Influence of Nitric Acid and Nitrous Acid on Oxidation and Extraction of Neptunium with Double Scrub Flow Sheet in Simplified Solvent Extraction Process

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A simplified solvent extraction process based on U, Pu and Np co-recovery using tri-n-butylphosphate (TBP) as an extractant has been developing for advanced aqueous reprocessing of fast neutron reactor fuel. The influence of the HNO3 concentration in the feed and scrubbing solutions on the behavior of Np was evaluated experimentally and found to be co-extracted into the TBP with U and Pu. Moreover, the leakage ratio of Np to the raffinate was calculated from the changes in HNO2 concentration in the feed solution. 9.89% of the Np leaked to the raffinate in low HNO3 concentration feed and high HNO3 concentration scrubbing solutions. Almost all the Np in a 4.9 mol/dm3 HNO3 feed solution was recovered with U and Pu, based on the experimental flow sheet with double scrubbing solutions of 9 and 1 mol/dm3 HNO3. The experimental results showed a large contribution from the HNO3 concentration in the feed solution and at the extraction section to Np(V) oxidation. On the other hand, calculation results showed that high HNO2 concentrations tended to leak Np into the raffinate. The DF of Cs for U, Pu and Np product achieved 105 in all runs.