Abstract
Redox interaction of reduced technetium forms and technetium(VII) with neptunium(III), neptunium(IV) and neptunium(VI) have been investigated using electrochemical and spectroscopic (Vis–NIR) techniques. The neptunium species most stable in 4 M H2SO4, i.e. Np(IV) ions, do not reduce Tc(VII) in contrast to Np(VI) ions which oxidize Tc(IV) species to Tc(VII). The interaction of pertechnetates with Np(III) leads to formation of Tc(IV) species. The Vis–NIR measurements showed the generation of intermediate Tc(V) and Np(V) forms during the oxidation of Tc(IV) and competitive reduction of Np(VI). Tc(V) and Np(V) forms are characterised by the bands at 460 and 980 nm respectively.
Highlights
Technetium and neptunium are artificial elements produced in relatively large amounts in nuclear power generation systems [1, 2]
The main technetium radioisotope presents in spent nuclear fuels (SNFs) is long living 99Tc (T1/2 = 2.13 9 105 year) which is a product of beta minus decay of 99Mo generated as a product of fission reaction of235U
The 99Tc yield in fission products is at the level of 6% [1], which corresponds to 1 kg of Tc in 1 ton of SNF from a typical LWR [3].237Np (T1/2 = 2.14 9 106 year) as the product of (n, 2n) reaction with238U [1, 2] is generated with a quantity of 0.40–0.48 kg in 1 ton of SNF [4]
Summary
Technetium and neptunium are artificial elements produced in relatively large amounts in nuclear power generation systems [1, 2]. According to Rotmanov et al [11] the dissolution of metallic Tc in an acid is accompanied by generation of reduced Tc species characterized spectroscopically by a band near 480 nm These authors attribute this signal to Tc(V) ions. This is in line with conclusions of Maslennikov et al [12] who reported that technetium species present in nitric acid solutions, most likely Tc(V) can be determined using a Vis band with the maximum at 480 nm. The other than described above technetium species were reported by Paquette [14] These authors determined spectroscopically Tc(III) ions in slightly basic media using weak bands in Vis range at 470 (and 630) nm. Np(III) and Np(VI) species were generated electrochemically by oxidation or reduction of Np(IV) stock solution, respectively. A potentiostat/galvanostat Autolab PGSTAT101 from Metrohm was used in the electrochemical experiments
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