Identifying the failure mechanisms of zirconium alloys from fractographic studies

The development of zirconium as a commercial alloy system has been largely associated with the development of water-cooled nuclear reactors. For such reactors, the good corrosion resistance in high-temperature (approximately 300 C) water, low neutron capture cross-section, and adequate mechanical properties make zirconium alloys the sole economic construction metal for the major structural parts of the reactor core. Thus, in the pressure vessel type reactors (PWRs and BWRs**) zirconium alloys are used for the fuel cladding and fuel boxes or channels, whereas some other components, present in small quantities (such as grids and springs) can be made from stainless steels or nickel alloys. In pressure tube reactors such as the CANDU** heavy-water reactors, where the use of natural uranium dioxide fuel renders neutron economy even more important, the fuel cladding; other structural components of the fuel bundle; the pressure tube; the calandria tube and the ''garter springs'' (which separate the last two tubes) are of zirconium alloys. The development of zirconium alloys from a metallurgical curiosity to the commercial alloy stage is one of the successes of the U.S. Naval Reactors program, and makes a fascinating story