A New Ni-Cr-Mo-Based Gadolinium Structural Alloy for Neutron Adsorption Application in Radioactive Material Packages

In order to avoid restrictive fissile loading limits in some types of US Department of Energy (DOE) spent nuclear fuel, nuclear criticality control measures are needed in standardized waste packages for long-term disposal of high-level radioactive materials in the proposed Yucca Mountain repository. This need has been addressed by development of a corrosion-resistant, neutron-absorbing structural alloy for nuclear criticality control. Applications for the alloy include internals (e.g., baskets) for storage, transportation, and disposal of radioactive material (RAM). This paper outlines results of a metallurgical development program that alloyed gadolinium into a nickel-chromium-molybdenum matrix. Gadolinium was chosen as a neutron-absorption alloying element due to its high thermal neutron absorption cross section and low solubility in the anticipated repository environment. The nickel-chromium-molybdenum alloy family was chosen for its known corrosion performance, mechanical properties, and weldability. An ASTM International Material Specification has been issued for the alloy and a Code Case has been approved by the American Society of Mechanical Engineers for RAM package applications. Mechanical and physical property data for the alloy are provided in this paper.