Denitration of concentrates from retreatment of medium level activity waste
In order to reduce the wastes released from the Marcoule reprocessing plant, the treatment of liquid waste of low and medium level activity by chemical precipitation has been replaced by evaporation. Due to the high nitrate content of liquid waste, encapsulation in bitumen of the concentrate leads to considerable volumes of waste to be stored in geological formations. For safety reasons and so as to reduce the volume of waste, the elimination of the nitrates is essential. Preliminary experiments led to the choice of calcination in a fluidised bed rather than chemical denitration, electrodialysis or biological denitration. Tests on a low temperature mock-up determined the choice of an injection system that operates with liquid under pressure with the nozzle situated inside the fluidised layer. To avoid the vaporisation of the liquid within, the injection piping also requires a cooling system using air, with a double casing. Differential themogravimetric and heat analyses have led to the following conclusions: (i) at temperatures below 500 C, the nitric acid, then the aluminium nitrate, decompose and produce alumina; (ii) between approximately 570 C and 630 C, the sodium nitrate in turn decomposes and reacts with the alumina to produce a sodium aluminate; (iii) finally, these tests established a reaction kinetics law of sodium nitrate decomposition in the temperature range of 500 C to 1000 C.
Bibliographic Reference: EUR 14587 FR (1993) 165 pp., FS, ECU 18.50
ISBN: ISBN 92-826-6076-1
Record Number: 199311060 / Last updated on: 1994-11-29
Original language: fr
Available languages: fr