A method for decontamination, smelting and recycling of radioactive scrap metal

Abstract

The present invention relates to the technical field of radioactive scrap metal treatment, and specifically discloses a method for decontamination, smelting and reusing radioactive scrap metal, comprising the following steps: step 1: scrap metal pretreatment; step 2: pre-decontamination; step 3: scrap metal crushing and packaging; step 4: radioactive contaminated scrap metal smelting; step 5: product processing. The method of the present invention has good decontamination effect and high unlimited utilization rate, opens up a one-stop productization process from radioactive scrap metal smelting to product production, and realizes the true recycling of radioactive scrap metal.

Description

Technical Field

[0001] The invention belongs to the technical field of radioactive waste metal treatment, and in particular relates to a method for decontamination, smelting and recycling of radioactive waste metal. Background Art

[0002] A large amount of radioactive scrap metal is generated during the decommissioning of old nuclear facilities and the operation of nuclear power plants in my country, and it is estimated that 2,500 tons of scrap metal will need to be processed annually. The temporary storage of these radioactive scrap metals takes up a lot of storage space, and direct disposal will incur high costs and waste metal resources, which violates the principle of waste minimization and also violates the national green and sustainable development strategy.

[0003] At present, my country's nuclear facilities that have built smelting and decontamination equipment mainly use smelting and decontamination technology to melt radioactive scrap metal into ingots for storage, thereby reducing the volume of scrap metal, but have not truly achieved the recycling of radioactive scrap metal smelting. The current smelting and decontamination industry chain is incomplete and lacks product production links; the acceptance limit for radioactive scrap metal is very low, most scrap metal cannot be brought into the factory for smelting, the production intelligence level is low, and the smelting and decontamination process needs to be upgraded and optimized.

[0004] Therefore, it is urgent to design a method for decontamination, smelting and recycling of radioactive waste metals to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a method for decontamination, smelting and recycling of radioactive scrap metal, which forms a decontamination pretreatment before smelting, smelting and casting machine processing technology after smelting.

[0006] The technical solution of the present invention is as follows:

[0007] A method for decontamination, melting and recycling of radioactive scrap metals, comprising the following steps:

[0008] Step 1: Scrap Metal Pretreatment

[0009] Through remote mechanization and intelligent control, scrap metal pretreatment is carried out, which includes the following steps:

[0010] 1.1 Sorting of scrap metals, first by carbon steel, stainless steel, then by shape and size;

[0011] 1.2 Cutting of scrap metals of different shapes and sizes, mainly hot cutting and supplemented by cold cutting;

[0012] 1.3 Use a surface dose monitor to detect the contact dose rate of artificial radionuclide contaminated metal surfaces on the cut scrap metal;

[0013] If the surface contact dose rate is > 15 μSv / h, it is transferred to the pre-decontamination plant for pre-decontamination and starts step 2;

[0014] If the surface contact dose rate is ≤15μSv / h, no pre-decontamination is required and the metal is directly sent to the metal crushing and baling machine for baling, and step 3 is started;

[0015] Step 2: Pre-decontamination

[0016] In the pre-decontamination workshop, high temperature oxidation decontamination, dry ice-shot blasting cycle decontamination and peelable film decontamination are used to pre-decontaminate scrap metal and tools;

[0017] Step 3: Scrap metal crushing and packaging

[0018] The pre-treated and pre-decontaminated scrap metal is transported to a metal crushing and baling machine through a conveyor belt for crushing and baling to obtain scrap metal bales;

[0019] Step 4: Smelting of radioactively contaminated scrap metal

[0020] The scrap metal bag is fed into the smelting chamber of the smelting furnace to smelt the scrap metal;

[0021] Step 5: Product processing

[0022] The smelted molten metal enters the product production area for processing and manufacturing for reuse.

[0023] Step 1.2 specifically includes the following operations:

[0024] 1.2.1 For pipes with a length greater than or equal to 1000mm, flame cutting or plasma cutting shall be used to cut the pipe to a length less than 1000mm; if there is a flange with a thickness of more than 10mm at the end of the pipe, it shall be cut off and processed separately from the pipe;

[0025] 1.2.2 For plates with a thickness greater than 10 mm, if the maximum radial circumscribed circle diameter is greater than 400 mm, flame cutting or plasma cutting should be used to cut the maximum circumscribed circle diameter to less than 400 mm;

[0026] 1.2.3 For large parts with a size greater than 1000mm×1000mm, flame cutting is used to cut them to a size of less than 1000mm×1000mm;

[0027] 1.2.4 Other scrap metal parts, no need to cut.

[0028] Step 2 includes sub-step 2.1:

[0029] Using high-temperature oxidation decontamination method, heat carbon steel scrap metal to 700-950℃ and keep it warm for 1.5-3.5 hours; heat stainless steel scrap metal to 950-1150℃ and keep it warm for 1.5-3.5 hours;

[0030] After heat preservation, it is cooled naturally. During the natural cooling process, most of the surface oxides will fall off automatically. For some surface oxides that have not fallen off, vibration is used to remove them.

[0031] Step 2 includes sub-step 2.2: removing the residual oxide film on the surface of the scrap metal by a shot peening-dry ice cycle decontamination method;

[0032] First, the steel shot in the shot peening system is sprayed onto the surface of the scrap metal to remove the stains, rust stains, radioactive material layers and other contaminants on the surface of the scrap metal;

[0033] Then, the contaminated steel shot enters the steel shot and pollutant separation system through the steel shot recovery channel under the action of negative pressure; under the action of high-pressure air flow, the steel shot is separated from the radioactive pollutants, wherein the steel shot enters the dry ice steel shot cleaning system, and the radioactive pollutants enter the waste temporary storage and rotation system;

[0034] Then the steel shot is decontaminated by dry ice in the dry ice steel shot cleaning system, the cleaned steel shot enters the steel shot inspection system, and the washed radioactive contaminants enter the waste temporary storage and rotation system;

[0035] The steel shots are inspected in the steel shot inspection system, and the steel shots that meet the requirements enter the steel shot return system, which uses air pressure to return the steel shots to the shot peening decontamination system; the scrap steel shots that do not meet the requirements are temporarily stored and transported separately from the radioactive pollutants, among which the scrap steel shots used as decontamination raw materials enter step 3, and the radioactive pollutants are returned to the source for subsequent centralized treatment and disposal.

[0036] Step 2 includes sub-step 2.3: using a peelable film decontamination method to decontaminate tools used in the production process;

[0037] Apply the peelable film decontaminant to the surface of the scrap metal by spraying; the amount of the peelable film decontaminant applied is 0.04-0.25 g / cm 2 , the drying time is 9 to 24 hours.

[0038] In step 2.3, the formula of the strippable film detergent is: polyvinyl alcohol concentration is 5-20%, carboxymethyl cellulose as a thickener concentration is 0.05-3%, sodium stearate concentration is 0.05-4%, disodium ethylenediaminetetraacetic acid as a chelating agent concentration is 0.05-3%, and the balance is water.

[0039] In step 2.3, when the amount of the strippable film detergent applied is 0.2 ± 0.05 g / cm 2The decontamination rate is the highest.

[0040] In step 4, the smelting furnace is an induction smelting furnace, an arc smelting furnace, an electroslag smelting furnace, a vacuum suspension smelting furnace or a plasma arc smelting furnace.

[0041] In step 5, adaptive transformation of lost foam technology and radiation protection design are performed to cast the molten metal into a shielding sleeve, a cylindrical casting or a flat casting;

[0042] The shielding sleeve and the cylindrical casting are used to replace the lead shielding, and the flat casting is welded into a steel box product.

[0043] In step 5, a rotating cone centrifugal atomization process is used in parallel with a radiation protection design to produce steel shots with a particle size of 1 to 5 mm for recycling.

[0044] The remarkable effects of the present invention are:

[0045] (1) The method of the present invention has good decontamination effect and high unlimited utilization rate. The total recycling rate reaches 90%, of which the unlimited utilization rate reaches 45% and above.

[0046] (2) The method of the present invention adds a pre-decontamination stage based on the previous single smelting decontamination process, and synergistically adopts high-temperature oxidation decontamination, shot peening cycle decontamination and stripping film decontamination technology; through the scrap metal crushing and baling machine, the situation of bulk loading in the past has been changed; automatic feeding methods such as conveyor belts have been used to replace manual loading.

[0047] (3) The method of the present invention increases the scrap metal acceptance limit and the overall decontamination factor, improves the quality of steel, and can significantly reduce energy consumption, which can significantly improve product quality and added value, expand product categories, and improve the economic benefits of the enterprise.

[0048] (4) The method of the present invention increases the acceptable surface contact dose rate of radioactive scrap metal from 15 μSV / h to more than 400 μSV / h, greatly increasing the amount of radioactive scrap metal that can be processed by the smelting process, opening up a one-stop product process from radioactive scrap metal smelting to product production, and realizing the true recycling of radioactive scrap metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a schematic diagram of the method flow chart;

[0050] Figure 2 Schematic diagram of the dry ice-shot blasting cycle decontamination device.

[0051] In the figure: 1- scrap metal cutting plant; 2- pre-decontamination plant; 3- scrap metal crushing and packaging; 4- integrated automatic feeding; 5- melting furnace; 6- product production area. DETAILED DESCRIPTION

[0052] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] like Figure 1 A method for decontamination, melting and recycling of radioactive scrap metals is shown, wherein the radioactive contaminated scrap metal materials mainly come from uranium mining and metallurgy projects, uranium enrichment plants, fuel element plants, military test reactors of some research units, decommissioning of old nuclear facilities, nuclear power plants and other scrap metals such as stainless steel, carbon steel, nickel, aluminum, and copper. The contamination forms include loose surface contamination and fixed contamination. The contaminating nuclides are natural radionuclides or artificial nuclides, and the surface contact dose rate is 400μSV / h or less.

[0054] The method comprises the following steps:

[0055] Step 1: Scrap Metal Pretreatment

[0056] Through remote mechanization and intelligent control, scrap metal pretreatment is carried out, which includes the following steps:

[0057] 1.1 Sorting of scrap metals, first by carbon steel, stainless steel, then by shape and size;

[0058] 1.2 Cutting of scrap metals of different shapes and sizes, mainly hot cutting and supplemented by cold cutting, including:

[0059] 1.2.1 For pipes with a length greater than or equal to 1000mm, flame cutting or plasma cutting methods shall be used to cut the pipe to a length less than 1000mm; if there is a flange with a thickness of more than 10mm at the end of the pipe, it shall be cut off and processed separately from the pipe;

[0060] 1.2.2 For plates with a thickness greater than 10 mm, such as flanges with a thickness greater than 10 mm, if the diameter is greater than 400 mm, flame cutting or plasma cutting should be used to cut the maximum circumscribed circle diameter to less than 400 mm;

[0061] 1.2.3 For large parts with a size greater than 1000mm×1000mm, flame cutting is used to cut them to a size of less than 1000mm×1000mm;

[0062] 1.2.4 Other scrap metal parts, no need to cut;

[0063] 1.3 Use a surface dose monitor to detect the contact dose rate of artificial radionuclide contaminated metal surfaces on the scrap metal after cutting;

[0064] If the surface contact dose rate is > 15 μSv / h, it is transferred to the pre-decontamination plant for pre-decontamination and starts step 2;

[0065] If the surface contact dose rate is ≤15μSv / h, no pre-decontamination is required and the metal is directly sent to the metal crushing and baling machine for baling, and step 3 is started;

[0066] Step 2: Pre-decontamination

[0067] In the pre-decontamination workshop, high temperature oxidation decontamination, dry ice-shot blasting cycle decontamination and peelable film decontamination are used to pre-decontaminate scrap metal and tools. The decontamination method is selected according to the scrap metal contamination situation to improve the scrap metal acceptance limit and the overall decontamination factor:

[0068] 2.1 Use high temperature oxidation decontamination method to heat carbon steel scrap metal to 700-950℃ and keep it warm for 1.5-3.5 hours; heat stainless steel scrap metal to 950-1150℃ and keep it warm for 1.5-3.5 hours;

[0069] After heat preservation, it is cooled naturally. Since the thermal expansion system of steel and its oxide is different, most of the surface oxides will fall off automatically during the natural cooling process. For some surface oxides that have not fallen off, vibration is used to remove them.

[0070] 2.2 Use shot blasting-dry ice cycle decontamination method to remove the residual oxide film on the surface of scrap metal;

[0071] like Figure 2 As shown, the dry ice-shot blasting cycle decontamination device is mainly divided into six parts: shot blasting decontamination system, steel shot and pollutant separation system, dry ice steel shot cleaning system, steel shot inspection system, steel shot return system, waste temporary storage and rotation system;

[0072] First, the steel shot in the shot peening system is sprayed onto the surface of the scrap metal to remove the stains, rust stains, radioactive material layers and other contaminants on the surface of the scrap metal;

[0073] Then, the contaminated steel shot enters the steel shot and pollutant separation system through the steel shot recovery channel under the action of negative pressure; under the action of high-pressure air flow, the steel shot is separated from the radioactive pollutants, wherein the steel shot enters the dry ice steel shot cleaning system, and the radioactive pollutants enter the waste temporary storage and rotation system;

[0074] Then the steel shot is decontaminated by dry ice in the dry ice steel shot cleaning system, the cleaned steel shot enters the steel shot inspection system, and the washed radioactive contaminants enter the waste temporary storage and rotation system;

[0075] The hardness, shape, and contamination degree of the steel shots are inspected in the steel shot inspection system. The steel shots that meet the requirements enter the steel shot return system, which uses air pressure to send the steel shots back to the shot peening decontamination system. The scrap steel shots that do not meet the requirements are temporarily stored and transported separately from the radioactive pollutants. The scrap steel shots used as decontamination raw materials enter step 3, and the radioactive pollutants are returned to the nuclear power plant and other sources of radioactive polluted scrap metal materials for subsequent centralized treatment and disposal.

[0076] 2.3 Use peelable film decontamination to decontaminate tools used in the production process;

[0077] Applying a peelable film detergent to the surface of the scrap metal by a spray gun; wherein the peelable film detergent has a formula of: polyvinyl alcohol at a concentration of 5 to 20%, carboxymethyl cellulose at a concentration of 0.05 to 3% as a thickener, sodium stearate at a concentration of 0.05 to 4%, disodium ethylenediaminetetraacetate at a concentration of 0.05 to 3% as a chelating agent, and the balance is water;

[0078] The amount of strippable film detergent applied is 0.04 to 0.25 g / cm 2 , drying time is 9 to 24 hours;

[0079] When the amount of strippable film detergent applied is 0.2±0.05g / cm 2 The decontamination rate is the highest when the water is used, which can reach 99.72%. The decontamination rates for stainless steel, glass, ceramics and plastics are all above 99%.

[0080] Step 3: Scrap metal crushing and packaging

[0081] The pre-treated and pre-decontaminated scrap metal and scrap steel shot are transported to a metal crushing and baling machine through a conveyor belt for crushing and baling to obtain scrap metal bags with a size of 200×200×200 mm;

[0082] Step 4: Smelting of radioactively contaminated scrap metal

[0083] The scrap metal bag is fed into the smelting chamber of the smelting furnace to smelt the scrap metal;

[0084] The smelting furnace is a radioactive scrap metal smelting furnace such as induction smelting (air induction, medium frequency induction, vacuum induction), arc smelting, electroslag smelting, vacuum suspension smelting or plasma arc smelting;

[0085] Step 5: Product processing

[0086] The molten metal after smelting enters the product production area for processing and manufacturing:

[0087] 5.1 Carry out adaptive transformation of lost foam technology and radiation protection design, and cast the molten metal into shielding sleeves, cylindrical castings or flat castings, etc.; shielding sleeves and cylindrical castings are used to replace lead shielding, and flat castings are welded into FA-Ⅳ and other steel box products;

[0088] 5.2 According to the characteristics of the steel shot required in step 2, the rotating cone centrifugal atomization process is used in parallel with the radiation protection design to produce steel shots with a particle size of 1 to 5 mm for recycling.

[0089] The method of the present invention adopts mechanical-physical-chemical-smelting coordinated decontamination and recycling technology, which can greatly improve the decontamination effect and recycling rate, and achieve a total recycling rate of 90%, of which the unlimited utilization rate also reaches 45% and above.

[0090] The above shows and describes the basic principles, main features and advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claim involved.

[0091] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for decontamination, smelting and recycling of radioactive waste metals, characterized in that: The following steps are involved: Step 1: Scrap Metal Pretreatment Through remote mechanization and intelligent control, scrap metal pretreatment is carried out, which includes the following steps: 1.1 Sorting of scrap metals, first by carbon steel, stainless steel, then by shape and size; 1.2 Cutting of scrap metals of different shapes and sizes, mainly hot cutting and supplemented by cold cutting; 1.3 Use a surface dose monitor to detect the contact dose rate of artificial radionuclide contaminated metal surfaces on the cut scrap metal; If the surface contact dose rate is > 15 μSv / h, it is transferred to the pre-decontamination plant for pre-decontamination and starts step 2; If the surface contact dose rate is ≤15μSv / h, no pre-decontamination is required and the metal is directly sent to the metal crushing and baling machine for baling, and step 3 is started; Step 2: Pre-decontamination In the pre-decontamination workshop, high temperature oxidation decontamination, dry ice-shot blasting cycle decontamination and peelable film decontamination are used to pre-decontaminate scrap metal and tools; The formula of the strippable film detergent is as follows: polyvinyl alcohol concentration is 5-20%, carboxymethyl cellulose as a thickener concentration is 0.05-3%, sodium stearate concentration is 0.05-4%, disodium ethylenediaminetetraacetate as a chelating agent concentration is 0.05-3%, and the balance is water; Step 3: Scrap metal crushing and packaging The pre-treated and pre-decontaminated scrap metal is transported to a metal crushing and baling machine through a conveyor belt for crushing and baling to obtain scrap metal bales; Step 4: Smelting of radioactively contaminated scrap metal The scrap metal bag is fed into the smelting chamber of the smelting furnace to smelt the scrap metal; Step 5: Product processing The molten metal after smelting enters the product production area for processing and manufacturing to achieve reuse; Step 2 includes sub-step 2.1: Using high-temperature oxidation decontamination method, heat carbon steel scrap metal to 700-950℃ and keep it warm for 1.5-3.5 hours; heat stainless steel scrap metal to 950-1150℃ and keep it warm for 1.5-3.5 hours; After heat preservation, it is cooled naturally. During the natural cooling process, most of the surface oxides will fall off automatically. For some surface oxides that have not fallen off, vibration is used to remove them.

2. A method for decontamination, smelting and recycling of radioactive waste metals as claimed in claim 1, characterized in that: Step 1.2 specifically includes the following operations: 1.2.1 For pipes with a length greater than or equal to 1000mm, flame cutting or plasma cutting shall be used to cut the pipe to a length less than 1000mm; if there is a flange with a thickness of more than 10mm at the end of the pipe, it shall be cut off and processed separately from the pipe; 1.2.2 For plates with a thickness greater than 10 mm, if the maximum radial circumscribed circle diameter is greater than 400 mm, flame cutting or plasma cutting should be used to cut the maximum circumscribed circle diameter to less than 400 mm; 1.2.3 For large parts with a size greater than 1000mm×1000mm, flame cutting is used to cut them to a size of less than 1000mm×1000mm; 1.2.4 Other scrap metal parts, no need to cut.

3. A method for decontamination, smelting and recycling of radioactive waste metals as claimed in claim 2, characterized in that: Step 2 includes sub-step 2.2: removing the residual oxide film on the surface of the scrap metal by a shot peening-dry ice cycle decontamination method; First, the steel shot in the shot peening system is sprayed onto the surface of the scrap metal to remove the stains, rust stains, radioactive material layers and other contaminants on the surface of the scrap metal; Then, the contaminated steel shot enters the steel shot and pollutant separation system through the steel shot recovery channel under the action of negative pressure; under the action of high-pressure air flow, the steel shot is separated from the radioactive pollutants, wherein the steel shot enters the dry ice steel shot cleaning system, and the radioactive pollutants enter the waste temporary storage and rotation system; Then the steel shot is decontaminated by dry ice in the dry ice steel shot cleaning system, the cleaned steel shot enters the steel shot inspection system, and the washed radioactive contaminants enter the waste temporary storage and rotation system; The steel shots are inspected in the steel shot inspection system, and the steel shots that meet the requirements enter the steel shot return system, which uses air pressure to return the steel shots to the shot peening decontamination system; the scrap steel shots that do not meet the requirements are temporarily stored and transported separately from the radioactive pollutants, among which the scrap steel shots used as decontamination raw materials enter step 3, and the radioactive pollutants are returned to the source for subsequent centralized treatment and disposal.

4. A method for decontamination, smelting and recycling of radioactive waste metals as claimed in claim 3, characterized in that: Step 2 includes sub-step 2.3: using a peelable film decontamination method to decontaminate tools used in the production process; Apply the peelable film decontaminant to the surface of the scrap metal by spraying; the amount of the peelable film decontaminant applied is 0.04-0.25 g / cm 2 , the drying time is 9 to 24 hours.

5. A method for decontamination, smelting and recycling of radioactive waste metals as claimed in claim 4, characterized in that: In step 2.3, when the amount of the strippable membrane detergent applied is 0.2 ± 0.05 g / cm 2 The decontamination rate is the highest.

6. A method for decontamination, smelting and recycling of radioactive waste metals as claimed in claim 1, characterized in that: In step 4, the smelting furnace is an induction smelting furnace, an arc smelting furnace, an electroslag smelting furnace, a vacuum suspension smelting furnace or a plasma arc smelting furnace.

7. A method for decontamination, smelting and recycling of radioactive waste metals as claimed in claim 1, characterized in that: In step 5, adaptive modification of lost foam technology and radiation protection design are performed to cast the molten metal into a shielding sleeve, a cylindrical casting or a flat casting; The shielding sleeve and the cylindrical casting are used to replace the lead shielding, and the flat casting is welded into a steel box product.

8. The method for decontamination, smelting and recycling of radioactive waste metals as claimed in claim 1, characterized in that: In step 5, a rotating cone centrifugal atomization process is used in parallel with a radiation protection design to produce steel shots with a particle size of 1 to 5 mm for recycling.

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