Development of solvent extraction scheme for reprocessing of advanced heavy water reactor spent fuel using N,N-Dihexyl octanamide as extractant

Distribution studies on Th(IV), Pa(V), U(VI) and Pu(IV) were carried out employing tri-n-butyl phosphate (TBP) and N, N-dihexyl octanamide (DHOA) as extractants under proposed advanced heavy water reactor (AHWR) spent fuel feed conditions. DHOA was found promising for selective extraction of U/Pu over Pa and Th as compared to TBP. Both Pu and Th formed trisolvated species with DHOA at 4 M HNO sub(3). Batch solvent extraction experiments were carried out for selective extraction of U and Pu from simulated AHWR spent fuel dissolver solution using 0.36 M DHOA and 0.18 M TBP dissolved in n-dodecane as solvents. Quantitative extraction of uranium and plutonium was achieved under experimental conditions leaving bulk of thorium in the raffinate. The co-extracted thorium from the organic phase was proposed to be scrubbed using 4 M HNO sub(3). A series of non-salt forming reductants were evaluated for their suitability for the partitioning of plutonium. Uranium from the Pu lean organic phase was proposed to be stripped using 0.01M HNO sub(3). The extraction behavior of fission products was also examined under the simulated AHWR spent fuel feed solution. Based on these observations, a reprocessing scheme has been proposed for the reprocessing of three component U, Pu and Th system arising out of the irradiated (Th, Pu)O sub(2) pins.