Determination of tungsten in composite nuclear fuels by differential-pulse polarography

Nuclear reactor fuels must comply with stringent composition requirements in order to guarantee safe operation and neutron economy.In this work, differential-pulse polarography was investigated as a means for the determination of tungsten impurities in composite nuclear fuels. The concentration range studied was 0.001–0.005% of tungsten. The proposed method is based on the dissolution of the sample in concentrated orthophosphoric acid under an inert atmosphere. No matrix separation is required and a suitable amount of sulphuric acid is added directly to the sample solution in order to obtain a 7.4 M H3PO4-4.5 M H2SO4 supporting electrolyte solution. After de-aeration of the solution, differential-pulse polarographic determination of tungsten(VI) was carried out at –0.250 V versus an Ag-AgCl reference electrode. The detection limit was found to be 1 µg ml–1 of tungsten(VI) with a relative standard deviation of about 5%.More than 25 elements were tested and only AsIII, MoVI, RuIII and SbV were found to interfere in the determination of tungsten(VI).