CN112893328B - Method for cleaning alkali metal residues and application thereof - Google Patents

Abstract

The invention relates to the field of industrial cleaning, in particular to a method for cleaning alkali metal residues and application thereof. The method comprises the following steps: contacting the dry gas stream with the surface having the alkali metal attached thereto, such that the alkali metal is released from the surface; the dry gas flow comprises a carrier gas and a solid cleaning medium, the cleaning medium comprises dry ice, and the content of the dry ice is more than 90 wt% based on the total weight of the cleaning medium. The method can realize drying and cleaning, avoids sodium water reaction, and greatly improves safety; residual sodium and other dirt can be removed quickly and effectively; the cleaning agent can almost have no residue and no secondary pollution after cleaning, and is clean and environment-friendly; can reduce the corrosion and damage to the cleaning surface and prolong the service life of the product.

Description

A kind of method and application of cleaning alkali metal residue

technical field

The invention relates to the field of industrial cleaning, in particular to a method for cleaning alkali metal residues and application thereof.

Background technique

Nuclear power is of great significance for solving energy shortages, environmental degradation and climate warming. Sodium-cooled fast reactor technology has become a key reactor type due to its inherent safety and high economy. As a heat transfer medium and coolant, sodium metal has high chemical activity and can burn in oxygen, chlorine, fluorine, and bromine vapor; it reacts violently with water or water vapor to release hydrogen, exothermic a lot, and burns or explodes; exposure It can burn itself in the air, and explode to make the melt splash; it can react violently with halogens, phosphorus, many oxides, oxidants and acids.

At present, there are six methods used in cleaning sodium-cooled fast reactors at home and abroad: water cleaning method, steam cleaning method, water mist cleaning method, alcohol cleaning method, vacuum distillation method and vacuum cleaning method. The water cleaning method is a simple and direct method of cleaning sodium equipment, that is, placing the sticky sodium equipment under the water spray head to shower, and the sodium can be completely removed. The steam cleaning method is the same as the water cleaning method, for example, after cleaning the sticky sodium equipment with a mixture of nitrogen and 15% water vapor, rinse with deionized water, and then dry with nitrogen or vacuum. The water mist cleaning method is to install a nozzle on the wall of the cleaning well, and the nozzle generates water mist, and the carrier gas is nitrogen, carbon dioxide or their mixture; the water mist formed by sodium and the mixture of small water droplets and carrier gas at ambient temperature gradually occurs. The reaction produces sodium hydroxide, and the hydrogen is filtered and diluted and discharged into the ventilation duct. Alcohol cleaning uses alcohol instead of water to react with sodium. The vacuum distillation method is to put the sodium-containing equipment into the cleaning container, heat it to 200 °C under normal pressure to melt the sodium and discharge it, then the cleaning container is heated to 500 °C, and the sodium remaining on the equipment is distilled by vacuuming. Sodium becomes carbonate and is preserved. The vacuum cleaning method is that under vacuum, sodium interacts with water and aqueous solutions, and the heat of reaction is brought out by the evaporation of water under vacuum.

The above-mentioned six methods currently used for cleaning sodium-cooled fast reactors all have many shortcomings such as serious safety hazards in actual operation, and the current cleaning regulations and related safety regulations for sodium-cooled fast reactors are still in a blank state.

From the experience of foreign decommissioning work, the removal of residual sodium accounts for a large workload in the cleaning process. Therefore, it is very important to find a safer, more efficient and environmentally friendly sodium removal process for the cleaning treatment of sodium-cooled fast reactors.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the defects such as serious potential safety hazards existing in the existing cleaning process for treating sodium residues, and provide a method for cleaning alkali metal residues and applications thereof. The method of the invention can realize dry cleaning, avoid sodium-water reaction, and greatly improve safety; can quickly and effectively remove residual sodium and other dirt; can realize almost no residue and no secondary pollution after cleaning, and is clean and environmentally friendly; It can reduce the corrosion and damage to the cleaning surface and improve the service life of the product.

The inventors of the present invention found that the current cleaning methods for sodium-cooled reactors generally have the following problems: first, the safety is extremely low, and a large amount of heat and hydrogen are often generated during the treatment process, which may cause combustion and explosion if not treated in time; second, clean The treatment takes a long time and needs to be forced to stop work for a long time; 3. A large amount of waste water is generated, and the discharge of waste water from the equipment and subsequent waste water treatment require a lot of manpower, financial resources and time costs; 4. When sandblasting or chemical purification is used When the cleaning medium is contaminated with radioactive elements, it will increase the time and money for wastewater treatment; etc.

The inventors of the present invention have found that by using dry ice in the cleaning of the sodium-cooled reactor, the metal sodium and other contaminants remaining in the equipment and components can be effectively removed; the cleaning is fast and accurate, and there is no need for long-term shutdown; the cleaning process does not generate High temperature and flammable and explosive gas, high safety; no waste water is generated after cleaning, and no complicated follow-up treatment is required. Further, the inventors of the present invention, through in-depth research, have found a more preferred cleaning method with higher cleaning efficiency and less amount of dry ice.

A first aspect of the present invention provides a method for cleaning alkali metal residues, the method comprising: contacting a drying gas stream with a surface adhering to the alkali metal, so that the alkali metal is detached from the surface; wherein the drying gas stream comprises a carrier gas and a A solid cleaning medium, the cleaning medium includes dry ice, and based on the total weight of the cleaning medium, the content of the dry ice is more than 90% by weight.

In the present invention, the air flow in contact with the alkali metal is a dry air flow, that is, it does not contain liquid water, thereby avoiding the serious safety hazard caused by the reaction between water and sodium to generate a large amount of heat and hydrogen, and solving the prior art There are many problems in the method of cleaning sodium-cooled fast reactors; in order to effectively remove alkali metals, the cleaning medium of the present invention uses dry ice as the main component, and solid dry ice particles are sprayed to the surface at high speed to produce impact micro-explosions, so that the dirt quickly condenses and becomes brittle. It is stable and non-flammable, and can dilute oxygen.

Therefore, the above-mentioned method for cleaning alkali metal residues of the present invention can solve the problems of the prior art and achieve good results. Further, the inventors of the present invention have conducted in-depth research on the cleaning method to achieve higher cleaning efficiency and less dry ice consumption.

In preferred embodiments of the present invention, the method of the present invention may be further defined by one or more of the following preferred features.

Since water will react violently with alkali metals and bring about potential safety hazards, the present invention has defined the airflow as dry airflow, that is, does not contain liquid water. For solid water, the present invention may not limit it, and within a safe range, the cleaning medium may contain a small amount of solid water (ice) and/or hydrate.

Preferably, the cleaning medium does not contain H ₂ O (eg, ice), so as to be more convenient for safety and subsequent processing.

Effective cleaning effect can be achieved when the content of dry ice in the cleaning medium is more than 90%. On the premise of not affecting the function of dry ice, the cleaning medium of the present invention may also contain other components. Preferably, based on the total weight of the cleaning medium, the content of the dry ice is more than 95% by weight; more preferably, the cleaning medium contains more than 99% by weight of dry ice. From the viewpoint of being more favorable for subsequent processing, the cleaning medium may be all dry ice.

In the present invention, the particle size of the dry ice can be selected within a wide range and can be adjusted according to specific working conditions, for example, the average particle size of the dry ice is 0.1-10 mm, preferably 1-6 mm.

In the present invention, the average particle size, average diameter, and average length can be observed by a cryomicroscope.

In the present invention, the composition type of the dry ice may not be limited. For example, in a specific embodiment, the average particle size of the dry ice is 1.5-3.5 mm.

The carrier gas in the drying gas stream is a compressed gas, preferably, the gas pressure of the carrier gas is 0.2-1.0 MPa, preferably 0.4-0.9 MPa, more preferably 0.5-0.8 MPa. The gas pressure in the present invention is absolute pressure.

Preferably, the carrier gas is an inert gas, preferably nitrogen.

Preferably, the speed of dry ice in the dry air flow is 0.001-0.1kg/s, preferably 0.01-0.09kg/s, more preferably 0.03-0.06kg/s.

When the alkali metal is completely removed, generally, the amount of the cleaning medium used in dry ice is 1-100 g, preferably 30-70 g, more preferably 40-60 g per gram of alkali metal.

In a more preferred embodiment, the dry ice includes Grade A dry ice, Grade B dry ice and Grade C dry ice, wherein Grade A dry ice is a sphere with an average particle size of 1-4mm (preferably 2-3mm), and B Grade C dry ice is a cylinder with an average diameter of 1-3mm (preferably 1.5-2.5mm) and an average length of 2-6mm (preferably 3-5mm), and Grade C dry ice is an average particle size of 1-6mm (preferably 3-5mm) Irregular polyhedron (ie, has more edges and corners).

Preferably, based on the total weight of the dry ice, the content of the Class A dry ice is 15-35% by weight, the content of the Class B dry ice is 10-40% by weight, and the content of the Class C dry ice is 30% by weight. -60 wt%.

More preferably, based on the total weight of the dry ice, the content of the Class A dry ice is 20-30% by weight, the content of the Class B dry ice is 20-30% by weight, and the content of the Class C dry ice is 40-55% by weight.

The inventors of the present invention found that by mixing the above-mentioned specific types of dry ice in a specific ratio, more alkali metal residues can be removed at a faster rate with a smaller amount of dry ice. Control parameters for the drying gas stream containing such specific dry ice when in contact with the alkali metal can be selected within the aforementioned ranges.

The drying gas stream may be continuously contacted with the alkali metal attached surface until the alkali metal is removed, or may be contacted in a pulsed manner. When contacting in a pulsed manner, preferably, the single contact time is 2-10s, and the interval time is 1-10s; more preferably, the single contact time is 4-8s, and the interval time is 2-5s.

After further research, the inventors of the present invention found that when two different specific drying air streams are alternately contacted with the surface with the alkali metal attached, the cleaning can be made more efficient.

According to a preferred embodiment, the dry air stream includes a first dry air stream and a second dry air stream, wherein the dry ice in the first dry air stream contains 15-70% by weight of B-grade dry ice and 30-85% by weight of dry ice % C grade dry ice, the dry ice in the second dry air stream contains 15-70 wt % A grade dry ice and 30-85 wt % B grade dry ice.

Preferably, the dry ice in the first dry air stream contains 20-60% by weight of B-grade dry ice and 40-80% by weight of C-grade dry ice; more preferably, the dry ice in the first dry air stream contains 30% by weight - 45 wt% Class B dry ice and 55-70 wt% Class C dry ice.

Preferably, the dry ice in the second dry air stream contains 30-70% by weight of A-grade dry ice and 30-70% by weight of B-grade dry ice; more preferably, the dry ice in the second dry air stream contains 40% by weight - 60 wt% Grade A dry ice and 40-60 wt% Grade B dry ice.

Preferably, the method includes: alternately contacting the first dry air flow and the second dry air flow with the surface to which the alkali metal is attached; each contact time is 2-10s, and the interval time is 1-10s .

More preferably, each contact time is 4-8s, and the interval time is 2-5s.

Preferably, the ice ejection speed of dry ice in the first drying airflow is 1.5-3 times, more preferably 2-2.5 times, the ice ejecting speed of the dry ice in the second drying airflow; and in the second drying airflow The ice discharge rate of the dry ice is 0.01-0.05 kg/s, more preferably 0.02-0.04 kg/s.

Preferably, the carrier gas pressure of the first dry gas stream is 0.4-0.9MPa, preferably 0.6-0.8MPa; and the carrier gas pressure of the second dry gas stream is 0.3-0.7MPa, more preferably 0.4-0.6MPa.

According to the alkali metal content in the specific working conditions, the amount of dry ice to be used is calculated. Based on the ratio between the amount of dry ice and the two dry air streams, the amount of each dry air stream is calculated.

In the present invention, the alkali metal is potassium or sodium.

In the present invention, preferably, the surface to which the alkali metal is attached is the surface of the equipment or component attached to sodium metal in the sodium-cooled reactor.

The second aspect of the present invention provides the application of the method described in the first aspect of the present invention in cleaning alkali metal residues in a sodium-cooled fast reactor.

In the application of the present invention, parts of equipment and components of sodium-cooled fast reactors with sodium residues can be treated according to the aforementioned method of the present invention.

In the application of the present invention, the equipment used may be a self-made or commercially available equipment capable of spraying dry ice at high pressure. For example, according to one embodiment, the apparatus for carrying and releasing the cleaning medium includes:

a cleaning medium storage assembly including a first container for storing the cleaning medium;

a carrier gas storage assembly including a second container for providing a carrier gas carrying the cleaning medium;

a release assembly, including a spray head, for releasing the airflow containing the cleaning medium to the target site;

a pressurizing assembly for pressurizing the carrier gas to form the gas stream containing the cleaning medium, including a third container that can be used for pressurization, at least one inlet of the third container and the carrier gas storage assembly communication, at least one outlet is in communication with the release assembly, and the cleaning medium storage assembly is in communication with the inlet and/or outlet of the pressurizing assembly so that the cleaning medium is in communication with the carrier gas before and/or or later mixed in;

a guide assembly, which communicates the pressing assembly and the releasing assembly, and enables the position and angle of the releasing assembly to be adjustable;

And, optionally (with or without) a control component may be included, and the control component is used to adjust the pressure of the pressurizing component and adjust the cleaning medium discharged from the cleaning medium storage component according to the alkali metal residual condition According to the ratio of the carrier gas released by the carrier gas storage component, the release amount of the release component is adjusted; and the movement of the drive component and the guide component is controlled to change the release direction of the release component.

Thus, in the application and method of the present invention,

The carrier gas from the carrier gas storage component is pressurized by the pressurizing component to obtain a high-pressure carrier gas;

The high-pressure carrier gas carries the cleaning medium from the cleaning medium storage component to obtain an air flow containing the cleaning medium;

The air flow containing the cleaning medium is released to the part to be treated through the release component, so that the alkali metal is cleaned;

The power assembly drives the device to move, and drives the guide assembly to move, so as to carry the release assembly to a new to-be-treated site.

In the present invention, the shape, size, distribution of spray holes, shape and size of spray holes, etc. of the release component (such as spray head) can be set, so that it can be better applied to the equipment of sodium-cooled fast reactor , so that the drying airflow can be smoothly released to all corners.

Through the above technical solutions, the present invention has at least the following advantages compared with the prior art:

(1) Dry cleaning is realized, sodium-water reaction is avoided, and the carbon dioxide generated is stable in nature and can dilute oxygen, which greatly improves safety;

(2) The processing is fast and efficient, the time-consuming is short, the production can be quickly resumed, and the long-term shutdown is avoided;

(3) The fixed-point treatment of alkali metal surfaces in different situations is more targeted and more accurate, which is conducive to the full cleaning of poly-alkali metal surfaces, and also avoids ineffective cleaning of low-metal surfaces, which improves the overall efficiency of the cleaning process;

(4) the cleaning product is gaseous carbon dioxide, which can be volatilized directly without burdening the environment, and the cleaning method of the present invention does not generate secondary pollutants such as waste water, does not require subsequent treatment, and is environmentally friendly;

(5) The financial cost of subsequent processing is reduced, and a lot of manpower and time costs are saved;

(6) It can reduce the corrosion and damage to the cleaning surface and improve the service life of the equipment;

(7) Reduce the risk of sodium leakage in nuclear power operation and improve the safety of nuclear power;

(8) There is no need to disassemble the equipment to ensure the accuracy of the equipment;

(9) It can effectively clean corners, crevices and dead corners without pollution and residue.

The endpoints of ranges and any values disclosed herein are not limited to the precise ranges or values, which are to be understood to encompass values proximate to those ranges or values. For ranges of values, the endpoints of each range, the endpoints of each range and the individual point values, and the individual point values can be combined with each other to yield one or more new ranges of values that Ranges should be considered as specifically disclosed herein.

Detailed ways

The present invention will be described in detail below by means of examples. The described embodiments of the present invention are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

In the following examples, in order to ensure the comparability between the effects, the cleaning objects in each example are selected from pipes that meet the following requirements: "a pipe with an inner diameter of about 40mm and a length of about 600mm, with about 300g of sodium remaining on it", if If there are no multiple pipelines that meet the requirements at the same time, when cleaning is required after the next production, select the pipelines that meet the requirements to clean and record according to the method in the corresponding embodiment.

Dry ice used in the following examples includes:

Grade A dry ice: spherical or nearly spherical, with an average particle size of 2.6mm;

Class B dry ice: cylindrical, with an average diameter in the range of 1.8mm and an average length in the range of 3.8mm;

Grade C dry ice: irregular polyhedron with an average particle size in the range of 4.2mm.

The following Group A examples are used to illustrate the case where the drying airflow is of the same composition.

Example A1

(1) Preparation of dry ice: composed of 25% by weight of A-grade dry ice, 25% by weight of B-grade dry ice, and 50% by weight of C-grade dry ice.

(2) Alternately spray the first dry air stream and the second dry air stream into the pipeline, the carrier is nitrogen, the single injection time is 7s, and the interval is 3s;

The ice discharge speed is 0.06kg/s, and the carrier gas pressure is 0.78MPa;

The cleaned sodium and other impurities are blown out and collected at the outlet (sodium is mainly in the form of sodium carbonate), and the sodium content on the pipe wall is detected by the detector head. When the sodium is cleaned, a total of 35 injections have passed , the total amount of dry ice is 14.5kg, and it takes 5min50s.

Example A2

(1) Preparation of dry ice: composed of 20% by weight of A-grade dry ice, 25% by weight of B-grade dry ice, and 55% by weight of C-grade dry ice.

(2) Alternately spray the first dry air stream and the second dry air stream into the pipeline, the carrier is nitrogen, the single injection time is 6s, and the interval is 4s;

The ice discharge speed is 0.05kg/s, and the carrier gas pressure is 0.65MPa;

When the sodium is cleaned, a total of 52 sprays are required, the total amount of dry ice is 15.5kg, and it takes 8min50s.

Example A3

(1) Preparation of dry ice: composed of 30% by weight of A-grade dry ice, 30% by weight of B-grade dry ice, and 40% by weight of C-grade dry ice.

(2) Alternately spray the first dry air stream and the second dry air stream into the pipeline, the carrier is nitrogen, the single injection time is 8s, and the interval is 2s;

The ice discharge speed is 0.042kg/s, and the carrier gas pressure is 0.52MPa;

When the sodium is cleaned, a total of 50 sprays are required, the total amount of dry ice is 16.6kg, and it takes 8min15s.

Example A4

The method of Example A1 was followed, except that all grade A dry ice was used.

When the sodium is cleaned, a total of 48 sprays are required, the total amount of dry ice is 20kg, and it takes 7min55s.

Example A5

According to the method of Embodiment A1, the difference is that instead of spraying at intervals, continuous spraying is adopted.

When the sodium is cleaned, the total spray time is 7min5s, and the total amount of dry ice is 25kg.

The following Group B examples are used to illustrate the case where the drying airflow is alternately performed by two airflows.

Example B1

The method of the present invention is used for processing, which specifically includes:

(1) Prepare two dry ice groups

Group 1: consists of 40% by weight of Class B dry ice and 60% by weight of Class C dry ice;

The second group: consisted of 40% by weight of Class A dry ice and 60% by weight of Class B dry ice.

(2) Alternately inject the first dry air stream and the second dry air stream into the pipeline, the carrier is nitrogen, the single injection time is 7s, and the interval is 3s; wherein,

The first dry air flow is composed of a carrier gas and the aforementioned first group of dry ices, the ice output speed is 0.08kg/s, and the carrier gas pressure is 0.75MPa;

The second dry air stream is composed of the carrier gas and the first group of dry ices, the ice output speed is 0.04kg/s, and the carrier gas pressure is 0.6MPa;

The cleaned sodium and other impurities are blown out and collected at the outlet (sodium is mainly in the form of sodium carbonate). When the sodium is cleaned, it has been sprayed 30 times in total. The total amount of dry ice is 12.5kg, which takes 5min2s.

Example B2

In the sodium-cooled fast reactor, a pipe with an inner diameter of 40mm and a length of about 600mm was selected, and about 300g of sodium remained on it. The method of the present invention is used for processing, which specifically includes:

(1) Prepare two dry ice groups

Group 1: consists of 30% by weight of Class B dry ice and 70% by weight of Class C dry ice;

The second group: consisted of 50% by weight of Class A dry ice and 50% by weight of Class B dry ice.

(2) Alternately spray the first dry air flow and the second dry air flow into the pipeline, the carrier is nitrogen, the single injection time is 8s, and the interval is 5s; wherein,

The first dry air flow is composed of a carrier gas and the aforementioned first group of dry ice, the ice output speed is 0.075kg/s, and the carrier gas pressure is 0.6MPa;

The second dry air stream is composed of the carrier gas and the first group of dry ice, the ice output speed is 0.03kg/s, and the carrier gas pressure is 0.4MPa;

When the sodium is cleaned, a total of 32 sprays are required, the total amount of dry ice is 13.2kg, and it takes 6min50s.

Example B3

In the sodium-cooled fast reactor, a pipe with an inner diameter of 40mm and a length of about 600mm was selected, and about 300g of sodium remained on it. The method of the present invention is used for processing, which specifically includes:

(1) Prepare two dry ice groups

Group 1: consisting of 45% by weight of Class B dry ice and 55% by weight of Class C dry ice;

The second group: consisted of 60% by weight of Class A dry ice and 40% by weight of Class B dry ice.

(2) Alternately spray the first dry air flow and the second dry air flow into the pipeline, the carrier is nitrogen, the single injection time is 4s, and the interval is 2s; wherein,

The first dry air flow is composed of a carrier gas and the first group of dry ices, the ice output speed is 0.07kg/s, and the carrier gas pressure is 0.7MPa;

The second dry air stream is composed of carrier gas and the aforementioned first group of dry ices, the ice output speed is 0.035kg/s, and the carrier gas pressure is 0.45MPa.

When the sodium is cleaned, a total of 64 sprays are required, and the total amount of dry ice is 13.4g, which takes 6min22s.

Example B4

According to the method of Embodiment B1, the difference is that the parameters of the first drying airflow and the second drying airflow are changed, specifically,

The first dry air flow is composed of a carrier gas and the aforementioned first group of dry ice, the ice output speed is 0.06kg/s, and the carrier gas pressure is 0.7MPa;

The second dry air stream is composed of a carrier gas and the aforementioned first group of dry ices, the ice output speed is 0.06kg/s, and the carrier gas pressure is 0.7MPa.

When the sodium is cleaned, a total of 32 sprays are required, the total amount of dry ice is 13.8kg, and it takes 5min30s.

Example B5

According to the method of Embodiment B1, the difference is that the parameters of the first drying airflow and the second drying airflow are changed, specifically,

The first dry air flow is composed of a carrier gas and the aforementioned first group of dry ice, the ice output speed is 0.04kg/s, and the carrier gas pressure is 0.5MPa;

The second dry air stream is composed of a carrier gas and the aforementioned first group of dry ices, the ice output speed is 0.08kg/s, and the carrier gas pressure is 0.7MPa.

When the sodium is cleaned, a total of 36 sprays are required, the total amount of dry ice is 15.2kg, and it takes 6min5s.

Comparative Example 1

The method of steam cleaning is adopted, and the specific method includes: the sodium pipe with an inner diameter of 40mm and a length of 607mm is selected for the equipment to be cleaned with residual sodium, and the sodium content is 306.7g. According to the above cleaning process steps, establish an inert environment, fill the system with nitrogen to 0.01MPa, hoist the pipeline to be cleaned and preheat the system so that the temperature of the cleaning tank is 70℃, and the pipeline connecting the electric steam generator and the cleaning tank is 100℃ , when the pressure of the nitrogen cleaning tank is 0.15MPa, open the steam inlet valve, control the temperature of superheated steam to 120℃, control the flow rate of water vapor to 72.1kg/h, and the flow rate of nitrogen gas to 43.9m ³ / h. After 15 minutes, the reading of the hydrogen analyzer is 1% (volume percentage), and the water vapor inlet valve is automatically closed; after 3 minutes, the hydrogen content is less than 0.5%, and the water vapor inlet valve is manually opened; Repeat the above operations until the hydrogen content in the exhaust gas is stable and less than 0.5%; then close the nitrogen inlet valve, and continue to introduce water vapor for 10 minutes. If the hydrogen analyzer has no reading display, the cleaning operation with water vapor and nitrogen will be terminated. The non-condensable gases such as nitrogen and the reaction product hydrogen in the cleaning are separated by the gas-liquid separator 9 and then discharged, and the water vapor becomes a condensed liquid and is discharged into the waste liquid collection tank 6 .

In the water washing stage, the hydrogen content did not appear to be greater than 0.5%. After the water cleaning is completed, the drying and cleaning waste liquid treatment and discharge procedures are completed. The upper flange of the cleaning tank is opened, and the sodium pipe is taken out from the hanging basket. It is found that the sodium in it has been cleaned and the appearance is normal.

It can be seen by comparing the above-mentioned embodiment and the comparative example that the method of the present invention can quickly remove the residual alkali metal on the surface of the equipment, and the time consumption is far less than that of the comparative example, and there is no need to disassemble the equipment, which is conducive to rapid recovery of production; The product of the invention is carbon dioxide, does not produce secondary pollutants such as waste water, does not require subsequent treatment, and is environmentally friendly; the reaction process does not generate heat and hydrogen, and there is no need to constantly monitor the hydrogen concentration as in Comparative Example 1, which greatly improves safety. In addition, it can be seen from the comparison between the examples that the more preferred embodiment can achieve lower dry ice dosage and/or shorter time consumption.

The preferred embodiments of the present invention have been described above in detail, however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, a variety of simple modifications can be made to the technical solutions of the present invention, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed in the present invention. All belong to the protection scope of the present invention.

Claims (11)

1. A method of cleaning alkali metal residue, the method comprising: contacting the drying gas stream with the surface having the alkali metal adhered thereto, such that the alkali metal is detached from the surface; the dry gas flow comprises a carrier gas and a solid cleaning medium, the cleaning medium comprises dry ice, and the content of the dry ice is more than 90 wt% based on the total weight of the cleaning medium;

the dry ice comprises grade A dry ice, grade B dry ice and grade C dry ice, wherein the grade A dry ice is a sphere with the average granularity of 1-4mm, the grade B dry ice is a cylinder with the average diameter of 1-3mm and the average length of 2-6mm, and the grade C dry ice is an irregular polyhedron with the average granularity of 1-6 mm;

the drying gas stream comprises a first drying gas stream and a second drying gas stream, wherein the dry ice in the first drying gas stream contains 15-70 wt% of B-grade dry ice and 30-85 wt% of C-grade dry ice, and the dry ice in the second drying gas stream contains 15-70 wt% of A-grade dry ice and 30-85 wt% of B-grade dry ice; the ice discharging speed of the dry ice in the first drying air flow is 1.5-3 times of the ice discharging speed of the dry ice in the second drying air flow, and the ice discharging speed of the dry ice in the second drying air flow is 0.01-0.05 kg/s;

the first drying air flow and the second drying air flow are sprayed in an alternating mode, the time of single spraying is 2-10s, and the interval time is 1-10 s;

the alkali metal is the alkali metal residue in the sodium-cooled fast reactor.

2. The method according to claim 1, wherein the dry ice is present in an amount of 95 wt% or more based on the total weight of the cleaning medium and does not contain H ₂ O。

3. A method according to claim 1 or 2, wherein the dry ice has an average particle size of 0.1-10mm, the gas pressure of the carrier gas is 0.2-1.0Mpa and the ice discharge rate of the dry ice in the drying gas stream is 0.001-0.1 kg/s.

4. A method according to claim 3, wherein the average particle size of the dry ice is 1-6mm, the gas pressure of the carrier gas is 0.4-0.9Mpa and the ice discharge rate of the dry ice in the drying gas stream is 0.01-0.09 kg/s.

5. The method as claimed in claim 1, wherein the grade a dry ice is present in an amount of 15-35% by weight, the grade B dry ice is present in an amount of 10-40% by weight, and the grade C dry ice is present in an amount of 30-60% by weight, based on the total weight of the dry ice.

6. The method of claim 5, wherein the contacting is pulsed, with a single contact time of 4-8s and an interval time of 2-5 s.

7. A method according to claim 1, wherein the dry ice in the first stream of dry gas comprises 20-60% by weight of class B dry ice and 40-80% by weight of class C dry ice.

8. The method according to claim 7, wherein the dry ice in the first stream of dry gas comprises 30-45% by weight of class B dry ice and 55-70% by weight of class C dry ice.

9. Method according to claim 1, wherein the ice removal rate of the dry ice in the first drying gas stream is 2-2.5 times the ice removal rate of the dry ice in the second drying gas stream and the ice removal rate of the dry ice in the second drying gas stream is 0.02-0.04 kg/s.

10. The method of claim 7, wherein the first dry gas stream has a carrier gas pressure of 0.4-0.9MPa and the second dry gas stream has a carrier gas pressure of 0.3-0.7 MPa.

11. The method of claim 10, wherein the carrier gas pressure of the first dry gas stream is 0.6-0.8MPa and the carrier gas pressure of the second dry gas stream is 0.4-0.6 MPa.