The determination of plutonium in refractory materials by electrometric methods after dissolution by fusion with ammonium hydrogen sulphate

Abstract

A fusion with ammonium hydrogen sulphate at 400° C has been developed for the dissolution of refractory materials containing plutonium dioxide. On cooling, each melt is leached with sulphuric acid to produce a solution suitable for analysis for plutonium by electrometric methods. Plutonium concentrations (about 2 mg per ml) are determined either by a potentiometric titration based on the reduction of plutonium(VI) to plutonium(IV), or by a controlled-potential coulometric method, the Pu3+-Pu4+ couple being used. Both techniques are suitable for the accurate determination of plutonium with a precision of better than 0·20 per cent. (coefficient of variation) for about 5-mg amounts or less. The behaviour of many other elements in these methods has been studied in some detail.The fusion technique has been found to be suitable for the dissolution of several refractory materials, including samples of PuO2-UO2 fired at 1550° C, and also samples of PuO2-ThO2 produced by the ignition at 900° C of the carbides of these elements coated with pyrolytic graphite. The determination of the plutonium contents of these samples was then completed directly by the electrometric methods.