Component-In-Grout Model Implementation for the E-Area Low-Level Waste Facility's Performance Assessment

Abstract

The component-in-grout (CIG) disposal units are below grade earthen trenches that contain grout encapsulated waste components. Components disposed of within the CIG segments consist of large radioactively contaminated equipment and smaller waste forms (e.g., B-25 boxes and SeaLand containers) to fill the space around and above the large equipment. In the 2022 revision of the E-Area Low-Level Waste Facility's (ELLWF) performance assessment, groundwater radionuclide contaminant transport through the vadose zone will be modeled using the PORFLOW software package for nine existing CIG segments located within the Slit Trench (ST) 23 footprint-no additional CIG segments are planned for at this time. The nine CIG segments have been placed within two of the nominally 20-foot-wide by 656-footlong ST segments and are surrounded by no less than 1 foot of grout on all sides and up to 4 feet of backfill material. The two most recently placed CIG segments have an additional reinforced concrete mat to improve structural stability.

Performance Assessment for the E-Area Low-Level Radioactive Waste Disposal Facility at the Savannah River Site: Appendix A

“…An operational stormwater runoff cover was placed over CIG-9 three months after placement of the final waste package (Section 4. Subsidence occurs at the end of the IC period for CIG trench segments without a reinforced-concrete mat that have subsidence potential (CIG-7 through CIG-7) (Danielson, 2020c).  D.7…”

“…Subsidence occurs 200 years after the end of the IC period for CIG trench segments with a reinforced-concrete mat (CIG-8 and CIG-9) (Danielson, 2020c;Peregoy, 2006a).  D.8…”

“…The overall length and the positioning of the CIG trench segments with respect to the crest of the final closure cap is accounted for when computing the infiltration rates (e.g., some CIG segments fall along the cap crest, some along the short slope, and some along the long slope of the bounding conceptual infiltration model -the upslope area to the cap is computed for each CIG trench segment) (Danielson, 2020c). …”