The chemistry of acetohydroxamic acid related to nuclear fuel reprocessing

Graduation date: 2011Used Nuclear Fuel (UNF) contains transuranic (TRU) elements and numerous fission products as a result of the uranium fission process and neutron activation that occur in commercial light water power reactors. Recent environmental and nuclear proliferation concerns have spawned the development of advanced reprocessing techniques to close the nuclear fuel cycle. By separating specific elemental groups, sustainable fuel sources\ud can be created while minimizing the need for long-term geologic storage of high-level radioactive waste and reducing nuclear proliferation risk by avoiding the isolation of Pu. To facilitate in the separation of specific elements, acetohydroxamic acid (AHA) is proposed to effectively partition Np and Pu from U. AHA forms hydrophilic acetohydroxamate complexes with Pu⁴⁺ and Np⁴⁺ and reduces NpO₂²⁺ to its inextractable NpO₂⁺ oxidation state. This study contributes fundamental knowledge of AHA chemistry\ud in relation to reprocessing techniques including its reactivity towards several elements present in UNF.\ud \ud The thermodynamic, kinetic, and extraction features of the chemistry of AHA with various metals were investigated. The complexation of Zr⁴⁺, UO₂²⁺, and Fe³⁺ with AHA was analyzed by UV-Vis spectroscopy. It was determined that the conditional stability constants of Zr·AHA complexes are four orders of magnitude greater than for uranyl·AHA complexes, indicating that AHA is a promising complexant to separate tetravalent metals from hexavalent uranium. The reduction kinetics of NpO₂²⁺ to NpO₂⁺\ud by AHA was monitored using near infrared spectroscopy with stopped-flow and standard 1cm cuvette apparatus. Results showed that AHA can be used to rapidly reduce NpO₂²⁺ to NpO₂⁺. Lastly, the effect of AHA on the distribution of selected metals and between nitric acid and 1.1 mol·L⁻¹ tri-n-butyl phosphate in n-dodecane was studied. AHA was found to significantly decrease the extraction of tetravalent metals without affecting the\ud extraction of uranium, which remained in the organic phase