Method for reconditioning reusable extractant

FIELD: recovery of irradiated nuclear fuel.

SUBSTANCE: proposed method for reconditioning reusable extractant includes treatment of the latter with aqueous alkali solution. Extractant containing uranium in amount of minimum 5 g/l is treated with alkali solution whose concentration is over 10 mole/l followed by sediment separation.

EFFECT: reduced radionuclide content of reusable extractant including difficult-to-remove radioactive ruthenium.

5 cl, 2 tbl, 2 ex

 

The invention relates to methods of regeneration recycling of the extractant and can be used in the technology for reprocessing of irradiated nuclear fuel.

When the extraction processing of irradiated standard uranium blocks in the circulating extractant (here under the extractant is understood as the solvent, for example, tributyl phosphate, in a hydrocarbon diluent to accumulate the products of its degradation, which have the ability to retain radionuclides. Part radionuclides laundered at inter-cycle regeneration, but some, such as radiolucency accumulate due to the formation of complexes with the products of nitration and oxidation of the extractant. This form of ruthenium strongly retained in the organic phase in the regeneration operation. In aqueous solutions there are various forms nitrosobutane that can follow one another and having different extractibility. The metal complexes with the products of destruction and nitration of extractant are not destroyed either by acid or alkaline treatment of irradiated organic solutions, which leads to their accumulation in the recycled extractant. In the process of Stripping the ruthenium held nitrated organic phase, partially enters reextract that, ultimately, affects the quality of the recycled uranium. P is this increase cleaning recycling of the extractant from the ruthenium is one of the major problems at the radiochemical production.

The wide industrial application have found ways regeneration of the extractant by water soda-alkaline treatments of the extractant.

Known methods of regeneration recycling of the extractant, whereby the spent solvent before returning to extraction washed with 0.04 M solution of nitric acid and 0.1 M solution of soda; 0.5 M solution of soda, demineralized water and 0.1 M sodium hydroxide solution. (Processing of nuclear fuel. Edited Stoler, M.: Atomizdat, 1964, c.139, 257, 266).

Known methods of regeneration extractants by chemical processing of various solutions, including concentrated (2-10 mol/l) solution of alkali (Gfedorov. Radiation chemistry of extraction systems. M.: Energoatomizdat, 1986, pp.182-187) prototype.

A disadvantage of the known methods used in industry, is the low efficiency of the washing of the extractant from radionuclides, especially from radiolucent.

The objective of the invention is to increase the degree of purification of radionuclides, especially from radiolucent.

The set task is solved by the fact that in the regeneration process of recycling of the extractant, including the processing of the aqueous solution of alkali, the extractant with a uranium content of not less than 5 g/l is treated with alkali solution with a concentration of more than 10 mol/l, followed by the separation of the precipitate.

The treatment machine e is strigent with a uranium content of 10-20 g/L.

Treatment is carried out with a solution with a concentration of NaOH from of 13.75 to 15 mol/L.

The alkaline solution is added in an amount to provide a residual uranium content in the extractant after the precipitate ≤0.05 g/l

Processing of the extractant is carried out at a temperature of 60-70°C.

Because the technology of reprocessing of irradiated nuclear fuel is not difficult to get working extractant containing a certain amount of uranium (for example, when incomplete Stripping), it is advisable to make use of the cation, which is available in the technology, i.e. hexavalent uranium, and not to enter for deposition of a foreign element, from which then the extractant must be released.

Example 1. Spend 4 series of experiments with recycling the extractant (30% TBP in the hydrocarbon diluent). All experiments use the same portion of the extractant. In working extractant administered hexavalent uranium. In the experiments of the first series change the concentration of hexavalent uranium extractant coming on treatment with alkali, from 5 to 30 g/L. In the second series change the concentration of the alkali solution from 8.75 to 15 mol/l In experiments 3 series range residual uranium content in the circulating solvent from 0.01 to 10 g/l after the treatment with alkali extractant and separating the resulting precipitate. In experiments 4-series temperature deposition ur is on alkali change from 20 to 100° C. In all series of experiments to determine the content of ruthenium-106 in the circulating extractant before and after precipitation and separation of uranium and counting efficiencies from ruthenium-106.

The results of the experiments are shown in table 1.

Table 1
the number of seriesContents [U] in the extractant before treatment with alkali, g/lContents [U] in the extractant after precipitation and separation of uranium, g/lContents [NaOH] in the processing solution, mol/lt °The purification coefficient KPTSRu-106
123456
150,01of 13.75604,0
100,01of 13.75604,5
200,01of 13.75604,5
300,01of 13.75604,5
2200,018,75603,7
200,0110,0060 4,0
200,0112,50604,2
200,01of 13.75604,5
200,0115,00604,5
3200,01of 13.75604.5
200,05of 13.75604,5
200,10of 13.75603,0
200,50of 13.75603,2
201,00of 13.75602,9
205,00of 13.75602,2
2010,00of 13.75601,3
4200,01of 13.75201,3
200,01of 13.75302,5
200,013,75 504,2
200,01of 13.75604,5
200,01of 13.75704,5
200,01of 13.75804,5
200,01of 13.7590the 4.7
200,01of 13.75100a 4.9

From the results of table 1 shows that the optimal conditions for purification of circulating extractant from radiolucent-106 (purification factor of 4.5) are the following: the content of uranium in the extractant coming to an alkaline treatment, 10-20 g/l (30 g/l impractical), the residual uranium content in the circulating extractant ≤0.05 g/l, the concentration of alkali in the processing solution of 13.75 from up to 15 mol/l, temperature of processing at least 60°C. the purification Coefficient of the extractant from radiolucent-106 increases with increasing temperature, but in the technology of processing of uranium blocks temperature limit 80°in accordance with requirements of fire-fighting and requirements for chemical resistance extraction solution, therefore, the best track is tons to read the temperature of 60-70° C.

Example 2. Conduct experiments with the selected optimal mode to determine the level of treatment, recycling of the extractant from all radionuclides present in it (zirconium-95, niobium-95, ruthenium-103, 106). In experiments were used recycled extractant 30% TBP in n-paraffin, the last pre-processing in the first extraction cycle soda solution.

Table 2
RadionuclideRadiochemical composition of the extractant, Bq/lKPTS
Before cleaningAfter cleaning
Zr-951,018·1061,668·10560,00
Nb-951,363·1065,442·10425,2
Ru-1032,291·1073,204·1067,15
Ru-1061,409·1083,111·1074,53

From the results of table 2 shows that the proposed method allows you to clear the current extractant not only from radionuclides ruthenium, but from zirconium and niobium.

After alkaline treatment of circulating extractant is separated from the pulp, clicks the functioning of the acid solution to neutralize the trapped alkali and return in the process.

The precipitate uranium containing radiolucency, dissolved in nitric acid, and the resulting solution was sent to the head of process for extraction. Radiolucency in return the uranium solution is mainly in extragonadal form, so when the extraction of radiolucency displayed in the raffinate and then goes to landfill. Thus provide the output radiolucency of technology.

The proposed method can significantly reduce the radionuclide content in the circulating extractant, including stubborn radiolucent.

1. The regeneration method of working extractant comprising processing the aqueous alkali solution, wherein the extractant with a uranium content of not less than 5 g/l, treated with alkali solution with a concentration of more than 10 mol/l, followed by the separation of the precipitate.

2. The method according to claim 1, characterized in that the processing is subjected to the extractant with a uranium content of 10-20 g/L.

3. The method according to claim 1, wherein the treatment is carried out with a solution with a concentration of NaOH from of 13.75 to 15 mol/L.

4. The method according to claim 1 or 3, characterized in that the alkaline solution is poured in an amount to provide a residual uranium content in the extractant after the precipitate ≤0.05 g/l

5. The method according to claim 1, characterized in that the treatment process is carried out at a temperature of 60-70°C.



 

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