The study of reactivity of actinide ions towards hydrated electrons and hydrogen atoms in acid aqueous solutions by a pulse radiolysis method

Abstract

The reactivity of actinide ions towards hydrated electrons (e - aq) and H atoms in acid aqueous solutions was studied by the pulse radiolysis method. The rate constant of reactions of e - aq with U(IV) Np(IV) and Pu(IV) were determined to be equal to (5.8 ± 1.0) × 10 10, (6.3 ± 1.2) × 10 10 and (3.3 ± 0.8) × 10 10 M -1 s -1, respectively. The rate constant of similar reaction for Ce(IV) is equal to (6.6 ± 1.2) × 10 10 M -1 s -1. Hydrogen atoms react much more slowly. The rate constants of the reactions U(IV) + H, 3p(III) + H (oxidation), Np(IV) + H (reduction), Np(VI) + H, Pu(III) + H (oxidation), Pu(IV) + H (reduction), Pu(VI) + H, Am(V) + (reduction) and Am(IV) + H are equal to (4.5 ± 0.5) × 10 7 (6.4 ± 1.2) × 10 7, <1 × 10 6, (4.0 ± 0.5) × 10 8, (6.0 ± 1.0) × 10 6 (sulphuric acid solution), (5.3 ± 0.5) × 10 7 (sulphuric acid solution), (2.0 ± 0.3) × 10 8, (2.0 ± 0.3) × 10 8 and (1.6 ± 0.2) × 10 9 M -1 s -1, respectively. An explanation of the results obtained is given.