(309b) Tank Closure Cesium Removal at Savannah River Site

High Level Waste (HLW) at the Savannah River Site (SRS) 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. Continued long-term storage of these radioactive wastes poses an environmental risk. The salt waste is currently treated to remove cesium by an interim solvent extraction process prior to disposal as grout in the Saltstone Disposal Facility. This interim process will be replaced with the Salt Waste Processing Facility (SWPF) to increase the salt waste treatment capacity. Treatment and disposal of the salt waste is the critical path to waste retrieval, risk reduction and closure of old style tanks at SRS.

Savannah River Remediation (SRR) is developing a supplemental at-tank ion exchange capability for the removal of cesium from liquid salt waste. Building on the conceptual development of the Small Column Ion Exchange (SCIX) process, the experience of modular commercial nuclear plant decontamination, and following the disaster response associated with Fukushima, SRR is deploying a modular at-tank treatment system for the selective removal of cesium from bulk salt waste effectively and efficiently. This Tank Closure Cesium Removal (TCCR) initiative will provide a supplemental treatment capability to existing and future salt processing and improve confidence in supporting the desired acceleration of waste retrieval and tank closure efforts.

The TCCR system configuration is consists of modular process structures located near Tank 10H and 11H. Salt waste will flow through a pre-filter to reject any solid material from entering the treatment system and be returned to Tank 10H. Clarified salt waste will then flow from the pre-filter into the first stage ion exchange column. The ion exchange media utilized will be highly selective for the removal of cesium and allow most other soluble constituents to pass through the media. Additional ion exchange columns are available and can be configured in series to improve decontamination factor, protect against flow “channeling” in the column, guard against media breakthrough, and allow for more continuous operation of the system. Decontaminated (cesium removed) effluent would flow from the ion exchange columns and sent to Tank 11H prior to being transferred to Saltstone for disposal.

Once the ion exchange media in a column becomes loaded with cesium to the extent practical (“spent”), the column with media will be removed from the system and replaced with a new ion exchange column loaded with fresh media. The spent column will be temporarily stored in an Interim Safe Storage (ISS) location within the SRS Tank Farm Facility. This ISS concept avoids the initial need for back-end process facilities (deferring the cost of these facilities) and allows for identification and evaluation of potential future disposal alternatives.

In addition to accelerating waste retrieval and tank closure activities, demonstration of this capability has several other benefits. Deployment of commercially available technologies with minor modification can expand Department of Energy (DOE) utilization of commercially supplied treatment processes. This “at-tank” treatment system could be modified to evaluate and demonstrate removal of other radioactive constituents (strontium, technetium, iodine, etc.) of bulk waste. The modular aspect of this capability can allow for additional units to be delivered and deployed at SRS, as well as, provide supplemental treatment capabilities for waste treatment at other DOE sites.