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Unreviewed Disposal Question Evaluation: Subsidence Study for Non-Crushable Containers in Slit Trenches (U)

Description: The Closure Plan for the E-Area low-level waste facility assumes that dynamic compaction performed at the end of the 100-year institutional control period will adequately stabilize all waste in Slit Trenches. However, some non-crushable waste containers with significant void space will not be stabilized by dynamic compaction. These non-crushable containers will gradually corrode, eventually collapse and cause the final closure cap to subside resulting in an increase of the infiltration rates. After subsidence occurs, the waste zone will be significantly reduced to concentrate waste in the lower portion of the slit trench, therefore increasing waste concentration. The trench subsidence may have an adverse impact on the 1000-year compliance specified in DOE Order 435.1. This study addresses the issue of trench subsidence, evaluates the resulting concentrations at the hypothetical 100-m well against those obtained based on the PA approach, and provides the maximum number of trenches that can subside without causing the well concentrations to be out of compliance.
Date: March 15, 2005
Creator: THONG, HANG
Partner: UNT Libraries Government Documents Department


Description: The formula for Savannah River Site (SRS) saltstone includes {approx}25 wt% slag to create a reducing environment for mitigating the subsurface transport of several radionuclides, including Tc-99. Based on laboratory measurements and two-dimensional reactive transport calculations, it was estimated that the SRS saltstone waste form will maintain a reducing environment, and therefore its ability to sequester Tc-99, for well over 10,000 years. For example, it was calculated that {approx}16% of the saltstone reduction capacity would be consumed after 213,000 years. For purposes of comparison, a second calculation was presented that was based on entirely different assumptions (direct spectroscopic measurements and diffusion calculations). The results from this latter calculation were near identical to those from this study. Obtaining similar conclusions by two extremely different calculations and sets of assumptions provides additional credence to the conclusion that the saltstone will likely maintain a reducing environment in excess of 10,000 years.
Date: January 22, 2007
Creator: Kaplan, D & Thong Hang, T
Partner: UNT Libraries Government Documents Department