Photochemical Valence Adjustment of Pu and Np in Nitric Acid Solution for Separation and Co-Extraction
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PHOTOCHEIICAL VALENCE ADJUSTMENT OF Pu ANDNp IN NITRIC ACID SOLUTION FOR SEPARATION ANDCO-EXTRACTION Y. WADA*.K. WORIMWTO*,T. GOIBUCHI* AND H. TOMIYASU** *Power Reactor and Nuclear Fuel Development Corp.. 4-33, Wuramatu, Tokai-Mura, Naka-Gun, Ibaraki Pref..319-11, Japan **Research Laboratory for Nuclear Reactors,Tokyo Institute of Technology. 2-12-1.0-okaysm,. Meguro-Ku. Tokyo, 152.Japan ABSTRACT Photochemical redox reaction tests were corried out where the experimental variables were irradiation rate using a Hg lamp light and molarity of nitric acid containing different reductant reagents such as hydroxylamine(HAN),hydrazine (HDZ) and urea. Based on these tests, we confirmed that the valences of Pu and Np were easily photochemically adjusted to two conditions of Pu(IV.VI)-Np(V) and Pu(IV.VI)-Np(VI), indicating that photochemical valence adjustment for the separation and co-extraction of Pu and Np has excellent potential as an advanced process technology. Introduction The valences of Plutonium(Pu) and Neptunium(Np) in nitric acid solution are generally Pu(IMl.IV,VI) and Np(IV, V,VI). All standard electrode potentials for these valences and the redox potential of the solvent ion.NO3-.are in the narrow region between 0.75 and 1.15V [1] .Therefore.these valences usually co-exist in a nitric acid solution, and it is difficult to control their valences using only chemical reagents for separation and co-extraction with TBP/n-dodecane. It is generally considered that photon energy has the potential for selective excitation, and as feasibility studies for a solution of the above problem, there have been several reports where photochemical processes were studied in order to adjust the valences of uranium(U) and Pu [2.3.43 . Therefore, we have been studying the technologies of the valence adjustment for Pu and Np in a nitric acid solution. EXPERIMENTAL The concentrations of Pu and Np in the test nitric acid solution were Ixl0- 3 mol. dm-3, and the test solutions were adjusted to the test conditions by changing the acidity and the kinds of the adding reagents. Zml of these solutions were irradiated by the light from the Hg lamp. The temparature and the homogeneity of the sample solution during the irradiation were kept constant using an electric cooling device and a stirrer. The valences of Pu and Np in these solution after various irradiation times were analyzed using a spectrophotometer. The irradiation tests were carried out to examine the feasibility of photochemical valence adjustment of Pu and Np in nitric acid solution by changing the following variables. I. Photochemical valence adjustment tests for separation These tests were carried out by the irradiation for the mixed Pu and Np nitric acid solution containing reductantsHAN and HDZof which molar quantity were 10 times that of Pu and Np. HDZ was added as the decomposing reagent for HN•2. the photolysis product. 2. Photochemical valence adjustment tests for co-extraction The irradiation tests similar to No. 1 were done for the mixed solutions containing urea which was
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