(96a) A Summary of the Solids Founds at the Modular Caustic-Side Solvent Extraction Unit Process

Since March 2008, the Actinide Removal Process-Modular Caustic-Side Solvent Extraction Unit (ARP-MCU) facility has successfully processed more than three million gallons of supernate.  The process has experienced a few outages arising from plugged coalescers.   Recently, the facility began an outage to perform maintenance activities aimed at extending the original life cycle for the facility in light of the future deployment of the Next Generation Solvent (NGS).  

The outage included cleaning and maintenance of the centrifugal contactors. Inspection of the extraction centrifuges revealed the presence of accumulated solids in the bottom channels of Extraction Contactor SEP-401. SEP-401, the first centrifuge the supernate enters the solvent extraction process, is where radioactive supernate from ARP meets solvent scrubbed with 0.05 M nitric acid. The aqueous carry over from the solvent mixes with the supernate possibly resulting in a lowering of its pH to the point of solid precipitation.

Any large variance in the concentration of the aluminum and silicon concentrations, elements known to readily precipitate throughout the tank farm, may indicate precipitation driven by a mild pH swing. A similar deposit discovery (sodium aluminosilicate) was also found on September 2010 at the Salt Solution Feed Tank.

This poster presents a summary of the solids found throughout the different components that are part of the MCU at the Savannah River Site (SRS)