Methods to Avoid Post-Filtration Precipitation in Treatment of High-Level Waste

Abstract

The Hanford Tank Waste Treatment and Immobilization Plant, currently under construction for treating high level waste at the Hanford Site, will rely on ultrafiltration to provide solids/liquid separation as a core part of the treatment process. A series of bench-scale simulant tests have been performed to evaluate the potential for post-filtration precipitation. These tests focused on identifying precipitation from a range of potential feed compositions and providing the data required to evaluate mitigation options. This data is also important to the Savannah River Site as they are also attempting to dissolve saltcake from their tanks. Inadvertent solids formation after saltcake dissolution, either within a staging tank or in transfer piping can have serious repercussions on the eventual retrieval and transfer of the waste. A series of tests were performed using a variety of simulant samples. These tests identified the expected extent of supersaturation that develops under normal operations and identified and characterized the solids phases that are expected to form when the filtrate solutions are stored. In addition, tests identified the potential to mitigate the formation of these solids through both dilution and the application of increased temperature.