Small-Column Ion-Exchange Alternative to Remove 137Cs from Low-Curie Salt Waste: Summary of Phase 1

A Small-Column Ion-Exchange (SCIX) system is being evaluated for removing cesium from the Type 2 and/or Type 3 dissolved saltcake wastes at the Savannah River Site (SRS) to ensure that the dissolved saltcake meets the waste acceptance criteria at the Saltstone Facility. Both crystalline silicotitanate (CST) and IONSIV{trademark} IE-96 zeolite were evaluated as the ion-exchange media. The accelerated alternative, using CST in the SCIX, could save as much as $3 billion in operating and storage costs and {approx}20 years in processing time compared to the current baseline. With its proven high cesium-loading capacity for the expected dissolved saltcake compositions and temperatures, CST is the preferred sorbent for SCIX. The low-cost alternative sorbent, zeolite, greatly increases the volume of sorbent required because of its much lower cesium-loading capacity. Thus, zeolite greatly increases the cost for the alternative, mainly because of the increased number of Defense Waste Processing Facility canisters required to dispose of the loaded sorbent (potentially over 7000 for zeolite, compared with <500 for CST). The models previously developed for predicting cesium loading on CST compared favorably with laboratory measurements of equilibrium distribution ratios and column loading performance using dissolved saltcake simulants. These models predict that a column of 432 gal of CST can operate at 25 gal/min and treat 100,000 to 900,000 gal of dissolved saltcake, depending on the solution composition. An average value of 300,000 gal per column was used for the cost benefit analysis. Predicted cesium loading on the CST is normally below 300 Ci/L; however, solutions with low salt concentrations could potentially load the CST to 630 Ci/L. Heat transfer calculations predict nonboiling temperatures for the small columns with loadings <100 Ci/L with only natural convection cooling. For the loadings up to the maximum calculated for the tank farm (630 Ci/L), a water cooling system is required to ensure that no boiling occurs in the column if the process flow is stopped. Dose rate calculations indicate that the maximum dose rate above the tank riser is expected to be {approx} 10{sup -2} mrem/h for a column loaded at 300 Ci/L in the riser. The risk analysis indicates a net beneficial impact with no major problems likely to prevent implementation or completion of saltcake treatment