Forming of zirconium and hafnium alloys

Closely related in their natural state in zircon ore, and with similar chemical properties (which makes them difficult to separate), the elements zirconium (Zr) and hafnium (Hf) possess singular and diametrically opposed neutron properties that make them of interest in nuclear applications. Zirconium's low neutron capture cross-section makes it the metal of choice for nuclear fuel assemblies. As hafnium has the opposite property, it can be used to regulate or stop the fission reaction. In addition to its exceptional neutron properties, zirconium has good resistance to corrosion, creep and irradiation, enabling it to meet the stringent safety requirements of the nuclear environment, by ensuring the integrity of the fuel cladding throughout its use and reprocessing.

Whether during extractive metallurgy operations, ingot production or the shaping of semi-finished and finished parts, the final properties of the product guide the choice of technologies and process parameters used. Indeed, many metallurgical parameters such as alloy chemistry, microstructure, crystallographic texture, chemical composition and precipitate size, which are inherited from the manufacturing range, have a direct influence on properties during use in reactors. While optimizing the economic performance of production lines, it is therefore essential to control all operations from a metallurgical point of view, so as to obtain a product that complies with the very demanding specifications of the nuclear industry.

The aim of this article is to review plastic deformation forming processes for zirconium and hafnium alloys, for the simple shapes (rods, tubes and flats) that make up nuclear fuel assemblies. After a brief review of metallurgy, which will provide a better understanding of the microstructure evolutions presented later, the focus is on process parameters that can influence downstream operations and final product properties, by highlighting evolutions in geometry, surface states and microstructure over the course of the range.

A glossary of terms is provided at the end of the article.