Abstract
The behavior of photochemical reactions of Np(V) in a nitric acid solution was studied under various test conditions as follows. As light sources, a mercury lamp and a semiconductor laser were used, and the light from the sources was irradiated on 2ml of neptunium nitric acid solutions in a quartz cell. The variables in these photochemical tests were the light irradiation rates (0.2 and 1.5W/cm2), the wavelength regions of the irradiation light (ultraviolet (UV) (250-400nm)), visible (400-600nm) and 980nm), the acidities of the nitric acid (1 and 3M) and the kinds of addition reagents (hydroxylamine+hydrazine and urea). The photochemical changes in Np valences in the test solutions depending on the irradiation times were analyzed using a spectrophotometer. Based on these tests, the following results were obtained.
• Neptunium(V) was photooxidized to Np(VI) by the irradiation of UV light on a nitric acid solution.
• The higher the irradiation rate and the concentration of nitric acid, the easier the photo-oxidation reaction of Np(V) progressed.
• The addition reagents influenced the oxidation reaction rate and the degrees of the progress in the photooxidation reaction of Np(V)→Np(VI).
Based on the results of these tests, the quantitative control of the photooxidation reaction of Np(V) was found to have much potential for a valence adjustment by selecting the appropriate conditions of the UV irradiation rates, the acidity of HNO3 and the kinds of reductants.
