A method for reducing the plutonium and neptunium content of the uranium product solution of the spent fuel reprocessing purex process

Abstract

The application discloses a method for reducing the content of plutonium and neptunium in a uranium product solution in a spent fuel reprocessing PUREX process, which comprises the following steps: adjusting the 2DF material liquid, washing the extraction organic phase by using a washing agent with complexing and reducing double effects in an extraction device, and reducing the content of neptunium and plutonium in the uranium-containing organic phase, so as to obtain a uranium product solution with greatly reduced content of plutonium and neptunium through back extraction. 2 The method has the advantages of simple process, and the decontamination factor of plutonium and neptunium is 10 4 orders of magnitude after 2D tank extraction and washing, and the content of plutonium and neptunium in the uranium product solution is greatly reduced after only one extraction cycle of the uranium line, so that the requirements for the operation control precision and the solvent quality of the process are reduced, the probability of unqualified uranium product solution due to the excessive content of plutonium and neptunium is greatly reduced, the quality of the uranium product is improved, the method has a remarkable removal effect on the fission products such as zirconium, niobium and ruthenium in the uranium product, and can be effectively applied to the PUREX process.

Description

Technical Field

[0001] This invention belongs to the field of nuclear chemical engineering and nuclear fuel cycle technology, and specifically relates to a method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process for spent fuel reprocessing. Background Technology

[0002] Nuclear fuel reprocessing primarily involves the extraction and purification of newly generated fissile material, the recovery and purification of residual fissile material and conversion materials, the extraction of useful fission products and transuranic elements, and the proper handling and safe disposal of radioactive waste. Currently, nuclear fuel reprocessing plants employ a water extraction process, known as the PUREX process, using inert solvents such as hydrogenated kerosene and hydrogenated tetrapropylene as diluents and tributyl phosphate (TBP) as the extractant. (See attached document.) Figure 1 A typical PUREX two-cycle process consists of three solvent extraction and back-extraction cycles: a co-decontamination separation cycle (extractors 1A, 1B, and 1C), a plutonium purification cycle (extractors 2A and 2B), and a uranium purification cycle (extractors 2D and 2E). The main task of the uranium purification cycle is to further extract and wash the uranium solution 1CU, which has already undergone preliminary separation of plutonium, neptunium, and fission products, based on the co-decontamination separation cycle, to further remove plutonium and fragment elements, obtaining a purer uranium solution. The uranium purification cycle consists of three process sections: conditioning, extraction, and back-extraction. Tank 2D serves as the uranium extraction tank for 1CU, where uranium is extracted to the organic phase. Tank 2E is called the uranium back-extraction tank, where uranium is back-extracted from the organic phase to the aqueous phase using dilute nitric acid; the resulting aqueous phase 2EU is the uranium product solution. The plutonium decontamination capability of the uranium purification cycle mainly comes from the uranium extraction process in tank 2D.

[0003] Nuclear fuel reprocessing imposes extremely strict requirements on the control of plutonium and neptunium content in uranium products. In the uranium product solution during reprocessing, the uranium concentration is typically tens of g / L, while the plutonium concentration usually needs to be controlled below 10 g / L. -6 Plutonium content is below the g / L level, meaning less than 1.0 × 10⁻⁶ g of plutonium per gram of uranium. -8 g, the neptunium content needs to be controlled to be less than 3.2 × 10 g per gram of uranium. -6 g. For uranium products, the decontamination coefficient of plutonium throughout the process must be as high as 1.0 × 10⁻⁶. 6 The decontamination coefficient for neptunium needs to reach 10. 4 The levels are above [amount missing]. However, during the operation of the reprocessing plant, it is extremely easy for the plutonium and neptunium content in the uranium product solution (2 EU) to exceed the standard. Summary of the Invention

[0004] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a method that can effectively reduce the plutonium and neptunium content in the uranium product solution of the PUREX process for spent fuel reprocessing.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing, comprising the following steps:

[0006] (1) Starting from the uranium-containing feed liquid 1CU of the co-decontamination separation cycle, the feed liquid 2DF with a suitable uranium concentration is prepared by evaporation concentration, acidity adjustment and uranium concentration adjustment;

[0007] (2) The above-mentioned extraction solution 2DF, extraction solvent 30% TBP-70% kerosene 2DX, nitric acid solution 2DS2 (a water-soluble compound with both complexing and reducing effects), and nitric acid solution 2DS1 are added to the 2D uranium extraction tank for uranium extraction and washing. The uranium extract in 2DF is then transferred to the organic phase solution 2DU. At the same time, the decontamination of neptunium, plutonium, and some fission products is achieved.

[0008] (3) Uranium back-extraction was performed on the above organic phase extract 2DU to obtain a uranium product solution.

[0009] Further, in step (1), an appropriate amount of high-concentration nitric acid is added to the 1CU of the extractant after extraction in the 1C extractor and stirred evenly to obtain the 2DF of the extractant to be extracted.

[0010] Further, in step (1), the 1CU extractant solution 1CU is evaporated to obtain concentrated 1CU solution, and an appropriate amount of nitric acid is added to the concentrated 1CU solution to adjust the uranium concentration and acid concentration, so as to obtain the extractant solution 2DF.

[0011] Further, in step (2), the extractant 2DX is 30% TBP-70% kerosene; the 2D uranium extraction tank is a mixing and clarification tank, a pulse extraction column, or a centrifugal extractor.

[0012] Furthermore, in step (2), the total number of extraction and washing stages is 8 to 20.

[0013] Further, in step (2), detergent 2DS2 is a nitric acid solution of glutarimide dioxime or succinimide dioxime and hydrazine nitrate, wherein the concentration of the reducing complexing agent is 0.1-0.4 mol / L, the concentration of hydrazine nitrate is 0.1-0.3 mol / L, the concentration of nitric acid is 0.5-1.0 mol / L, and detergent 2DS1 is a nitric acid solution with a concentration of 1.0-3.0 mol / L.

[0014] Furthermore, in step (2), the flow ratio of 2DX to 2DF is determined by the concentration of uranium in 2DF, such that the concentration of uranium in the organic phase 2DU after extraction is about 90 g / L, the flow ratio of 2DS1 to 2DX is 0.2 to 0.5:1, and the flow ratio of 2DS2 to 2DX is 0.05 to 0.5:1.

[0015] Further, in step (3), the uranium back-extraction agent 2EX is dilute nitric acid, and back-extraction is carried out at a certain flow ratio and temperature to back-extract uranium from the organic phase 2DU into the aqueous phase 2EU to obtain a uranium product solution.

[0016] The beneficial effects of adopting the technical solution of the present invention are as follows: A method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing. This method involves adjusting the concentrations of uranium and nitric acid in the 2DF extractant, followed by extraction with 30% TBP-70% kerosene in a 2D extractor, and washing with a water-soluble compound that has both complexing and reducing effects. The resulting uranium-containing organic phase is then back-extracted with dilute nitric acid in a 1C extractor to obtain a uranium product solution with very low plutonium and neptunium content. For plutonium, the possible valence states of plutonium in the 2DF feed solution are +3, +4, and +6 (plutonium ion). Among them, trivalent plutonium is not extracted, hexavalent plutonium is reduced to a lower valence state by the detergent used in this invention, and tetravalent plutonium is extracted into the organic phase, thus affecting the decontamination of uranium products. The aqueous detergent used in this invention has a strong complexing effect with tetravalent plutonium ions, which can wash tetravalent plutonium into the aqueous phase. In the aqueous phase, the complexing reducing agent can reduce tetravalent plutonium to trivalent plutonium, while trivalent plutonium is not extracted by tributyl phosphate and its degradation products, thereby further enhancing the removal capacity of plutonium. For neptunium, the possible valence states of neptunium in the 2DF feed solution are +4, +5 (neptunyl), and +6 (neptunyl). Among them, pentavalent neptunium is not extracted, hexavalent neptunium is reduced by the detergent used in this invention, and tetravalent neptunium is extracted into the organic phase, thus affecting the decontamination of uranium products. The detergent used in this invention has a strong complexing effect with tetravalent neptunium, which can wash tetravalent neptunium into the aqueous phase, thereby reducing the neptunium content in the uranium-containing organic phase feed solution. Compared to plutonium and neptunium ions in the +4 valence state, the complexing reducing agent used in this invention does not reduce uranyl ions and has a much weaker complexing ability with uranyl ions. Therefore, while washing away plutonium and neptunium, it does not affect the chemical yield of uranium in the process. All chemical reagents used in this invention are salt-free. The method of this invention is simple, removing plutonium and neptunium simultaneously through a single uranium purification and extraction cycle, significantly reducing the plutonium and neptunium content in the uranium product solution while meeting the requirements for uranium chemical yield. Furthermore, it eliminates the need for the step of conditioning 2DF with hydrazine, hydroxylamine, etc., and also reduces the requirements for process operation control precision, thereby reducing the probability of the uranium product solution failing due to excessive plutonium and neptunium content. This method also significantly enhances the decontamination of fission products such as zirconium, niobium, and ruthenium, and can be effectively applied to the post-processing PUREX process. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the existing process for reducing the plutonium and neptunium content in uranium product solutions in the PUREX process.

[0018] Figure 2 This is a schematic diagram of the process flow for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing, according to an embodiment of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] Example 1

[0021] See attached document Figure 2 This invention provides a method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing, comprising the following steps:

[0022] (1) Starting from the uranium-containing feed liquid 1CU of the co-decontamination and separation cycle, the feed liquid 2DF to be extracted is prepared by evaporation concentration, acidity adjustment and uranium concentration adjustment.

[0023] (2) Add the above-mentioned extraction liquid 2DF, extraction solvent 30% TBP-70% kerosene 2DX, and detergent 2DS with complexing and reducing effects to the 2D uranium extraction tank for uranium extraction and washing, and transfer the uranium in 2DF into the organic phase liquid 2DU.

[0024] (3) Uranium back-extraction was performed on the above organic phase extract 2DU to obtain a uranium product solution.

[0025] Preferably, in step (1), the aqueous phase solution 1CU extracted by the 1C extractor is evaporated to obtain concentrated 1CU solution. An appropriate amount of high-concentration nitric acid is added to the concentrated 1CU solution to adjust the acid concentration to 0.3-0.7 mol / L and the uranium concentration to 380-430 g / L. After cooling, the extractable solution 2DF is obtained.

[0026] Preferably, in step (1), the 1CU extractant solution after extraction by the 1C extractor is evaporated and concentrated, and an appropriate amount of nitric acid is added to the concentrated 1CU solution to adjust the uranium concentration and acid concentration. After cooling, the extractant solution 2DF is obtained.

[0027] Preferably, in step (2), the extractant 2DX is 30% TBP-70% kerosene; the 2D uranium extraction tank is one of a mixing and clarification tank, a pulse extraction column, or a centrifugal extractor.

[0028] Preferably, in step (2), the total number of extraction and washing stages is 8 to 20.

[0029] Preferably, in step (2), detergent 2DS2 is a mixed nitric acid solution of glutarimide dioxime (H2A) and hydrazine nitrate, and 2DS1 is a nitric acid solution of appropriate concentration.

[0030] Preferably, in step (2), the two detergents are added at different stages. Detergent 2DS2 is a nitric acid solution of a reducing complexing agent, glutarimide dioxime or succinimide dioxime, and hydrazine nitrate. The concentration of the reducing complexing agent is 0.1–0.4 mol / L, the concentration of hydrazine nitrate is 0.1–0.3 mol / L, the concentration of nitric acid is 0.5–1.0 mol / L, and detergent 2DS1 is a nitric acid solution with a concentration of 1.0–3.0 mol / L.

[0031] Preferably, the glutarimide dioxime (H2A) has the following structure:

[0032]

[0033] The glutarimide dioxime exhibits strong coordination ability with +4 valence plutonium and neptunium ions under high acidity, enabling the back-extraction of +4 valence plutonium and neptunium ions retained in the organic phase to the aqueous phase via complexation. Under suitable reaction conditions, H2A further reduces the +4 valence plutonium to the +3 valence state, thereby further reducing the extraction ability of the extractant (tributyl phosphate and its degradation products) for plutonium in the organic phase. Compared with +4 valence plutonium ions, H2A has a much weaker coordination ability with uranyl ions, thus enhancing the purification effect of uranium products on plutonium and neptunium without reducing the chemical yield of uranium in the process. For +6 valence plutonium ions (plutonyl) and neptunium ions (neptunyl), hydrazine nitrate in detergent 2DS2 reduces them to the +5 valence state, and further reduces them to the +4 or +3 valence state.

[0034] Preferably, in step (2), the flow ratio of 2DX to 2DF is determined by the uranium concentration of 2DF, such that the uranium concentration in the organic phase 2DU after extraction is about 90 g / L, the flow ratio of 2DS1 to 2DX is 0.2 to 0.5:1, and the flow ratio of 2DS2 to 2DX is 0.05 to 0.5:1.

[0035] Preferably, in step (3), the uranium back-extraction agent 2EX is dilute nitric acid, and back-extraction is carried out at a certain flow ratio and temperature to back-extract uranium from the organic phase 2DU into the aqueous phase 2EU to obtain a uranium product solution.

[0036] Example 2

[0037] The method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing, using the method of Embodiment 1 of the present invention, includes the following steps:

[0038] (1) Take 1 CU of feed liquid obtained from a co-decontamination separation cycle of a certain nuclear fuel reprocessing process research thermal test. Its acidity is 0.07 mol / L, the concentration of uranium is 75.0 g / L, and the concentration of plutonium is 2.0 × 10⁻⁶ g / L. -3 g / L; Add an appropriate amount of 6.0 mol / L nitric acid to the uranium solution to adjust the nitric acid concentration of the solution to 1.0 mol / L, and the uranium concentration to be approximately 65.0 g / L, which will be used as the 2DF extraction feed solution;

[0039] (2) 30% TBP-70% kerosene was used as the extraction organic solvent, and 0.80 mol / L nitric acid solution containing 0.40 mol / L glutarimide dioxime (H2A) and 0.3 mol / L hydrazine nitrate was used as detergent 2DS2. 2.0 mol / L nitric acid solution was used as 2DS1. The extraction was carried out in an 18-stage mixing and clarifying tank to obtain the extract. Among them, 2DF was fed in the 10th stage, 2DX was fed in the 1st stage, 2DS2 was fed in the 18th stage, and 2DS1 was fed in the 12th stage. The flow ratio of 2DF:2DX:2DS1:2DS2 was 1.0:0.7:0.3:0.1.

[0040] (3) The 2E tank uses 0.01mol / L nitric acid as the back-extraction agent 2EX. It uses a 10-stage mixing and clarification tank, with 2DU as the first stage feed and 2EX as the tenth stage feed. The flow ratio of 2DU to 2EX is 1.0:1.2, and the back-extraction operating temperature is 55℃.

[0041] After the operation stabilized, the concentration of plutonium in the 2EU feed solution was analyzed, and the result was 5.2 × 10⁻⁶. -7 g / L. The calculated decontamination factor for plutonium in the uranium purification cycle is 3500, which is much larger than the 5-50 plutonium decontamination factor in the conventional uranium purification cycle. Furthermore, by analyzing the uranium concentration in 2EW and 2DW, the calculated chemical yield of uranium is 99.95%.

[0042] Example 3

[0043] The method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing, using the method of Embodiment 1 of the present invention, includes the following steps:

[0044] (1) Take 1 CU of feed liquid obtained from a co-decontamination separation cycle of a certain nuclear fuel reprocessing process research thermal test. Its acidity is 0.07 mol / L, the concentration of uranium is 75.0 g / L, and the concentration of plutonium is 2.0 × 10⁻⁶ g / L. -3g / L; After evaporating and concentrating the 1CU feed solution 6 times, add an appropriate amount of 12.0mol / L nitric acid to adjust the nitric acid concentration of the solution to 0.75mol / L and the uranium concentration to 428.0g / L, which will be used as the 2DF extraction feed solution;

[0045] (2) 30% TBP-70% kerosene was used as the extraction organic solvent 2DX, 0.70 mol / L nitric acid solution containing 0.40 mol / L glutarimide dioxime (H2A) and 0.3 mol / L hydrazine nitrate was used as the detergent 2DS2, and 2.6 mol / L nitric acid solution was used as the detergent 2DS1; an 18-stage mixing and clarifying tank was used for extraction; wherein 2DF was fed in stage 10, 2DX in stage 1, 2DS2 in stage 18, and 2DS1 in stage 14; the flow ratio of 2DF:2DX:2DS1:2DS2 was 1.0:4.75:0.35:0.35;

[0046] (3) The 2E tank uses 0.01mol / L nitric acid as the back-extraction agent 2EX. It uses a 10-stage mixing and clarification tank, with 2DU as the first stage feed and 2EX as the tenth stage feed. The flow ratio of 2DU to 2EX is 1.0:1.2, and the back-extraction operating temperature is 55℃.

[0047] After the operation stabilized, the concentration of plutonium in the 2EU feed solution was analyzed, and the result was 3.1 × 10⁻⁶. -7 g / L. The calculated decontamination factor for plutonium in the uranium purification cycle is 2500, which is much greater than the plutonium decontamination factor of 5-50 in the conventional uranium purification cycle; by analyzing the uranium concentration in 2EW and 2DW, the chemical yield of uranium was calculated to be 99.93%.

[0048] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. A method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing, characterized in that, Includes the following steps: (1) Starting from the uranium-containing feed liquid 1CU of the co-decontamination and separation cycle, the feed liquid 2DF to be extracted is prepared by evaporation concentration, acidity adjustment and uranium concentration adjustment. (2) The above-mentioned extraction solution 2DF, extraction solvent 30% TBP-70% kerosene 2DX, and detergent 2DS with dual functions of complexing and reduction are added to the 2D uranium extraction tank for uranium extraction and washing. The uranium in 2DF is transferred to the organic phase solution 2DU, and at the same time, the neptunium, plutonium and some fission products are decontaminated. The two detergents are added in different stages. Detergent 2DS2 is a nitric acid solution of glutarimide dioxime or succinimide dioxime and hydrazine nitrate. The concentration of the reducing complexing agent is 0.1-0.4 mol / L, the concentration range of hydrazine nitrate is 0.1-0.3 mol / L, the concentration range of nitric acid is 0.5-1.0 mol / L, and detergent 2DS1 is a nitric acid solution with a concentration of 1.0-3.0 mol / L. (3) Uranium back-extraction was performed on the above organic phase extract 2DU to obtain a uranium product solution.

2. The method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing according to claim 1, characterized in that, In step (1), an appropriate amount of high-concentration nitric acid is added to the aqueous phase feed solution 1CU after uranium back-extraction in the 1C extractor, and the concentration of nitric acid is adjusted to 0.3-0.7 mol / L to obtain the feed solution 2DF to be extracted.

3. The method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing according to claim 1, characterized in that, In step (1), the aqueous phase solution 1CU extracted by the 1C extractor is evaporated to obtain concentrated 1CU solution. An appropriate amount of high-concentration nitric acid is added to the concentrated 1CU solution to adjust the acid concentration to 0.3-0.7 mol / L and the uranium concentration to 380-430 g / L. After cooling, the extractable solution 2DF is obtained.

4. The method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing according to claim 1, characterized in that, In step (2), the extractant 2DX is 30% TBP-70% kerosene; the 2D uranium extraction tank is one of a mixing and clarification tank, a pulse extraction column, or a centrifugal extractor.

5. The method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing according to claim 1, characterized in that, In step (2), the total number of extraction and washing stages is 8 to 20.

6. The method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing according to claim 1, characterized in that, In step (2), the flow ratio of 2DX to 2DF is determined by the uranium concentration of 2DF, so that the uranium concentration in the organic phase 2DU after extraction is about 90 g / L, the flow ratio of 2DS1 to 2DX is 0.2 to 0.5:1, and the flow ratio of 2DS2 to 2DX is 0.05 to 0.5:

1.

7. The method for reducing the plutonium and neptunium content in the uranium product solution of the PUREX process in spent fuel reprocessing according to claim 1, characterized in that, In step (3), the uranium back-extraction agent 2EX is dilute nitric acid. Back-extraction is carried out at a certain flow ratio and temperature to back-extract uranium from the organic phase 2DU into the aqueous phase 2EU to obtain a uranium product solution.

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