The142/140Ce unit separation factor (q) for Ce(III)-Ce(IV) exchange reaction in an extraction system containing Ce(IV) in tri-n-butyl phosphate (TBP) and Ce(III) in hydrochloric acid has been determined. The value of q was found to be 0.9996±0.0001 (2δ) in the 12M HCl/TBP extraction system. The properties of the extraction systems containing nitric and hydrochloric acids in regard to isotope partition have been discussed.

The Ce-142/140 unit separation factors (q) for cerium(III)-cerium(IV) exchange reaction in an extraction system containing Ce(IV) in tri-n-butyl phosphate (TBP) or di(2-ethylhexyl) phosphoric acid (HDEHP) and Ce(III) in nitric acid were determined. The value of q was found to be 1.00054 +/- 0.00012 (2-sigma) in 6M HNO3/TBP and 1.00078 +/- 0.00028 in 6M HNO3/HDEHP extraction systems. The dehydration and complex formation processes and their contribution to reduced partition function ratios (RPFR's) are discussed.

The142/140Ce unit separation factors (q) for cerium(III)-cerium(IV) exchange reaction in an extraction system containing Ce(IV) in tri-n-butyl phosphate (TBP) or di(2-ethylhexyl) phosphoric acid (HDEHP) and Ce(III) in nitric acid were determined. The value of q was found to be 1.00054±0.00012 (2σ) in 6M HNO3/TBP and 1.00078±0.00028 in 6M HNO3/HDEHP extraction systems. The dehydration and complex formation processes and their contribution to reduced partition function ratios (RPFR's) are discussed.

The measurement of the isotope-exchange reaction between U/IV/ in the organic phase and U/III/ in the aqueous phase in the extraction systems: 7-8M HCl—5–40% TBP /aromatic diluent or CCL4/ were made. The high rate of exchange with the rate constant >102M−1min−1 was observed.

An approach is proposed to use the isotope ratios93Zr/96Zr,91Zr/96Zr and101Ru/104Ru for the determination of plutonium contriubtion to the total burnup of a spent nuclear reactor fuel of low initial enrichment in235U (3.6%). This approach was verified by determining the total burnup of the fuel from the137Cs and148Nd monitors and subtracting the partial burnup due to235U from the value obtained.