Management of metal chlorides in high temperature processes--application to the nuclear wastes treatment.

Thermal processes are now the benchmark for the destruction of some waste whose toxicity requires special attention and management. Over many years the Commissariat à l'Énergie Atomique (French atomic energy commission) has developed technologies to process radioactive waste containing many metals together with chlorine, and thus with a major risk of producing volatile chlorides with potentially catastrophic effects on plant facilities. To mitigate these difficulties in an incineration process for radioactive waste contaminated by plutonium (IRIS), the CEA has investigated the processes by which potentially hazardous compounds are produced in order to eliminate them or prevent their formation. The studies have led to propose a phosphate-based stabilization technique thanks to an addition of phosphorus in the waste. Through a reaction occurring in gas phase, the metals are stabilized under a phosphate form when the formation of volatiles chlorides is avoided. While this technique has substantially improved process maintenance and security, it has revealed other difficulties related to potentially large phosphate deposits capable to cause unacceptable pressure drops detrimental to the gas flow conditions. This article describes the results of recent studies seeking to prevent the formation of volatile chlorides and phosphate deposits liable to obstruct the system flow lines.