The Tank Side Cesium Removal (TSCR) system is currently being constructed to process Hanford tank waste supernates for vitrification. TSCR incorporates a filtration system and cesium (Cs) removal system using columns filled with crystalline silicotitanate (CST) ion exchanger, produced by Honeywell UOP, LLC (product IONSIV™ R9140-B).
Laboratory-scale ion exchange processing using TSCR prototypic unit operations continue to contribute toward Washington River Protection Solutions (WRPS) establishing accurate process flowsheets for the individual feed campaigns planned for TSCR. The Test Platform established at the Pacific Northwest National Laboratory (PNNL) Shielded Analytical Laboratory has been used to conduct laboratory-scale unit operation process steps on several Hanford tank wastes at ambient temperature This report describes the small-scale ion exchange testing with 8.0 L of filtered supernate from tank 241-AP-107 (AP-107) at 16 °C (62 °F) to demonstrate processing at temperature conditions that are more prototypic of what the TSCR system could experience during colder seasons of the year.
One of the waste acceptance criteria (WAC) for the Hanford Waste Treatment and Immobilization Plant Low-Activity Waste vitrification facility is that the waste must contain less than 3.18×10-5 Ci 137Cs per mole of Na. For the AP-107 tank waste to meet this criterion, only 0.114% of the influent 137Cs concentration may be delivered to the WTP; this requires a Cs decontamination factor of 878. Prototypic TSCR operations are intended to utilize a lead-lag column configuration until the lag column reaches the WAC, then a polish column will be brought online for a lead-lag-polish column configuration. However, for the testing reported herein, the lag column did not reach the WAC until all the feed had been processed so no polish column was used. Flowrate was adjusted to match the CST contact time expected for the full-scale operation, i.e., matched bed volumes per hour (BV/h) flowrate. The feed was processed downflow through the lead column, then through the lag column at an average of 1.90 BV/h until the entire available AP-107 feed was processed. The Cs-decontaminated product was retained for vitrification testing (to be reported separately).
The lead column only reached 22% Cs breakthrough after processing 799 BVs of feed; the 50% Cs breakthrough was extrapolated to occur at ~1100 BVs. This extrapolated 50% Cs breakthrough value was lower than the batch contact estimate (1255 BVs ) by 11%. Given the extrapolation from column processing and the overall measurement uncertainties, the agreement within 11% was considered reasonable. Testing confirmed that 200 more BVs can be processed to 50% breakthrough at 16 °C than at 28 °C, demonstrating improved operating performance (i.e., higher Cs capacity) at the lower temperature. The Cs effluent from the lag column reached the WAC after processing 799 BVs. Cs breakthrough from the lag column began at 400 BVs, reaching 1.82×10-1 µCi/mL, or 0.112 % Cs breakthrough, after processing all 799 BVs of feed. Table S.1 and Figure S.1 summarize the observed column performance and relevant Cs loading characteristics.