Coulometric determination of U and Pu from HNO3 solutions of mixed fuel

A method is developed for precise determination of U and Pu in the presence of each other by controlled potential coulometry of a single sample. The determination is carried out in supporting electrolyte by completing an electrochemical cycle including successive reduction of U and Pu to U(IV) and Pu(III), oxidation of all U and Pu to U(VI) and Pu(IV), and then separate reduction of Pu(IV) to Pu(III) and U(VI) to U(IV). The accuracy of the coulometric determination of U and Pu is increased by stabilizing the background current of the Pt electrode through addition to the atmosphere of the electrochemical cell of measured amounts of H2. The uncertainty in the U and Pu determination for ∼15 and 10 mg, respectively, in the sample reaches 0.02% for U and 0.03% for Pu