A method for retaining plutonium in contaminated solvents after neutral complexing agent elution and post-treatment process.

Abstract

This invention discloses a method for retaining plutonium in a contaminated solvent after elution with a neutral complexing agent. An acidic solution of the neutral complexing agent TMDGA is used to complex with Pu(IV) in the contaminated solvent, eluting plutonium bound to TBP and its degradation products HDBP, H2MBP, etc., from the organic phase into the aqueous phase. The single-stage elution efficiency of TMDGA reaches over 96.8% under different nitric acid concentrations; the plutonium content in the eluted contaminated solvent can reach 1.0 × 10⁻⁶. ‑4 The plutonium content in the organic phase is below g / L, meeting the requirements for plutonium content in the waste treatment process. The waste solvent washing method of the present invention can be used for the treatment of high plutonium-retaining waste solvents under abnormal operating conditions in spent fuel reprocessing plants, and can also be used for the deep purification of waste solvents under normal operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of spent fuel reprocessing and radioactive waste treatment technology, specifically relating to a method for retaining plutonium in the waste solvent during a neutral complexing agent elution post-treatment process. Background Technology

[0002] my country adopts a closed-loop nuclear fuel cycle, which involves reprocessing spent fuel from nuclear power plants to recover fissile nuclear materials such as uranium and plutonium. The PUREX (Plutonium Uranium Reduction Extraction) process uses solvent extraction, employing tributyl phosphate (TBP) as the extractant and hydrogenated kerosene, tetrapropylene hydrogenate (TPH), or n-dodecane as diluents. It selectively extracts uranium and plutonium, achieving the separation of nuclides through multi-stage countercurrent extraction. However, in practical applications, the TBP-kerosene-HNO3 system is continuously exposed to chemical and radiation exposure, resulting in degradation products. The main degradation products of TBP are dibutyl phosphate (HDBP), monobutyl phosphate (H2MBP), and H3PO4; the degradation of the diluent and nitric acid produces organic nitro compounds such as aldehydes, carboxylic acids, and hydroxamic acids.

[0003] The degradation products of TBP-kerosene accumulate continuously during process operation. Some degradation products, such as HDBP and H2MBP, form very stable complexes with uranium and plutonium, causing metal ions, especially plutonium, to be retained in the organic phase, affecting the normal operation of the process. As the process continues to run, the plutonium content retained in the organic phase increases, resulting in the total radioactivity of the organic phase far exceeding the standard. This high-plutonium-retained waste solvent cannot be directly discharged to the waste liquid treatment unit, nor can it be returned to the process for reuse.

[0004] For contaminated solvents caused by degradation products, the current common practice is to use Na2CO3 solution to wash away HDBP, H2MBP, and H3PO4 to reduce the impact of degradation products on the organic phase. However, after several cycles of washing and reuse of the organic phase in the process, the problem of excessive plutonium content and total radioactivity in the organic phase still occurs, and further recycling with Na2CO3 washing is not possible. Therefore, Na2CO3 washing cannot completely solve the problem of high plutonium retention. For contaminated solvents where the plutonium content and degradation product content exceed the process standard limits, new and effective plutonium elution methods still need to be sought. Summary of the Invention

[0005] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a method for effectively eluting retained plutonium from spent fuel reprocessing process contaminated solvents using a neutral complexing agent.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows: A method for retaining plutonium in the contaminated solvent after neutral complexing agent elution treatment process, comprising the following steps:

[0007] (1) Dissolve an appropriate amount of complexing agent N,N,N′,N′-tetramethylbisamide ether (TMDGA) in nitric acid solution to obtain a stripping agent;

[0008] (2) Take an appropriate amount of the contaminated solvent for liquid scintillation measurement and calculate the plutonium content in the contaminated solvent;

[0009] (3) Take an appropriate amount of the above-mentioned back-extraction agent and the dirty solvent and mix them in a batch extraction device such as a tank scrubber or ball scrubber for a certain period of time. After centrifugation or standing, the aqueous phase and organic phase are obtained by gravity separation.

[0010] (4) Take an equal amount of the separated organic phase from step (2) and perform liquid scintillation measurement to calculate the plutonium back-extraction rate.

[0011] Further, in step (1), the structural formula of the N,N,N′,N′-tetramethylbisamide ether is:

[0012]

[0013] Further, in step (1), the concentration of TMDGA in the stripping agent is 0.5 mol / L, and the concentration of nitric acid is 4 to 8 mol / L.

[0014] Further, in step (2), the amount of pollutant solvent is calculated. 241 Pu content.

[0015] Furthermore, in step (3), the ratio of the back-extraction agent to the contaminating solvent is 1:1 to 1:10.

[0016] Furthermore, in step (3), the back-extraction agent and the waste solvent are mixed and back-extracted at a certain temperature, and after phase separation, a separate aqueous phase and an organic phase are obtained.

[0017] Furthermore, in step (3), back-extraction is performed using a tank scrubber or ball scrubber intermittent extraction equipment, or a multi-stage mixing clarification tank or a pulse extraction column continuous extraction equipment.

[0018] Further, in step (3), the plutonium back-extraction rate = (1 - plutonium content in the eluted solvent / plutonium content in the initial eluted solvent) × 100%.

[0019] The beneficial effects of adopting the technical solution of this invention are as follows: a method for retaining plutonium in the contaminated solvent after neutral complexing agent elution, using an acidic solution of the neutral complexing agent TMDGA, can complex with Pu(IV) in the contaminated solvent under different acidic conditions, reducing the binding of Pu(IV) with HDBP and H2MBP; the single-stage elution efficiency reaches over 96.8%; and the plutonium content in the contaminated solvent after elution can reach 1.0 × 10⁻⁶. -4 The plutonium content is below g / L, meeting the requirements for plutonium content in the organic phase during waste treatment. The waste solvent washing method of this invention can be used for treating high-plutonium-retaining waste solvents under abnormal operating conditions in spent fuel reprocessing plants, and also for deep purification of waste solvents under normal operating conditions. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for retaining plutonium in a contaminated solvent after neutral complexing agent elution and post-treatment process according to an embodiment of the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] See attached document Figure 1 This invention provides a method for retaining plutonium in a contaminated solvent after elution with a neutral complexing agent, comprising the following steps:

[0023] (1) Take an appropriate amount of complexing agent N,N,N′,N′-tetramethylbisamide ether (TMDGA) and dissolve it in nitric acid solution to obtain the stripping agent; TMDGA coordinates with plutonium ions in a tripentate coordination manner, and one plutonium ion combines with three TMDGA molecules to form a complex. At the same time, the presence of nitric acid can inhibit the binding of degradation products HDBP and H2MBP with plutonium ions;

[0024] (2) Take an appropriate amount of the contaminated solvent for liquid scintillation measurement and calculate the plutonium content in the contaminated solvent;

[0025] (3) After mixing the above-mentioned back-extraction agent with the waste solvent and performing single-stage back-extraction at a certain temperature for a certain time, centrifuge or let stand to separate the phases to obtain the separated aqueous phase and organic phase; at this time, most of the plutonium is eluted into the aqueous phase.

[0026] (4) Take an equal amount of the separated organic phase from step (2) and perform liquid scintillation measurement to calculate the plutonium back-extraction rate.

[0027] Preferably, in step (1), the structural formula of the N,N,N′,N′-tetramethylbisamide ether is:

[0028]

[0029] Preferably, in step (1), the concentration of TMDGA in the stripping agent is 0.5 mol / L, and the concentration of nitric acid is 4.0 to 8.0 mol / L.

[0030] Preferably, in step (2), the amount of pollutant solvent is calculated. 241 Pu content.

[0031] Preferably, in step (3), the ratio of the back-extraction agent to the contaminating solvent is 1:1 to 1:10.

[0032] Preferably, in step (3), the back-extraction agent and the contaminated solvent are shaken at room temperature for 30 minutes and centrifuged to obtain the separated aqueous phase and organic phase.

[0033] Preferably, in step (3), back-extraction is performed using intermittent extraction equipment such as tank scrubbers or ball scrubbers, or using multi-stage mixing and clarification tanks, pulse extraction columns, or other continuous extraction equipment.

[0034] Preferably, in step (3), the plutonium back-extraction rate = (1 - plutonium content in the eluted solvent / plutonium content in the initial eluted solvent) × 100%.

[0035] Example 2

[0036] The method of Embodiment 1 of this invention is used to elute a 2BW feed solution obtained from a thermal experiment, comprising the following steps:

[0037] (1) Weigh a certain amount of TMDGA solid into two centrifuge tubes, add HNO3 solutions of different concentrations, and prepare 0.5 mol / L TMDGA-4.0 mol / L HNO3 solution and 0.5 mol / L TMDGA-8.0 mol / L HNO3 solution as back-extraction agents;

[0038] (2) Take 10 μL of the contaminated solvent for liquid scintillation measurement and calculate the concentration of the liquid. 241 The content of Pu is 0.057 g / L; the contaminated solvent is a 2BW solution obtained from a thermal experiment, which has been stored for more than 5 years and appears as a clear, yellowish-brown solution; the main components are: 30% (volume percentage) tributyl phosphate (TBP) and 70% (volume percentage) hydrogenated kerosene, wherein the plutonium content is 0.057 g / L, the nitric acid content is 0.03 mol / L, the dibutyl phosphate (DBP) content is 0.14 mol / L, and the monobutyl phosphate (MBP) content is 2.30 × 10⁻⁶. -4 mol / L;

[0039] (3) Add 0.5 mL of stripping agent and 0.5 mL of contaminated solvent, 0.5 mL of stripping agent and 0.5 mL of contaminated solvent, 0.3 mL of stripping agent and 3 mL of contaminated solvent, and 0.5 mL of stripping agent and 0.5 mL of contaminated solvent to four polypropylene centrifuge tubes numbered 1, 2, 3, and 4, respectively. The stripping agents are 0.5 mol / L TMDGA–4.0 mol / L HNO3 solution, 0.5 mol / L TMDGA–8.0 mol / L HNO3 solution, 0.5 mol / L TMDGA–4.0 mol / L HNO3 solution, and 0.5 mol / L Na2CO3–0.1 mol / L NaHCO3 solution, respectively, where NaHCO3 is used to adjust the pH value of the solution. Shake at room temperature for 30 minutes. After centrifugation, take 10 μL of organic phase for liquid scintillation measurement and calculate the stripping rate of plutonium. The results are shown in Table 1.

[0040] Table 1. Plutonium retention rate in the back-extraction solvent of 0.5 mol / L TMDGA under different conditions.

[0041]

[0042] As can be seen from the data in the table, the method of this embodiment of the invention uses TMDGA as an aqueous complexing agent. Under acidic conditions, when the ratio is 1:1, the elution rate of plutonium can reach more than 99.0%, and when the ratio is 1:10, the elution rate of plutonium can also reach 96.8%. This indicates that the method of this embodiment of the invention can effectively elute plutonium from the contaminated solvent with high plutonium retention in the post-treatment process.

[0043] 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 retaining plutonium in a contaminated solvent after elution with a neutral complexing agent, characterized in that: it includes... The following steps: (1) Take an appropriate amount of complexing agent N,N,N',N'-tetramethylbisamide ether (TMDGA) and dissolve it in nitric acid solution to obtain a stripping agent; the concentration of TMDGA in the stripping agent is 0.5 mol / L and the concentration of nitric acid is 4.0~8.0 mol / L; (2) Take an appropriate amount of the contaminated solvent from the PUREX process for liquid flash measurement and calculate the plutonium content in the contaminated solvent; (3) Take an appropriate amount of the above-mentioned back-extraction agent and the dirty solvent, mix and back-extract them in a single stage at a certain temperature for a certain time, and then centrifuge to obtain the separated aqueous phase and organic phase; (4) Take an equal amount of the separated organic phase from step (2) and perform liquid scintillation measurement to calculate the plutonium back-extraction rate.

2. The method for retaining plutonium in the contaminated solvent after neutral complexing agent elution as described in claim 1, characterized in that: In step (1), the structural formula of the N,N,N',N'-tetramethylbisamide ether is: 。 3. The method for retaining plutonium in the contaminated solvent in the post-elution treatment process of a neutral complexing agent according to claim 1, characterized in that: In step (2), the amount of waste solvent is calculated. 241 Pu content.

4. The method for retaining plutonium in the contaminated solvent in a neutral complexing agent elution post-treatment process according to claim 1, characterized in that: In step (3), the ratio of the back-extraction agent to the contaminating solvent is 1:1 to 1:

10.

5. The method for retaining plutonium in the contaminated solvent in a neutral complexing agent elution post-treatment process according to claim 1, characterized in that: In step (3), the back-extraction agent and the dirty solvent are shaken at room temperature for 30 min and centrifuged to obtain the separated aqueous phase and organic phase.

6. The method for retaining plutonium in the contaminated solvent in a neutral complexing agent elution post-treatment process according to claim 1, characterized in that: In the washing operation of step (3), either an intermittent extraction device or a continuous extraction device is used for back-extraction.

7. The method for retaining plutonium in the contaminated solvent in a neutral complexing agent elution post-treatment process according to claim 1, characterized in that: In step (4), the plutonium back-extraction rate = (1 - plutonium content in the eluted solvent / plutonium content in the initial eluted solvent) × 100%.

Images