Determination of microamounts of neptunium by differential pulse polarography

Abstract

Neptunium is produced in significant amounts in the “light-water” reactors and must be controlled at different steps of fuel reprocessing. For this purpose, we have developed a method of differential pulse polarography. A tight cell containing 10 ml solution is set up in a Faraday cage. Adjustment to the tetravalent state, Np(IV), is carried out electrochemically on a mercury layer and the Np(IV) concentration is determined by differential pulse polarography, using a dropping mercury electrode. In 0.5M sulfuric acid medium, the redox potential of the reversible couple Np(IV)/Np(III) is-0.3V/SCE. Concentrations as low as 5·10−7M neptunium can be measured and detection at the 2·10−7 M level is still possible. (0.5μg in the polarographic cell). Precision is about 2% in the 10−5M and 10% in the 10−6M range. The method has been applied to aqueous and organic (TBP_dodecane) solutions. Neptunium can be determined without separation in the presence of plutonium or uranium at M/Np ratios of 103 and 5·104, respectively. In the presence of fission products a separation is needed.