Zirconium Alloys Round Bars

ZIRCONIUM ALLOYS Zirconium is a commercially available refractory metal with excellent corrosion resistance, good mechanical properties, very low thermal neutron cross section, and can be manufactured using standard fabrication techniques. The unique properties of zirconium made ideal cladding material for the U.S. Navy nuclear propulsion program in the 1950's. The initial commercial nuclear power reactors used stainless steel to clad the uranium dioxide fuel due to cost. But by mid-1960 zirconium alloys were the principle cladding material due to the superior neutron economy and corrosion resistance. These same zirconium alloys are available to designers of high level nuclear waste disposal containers as internal components or external cladding. Additional advantages of zirconium alloys for long term nuclear waste disposal include excellent radiation stability and 100% compatibility with existing Zircaloy fuel cladding to alleviate any concerns of galvanic corrosion. The various zirconium alloy grades used in water-cooled nuclear reactors are also available for nuclear waste disposal components. Reactor grade designates that the material has low hafnium content suitable for nuclear service. The hafnium is typically 0.010% maximum. The American Society for Testing and Materials (ASTM) offers widely recognized grades of zirconium alloys. Zircaloy-2 (Grade R60802) is composed of Zr-1.5%Sn- 0.15þ-0.1%Cr-0.05%Ni and has been predominantly used as fuel cladding in Boiling Water Reactors (BWR) and as calandria tubing in CANadian Deuterium Uranium (CANDU) reactor types. Zircaloy-4 (Grade R60804) has removed the nickel and increased the iron content for less hydrogen uptake in certain reactor conditions. The alloy is typically used as fuel cladding in Pressurized Water Reactors (PWR) and CANDU reactors. The nominal Zircaloy-4 composition is Zr-1.5%Sn-0.2þ-0.1%Cr. Refinements in the ingot homogeneity have allowed tighter control of the alloy elements within the ASTM specification. Controlled Composition Zircaloy offers optimized in-reactor corrosion resistance by adjusting the alloy aim point within the ASTM specification ranges. Controlled Composition Zircaloy-4 has lower tin (1.3%) and higher iron (0.22%) than the standard grade. Zr-2.5Nb (Grade R60904) is a binary alloy with niobium to increase the strength. The alloy has been utilized for pressure tubes in CANDU reactors. Non-reactor grade Zirconium 702 (Grade R60702) has 4.5% maximum hafnium and is also available from Wah Chang. Zirconium alloys have superior thermal properties compared to other traditional materials in consideration for spent nuclear fuel containers. Zirconium alloys have a thermal conductivity more than 30% higher than stainless steel alloys. The linear coefficient of thermal expansion for Zirconium alloys is nearly one-third the value for stainless steel giving zirconium alloys superior dimensional stability at elevated temperatures. This is an advantage in nuclear waste containers where temperatures could exceed 200ºC for hundreds of years. Zircaloy-2 and Zircaloy-4 have a hexagonal close-packed (HCP) crystal structure at room temperature as an alpha phase. The beta phase is body centered cubic (BCC) and begins to form upon heating to approximately 810ºC. The fraction of beta phase increases with temperature until complete transformation to beta phase