Method for testing corrosion of spent fuel metal materials under nitric acid atmosphere

Abstract

The application discloses a method for testing the corrosion of spent fuel metal materials in a nitric acid atmosphere. The method uses a testing device, a temperature controller controls the heating of the heating sheet, the temperature of the heating is higher than the decomposition temperature of the nitric acid solution, and the temperature is kept constant, so that the cavity is filled with a high-temperature mixed atmosphere containing NO2 and O2. The time of each holding is set, the sample is taken out, weighed and recorded; the heating and weighing are repeated until the cumulative constant temperature time ends. The application uses the method of heating the nitric acid solution to decompose it to obtain a high-temperature NO2 and O2 mixed atmosphere, and then uses the designed device to study the corrosion behavior of the material. The method and device help to simulate the actual service conditions of the material in the rotary calcining furnace and can characterize the corrosion performance. The test results obtained by the test method can better reflect the corrosion behavior of the sample in the actual high-temperature NO2 and O2 mixed atmosphere.

Description

Technical Field

[0001] This invention pertains to high-temperature corrosion and oxidation testing technology, and specifically relates to a method for testing the corrosion of spent fuel metal materials under a nitric acid atmosphere. Background Technology

[0002] Nuclear power, as a clean and efficient energy source, can increase energy supply, optimize the energy structure, and significantly reduce greenhouse gas and pollutant emissions, making it a key focus of China's energy strategy. Spent fuel reprocessing is the most critical stage in the later stages of the nuclear fuel cycle and is currently the most widely used method for processing spent fuel discharged from nuclear reactors. During spent fuel reprocessing, the equipment used is often in a high-temperature corrosive environment, making its structural materials highly susceptible to severe corrosion. In particular, the rotary kiln used for spent fuel reprocessing is constantly exposed to a high-temperature mixed atmosphere of NO2 and O2, generated by the decomposition of nitrates and nitric acid solutions in high-level radioactive waste, which causes high-temperature corrosion of materials. Therefore, simulating the corrosive environment of the rotary kiln and screening materials with excellent high-temperature corrosion resistance for spent fuel reprocessing has significant application value. However, current research on the corrosion of metallic materials under high-temperature NO2 and O2 mixed atmospheres is limited, and no testing methods or equipment have been reported in the literature. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a corrosion testing method for spent fuel metal materials under a nitric acid atmosphere, which can be used to study the corrosion behavior of samples under a high-temperature NO2 and O2 mixed atmosphere.

[0004] To achieve the above-mentioned objectives, the technical solution of this invention is as follows:

[0005] A method for testing the corrosion of spent fuel metallic materials under a nitric acid atmosphere, wherein the method employs the following testing apparatus.

[0006] The testing apparatus is described below:

[0007] The working platform 1 is provided with a protective chamber 11, and the protective chamber 11 is provided with an atmosphere chamber 9; the testing device also includes a temperature controller 12, a liquid injection device 13, a nitric acid solution 14, a gas extraction device 15, and a waste gas treatment device 16.

[0008] A sample suspension device is provided in the atmosphere chamber 9. The sample suspension device includes a sample 5, a ceramic rod 6, and a platinum wire 8. One end of the platinum wire 8 is connected to the ceramic rod 6, and the other end is connected to the sample 5, so that the sample 5 is suspended in the atmosphere chamber 9.

[0009] The liquid injection device 13 is connected to the atmosphere chamber 9 and provides nitric acid solution 14 to the atmosphere chamber 9 through the solution channel 91. A heating element 7 controlled by a temperature controller 12 is installed at the lower part of the sample 5 in the atmosphere chamber 9. Insulation cotton 3 is placed at the lower part of the heating element 7. The solution channel 91 is located below the insulation cotton 3. The solution channel 91 is vented to the atmosphere chamber 9 through the third vent 103, so that the heating element 7 heats up and decomposes the nitric acid solution in the solution channel 91. A high-temperature NO2 and O2 mixed atmosphere corrosion test environment is formed in the atmosphere chamber 9 through the third vent 103.

[0010] Meanwhile, the upper parts of the atmosphere chamber 9 and the protective chamber 11 are respectively provided with a second vent 102 and a first vent 101. The first vent 101 is connected to the air extraction device 15, and the air extraction device 15 is connected to the waste gas treatment device 16.

[0011] The testing method is as follows:

[0012] The heating element 7, controlled by the temperature controller 12, heats up to a temperature higher than that of nitric acid solution decomposition and maintains a constant temperature, so that the atmosphere chamber 9 is filled with a fluid high-temperature mixed atmosphere containing NO2 and O2.

[0013] Set the holding time for each heat treatment, take out 5 samples, weigh and record the weight;

[0014] Repeatedly heat and weigh until the cumulative constant temperature time is reached.

[0015] Preferably, the heating temperature is 360°C higher than the decomposition temperature of nitric acid solution.

[0016] Preferably, the heat preservation time is 5h, 20h, 40h, 60h and 100h respectively. Beneficial effects

[0017] This invention uses a method of heating a nitric acid solution to decompose it to obtain a high-temperature NO2 and O2 mixed atmosphere. Then, the designed device is used to study the corrosion behavior of the material. This method and device help to simulate the actual service conditions of the material in a rotary kiln and can characterize its corrosion performance.

[0018] This invention provides a corrosion testing device for high-temperature NO2 and O2 mixed atmospheres with arbitrarily controllable testing time. As the testing device heats up, the nitric acid solution begins to decompose and erode the surface of the test sample in the form of a high-temperature NO2 and O2 mixed atmosphere. Under constant temperature conditions, the test sample is held at this temperature for a certain period, then removed, weighed, and recorded. This cycle of high-temperature corrosion, weighing, and recording is repeated until the required testing time is reached, at which point data acquisition ends. The recorded weighing data is then analyzed. Furthermore, the test results obtained by this method better reflect the corrosion behavior of the sample in actual high-temperature NO2 and O2 mixed atmospheres. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention.

[0020] The numbers in the diagram represent:

[0021] 1-Working platform; 2-Protective cover; 3-Insulation cotton; 4-Insulation cover; 5-Sample; 6-Ceramic rod; 7-Heating element; 8-Platinum wire; 9-Atmosphere chamber; 101-First vent; 102-Second vent; 103-Third vent; 11-Protective chamber; 12-Temperature controller; 13-Peristaltic pump; 14-Nitric acid solution; 15-Suction pump; 16-Waste gas treatment device (alkali solution).

[0022] Figure 2 This is a graph showing the oxidation kinetics of the sample. Implementation

[0023] The working principle and usage of the present invention will be described in detail below with reference to the accompanying drawings in the embodiments:

[0024] Reference Appendix Figure 1 A corrosion testing device for spent fuel metal materials under nitric acid atmosphere, the device comprising a working platform 1, a protective cover 2, insulation cotton 3, insulation cover 4, a sample 5, a ceramic rod 6, a heating element 7, a platinum wire 8, an atmosphere chamber 9, a first vent 101, a second vent 102, a third vent 103, a protective chamber 11, a temperature controller 12, a liquid injection device 13, a nitric acid solution 14, a vacuum device 15, and a waste gas treatment device 16;

[0025] A protective chamber 11 is formed inside the protective cover 2, and an atmosphere chamber 9 is formed inside the heat insulation cover 4;

[0026] The working platform 1 is provided with a protective chamber 11, and the protective chamber 11 is provided with an atmosphere chamber 9; the testing device also includes a temperature controller 12, a liquid injection device 13, a nitric acid solution 14, a gas extraction device 15, and a waste gas treatment device 16.

[0027] A sample suspension device is provided in the atmosphere chamber 9. The sample suspension device includes a sample 5, a ceramic rod 6, and a platinum wire 8. One end of the platinum wire 8 is connected to the ceramic rod 6, and the other end is connected to the sample 5, so that the sample 5 is suspended in the atmosphere chamber 9.

[0028] The liquid injection device 13 is connected to the atmosphere chamber 9 and provides nitric acid solution 14 to the atmosphere chamber 9 through the solution channel 91. A heating element 7 controlled by a temperature controller 12 is installed at the lower part of the sample 5 in the atmosphere chamber 9. Insulation cotton 3 is placed at the lower part of the heating element 7. The solution channel 91 is located below the insulation cotton 3. The solution channel 91 is vented to the atmosphere chamber 9 through the third vent 103, so that the heating element 7 heats up and decomposes the nitric acid solution in the solution channel 91. A high-temperature NO2 and O2 mixed atmosphere corrosion test environment is formed in the atmosphere chamber 9 through the third vent 103.

[0029] Meanwhile, the upper parts of the atmosphere chamber 9 and the protective chamber 11 are respectively provided with a second vent 102 and a first vent 101. The first vent 101 is connected to the air extraction device 15, and the air extraction device 15 is connected to the waste gas treatment device 16, so as to enable the flow of gas in the atmosphere chamber 9.

[0030] In this example, the injection device 13 includes a peristaltic pump and a conduit, which can inject nitric acid solution 14 into the solution channel 91 on the outer wall of the atmosphere chamber 9, and the injection rate is adjustable. The extraction device 15 is an extraction pump. The waste gas treatment device 16 contains alkaline solution.

[0031] The protective chamber 11 and the atmosphere chamber 9 are made of high-temperature nickel-based alloy and are painted on their surfaces.

[0032] The temperature rise, fall, and constant temperature control in the atmosphere chamber 9 are achieved by a temperature controller 12 connected to the heating element 7 inside the atmosphere chamber 9.

[0033] Before the test begins, measure out a sufficient amount of nitric acid solution according to the time required for the test. In this example, the nitric acid solution is a nitric acid solution with a mass fraction of 14.625%.

[0034] The testing method is as follows:

[0035] The heating element 7, controlled by the temperature controller 12, heats up to a temperature higher than that of nitric acid solution decomposition and maintains a constant temperature, so that the atmosphere chamber 9 is filled with a fluid high-temperature mixed atmosphere containing NO2 and O2.

[0036] Set the holding time for each heat treatment, take out 5 samples, weigh and record the weight;

[0037] Repeatedly heat and weigh until the cumulative constant temperature time is reached.

[0038] Based on the required test temperature (above the decomposition temperature of nitric acid solution), the test temperature in this embodiment is 600℃. The temperature control program of the temperature controller 12 is set; the program is started, and the heating element 7 begins to work; the injection speed of the peristaltic pump 13 is adjusted so that the nitric acid solution 14 flows into the solution channel in the wall of the atmosphere chamber 9 through the peristaltic pump 13. When the temperature reaches above the decomposition temperature of nitric acid, the nitric acid decomposes to produce a high-temperature NO2 and O2 mixed gas, which flows into the atmosphere chamber 9. The sample 5 is corroded under constant temperature control at the set test temperature. To increase the contact area between the sample 5 and the high-temperature gas, it is suspended in the atmosphere chamber 9.

[0039] Test Example 1

[0040] Test sample 5 was made of nickel-based 625 alloy, and the sample was a circular piece with a diameter of 15mm × 3mm. After surface grinding, polishing, cleaning, drying, and surface area measurement, the sample was weighed and then suspended in the atmosphere chamber using a suspension device. A certain distance was maintained between the sample and the heating element below the atmosphere chamber to ensure sufficient contact between the sample and the corrosive gas during the corrosion process. The heating temperature was set to 600℃, the peristaltic pump infusion rate was 0.5mL / min, and the holding times were set to 5h, 20h, 40h, 60h, 80h, and 100h. After the required corrosion time was reached, the sample was cooled to room temperature and then removed from the atmosphere chamber. The accuracy was 10. -5 Weigh the sample using a balance of g. To ensure experimental accuracy, at least three parallel samples were measured under the same conditions, and the average value was taken as the final mass change. Based on the mass change of the samples, an oxidation kinetic curve was plotted. Figure 2 ).

[0041] Test Example 2

[0042] Test sample 5 was made of nickel-based 690 alloy, and the sample was a circular piece with a diameter of 15mm × 3mm. After surface grinding, polishing, cleaning, drying, and surface area measurement, the sample was weighed and then suspended in the atmosphere chamber using a suspension device. A certain distance was maintained between the sample and the heating element below the atmosphere chamber to ensure sufficient contact between the sample and the corrosive gas during the corrosion process. The heating temperature was set to 600℃, the peristaltic pump infusion rate was 0.5mL / min, and the holding times were set to 5h, 20h, 40h, 60h, 80h, and 100h. After the required corrosion time was reached, the sample was cooled to room temperature and then removed from the atmosphere chamber. The accuracy was 10. -5 Weigh the sample using a balance of g. To ensure experimental accuracy, at least three parallel samples were measured under the same conditions, and the average value was taken as the final mass change. Based on the mass change of the samples, an oxidation kinetic curve was plotted. Figure 2 ).

[0043] Test Example 3

[0044] Test sample 5 was made of Hastelloy N alloy, and the sample was a circular disc with a diameter of 15mm × 3mm. After surface grinding, polishing, cleaning, drying, and surface area measurement, the sample was weighed and then suspended in the atmosphere chamber using a suspension device. A certain distance was maintained between the sample and the heating element below the atmosphere chamber to ensure sufficient contact between the sample and the corrosive gas during the corrosion process. The heating temperature was set to 600℃, the peristaltic pump infusion rate was 0.5mL / min, and the holding times were set to 5h, 20h, 40h, 60h, 80h, and 100h. After the required corrosion time was reached, the sample was cooled to room temperature and then removed from the atmosphere chamber. The accuracy was 10. -5 Weigh the sample using a balance of g. To ensure experimental accuracy, at least three parallel samples were measured under the same conditions, and the average value was taken as the final mass change. Based on the mass change of the samples, an oxidation kinetic curve was plotted. Figure 2 ).

[0045] In this invention, the nitric acid solution and the test sample 5 are not in direct contact. The temperature controller 12 controls the heating element 7 to heat the nitric acid solution to a high temperature to decompose it and obtain a high-temperature NO2 and O2 mixed gas. This high-temperature mixed gas will come into contact with the sample 5, thereby causing corrosion.

[0046] The testing method and testing device of the present invention can more realistically reflect the corrosion behavior of sample 5 in the mixed atmosphere of high temperature decomposition of nitric acid solution. When the required corrosion time is reached, the heating plate 7 and peristaltic pump 13 automatically stop, and then sample 6 is taken out, weighed, and recorded. The operation is repeated until the required total corrosion time is reached.

[0047] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various equivalent modifications can be made to the technical solutions of the present invention, and all such equivalent modifications fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.

Claims

1. A method for testing the corrosion of spent fuel metallic materials under nitric acid atmosphere, characterized in that: The method is tested using the following testing equipment. The testing apparatus is described below: A protective chamber (11) is provided on the working platform (1), and an atmosphere chamber (9) is provided inside the protective chamber (11); the testing device also includes a temperature controller (12), a liquid injection device (13), a nitric acid solution (14), a gas extraction device (15), and a waste gas treatment device (16); A sample suspension device is set in an atmosphere chamber (9). The sample suspension device includes a sample (5), a ceramic rod (6), and a platinum wire (8). One end of the platinum wire (8) is connected to the ceramic rod (6), and the other end is connected to the sample (5), so that the sample 5 is suspended in the atmosphere chamber (9). The liquid injection device (13) is connected to the atmosphere chamber (9) and provides nitric acid solution (14) to the atmosphere chamber (9) through the solution channel 91; a heating element (7) controlled by a temperature controller (12) is set at the bottom of the sample (5), and a heat insulation cotton (3) is placed at the bottom of the heating element (7). The solution channel (91) is located below the heat insulation cotton (3). The solution channel (91) is vented to the atmosphere chamber (9) through the third vent (103), so that the heating element (7) heats up and decomposes the nitric acid solution in the solution channel (91), and forms a high-temperature NO2 and O2 mixed atmosphere corrosion test environment in the atmosphere chamber (9) through the third vent (103); Meanwhile, the upper parts of the atmosphere chamber (9) and the protective chamber (11) are respectively provided with a second vent (102) and a first vent (101). The first vent (101) is connected to the air extraction device (15), and the air extraction device (15) is connected to the waste gas treatment device (16). The testing method is as follows: The heating element (7) controlled by the temperature controller (12) heats up, and the heating temperature is higher than the decomposition temperature of nitric acid solution, and the temperature is kept constant, so that the atmosphere chamber (9) is filled with a fluid high-temperature mixed atmosphere containing NO2 and O2. Set the time for each heat preservation, take out the sample (5), weigh and record it; Repeatedly heat and weigh until the cumulative constant temperature time is reached.

2. The test method according to claim 1, characterized in that... The heating temperature is 360℃ higher than the decomposition temperature of nitric acid solution.

3. The test method according to claim 1, characterized in that... The insulation time lengths are 5h, 20h, 40h, 60h and 100h respectively.

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