Inductively Coupled Plasma Mass Spectrometry (icp-ms) Measurement Of Trace Rare Earth Impurities In The Uranium Method

Rare earth elements (REES) have a strong ability to absorb neutrons. The presence of them beyond specified limits in the nuclear fuel of uranium might severely affect the neutron economy of 235U. For nuclear purpose, the purity of uranium needs to be up to a certain level, that is, the impurity content must be less than 10-6-10-5(0.01 -0.1 μg/g U). Though there are some records of analyzing REES in uranium, they can't fully meet the requirements of routine analysis, especially in terms of reliability, analysis speed, safety precaution, etc. So, it is necessary to found a quick, accurate and sensitive method to analyze trace REES in uranium.In this research, Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) was adopted as the means of determination and Desolvating- Microconcentric Nebulizer (D-MCN) as the introduction system. On one hand, this technique could simultaneously detect many elements with high scanning speed; on the other hand, it greatly reduced interferences and thus increased sensitivities by one order of magnitude. Meanwhile, the use of 103Rh as an inner standard not only compensated the matrix effect so greatly that the matrix(uranium) content as high as 50μ g/mL still did not affect the determination of REES, but also apparently improved the linearity of the working curves. Through the optimization of operational parameters and the selection of non-interference isotopes, the accuracy of determination was further increased. Also, a kind of pressurized & evacuated separation technique was utilized to separate trace REES in uranium. The inner diameter of the column was 4mm and the anion exchange resins were 200-400 meshes. The whole separation process was completed within 20 minutes. What is more, the reagent dosages for eluting REES by 6 mol/L HC1 and uranium by H2O could be less than 5mL respectively. By the application of the pressurized & evacuated separation technique, the purpose of high separation efficiency, high speed, less dosage consumption and less waste was fulfilled. The solution determination limits of this method was as low as 1 × 10-13g/mL andthat of solid sample was 1 × 10-12g/g.In order to guarantee the quality of the analysis work, the uncertainty of the analysis results was evaluated in internationally current ways. Also, all the parameters needed for the calculation was collected and calculated and the standard uncertainty, combined standard uncertainty, degrees of freedom and expanded uncertainty were evaluated.Lastly, to examine the present method, four REES (Snu Eu, Gd, Dy) in two U3O8 standard materials (GBW04207 and GBW04205) were analyzed respectively. When the level of confidence was 95%, the results tallied with the standard and reference values perfectly, which proved that the method is effective and reliable, and can be applied to analyze trace REES in uranium and its oxides well.