Optimization of ADU Precipitation Process Parameters to Compensate for Detrimental Effect of EDTA

Abstract

Nuclear Fuel Complex at Hyderabad, India, is engaged in the manufacture of natural uranium fuel for use in all the Pressurized Heavy Water Reactors. The fuel is in the form of high-density Uranium di-oxide (UO₂) pellets clad in zircalloy tubes. The UO₂ powder is produced through the ammonium di-uranate (ADU) precipitation route.

The Precipitation process is the most critical operation in the UO₂ production process, since this is the first stage wherein the solid formation occurs and the powder morphology gets characterized. Ethylene di-amine tetra acetic acid (EDTA) is added (in ppm. quantities), to uranyl nitrate pure solution (UNPS), to chelate out rare earth elements as and when required during precipitation process.

Addition of EDTA was found to have a marked effect on the quality of the ADU precipitate produced, which in turn affected the sinterability/ metallurgical behaviour of the UO₂ powder. Studies were carried out to understand the EDTA effect and optimize the precipitation process parameters so as to ensure the sinterability of the UO₂ powder produced, with and without EDTA addition.

The observations and results of above studies are presented in this paper.