Determination of U(VI) and U(IV) concentrations in aqueous samples containing strong luminescence quenchers using TRLFS

Progress of energy-related radiochemistry and radionuclide production in the Republic of Korea

The field of radiochemistry in the Republic of Korea has expanded greatly over the last three decades to meet the rapid growth of technological demands in various areas such as nuclear energy and nuclear technologies for human health and environmental protection. Major research activities, which were initially centered at the Korea Atomic Energy Research Institute (KAERI), have gradually spread to major universities and the commercial sector. In this review, progress and recent research trends in nuclear and radiochemistry in Korea are summarized. The main research outcomes achieved by KAERI scientists are highlighted, with emphasis on basic actinide chemistry in nuclear fuel cycles, the radioanalytical chemistry of various radionuclides from radioactive waste and the environment, and medical radionuclide production. In addition, recent efforts to promote radiochemical education and future perspectives are briefly outlined.

Studies of aqueous U(iv) equilibrium and nanoparticle formation kinetics using spectrophotometric reaction modeling analysis

Hydrolysis of tetravalent uranium (U(iv)) and U(iv)-nanoparticle formation kinetics were examined over a wide range of temperatures using spectrophotometric reaction modeling analysis. The characteristic absorption bands representing U⁴⁺, U(OH)³⁺, and a proposed oxohydroxo species were newly identified in the UV region (190–300 nm). Dynamic absorption band changes in the UV and visible regions (360–800 nm) were explored to reevaluate the binary ion interaction coefficients for U(iv) ions and the thermodynamic constants of the primary hydrolysis reaction, including complexation constants, enthalpy, and entropy. No further hydrolysis equilibrium beyond the formation of U(OH)³⁺ was identified. Instead, an irreversible transformation of U(iv) ions to U(iv)-nanoparticles (NPs) was found to occur exclusively via the formation of a new intermediate species possessing characteristic absorption bands. The kinetic analysis, based on a two-step, pseudo-first-order reaction model, revealed that the rate of the initial step producing the intermediates is highly temperature-dependent with the measured kinetic energy barrier of ∼188 kJ mol⁻¹. With additional experimental evidence, we conclude that the intermediates are oligomeric oxohydroxo U(iv) species occurring from the condensation of U(iv) ions and simultaneously participating in the nucleation and growth process of UO₂(cr)-NPs.

The primary hydrolysis equilibrium of U⁴⁺ and the kinetics of U(iv)-nanoparticle formation were investigated by using spectrophotometric reaction modeling analysis and the spectral data collected in the UV and visible regions.