A plutonium reduction stripping method

Abstract

The application belongs to the technical field of spent fuel reprocessing, and particularly relates to a plutonium reduction back extraction method. The method comprises the following steps: controlling the initial concentration of plutonium in 2AF according to the flow ratio and the concentration multiple of plutonium; controlling the liquid flow rate to be 160-200 L / h when 2AF liquid passes through an oxidation column; controlling the liquid flow rate to be 160-200 L / h when 2AF liquid passes through a degassing column; and completely removing the bottom liquid in the 2AF feeding tank every two or three batches, and completely removing the waste coal oil in the oil removal tank by one-time passing through a pulse extraction column. The method can reduce the content of nitrous acid in the plutonium second-cycle organic phase, avoid the accumulation of nitrous acid in the 2AF liquid and the organic phase, reduce the thermal effect of plutonium accumulation, and is suitable for long-term continuous operation of the system. Through repeated experiments, the system can be stably operated, and the column temperature and the hydrodynamic parameters of the 2BX column are stable.

Description

Technical Field

[0001] This application belongs to the field of spent fuel reprocessing technology, specifically relating to a plutonium reduction and back-extraction method. Background Technology

[0002] During the commissioning and operation of the plutonium reduction and back-extraction column (2BX column) in the Purex process plutonium purification cycle, abnormal increases in column temperature, excessively high interface temperature, and excessively high organic phase density were observed. Analysis revealed that nitrite ions entrained in the organic phase of the feed solution were difficult to remove, causing them to react with the reducing agent and supporting reducing agent within the 2BX column. This resulted in instability in the 2BX column operation and, in severe cases, even plutonium loss.

[0003] The sources of nitrite in the organic phase are nitrite entrained in the periodically refluxed kerosene and oxidative adjustment in the plutonium secondary cycle feed solution (1BP feed solution). Generally, nitrous gas is used to adjust the trivalent plutonium in the 1BP feed solution to tetravalent plutonium. After adjustment, nitrite and nitrous gas in the solution need to be removed to a certain level. Current engineering practices utilize degassing columns, supplemented by heating measures, to remove nitrite from the solution as nitrogen oxides.

[0004] However, the 1BP feed solution, 2BP feed solution, and reflux washing acid usually contain a certain amount of organic phase, making it difficult to remove nitrite ions trapped in the organic phase. In addition, plutonium, as a radioactive nuclide, releases a large amount of heat during radioactive decay. The higher the plutonium concentration, the more neutrons are produced during decay, and the greater the heat generated. This large amount of heat will further exacerbate the autocatalytic reaction of hydroxylamine. Summary of the Invention

[0005] The purpose of this application is to provide a plutonium reduction and back-extraction method to solve the problem of the difficulty in removing nitrite ions entrained in the organic phase in the prior art.

[0006] The technical solution to achieve the purpose of this application is as follows:

[0007] This application provides a plutonium reduction and back-extraction method, the method comprising:

[0008] The initial concentration of plutonium in 2AF was controlled based on the flow rate ratio and the plutonium enrichment factor.

[0009] When the 2AF feed liquid passes through the oxidation column, the flow rate is controlled at 160-200 L / h;

[0010] When the 2AF feed liquid passes through the degassing column, the liquid flow rate is controlled at 160-200 L / h;

[0011] The bottom liquid in the 2AF feeding tank is thoroughly processed every two or three batches, and the waste kerosene in the oil removal tank is completely processed through the pulse extraction column in one go.

[0012] Optionally, the method further includes:

[0013] When the 2AF feed solution passes through the oxidation column, NO is controlled. x The ratio of the reduction value to 2AF is 1.8 to 2.2.

[0014] Optionally, the method further includes:

[0015] The temperature of the 2AF feed liquid is 50±5℃ when it passes through the degassing column.

[0016] Optionally, the method further includes:

[0017] When the 2AF feed liquid passes through the degassing column, the air flow rate control adjustment range is 2-4m. 3 / h.

[0018] Optionally, the residual liquid in the 2AF feeding tank is thoroughly maintained every two or three batches of operation, specifically including:

[0019] When the liquid level in the 2AF feeding tank reaches 200mm, the flow rate of 2AF is controlled to 45±2.25L / h and the flow rate of 2AX is controlled to 20±1L / h.

[0020] Optionally, the residual liquid in the 2AF feeding tank is thoroughly maintained every two or three batches of operation, specifically including:

[0021] When the liquid level in the 2AF feed primary air lift constant level pre-tank rises, or when the liquid level in the 2AX column organic phase outlet separator rises above the preset threshold, the 2AF flow rate is controlled to 55L / h and the 2AX flow rate is controlled to 10L / h.

[0022] Optionally, the method further includes:

[0023] AF flow rate is controlled to 55L / h, and 2AX flow rate is controlled to 10L / h.

[0024] The beneficial technical effects of this application are as follows:

[0025] This application provides a plutonium reduction and back-extraction method, comprising: controlling the initial concentration of plutonium in 2AF according to the flow rate ratio and the plutonium concentration factor; controlling the flow rate at 160-200 L / h when the 2AF feed solution passes through the oxidation column; controlling the flow rate at 160-200 L / h when the 2AF feed solution passes through the degassing column; ensuring the bottom feed solution in the 2AF feed tank is thoroughly processed every two or three batches; and completing the waste kerosene from the oil removal tank in one pass through the pulse extraction column. This method can reduce the nitrite content in the organic phase of the plutonium secondary cycle, avoid the accumulation of nitrite ions in the 2AF feed solution and the organic phase, reduce the thermal effect of plutonium accumulation, and is suitable for long-term continuous operation of the system. After repeated experiments, the system can achieve stable operation, and the column temperature and hydraulic parameters of the 2BX column are stable. Attached Figure Description

[0026] Figure 1 A schematic flowchart of a plutonium reduction and back-extraction method provided in an embodiment of this application;

[0027] Figure 2 A model diagram of the 2AF oxidation and valence adjustment process in a plutonium reduction back-extraction method provided in this application embodiment;

[0028] Figure 3 A model diagram of the 2AF operation flow in a plutonium reduction and back-extraction method provided in an embodiment of this application;

[0029] Figure 4 This is a model diagram of the organic phase operation process in a plutonium reduction and back-extraction method provided in an embodiment of this application.

[0030] In the picture:

[0031] 1-2AF price adjustment feed tank; 2-Oxidation column; 3-2AF intermediate tank; 4-Degassing column; 5-2AF receiving tank; 6-2AF feed liquid; 7-2AF acid adjustment tank; 8-2AF feed tank; 9-2AX column; 10-2AF; 11-2AX feed liquid; 12-Pulse extraction column; 13-Oil removal tank; 14-Ket oil storage tank; 15-Refined kerosene; 16-Circulating kerosene. Detailed Implementation

[0032] To enable those skilled in the art to better understand this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only a part of the embodiments of this application, and not all of them. Based on the embodiments described in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] See Figure 1 The figure is a schematic flowchart of a plutonium reduction and back-extraction method provided in an embodiment of this application.

[0034] Combination Figure 2-4 This application provides a plutonium reduction and back-extraction method, comprising:

[0035] Step S101: Control the initial concentration of plutonium in the 2AF feed solution according to the flow rate ratio and the plutonium concentration factor;

[0036] Step S102: When the 2AF feed liquid passes through the oxidation column, control the liquid flow rate to be 160-200 L / h;

[0037] Step S103: When the 2AF liquid feed passes through the degassing column, control the liquid flow rate to be 160-200 L / h;

[0038] Step S104: The bottom liquid in the 2AF feeding tank is thoroughly run every two or three batches, and the waste kerosene in the oil removal tank is completely run through the pulse extraction column in one go.

[0039] It should be noted that the main reaction equation for the reaction of nitrogen oxides with water to produce nitrous acid is shown in equation (1):

[0040] 2NO2 + H2O → HNO2 + HNO3 (1)

[0041] Nitric acid can react with the reducing agent hydroxylamine nitrate and the supporting reducing agent hydrazine nitrate in the 2BX column. The reaction generates a large amount of heat and gas. Under the action of nitric acid, hydroxylamine nitrate is also autocatalytically oxidized by nitrous acid, resulting in the continuous consumption of hydroxylamine. The reaction formula is shown in equation (2):

[0042] NH3OH + +2HNO3+2HNO2→5HNO2+H3O + (2)

[0043] This often seriously affects the stability of the system operation, leading to inaccurate measurements of the system interface, overflow of the aqueous phase in the organic phase, and even plutonium loss in severe cases. Therefore, it is necessary to finely control the feed gas and liquid flow rates and flow ratio of the oxidation column (2).

[0044] Considering system operation, in this embodiment, the feed gas flow rate of the oxidation column (2) needs to be controlled at 160-200 L / h. The reduction value of system 2AF can be obtained by sampling. It is known that NO... x The percentage content of NO, with a molar volume constant of 22.4 mol / L under standard gas conditions, is [missing information]. x The reference value for the ratio of NO to 2AF restoration value consumption is 2; therefore, NO x The amount of gas used can be controlled with reference to formula (3).

[0045] In this method, it is known that F is stable, h can be obtained by sampling, C is a constant, and V can be effectively controlled by selecting different magnifications of n. It is specified that n is selected from magnifications of 1.8 to 2.2.

[0046] V=F×h×n×22.4 / C / 1000 (3)

[0047] Where V is NO x Feed gas flow rate, F is the feed gas flow rate of 2AF liquid, h is the reduction concentration of 2AF liquid, and n is the NO concentration. x The ratio of the reduction value of 2AF to the value of NO, C is NO x The percentage of content.

[0048] For the removal of nitrous acid, the current engineering application uses a degassing column (4). AS3 compressed air is introduced into the column to purge the nitrous acid-containing liquid, supplemented by a jacketed water bath heating method. The nitrous acid in the solution is carried away as nitrogen oxides through water bath heating and air bubbling. In this embodiment, the degassing column (4) is specified to have a liquid flow rate of 160–200 L / h, a temperature of 50 ± 5℃, and a gas flow rate control adjustment range of 2–7 m. 3 / h, select 2-4m 3 / h.

[0049] The above method can reduce the nitrite content in the aqueous phase to below the limit. However, the 2AF feed solution will contain organic phase, and some of the nitrite that has not been removed will be carried into the organic phase. The nitrite in the organic phase is difficult to remove by water bath heating and air bubbling. It will often eventually interact with the reducing agent in the 2BX column, which will have an adverse effect on the stable operation of the system. In order to remove the influence of the organic phase in the 2AF feed solution entering the system, the embodiments of this application specify that the 2AF feed solution is run thoroughly in batches. The bottom feed solution in the 2AF feed tank is run thoroughly every two or three batches.

[0050] The system operates by long-term self-circulation of kerosene and periodic one-time complete reflux. During the self-circulation process, the kerosene is in contact with the aqueous feed liquid for a long time, which often leads to the accumulation of some nitrite in the kerosene. During the one-time complete reflux, the nitrite entrained in the kerosene will also interact with the reducing agent in the 2BX column, which will have an adverse effect on the operation of the system.

[0051] The waste kerosene in the deoiling tank (13) carries nitrite. The operation of the circulating kerosene (16) leads to the accumulation of nitrite. The operation mode of the kerosene is specified so that the waste kerosene in the deoiling tank is completely processed by passing through the pulse extraction column (12) in one go, without the circulation operation.

[0052] The accumulation of plutonium releases a significant amount of heat, which in turn exacerbates the autocatalytic reaction of hydroxylamine. By controlling the initial concentration of plutonium in the 2AF feed solution, the upward trend of plutonium concentration during the plutonium reduction and back-extraction process can be controlled, thereby further controlling the heat release. For example, based on the flow rate ratio and the plutonium concentration factor, the initial concentration of plutonium in 2AF can be controlled at A ± 0.5 g / L.

[0053] In some possible implementations of the embodiments of this application, the method may further include:

[0054] When the 2AF feed solution passes through the oxidation column, NO is controlled. x The ratio of the reduction value to 2AF is 1.8 to 2.2.

[0055] In some possible implementations of the embodiments of this application, the method may further include:

[0056] The temperature of the 2AF feed liquid is 50±5℃ when it passes through the degassing column.

[0057] In one example, the method further includes:

[0058] When the 2AF feed liquid passes through the degassing column, the air flow rate control adjustment range is 2-4m. 3 / h.

[0059] In some possible implementations of the embodiments of this application, the residual liquid in the 2AF feeding tank is thoroughly processed every two or three batches, specifically including:

[0060] When the liquid level in the 2AF feeding tank reaches 200mm, the flow rate of 2AF is controlled to 45±2.25L / h and the flow rate of 2AX is controlled to 20±1L / h.

[0061] In some possible implementations of the embodiments of this application, the residual liquid in the 2AF feeding tank is thoroughly processed every two or three batches, specifically including:

[0062] When the liquid level in the 2AF feed primary air lift constant level pre-tank rises, or when the liquid level in the 2AX column organic phase outlet separator rises above the preset threshold, the 2AF flow rate is controlled to 55L / h and the 2AX flow rate is controlled to 10L / h.

[0063] In some possible implementations of the embodiments of this application, the method further includes:

[0064] AF flow rate is controlled to 55L / h, and 2AX flow rate is controlled to 10L / h.

[0065] This application embodiment found a stable plutonium reduction and back-extraction operation method by redefining the operation of the oxidation column (2), the degassing column (4), the complete operation of 2AF, the kerosene operation mode, and the initial plutonium concentration of 2AF, which helps to stabilize the subsequent system operation. It can achieve the goal of reducing the nitrite content in the organic phase of the plutonium second cycle, avoiding the accumulation of nitrite ions in the 2AF feed liquid and the organic phase, reducing the thermal effect of plutonium accumulation, and is suitable for long-term continuous system operation. Through repeated experiments, stable system operation was achieved, and the column temperature and hydraulic parameters of the 2BX column remained stable.

[0066] Example 1

[0067] This embodiment provides a method for stable plutonium reduction and back-extraction operation. The method includes: 2AF operation via an oxidation column, a degassing column, and complete 2AF operation; a one-time pass-through of waste kerosene; and specifying the initial plutonium concentration in the 2AF. The apparatus is shown in the attached diagram. Figure 1 Appendix Figure 2 Appendix Figure 3 As shown.

[0068] The method includes the following steps:

[0069] When S1 and 2AF feed solutions pass through the oxidation column, the flow rate is controlled at 160-200 L / h, and n is selected as 1.8;

[0070] When S2 and 2AF feed liquids pass through the degassing column, the flow rate is controlled at 160-200 L / h, and the temperature is 50°C.

[0071] ±5℃, air flow rate selected: 3m 3 / h;

[0072] S3 and 2AF are run thoroughly, and the bottom liquid in the 2AF feeding tank is run thoroughly every 2 batches.

[0073] S4. In case 1, the liquid level in the 2AF feed tank is 200mm, the flow rate of 2AF is controlled to 45±2.25L / h, and the flow rate of 2AX is controlled to 20±1L / h.

[0074] S5. Waste kerosene from the oil removal tank is completely processed through the pulse extraction column in one go.

[0075] S6. Control the initial concentration of plutonium in 2AF to A ± 0.5 g / L.

[0076] Sampling and analysis of nitrite content in the 2AF feed tank effectively controlled the nitrite content at 3-5 mg / L. The operation of the 2BX column was observed. Stable operation was characterized by column temperature maintained at 45±5℃, stable fluctuations in interface, column weight, and density, and no occurrence of situation 2, indicating no organic phase entrainment. Through the above methods, stable operation of plutonium reduction and back-extraction was achieved.

[0077] In this embodiment, the goal of stable operation of plutonium reduction and back-extraction was achieved, with stable column temperature of the 2BX column and stable fluctuations in interface, column weight, and density.

[0078] Example 2

[0079] This embodiment provides a method for stable plutonium reduction and back-extraction operation. The method includes: 2AF operation via an oxidation column, operation via a degassing column, complete 2AF operation, one-time passage of waste kerosene, and specifying the initial plutonium concentration in 2AF. The apparatus is shown in the attached diagram. Figure 1 Appendix Figure 2 Appendix Figure 3 As shown.

[0080] The method includes the following steps:

[0081] When S1 and 2AF feed solutions pass through the oxidation column, the flow rate is controlled at 160-200 L / h, and n is selected as 2.2;

[0082] When S2 and 2AF feed liquids pass through the degassing column, the liquid flow rate is controlled at 160-200 L / h, and the gas flow rate is 3±1 m³ / h. 3 / h, temperature 50±5℃;

[0083] S3 and 2AF are run thoroughly, and the bottom liquid in the 2AF feeding tank is run thoroughly every 3 batches.

[0084] S4. In case 1, the liquid level in the 2AF feed tank is 200mm, the flow rate of 2AF is controlled to 45±2.25L / h, and the flow rate of 2AX is controlled to 20±1L / h.

[0085] The liquid level in the feed tank of S5 and 2AF first-stage airlift constant level rises, followed by a significant rise in the liquid level in the organic phase outlet separator of column 2AX.

[0086] In S6 and Case 2, the flow rate of 2AF is controlled to 55±5.5L / h and the flow rate of 2AX is controlled to 10L / h.

[0087] S7. Waste kerosene from the oil removal tank is completely processed through the pulse extraction column in one go;

[0088] S8. The initial concentration of plutonium in 2AF is controlled at A ± 0.5 g / L.

[0089] In case 2, it can be determined that 2AF has been running into the organic phase. Sampling and analysis of the nitrite content in the 2AF feed tank showed that the content was slightly higher than that in Example 1. It can be determined that when n is increased, the gas flow rate of the degassing column also needs to be appropriately increased. The entrainment of nitrite in the organic phase can be determined. The operation of 2BX column fluctuated slightly but was generally stable. The column temperature was maintained at 45±5℃, and the interface, column weight, and density fluctuated stably.

[0090] In this embodiment, stable operation of plutonium reduction and back-extraction is achieved, the 2BX column temperature is stable, and the interface, column weight, and density fluctuate stably.

[0091] Example 3

[0092] This embodiment provides a method for stable plutonium reduction and back-extraction operation. The method includes: 2AF operation via an oxidation column, operation via a degassing column, complete 2AF operation, one-time passage of waste kerosene, and specifying the initial plutonium concentration in 2AF. The apparatus is shown in the attached diagram. Figure 1 Appendix Figure 2 Appendix Figure 3 As shown.

[0093] The method includes the following steps:

[0094] When S1 and 2AF feed solutions pass through the oxidation column, the flow rate is controlled at 160-200 L / h, and n is selected as 2.2;

[0095] When S2 and 2AF feed liquids pass through the degassing column, the liquid flow rate is controlled at 160-200 L / h, and the gas flow rate is 7±1 m³ / h. 3 / h, temperature 50±5℃;

[0096] S3. Slight entrainment was found in the washing acid solution, and the plutonium concentration was slightly increased in the sample analysis.

[0097] S4 and 2AF are run thoroughly, and the bottom liquid in the 2AF feeding tank is run thoroughly every 2 batches.

[0098] S5. Waste kerosene from the oil removal tank is completely processed through the pulse extraction column in one go.

[0099] S6. Control the initial concentration of plutonium in 2AF to A ± 0.5 g / L.

[0100] The rise in the washing acid level caused by the change in the degassing column gas flow rate indicates that increasing the degassing column gas flow rate too high will result in severe phase entrainment. Therefore, it is recommended to control the degassing column gas flow rate within the method range. Sampling and analysis of the nitrite content in the 2AF feed tank effectively controlled the nitrite content at 3-5 mg / L. The operation of the 2BX column was observed, and the column temperature was maintained at 45±5℃. The interface, column weight, and density fluctuated stably, indicating stable operation.

[0101] In this embodiment, stable plutonium reduction and back-extraction operation is achieved, the 2BX column temperature is stable, and the interface, column weight, and density fluctuate stably.

[0102] The present application has been described in detail above with reference to the accompanying drawings and embodiments. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present application. All content not described in detail in this application can be derived from existing technology.

Claims

1. A plutonium reduction and back-extraction method, characterized in that, The method includes: The initial concentration of plutonium in 2AF was controlled based on the flow rate ratio and the plutonium enrichment factor. When the 2AF feed liquid passes through the oxidation column, the flow rate is controlled at 160-200 L / h; When the 2AF feed liquid passes through the degassing column, the liquid flow rate is controlled at 160-200 L / h; The bottom liquid in the 2AF feeding tank is thoroughly processed every two or three batches, and the waste kerosene in the oil removal tank is completely processed through the pulse extraction column in one go.

2. The plutonium reduction and back-extraction method according to claim 1, characterized in that, The method further includes: When the 2AF feed solution passes through the oxidation column, NO is controlled. x The ratio of the reduction value to 2AF is 1.8~2.

2.

3. The plutonium reduction and back-extraction method according to claim 1, characterized in that, The method further includes: The temperature of the 2AF feed liquid is 50±5℃ when it passes through the degassing column.

4. The plutonium reduction and back-extraction method according to claim 3, characterized in that, The method further includes: When the 2AF feed liquid passes through the degassing column, the air flow rate control adjustment range is 2-4 m³ / h.

5. The plutonium reduction and back-extraction method according to claim 1, characterized in that, The residual liquid in the 2AF feeding tank is thoroughly removed every two or three batches, specifically including: When the liquid level in the 2AF feeding tank reaches 200mm, the flow rate of 2AF is controlled to 45±2.25 L / h and the flow rate of 2AX is controlled to 20±1 L / h.

6. The plutonium reduction and back-extraction method according to claim 1, characterized in that, The residual liquid in the 2AF feeding tank is thoroughly removed every two or three batches, specifically including: When the liquid level in the 2AF feed primary air extraction constant level pre-tank rises, or when the liquid level in the 2AX column organic phase outlet separator rises above the preset threshold, the 2AF flow rate is controlled to 55 L / h and the 2AX flow rate is controlled to 10 L / h.

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