In this study, we have systematically investigated corrosion and mass transport processes in carbon steel miniature waste packages (MWP) in dynamic systems (water in, water out) under varying chemical conditions. The MWP were fabricated to have similar configuration to the DOE Spent Nuclear Fuel (SNF) waste package and that individual components to be in scale with each other compare to the SNF waste package. Two MWP configurations were studied: a "bathtub" model and a "flow-through" model. By slowly dripping 4 different solutions (groundwater obtained from well water J-13 located near Yucca Mountain, and J-13 water adjusted to low-pH, high-salinity, and high salinity-high nitrate) into the MWP, we were able to investigate the manner of oxidation, identify transported minerals contained in the effluent, and characterize the mass transport in terms of particle size. Manner of oxidation. Through time-lapse digital photography, we were able to document the process of corrosion within a glass walled MWP. Formation of colored corrosion products including short-lived colored complexes was noted. A sequence of possible corrosion products was proposed. The availability of oxygen and limitation of diffusion through corrosion products lowers the rate of the corrosion process. In most cases the MWP exit hole sealed within 4 weeks of water introduction, resulting in overflow from the top of the MWP. This self-sealing is likely due to the larger molar volume of the corrosion products. The overflow water traveled on the outer surface of the MWP and hung at bottom before dripping out. Under these conditions corrosion to the bottom of the MWP was observed and eventual bottom failure is likely. It is recommended an addition of a skirt to the actual waste packages to deflect water away from the waste package. Identification of Transported Minerals. Through X-Ray Diffraction and Scanning Electron Microscopy studies of solids in the MWP effluent, we discovered that secondary minerals, such as goethite were prevalent. Many of these corrosion products were amorphous and would expect to have different properties (buffering, sorption) compared to more crystalline minerals. Individual particles ranged from about 0.2 to 0.8 (J,m in diameter and larger conglomerates of particles up to several um in diameter were also present. Mass Transport of Solids. The greatest mass of solids transported out of the MWP occurred under acidic conditions followed by the control (J-13) solution. The salt (high ionic strength) solutions were more variable due to experimental difficulties but appear not to enhance the corrosion process. The nature of the transported material also differed by solution-type. As expected, most of the iron (>80%) was found in the dissolved state under acidic conditions, while solids (>0.45um in diameter) dominated in the effluent of the other solutions.
Carbon steel – Corrosion; Nevada – Yucca Mountain; Radioactive waste canisters – Corrosion; Radioactive wastes – Storage
Chemistry | Environmental Chemistry | Materials Science and Engineering | Metallurgy
Smiecinski, A. J.
Corrosion and mass transport processes in Carbon steel miniature waste packages.
Available at: http://digitalscholarship.unlv.edu/yucca_mtn_pubs/72