Method for dissolving solids formed in a nuclear installation

Abstract

Method of dissolving the solids formed in the apparatus and pipework of a nuclear plant, in which said solids are brought into contact with an aqueous dissolving solution chosen from aqueous solutions of carbonate ions having a concentration of greater than or equal to 0.3M, aqueous solutions of bicarbonate ions, and solutions of a mixture of nitric acid and of a polycarboxylic acid chosen from oxalic acid and triacids.

1 . Method of dissolving the solids formed in the apparatus and pipework of a nuclear plant, in which said solids are brought into contact with an aqueous dissolving solution chosen from aqueous solutions of carbonate ions having a concentration of greater than or equal to 0.3M, aqueous solutions of bicarbonate ions, and solutions of a mixture of nitric acid and of a polycarboxylic acid chosen from oxalic acid and triacids.  
     
     
         2 . Method according to  claim 1 , in which the contacting is carried out at a temperature of 20° C. to 80° C. for a time of 1 to 24 hours.  
     
     
         3 . Method according to  claim 1 , in which the aqueous dissolving solution is a carbonate ion solution.  
     
     
         4 . Method according to  claim 3 , in which the carbonate ion concentration of the aqueous dissolving solution is from 0.3M to the solubility limit in water of the carbonate salt from which the ion derives.  
     
     
         5 . Method according to either of claims  3  and  4 , in which the carbonate ions derive from a salt chosen from carbonates of alkali metals such as sodium and potassium, carbonates of alkaline-earth metals and ammonium carbonates.  
     
     
         6 . Method according to any one of  claims 3  to  5 , in which, after the contacting step, an acid solution, preferably a nitric acid solution, is added to the aqueous dissolving solution.  
     
     
         7 . Method according to any one of  claims 3  to  6 , in which the volume of dissolving solution is from 3 ml to 100 ml per g of solids.  
     
     
         8 . Method according to  claim 1 , in which the aqueous dissolving solution is a bicarbonate ion solution with a concentration of 0 to 2M.  
     
     
         9 . Method according to  claim 1 , in which the aqueous dissolving solution is an aqueous solution comprising a mixture of nitric acid and of a polycarboxylic acid chosen from oxalic acid and triacids.  
     
     
         10 . Method according to  claim 9 , in which the nitric acid concentration is from 0.05 to 1M and the polycarboxylic acid concentration is from 0.3M to 1M.  
     
     
         11 . Method according to either of claims  9  and  10 , in which the polycarboxylic acid is citric acid.  
     
     
         12 . Method according to any one of  claims 9  to  11 , in which, after the contacting step, the acids of the dissolving solution are destroyed by oxidation.  
     
     
         13 . Method according to any one of  claims 1  to  12 , in which the compound or compounds involved in the composition of the solids to be dissolved is/are chosen from: 
 zirconium molybdate and mixed zirconium plutonium molybdate;  
 zirconium phosphates and associated gels;  
 cesium phosphomolybdate;  
 plutonium phosphate;  
 molybdenum, zirconium and plutonium oxides;  
 iron phosphate; and  
 barium sulphate.