Patent Number: 
Section: claims

1. A radioactive carbon containment process, comprising a step of containing said radioactive carbon in a mixed carbonate of formula AB(CO3)(n+m)/2, the sintering temperature of which is below the decarbonation temperature of the mixed carbonate and the hardness of which is greater than or equal to 4 on the Mohs scale, in which A and B are different and chosen from the group consisting of alkali metals, alkaline-earth metals and rare earths, and in which n and m are positive integers such that the charge of AB(CO3)(n+m)/2 is neutral. 2. The radioactive carbon containment process as claimed in claim 1, in which A and B are different and chosen from the group consisting of Na, K, Ca, Ba, Mg and Sr. 3. The radioactive carbon containment process as claimed in claim 1, in which the mixed carbonate is BaCa(CO3)2. 4. The radioactive carbon containment process as claimed in claim 1, in which the mixed carbonate is sintered for the containment of the radioactive carbon. 5. The radioactive carbon containment process as claimed in claim 1, in which the radioactive carbon comes from a gaseous effluent of an irradiated nuclear fuel reprocessing plant. 6. A radio carbon containment process, comprising the following steps:a) mixing CO2 having a radioactive carbon to be contained, or a simple carbonate of an alkali, alkaline-earth or rare-earth metal having a radioactive carbon to be contained, with an aqueous solution of a mixture of ACln and BClm or with an aqueous solution of a mixture of A(OH)n and B(OH)m in order to obtain a precipitate of AB(CO3)(n+m)/2 where A and B are different and chosen from the group consisting of alkali metals, alkaline-earth metals, alkaline-earth metals and rare earths, and n and m are positive integers such that the charge of Aln, BClm, A(OH)n and B(OH)m is neutral;b) recovering the AB(CO3)2 precipitate obtained in step a) in powder form;c) optionally rinsing said powder; andd) pressing the powder and sintering it at a sintering temperature below the decarbonation temperature of the synthesized mixed carbonates in order to obtain sintered pellets of mixed carbonates of formula AB(CO3)(n+m)/2, the hardness of which is greater than or equal to 4 on the Mohs scale, and containing the radioactive carbon in the sintered pellets of mixed carbonates. 7. The process as claimed in claim 6, in which A and B are different and chosen from the group consisting of Na, K, Ca, Ba, Mg and Sr. 8. The process as claimed in claim 6, in which the mixed carbonate is BaCa(CO3)2. 9. The process as claimed in claim 6, in which the pressing is carried out at a pressure ranging from 10 to 20 MPa, and the sintering at said temperature for 1 to 3 hours. 10. The Process as claimed in claim 6, in which the pressing is carried out at a pressure of 14 to 16 MPa, and the sintering at a temperature of 550° C. to 600° C. for 1 hour 45 minutes to 2 hours 30 minutes. 11. The process as claimed in claim 6, in which the simple carbonate is obtained by trapping the radioactive carbon, in CO2 form, in accordance with a process chosen from the group consisting of a double alkali process, a direct hydroxide reaction process and a gas/solid process. 12. The process as claimed in claim 6, in which the CO2 having a radioactive carbon to be contained, or a simple carbonate of an alkali, alkaline-earth or rare-earth metal having a radioactive carbon to be contained, comes from an effluent of an irradiated nuclear fuel reprocessing plant.