Radioactive waste organic phase rectification pretreatment method

Abstract

A radioactive waste organic phase rectification pretreatment method comprises the following steps that a waste organic phase is conveyed into a mixing and clarifying tank A and a mixing and clarifying tank B through a waste organic phase metering pump, deionized water is conveyed into the mixing and clarifying tank A and the mixing and clarifying tank B through a deionized water tank, and water removal treatment is conducted in the mixing and clarifying tank A and the mixing and clarifying tank B; waste organic phases in the mixing and clarifying tank A and the mixing and clarifying tank B flow into a feeding tank after being pretreated, and water phases flow into an inorganic waste liquid tank.

Description

Technical Field

[0001] The invention relates to the technical field of radioactive waste organic phase treatment, and specifically to a radioactive waste organic phase distillation pretreatment device and method. Background Art

[0002] The radioactive waste organic phase distillation treatment facility is an important part of the closed cycle of spent fuel organic phase. It has been first applied in a nuclear facility operator in my country. It mainly recycles kerosene and TBP through distillation of waste organic phase to meet the principle of minimizing radioactive waste. The properties of TBP and kerosene are different from the boiling points of many degradation products. The boiling points of metal complexes and polymers are higher than TBP, while the boiling points of low-carbon alkanes and olefins are lower than kerosene. Therefore, the difference between the boiling points can be used to regenerate the contaminated solvent by distillation.

[0003] Entering the 21st century, a certain unit made technical improvements based on the vacuum flash distillation process, built a contaminated solvent distillation treatment facility, and verified it through bench and engineering chemical commissioning. The distillation products met the needs, but the shortcoming was that it did not take into account that TBP could not withstand high temperatures in a strong acidic atmosphere, so it was not continuously and stably applied through cold uranium engineering commissioning. At the same time, the TBP concentration in the TBP distillation tower was unbalanced, and the actual feed inlet was lower than the production outlet in the middle section of the TBP distillation tower. There was a problem of mixing raw materials and products, which reduced the separation efficiency of TBP and kerosene. Although the Karlsruhe plant in Germany and the Agge plant in France have achieved the recycling of waste organic phases through distillation and achieved a closed cycle of organic phases, the disadvantages are that the process is relatively complicated, there are many impurities in the raw materials, and the radioactive concentration of the products is relatively high.

[0004] At present, there is no clear engineering technology for the distillation and recycling of waste organic phase in spent fuel reprocessing plants. This is mainly because the waste organic phase after uranium and plutonium extraction will be subjected to radiolysis, pyrolysis and acidolysis, resulting in a large amount of impurities in the waste organic phase. For example, the presence of free water directly entering the distillation tower will cause the system temperature and pressure to be unstable. The presence of complex salts will cause coking and blockage of pipelines during the distillation process, and the system will not be able to operate continuously and stably. When the pH of the waste organic phase does not meet the distillation requirements, it will accelerate the deterioration rate of the organic phase in the reprocessing plant, resulting in a sharp increase in processing costs. Therefore, this patent designs and invents a waste organic phase pretreatment process to ensure that impurities in the waste organic phase before distillation are effectively removed, thereby ensuring the continuous and stable operation of the distillation facilities and realizing the recycling of radioactive waste organic phase in engineering. Summary of the invention

[0005] The purpose of the present invention is to provide a radioactive waste organic phase distillation pretreatment device and method, which overcomes the shortcomings of the waste organic phase entraining free water, inorganic salts and TBP complexing in the waste organic phase, and the waste organic phase showing strong acid properties in the uranium and plutonium separation process, which make the distillation process unable to operate continuously and stably.

[0006] The technical solution of the present invention is as follows: A method for pre-treatment of radioactive waste organic phase by distillation, comprising the following steps:

[0007] The waste organic phase is transported into the mixing and clarifying tank A and the mixing and clarifying tank B by the waste organic phase metering pump, and the deionized water tank transports the deionized water into the mixing and clarifying tank A and the mixing and clarifying tank B, and the water removal treatment is performed in the mixing and clarifying tank A and the mixing and clarifying tank B;

[0008] The waste organic phase in the mixing and settling tank A and the mixing and settling tank B flows into the feed tank after pretreatment, while the water phase flows into the inorganic waste liquid tank.

[0009] The deionized water tank transports deionized water into the mixing and clarifying tank A and mixing and clarifying tank B at a flow rate of 40-100L / h.

[0010] The flow rate of the waste organic phase entering the mixing and settling tank A and the mixing and settling tank B is controlled to be 400-1000L / h by the waste organic phase metering pump.

[0011] If the interface between the aqueous phase and the organic phase rises, the aqueous phase in the mixing and clarifying tank A and the mixing and clarifying tank B is discharged, or the deionized water flowing into the mixing and clarifying tank B from the deionized water tank is reduced.

[0012] If the waste organic phase at the outlet of mixing and settling tank A and mixing and settling tank B is greater than half of the total liquid level, deionized water will flow into mixing and settling tank B through the added deionized water tank.

[0013] If the waste organic phase in the feed tank still contains free water, the waste organic phase in the feed tank is returned to the dirty solvent buffer tank for reprocessing.

[0014] If the Na+ content in the waste organic phase of the feed tank increases by more than 20% compared to the Na+ content in the dirty solvent buffer tank, the nitric acid in the dilute nitric acid tank is allowed to enter the mixing and settling tank A and the mixing and settling tank B.

[0015] The flow ratio of the spent organic phase to the nitric acid is 10:1 to 20:1.

[0016] When the pH value of the waste organic phase in the mixing and settling tank A and the mixing and settling tank B does not meet the requirement of 5-7, the nitric acid in the nitric acid tank or the sodium hydroxide in the sodium hydroxide tank is introduced into the mixing and settling tank A and the mixing and settling tank B through the pipeline in a certain proportion, so as to adjust the pH value of the waste organic phase.

[0017] The flow ratio of the waste organic phase from the dirty solvent buffer tank to the nitric acid in the nitric acid tank or the sodium hydroxide in the sodium hydroxide tank is 10:1 to 15:1.

[0018] The remarkable effects of the present invention are:

[0019] 1. Removal of free water

[0020] When treating the waste organic phase containing free water, the present invention introduces a mixing and settling tank for pretreatment. By accurately controlling the interfaces and liquid levels at various levels in the mixing and settling tank, free water is effectively removed to prevent it from entering the TBP distillation tower, thereby avoiding the problem of unstable pressure in the TBP distillation tower. This pretreatment step is of great significance for ensuring the stable operation of the distillation tower. When stratification occurs in the received waste organic phase, measures need to be taken to separate the free water. Static stratification can separate a portion of water, but in the engineering radioactive stage, the waste organic phase may enter the waste liquid tank together with the water, further increasing the subsequent separation process. It is more economical and convenient to directly use a mixing and settling tank for pretreatment of the waste organic phase received from the upstream. In the process of free water separation, it is necessary to pay close attention to the interface and liquid level at one end of the water phase outlet of the mixing and settling tank. When the interface shows an obvious upward trend, it is necessary to adjust the water phase inlet flow to avoid the free water in the waste organic phase from entering and affecting the balance of the mixing and settling tank. During the process, the height difference between the interface and the liquid level is kept above 100 mm to avoid the water phase from entering the rear end waste organic phase storage tank.

[0021] 2. Removal of complex salts

[0022] The present invention aims at the problem of high complex salt content (such as Na+ content) in the waste organic phase, and removes about 20% of the salt by dilute acid washing, the concentration of dilute acid generally does not exceed 0.2 mol / L, and further reduces the salt content in the residual liquid by distillation treatment, thereby reducing the pipeline slagging rate. When the Na+ content in the waste organic phase is high, it will cause residues in the pipeline, and as the running time increases, the salt will precipitate on the inner wall of the pipeline until the pipeline is blocked.

[0023] 3. pH adjustment

[0024] When the pH value of the waste organic phase does not meet the requirement of 5-7, the present invention adjusts the pH in the mixing and settling tank. This step not only avoids acid hydrolysis or scaling of the residual liquid pipeline, but also ensures the smooth progress of the subsequent distillation process. When the pH of the waste organic phase is less than 5, it can be washed with a dilute alkaline solution, and when the pH is greater than 7, it can be washed with a dilute acid solution. When sodium hydroxide solution is used as the dilute alkaline solution for adjustment, the generated inorganic waste liquid has a radioactive α level that does not meet the conditions for evaporation of low-level waste liquid.

[0025] 4. Evaporation of pre-treatment wastewater

[0026] The inorganic waste liquid generated during the implementation of the present invention meets the conditions for evaporation treatment. The wastewater in the process of removing free water from the waste liquid is evaporated as low-level waste liquid. The radioactivity of the waste liquid generated during the pickling and desalting process meets the conditions for low-level waste liquid, and the acidity is adjusted according to a certain ratio to meet the low-level evaporation adjustment pH of 7-9. The waste organic phase is acidic. When the pH is less than 5, the radioactive alpha level of the inorganic waste liquid generated after washing with 1-5% sodium hydroxide solution will generally increase. The final analysis results will determine whether the waste liquid is treated as low-level waste liquid or medium-level waste liquid. When the pH of the waste organic phase is greater than 7, a dilute nitric acid solution with an acidity of ≤0.1 mol / L is generally used for adjustment, and the radioactivity of the inorganic waste liquid generated meets the evaporation treatment adjustment for low-level waste liquid treatment.

[0027] 5. Operation method

[0028] When the waste organic phase contains impurities, pre-treatment is performed by running the mixing and settling tank. Before the mixing and settling tank is operated, the tank filling operation is performed first, that is, the organic phase inlet and outlet valves and the water phase outlet valves of the mixing and settling tank are all closed, and only the water phase inlet valve is opened to fill the mixing and settling tank with water. When the liquid level of each level of the mixing and settling tank remains unchanged between 380-395mm, the tank filling is completed and the water phase inlet is closed.

[0029] Start the stirring paddles at each level of the mixing and clarifying tank, set the speed to 350r / min-410r / min, open the organic phase inlet valve, organic phase outlet valve, aqueous phase inlet valve, aqueous phase outlet valve, start the organic phase feed pump, control the organic phase feed rate to about 400L / h-480L / h, start the aqueous phase inlet control main valve, control the aqueous phase feed rate to about 40L / h-120L / h, control the liquid level at each level to 390mm-415mm by adjusting the stirring paddle speed and feed flow rate, and control the interface at each level to 200mm-320mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of a radioactive waste organic phase distillation pretreatment device;

[0031] Marks and corresponding parts names in the attached drawings:

[0032] In the figure: a dirty solvent buffer tank (1), a waste organic phase metering pump 2, a mixing and settling tank A (3), a mixing and settling tank B (4), a nitric acid tank (5), a deionized water tank (6), a sodium hydroxide tank (7), an inorganic waste liquid tank 8, and a feed tank 9. DETAILED DESCRIPTION

[0033] Many specific details are described in the following description to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present application, so the present application is not limited by the specific implementation disclosed below.

[0034] The terms used in one or more embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit one or more embodiments of the present application. The singular forms of "a", "said" and "the" used in one or more embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of the present application refers to and includes any or all possible combinations of one or more associated listed items.

[0035] It should be understood that, although the terms first, second, etc. may be used to describe various information in one or more embodiments of the present application, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of one or more embodiments of the present application, the first may also be referred to as the second, and similarly, the second may also be referred to as the first.

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0037] The technical scheme of the present invention is to add a waste organic phase pretreatment process, so that the organic phase entering the distillation tower meets the distillation requirements after being treated. First, the dissolved water content in the waste organic phase does not exceed 1%, and free water is not allowed to be contained. In order to avoid the radioactive waste organic phase containing free water, the free water is reasonably removed by utilizing the characteristics of free water and waste organic phase separation; second, TBP in the waste organic phase can extract many inorganic salts, especially easy to form a stable complex with nitrate, and part of the inorganic salts are removed by utilizing the principle of dilute acid washing; third, the pH value of the raw material is required to be 5-7 in the waste organic phase distillation process. When the acidity of the waste organic phase is too high, in order to avoid further increase of the acidity of the residual liquid caused by concentration, the thermal decomposition, hydrolysis and acidolysis of TBP are accelerated, and the waste organic phase that does not meet the pH standard can be further washed to meet the distillation requirements.

[0038] To achieve the above objectives, two to four mixing and clarifying tanks are added to the process flow shown at the front end of the TBP distillation tower to preliminarily pretreat the waste organic phase carrying impurities to prevent the impurities from affecting the stable operation of the TBP distillation tower.

[0039] The principle of the mixing and settling tank is mainly based on the different densities of the organic phase and the aqueous phase. According to the different interface and liquid level indication values, the waste organic phase is pretreated. The actual number of stirring stages is controlled by controlling the number of stirring motors. Each stage contains a mixing chamber and a clarification chamber. The dirty solvent enters from the first mixing chamber of the mixing and settling tank, and the treated liquid enters from the second mixing chamber of the mixing and settling tank. The two phases are in contact with each other to establish hydraulic equilibrium, and the pretreatment of the waste organic phase is achieved. The raw materials are purified for the first time before the dirty solvent enters the distillation tower to prevent impurities from entering the TBP distillation tower and affecting the operation of the system.

[0040] The free water carried by the waste organic phase, the complexation of inorganic salts with TBP in the waste organic phase, and the strong acid characteristics of the waste organic phase can all be passed through the mixing and clarification tank according to the attached Figure 1 The process pre-treats the raw materials. The pre-treatment process is as follows.

[0041] A radioactive waste organic phase distillation pretreatment device comprises a contaminated solvent buffer tank (1), the contaminated solvent buffer tank (1) is connected to a mixing and clarifying tank A (3) via a waste organic phase metering pump 2, the mixing and clarifying tank A (3) is connected to a mixing and clarifying tank B (4), and the mixing and clarifying tank A (3) and the mixing and clarifying tank B (4) are bidirectionally connected; the mixing and clarifying tank A (3) and the mixing and clarifying tank B (4) are both connected to an inorganic waste liquid tank 8 and a feed tank 9, and the nitric acid tank (5), a deionized water tank (6), and a sodium hydroxide tank (7) are all connected to the mixing and clarifying tank B (4);

[0042] A method for pretreatment of radioactive waste organic phase by distillation:

[0043] When the waste organic phase contains free water, the waste organic phase received from the upstream is first received into the dirty solvent buffer tank (1), and the waste organic phase is transported into the mixing and clarifying tank A (3) and the mixing and clarifying tank B (4) by the waste organic phase metering pump 2. Then, the deionized water and the waste organic phase are separated and dewatered in the mixing and clarifying tank A (3) and the mixing and clarifying tank B (4). The deionized water in the mixing and clarifying tank A (3) and the mixing and clarifying tank B (4) is provided by the front-end deionized water tank (6) and enters the mixing and clarifying tank A (3) and the mixing and clarifying tank B (4) by gravity. The water phase flow rate is controlled to 40-100 L / h, and the waste organic phase flow rate is controlled to 400-1000 L / h by the waste organic phase metering pump 2. The waste organic phase in the mixing and clarifying tank A (3) and the mixing and clarifying tank B (4) flows into the feed tank 9 after pretreatment.

[0044] The waste organic phase in the mixing and settling tank A (3) and the mixing and settling tank B (4) flows into the feed tank 9 after pretreatment, while the aqueous phase flows into the inorganic waste liquid tank 8.

[0045] In the mixing and settling tank A (3) and the mixing and settling tank B (4), the upper layer is the waste organic phase and the lower layer is the water phase. The interface between the waste organic phase and the water phase is the interface, and the top of the upper waste organic phase is the total liquid level. During operation, attention is paid to the total liquid level and the interface in the mixing and settling tank A (3) and the mixing and settling tank B (4). If the interface between the water phase and the waste organic phase rises, it means that the water content in the waste solvent from the waste solvent buffer tank (1) has increased. It is necessary to adjust the water phase inlet flow rate to discharge the water phase in the mixing and settling tank A (3) and the mixing and settling tank B (4), or reduce the deionized water flowing into the mixing and settling tank B (4) from the deionized water tank (6). Ensure that the interface of the waste organic phase outlet remains stable and does not exceed half of the total liquid level to avoid the organic phase after washing from carrying free water. If the waste organic phase in the feed tank 9 still contains free water, the waste organic phase in the feed tank 9 is continued to be returned to the waste solvent buffer tank (1) and further washed according to the above steps.

[0046] When the inorganic salt content of the waste organic phase affects the operation of the system, the Na+ content in the waste organic phase in the feed tank 9 is detected to be higher than 20% compared with the Na+ content in the dirty solvent buffer tank (1), and a dilute acid (molar concentration ≤ 0.2 mol / L) is used to reduce the salt content in the waste organic phase. The nitric acid passes through the dilute nitric acid tank (5) and enters the mixing and settling tank A (3) and the mixing and settling tank B (4). The flow ratio of the waste organic phase to the nitric acid is 10:1 to 20:1.

[0047] When the pH value of the waste organic phase in the mixing and settling tank A (3) and the mixing and settling tank B (4) does not meet the requirement of 5-7, according to the pH value of the waste organic phase in the waste solvent buffer tank, the nitric acid in the nitric acid tank (5) or the sodium hydroxide in the sodium hydroxide tank (7) is introduced into the mixing and settling tank A (3) and the mixing and settling tank B (4) through the pipeline in a certain proportion, and the pH value of the waste organic phase is adjusted according to the flow ratio of the waste organic phase from the waste solvent buffer tank (1) and the water phase supplied from 5 or 7 of 10:1 to 15:1 until the distillation requirement is met.

[0048] The radioactive inorganic waste liquid generated by the above-mentioned pretreatment of the radioactive waste organic phase meets the standards for medium and low-level waste liquid after adjustment, so it is treated by evaporation to achieve closed-loop treatment of the waste liquid.

[0049] The above description is only a preferred embodiment of this patent and is not intended to limit this patent. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this patent should be included in the scope of protection of this patent.

[0050] It should be noted that, for the above-mentioned method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the described action sequence, because according to the present application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present application.

[0051] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0052] The preferred embodiments of the present application disclosed above are only used to help explain the present application. The optional embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of the present application. The present application selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can understand and use the present application well.

Claims

1. A method for pretreatment of radioactive waste organic phase by distillation, characterized in that: The following steps are involved: The waste organic phase is transported into the mixing and settling tank A (3) and the mixing and settling tank B (4) through the waste organic phase metering pump (2), and the deionized water tank (6) transports deionized water into the mixing and settling tank A (3) and the mixing and settling tank B (4), and dewatering treatment is performed in the mixing and settling tank A (3) and the mixing and settling tank B (4); The waste organic phase in the mixing and settling tank A (3) and the mixing and settling tank B (4) flows into the feed tank 9 after pretreatment, while the aqueous phase flows into the inorganic waste liquid tank (8).

2. A method for pretreatment of radioactive waste organic phase by distillation according to claim 1, characterized in that: The deionized water tank (6) transports deionized water into the mixing and settling tank A (3) and the mixing and settling tank B (4) at a flow rate of 40-100 L / h.

3. A method for pretreatment of radioactive waste organic phase by distillation according to claim 1, characterized in that: The waste organic phase metering pump (2) controls the flow rate of the waste organic phase entering the mixing and settling tank A (3) and the mixing and settling tank B (4) to be 400-1000 L / h.

4. A method for pretreatment of radioactive waste organic phase by distillation according to claim 1, characterized in that: If the interface between the aqueous phase and the organic phase rises, the aqueous phase in the mixing and settling tank A (3) and the mixing and settling tank B (4) is discharged, or the deionized water flowing from the deionized water tank (6) into the mixing and settling tank B (4) is reduced.

5. A method for pretreatment of radioactive waste organic phase by distillation according to claim 1, characterized in that: If the waste organic phase at the outlet of the mixing and settling tank A (3) and the mixing and settling tank B (4) is greater than half of the total liquid level, deionized water is added to flow into the mixing and settling tank B (4) through a deionized water tank (6).

6. A method for pretreatment of radioactive waste organic phase by distillation according to claim 1, characterized in that: If the waste organic phase in the feed tank (9) still contains free water, the waste organic phase in the feed tank (9) is returned to the dirty solvent buffer tank (1) for reprocessing.

7. A method for pretreatment of radioactive waste organic phase by distillation according to claim 1, characterized in that: If the Na+ content in the waste organic phase of the feed tank (9) increases by more than 20% compared to the Na+ content in the dirty solvent buffer tank (1), the nitric acid in the dilute nitric acid tank (5) is allowed to enter the mixing and settling tank A (3) and the mixing and settling tank B (4).

8. A method for pretreatment of radioactive waste organic phase by distillation according to claim 7, characterized in that: The flow ratio of the spent organic phase to the nitric acid is 10:1 to 20:

1.

9. A method for pretreatment of radioactive waste organic phase by distillation according to claim 1, characterized in that: When the pH value of the waste organic phase in the mixing and settling tank A (3) and the mixing and settling tank B (4) does not meet the range of 5-7, nitric acid in the nitric acid tank (5) or sodium hydroxide in the sodium hydroxide tank (7) is introduced into the mixing and settling tank A (3) and the mixing and settling tank B (4) through a pipeline in a certain proportion, thereby adjusting the pH value of the waste organic phase.

10. A method for pretreatment of radioactive waste organic phase by distillation according to claim 9, characterized in that: The flow ratio of the waste organic phase from the dirty solvent buffer tank (1) to the nitric acid in the nitric acid tank (5) or the sodium hydroxide in the sodium hydroxide tank (7) is 10:1 to 15:1.

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