Trace Metal Characterization of the U-AI Matrix by Atomic Spectroscopy

Uranium-aluminum alloys with a significant enrichment of uranium with ²³³U or ²³⁵U serve as nuclear fuels in research reactors. The quality assurance of this fuel requires, among other things, precise knowledge that all trace metal constituents that affect neutron economy, fuel integrity, and fuel fabrication process parameters are well within the specification limits. Trace metal characterization of ²³³U-Al alloy has been carried out by atomic spectrometry. The trace metal constituents of interest are grouped into common metals (silver, boron, calcium, cadmium, cobalt, chromium, copper, iron, magnesium, manganese, molybdenum, sodium, nickel, lead, silicon, tin, titanium, vanadium, tungsten, and zinc) and lanthanides (cerium, dysprosium, europium, gadolinium, holmium, lutetium, samarium, and terbium). The elements yttrium and zirconium are grouped with the latter in view of the chemical separation procedure used. The alloy samples are dissolved in 6 M HCl and evaporated to dryness with nitric acid, and the residue is ignited to oxide. The common metals other than silver are determined in the oxide samples using carrier excitation  of the analyte spectra obtained using a computer-controlled multichannel direct reading spectrometer. Electrothermal atomization atomic absorption spectrometry is used for determining silver, using the nitric acid solution of the alloy. The rare earth elements yttrium and zirconium are determined after separation from the U-Al matrix, using a sequence of chemical procedures. In the first stage, uranium is separated by solvent extraction using a TnOA/xylene/HCl system and in the second stage aluminum is separated as sodium-aluminate. The trace elements are determined by a dc arc emission spectrographic method after chemical separation. Of these, dysprosium, europium, gadolinium, and samarium are determined by inductively coupled plasma-atomic emission spectrometry also. These methods are found to be quite adequate for the requirements of U-Al alloy fuel samples. Typical detection limits of these analytes varied in the 0.01-to 1.25-µg range. The precision varied in the 10 to 35% range. The waste generated in these processes has been treated for quantitative recovery of ²³³U.