Use of automated controlled-potential coulometry system for plutonium product accountancy analysis at Tokai reprocessing plant

The controlled-potential coulometry has been adopted for plutonium product accountancy analysis at the Tokai reprocessing plant since 1985. The reliability of plutonium product analysis has been improved by introducing this method which is capable of better precision than the titration that was previously used. It has been found that the impurities such as neptunium, chromium and americium, which are thought to interfere with AgO-Fe(II)-Cr(VI) titration method, do not affect the controlled-potential coulometry. Iron, which is regarded as an impurity interfering with the coulometry, is corrected with simple measurement procedure using spectrophotometer. The fully automated coulometry system has been developed based on the experience of using manually operated system. The system consists of two symmetric parts. Each has one measurement position and one electrode washing position and is designed to load up to six cells. The system is calibrated with iron standard sample, because no significant difference between calibrations using metallic standard of plutonium and that of iron has been found. Precision of the automated system is within 0.1%