Inline Monitors for Measuring Cs-137 in the SRS Caustic Side Solvent Extraction Process

The Department of Energy (DOE) selected Caustic-Side Solvent Extraction (CSSX) as the preferred technology for the removal of radioactive cesium from High-Level Waste (HLW) at the Savannah River Site (SRS). Before the full-scale Salt Waste Processing Facility (SWPF) becomes operational, a portion of dissolved saltcake waste will be processed through a Modular CSSX Unit (MCU). The MCU employs the CSSX process, a continuous process that uses a novel solvent to extract cesium from waste and concentrate it in dilute nitric acid. Of primary concern is Cs-137 which makes the solution highly radioactive. Since the MCU does not have the capacity to wait for sample results while continuing to operate, the Waste Acceptance Strategy is to perform inline analyses. Gamma-ray monitors are used to: measure the Cs-137 concentration in the decontaminated salt solution (DSS) before entering the DSS Hold Tank; measure the Cs-137 concentration in the strip effluent (SE) before entering the SE Hold Tank; and verify proper operation of the solvent extraction system by verifying material balance within the process. Since this gamma ray monitoring system application is unique, specially designed shielding was developed and software was written and acceptance tested by Savannah River National Laboratory (SRNL) personnel. The software is a LabView-based application that serves as a unified interface for controlling the monitor hardware and communicating with the host Distributed Control System. This paper presents the design, fabrication and implementation of this monitoring system