Some thoughts on the mechanisms of in-reactor corrosion of zirconium alloys

Precipitation morphology and habit planes of the delta-phase Zr hydrides, which were precipitated within the a-phase matrix grains and along the grain boundaries of recrystallized Zircaloy-2 cladding tube, have been examined by electron backscatter diffraction (EBSD). Radially-oriented hydrides, induced by residual tensile stress, precipitated in the outside region of the cladding, and circumferentially-oriented hydrides in the stress-free middle region of the cladding. The most common crystallographic relationship for both types of the hydrides precipitated at the inter- and intra-granular sites was identical at (0001)(alpha) // {111}(delta), with {1017}(alpha) // {111}(delta) being the occasional exception only for the inter-granular radial hydrides. When tensile stress was loaded, the intra-granular hydrides tended to preferentially precipitate in the grains with circumferential basal pole textures. The inter-granular hydrides tended to preferentially precipitate on the grain faces opposite to tensile axis. The change of prioritization in the precipitation sites for the hydrides due to tensile stress could be explained in terms of the relaxation effect of constrained elastic energy on the terminal solid solubility of hydrogen at hydride precipitation.

https://www.tandfonline.com/doi/pdf/10.1080/18811248.2004.9715540

Crystallography of Zirconium Hydrides in Recrystallized Zircaloy-2 Fuel Cladding by Electron Backscatter Diffraction

Long-term corrosion of Zircaloy before and after irradiation

A metallographic and fractographic study of outside-in cracking caused by power ramp tests

Apparatus and method are disclosed for machining and, in particular, welding a work piece in an environment comprised of a gas non-reactive to the material of the work piece to minimize the contamination of the welds effected on the work piece. In an illustrative embodiment of this invention, there is provided a welding chamber for receiving the work piece and for establishing the welding environment therein. The welding chamber has an input port disposed in a bottom portion thereof, that is coupled to means in the form of a controllable pump for directing or pumping the non-reactive or inert gas, e.g. argon, through the input port and into the welding chamber. The welding chamber also includes an output port, whereby the non-reactive gas may escape from the welding chamber. A diffuser plate distributes the non-reactive gas substantially uniformly across the cross section of the welding chamber, whereby a laminar flow of the non-reactive gas is directed over the work piece and is permitted to escape through the output port.

W. Kaden

Papers

External corrosion of cladding in PWRs