RU1804652C - Reconditioning method for radiated fuel elements - Google Patents

Abstract

SUMMARY OF THE INVENTION: Due to the withdrawal of the strongly acidic and slightly acidic wash solutions for an additional extraction operation, stable zirconium is discharged into a low active stream. The nitric acid content in the extract zone is more than 7.4 mol / l. 1 ill., 4 tab.

Description

The invention relates to the field of regeneration of irradiated nuclear fuel (SNF), in particular, to extraction processes for processing irradiated fuel elements of nuclear power plants.

;: The purpose of the invention is the localization of tritium in a significantly smaller (1.6-2.0 times) volume of highly active raffinate, as well as the simplification of its further processing by removing macro amounts of stable zirconium from it. The absence of zirconium in highly active raffinates will make it possible to increase their evaporation by 5–10 times (compared with the existing evaporation process) without the risk of precipitation.

This goal is achieved in that the extraction of actinides from solutions of irradiated fuel elements of VVER is carried out at a content of nitric acid in the extraction

a zone of more than 4.7 mol / L, and washings without combining with highly active raffins are removed for an additional extraction operation. Moreover, all tritium is localized in a limited volume equal to the volume of the initial solution, and more than 90% of stable zirconium is discharged into a low-active solution, allowing the highly active raffinate to be evaporated more than 100 times without the risk of precipitation.

The specified content of nitric acid in the extraction zone of more than 4.7 mol / l, together with the withdrawal of strongly acid and weakly acid wash solutions into a separate stream, provides, according to the method, the withdrawal of zirconium by more than 90% into a low-active solution, reducing the volume of highly active tritium-containing

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raffinate 1.6-2.0 times and thereby achieve the object of the invention.

A method for processing irradiated WWER fuel rods is explained using the flow chart shown in the drawing.

Extraction of actinides and washing of the extract is carried out in the extraction apparatus 1, which consists of sixteen extraction stages. The extraction operation is carried out in ten steps. Extractant 2 (30% TBP solution in a hydrocarbon breaker) is supplied to the first stage, the initial aqueous solution of 3 irradiated WWER fuel rods to the tenth. A strongly acidic wash solution 4 enters the thirteenth step, and a weakly acid solution 5 goes to the sixteenth. A highly active raffinate 6 comes out of the first stage of the apparatus 1, a strongly and weakly acid wash solutions 7, 8 are released from the eleventh and fourteenth, and washed actinide extract is from the sixteenth. The washing solutions 7, 8 are directed to an additional extraction operation carried out in an extraction apparatus 10 consisting of nine extraction stages. The combined washing solutions 11 enter the seventh stage of the extraction apparatus 10. Extractant 12 is supplied to the first stage of the same apparatus, concentrated nitric acid 13 to the sixth, and weakly acidic washing solution 14 to the ninth. Low-level raffinate 15 leaves the first stage of the apparatus 10, and of the ninth, extract 16, which combines with extract 9 exiting the apparatus

1..

The process is carried out as follows. The ratio of the extractant: initial solution streams is maintained at a level of more than 2.5, which ensures that the nitric acid content in the extraction zone of apparatus 1 is more than 4.7 mol / l. With this acidity, zirconium together with actinides is effectively extracted into the organic phase. 3-7% of zirconium from its content in the initial solution 3 enters the highly active raffinate 6.

When the extract is washed with strongly and weakly acid solutions 7 and 8, zirconium is washed out of the organic phase and flows to an additional apparatus 10 with a stream 11. Where the part of actinides that were supplied with the washing solutions 7 and 8 is extracted and washed, the acid regime is maintained in apparatus 10 (3 mol / L nitric acid in the extraction zone), allows all zirconium to be dumped into the low-activity raffinate 15.

EXAMPLE 1 An initial solution simulating the composition of a solution after dissolving WWER fuel rods was fed to the tenth stage of extraction apparatus 1. The extracts were washed in 3 steps of strongly acidic and 3 steps of weakly acidic washing with nitric acid solutions. The washing solutions after washing the extract 7, 8 were sent to an additional extraction apparatus 10. In parallel, an experiment was carried out according to the prototype technological scheme. The initial conditions for both schemes were the same. The compositions and costs of technological products are presented in table 1. Wherein

the nitric acid content in steps 3-8 of apparatus 1 in the prototype method was 3.90-3.94 mol / l, while in the technical solution the nitric acid content was 4.76-4.84 mol / l, t .e. one that provides increased zirconium extraction.

PRI me R 2, Extraction of zirconium in the scheme with a separation of the wash zone is.

It depends on the concentration of nitric acid in the extraction zone.

Table 2 shows the data on the release of zirconium into highly active raffinate 6 and washing strongly acid solution 7, depending on the concentration of nitric acid in the extraction zone.

Different nitric acid contents with the same content in the initial solution (3 mol / l) and washings

solutions (4 mol / L and 0.5 mol / L) in this case was provided by changing the ratio of the flows of the organic and aqueous phases (reducing the consumption of extractant). Saturation of the organic phase with uranium at the exit from

apparatus in all cases supported

at the level of 94-96 g / l. A decrease in acidity in the extraction zone leads to an increase in the yield of zirconium in the highly active raffinate 6. An increase in acidity in

the extraction zone from 4.7 mol / l, up to 19 mol / l, provides the withdrawal of zirconium by more than 90% in strongly acid washing 7 and 3-7% in highly active raffinate 6 (table 3). In the prototype method, 100% zirconium is excreted in highly active raffinate 6.

The upper limit of acidity is 19 mol-L - the maximum possible concentration of nitric acid with such a uranium content.

The discharge of zirconium into the raffinate within 3-7% of the extraction obtained with the initial solution does not significantly affect the rate of subsequent evaporation of the highly active raffinate, which can be evaporated more than 100 times at this zirconium content. The zirconium content in the highly active raffinate of more than 3-7% significantly reduces the multiplicity of evaporation of the raffinate, since it leads to precipitation based on zirconium.

EXAMPLE 3. Extraction of zirconium under the conditions of the additional apparatus 10 also largely depends on the acid regime. The proposed structure of additional steps with washing the extract with 0.5 mol / L of nitric acid 14 and loxidation in the extraction zone 13, with an acidity of the output raffinate of the order of 3 mol / L, allows dumping almost all zirconium into a weakly active raffinate 15. In table. 4 shows the zirconium distribution balances for the prototype method and for the proposed method.

Claims (1)

The claims A method of processing irradiated fuel elements, including sequentially extracting zctinides of a solution of tributyl phosphate in a hydrocarbon diluent, two-zone strong and weakly acidic washing of the extract, sharpening of actinides, characterized in that, in order to reduce the volume of highly active tritium-containing raffinate and simplification of the process of further processing of highly active raffinate by increasing the rate of evaporation due to the withdrawal of stable zirconium in a low-active solution, extraction is carried out at a content and nitric acid in the extraction zone of more than 4.7 mol / L, and the two-zone strong and weak acid washings are withdrawn in separate streams for an additional extraction operation to withdraw stable zirconium to the low active stream. Table 1 ototype stock solution Extractant Strongly acid flushing solution Slightly acidic flushing solution U - 270 g / l; 1.0 HH05 - 3 zero / l; Zr- - 1 g / l; Tc - 100 mg / l and other impurities 30% TBP in a hydrocarbon 3.0 diluent k, 0 mol / L 0.3-0.5 0.5 mol / L 0.3-0.5 apparatus 1. Stock solution Extractant Strongly acid  flushing solution Slightly acidic flushing solution Parat 10 Extractant Wash solution U - 270 g / l; 1.0 1 Ш03 - 3 mol / l; Zr - 1 g / l; Tc - 100 mg / l 30 TBP on a hydrocarbon 2.6 diluent 1 |, 0 mol / L 0.3-0.5 0.5 mol / L 0.3-0.5 30% TBP in hydrocarbon-O, 1 nom diluent 0.5 mol / L 0.06 12 mol / L 0.1 table 2 Table 3 Table 4