(153i) Radioactive Waste Simulant Testing and Permanganate Oxidation of Organics for Legacy Waste Disposition

Among the legacy nuclear waste stored at the Savannah River Site (SRS), Tank 48 holds over 250,000 gallons of product formed during initial In-Tank Precipitation (ITP) of radioactive nuclides. The main objective of various disposition methods over the previous 27 years has been to safely decompose major ITP products, including precipitated tetraphenylborate (TPB) salts, in order to free up valuable real estate in the tank farm at SRS while simultaneously falling within acceptable standards for further processing through the Saltstone and Defense Waste Processing Facilities (DWPF). This work will highlight historically attempted methods while discussing current radioactive and simulant testing of a permanganate oxidation reaction to chemically degrade TPB and simpler organics within the waste.

Several primary difficulties in disposition of the Tank 48 waste include a unique chemical profile, radioactive and flammable hazards, and the scale at which the implemented reaction is planned to occur. The initial halt of the ITP process was called due to a buildup of benzene in the head space of the tank, and the production of benzene and other flammable gasses has been a constant concern for all subsequent efforts to neutralize the waste. One of the most valuable process and safety control methods used in determining an appropriate disposition method for any radioactive waste at SRS has been the implementation of a complex chemical simulant. Current characterization of Tank 48 samples includes a battery of physical and chemical analytical testing and nuclear measurements to establish a profile of current tank sample properties. Samples of the current radioactive waste undergo batch oxidation tests in the Savannah River National Lab (SRNL) Shielded Cells (SC) facility to mirror testing done on simulants specifically formulated to model the Tank 48 chemical matrix.

Parameters of interest in the permanganate oxidation testing include the ratio of permanganate to TPB, further destruction of permanganate decomposition products, temperature of reaction, and volatile organic compound production. In addition to the smaller batch testing of simulant to mirror SC testing of radioactive samples, larger batches of simulant can be processed through a setup including in-situ UV-Vis monitoring and offgas analysis of products to more thoroughly round out the reaction mechanism and relevant process characteristics.