No abstract

No abstract

Some of the distribution coefficient (K d ) values in Table ES-1 indicate that the measured value exceeds the calculated value. This difference in measured versus predicted is attributed to error in the measurements and reference state of the material. Because of the way that the distribution coefficient is calculated, small variance in measurements of mass and analytical instrument results can cause large changes in the observed value. The predicted distribution coefficients were calculated using the ZAM computer model, which is based on the powdered form of CST, and there is typically an adjustment of the output to account for the dilution factor due to the binder present in IE-911. The absence of the need for a dilution factor adjustment for this batch of material is attributed to different initial conditions for the material such as preconditioning steps and drying. The loading measurements (Q) match the predicted values very well. This Q parameter is less sensitive than the distribution coefficient parameter to slight variance in measurements performed during testing.

Pretreatment processes at the Savannah River Site will separate 90 Sr, alpha-emitting and radionuclides (i.e., actinides) and 137Cs prior to disposal of the high-level nuclear waste.Separation of 90 Sr and alpha-emitting radionuclides occurs by ion exchange/adsorption using an inorganic material, monosodium titanate (MST). Previously reported testing with simulants indicates that the MST exhibits high selectivity for strontium and actinides in high ionic strength and strongly alkaline salt solutions. This paper provides a summary of data acquired to measure the performance of MST to remove strontium and actinides from actual waste solutions. These tests evaluated the effects of ionic strength, mixing, elevated alpha activities, and multiple contacts of the waste with MST. Tests also provided confirmation that MST performs well at much larger laboratory scales (300 2 -700 times larger) and exhibits little affinity for desorption of strontium and plutonium during washing.3

Researchers at the Savannah River Technology Center (SRTC) successfully demonstrated the Caustic-Side Solvent Extraction (CSSX) process flow sheet using a 33-stage, 2-cm centrifugal contactor apparatus in two 24-hour tests using actual high level waste. The CSSX process for removal of cesium from alkaline solutions is the reference process for decontamination of high level waste (HLW) at the Savannah River Site (SRS). The solvent consists of a calix [4]arene-crown-6 extractant (BOBCalix), an alkylphenoxy alcohol modifier, and trioctylamine (TOA) dissolved in an inert hydrocarbon matrix (Isopar ® L). Previously, we demonstrated the solvent extraction process with actual SRS HLW supernatant solution using a non-optimized solvent formulation. Following that test, the solvent system was optimized to enhance extractant solubility in the diluent by increasing the modifier concentration. We now report results of two tests with the new and optimized solvent. The first test used a composite of supernatant solutions from two waste tanks and the second test used a solution derived from dissolved salt cake. Test results showed that the CSSX process using the optimized solvent reduces 137 Cs in HLW supernatant solutions to concentrations below the waste acceptance criterion (WAC) of 45 nCi/g for disposal as low-level waste (called "Saltstone"). Waste decontamination factors as high as three million were achieved during testing. Test durations exceeded 24 hours of uninterrupted operation and demonstrated hydraulic stability of the contactor array while operating with the optimized solvent. Carryover of organic solvent in aqueous streams (and aqueous in organic streams) was found to be less than 1%. The concentration factor (i.e., the ratio of the cesium concentration in the strip raffinate to the concentration in the waste) averaged approximately 13 during both tests, slightly below the process requirement of 15. Uncertainties in process flow rate measurement and control prevented the test from achieving the target of 15.