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Title: Caustic-Side Solvent Extraction: Prediction of Cesium Extraction for Actual Wastes and Actual Waste Simulants

Abstract

This report presents the work that followed the CSSX model development completed in FY2002. The developed cesium and potassium extraction model was based on extraction data obtained from simple aqueous media. It was tested to ensure the validity of the prediction for the cesium extraction from actual waste. Compositions of the actual tank waste were obtained from the Savannah River Site personnel and were used to prepare defined simulants and to predict cesium distribution ratios using the model. It was therefore possible to compare the cesium distribution ratios obtained from the actual waste, the simulant, and the predicted values. It was determined that the predicted values agree with the measured values for the simulants. Predicted values also agreed, with three exceptions, with measured values for the tank wastes. Discrepancies were attributed in part to the uncertainty in the cation/anion balance in the actual waste composition, but likely more so to the uncertainty in the potassium concentration in the waste, given the demonstrated large competing effect of this metal on cesium extraction. It was demonstrated that the upper limit for the potassium concentration in the feed ought to not exceed 0.05 M in order to maintain suitable cesium distribution ratios.

Authors:
; ; ;
Publication Date:
Research Org.:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN
Sponsoring Org.:
USDOE Office of Science and Technology (EM-50)
OSTI Identifier:
944075
Report Number(s):
ORNL/TM-2003/011
TRN: US0900597
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; CESIUM; DATA; DISTRIBUTION; FORECASTING; PERSONNEL; POTASSIUM; SOLVENT EXTRACTION; TANKS; WASTES

Citation Formats

Delmau, L.H., Haverlock, T.J., Sloop, F.V., Jr., and Moyer, B.A. Caustic-Side Solvent Extraction: Prediction of Cesium Extraction for Actual Wastes and Actual Waste Simulants. United States: N. p., 2003. Web. doi:10.2172/944075.
Delmau, L.H., Haverlock, T.J., Sloop, F.V., Jr., & Moyer, B.A. Caustic-Side Solvent Extraction: Prediction of Cesium Extraction for Actual Wastes and Actual Waste Simulants. United States. doi:10.2172/944075.
Delmau, L.H., Haverlock, T.J., Sloop, F.V., Jr., and Moyer, B.A. Sat . "Caustic-Side Solvent Extraction: Prediction of Cesium Extraction for Actual Wastes and Actual Waste Simulants". United States. doi:10.2172/944075. https://www.osti.gov/servlets/purl/944075.
@article{osti_944075,
title = {Caustic-Side Solvent Extraction: Prediction of Cesium Extraction for Actual Wastes and Actual Waste Simulants},
author = {Delmau, L.H. and Haverlock, T.J. and Sloop, F.V., Jr. and Moyer, B.A.},
abstractNote = {This report presents the work that followed the CSSX model development completed in FY2002. The developed cesium and potassium extraction model was based on extraction data obtained from simple aqueous media. It was tested to ensure the validity of the prediction for the cesium extraction from actual waste. Compositions of the actual tank waste were obtained from the Savannah River Site personnel and were used to prepare defined simulants and to predict cesium distribution ratios using the model. It was therefore possible to compare the cesium distribution ratios obtained from the actual waste, the simulant, and the predicted values. It was determined that the predicted values agree with the measured values for the simulants. Predicted values also agreed, with three exceptions, with measured values for the tank wastes. Discrepancies were attributed in part to the uncertainty in the cation/anion balance in the actual waste composition, but likely more so to the uncertainty in the potassium concentration in the waste, given the demonstrated large competing effect of this metal on cesium extraction. It was demonstrated that the upper limit for the potassium concentration in the feed ought to not exceed 0.05 M in order to maintain suitable cesium distribution ratios.},
doi = {10.2172/944075},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Feb 01 00:00:00 EST 2003},
month = {Sat Feb 01 00:00:00 EST 2003}
}

Technical Report:

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  • A caustic-side solvent extraction (CSSX) process to remove cesium from Savannah River Site (SRS) high-level waste was tested in a minicontactor (2-cm centrifugal contactor). In the first phase of this effort, the minicontactor stage efficiency was improved from 60% to greater than 80% to meet the SRS process requirements using a 32-stage CSSX flowsheet. Then, the CSSX flowsheet was demonstrated in a 32-stage unit, first without solvent recycle, then with it. In both cases, the key process goals were achieved: (1) the cesium was removed from the waste with decontamination factors greater than 40,000 and (2) the recovered cesium wasmore » concentrated by a factor of 15 in dilute nitric acid. Oak Ridge National Laboratory (ORNL) analysis of the recycled solvent showed no evidence of impurity buildup.« less
  • A caustic-side solvent extraction (CSSX) process to remove cesium from Savannah River Site (SRS) high-level waste was tested for 71 hours in a 33-stage minicontactor (2-cm centrifugal contactor). This multi-day demonstration used an average SRS simulant for the waste feed. The two key process goals were achieved: (1) the cesium was removed from the waste with decontamination factors greater than 40,000, and (2) the recovered cesium was concentrated by a factor of 15 in dilute nitric acid. These goals were maintained for 71 h as 1.4 L of solvent was recycled 42 times at 14 mL/min while processing 180 Lmore » of SRS simulant at 43 mL/min. The average decontamination factor was 159,000 for cesium and the average concentration factor was 14.9. The process had to be shut down twice for minor problems, which were fixed and testing resumed. The results confirmed that the CSSX process could be used to help decontaminate the millions of gallons of SRS waste now stored in underground tanks.« less
  • A 32-stage centrifugal contactor underwent proof-of-concept testing for its potential use in caustic-side solvent extraction for removal of cesium from radioactive waste now stored in underground tanks at the Savannah River Site. This contactor met the performance goals. Maintaining this performance, however, depends on adequate temperature management. Subsequent calculations and measurements determined the effect of several sources of heat on the temperature of the liquid inside the contactor stages: heats of solvation and dilution, heat generated by the rotor in the mixing zone, and heat from the motor used to spin the rotor. The results indicated that over 90% ofmore » the heat comes from the motors, generating 12 W of thermal energy per stage. It was concluded that satisfactory temperature management of the contactor should be achievable by cooling the extraction section to remove 12 W of heat per stage.« less
  • To demonstrate that the caustic-side solvent extraction (CSSX) process could remove cesium from Savannah River Site (SRS) high-level waste over long periods of time, an improved minicontactor (2-cm centrifugal contactor) was needed that could be operated for several days. In particular, the contractor temperature had to be controlled and contactor hydraulic performance needed to be improved. Because the process was to be continuous, provisions were made for a three-shift operation. With the improvements made and the operators trained, the CSSX process was run in a 33-stage minicontactor over a period of three days to remove cesium from an average SRSmore » siumulant for the waste feed. The two key process goals were achieved: (1) the cesium was removed from the waste with decontamination factors greater than 40,000 and (2) the recovered cesium was concentrated by a factor of 15 in dilute nitric acid. These goals were maintained for 71 h as 1.4 L of solvent was recycled 42 times while processing 180 L of SRS simulant. The average decontamination factor for cesium was 157,000 and the average concentration factor was 14.9. The process had to be shut down twice for minor problems, which were fixed and testing resumed. This multi-day demonstration confirmed that the CSSX process could be used to help decontaminate the millions of gallons of SRS waste now stored in underground tanks.« less
  • This report presents the results of a conceptual design of a solvent extraction process for the selective removal of {sup 137}Cs from high-level radioactive waste currently stored in underground tanks at the U.S. Department of Energy's Savannah River Site (SRS). This study establishes the need for and feasibility of deploying a simplified version of the Caustic-Side Solvent Extraction (CSSX) process; cost/benefit ratios ranging from 33 to 55 strongly support the considered deployment. Based on projected compositions, 18 million gallons of dissolved salt cake waste has been identified as having {sup 137}Cs concentrations that are substantially lower than the worst-case designmore » basis for the CSSX system that is to be deployed as part of the Salt Waste Processing Facility (SWPF) but that does not meet the waste acceptance criteria for immobilization as grout in the Saltstone Manufacturing and Disposal Facility at SRS. Absent deployment of an alternative cesium removal process, this material will require treatment in the SWPF CSSX system, even though the cesium decontamination factor required is far less than that provided by that system. A conceptual design of a CSSX processing system designed for rapid deployment and having reduced cesium decontamination factor capability has been performed. The proposed accelerated-deployment CSSX system (CSSX-A) has been designed to have a processing rate of 3 million gallons per year, assuming 90% availability. At a more conservative availability of 75% (reflecting the novelty of the process), the annual processing capacity is 2.5 million gallons. The primary component of the process is a 20-stage cascade of centrifugal solvent extraction contactors. The decontamination and concentration factors are 40 and 15, respectively. The solvent, scrub, strip, and wash solutions are to have the same compositions as those planned for the SWPF CSSX system. As in the SWPF CSSX system, the solvent and scrub flow rates are equal. The system is designed to facilitate remote operation and direct maintenance. Two general deployment concepts were considered: (1) deployment in an existing but unused SRS facility and (2) deployment in transportable containers. Deployment in three transportable containers was selected as the preferred option, based on concerns regarding facility availability (due to competition from other processing alternatives) and decontamination and renovation costs. A risk assessment identified environmental, safety, and health issues that exist. These concerns have been addressed in the conceptual design by inclusion of mitigating system features. Due to the highly developed state of CSSX technology, only a few technical issues remain unresolved; however, none of these issues have the potential to make the technology unviable. Recommended development tasks that need to be performed to address technical uncertainties are discussed in this report. Deployment of the proposed CSSX-A system provides significant qualitative and quantitative benefits. The qualitative benefits include (1) verification of full-scale contactor performance under CSSX conditions that will support SWPF CSSX design and deployment; (2) development of design, fabrication, and installation experience bases that will be at least partially applicable to the SWPF CSSX system; and (3) availability of the CSSX-A system as a means of providing contactor-based solvent extraction system operating experience to SWPF CSSX operating personnel. Estimates of fixed capital investment, development costs, and annual operating cost for SRS deployment of the CSSX-A system (in mid-2003 dollars) are $9,165,199, $2,734,801, and $2,108,820, respectively. When the economics of the CSSX-A system are compared with those of the baseline SWPF CSSX system, benefit-to-cost ratios ranging from 20 to 47 are obtained. The benefits in the cost/benefit comparison arise from expedited tank closure and reduced engineering, construction, and operating costs for the SWPF CSSX system. No significant impediments to deployment were determined in the reported analysis, and where technical uncertainties were identified, development tasks to mitigate them are indicated. It is recommended that deployment of the CSSX-A system be pursued in a timely manner in order to derive the greatest possible cost and accelerated treatment benefits.« less