Spent fuel reprocessing is most usually performed using the well proven hydrometallurgical PUREX (plutonium uranium refining by extraction) process.

Several organic compounds were tested and eventually tri-butyl-phosphate (TBP), diluted in an alkane solvent, was selected. TBP is an organo-phosphorus compound with the formula (CH3CH2CH2CH2O)3PO.

CH3-CH2-CH2-CH2-0

CH3-CH2-CH2-CH2-0-P = о

/

CH3-CH2-CH2-CH2-0

16.3.1 Description of the main steps of the PUREX process

The main steps (Fig. 16.2) include:

• Head operations leading to the dissolution of the fuel. These comprise reception at the reprocessing plant, storage, shearing, dissolution, clarification (Section 16.3.2).

• Operations for separating uranium and plutonium from fission products followed by uranium/plutonium partition (Section 16.3.3).

• Purification of plutonium and uranium (in order to comply with the required purity for end products) and, possibly, conversion into oxides.

• Ancillary operations for conditioning solid wastes and effluent treatments.