Modular Caustic-Side Solvent Extraction Unit (MCU) Improved Solvent Quality and Processing Results - 17496
- Savannah River Remediation, LLC (United States)
The Modular Caustic-Side Solvent Extraction (CSSX) Unit (MCU) is a process for Cs-137 removal from legacy nuclear waste. MCU began hot operations in 2008 with an initial planned operating life of three years and a design life of five years. After eight years of operation, MCU has processed more than 23.8 million liters (6.3 million gallons) of waste. The MCU process uses a solvent developed by Oak Ridge National Laboratory (ORNL) to extract the fission product Cs-137 from liquid salt waste, or salt solution (SS), stored in the Tank Farms at Savannah River Site (SRS) after the material has been treated through the Actinide Removal Process (ARP). Batches of SS are prepared and first fed to the ARP, where it is treated to become clarified SS (CSS), then fed to MCU. Once the Cs-137 has been extracted by the solvent, the CSS becomes decontaminated SS (DSS), which is ultimately processed into a cementitious grout at the Saltstone Production Facility (SPF) and subsequently disposed of at the Saltstone Disposal Facility (SDF). The Cs-137 is then stripped from the solvent into an aqueous strip effluent (SE) stream for incorporation into borosilicate glass at the Defense Waste Processing Facility (DWPF). The solvent used in the MCU process is made of four components: the extractant (extracts Cs-137 from CSS), the modifier (increases solubility of extractant and suppressor in the diluent), the suppressor (suppresses the effects of anions and improves stripping), and the diluent (controls density and viscosity). There have been two solvents utilized during the lifetime of MCU. The first solvent was developed by ORNL and was used to design the plant based on its cesium removal capability. Due to the extended life of MCU, in order to continue to minimize the curies disposed at SDF, a new solvent capable of removing more cesium from the CSS was developed by ORNL and implemented at MCU. The second MCU solvent, Next-Generation Solvent (NGS), uses the same modifier and diluent as the original solvent, but a different extractant and suppressor. Subsequent changes to the overall MCU flowsheet were made for the use of NGS. The success of cesium removal from the CSS is often presented as the cesium decontamination factor (DF) achieved for each batch processed. The DF is the ratio of the concentration of cesium in the CSS to the cesium concentration in the DSS. The BOBCalixC6 based solvent was capable of achieving DFs between 100 and 400 for each DSS batch. The NGS solvent is capable of achieving DFs greater than 40,000 for each DSS batch. The NGS blend solvent is currently meeting the goals of the pure NGS solvent. (authors)
- Research Organization:
- WM Symposia, Inc., PO Box 27646, 85285-7646 Tempe, AZ (United States)
- OSTI ID:
- 22802475
- Report Number(s):
- INIS-US-19-WM-17496; TRN: US19V0487046869
- Resource Relation:
- Conference: WM2017: 43. Annual Waste Management Symposium, Phoenix, AZ (United States), 5-9 Mar 2017; Other Information: Country of input: France; 11 refs.; available online at: http://archive.wmsym.org/2017/index.html
- Country of Publication:
- United States
- Language:
- English
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