Fig. 4-4 Concept of spent solvent treatment by submerged combustion technique The high-temperature and corrosive combustion gas is directed into a solution in a recovery tank connected to the combustion furnace. This cools the combustion gas rapidly and traps combustion products effectively.

Fig. 4-5 TRU waste volume generated in treatment of distillation residues of spent solvent TRU waste volume generated in the treatment of distillation residue of spent solvents by submerged combustion technique will have about one percent the volume of other techniques.

Mixed organic solvents such as tri-n-butyl phosphate (TBP) and normal dodecane (nDD) are used for recovery of uranium (U) and plutonium (Pu) from spent fuels. These organic solvents are radiologically and chemically degraded with repeating usage and become unsuitable for reuse. Presently, degraded spent organic solvents containing transuranic (TRU) elements and fission products (FP) are solidified directly with plastic or the pyrolyzed matter from the solvents. In the near future, high-burn up fuels and U-Pu mixed oxide fuels will need to be reprocessed. The amounts of TRU elements contained in spent solvents will then increase. JAERI has developed an innovative submerged combustion technique that is capable of decomposing spent organic solvents used for separation of TRU elements. This method is able to completely trap decomposition products containing TRU and FP elements in water. Storage of TRU bearing wastes is required for a long period, so the development of the submerged combustion technique provides safe storage and does it economically.

Reference G. Uchiyama et al., Development of Spent Solvent Treatment Process by Submerged Combustion Technique, J. Nucl. Sci. Technol., 31(3), 228 (1994).

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