High Temperature, Low Activation, Refractory Alloys for Generation IV Nuclear Reactor Construction

No material of construction is currently approved for use in the proposed, high temperature, Generation IV nuclear reactors. Normal austenitic and ferritic steels lose most of their strength between 800 and 1000°C, which happens to be the temperature range at which the Gas-cooled Fast Reactor (GFR), the Gas Turbine Modular He Reactor (GT-MHR), and the Pebble Bed Reactor (PBR) are designed to operate. While high-Ni and high-Co alloys have adequate strength at these temperatures, they produce intensely radioactive byproducts, necessitating disposal of the reactor core materials by deep underground burial at a central site like Yucca Mountain. This project will investigate two refractory alloys that could meet the needs of high temperature, Generation IV reactors: one is well known (Nb-1%Zr, which is widely used in the chemical industry) and the other is new (orthorhombic Ti2AlNb, 50at.%Ti, 25at.%Al, and 25at.%Nb). Both would be expected to provide much better high-temperature creep strength than the steels currently in use, and both should result in containments that are much less heavily activated by exposure to neutrons, compared to comparable steel containments. The main potential problem with both alloys is embrittlement by the small amounts of hydrogen and/or oxygen that will be present within the nuclear reactor. Therefore, Phase I will measure the degree of embrittlement and analyze a method ¿ adding a small amount of air to the He coolant of the reactor ¿ to prevent this embrittlement. Phase II will investigate neutron irradiation effects on plate material and weldments. Commercial Applications and other Benefits as described by the awardee: The alloys should be attractive for many applications beyond the generation IV nuclear reactors: tank armor, turbine blades, light-weight aircraft components, and prosthetic implants.