Impact of Standing Bleed Water on Saltstone Placement

The amount of water present during placement and subsequent curing of saltstone has the potential to impact several properties important for grout quality. An active drain water system can remove residual standing water and expose the surface of the placed saltstone to air. Oxidation of the saltstone may result in an increase in the leachability of redox sensitive elements. A dry surface can lead to cracking, causing an increase in hydraulic conductivity. An inactive drain water system can allow standing water that generates unnecessary hydrostatic head on the vault walls. Standing water that cannot be removed via the drain system will be available for potential incorporation into subsequent grout placements. The objective of this work is to study the impact of standing water on grout quality pertaining to disposal units. A series of saltstone mixes were prepared, and cured at ambient temperature to evaluate the impact of standing water on saltstone placement. The samples were managed to control drying effects on leachability by either exposing or capping the samples. The water to premix ratio was varied to represent a range of processing conditions. Samples were analyzed for density, leachability, and hydraulic conductivity. A monolith of each composition was cut into four sections to analyze the homogeneity of the sample with respect to vertical position within the sample. The density of each section was measured by two methods, helium pycnometry and by ASTM 642-06. The results show a trend of increasing density with increasing depth in the samples. This effect is more pronounced with the inclusion of excess bleed water and indicative of increased settling. The leachability of the eight different samples was analyzed by ANS/ANSI 16.1 method. These results indicate that drying of the saltstone during curing leads to decreased Leachability Indices (indicative of more release) for potassium, sodium, rhenium, nitrite, and nitrate. This may be caused by shrinkage crack. Authors: Cozzi, A. D. [Savannah River National Laboratory (SRNL), Aiken, SC (United States)]; Pickenheim, B. R. [Savannah River National Laboratory (SRNL), Aiken, SC (United States)]. DOE Contract: AC09-08SR22470. Subjects: 12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; Saltstone; Saltstone Disposal Unit