A method for denitrification using a batch evaporator in spent fuel reprocessing

Abstract

A method for denitrification using a stirred tank evaporator in spent fuel reprocessing includes the following steps: S1: Feeding radioactive waste liquid into the stirred tank evaporator through a radioactive waste liquid feed pipe; S2: Heating the solution using a heating coil outside the stirred tank evaporator; S3: Continuing to feed radioactive waste liquid into the stirred tank evaporator through the radioactive waste liquid feed pipe; S4: Observing changes in the thermometer and hydrometer, and determining the solution density at the bottom when it reaches 1.112 g / cm³. 3 When the temperature reaches 105℃, formaldehyde solution is added to the autoclave through the formaldehyde pipeline; S5: When the density of the solution at the bottom of the autoclave reaches 1.125 g / cm³. 3 When the temperature reaches 110℃, stop adding the radioactive waste liquid and only add formaldehyde solution; S6: When the density of the solution at the bottom of the autoclave decreases to 1.112-1.125 g / cm³ 3 When the temperature drops to 103-105℃, repeat S4; when the density of the lower part of the solution drops to 1.08-1.112 g / cm³. 3 When the temperature drops to 97-99 degrees Celsius, repeat S3.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear waste treatment, in particular to a method for removing nitrate from a kettle evaporator in spent fuel reprocessing. BACKGROUND

[0002] Radioactive waste liquid in spent fuel reprocessing is treated by evaporation. The evaporation method uses the characteristics that salt and most radioactive substances in the radioactive waste liquid are not easy to evaporate, so as to achieve the purpose of concentrating and purifying the waste liquid. Generally, kettle evaporators or externally heated natural circulation evaporators are used for evaporation treatment, and the kettle evaporator has the advantages of simple operation, convenient maintenance, and easy implementation of continuous evaporation-nitrate removal. In spent fuel reprocessing, kettle evaporators are used for evaporation and concentration of intermediate-level waste liquid. In order to reduce the corrosion of the equipment during the boiling process of the acidic intermediate-level waste liquid, and to improve the concentration multiple and the storage performance of the waste liquid, formaldehyde needs to be added to the waste liquid during the treatment process to remove nitrate and reduce the concentration of nitric acid in the concentrated liquid. In the past formaldehyde removal process of intermediate-level waste liquid, there is no clear specification for the operation mode, removal time, formaldehyde addition amount, and acidity control of the removal process, which leads to many problems in the removal process, such as high acidity of the concentrated liquid, which is not conducive to storage in a large tank; long removal time and high formaldehyde consumption; unstable removal, accumulation of formaldehyde, leading to unstable negative pressure of the kettle evaporator; poor removal effect, leading to high acidity of the secondary steam condensate, affecting the next stage of evaporation, etc. The control of the removal process is crucial for the stable and effective operation of the evaporator. SUMMARY

[0003] The purpose of the present application is to fix the removal parameters by applying them in actual operation, forming a new removal method, to overcome the shortcomings of existing removal technologies. In the removal process of intermediate-level waste liquid, the new method improves the processing efficiency of the kettle evaporator, increases the concentration multiple of the intermediate-level waste liquid, controls the acidity of the concentrated liquid for easy storage, reduces the amount of formaldehyde added, avoids excessive addition of formaldehyde leading to unstable negative pressure or boiling, and controls the removal process of the intermediate-level waste liquid for safe and stable operation.

[0004] The technical solution of the present application is as follows: a method for removing nitrate from a kettle evaporator in spent fuel reprocessing, comprising the following steps:

[0005] S1: delivering the intermediate-level radioactive waste liquid to the kettle evaporator through the intermediate-level radioactive waste liquid feeding pipeline;

[0006] S2: heating by the heating coil outside the kettle evaporator;

[0007] S3: continuously feeding the intermediate-level radioactive waste liquid to the kettle evaporator through the intermediate-level radioactive waste liquid feeding pipeline;

[0008] S4: Observe the changes in the thermometer and hydrometer. When the density of the lower part of the solution reaches 1.112 g / cm³... 3 When the temperature reaches 105℃, formaldehyde solution is added into the autoclave through the formaldehyde pipeline.

[0009] S5: When the density of the solution at the bottom of the autoclave reaches 1.125 g / cm³ 3 When the temperature reaches 110℃, stop adding the radioactive waste liquid and only add formaldehyde solution.

[0010] S6: When the density of the solution at the bottom of the autoclave decreases to 1.112-1.125 g / cm³ 3 When the temperature drops to 103-105℃, repeat S4; when the density of the lower part of the solution decreases to 1.08-1.112 g / cm³. 3 When the temperature drops to 97-99 degrees Celsius, repeat S3.

[0011] In S1, S3, and S4, the acidity of the radioactive waste liquid is 1.8-2.1 mol / L.

[0012] In S1 and S3, the liquid level inside the autoclave is maintained at 3400mm-3600mm.

[0013] In S2, when the liquid level in the autoclave begins to drop, it indicates that the radioactive waste liquid in the autoclave has been heated to boiling, with a temperature of 97-99°C.

[0014] In S4, a 37% formaldehyde solution is added to the autoclave via a formaldehyde pipeline at a flow rate of 30-50 L / h.

[0015] In S4, the thermometer and hydrometer are used to observe how the density of the solution in the lower part of the autoclave is maintained relatively stable by adjusting the amount of radioactive waste liquid and formaldehyde added.

[0016] In S5, if only formaldehyde solution is added, and the density of the solution at the bottom of the autoclave no longer decreases, or the temperature no longer decreases, it indicates that the concentration is complete.

[0017] The concentrated liquid in the autoclave is transferred out using a conveying device, and new radioactive waste liquid is added back in, repeating the above steps S1-S5.

[0018] In S6, when the density of the solution at the bottom of the autoclave decreases to 1.112-1.125 g / cm³... 3 When the temperature drops to 103-105℃, repeat S4.

[0019] In S6, when the density of the lower part of the solution decreases to 1.08-1.112 g / cm³ 3 When the temperature drops to 97-99, repeat S3.

[0020] The significant advantages of this invention are:

[0021] (1) The denitrification process of the intermediate-stage waste liquid is safe and stable;

[0022] (2) Reduce the amount of formaldehyde added to avoid formaldehyde accumulation in the evaporator and avoid negative pressure instability or boiling phenomenon.

[0023] (3) The waste liquid treatment efficiency is high, the waste liquid concentration factor is increased, and the waste liquid volume is reduced;

[0024] (4) Control the acidity of the concentrate to ensure stability, facilitate storage, and reduce corrosion of the evaporator and storage tank;

[0025] (5) Improved denitrification efficiency and low acidity of secondary steam condensate, reducing the pressure of the next stage of evaporation. Attached Figure Description

[0026] Figure 1 A schematic diagram of denitrification using a batch evaporator in spent fuel reprocessing;

[0027] In the diagram: 1. Thermometer and hydrometer; 2. Inlet pipe for radioactive waste liquid; 3. Formaldehyde pipe; 4. Heating coil; 5. Hydrometer; 6. Level gauge. Detailed Implementation

[0028] Many specific details are set forth in the following description to provide a full understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of this application; therefore, this application is not limited to the specific embodiments disclosed below.

[0029] The terminology used in one or more embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the scope of one or more embodiments of this application. The singular forms “a,” “the,” and “the” used in one or more embodiments of this application and in the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” used in one or more embodiments of this application refers to and includes any or all possible combinations of one or more associated listed items.

[0030] It should be understood that although the terms first, second, etc., may be used to describe various information in one or more embodiments of this application, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first may also be referred to as second without departing from the scope of one or more embodiments of this application, and similarly, second may also be referred to as first.

[0031] The patent will now be described in further detail with reference to the accompanying drawings.

[0032] A kettle-type evaporator has an externally wound heating coil 4 and an internally connected conveying device that can convey liquid into the kettle-type evaporator. A thermometer 1, a densitometer 5, and a level gauge 6 are installed at the bottom. A radioactive waste liquid inlet pipe 2 and a formaldehyde pipe 3 are installed inside. The densitometer 5 is used to measure the density of the solution at the bottom of the kettle-type evaporator.

[0033] A method for denitrification using a batch evaporator in spent fuel reprocessing includes the following steps:

[0034] S1: The intermediate radioactive waste liquid (acidity: 1.8-2.1 mol / L) is transported into the autoclave through the intermediate radioactive waste liquid feed pipe 2 until the liquid level reaches 3400mm-3600mm. At this time, the volume of intermediate radioactive waste liquid in the autoclave is the initial volume.

[0035] S2: Heated by heating coil 4 outside the kettle evaporator. When the liquid level in the kettle evaporator begins to drop, it indicates that the radioactive waste liquid in the kettle evaporator has been heated to boiling, with a temperature of 97-99℃.

[0036] S3: Continue to feed the intermediate radioactive waste liquid (acidity: 1.8-2.1 mol / L) into the autoclave through the intermediate radioactive waste liquid feed pipe 2, so that the liquid level in the autoclave is always maintained at 3400mm-3600mm. This stage is the cleaning operation stage; as the feed rate increases, the temperature will gradually rise.

[0037] S4: Observe the changes in the thermometer and hydrometer. When the density of the lower part of the solution reaches 1.112 g / cm³... 3 When the temperature reaches 105℃, a 37% (v / v) formaldehyde solution is added to the autoclave evaporator through formaldehyde pipeline 3 at a flow rate of 30-50 L / h, depending on the acidity of the radioactive waste liquid. This stage is the continuous feeding denitrification stage, where radioactive waste liquid (acidity: 1.8-2.1 mol / L) and formaldehyde solution are simultaneously fed into the autoclave evaporator. The thermometer and hydrometer 1 are monitored, and the density of the solution in the autoclave evaporator is maintained relatively stable by adjusting the amount of radioactive waste liquid and formaldehyde added, ensuring that the density does not increase or decrease rapidly.

[0038] S5: As the concentration factor of the waste liquid increases, the density will increase. When the density of the solution at the bottom of the autoclave reaches 1.125 g / cm³... 3When the temperature reaches 110℃, stop adding the intermediate radioactive waste liquid and only add formaldehyde solution. This stage is the heat preservation and denitrification stage. If it is found that the density of the solution at the bottom of the kettle evaporator no longer decreases or the temperature no longer decreases after adding only formaldehyde solution, it indicates that the concentration is complete. Transfer the concentrated liquid in the kettle evaporator through the conveying equipment and add new intermediate radioactive waste liquid (acidity: 1.8-2.1 mol / L) to repeat the above steps.

[0039] S6: When only formaldehyde solution is added, the solution density in the autoclave will gradually decrease. When the density of the solution at the bottom of the autoclave decreases to 1.112-1.125 g / cm³... 3 When the temperature drops to 103-105℃, repeat step S4; when the density drops to 1.08-1.112 g / cm³... 3 When the temperature drops to 97-99°C, repeat S3;

[0040] The above description is merely 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 shall be included within the scope of protection of this patent.

[0041] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0042] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0043] The preferred embodiments disclosed above are merely illustrative of this application. The optional embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this application. These embodiments are selected and specifically described in this application to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to better understand and utilize this application.

Claims

1. A method for denitration in a post-treatment of spent fuel in a kettle evaporator, characterized by: The method comprises the following steps: S1: delivering the medium radioactive waste liquid into the kettle evaporator through the medium radioactive waste liquid feeding pipeline (2); S2: heating by the heating coil (4) outside the kettle evaporator; S3: continuously delivering the medium radioactive waste liquid into the kettle evaporator through the medium radioactive waste liquid feeding pipeline (2); S4: Observe the changes in the thermometer (1) and the hydrometer (5). When the density of the lower part of the solution reaches 1.112 g / cm³... 3 When the temperature reaches 105℃, formaldehyde solution is added into the autoclave through the formaldehyde pipeline (3); S5: When the density of the solution in the kettle evaporator reaches 1.125 g / cm 3 or the temperature reaches 110°C, stop adding the medium radioactive waste liquid and only add the formaldehyde solution; if only the formaldehyde solution is added, the density of the solution in the kettle evaporator no longer decreases, or the temperature no longer decreases, indicating that the concentration is complete. S6: when the solution lower density in the kettle evaporator drops to 1.112-1.125 g / cm 3 S4 is repeated; when the solution lower density drops to 1.08-1.112 g / cm 3 S3 is repeated.

2. The method of claim 1, wherein the method is used in a reprocessing of spent fuel. In S1, S3 and S4, the acidity of the medium radioactive waste liquid is 1.8-2.1 mol / L.

3. The method of claim 1, wherein the method is used in a reactor vessel of a nuclear fuel reprocessing plant. In S1 and S3, the liquid level in the kettle evaporator is kept at 3400-3600 mm.

4. The method of claim 1, wherein the method is a method of removing nitrogen oxides from a spent fuel reprocessing batch evaporator. In S2, when the liquid level in the kettle evaporator starts to drop, it indicates that the medium radioactive waste liquid in the kettle evaporator has been heated to boiling, and the temperature is 97-99 ℃.

5. The method of claim 1, wherein the method is used in a reactor vessel of a nuclear fuel reprocessing plant. In S4, the kettle evaporator is added with a formaldehyde solution with a volume fraction of 37% through the formaldehyde pipeline (3), and the flow rate is 30-50 L / h.

6. The method of claim 1, wherein the method is used in a reactor vessel of a nuclear fuel reprocessing plant. In S4, the thermometer (1) and the densimeter (5) are observed, and the addition amount of the medium radioactive waste liquid and the formaldehyde is adjusted to keep the density of the solution in the lower part of the kettle evaporator relatively stable.

7. The method of claim 1, wherein the method is a method of removing nitrogen oxides from a spent fuel reprocessing batch evaporator. After the concentration is completed, the concentrated liquid in the kettle evaporator is transferred out through the conveying equipment, new medium radioactive waste liquid is added, and the above steps S1-S5 are repeated.

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