Determination of acidity in nitric acid solutions containing plutonium and/or uranium at high concentration by electric conductivity measurement

In Plutonium Conversion Development Facility (PCDF), after plutonium nitrate solution (∼200 g/L) and uranyl nitrate solution (∼400 g/L) are mixed with an appropriate ratio, uranium-plutonium mixed oxide (MOX) powder is made by doing calcinations-reduction the denitrated powder obtained by microwave-heating method. When acidity in nitric acid solution containing plutonium (Pu) decreases remarkably, it is known the colloid and precipitate are generated by the hydrolysis of Pu. Therefore, acidity in nitric acid solution containing Pu handled in PCDF is an important parameter, from the viewpoint to prevent the hydrolysis of Pu in the process. Using the correlation between electric conductivity and acidity in solution, we have investigated an analytical method that is able to determine acidity in the nitric acid solution by measuring electric conductivity of sample diluted with distilled water, and correcting the electric conductivity for Pu and uranium(U) using multivariate analysis method. We obtained good results as follows, (1) Acidity in the nitric acid solutions containing Pu and U obtained by this method was good agreement, within 10%, compared with the acidity measured by potentiometric titration method. (2) For plutonium nitrate solution and uranium-plutonium mixed nitrate solution, the repeatability and reproducibility for the measurement of electric conductivity at 25.0degC were less than 0.52%, and 1.53% respectively. (3) Impurities such as americium and iron in the solutions did not influence to the measurement of electric conductivity, if total amounts of these impurities were less than 1% compared with those of Pu and U. From the results described above, electric conductivity measuring method has been applying to analysis of acidity in the nitric acid solutions containing Pu and U at high concentration handled in PCDF. Furthermore, this method can be expected for the application to analysis of acidity in nitric acid solutions containing Pu and U for reprocessing process. (author)