Improvement Initiatives for the Tank Closure Cesium Removal (TCCR) Unit for Processing Tank 9 Salt Solution - 21345

Savannah River Remediation manages and operates the liquid waste facilities at Savannah River Site for the Department of Energy. High Level Waste at the Savannah River Site is currently stored in aging underground storage tanks. This waste is a complex mixture of insoluble solids (sludge) and soluble salts in an alkaline solution. Savannah River Remediation has deployed the Tank Closure Cesium Removal system, a tank-side ion exchange process, to remove radioactive cesium from salt waste and enable onsite disposal of the resulting decontaminated salt solution as low-level waste at the Saltstone facilities. This system also allows for bulk waste removal of waste tanks in preparation for eventual final tank closure. The Tank Closure Cesium Removal system consists of two prefilters, four ion exchange columns, one resin trap, and a ventilation system. The ion exchange process uses a form of inorganic crystalline silicotitanate, which has a high affinity for cesium and other alkali metals, strontium, and actinides. The Tank Closure Cesium Removal system started radioactive operations in 2019 and has successfully processed ∼1,135,500 L (∼300,000 gal) of salt solution from Tank 10 despite the challenges of double salts of sulfates-carbonates present in Tank 10. Savannah River Remediation has elected to utilize the Tank Closure Cesium Removal system for the processing of Tank 9 salt solution. A few physical changes will be made to the Tank Closure Cesium Removal system to enhance the operation. The first is the ion exchange column design [changing to a 48.26 cm (19'') outside diameter vs. 50.8 cm (20'') outside diameter]; the second is a design change that allows the column flushes to be returned to Tank 10 (bypassing the filter units); the third is potential introduction of a different filter media for filtering the salt solution; the fourth is enhancing the detection capability of radiation monitors located on the decontaminated salt solution line exiting the Tank Closure Cesium Removal system; the fifth is the installation of passive vents in the enclosure; and the last is the resin fill nozzle on the ion exchange column will be blind flanged vs. welded. The media used in the ion exchange column will remain as crystalline silicotitanate, but the mean particle size of the media will be reduced to enhance the removal kinetics of cesium from the salt solution. The new reduced particle size of crystalline silicotitanate is called 'R9120-B 30X60 Non-CW CST Resin'. R9120-B 30X60 Non-CW CST Resin is an engineered inorganic ion exchange material that contains an inert binder. The Tank Closure Cesium Removal system holds a total of four ion exchange columns. The installation work for putting the new ion exchange columns into the Tank Closure Cesium Removal unit with the R9120-B 30X60 Non-CW CST Resin began after the completion of Batch 3 processing from Tank 10 in August of 2020. Based on all the enhancements mentioned above for the processing of Tank 9 salt solution, the Tank Closure Cesium Removal system will be referred to as Tank Closure Cesium Removal 1A. The Tank Closure Cesium Removal 1A feed will be created from salt cake in Tank 9 through a dissolution process and/or from heel left in Tank 10. Once enough salt has been dissolved in Tank 9, the batch will be transferred to Tank 10 to form a larger batch for qualification. Tank 10 will now serve as a holding and feed tank for the Tank Closure Cesium Removal 1A process. Similar to the demonstration performed with the Tank Closure Cesium Removal system, the waste is filtered through a set of two shielded, dead-end prefilters that prevent solids buildup in the columns. The filtered salt solution then travels to the shielded ion exchange columns, which can be operated individually or in series, where the cesium is sorbed on the crystalline silicotitanate media. The decontaminated salt solution then travels through a resin trap and out of the module to Tank 11. This paper describes the planned improvement initiatives learned from the Tank Closure Cesium Removal system and laboratory testing completed for Tank Closure Cesium Removal 1A and is expected to be of interest to liquid waste treatment facilities as it discusses improvement initiatives for tank side solids filtering and ion exchange process for removal of radioactive cesium. (authors)