Performance of BDD Anode for Dechlorination of Nitric Acid and Regeneration of Silver (II) in a Tubular Reactor for the Treatment of Solid Wastes Containing Plutonium

Abstract

One of the problems frequently encountered in the processing of nuclear fuels is the recovery of plutonium present in solid wastes. The difficulty is to make soluble the plutonium present as the refractory oxide PuO₂. The dissolution of this oxide in nitric acid solutions is easily performed by means of silver(II) a strong oxidizing agent which is usually electrochemically generated on a platinum anode. However, certain solid residues capable of being treated to separate actinides contain important quantities of chloride ions that require an additional electrochemical step to be removed as gaseous chlorine from nitric acid before introducing Ag(I) for Ag(II) electrogeneration. Researches are developed to find electrocatalytic materials being able to replace platinum in view to limit capital costs. In the present work a set-up including a two compartment tubular reactor with recirculation of electrolytes was tested with anodes made of boron doped diamond coated niobium (Nb/BDD) and platinum coated titanium (Ti/Pt) grids for the removal of chloride (up to 0.1 M) and for silver(II) regeneration. The study showed that Nb/BDD anodes eliminate chloride contained in a solution of 6M HNO₃ in gaseous chlorine as well as anodes of Ti/Pt, without producing the unwanted oxoanions of chlorine. Furthermore, the regeneration rate of silver(II) on BDD anode is approximately equal to that obtained on platinum coated titanium anode for the same hydrodynamic conditions in the tubular reactor. Accordingly, dechlorination as well as silver(II) regeneration can be performed in the same electrochemical cell with a Nb/BDD anode. Besides, the service life of Nb/BDD anodes estimated by accelerated life tests conducted in 6M HNO₃ can be considered as very satisfactory compared to that observed with Ti/Pt anodes.