Modeling of the Sub-Surface Reducing Environment of the Z-Area Saltstone Disposal Facility at the Savannah River Site

摘要

Low-level radioactive liquid wastes at the U.S. Department of Energy Savannah River Site are treated by mixing the wastes with Saltstone grout to generate the Saltstone waste form that is poured into the concrete vaults for long-term disposal. The formula for Saltstone includes ～25 wt% slag to create a reducing environment for mitigating the sub-surface transport of several radionuclides, including Tc-99. A two-dimensional reactive transport model was developed to estimate how long the Z-Area Saltstone will maintain a reducing environment, and therefore its ability to sequester Tc-99. The model predicted that ～16% of the Saltstone reduction capacity would be consumed after 213,000 years. Independent calculations published by other researchers yielded nearly identical results. The general modeling approach and the study results are presented in this paper.