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U(IV) can be photochemically produced in tri-n-butyl phosphate solutions from uranyl nitrate and used to reduce Pu(IV). Nitrite production can be controlled by filtering out light having wavelengths of < 350 nm and by keeping the temperature of the reaction mixture below 10/sup 0/C. Another product of the photolysis, di-n-butyl phosphate, can interfere with the reduction, but no effect was apparent in our experiments. Conventional solvent cleanup procedures should remove photolysis side products. The application of this process to the reprocessing of nuclear fuel would require commercially available light sources that can be located outside the hot zone of the plant and a reactor vessel with windows within the hot zone. 1 figure, 1 table.

Solvent extraction of thorium by 30 vol % dibutyl butylphosphonate-70 vol % Isopar H from salted and nonsalted nitric acid solutions was studied. Thorium distribution coefficients D/sub Th/'s were obtained for nitric acid solutions of approx. 0.3 to approx. 12 N and for solutions of 1 and 2 M NH/sub 4/NO/sub 3/ over the HNO/sub 3/ concentration range of approx. 0.5 to approx. 9 N. The nitric acid solution D/sub Th/'s varied from approx. 4.3 at the lowest acidity, increased to a maximum of approx. 40 at approx. 3-4 N H/sup +/, and then gradually decreased to approx. 18 at approx. 11.5 N H/sup +/. The solutions containing 1 and 2 M NH/sub 4/NO/sub 3/ gave definite salting-out effects with D/sub Th/'s of 79 to 90, respectively, at the lowest acidities; these values then decreased with acidity increases to those of the nonsalted acid solutions at approx. 5 N HNO/sub 3/ and paralleled the acid solution values up to approx. 12 N.