A high throughput test apparatus and method for simulating spent fuel reprocessing boiling nitric acid crevice corrosion

Abstract

The application relates to a high-throughput testing device and method for simulating the crevice corrosion of spent fuel reprocessing boiling nitric acid, and belongs to the field of spent fuel reprocessing boiling nitric acid corrosion testing devices. The device combines continuously changing crevice widths with wire beam electrodes, so that each rod-shaped sample corresponds to different crevice widths, and the crevice corrosion electrochemical signals under different crevice widths are monitored at one time. Therefore, the device can capture the corrosion signals of a micro area, obtain the corrosion rules under different crevice widths, complete high-throughput electrochemical testing, integrate the signals captured by each micro electrode, and obtain the corrosion condition of the whole material. Meanwhile, polytetrafluoroethylene is used as raw material to manufacture a top wire, a bolt, a nut and a bottom support in the device, the device has good electric insulation performance and strong corrosion resistance, and can meet the electrochemical experiment under a high-temperature concentrated nitric acid environment for a long time. The simulation and research of the crevice corrosion under the boiling concentrated nitric acid environment are realized.

Description

Technical Field

[0001] The invention belongs to the field of spent fuel post-processing boiling nitric acid corrosion test devices, and in particular relates to a high-throughput test device and method for simulating spent fuel post-processing boiling nitric acid crevice corrosion. Background Art

[0002] The service performance of metal materials in extreme environments is attracting increasing attention. For example, in the aqueous reprocessing of spent fuel, the metal containers that hold the spent fuel must withstand the harsh environment of radioactive, high-temperature, concentrated nitric acid. Actual data shows that crevice corrosion is one of the main failure modes of structural materials. Compared with other localized corrosion, crevice corrosion has a long incubation period and is difficult to detect in the early stages of corrosion, which can easily cause sudden failure of structural material performance and pose a huge risk. Therefore, studying the manifestations and occurrence mechanisms of crevice corrosion in materials under high-temperature, concentrated nitric acid, understanding the nature of crevice corrosion, and finding preventive measures can effectively reduce economic losses and are of great significance to the inspection and maintenance of equipment in the spent fuel reprocessing process.

[0003] Currently, few researchers have studied crevice corrosion in high-temperature concentrated nitric acid environments, and there are no relevant standards. Existing devices cannot meet the requirements for conducting experiments in harsh environments such as boiling concentrated nitric acid. Therefore, it is very necessary to design a research device and test method that can be used to test crevice corrosion in boiling concentrated nitric acid environments. In particular, the continuously changing gap width is combined with the wire beam electrode, so that each electrode corresponds to a precise gap width. The microelectrodes can be coupled with each other to obtain the average corrosion situation of the entire material, and can independently measure the corrosion situation of small areas. The distribution of current and potential at different gap widths can be obtained at one time, realizing electrochemical high-throughput testing of crevice corrosion. Through this device, the working conditions of structural materials in harsh environments such as spent fuel reprocessing are simulated, and the crevice corrosion mechanism and law of key materials in the nuclear industry can be studied. Summary of the Invention

[0004] The present invention aims to provide a high-throughput electrochemical testing device and method for crevice corrosion simulation in the boiling nitric acid environment of spent fuel reprocessing, while also providing a precise, continuously variable crevice width. By monitoring crevice corrosion signals using wire beam electrodes, high-throughput electrochemical testing of crevice corrosion is possible, enabling research into the mechanisms and patterns of crevice corrosion in these harsh environments.

[0005] The technical solution adopted in the present invention is:

[0006] A high-throughput testing device simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing, comprising: a crevice corrosion device, a heating jacket, a counter electrode, a heatable electrolytic cell, a polytetrafluoroethylene (PTFE) cover, an electrochemical workstation, a salt bridge, a reference electrode, a beaker, wire I, wire II, and wire III. The crevice corrosion device includes a polytetrafluoroethylene (PTFE) set screw, a butterfly-shaped polytetrafluoroethylene (PTFE) nut, a polytetrafluoroethylene (PTFE) bolt, a glass plate, a polytetrafluoroethylene (PTFE) nut, a polytetrafluoroethylene (PTFE) base, and a wire bundle electrode, wherein the wire bundle electrode is composed of a rod-shaped sample and a polytetrafluoroethylene (PTFE) cylinder.

[0007] The rod-shaped sample is composed of several thin metal rods. The height of the polytetrafluoroethylene cylinder is greater than or equal to the length of the rod-shaped sample, and filamentary through holes arranged in a matrix are cast from one bottom surface to the other bottom surface. A wire is welded to one end of the rod-shaped sample for connection to an electrochemical workstation, and the other end is inserted from one bottom surface of the polytetrafluoroethylene cylinder into the filamentary through holes of the polytetrafluoroethylene cylinder, and the inserted end of the rod-shaped sample is flush with the other bottom surface of the polytetrafluoroethylene cylinder, thereby manufacturing a wire bundle electrode.

[0008] One end of the wire beam electrode connecting wire I is the bottom of the wire beam electrode, and the other end is the top of the wire beam electrode. The wire beam electrode is fixed in the cylinder of the polytetrafluoroethylene base. The polytetrafluoroethylene base is in an I-shape, with two circular upper and lower planes and a cylindrical middle. The upper and lower through holes are used to expose the top of the wire beam electrode. The opening diameter of the bottom through hole is smaller than the diameter of the wire beam electrode, which is used to lead out the wire of the wire beam electrode and fix the wire beam electrode. The top of the wire beam electrode is flush with the upper plane of the polytetrafluoroethylene base. The wire I connected to the wire beam electrode extends out from the lower through hole of the polytetrafluoroethylene base. A polytetrafluoroethylene top screw and a polytetrafluoroethylene bolt are provided on the upper plane of the polytetrafluoroethylene base and cover the glass plate. The polytetrafluoroethylene top screw is screwed upward to lift the glass plate to create a gap and control the size of the gap. The polytetrafluoroethylene bolt is installed downward to fix the glass plate. The polytetrafluoroethylene top screw is fixed by a butterfly polytetrafluoroethylene nut. The polytetrafluoroethylene bolt cooperates with the polytetrafluoroethylene nut to fix the four corners of the glass plate to form a crevice corrosion device.

[0009] The crevice corrosion device and the counter electrode are placed in a solution in a heatable electrolytic cell; the counter electrode, a salt bridge, and a through hole for connecting the wire bundle electrode and the electrochemical workstation are provided on the polytetrafluoroethylene cover; the reference electrode is placed in a beaker filled with a saturated potassium chloride solution; the beaker filled with the saturated potassium chloride solution is connected to the solution in the heatable electrolytic cell via the salt bridge; the wire bundle electrode, the counter electrode, and the reference electrode form a three-electrode system, which is connected to the electrochemical workstation via wire I, wire II, and wire III, respectively; and the heating jacket is placed outside the heatable electrolytic cell to control the system temperature.

[0010] The high-throughput test device for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing, wherein:

[0011] The rod-shaped samples are composed of several metal rods with a diameter of 0.6mm-2mm and a length of 30-40mm. The number of metal rods is greater than or equal to 25, preferably between 25-100, with a spacing of 2mm-4mm, and are arranged in a matrix. The number and spacing of the samples are adjusted according to actual conditions.

[0012] The reference electrode adopts an external saturated calomel electrode.

[0013] The gap width is determined by the wire beam electrode and the glass plate. The glass plate covers the entire upper surface of the PTFE base. The distance between the glass plate and the upper surface of the PTFE base is equal to the distance between the glass plate and the wire beam electrode, which is the gap width. The glass plate is moved up and down by the PTFE screw to adjust the gap size. The gap size is calculated by the angle and pitch of the PTFE screw. The details are as follows:

[0014]

[0015] Where, L is the gap width, mm; ω is the rotation angle of the PTFE top screw, °; P is the PTFE top screw pitch, mm.

[0016] Initially, the head of the PTFE screw is flush with the top of the wire-beam electrode and the upper surface of the PTFE base, resulting in a zero gap between the glass plate and the wire-beam electrode. As the PTFE screw is screwed upward, the head of the screw rises above the top of the wire-beam electrode and the upper surface of the PTFE base, lifting the glass plate. The gap width between the glass plate and the wire-beam electrode now equals the distance the PTFE screw has been screwed upward. This distance is calculated based on the screw angle and the screw pitch. When the PTFE screw is rotated at the same angle, a uniform gap is formed between the glass plate and the wire-beam electrode. When the screw is rotated at different angles, a gap of continuously varying width is formed between the glass plate and the wire-beam electrode. To ensure a constant gap width during the experiment, after the PTFE screw is rotated to the appropriate position, it is secured in place with a butterfly PTFE nut to ensure a constant gap width. Use PTFE bolts and PTFE nuts to fix the glass plate on the upper surface of the PTFE base to ensure that the glass plate cannot move up and down.

[0017] A high-throughput testing method for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing is implemented using the high-throughput testing device for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing. The specific operating steps include:

[0018] Step 1: Cast a matrix of filamentary through-holes on a polytetrafluoroethylene cylinder. Connect one end of a rod-shaped sample to a copper wire and insert the other end into the through-hole of the polytetrafluoroethylene cylinder. Then, heat and extrusion are used to eliminate the pores between the rod-shaped sample and the polytetrafluoroethylene cylinder, and the upper surface of the rod-shaped sample is flush with the upper surface of the polytetrafluoroethylene cylinder to achieve sealing of the rod-shaped sample, thus making it a wire bundle electrode.

[0019] Step 2: Fix the wire bundle electrode on the polytetrafluoroethylene base, keeping the top of the wire bundle electrode level with the upper surface of the polytetrafluoroethylene base;

[0020] Step 3: Set the PTFE screw and PTFE bolt on the ear of the upper plane of the PTFE base and cover the glass plate. The glass plate covers the upper plane of the PTFE base and the top of the wire beam electrode, and fix the glass plate to the upper plane of the PTFE base with PTFE bolts and PTFE nuts. The PTFE screw is rotated to lift the glass plate upward to form a gap between the glass plate and the wire beam electrode. After connecting the parts according to the above steps, rotate the PTFE screw to 0° and 360° respectively, and the gap width range is calculated as That is, at this time, the range of the gap width changes continuously between 0 mm and 1 mm, and each thin rod sample of the rod-shaped sample corresponds to a gap width;

[0021] Step 4: Fix the glass plate to the upper surface of the PTFE base with PTFE bolts and PTFE nuts to ensure that the position of the glass plate does not change, that is, the gap width range does not change;

[0022] Step 5: Place the assembled crevice corrosion device and counter electrode in a heatable electrolytic cell, pour nitric acid solution into the electrolytic cell, and make the solution interface submerge the crevice corrosion device and counter electrode. Pass the wire beam electrode and counter electrode through the through-holes on the polytetrafluoroethylene cover and connect them to the electrochemical workstation respectively. One end of the salt bridge is placed in the nitric acid solution in the heatable electrolytic cell, and the other end is placed in a beaker filled with saturated potassium chloride solution to conduct the circuit. The reference electrode is a saturated calomel electrode, which is placed in the beaker and connected to the electrochemical workstation via a wire. The wire beam electrode, counter electrode and reference electrode form a three-electrode system for electrochemical testing of crevice corrosion.

[0023] Step 6: Place the heatable electrolytic cell into the heating jacket, turn on the power of the heating jacket, and set the temperature of the heating jacket through the temperature control panel to heat the three-electrode system;

[0024] Step 7: After the temperature reaches the experimental temperature and stabilizes, soak the sample in nitric acid solution and turn on the electrochemical workstation to perform electrochemical testing of crevice corrosion. The specific method is as follows:

[0025] (1) Electrochemical impedance data of rod-shaped samples were obtained through electrochemical testing. The sizes of the capacitive arcs in the Nyquist plot of the electrochemical impedance data were compared to obtain the thin rods with the most severe corrosion within the width range of 0 mm to 1 mm and their locations. The crevice width corresponding to the thin rod with the most severe crevice corrosion was calculated using the principle of similar triangles, and this crevice width was called the crevice corrosion sensitive width.

[0026] (2) Given the crevice corrosion sensitive width L, the formula Calculate the size of ω, that is, the angle that the PTFE top screw should be rotated, and then rotate the PTFE top screw by ω°. At this time, the width between the glass plate and the wire beam electrode is the crevice corrosion sensitive width;

[0027] (3) Repeat step 4 to ensure that the gap width does not change;

[0028] (4) Repeat steps 5-7 to perform crevice corrosion electrochemical testing on the wire beam electrode at the crevice corrosion sensitive width to obtain the electrochemical impedance data of the rod sample at the crevice corrosion sensitive width. By comparing and analyzing the electrochemical impedance data of the rod sample, the crevice corrosion resistance of the wire beam electrode surface can be obtained, reflecting the crevice corrosion information of the metal sample in the crevice corrosion.

[0029] During the above operation, if the PTFE screw is screwed in at the same angle, the gap width between the glass plate and the rod sample remains uniform. If the PTFE screw is screwed in at different angles, the gap width between the glass plate and the rod sample varies continuously. When the gap width varies continuously, the gap width at each location on the rod sample can be accurately calculated using the principle of similar triangles.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention provides a high-throughput electrochemical testing device and method for simulating crevice corrosion in a boiling nitric acid environment during spent fuel reprocessing. A crevice is formed by a rod-shaped sample and a glass plate above it. The glass plate is controlled to move up and down by a plurality of screws to adjust the size of the crevice. The size of the crevice can be calculated based on the angle and pitch of the screws. To ensure that the crevice width remains constant, after the screws are screwed into the appropriate position, they are fixed in place with nuts, and the glass plate is secured to a polytetrafluoroethylene base with bolts and nuts. The entire crevice corrosion device is placed in a heatable electrolytic cell and connected to an electrochemical workstation to obtain electrochemical signals.

[0032] The device of the present invention combines a continuously changing gap width with a wire beam electrode, allowing each rod-shaped sample to correspond to a different gap width, and monitors the electrochemical signals of crevice corrosion under different gap widths at one time. Therefore, the device can not only capture the corrosion signals of tiny areas, obtain the corrosion laws under different gap widths, and complete high-throughput electrochemical testing, but also integrate the signals captured by each microelectrode to obtain the overall corrosion status of the material. At the same time, the device uses polytetrafluoroethylene as the raw material to make the top screw, bolts, nuts and bottom bracket, which have good electrical insulation properties and strong corrosion resistance, and can meet the needs of long-term electrochemical experiments in a high-temperature concentrated nitric acid environment. The simulation and study of crevice corrosion in a boiling concentrated nitric acid environment have been realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 、 Figure 2 、 Figure 3 and Figure 4 This is a structural diagram of the device of the present invention. Figure 1 This is the main view of the crevice corrosion device. Figure 2 This is the top view of the crevice corrosion device. Figure 3 Schematic diagram of wire beam electrode. Figure 4 This is a schematic diagram of the overall electrochemical test structure. In the figure, 1 - PTFE screw; 2 - butterfly PTFE nut; 3 - PTFE bolt; 4 - glass plate; 5 - PTFE nut; 6 - PTFE base; 7 - wire bundle electrode; 8 - rod sample; 9 - PTFE cylinder; 10 - crevice corrosion apparatus; 11 - heating jacket; 12 - counter electrode; 13 - heatable electrolytic cell; 14 - PTFE cover; 15 - electrochemical workstation; 16 - salt bridge; 17 - reference electrode; 18 - beaker; 19 - lead I; 20 - lead II; 21 - lead III.

[0034] Figure 5 is the Nyquist diagram of crevice corrosion under boiling concentrated nitric acid, where Figure 5 (a) is the Nyquist diagram for gap widths of 0.1 mm, 0.2 mm, and 0.3 mm. Figure 5 (b) Nyquist diagram at different times when the gap width is 0.1 mm. DETAILED DESCRIPTION

[0035] like Figures 1-4As shown, the present invention provides a high-throughput testing device for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing. The device includes: 10-crevice corrosion device, 11-heating jacket, 12-counter electrode, 13-heatable electrolytic cell, 14-PTFE cover, 15-electrochemical workstation, 16-salt bridge, 17-reference electrode, 18-beaker, 19-wire I, 20-wire II, and 21-wire III. The crevice corrosion device 10 is composed of 1-PTFE top screw, 2-butterfly PTFE nut, 3-PTFE bolt, 4-glass plate, 5-PTFE nut, 6-PTFE base, and 7-wire bundle electrode; the wire bundle electrode 7 is composed of 8-rod sample and 9-PTFE cylinder.

[0036] The rod-shaped sample 8 is composed of 25 titanium alloy thin rods with a diameter of 1 mm and a length of 30 mm. The polytetrafluoroethylene cylinder 9 is 30 mm high and has 25 filamentary through holes arranged in a matrix from one bottom surface to the other. A wire I19 is welded to one end of the rod-shaped sample 8 for connecting to the electrochemical workstation 15 (this wire is the wire I19 that connects the wire bundle electrode 7 to the electrochemical workstation 15). The other end of the rod-shaped sample 8 is inserted from one bottom surface of the polytetrafluoroethylene cylinder 9 into the filamentary through hole of the polytetrafluoroethylene cylinder 9, and the inserted end of the rod-shaped sample 8 is made flush with the other bottom surface of the polytetrafluoroethylene cylinder 9 to form a wire bundle electrode 7.

[0037] One end of the wire bundle electrode 7 connecting lead I19 is defined as the bottom of the wire bundle electrode 7, and the other end is defined as the top of the wire bundle electrode 7. The wire bundle electrode 7 is fixed within the cylindrical body of the polytetrafluoroethylene base 6. The polytetrafluoroethylene base 6 is I-shaped, with circular upper and lower surfaces and a cylindrical center. The cylinder is 30 mm tall and contains upper and lower through holes with diameters commensurate with the diameter of the wire bundle electrode 7. The upper through hole exposes the top of the wire bundle electrode 7, while the bottom through hole has a smaller opening diameter than the wire bundle electrode 7 and is used to guide the wire bundle electrode 7 and secure it. The top of the wire bundle electrode 7 is flush with the upper surface of the polytetrafluoroethylene base 6, and the wire bundle electrode 7 connecting lead I19 extends from the bottom through hole of the polytetrafluoroethylene base 6. Two polytetrafluoroethylene top screws 1 and four polytetrafluoroethylene bolts 3 are provided on the upper surface of the polytetrafluoroethylene base 6 and covered by a glass plate 4. The glass plate 4 covers the entire upper surface of the PTFE base 6. The top of the wire beam electrode 7 is level with the upper surface of the PTFE base 6. The distance between the glass plate 4 and the upper surface of the PTFE base 6 is equal to the distance between the glass plate 4 and the wire beam electrode 7, which is the gap width. The PTFE screw 1 is screwed upward to control the gap size, and the PTFE bolt 3 is installed downward to fix the position of the glass plate 4. In the initial state, the head of the PTFE screw 1 is aligned with the top of the wire beam electrode 7 and the upper surface of the PTFE base 6. At this time, the gap width between the glass plate 4 and the wire beam electrode 7 is zero. When the PTFE screw 1 is screwed in upward, the head of the PTFE screw 1 is higher than the top of the wire beam electrode 7 and the upper plane of the PTFE base 6, and the glass plate 4 is lifted up. At this time, the width of the gap between the glass plate 4 and the wire beam electrode 7 is the distance that the PTFE screw 1 is screwed in upward. This distance is calculated by the screwing angle of the PTFE screw 1 and the pitch of the PTFE screw 1. The specific formula is as follows:

[0038]

[0039] Where L is the gap width, mm; ω is the rotation angle of the PTFE top screw, °; P is the pitch of the PTFE top screw, mm.

[0040] The butterfly-shaped PTFE nut 2 secures the PTFE screw 1, ensuring that the portion of the PTFE screw 1 protruding from the plane remains unchanged, thus maintaining the gap width. The PTFE nut 5, in conjunction with the PTFE bolt 3, secures the four corners of the glass plate 4, ensuring that the gap width between the glass plate 4 and the wire beam electrode 7 remains constant. The PTFE screw 1, butterfly-shaped PTFE nut 2, PTFE bolt 3, glass plate 4, PTFE nut 5, PTFE base 6, and wire beam electrode 7 together constitute the crevice corrosion device 10.

[0041] The crevice corrosion device 10 and the counter electrode 12 are placed in the solution in the heatable electrolytic cell 13. The counter electrode 12, the salt bridge 16, and a through hole for connecting the wire beam electrode 7 and the electrochemical workstation 15 are provided on the polytetrafluoroethylene cover 14. The reference electrode 17 adopts an external saturated calomel electrode, which is placed in a beaker 18 filled with a saturated potassium chloride solution. The beaker 18 filled with a saturated potassium chloride solution is connected to the solution in the heatable electrolytic cell 13 through the salt bridge 16. The wire beam electrode 7, the counter electrode 12 and the reference electrode 17 form a three-electrode system, which are respectively connected to the electrochemical workstation 15 through the wire I19, the wire II 20 and the wire III 21. The heating jacket 11 is placed outside the heatable electrolytic cell to control the temperature of the system.

[0042] A high-throughput testing method for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing is implemented using the high-throughput testing device for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing. The specific operating steps include:

[0043] Step 1: Prefabricate a polytetrafluoroethylene (PTFE) cylindrical mold and process it at 327-342°C. Cast a 5×5 matrix of filamentary through-holes on the polytetrafluoroethylene (PTFE) cylinder 9, with a center-to-center distance of 2 mm between each through-hole. Prepare 25 titanium alloy thin rod samples with a diameter of 1 mm and a length of 30 mm to form rod-shaped sample 8, with each thin rod sample corresponding to the through-holes. Connect one end of the rod-shaped sample 8 to a copper wire, and insert the other end into the through-hole of the polytetrafluoroethylene (PTFE) cylinder 9. Then, use a heated extrusion method to eliminate the pores between the rod-shaped sample 8 and the polytetrafluoroethylene (PTFE) cylinder 9, leaving only the top surface of the rod-shaped sample 8 exposed. The top surface is flush with the top surface of the polytetrafluoroethylene (PTFE) cylinder 9, thus sealing the rod-shaped sample and producing the wire bundle electrode 7.

[0044] Step 2: Fix the wire bundle electrode 7 on the polytetrafluoroethylene base 6, and keep the top of the wire bundle electrode 7 flush with the upper surface of the polytetrafluoroethylene base 6.

[0045] Step 3: Set two PTFE top screws 1 and four PTFE bolts 3 on both sides of the flat ear of the PTFE base 6, and process a thread with a pitch of 1mm on the PTFE top screw 1. The glass plate 4 covers the upper plane of the PTFE base 6 and the top of the wire beam electrode 7, and the glass plate is fixed to the upper plane of the PTFE base 6 with the PTFE bolts 3 and the PTFE nuts 5. The PTFE top screw 1 is rotated to lift the glass plate 4 upward to form a gap between the glass plate 4 and the wire beam electrode 7. After connecting the parts according to the above steps, rotate the two PTFE top screws 1 to 0° and 360° respectively, and the gap width range is calculated as That is, the gap width varies continuously between 0 mm and 1 mm, and each thin rod sample of the rod-shaped samples 8 corresponds to a gap width.

[0046] Step 4: Fix the glass plate 4 on the upper plane of the polytetrafluoroethylene base 6 by using the polytetrafluoroethylene bolts 3 and polytetrafluoroethylene nuts 5 to ensure that the position of the glass plate 4 does not move, that is, the gap width range does not change.

[0047] Step 5: Place the assembled crevice corrosion apparatus 10 and counter electrode 12 in a heatable electrolytic cell 13. Pour nitric acid solution into the electrolytic cell, ensuring that the solution interface covers the crevice corrosion apparatus 10 and counter electrode 12. Wire I19 connected to the wire bundle electrode 7 and wire II 20 connected to the counter electrode 12 are passed through the through holes in the polytetrafluoroethylene cover 14 and connected to the electrochemical workstation 15. One end of the salt bridge 16 is placed in the nitric acid solution in the heatable electrolytic cell 13, and the other end is placed in a beaker 18 filled with saturated potassium chloride solution to complete the circuit. The reference electrode 17 is a saturated calomel electrode placed in the beaker 18 and connected to the electrochemical workstation 15 via a wire III 21. The wire bundle electrode 7, counter electrode 12, and reference electrode 7 form a three-electrode system for electrochemical testing of crevice corrosion.

[0048] Step 6: Place the heatable electrolytic cell 13 into the heating jacket 11. Turn on the power of the heating jacket and set the temperature of the heating jacket via the temperature control panel to heat the three-electrode system to 100°C.

[0049] Step 7: After the temperature reaches the experimental temperature and stabilizes, soak the sample in a 100°C nitric acid solution for a period of time, and then turn on the electrochemical workstation 15 to perform the electrochemical test of crevice corrosion. The specific operation is as follows:

[0050] (1) The electrochemical impedance data corresponding to each thin rod sample can be obtained through electrochemical testing, such as the Nyquist plot. By comparing the size of the capacitive reactance arc in the Nyquist plot of thin rod samples at different positions, the thin rod sample with the most severe corrosion and its position within the gap width range of 0mm-1mm are obtained. By using the principle of similar triangles, the gap width corresponding to the thin rod sample with the most severe crevice corrosion is calculated, and this gap width is called the crevice corrosion sensitive width. In this embodiment, the Nyquist plots of thin rod samples with corresponding gap widths of 0.1mm, 0.2mm and 0.3mm are selected for comparison. Figure 5 (a) It can be seen that when the gap width is 0.1mm, the capacitive reactance arc of its Nyquist diagram is the smallest, so 0.1mm can be considered as the sensitive gap width;

[0051] (2) After obtaining the crevice corrosion sensitive width, the crevice corrosion behavior under this crevice width is further studied. Since the crevice corrosion sensitive width L is known to be 0.1 mm, it can be calculated by the formula Calculate the value of ω, which means the angle that the PTFE screw 1 should be rotated to is 36°. Then rotate both PTFE screws 1 by 36°. At this point, the width between the glass plate 4 and the wire beam electrode 7 is 0.1 mm.

[0052] (3) Repeat step 4 to ensure that the gap width does not change.

[0053] (4) Repeat steps 5-7. Extend the immersion time to 240h, and test the electrochemical impedance of the sample at regular intervals. Obtain the change of the sample's crevice corrosion resistance over time when the crevice width is 0.1mm. Figure 5 (b) It can be seen that as time goes by, the crevice corrosion resistance of the sample becomes weaker and weaker.

[0054] The above examples prove that the high-throughput test device for crevice corrosion is reliable and can meet the requirements of electrochemical testing of crevice corrosion under boiling nitric acid.

Claims

1. A high-throughput test device simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing, characterized in that: The device comprises: a crevice corrosion device, a heating jacket, a counter electrode, a heatable electrolytic cell, a polytetrafluoroethylene cover, an electrochemical workstation, a salt bridge, a reference electrode, a beaker, a wire I, a wire II, and a wire III; wherein the crevice corrosion device comprises a polytetrafluoroethylene top screw, a butterfly polytetrafluoroethylene nut, a polytetrafluoroethylene bolt, a glass plate, a polytetrafluoroethylene nut, a polytetrafluoroethylene bottom support, and a wire bundle electrode; the wire bundle electrode is composed of a rod-shaped sample and a polytetrafluoroethylene cylinder; The rod-shaped sample is composed of several thin metal rods. The height of the polytetrafluoroethylene cylinder is greater than or equal to the length of the rod-shaped sample. Wire-shaped through holes arranged in a matrix are cast from one bottom surface to the other bottom surface. A wire is welded to one end of the rod-shaped sample for connection to an electrochemical workstation, and the other end is inserted from one bottom surface of the polytetrafluoroethylene cylinder into the wire-shaped through hole of the polytetrafluoroethylene cylinder, and the inserted end of the rod-shaped sample is flush with the other bottom surface of the polytetrafluoroethylene cylinder to produce a wire bundle electrode. One end of the wire beam electrode connecting wire I is the bottom of the wire beam electrode, and the other end is the top of the wire beam electrode. The wire beam electrode is fixed in the cylinder of the polytetrafluoroethylene base. The polytetrafluoroethylene base is in an I-shape, with two circular upper and lower planes and a cylindrical middle. The upper and lower through holes are used to expose the top of the wire beam electrode. The opening diameter of the bottom through hole is smaller than the diameter of the wire beam electrode, which is used to lead out the wire of the wire beam electrode and fix the wire beam electrode. The top of the wire beam electrode is flush with the upper plane of the polytetrafluoroethylene base. The wire I connected to the wire beam electrode extends out from the lower through hole of the polytetrafluoroethylene base. A polytetrafluoroethylene top screw and a polytetrafluoroethylene bolt are provided on the upper plane of the polytetrafluoroethylene base and cover the glass plate. The polytetrafluoroethylene top screw is screwed upward to lift the glass plate to create a gap and control the size of the gap. The polytetrafluoroethylene bolt is installed downward to fix the glass plate. The polytetrafluoroethylene top screw is fixed by a butterfly polytetrafluoroethylene nut. The polytetrafluoroethylene bolt cooperates with the polytetrafluoroethylene nut to fix the four corners of the glass plate to form a crevice corrosion device. The crevice corrosion device and the counter electrode are placed in a solution in a heatable electrolytic cell. The polytetrafluoroethylene cover is provided with a counter electrode, a salt bridge, and a through hole for connecting the wire bundle electrode and the electrochemical workstation. The reference electrode is placed in a beaker filled with a saturated potassium chloride solution, and the beaker filled with the saturated potassium chloride solution is connected to the solution in the heatable electrolytic cell via the salt bridge. The wire bundle electrode, the counter electrode, and the reference electrode form a three-electrode system, which is connected to the electrochemical workstation via wires I, II, and III, respectively. A heating jacket is placed outside the heatable electrolytic cell to control the system temperature. The rod-shaped sample is composed of several thin metal rods with a diameter of 0.6 mm to 2 mm and a length of 30 mm to 40 mm. The number of the thin metal rods is greater than or equal to 25 and is arranged in a matrix.

2. A high-throughput testing device for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing according to claim 1, characterized in that: The number of the thin metal rods is between 25 and 100, and the spacing between them is between 2 mm and 4 mm.

3. The high-throughput testing device for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing according to claim 1, characterized in that: The reference electrode adopts an external saturated calomel electrode.

4. The high-throughput testing device for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing according to claim 1, characterized in that: The size of the gap width is formed by the wire beam electrode and the glass plate. The distance between the glass plate and the upper plane of the polytetrafluoroethylene base is equal to the distance between the glass plate and the wire beam electrode, which is the size of the gap. The glass plate is controlled to move up and down by the polytetrafluoroethylene top screw to adjust the size of the gap. The size of the gap is calculated by the rotation angle and pitch of the polytetrafluoroethylene top screw. The specific formula is: ; Wherein, L is the gap width, mm; ω is the rotation angle of the PTFE top screw, °; P is the pitch of the PTFE top screw, mm.

5. A high-throughput testing method for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing, characterized in that: The high-throughput testing device for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing according to claim 1 is used, and the operating steps include: Step 1: Cast a matrix of filamentary through-holes on a polytetrafluoroethylene cylinder. Connect one end of a rod-shaped sample to a copper wire and insert the other end into the through-hole of the polytetrafluoroethylene cylinder. Use heat extrusion to eliminate the gap between the rod-shaped sample and the polytetrafluoroethylene cylinder, and make the upper surface of the rod flush with the upper surface of the polytetrafluoroethylene cylinder to achieve sealing of the rod-shaped sample, thus making it a wire bundle electrode. Step 2: Fix the wire bundle electrode on the polytetrafluoroethylene base, keeping the top of the wire bundle electrode level with the upper surface of the polytetrafluoroethylene base; Step 3: Set the PTFE screw and PTFE bolt on the ear of the upper plane of the PTFE base and cover the glass plate. The glass plate covers the upper plane of the PTFE base and the top of the wire beam electrode, and fix the glass plate to the upper plane of the PTFE base with PTFE bolts and PTFE nuts. The PTFE screw is rotated to lift the glass plate upward to form a gap between the glass plate and the wire beam electrode. After connecting the parts according to the above steps, rotate the PTFE screw to 0° and 360° respectively, and the gap width range is calculated as 、 ; That is, at this time, the range of the gap width changes continuously between 0 mm and 1 mm, and each thin rod sample of the rod-shaped sample corresponds to a gap width; Step 4: Fix the glass plate to the upper surface of the PTFE base with PTFE bolts and PTFE nuts to ensure that the position of the glass plate does not change, that is, the gap width range does not change; Step 5: Place the assembled crevice corrosion device and counter electrode in a heatable electrolytic cell, pour nitric acid solution into the electrolytic cell, and make the solution interface submerge the crevice corrosion device and counter electrode. Pass the wire beam electrode and counter electrode through the through-holes on the polytetrafluoroethylene cover and connect them to the electrochemical workstation respectively. One end of the salt bridge is placed in the nitric acid solution in the heatable electrolytic cell, and the other end is placed in a beaker filled with saturated potassium chloride solution to conduct the circuit. The reference electrode is a saturated calomel electrode, which is placed in the beaker and connected to the electrochemical workstation via a wire. The wire beam electrode, counter electrode and reference electrode form a three-electrode system for electrochemical testing of crevice corrosion. Step 6: Place the heatable electrolytic cell into the heating jacket, turn on the power of the heating jacket, and set the temperature of the heating jacket through the temperature control panel to heat the three-electrode system; Step 7: After the temperature reaches the experimental temperature and stabilizes, soak the sample in nitric acid solution and turn on the electrochemical workstation to perform electrochemical testing of crevice corrosion.

6. The high-throughput testing method for simulating crevice corrosion in boiling nitric acid during spent fuel reprocessing according to claim 5, characterized in that: Conduct electrochemical testing for crevice corrosion, including: (1) The electrochemical impedance data of the rod samples were obtained by electrochemical testing. The most severely corroded thin rods and their positions within the width range of 0 mm to 1 mm were obtained by comparing the sizes of the capacitive arcs in the Nyquist diagram of the electrochemical impedance data. The crevice width corresponding to the thin rod with the most severe crevice corrosion was calculated by the principle of similar triangles, and this crevice width was called the crevice corrosion sensitive width. (2) The crevice corrosion sensitive width L is known, and the formula , calculate the size of ω, that is, the angle that the PTFE top screw should be rotated, and then rotate the PTFE top screw by ω°. At this time, the width between the glass plate and the wire beam electrode is the crevice corrosion sensitive width; (3) Repeat step 4 to ensure that the gap width does not change; (4) Repeat steps 5-7 to perform crevice corrosion electrochemical testing on the wire beam electrode at the crevice corrosion sensitive width to obtain the electrochemical impedance data of the rod sample at the crevice corrosion sensitive width. By comparing and analyzing the electrochemical impedance data of the rod sample, the crevice corrosion resistance of the wire beam electrode surface can be obtained, reflecting the crevice corrosion information of the metal sample in the crevice corrosion.

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