RECOVERY OF NEPTUNIUM FROM HIGHLY RADIOACTIVE-WASTE SOLUTIONS OF PUREX ORIGIN USING TRIBUTYL-PHOSPHATE

The present work deals with the extraction of neptunium into the TBP/d odecane phase under conditions relevant to highly radioactive waste so lutions, along with uranium and plutonium, by oxidizing it to the hexa valent state using 0.01 M K2Cr2O7 and subsequently recovering it by se lective stripping. Three types of simulated HLW solutions, namely sulf ate-bearing (SB, in similar to 0.3 M HNO3) and nonsulfate wastes origi nating from the reprocessing of fuels from pressurised heavy water rea ctors (PHWR) and fast breeder reactors (FBR) (both in 3.0 M HNO3), hav e been employed in this study. Very high extraction of U(VI), Np(VI), and Pu(VI) was obtained from PHWR and FBR-HLW solutions, whereas extra ction was less but reasonably high from the SB-HLW solution. The uptak e of cerium at tracer level concentrations in the millimolar range (en countered in HLW solutions) and from the simulated HLW solutions conta ining 0.01 M K2Cr2O7 by 30% TBP has shown that its extraction takes pl ace only at tracer level concentrations and not at millimolar levels. The stripping of the metal ions from the loaded organic phase was done with a mixture of 0.01 M ascorbic acid and 0.1 M H2O2 in 2.0 M HNO3 a t organic to aqueous phase ratios of 1:1, 2:1, and 4:1. Quantitative r ecovery of neptunium and plutonium was achieved. Based on these result s, a scheme was formulated for the recovery of neptunium, and it was t ested using the actual high level waste solution originating from the reprocessing of research reactor fuels.