Processing of LEU targets for {sup 99}Mo production -- Dissolution of metal foil targets by alkaline hydrogen peroxide

Abstract

In FY 1995, the authors started studies on a new process for dissolution of low-enriched uranium (LEU) targets for {sup 99}Mo production. In this process, an LEU metal foil target is dissolved in a mixture of sodium hydroxide and hydrogen peroxide, then {sup 99}Mo is recovered from the dissolved solution. They focused on the dissolution kinetics to develop a mechanistic model for predicting the products and the rate of uranium dissolution under process conditions. They thoroughly studied the effects of hydrogen peroxide concentration, sodium hydroxide concentration, and temperature on the rate of uranium dissolution. It was found that uranium dissolution can be classified into a low-base (< 0.2M) and a high-base (> 0.2M) process. In the low-base process, both the equilibrium hydrogen peroxide and hydroxide concentrations affect the rate of uranium dissolution; in the high base process, uranium dissolution is a 0.25th order reaction with respect to the equilibrium hydrogen peroxide. The dissolution activation energy was experimentally determined to be 48.8 kJ/mol. Generally, the rate of uranium dissolution increases to a maximum as the hydroxide concentration is increased from 0.01 to about 1.5M, then it decreases as the hydroxide concentration is further increased. The alkalinity of the dissolution solution is an important factor that affects not only the dissolution rate, but also the amount of radioactive waste.