Generating an Estimate of the Capacity of the Near-Tank Treatment System for Processing S/SX Tank Waste

Abstract

In order to reduce the number of high level waste canisters that will have to be produced by the Hanford Tank Waste Treatment and Immobilization Plant, supplemental waste treatment technologies are being investigated. One such technology is the Near-Tank Treatment System (NTTS), which uses continuous sludge leaching, filtration, and ion exchange to process the waste in a simple, compact system. The NTTS is ideally suited for handling Hanford tanks with large amounts of boehmite, a difficult aluminum phase to dissolve. Processing of boehmite by caustic leaching is the throughput limiter in the NTTS. A model was developed to estimate the capacity of the NTTS based on boehmite kinetics and the contents of the waste tanks considered for processing. Using this model, the lifecycle of the NTTS is estimated to be 11 years. Examples of optimizing NTTS performance are presented using the model. Model results are also compared with recently conducted pilot-scale tests.

Keywords:

• caustic leaching
• nuclear waste treatment
• numerical modeling

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the contributions of PNNL staff members David Blanchard, Matthew Fountain, Samuel Bryan, and Cynthia Niver who have been involved with bench-scale testing and development of the NTTS system. Special thanks is also due to Parsons Infrastructure and Technology Group, Inc. and staff members Collin Smith, Rhett Tranbarger, Doug Dunlap, and Tom Frater who performed the pilot scale testing as described in Schonewill et al. (9). The work described in this article was performed by Pacific Northwest National Laboratory, which is operated by Battelle for the U.S. Department of Energy under Contract DE-AC05-76RL01830. This work was funded by the U.S. Department of Energy through the Office of Environmental Management.

Notes

^a All cases run for 20,000 hours (except Nos. 4 and 9, which required 30,000) at a dt = 0.5 hours.

^b Initially, the 0.06/0.18/6 parameter set is run for 100 hours. Then, alternatingly, the 0.18/0.06/6 set is run for 25 hours and the 0.06/0.18/6 set is run for 50 hours.

^c As b), expect the concentration factor was 12 for each alternating case.

^d Initially, the 0.06/0.18/6 parameter set is run for 100 hours. Then, alternatingly, the 0.18/0.06/6 set is run for 50 hours. and the 0.06/0.18/6 set is run for 100 hours.

^a All cases run for 15,000 hours (except No. 2, which required 25,000 hours) at a dt = 0.5 hours.