Alternative Conceptual Model for Colloid Generation from Commercial Spent Nuclear Fuel

DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor Battelle Memorial Institute, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Summary Yucca Mountain is the Department of Energy's potential geologic repository designed to store and dispose of commercial spent nuclear fuel (CSNF) and other high-level radioactive waste forms. If approved, the site would be the Nation's first geologic repository for disposal of this type of radioactive waste. Yucca Mountain is located in a remote desert on federally protected land within the secure boundaries of the Nevada Test Site in Nye County, Nevada. It is approximately 100 miles northwest of Las Vegas, Nevada. CSNF makes up most of the spent nuclear fuel that requires disposal at Yucca Mountain. The waste-form degradation process models provide technically defensible methods for predicting the long-term capability of the waste forms to control radionuclide release from the immediate vicinity of the waste. These models were provided as eight key feeds to the Total Systems Performance Assessment: radionuclide inventory, in-package chemistry model, cladding degradation model, commercial spent fuel degradation model, high-level waste glass degradation model, other waste-form degradation models, solubility model, and colloid model. Colloid generation from CSNF has been deemed to require further qualification by the present waste-form colloid model. The present colloid model considers the effects of pH and ionic strength on the stability of ideal colloid phases. The location of the boundaries between pH and ionic strength regimes in which colloids are stable or unstable are defined together with the colloid mass concentration in each regime. Colloids may have the potential to transport strongly sorbing radionuclide contaminants in soils and groundwater aquifers (McCarthy and Zachara 1989). Recent studies from the Nevada Test Site (NTS), …