The method of preparation of highly active nitrate solution to curing

 

(57) Abstract:

The invention relates to technological processes of processing of radioactive solutions generated during the reprocessing of irradiated nuclear fuel reprocessing plants. The inventive method comprises the evaporation of the solution, the distillation of nitric acid, obtaining VAT residue and fluxing. Additionally, the solution injected sodium nitrate or sodium nitrate and sodium hydroxide, or sodium nitrate and phosphoric acid, or sodium nitrate, sodium hydroxide and phosphoric acid, it is also possible introduction into the solution of the condensate of the heating steam in the amount of 1 - 5 volumes one stripped off solution. Effect: increase in the rate of distillation of nitric acid in the process of evaporation and concentration of salts as residue directed to curing, while maintaining its homogeneity. 5 C.p. f-crystals, 1 table.

The invention relates to technological processes of processing of radioactive solutions generated in the nuclear industry, in particular to methods of preparation of high-level and intermediate-level solutions to curing at radiochemical plants for the reprocessing of irradiated nuclear fuel.

The disadvantages of the methods [1, 2, 3] are high corrosion of structural materials in the process of calcination of highly active salts, the formation of large volumes of gas that has been contaminated by decomposition products of nitric acid and an organic reducing agent.

The closest in technical essence and the achieved effect is a widely known method [4] preparation of highly active nitrate solutions, which is that previously accumulated solutions with concentration of nitric acid of 1.5 to 3.5 mol/l evaporated with multiplicity 30-120 in evaporation apparatus with an external heating chamber.

During evaporation the solution contains nitric acid Argonauts with a steam phase, and nitrate salts of fission products and corrosion concentrate as residue and removed from the evaporator.

The method allows to obtain the condensate of the vapor phase with a content of nitric acid in the range of 0.8 to 1.5 mol/l, and as residue 5-6,5 mol/L.

Homage and then vitrification.

The disadvantages of this method are the high content of nitric acid as residue and as a result, low concentration of salts entering the curing, a large ratio of evaporation, leading to increased consumption of heating steam, low degree distillation of nitric acid from parivesh solutions.

An object of the invention is to increase the degree of distillation of nitric acid in the process of evaporation of highly active nitrate solution and an increase in the concentration of salts in the VAT residue directed to the curing method of vitrification, while maintaining its homogeneity.

This object is achieved in that in the highly nitric acid solution injected sodium nitrate, or sodium nitrate and sodium hydroxide, or sodium nitrate and phosphoric acid, or sodium nitrate, sodium hydroxide and phosphoric acid. As solutions containing sodium nitrate or sodium nitrate and sodium hydroxide introduced into high-level solutions can be used for liquid radioactive waste, such as distillation residues from the evaporation of intermediate level liquid waste and/or concentrates from the storage of liquid radioactive waste. Processing of high-level radioactive solutions casement carrying out this process.

Prepared in this way high-level nitrate solutions warialda under reduced pressure and a temperature of 90-100oC. Evaporation under reduced pressure of the prepared solutions due to the need to reduce the corrosive effect of solvents on the structural materials of the evaporator. After evaporation in CBM solution is injected condensate of the heating steam in an amount of from 1 to 5 volumes of solution of the cubic. The number of volumes of condensate is determined by the concentration of nitric acid in the vapor phase in the process of distillation.

Example 1 (prototype). Processed high-level nitrate solution of the following composition: NGO3- 145,0 g/l; TBP - 0.2 g/l, paraffin - 0.2 g/l; U-1.5 g/l; Ri - 0.05 g/l; volume activity is 0.55 TBq/l (15 CI/l); total beta activity 2.1011Bq/l (5,7 CI/l); the amount of nitrate salts of fission products and corrosion of less than 0.2 wt.% in terms of dry residue.

The solution was evaporated in a continuous mode at a constant level of the cubic solution of 100 cm3. Vapor phase was condensed and collected in the receiving tank. The pressure in the apparatus was maintained in the range 0,4-0,55 MPa, and the temperature of the solution was equal to 90-100is the solution of the cubic content of nitric acid. The rate of evaporation of the solution amounted in experiments 3-10.

Examples 2-9 illustrate the inventive method.

Example 2. Processed high-level nitric acid solution of the composition shown in example 1 and VAT residue from evaporation of intermediate level liquid waste having the composition: NN3- 500.0 g/l; SGAs42-- 4.3 g/l; F' - 1.4 g/l; S042-- 0.7 g/l; U - 0.5 g/l; Pu - 0.015 g/l; CL' - 1.5 g/l; F - 0.25 g/l; Al - 0.35 g/l; Mn - 0.12 g/l; IG - 0.1 g/l; volume activity 111 GBq/l (3,0 CI/l).

The experiments were conducted as follows. Mixed 390 m3high-level nitrate solution with 80 m3VAT residue. Content in the mixture of solutions of NaNO3and HNO3respectively of 83.3 g/l, 127,0 g/l Evaporation prepared mixture of solutions was carried out similarly to example 1.

Example 3. The method of preparation of highly active nitrate solution is carried out analogously to example 2 with the difference that the amount of highly radioactive nitrate solution in the experiment was equal to 570 cm3and intermediate level VAT residue 30 cm3. The concentration of major components in the mixture are respectively equal to: NN3- 25 g/l; NGO3- 142,0 g/l Evaporation of the mixture of solutions similar to Primo example 2 with the difference, to a mixture of highly active nitrate solution and VAT residue add phosphoric acid based on its content in the mixture of 1 mol/L. Prepared mixture composition: NN3- 25 g/l; NGO3- 117,2 g/l; N3RHO4- 98 g/l; volume activity - 0,54 TBq/l (14,5 CI/l) was evaporated as in example 1.

Example 5. The method of preparation of highly active nitrate solutions as in example 2 with the difference that a mixture of highly active nitrate solutions and VAT residue add phosphoric acid based on its content in the mixture of 0.1 mol/l Prepared mixture of ingredients: NaNO3- 25 g/l; HNO3- 156,0 g/l; N3RHO4and 9.8 g/l; volume activity - 0,54 TBq/l (14,5 CI/l) was evaporated as in example 1.

Example 6. The method of preparation of highly active nitrate solutions carried out analogously to example 1 with the difference that high-level solutions add VAT residue from evaporation of intermediate level waste containing sodium nitrate, concentrate storage, containing sodium hydroxide, and phosphoric acid from the calculation of its content in a mixture of 0.2 mol/l Prepared mixture composition in terms of NGO3- 150,0 g/l; NaNO3- 50 g/l; NaOH - 100 g/l; N3RHO4- 19,6 gr 7. Processed high-level nitric acid solution of the composition shown in example 1, and the concentrate storage of liquid radioactive waste composition: NaOH - 201,0 g/l; NN3120 g/l; CL - 0.35 g/l; F - 0.1 g/l; SO42-- 1.2 g/l; Fe - 0.25 g/l; Cr - 4.0 g/l; Mg - 0.1 g/l; Cs137- 0.03 g/l; Cs134- 0.02 g/l; CE144- 0.04 mg/l; volume activity 1,31011Bq/l (3.5 Ku/l). The experiments were conducted as follows. Mixed 976 cm3high-level nitrate solution and 24 cm3liquid concentrate from the storage of liquid radioactive waste. After mixing solutions of contents NGO3in the mix was equal 142,0 g/l, a NaNO3- 13 g/l; volume activity - 0,54 TBq/l (14,5 CI/l). The prepared mixture was evaporated as in example 1.

Example 8. The method of preparation of highly active nitrate solutions analogously to example 7 with the difference that a mixture of highly active nitrate solution and the liquid concentrate from the storage of liquid radioactive waste is added to the phosphoric acid based on its content in the mixture of 0.1 mol/l Prepared mixture was evaporated as in example 1.

Example 9. The method of preparation of highly active nitrate solutions as in example 2, characterized in that the number from 3 to 5 volumes one stripped off solution.

The results obtained in examples 1 to 9 shown in the table.

The proposed method allows to obtain the following advantages in comparison with prototype: to increase the degree of distillation of nitric acid from parivesh solutions with the same ratio of evaporation (3-7 times); to reduce the concentration of nitric acid as residue 1 to 2 mol/l; to increase the concentration of salts in the VAT residue to 250-350 g/l while maintaining its homogeneity; to reduce the rate of evaporation and the heating steam consumption; to dispose of distillation residues from the evaporation of intermediate level liquid waste and liquid concentrates from the storage of liquid radioactive waste containing radionuclides.

Sources of information

1. G. Kesler. Of nuclear energy. M, Energoatomizdat, 1986, S. 185-187.

2. The application of Germany (FRG), OS-3243840, CL G 21 F 9/06, 02 F 1/58, 1984

3. The application of Germany (FRG), OS-3243841, CL G 21 F 9/06, 02 F 1/62, 1984

4. B. N. Swedes, C. N. Serov and other Nuclear technology. M, Atomizdat, 1979, S. 239-240.

1. The method of preparation of highly active nitrate solution to curing, including evaporation, distillation of nitric acid, obtaining VAT residue, fluxing, characterized in that the high and phosphoric acid, or sodium nitrate, sodium hydroxide and phosphoric acid.

2. The method according to p. 1, characterized in that the sodium nitrate is injected in the amount of 10-100 g/l

3. The method according to any of paragraphs. 1 and 2, characterized in that sodium hydroxide is injected in the amount of 10-50 g/l

4. The method according to any of paragraphs. 1-3, characterized in that the phosphoric acid is administered in an amount of 0.01-1.0 mol/L.

5. The method according to any of paragraphs. 1-4, characterized in that the quality of solutions containing sodium nitrate and/or sodium hydroxide, using VAT residue from evaporation of intermediate level liquid waste and/or concentrates from the storage of liquid radioactive waste,

6. The method according to any of paragraphs. 1-5, characterized in that one stripped off solution is injected condensate of the heating steam in the amount of 1-5 volumes one stripped off solution.

 

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