DETERMINATION OF THE IMPACT OF GLYCOLATE ON ARP AND MCU OPERATIONS
Savannah River Remediation (SRR) is evaluating an alternate flowsheet for the Defense Waste Processing Facility (DWPF) using glycolic acid as a reductant. An important aspect of the development of the glycolic acid flowsheet is determining if glycolate has any detrimental downstream impacts. Testing was performed to determine if there is any impact to the strontium and actinide sorption by monosodium titanate (MST) and modified monosodium titanate (mMST) or if there is an impact to the cesium removal at the Modular Caustic-Side Solvent Extraction Processing Unit (MCU). Sorption testing was performed using both MST and modified MST (mMST) in the presence of 5,000 and 10,000 ppm (mass basis) glycolate. 10,000 ppm is the estimated bounding concentration expected in the DWPF recycle stream based on DWPF melter flammable gas model results. The presence of glycolate was found to slow the removal of Sr and Pu by MST, while increasing the removal rate of Np. Results indicate that the impact is a kinetic effect, and the overall capacity of the material is not affected. There was no measurable effect on U removal at either glycolate concentration. The slower removal rates for Sr and Pu at 5,000 and 10,000 ppm glycolate could result in lower DF values for these sorbates in ARP based on the current (12 hours) and proposed (8 hours) contact times. For the highest glycolate concentration used in this study, the percentage of Sr removed at 6 hours of contact decreased by 1% and the percentage of Pu removed decreased by nearly 7%. The impact may prove insignificant if the concentration of glycolate that is returned to the tank farm is well below the concentrations tested in this study. The presence of glycolate also decreased the removal rates for all three sorbates (Sr, Pu, and Np) by mMST. Similarly to MST, the results for mMST indicate that the impact is a kinetic effect, and the overall capacity of the material is not affected. The presence of glycolate did not change the lack of affinity of mMST for U. Pre-contacting the MST or mMST with glycolate did not have a significant effect on the performance of the materials when compared to tests having the same concentration of glycolate present in the simulant. These findings suggest that the glycolate is likely influencing removal by sorbate complexation and not by depositing onto or forming a film on the surface of the MST solids. Since the DF values are salt batch dependent, it is not possible to a priori quantify the impacts of glycolate on future processing campaigns. However, we recommend that the impacts of glycolate be evaluated during each salt batch qualification when a final processing concentration is defined, and recommendations can then be made on how to mitigate negative impacts, if needed. Impacts to the performance of the MST or mMST could be mitigated by increasing contact time or increasing sorbent concentrations. In addition to the MST and mMST testing, testing was performed to determine if there is an impact to the cesium removal at Modular Caustic-Side Solvent Extraction Processing Unit (MCU). An Extraction-Scrub-Strip (ESS) test routine was used to simulate cesium removal at the MCU. For this, SRNL performed three ESS tests, using the same basic aqueous waste simulant and solvent. For one test, SRNL added 5,000 ppm (mass basis) of glycolate and added 10,000 ppm of glycolate to a second test. A control test contained no glycolate. The results of all three tests were virtually identical for all the extraction, scrub and strip tests. (A single data point in the 5,000 ppm test is physically impossible and SRNL is currently resolving this obvious error.) At this time, SRNL concludes that the presence of up to 10,000 ppm of glycolate does not affect cesium removal by the current solvent system used in the MCU. Although not tested, the impact of glycolate for the Next Generation Solvent - that replaces BOBCalixC6 with MaxCalix - is expected to be very similar to that for the baseline solvent. Testing is needed to confirm. Additional testing is recommended to both further examine the nature of the interaction of glycolate with MST and mMST and also to help address some postulated risks on ARP/MCU operations with implementation of the glycolate flowsheet. The additional testing includes FTIR and Raman spectroscopy to examine the surface of the MST and mMST particles, iodometric titrations to determine the peroxide content in the mMST before and after exposure to glycolate, particle size measurements of the MST and mMST from the experiments performed with glycolate, and measurements of soluble Ti in the supernate from these glycolate experiments. With regards to MCU impacts, the following tests are also recommended based on the premortem risk assessment.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-08SR22470
- OSTI ID:
- 1043255
- Report Number(s):
- SRNL-STI-2012-00218; TRN: US1203266
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ACTINIDES
AFFINITY
CESIUM
FLOWSHEETS
GLYCOLIC ACID
IMPLEMENTATION
KINETICS
PARTICLE SIZE
PEROXIDES
PHYSICAL PROPERTIES
POLYMERS
RAMAN SPECTROSCOPY
RISK ASSESSMENT
SOLVENT EXTRACTION
SOLVENTS
SORPTION
STORAGE FACILITIES
STRONTIUM
TESTING
TITANATES
WASTE PROCESSING
WASTES