Peroxide Formation, Destruction, and Precipitation in Uranyl Sulfate Solutions: Simple Addition and Radiolytically Induced Formation

Abstract

SHINE Medical Technologies plans to use fissioning of a low enriched uranium (LEU) solution as uranyl sulfate for molybdenum-99 production. One of the major concerns for SHINE is peroxide formation from radiolysis, which can lead to precipitation of uranyl peroxide. Bench-top experiments where peroxide was added directly to a uranyl sulfate solution were performed to determine the concentration where precipitation occurs as a function of temperature and concentration of ferrous or ferric ion to aid in peroxide destruction. Based on the experimental results and relevant literature, a thermodynamic/kinetic model for the precipitation of uranyl peroxide for a given set of conditions was developed and tested. The conditions that must be specified in the model are temperature, uranyl sulfate concentration, ferrous-or ferric-ion concentration, and the H 2 O 2 production rate. Additionally, experiments were performed using the Van de Graaff accelerator as a radiation source for radiolytically induced peroxide formation. Uranyl peroxide precipitated at 12°C when a uranyl sulfate solution was exposed to a radiation dose of 7900 Mrad in the pulse mode, but precipitation did not occur in the direct current (DC) mode at much higher powers. Because precipitation could not be achieved in the DC mode for this set of experiments, the effects of temperature and power on uranyl peroxide formation could not be determined. Future experiments will monitor current continuously, measure gas flow rates continuously, and use a uranyl sulfate solution that contains little to no iron impurity.

Fission Induced Radiolysis of Uranyl Sulfate Solutions

“… Precipitation is avoided if the production and decomposition of H2O2 and uranyl peroxide are equal while keeping the latter below its solubility limit. Past experiments [6] and modeling show that the relevant conditions that affect the production and precipitation of uranyl peroxide are temperature, uranyl sulfate concentration, ferrous iron concentration, and H2O2 production rate. The rate of H2O2 production is directly proportional to power deposition.…”

“… At a higher temperature, the decomposition rate of peroxides increases. If the solution should not be allowed to boil, a temperature of 80°C would provide maximum peroxide decomposition while staying below the precipitation threshold [6].  A decrease in solution pH can indicate the formation of uranyl peroxide in solution, due to formation of H3O + by complexation reaction between UO2 2+ and H2O2 (eq.…”

“…It should be noted that uranyl peroxide precipitate forms only in conditions where its concentration exceeds the solubility limit. Early experiments [6] and modeling of the 99 Mo process showed that the conditions that affect the production and precipitation of uranyl peroxide are temperature, uranyl sulfate concentration, ferrous iron concentration, and H2O2 production rate. In those experiments, uranyl sulfate solutions were titrated with H2O2 until the peroxide of uranium precipitated.…”

Low LET Irradiations of Uranyl Sulfate Solutions in the Absence and Presence of Fe⁺² and Fe⁺³ ions

“…nH2O). Through a series of reactions, hydrogen peroxide is generated in solution by the radiolysis of water, which can react with the uranyl ion to form uranyl peroxide, thus forming a precipitate [1][2][3][4][5]. Uranyl-peroxide precipitation must be avoided for safe production of Mo-99 during the proposed process.…”

Analysis of Radiolytically Generated Gases in Mini-AMORE Experiment

“…The rate of generation is dependent upon the power deposition into the solution with the main contribution coming from the fissioning of uranium. Hydrogen peroxide can react with the uranyl ion to form uranyl peroxide, thus forming a precipitate [1,2]. Uranyl-peroxide precipitation must be avoided for the safe production of Mo-99 during the proposed process.…”