Kettle evaporator denitration method in spent fuel post-treatment

Abstract

The invention discloses a method for denitration of a kettle type evaporator in spent fuel post-treatment. The method comprises the following steps: S1, medium radioactive waste liquid is conveyed into the kettle type evaporator through a medium radioactive waste liquid feeding pipeline; s2, heating through a heating coil outside the kettle type evaporator; s3, medium radioactive waste liquid is continuously conveyed into the kettle type evaporator through a medium radioactive waste liquid feeding pipeline; s4, observing the change of a thermometer and the change of a densimeter, and when the density of the lower part of the solution reaches 1.112 g / cm < 3 > or the temperature reaches 105 DEG C, adding a formaldehyde solution into the kettle type evaporator through a formaldehyde pipeline; s5, when the density of the lower part of the solution in the kettle type evaporator reaches 1.125 g / cm < 3 > or the temperature reaches 110 DEG C, stopping adding the radioactive waste liquid, and only adding the formaldehyde solution; s6, when the density of the lower part of the solution in the kettle type evaporator is reduced to 1.112-1.125 g / cm < 3 >, or the temperature is reduced to 103-105 DEG C, repeating the step S4; and when the density of the lower part of the solution is reduced to 1.08-1.112 g / cm < 3 >, or the temperature is reduced to 97-99, repeating the step S3.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear waste treatment, and more particularly to a method for denitrification of a kettle evaporator in spent fuel post-processing. Background Art

[0002] Radioactive liquid waste in spent fuel reprocessing is treated by evaporation. The evaporation method uses the characteristics of salt and most radioactive substances in radioactive liquid waste that are not easy to volatilize, so as to achieve the purpose of concentrating and purifying the waste liquid. Generally, evaporation treatment uses a kettle evaporator or an externally heated natural circulation evaporator. The kettle evaporator has the advantages of simple operation, convenient maintenance, and easy to achieve continuous evaporation-denitrification. In the reprocessing of spent fuel, intermediate-level waste liquid is evaporated and concentrated by a kettle evaporator. In order to reduce the corrosion of the equipment during the boiling process of the acidic intermediate-level waste liquid, as well as to increase the concentration multiple and improve the storage performance of the waste liquid, formaldehyde needs to be added during the waste liquid treatment process to denitrify the waste liquid to reduce the nitric acid concentration of the concentrated liquid. In the previous formaldehyde denitrification process of intermediate waste liquid, there were no clear regulations on the denitrification operation mode, denitrification time, formaldehyde addition amount, and acidity control, which led to many problems in the denitrification process, such as the concentrated liquid acidity was too high, which was not conducive to storage in large tanks; the denitrification time was long, and the formaldehyde consumption increased; the denitrification was unstable, and formaldehyde accumulated, resulting in unstable negative pressure in the kettle evaporator; the denitrification effect was poor, resulting in the secondary steam condensate acidity being too high, affecting the next stage of evaporation, etc. The control of the denitrification process is crucial for the stable and effective operation of the evaporator. Summary of the invention

[0003] The purpose of the present invention is to fix the denitration parameters and form a new denitration method by applying it in the actual operation process to the deficiencies existing in the existing denitration technology. In the process of denitration of intermediate-level waste liquid, the new method is used to improve the processing efficiency of the kettle evaporator; increase the concentration multiple of the intermediate-level waste liquid; control the acidity of the concentrated liquid for easy storage; reduce the amount of formaldehyde added to avoid excessive formaldehyde addition leading to negative pressure instability or violent boiling; control the denitration process of the intermediate-level waste liquid for safe and stable operation.

[0004] The technical solution of the present invention is as follows: A method for denitrification of a kettle evaporator in spent fuel post-processing, comprising the following steps:

[0005] S1: transporting the intermediate radioactive waste liquid into the kettle evaporator through the intermediate radioactive waste liquid feeding pipeline;

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

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

[0008] S4: Observe the changes in the thermometer and the density meter. When the density of the lower part of the solution reaches 1.112 g / cm 3 When the temperature reaches 105°C, formaldehyde solution is added into the kettle evaporator through the formaldehyde pipeline;

[0009] S5: When the density of the lower part of the solution in the kettle evaporator reaches 1.125g / cm 3 When the temperature reaches 110℃, stop adding the radioactive waste liquid and only add the formaldehyde solution;

[0010] S6: When the density of the lower part of the kettle evaporator solution drops to 1.112-1.125 g / cm 3 When the temperature drops to 103-105℃, repeat S4; when the density of the lower part of the solution drops to 1.08-1.112g / cm 3 When the temperature drops to 97-99, repeat S3.

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

[0012] In S1 and S3, the liquid level in the kettle evaporator is maintained at 3400mm-3600mm.

[0013] In S2, 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, and the temperature is 97-99°C.

[0014] In S4, a formaldehyde solution with a volume fraction of 37% is added to the kettle evaporator through a formaldehyde pipeline, and the addition flow rate is 30-50 L / h.

[0015] In S4, the thermometer and the density meter are observed, and the density of the lower part of the solution in the kettle evaporator is maintained relatively stable by adjusting the amount of radioactive waste liquid and formaldehyde added.

[0016] In S5, if only formaldehyde solution is added, the density of the lower part of the solution in the kettle evaporator no longer decreases, or the temperature no longer decreases, indicating that the concentration has been completed.

[0017] The concentrated liquid in the kettle evaporator is transferred out through the conveying equipment, and new intermediate radioactive waste liquid is added again, and the above S1-S5 are repeated.

[0018] In S6, when the density of the lower part of the kettle evaporator solution drops to 1.112-1.125 g / cm 3 When the temperature drops to 103-105°C, S4 is repeated.

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

[0020] The remarkable effects of the present invention are:

[0021] (1) During the denitrification process of the intermediate waste liquid, the operation is safe and stable;

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

[0023] (3) The waste liquid treatment efficiency is high, the waste liquid concentration multiple 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 to the evaporator and storage tank;

[0025] (5) The denitrification efficiency is improved, and the acidity of the secondary steam condensate is low, which reduces the evaporation pressure of the next stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of denitrification in a kettle evaporator in spent fuel reprocessing;

[0027] In the figure: thermometer and density meter 1, medium radioactive waste liquid feed pipeline 2, formaldehyde pipeline 3, heating coil 4, density meter 5, liquid level meter 6. DETAILED DESCRIPTION

[0028] 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.

[0029] 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.

[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 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.

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0032] A kettle evaporator, with a heating coil 4 wound around the outside, and a conveying device connected inside the kettle evaporator, through which liquid can be conveyed into the kettle evaporator; a thermometer 1, a density meter 5, and a liquid level meter 6 are installed at the bottom; a radioactive waste liquid feed pipeline 2 and a formaldehyde pipeline 3 are installed inside; the density meter 5 is used to measure the bottom density of the solution in the kettle evaporator;

[0033] A method for denitrification of a kettle evaporator in spent fuel post-processing, comprising the following steps:

[0034] S1: delivering the intermediate radioactive waste liquid (acidity: 1.8-2.1 mol / L) into the kettle evaporator through the intermediate radioactive waste liquid feed pipeline 2 until the liquid level reaches 3400 mm-3600 mm, at which time the volume of the intermediate radioactive waste liquid in the kettle evaporator is the initial volume;

[0035] S2: Heating is performed by the 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, and the temperature is 97-99°C;

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

[0037] S4: Observe the changes in the thermometer and the density meter. When the density of the lower part of the solution reaches 1.112 g / cm 3 When the temperature reaches 105°C, a 37% formaldehyde solution is added to the kettle evaporator through the formaldehyde pipeline 3, and the addition flow rate is 30-50L / h, which is determined by the acidity of the intermediate radioactive waste liquid. This stage is the continuous feeding denitrification stage, that is, the intermediate radioactive waste liquid (acidity: 1.8-2.1mol / L) and the formaldehyde solution are simultaneously delivered to the kettle evaporator, and the thermometer and the density meter 1 are observed at the same time. By adjusting the addition amount of the intermediate radioactive waste liquid and formaldehyde, the density of the solution in the kettle evaporator is maintained relatively stable, neither increasing nor decreasing too quickly.

[0038] S5: As the concentration of waste liquid increases, the density will increase. When the density of the lower part of the kettle evaporator solution reaches 1.125g / cm 3When the temperature reaches 110°C, stop adding the intermediate-level radioactive waste liquid and only add the formaldehyde solution. This stage is the insulation and denitrification stage. If it is found that only the formaldehyde solution is added and the density of the lower part of the kettle evaporator solution no longer decreases, or the temperature no longer decreases, indicating that the concentration has been completed, the concentrated liquid in the kettle evaporator is transferred out through the conveying equipment, and new intermediate-level radioactive waste liquid (acidity: 1.8-2.1 mol / L) is added again, and the above steps are repeated.

[0039] S6: Only formaldehyde solution is added, and the density of the solution in the kettle evaporator will gradually decrease. When the density of the lower part of the kettle evaporator drops to 1.112-1.125g / cm 3 When the temperature drops to 103-105℃, repeat S4; when the density drops to 1.08-1.112g / cm 3 When the temperature drops to 97-99, repeat S3;

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 denitrification of a kettle evaporator in spent fuel post-processing, characterized in that: The following steps are involved: S1: transporting the intermediate radioactive waste liquid to the kettle evaporator through the intermediate radioactive waste liquid feed pipeline (2); S2: Heating by the heating coil (4) outside the kettle evaporator; S3: continuing to transport the intermediate-level radioactive waste liquid into the kettle evaporator through the intermediate-level radioactive waste liquid feeding pipeline (2); S4: Observe the changes in the thermometer (1) and the density meter (5). When the density of the lower part of the solution reaches 1.112 g / cm 3 When the temperature reaches 105°C, formaldehyde solution is added into the kettle evaporator through the formaldehyde pipeline (3); S5: When the density of the lower part of the solution in the kettle evaporator reaches 1.125g / cm 3 When the temperature reaches 110℃, stop adding the radioactive waste liquid and only add the formaldehyde solution; S6: When the density of the lower part of the kettle evaporator solution drops to 1.112-1.125 g / cm 3 When the temperature drops to 103-105℃, repeat S4; when the density of the lower part of the solution drops to 1.08-1.112g / cm 3 When the temperature drops to 97-99°C, repeat S3.

2. The method for denitrification using a kettle evaporator in spent fuel post-processing according to claim 1, characterized in that: In S1, S3 and S4, the acidity of the intermediate radioactive waste liquid is 1.8-2.1 mol / L.

3. The method for denitrification using a kettle evaporator in spent fuel post-processing according to claim 1, characterized in that: In S1 and S3, the liquid level in the kettle evaporator is maintained at 3400mm-3600mm.

4. The method for denitrification using a kettle evaporator in spent fuel post-processing according to claim 1, characterized in that: In S2, 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, and the temperature is 97-99°C.

5. The method for denitrification using a kettle evaporator in spent fuel post-processing according to claim 1, characterized in that: In S4, a formaldehyde solution with a volume fraction of 37% is added to the kettle evaporator through the formaldehyde pipeline (3) at a flow rate of 30-50 L / h.

6. The method for denitrification using a kettle evaporator in spent fuel post-processing according to claim 1, characterized in that: In S4, the thermometer (1) and the density meter (5) are observed, and the density of the lower part of the solution in the kettle evaporator is maintained relatively stable by adjusting the amount of radioactive waste liquid and formaldehyde added.

7. The method for denitrification using a kettle evaporator in spent fuel post-processing according to claim 1, characterized in that: In S5, if only formaldehyde solution is added, the density of the lower part of the solution in the kettle evaporator no longer decreases, or the temperature no longer decreases, indicating that the concentration has been completed.

8. The method for denitrification using a kettle evaporator in spent fuel post-processing according to claim 7, characterized in that: The concentrated liquid in the kettle evaporator is transferred out through the conveying equipment, and new intermediate radioactive waste liquid is added again, and the above S1-S5 are repeated.

9. The method for denitrification using a kettle evaporator in spent fuel post-processing according to claim 1, characterized in that: In S6, when the density of the lower part of the kettle evaporator solution drops to 1.112-1.125 g / cm 3 When the temperature drops to 103-105°C, S4 is repeated.

10. The method for denitrification using a kettle evaporator in spent fuel post-processing according to claim 9, characterized in that: In S6, when the density of the lower part of the solution drops to 1.08-1.112 g / cm 3 When the temperature drops to 97-99, repeat S3.

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