SPECTROSCOPIC DETECTION OF HYDROGEN PEROXIDE GENERATED BY ALPHA RADIOLYSIS IN SOLUTION

摘要

During the long-term disposal of used nuclear fuel, the near-surface alpha dose remains significant long after beta and gamma doses decrease. Among the radiolysis products of water, hydrogen peroxide is a dominant oxidizing species, even under reducing or anaerobic conditions. In addition to oxidizing U(Ⅳ) to U(Ⅳ) in the fuel matrix, sufficient concentrations of hydrogen peroxide in solution may also stabilize uranyl peroxide phases such as studtite or metastudtite at the fuel surface. In order to predict the long-term behavior of nuclear materials, radiolysis models help bridge the gap between short-term bench-top experiments (e.g., 0-10 years) and long-term natural analogue studies (e.g., 10~6 years). Here, spectroscopic methods are used to measure the amount of hydrogen peroxide generated by the alpha radiolysis of water in the presence of dissolved Americium-241 for comparison with alpha radiolysis models. The colorless compound, titanyl sulfate (Ti(Ⅳ)OSO_4), complexes strongly with colorless H_2O_2 in solution, yielding absorption in the visible region (≈ 405 nm). Additionally, experiments here show that Ti(Ⅳ)OSO_4 peroxide complexes remain stable for months when solutions are refrigerated between measurements. Using a 1 cm path-length UV-Vis set-up, detection limits of mid 10~(-6) M H_2O_2 were achieved; coupling a longer path-length (5 m) cell to the UV- Vis detector allows for mid 10~(-7) M H_2O_2 detection limits. This range of values is of interest for comparison with equilibrium values predicted by alpha radiolysis models. In order to evaluate total hydrogen peroxide generation as a Junction of time, small aliquots of Am-241 nitrate solution (2.09 mM) are added to 0.5 M Ti(Ⅳ)OSO_4 solutions, sealed in a vial, and measured at different time points. For an equilibrium kinetics study, "time zero " is established for a series of samples and spectra are taken for each vial at specified time-points with indicator solution being added immediately prior to measurement. Factors such as temperature are evaluated for comparison with radiolytic models. This study is an example of alpha radiolysis product detection using a homogeneous (e.g., liquid / liquid rather than solid /liquid or ion-beam/liquid) approaches to dose generation.