Aspects of zircaloy core materials for advanced LWRs

Zircaloy has been successfully used as the primary light water reactor (LWR) core structural material since its introduction in the early days of the US naval nuclear program. Its unique combination of low neutron absorption cross section, fabricability, mechanical strength, and corrosion resistance in high-temperature water has resulted in remarkable reliability of operation of pressurized and boiling water reactor (PWR, BWR) fuel through the years. Currently, BWRs use Zircaloy-2 for fuel cladding and Zircaloy-4 for channels and spacers, while PWRs use Zircaloy-4 for fuel cladding, spacer grids, and control rod guide tubes. As required fluences continue to increase and as a more statistically significant number of components reach ultra-high burnups, however, Zircaloy as a material is liable to be pushed to its operating limits. This paper discusses those areas to which fuel vendors are giving attention; e.g., microstructure, corrosion, irradiation growth and creep, and mechanical properties.