Waste supemate

AL Marston. Analysis of radioactive waste supemate by laser-Raman spectrometry. Nucl Technol 25 576-579, 1975. 

Norato, M. A., Cambell, S. G., Crowder, M. L., Geeting, M. W., Kessinger, G. F., Pierce, R. A., and Walker, D. D. High-Level Waste Demonstration of the Caustic-Side Solvent Extraction Process with Optimized Solvent in the 2-cm Centrifugal Contactor Apparatus Using Tank 37H/44F Supemate, Report WSRC-TR-2002-00243, Rev. 0, Westinghouse Savannah River Company, Aiken, SC, November 1, 2002. 

Contaminant Concentrations in Simulated Supemate Waste from Hanford Tank, their Waste Forms, and the TCLP Results. 

In the conceptual waste processing plant, supemate will be separated from sludge because the high salt content of supemate would adversely affect any of the promising waste forms. The sludge will then be dried to convert it to a more easily handled form and washed to remove most of the residual soluble salt. The sludge will then be dried again for incorporation into one of these waste forms. 

The decontaminated supemate may be evaporated to a solid salt in a wiped film evaporator. For the design basis assumed in this study, the total volume of solidified salt would be about 100 million 1. (/ 25 million gal). Since the heat-producing isotopes will be removed, this material can be stored in large containers in bulk storage. It is expected that the decontamination of this material will be sufficient that the principal hazard in the salt cake will be the nitrate itself. The activity left in the salt may well be less than that left in waste tanks after final decontamination. On this basis, further processing of this material into a less leachable form would probably not be necessary. However, it is presently assumed that this material cannot be dispersed to the environment. 

The waste at SRP exists in three forms sludge, saltcake, and salt-supemate solution. The sludge, comprising approximately 10% of the stored waste, consists primarily of precipitates of the hydroxides of Fe, Al, and Mn. This waste contains most of the radioactivity, including small amounts of actinides not recovered in the reprocessing plants and most of the fission products, except for Cs. The salt is largely NaNOj, NaA102, and NaOH. Most of the Cs is contained in the salt-supemate solution. 

The salt-supemate solution is decontaminated for disposal as low-level waste by removing the radionuclides by precipitation and sorption. A solution of sodium tetraphenylborate is added to precipitate K, Cs, and NH4 as insoluble tetraphenylborate salts. These salts are further processed to remove most of the organic carbon. About 90% of the phenyl groups on the salt are converted to an immiscible BZ phase by formic acid hydrolysis. Currently, the BZ is steam distilled, further decontaminated if necessary, and incinerated as a low-level radioactive and hazardous (mixed) waste. Since there is tremendous public concern about incineration of mixed waste, alternative technologies are of particular interest. 

Medium-active waste also can be treated by floe precipitation processes similar in character to those widely used in water treatment. Precipitants are required which will remove the unwanted radioactive species from the waste solution and quickly settle, carrying the radioactivity into a small bulk of sludge. The supemate can be treated as a low-active waste and discharged locally to the environment. Typical precipitants for common cations are as follows. 

The supemate would be transferred to a dedicated tank and decontaminated by adding tetraphenylborate causing the Cs, K, and Na to precipitate out of solution. Also, sodium titanate would be added to adsorb Sr, U, and Pu. This mixture of solids would than be concentrated by filtration forming a precipitate slurry and low level waste solution. The solution would be processed into grout at the Saltstone facility while the precipitate sluny would be transferred to the DWPF. 

Chemical Characterisation ofSRP Waste Tank Sludge and Supemates, Du Pont Savannah River Laboratory, 140 pp. 

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