Method of dissolving the solids formed in a nuclear plant

1. A 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 of a mixture of nitric acid and of a polycarboxylic acid chosen from oxalic acid and triacids, wherein the nitric acid concentration is from 0.05 to 1M and the polycarboxylic acid concentration is from 0.3M to 1M, wherein said solids are in the form of layers of scale on the walls within the inner surfaces of the apparatus and/or pipework or are in the form of solid deposits accumulated at the bottom of the apparatus, and wherein the solids are dissolved in situ while attached to the walls of the apparatus and the pipework, and wherein said solids are formed from side reactions and not as a result of a normal process.

2. The 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. The method according to claim 1 , in which the polycarboxylic acid is citric acid.

4. The method according to claim 1 , in which, after the contacting step, the acids of the dissolving solution are destroyed by oxidation.

5. The method according to claim 1 , 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.

6. The method according to claim 1 , wherein the nuclear plant is a nuclear fuel reprocessing plant.