Waste Tank Heel Chemical Cleaning Summary

Abstract

At the Savannah River Site in Aiken, South Carolina, there are approximately 40 million gallons of legacy High Level Waste stored in large capacity sub-surface tanks. Twelve of these tanks are single-containment, non-conforming tanks with leaks. These tanks were built in the 1950s. Some of these tanks contain sludge heels and are being considered for near-term removal efforts and vitrification. Currently, only mechanical methods (i.e., pumps) are used to remove the sludge waste with varying degrees of success. To provide for additional levels of removal, chemically-aided techniques are being considered. The objective of the was to collect and evaluate information available on chemical-based methods for removing residual solids from the Site's waste tanks. As part of this study, the team was requested to develop recommendations for chemical treatments to remove residual heels (primarily sludge). Ideally, one agent alone would be efficient at dissolving all residual tank heels and yet satisfy all safety and process concerns. No such chemical cleaning agent was found. The cleaning agents identified from the literature, included oxalic acid, a mixture of oxalic acid and citric acid, a combination of oxalic acid with hydrogen peroxide, nitric acid, formic acid, and organics. A criteria matrix for evaluating themore » various cleaning agents was developed. The results of the evaluation conclusively support oxalic acid as the cleaning agent of choice for the immediate future. Oxalic acid scored nearly double the next closest cleaning agent. Nitric acid, formic acid, and oxalic acid with hydrogen peroxide were all closely grouped for the next best choice. The mixture of oxalic acid and citric acid rated poorly. Organics rated even more poorly due to large uncertainties in performance and downstream impacts.« less