Photo-enhancement Effect on Oxidation Reaction of Uranium(IV) by NO-3 in Perchloric Acid Solutions.

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  • HATAKEYAMA Koh
    Research Laboratory for Nuclear Reactors Tokyo Institute of Technology Naka Energy Research Center, Mitsubishi Materials Co.
  • PARK Yoon-Yul
    Research Laboratory for Nuclear Reactors Tokyo Institute of Technology Pusan Junior College
  • TOMIYASU Hiroshi
    Research Laboratory for Nuclear Reactors Tokyo Institute of Technology
  • WADA Yukio
    Nuclear Fuel Technology Development Division Power Reactor and Nuclear Fuel Development Corp.
  • IKEDA Yasuhisa
    Kashiwa Laboratory Institute of Research and Innovation

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  • Photo-enhancement Effect on Oxidation Reaction of Uranium(4)by NO3 in Perchloric Acid Solutions
  • Photo-enhancement Effect on Oxidation R

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Abstract

Kinetic studies on the oxidation reactions of U(IV) by NO-3 in HClO4 solutions have been carried out spectrophotometrically in the dark and under irradiation with Xe light. Remarkable photo-enhancement effect on the oxidation reaction was observed under the irradiation with UV light below 420nm. This indicates that the photo-enhanced oxidation of U(IV) is not due to the excitation of U(IV) but the excitation of NO-3. It was found that apparent first-order rate constants in both dark (κobs) and photo-reactions (κ*obs) increase with increasing [NO-3] and approach to constant values. This relation is well correlated with the distribution of nitrato complexes of U(IV). Furthermore, the oxidation rates were found to be independent of [H+](0.5-3.5M(=mol•dm-3)). From these results, it is proposed that the oxidation of U(IV) by NO-3 proceeds through two paths, i.e., one is the two-electron transfer between U(IV)[U4+ and U(NO3)3+ species] and NO-3, and another is the oxygen atom transfer from the coordinated NO-3 to U(IV) in U(NO3)2+2. Kinetic parameters are as follows: κobs(25°C)=7.0×10-6 s-1, ΔH≠=60.8kJ•mol-1, ΔS≠=-140J.K-1.mol-1 and κ*obs(25°C)=3.0×10-5s-1, ΔH≠=26.3kJ.mol-1, ΔS≠=-243J.K-1.mol-1.

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