature of this strain is itself anisotropic. This anisotropy is partly due to the anisotropic shape change of the crystal structure during precipitation, and partly due to anisotropic plastic relaxation of the zirconium matrix. It is not well-explained by current models of hydride formation.
In order to achieve the necessary measurements, samples of zirconium alloy pressure tubes will be prepared with the assistance of Nu-Tech Precision Metals, the manufacturing firm responsible for the production of in-reactor pressure tubes used in CANDU reactors, and Atomic Energy Canada Limited (AECL), the Crown-corporation responsible for the design of CANDU technology. Hydrogen will be directly deposited in the samples to simulate the state of in-reactor material, and a specialized furnace and pressure rig will be used to simulate in-reactor conditions for hydride formation.
The strain of hydride formation can then be measured. Several approaches will be taken to perform strain measurements: a high-precision laser measurement system, micrograph image analysis and electron microscopy. Each of these approaches acts on different lengths scales, allowing reconciliation with different models. The results of these measurements will be used in the development of a more complete model of hydride formation and the strains associated with it.
A thorough understanding of the nature of the hydride formation strain and its accomodation is necessary to fully understand the phenomenon of delayed hydride cracking, an ongoing concern in the Canadian nuclear industry. This work is part of the combined academic and industrial effort to ensure the continued operation and safety of Canada's nuclear power reactors and to help guide the decisions made in the design of future CANDU technology.
Publications:
J.E. Sonier, C.V. Kaiser, V. Pacradouni, S.A. Sabok-Sayr, C. Cochrane, D.E. MacLaughlin, S. Komiya, N.E. Hussey. Direct Search for a Ferromagnetic Phase in a Heavily Overdoped Non-Superconducting Copper Oxide. Proceedings of the National Academy of Sciences of the United States of America. (In press: Accepted August 17, 2010)