Carbonation Process Efficiency: Effect of Cutting Procedures on Sodium-filled Containers

In the context of the decommissioning of the three French sodium-fast reactors, France has chosen a common dismantling strategy in which the design of the processes is focused on eliminating the chemical risks associated with the high reactivity of sodium with air and water.These include the carbonation process which converts sodium into chemically inert compounds such as sodium carbonate and hydrogencarbonate.This is a gentle, controlled and slow process making it very attractive.The gaseous reagents are water and carbon dioxide diluted in nitrogen gas as carrier gas: the water vapour first reacts with sodium to form sodium hydroxide that is instantaneously consumed by carbon dioxide to produce sodium carbonate, in chemical equilibrium with sodium hydrogencarbonate.However, the reactional surface available and the geometric constraints of the steel containers in which sodium is confined can strongly influence the carbonation efficiency.The aim of this work is to understand the influence of the steel container geometries containing sodium (e.g.rectangular tubes or squares having different cutting directions).It is shown that the efficiency of the carbonation process is significantly enhanced when cutting direction offer a higher reactional surface despite structures geometric constraints.X-ray diffraction reveals that the carbonation process lead to the formation of sodium hydrogencarbonate phase which can be explained by a higher carbon dioxide concentration used (20%vol).