Studies on the Thoria Fuel Recycling Loop Using Triflic Acid: Effects of Powder Characteristics, Solution Acidity, and Radium Behavior
Abstract
A convenient recycling loop is one of the key factors that will help to implement the thorium-based nuclear fuel cycle in the future. Herein, a study is presented concerning the recycling loop of thoria production scrap using dissolution with trifluoromethanesulfonic (triflic) acid and recovery by precipitation with oxalic acid.
The kinetics of thoria powders and pellet dissolution was assessed and compared with the THOREX process. The effect of the triflic acid concentration on the recovery yield of thorium during oxalate precipitation was examined, as well as the behavior of radium during this reaction.
Finally, the effect of the triflic acid concentration on the recovered thoria morphology was investigated. The triflic acid has minimal effect on the recovery yield during oxalate precipitation even in the case of high acid concentrations.
In general, the solubility of radium(II) oxalate is higher than for thorium(IV) and has a maximum at a triflic acid solution of 4 M. An interesting observation was that a stable dihydrate of thorium(IV) oxalate is formed in solution of high triflic acid concentration.
It might be explained by the hygroscopic medium during precipitation of the oxalate. All above mentioned observations confirm the benefits of usage of the triflic acid-based closed recycling loop for thorium dioxide-based nuclear fuel.