The subsurface radioactive disposal facility located at the U.S. Department of Energy’s Idaho site contains neutron-activated metals from non-fuel nuclear-reactor-core components. A long-term corrosion study is being conducted to obtain site-specific corrosion rates to support efforts to more accurately estimate the transfer of activated elements in an arid vadose zone environment. The study uses non-radioactive metal coupons representing the prominent neutron-activated material buried at the disposal location, namely, two types of stainless steels, welded stainless steel, welded nickel-chromium steel alloy, zirconium alloy, beryllium, and aluminum. Additionally, carbon steel (the material used in cask disposal liners and other disposal containers) and duplex stainless steel (high-integrity containers) are also included in the study. This paper briefly describes the test program and presents the corrosion rate results through twelve years of underground exposure.
The long-term corrosion test is designed to assist in the determination of site-specific corrosion rates of neutron-irradiated metals buried in an arid vadose zone environment at the radioactive disposal facility at Idaho National Laboratory. Corrosion rates are based on total mass loss from nonradioactive metal coupons exposed to underground site conditions. The corrosion rates, once determined, reduce the uncertainty of the site-specific transfer of radioactive isotopes to the environment (radiological release rates). Of interest are the metals used to fabricate nuclear reactor components that, when exposed to high neutron fluxes in a reactor environment, become activated with long-lived radioactive isotopes. After disposal, corrosion processes can cause these radioactive isotopes to be released from the irradiated metallic waste to the environment. The long-term corrosion study includes parameters known to influence underground metal corrosion. As well as direct corrosion testing (i.e., burying metal coupons in the soil) and real-time monitoring (i.e., using electrical resistance corrosion probes), soil characterization, sampling, and analysis for physical, chemical, hydraulic, and microbiological properties;