Testing of Enhanced Chemical Cleaning of SRS Actual Waste Tank 5F and Tank 12H Sludges

摘要

In support of Savannah River Site (SRS) tank closure efforts, the Savannah River National Laboratory (SRNL) conducted Real Waste Testing (RWT) to evaluate an alternative to the baseline 8 wt% oxalic acid (OA) chemical cleaning technology for tank sludge heel removal. The large quantities of sodium oxalate and other metal oxalates formed impact downstream processes by requiring additional washing during sludge batch preparation and increase the amount of material that must be processed in the tank farm evaporator systems and the Saltstone Processing Facility. Enhanced Chemical Cleaning (ECC) was identified as a potential method for greatly reducing the impact of oxalate additions to the SRS Tank Farms without adding additional components to the waste that would extend processing or increase waste form volumes. ECC is a promising alternative to bulk OA cleaning, which utilizes a more dilute OA and an oxalate destruction technology. Sludge is dissolved in a Treatment Tank by adding 2 wt% OA and mixing the tank contents. The mixture of dissolved sludge and suspended insoluble solids is transferred to the ECC reactor, where the OA and other oxalates are decomposed. Concentrated ozone gas is added to the reactor, resulting in soluble ozone and hydroxyl radicals that aid the decomposition of oxalate ion to carbon dioxide gas and raise the pH of the liquid. The change in chemistry inside the ECC reactor causes the dissolved sludge to precipitate, mostly in the form of metal oxides. Ultraviolet (UV) light can also be used to augment the decomposition of OA.