Method for removing oxide layer of retired facility by electrochemical denucleation based on synergistic acidic electrolyte

Abstract

The invention discloses an electrochemical denucleation decommissioning facility oxide layer method based on a synergistic acidic electrolyte, and relates to the technical field of cleaning. The method comprises the following steps: by taking a polluted metal component as an anode and an inert electrode as a cathode, immersing the polluted metal component into a synergistic acidic electrolyte of a low-concentration acidic medium, and stripping an oxide layer on the surface of the polluted metal component until a clear grain boundary is exposed at the temperature of lower than 40 DEG C in a high-voltage direct-current electrolysis mode. By developing a synergistic enhanced acidic electrolyte system, high decontamination rate is realized in a low-concentration sulfuric acid medium, radionuclide stripping is accurately controlled to avoid matrix pitting corrosion damage, and high-valence nuclides in a compact oxide layer are deeply removed, so that the decontamination efficiency is improved. Finally, an efficient, low-damage and stable-process radioactive contamination metal treatment scheme is provided for nuclear facility decommissioning engineering. The method is suitable for removing radioactive contamination oxidation layers on the surfaces of the inner walls of stainless steel pipelines and reactor containers in nuclear facility decommissioning projects, and radionuclides are enriched in the oxidation layers.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cleaning, in particular to an electrochemical de-nucleation method for oxide layer of decommissioned facilities based on synergistic acidic electrolyte. BACKGROUND

[0002] During the long-term operation and decommissioning of nuclear facilities, the surface of metal components (especially stainless steel materials) will form a dense and complex oxide layer due to exposure to radioactive waste liquid environment. This oxide layer is rich in fissile product nuclides (such as Sr, 90 Sr, 137 Cs, Mo, La, etc.), which poses a potential risk of radioactive diffusion and is one of the key challenges in the decommissioning of nuclear facilities and waste minimization.

[0003] The current mainstream technology for nuclear pollution decontamination has problems such as low efficiency, substrate damage, and difficulty in removing deep nuclides. Chemical soaking method is to dissolve the pollutants by using high-concentration strong acid. This method is relatively simple to operate, but its decontamination efficiency is generally low, and it is difficult to effectively remove deep nuclides, while generating a large amount of secondary waste liquid containing high-activity radioactive nuclides, increasing the difficulty and cost of subsequent treatment. Mechanical decontamination method removes the oxide layer through physical actions such as sandblasting and grinding. This method is easy to cause mechanical damage to the metal substrate, destroy the integrity of the substrate and change the geometric size of the component, affecting the safety of the component's re-service.

[0004] Traditional electrochemical decontamination method based on anodic oxidation process of acidic electrolyte (such as pure sulfuric acid, nitric acid solution) to treat radioactive nuclides still faces multiple technical bottlenecks. First, the low concentration of acid solution has insufficient conductivity, making it difficult to efficiently remove the oxide layer, while increasing the acid concentration of the acid solution will exacerbate the acid corrosion of the metal substrate. Second, the anodic polarization effect causes uneven distribution of current on the electrode surface, resulting in excessive corrosion in local areas while other areas are not cleaned enough. Third, the dissociation ability of high-valence radioactive nuclides (such as Mo, La, etc.) tightly bound in the dense oxide layer is weak, and experimental data shows that the residual rate is high. The above defects seriously restrict the engineering application of existing electrochemical decontamination technology in efficient, low-damage, and deep removal of radioactive nuclides. SUMMARY

[0005] The application aims to provide an electrochemical de-nucleation method for oxide layers of decommissioned facilities based on a synergistic acidic electrolyte, to overcome the technical bottlenecks in the existing electrochemical decontamination technology for radioactive contaminated metal surfaces, such as low decontamination efficiency, easy damage to the metal substrate, difficulty in effectively removing deeply embedded high-valence radionuclides, and poor process stability. By developing a graphene-anion surfactant synergistically enhanced acidic electrolyte system, high decontamination efficiency is achieved in a low-concentration sulfuric acid medium, while the peeling of radionuclides is precisely controlled to avoid substrate pitting damage, and high-valence nuclides in the dense oxide layer are deeply removed, ultimately providing an efficient, low-damage and stable process for the treatment of radioactive contaminated metals in nuclear facility decommissioning projects.

[0006] Based on the above purpose, the application discloses an electrochemical de-nucleation method for oxide layers of decommissioned facilities based on a synergistic acidic electrolyte. The contaminated metal component is an anode, the inert electrode is a cathode, and the contaminated metal component is immersed in a synergistic acidic electrolyte in a low-concentration acidic medium. The temperature is lower than 40 DEG C, 40 DEG C is prevented from SDS cloud point effect, the treatment time is less than 3 hours, and the high-voltage direct current electrolysis mode is adopted. The surface oxide layer of the contaminated metal component is peeled off to expose clear grain boundaries, and micron-sized pitting pits are formed on the substrate surface.

[0007] Preferably, the synergistic acidic electrolyte comprises a low-concentration inorganic acid, graphene functional conductive suspended particles and an anion surfactant.

[0008] Preferably, the low-concentration inorganic acid is sulfuric acid or nitric acid, and the anion surfactant is sodium dodecyl sulfate.

[0009] Preferably, the concentration of the low-concentration inorganic acid is 0.1-0.2 mol / L; the concentration of the graphene functional conductive suspended particles is 0.01-0.07 g / L; and the concentration of the anion surfactant is 0.02-0.14 g / L.

[0010] Preferably, in the high-voltage direct current electrolysis mode, the input voltage is 3-6 V, and the output voltage is 30-70 V.

[0011] Preferably, the method comprises the following steps:

[0012] (1) configuring a synergistic acidic electrolyte, diluting the acid to the target concentration when preparing, adding SDS and stirring magnetically for 10 minutes to dissolve, and then slowly adding graphene and ultrasonically dispersing for 30 minutes to form a stable suspension;

[0013] (2) adjusting parameters, and electrochemically de-nucleating oxide layers of decommissioned facilities;

[0014] (3) quantifying the decontamination rate based on the dry weight change rate;

[0015] (4) SEM observation of surface morphology to confirm the exposure of grain boundaries and the peeling of the oxide layer; and EDS analysis of high-valence element signals to test the degree of oxide layer peeling; if the oxide layer is not completely peeled off, repeat step (2);

[0016] (5) Dynamically adjust the electrolysis parameters according to the thickness and the target decontamination rate to optimize the electrochemical decontamination process parameters.

[0017] Real-time monitoring of key parameters during the process, and safe discharge of byproduct hydrogen through airtight tank cover gas guide pipe to ensure process stability.

[0018] Preferably, the method is suitable for removing the oxide layer of the stainless steel pipeline and the inner wall surface of the reactor vessel in the nuclear facility decommissioning project, and the oxide layer is enriched with radioactive nuclides.

[0019] Therefore, the present application adopts the above-mentioned electrochemical decontamination method based on the synergistic acidic electrolyte for removing the oxide layer of the decommissioned nuclear facility, and has the following beneficial effects:

[0020] (1) The present application successfully breaks through the technical bottleneck of traditional acid electrochemical decontamination through material synergistic effect. The electronic transmission channel constructed by graphene greatly enhances the ion migration efficiency under low acid concentration, so that the system can achieve the decontamination ability of high-concentration acid under mild acid conditions, thereby fundamentally avoiding the damage risk of high-acid corrosion to the metal substrate. The directional arrangement of SDS molecules on the electrode surface effectively homogenizes the current distribution, inhibits the local over-corrosion phenomenon caused by current focusing in the traditional anodic oxidation process, ensures the uniformity and controllability of the oxide layer peeling process, and eliminates the hidden dangers of pitting and intergranular corrosion. Therefore, the dual action mechanism of graphene and sodium dodecyl sulfate (SDS) in low-concentration sulfuric acid medium, which forms a three-dimensional conductive network and a directional adsorption layer, not only significantly improves the conductivity of the electrolyte, but also realizes the selective deep removal of radioactive nuclides through interface regulation. The defects of the nitric acid system are caused by the continuous decontamination reaction, which leads to the existence of residual oxide layer and passivation-pitting mechanism; optimization is required to increase the acid concentration and inhibit the oxidation / passivation reaction;

[0021] (2) The present application adopts acid electrochemical decontamination technology, which can effectively remove the passivation layer containing radioactive nuclides. The high-valence nuclides (such as Mo, La) enriched on the surface layer of the oxide layer and existing in the form of oxides and having higher electrochemical activity are removed, so that they are more likely to undergo oxidation-reduction reaction in the electrolyte. In the sulfuric acid system (Example 1), through directional oxidation dissolution, Mo and La signals can be completely removed ( Figure 6 ), while maintaining the integrity of the substrate Cr and Fe. The appropriate addition of graphene can form a three-dimensional conductive network to uniformly disperse the current to avoid local charge accumulation; but excessive addition will cause graphene to be adsorbed on the electrode surface, reducing the effective contact area and thus weakening the decontamination effect ( Figure 30). By precisely controlling the current, voltage, the over electrolysis phenomenon in the electrochemical decontamination process can be reduced. The temperature parameter also needs to be controlled during the experiment. When the temperature of the electrolyte exceeds 40 DEG C, the surfactant SDS will reach the cloud point and lose effectiveness, causing a large amount of foaming and leading to the settlement of graphene, resulting in a sharp drop in conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The schematic diagram of the electrochemical decontamination equipment of the present application is shown in the figure.

[0023] Figure 2 The process flow chart of the electrochemical decontamination process of the present application is shown in the figure.

[0024] Figure 3 The micro-morphology graph of the sample of example 1 of the present application after electrolysis for 8 minutes is shown in the figure.

[0025] Figure 4 The EDS energy spectrum graph of the sample of example 1 of the present application after electrolysis for 8 minutes is shown in the figure.

[0026] Figure 5 The micro-morphology graph of the sample of example 1 of the present application after complete electrolysis is shown in the figure; wherein a is the micro-morphology graph under the scale of 50 mu m; b is the micro-morphology graph under the scale of 20 mu m.

[0027] Figure 6 The EDS energy spectrum graph of the sample of example 1 of the present application after complete electrolysis is shown in the figure.

[0028] Figure 7 The morphology graph of the sample of example 1 of the present application before electrolysis is shown in the figure; wherein a is the sample photo; b is the microscope graph.

[0029] Figure 8 The morphology graph of the sample of example 1 of the present application after electrolysis for 8 minutes is shown in the figure; wherein a is the sample photo; b is the microscope graph.

[0030] Figure 9 The photo of the sample of example 1 of the present application after complete electrolysis is shown in the figure.

[0031] Figure 10 The morphology graph of the sample of example 2 of the present application before electrolysis is shown in the figure; wherein a is the sample photo; b is the microscope graph.

[0032] Figure 11 The microscope graph of the sample of example 2 of the present application after electrolysis for 8 minutes is shown in the figure.

[0033] Figure 12 The photo of the sample of example 2 of the present application after complete electrolysis is shown in the figure.

[0034] Figure 13 The morphology graph of the sample of example 3 of the present application before electrolysis is shown in the figure; wherein a is the sample photo; b is the microscope graph.

[0035] Figure 14 The morphology diagram of the sample of the present application embodiment 3 electrolysis for 8 minutes; wherein, a is the sample photo; b is the microscope diagram;

[0036] Figure 15 The photo of the sample of the present application embodiment 3 after complete electrolysis;

[0037] Figure 16 The morphology diagram of the sample of the present application embodiment 4 before electrolysis; wherein, a is the sample photo; b is the microscope diagram;

[0038] Figure 17 The morphology diagram of the sample of the present application embodiment 4 electrolysis for 8 minutes; wherein, a is the sample photo; b is the microscope diagram;

[0039] Figure 18 The photo of the sample of the present application embodiment 4 after complete electrolysis;

[0040] Figure 19 The morphology diagram of the sample of the present application embodiment 5 before electrolysis; wherein, a is the sample photo; b is the microscope diagram;

[0041] Figure 20 The morphology diagram of the sample of the present application embodiment 5 electrolysis for 8 minutes; wherein, a is the sample photo; b is the microscope diagram;

[0042] Figure 21 The morphology diagram of the sample of the present application embodiment 6 before electrolysis; wherein, a is the sample photo; b is the microscope diagram;

[0043] Figure 22 The morphology diagram of the sample of the present application embodiment 6 electrolysis for 8 minutes; wherein, a is the sample photo; b is the microscope diagram;

[0044] Figure 23 The photo of the sample of the present application embodiment 6 after complete electrolysis;

[0045] Figure 24 The morphology diagram of the sample of the present application embodiment 7 before electrolysis; wherein, a is the sample photo; b is the microscope diagram;

[0046] Figure 25 The morphology diagram of the sample of the present application embodiment 7 electrolysis for 8 minutes; wherein, a is the sample photo; b is the microscope diagram;

[0047] Figure 26 The photo of the sample of the present application embodiment 7 after complete electrolysis;

[0048] Figure 27 The morphology diagram of the sample of the present application embodiment 8 before electrolysis; wherein, a is the sample photo; b is the microscope diagram;

[0049] Figure 28 The morphology diagram of the sample electrolysis of the embodiment 8 of the application for 8 minutes; wherein, a is the sample photo; b is the microscope diagram;

[0050] Figure 29 The photo of the sample after complete electrolysis of the embodiment 8 of the application;

[0051] Figure 30 The decontamination rate of the sample electrolysis of the embodiments 1-8 of the application for 8 minutes. DETAILED DESCRIPTION

[0052] The technical solutions of the application are further described below through the drawings and embodiments.

[0053] The application discloses an electrochemical deoxidation method for oxide layers of decommissioned facilities based on a synergistic acidic electrolyte. Figure 1 As shown in the figure, the polluted metal component is an anode, the inert electrode is a cathode, the synergistic acidic electrolyte is immersed in a low-concentration acidic medium, the temperature is lower than 40 DEG C, and the SDS cloud point effect is placed; a high-voltage direct-current electrolysis mode is used to strip the surface oxide layer of the polluted metal component to expose clear grain boundaries and form micron-level pitting pits on the surface of the substrate. Real-time monitoring of key parameters during the process, safe discharge of byproduct hydrogen gas through airtight tank cover gas guide pipe, and ensuring process stability.

[0054] The synergistic acidic electrolyte mainly uses a low-concentration inorganic acid as a main body, introduces graphene functional conductive suspended particles and an anionic surfactant to construct a synergistically enhanced system. The graphene forms a three-dimensional conductive network by virtue of the ultra-high specific surface area and electron mobility, and significantly improves the charge transport efficiency; the SDS inhibits agglomeration through electrostatic repulsion and steric hindrance effect, and ensures dispersion stability. When preparing, the acid solution needs to be diluted to the target concentration first, the SDS is added, magnetically stirred for 10 minutes to dissolve, and then the graphene is slowly added and ultrasonically dispersed for 30 minutes to form a stable suspension.

[0055] The low-concentration inorganic acid is sulfuric acid, and the anionic surfactant is sodium dodecyl sulfate. The concentration of sulfuric acid is 0.1-0.2 mol / L; the concentration of graphene functional conductive suspended particles is 0.01-0.07 g / L; and the concentration of anionic surfactant is 0.02-0.14 g / L.

[0056] In the high-voltage direct-current electrolysis mode, the input voltage is 3-6 V, and the output voltage is 30-70 V.

[0057] The process flow chart of the application is shown in the figure, which includes the following steps: Figure 2

[0058] (1) configuring a synergistic acidic electrolyte;

[0059] (2) adjusting parameters, and electrochemically deoxidizing oxide layers of decommissioned facilities;​

[0060] (3) Quantify the decontamination rate based on the change rate of dry weight;

[0061] (4) SEM observation of surface morphology to confirm the exposure of grain boundaries and the peeling of the oxide layer; and EDS analysis of high-valence element signals to test the degree of oxide layer peeling; if the oxide layer is not completely peeled, repeat step (2);

[0062] (5) Dynamically adjust the electrolysis parameters in combination with the thickness and the target decontamination rate to optimize the electrochemical decontamination process parameters.

[0063] The method is suitable for removing the oxide layer of the stainless steel pipeline and the inner wall surface of the reactor vessel in the nuclear facility decommissioning project, and the oxide layer is enriched with radioactive nuclides.

[0064] Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the usual meaning understood by a person skilled in the art in the field to which the present application belongs.

[0065] In addition, it should be understood that although the present specification is described in terms of embodiments, each embodiment does not necessarily contain only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand. These other embodiments are also covered by the protection scope of the present application.

[0066] In the following examples, the test samples are all 304L stainless steel metal sheets with a size of 1 cm x 1 cm and a thickness of 2 mm, which are treated by 700℃ simulated nuclear waste liquid (pH = 6-6.5) for 500 hours to form a dense oxide layer enriched with simulated radioactive nuclides (such as Sr, Cs, Mo, La, etc.).

[0067] In the following examples, the electrochemical decontamination equipment shown in Figure 1 is used for operation.

[0068] Example 1

[0069] The present embodiment provides a method for electrochemically removing the oxide layer of a decommissioned nuclear facility based on a synergistic acidic electrolyte, comprising the following steps:

[0070] (1) Configure the synergistic acidic electrolyte: when preparing, the acid solution needs to be diluted to the target concentration first, SDS is added and stirred magnetically for 10 minutes until dissolved, and then graphene is slowly added and ultrasonically dispersed for 30 minutes to form a stable suspension. In this embodiment, the system is 0.1 mol / L sulfuric acid + 0.01 g / L graphene + 0.02 g / L SDS.

[0071] (2) Adjusted parameters, electrochemical parameters are voltage 55.1 V, current 5.158 A, power 284.2 W.

[0072] (3) The mass of the sample before decontamination is 5.9174 g, and the mass decreases to 5.6857 g after 8 minutes of electrolysis. The dry weight after complete decontamination is 5.4963 g. Based on the dry weight change rate, the decontamination rate after 8 minutes of electrolysis is 55%.

[0073] The micro-morphology of the sample after 8 minutes of electrolysis is shown in Figure 3 . The surface of the non-decontaminated area is rough, and the surface of the decontaminated area is significantly smooth, and the grain boundaries of the alloy matrix are clearly exposed. The surface after decontamination shows a certain degree of unevenness, which is mainly caused by the oxide pits left after the removal of the metal oxide layer. EDS spectrum analysis confirms that the oxide layer has a multi-layer structure, with Ni and Fe oxides on the surface layer and a Cr-rich oxide layer below. The signal of the enriched high-valence actinides (such as Mo) is significantly attenuated Figure 4 , indicating that the technology has good decontamination effect on high-valence actinides. Cs and other elements are not enriched in the outermost layer of the metal and have low concentration, so their enrichment cannot be observed in the EDS spectrum.

[0074] The SEM and EDS spectra after complete electrolysis are shown in Figure 5 and Figure 6 . The metal surface grain boundaries are clearly exposed, and the micron-sized pitting indicates that the upper limit of the electrolysis rate needs to be controlled. The element spectrum completely presents the metal substrate signal, verifying the complete removal of the oxide layer and actinides, and verifying that the electrolytic decontamination process can completely remove the metal surface oxide layer and achieve excellent decontamination effect.

[0075] The surface morphology of the sample before electrolysis in this system is shown in Figure 7 . The surface morphology of the sample after 8 minutes of electrolysis is shown in Figure 8 . The surface morphology after complete electrolysis is shown in Figure 9 . The surface morphology of the sample before electrolysis is mainly composed of an oxide layer, and the surface is relatively flat with fine particles. After 8 minutes of electrolysis, the sample surface appears to be layered, with a light-colored upper layer of residual oxide layer and a dark-colored lower layer exposing the substrate metal, and no particles are left on the surface. After complete electrolysis, the metal oxide on the surface of the sample is completely removed, and the whole surface presents the metal substrate, confirming that the electrolytic decontamination has completely removed the surface oxide layer and achieved good results.

[0076] Example 2

[0077] The embodiment provides a method for electrochemically removing the oxide layer of a decommissioned facility based on a synergistic acidic electrolyte, and the steps are the same as those in Embodiment 1, and the only difference is that the electrolyte composition is 0.1 mol / L sulfuric acid, the electrochemical parameters are voltage 32 V, current 4.674 A, and power 153.6 W, and the final decontamination rate is 30%. The surface morphology diagram of the sample before electrolysis in the system is as shown in Figure 10 The surface morphology diagram of the sample after electrolysis for 8 minutes is as shown in Figure 11 The surface morphology after complete electrolysis is as shown in Figure 12

[0078] Embodiment 3

[0079] The embodiment provides a method for electrochemically removing the oxide layer of a decommissioned facility based on a synergistic acidic electrolyte, and the steps are the same as those in Embodiment 1, and the only difference is that the electrolyte composition is 0.1 mol / L sulfuric acid+0.03g / L graphene+0.06g / L SDS, the electrochemical parameters are voltage 61.55 V, current 1.644 A, and power 101.1 W, and the final decontamination rate is 35%. The surface morphology diagram of the sample before electrolysis in the system is as shown in Figure 13 The surface morphology diagram of the sample after electrolysis for 8 minutes is as shown in Figure 14 The surface morphology after complete electrolysis is as shown in Figure 15

[0080] Embodiment 4

[0081] The embodiment provides a method for electrochemically removing the oxide layer of a decommissioned facility based on a synergistic acidic electrolyte, and the steps are the same as those in Embodiment 1, and the only difference is that the electrolyte composition is 0.1 mol / L sulfuric acid+0.05g / L graphene+0.10g / L SDS, the electrochemical parameters are voltage 61.59 V, current 3.779 A, and power 232.7 W, and the final decontamination rate is 40%. The surface morphology diagram of the sample before electrolysis in the system is as shown in Figure 16 The surface morphology diagram of the sample after electrolysis for 8 minutes is as shown in Figure 17 The surface morphology after complete electrolysis is as shown in Figure 18

[0082] Embodiment 5

[0083] The embodiment provides a method for electrochemically removing the oxide layer of a decommissioned facility based on a synergistic acidic electrolyte, and the steps are the same as those in Embodiment 1, and the only difference is that the electrolyte composition is 0.1 mol / L sulfuric acid+0.07g / L graphene+0.14g / L SDS, the electrochemical parameters are voltage 61.58 V, current 3.957 A, and power 243.6 W, and the final decontamination rate is 39%. The surface morphology diagram of the sample before electrolysis in the system is as shown in Figure 19 The surface morphology diagram of the sample after electrolysis for 8 minutes is as shown in​​​Figure 20 Figure 6 shows the surface morphology of the sample before electrolysis in the system of Example 6.

[0084] Example 6

[0085] This example provides a method for electrochemical removal of oxide layers from decommissioned facilities based on a synergistic acidic electrolyte. The steps are the same as in Example 1, except that the electrolyte composition is 0.2 mol / L nitric acid, the electrochemical parameters are a voltage of 29.53 V, a current of 5.156 A, and a power of 152.2 W, and the final decontamination rate is 52.8% with residual oxide layer. The surface morphology of the sample before electrolysis in this system is shown in Figure 6, the surface morphology of the sample after 8 minutes of electrolysis is shown in Figure 7, and the surface morphology after complete electrolysis is shown in Figure 8. Figure 21 Figure 22 Figure 23

[0086] Example 7

[0087] This example provides a method for electrochemical removal of oxide layers from decommissioned facilities based on a synergistic acidic electrolyte. The steps are the same as in Example 1, except that the electrolyte composition is 0.2 mol / L nitric acid + 0.01 g / L graphene + 0.02 g / L SDS, the electrochemical parameters are a voltage of 25.61 V, a current of 4.73 A, and a power of 121.1 W, and the decontamination rate is 38.6%. The surface morphology of the sample before electrolysis in this system is shown in Figure 9, the surface morphology of the sample after 8 minutes of electrolysis is shown in Figure 10, and the surface morphology after complete electrolysis is shown in Figure 11. There is local overcorrosion on the surface and residual oxide layer. Figure 24 Figure 25 Figure 26

[0088] Example 8

[0089] This example provides a method for electrochemical removal of oxide layers from decommissioned facilities based on a synergistic acidic electrolyte. The steps are the same as in Example 1, except that the electrolyte composition is 0.2 mol / L nitric acid + 0.03 g / L graphene + 0.06 g / L SDS, the electrochemical parameters are a voltage of 34.61 V, a current of 5.156 A, and a power of 178.4 W, and the surface morphology of the sample before electrolysis in this system is shown in Figure 12, the surface morphology of the sample after 8 minutes of electrolysis is shown in Figure 13, and the surface morphology after complete electrolysis is shown in Figure 14. There is an abnormal increase in dry weight and the oxide layer is not completely removed. Figure 27 Figure 28 Figure 29

[0090] ​​​​​​​​​By comparing the systematic examples (Examples 1-8), it is confirmed that the optimal electrolyte formula is 0.1 mol / L H2SO4+0.01 g / L graphene+0.02 g / L SDS (Example 1), which achieves a decontamination rate of 55% under the conditions of a voltage of 55.1 V, a current of 5.158 A, and a power of 284.2 W, which is significantly better than other schemes. As shown in Figure 30 When the concentrations of graphene and SDS are 0.01 and 0.02 g / L respectively (Example 1), the increase in the conductivity of the electrolyte promotes the simultaneous improvement of the electrolysis efficiency, while excessive addition (Examples 2-5) can cause the supersaturation adsorption of graphene on the electrode surface, reduce the effective current contact area, and lead to the decay of electrolysis efficiency, ultimately affecting the decontamination rate. The optimal formula (Example 1) achieves complete peeling of the oxide layer, and after electrolysis, the metal surface is exposed to clear grain boundaries, and the substrate damage is controllable, only forming micron-level pitting pits, without the local excessive corrosion phenomenon of the nitric acid system. Even if the components of the nitric acid system (Examples 6-8) are optimized, there are still residual oxide layers after 8 minutes of electrolysis, and the rust cannot be completely removed subsequently, resulting in an increase in dry weight, making the measured decontamination rate artificially high, and the system also has the problem of harmful pitting pits.

[0091] Therefore, the present application discloses an electrochemical de-nucleation method for decommissioning facilities based on a synergistic acidic electrolyte, which develops a graphene-anion surfactant synergistically enhanced acidic electrolyte system, achieves high decontamination rate in a low concentration sulfuric acid medium, precisely controls the stripping of radionuclides to avoid substrate pitting damage, and deeply removes high-valence radionuclides in dense oxide layers, ultimately providing an efficient, low-damage, and process-stable radioactive contaminated metal treatment scheme for nuclear facility decommissioning projects.

[0092] The above specific embodiments further illustrate the purpose, technical solutions, and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application, and does not limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An electrochemical method for de-nucleation of oxide layers from decommissioned facilities based on a synergic acidic electrolyte, characterized in that, The contaminated metal component is an anode, the inert electrode is a cathode, and the contaminated metal component is immersed in a synergistic acidic electrolyte of a low-concentration acidic medium, the temperature is lower than 40 DEG C, and the surface oxide layer of the contaminated metal component is stripped to expose clear grain boundaries by using a high-voltage direct-current electrolysis mode.

2. The method for electrochemical removal of oxide layers from decommissioned facilities based on a synergistic acidic electrolyte according to claim 1, characterized in that, The synergistic acidic electrolyte comprises a low-concentration inorganic acid, graphene functional conductive suspended particles and an anionic surfactant.

3. The method for electrochemical removal of oxide layers from decommissioned facilities based on a synergistic acidic electrolyte according to claim 2, characterized in that, The low-concentration inorganic acid is sulfuric acid or nitric acid, and the anionic surfactant is sodium dodecyl sulfate.

4. The method of claim 3, wherein the method is a synergistic acid electrolyte based electrochemical de-nucleation of decommissioning facility oxide layer method, characterized in that, The concentration of the low-concentration inorganic acid is 0.1-0.2 mol / L, the concentration of the graphene functional conductive suspended particles is 0.01-0.07 g / L, and the concentration of the anionic surfactant is 0.02-0.14 g / L.

5. The synergistic acid electrolyte based electrochemical method for de-nucleation of oxide layer of decommissioned facilities as claimed in claim 1 wherein, In the high-voltage direct-current electrolysis mode, the input voltage is 3-6 V, and the output voltage is 30-70 V.

6. The synergistic acid electrolyte based electrochemical method for de-nucleation of oxide layer of decommissioned facilities according to claim 1, wherein, The method comprises the following steps: (1) configuring a synergistic acidic electrolyte; (2) adjusting parameters and electrochemically removing the oxide layer of decommissioned facilities; (3) quantifying the decontamination rate based on the dry weight change rate; (4) observing the surface morphology by SEM, confirming the exposure of grain boundaries and the stripping of the oxide layer, and testing the degree of stripping of the oxide layer by EDS analysis of high-valence nuclide signals; if the oxide layer is not completely stripped, repeat step (2); (5) dynamically adjusting the electrolysis parameters in combination with the thickness and the target decontamination rate, and optimizing the electrochemical decontamination process parameters.

7. The synergistic acid electrolyte based electrochemical method for de-nucleation of oxide layer of decommissioned facilities according to claim 1, wherein, The method is suitable for removing the radioactive oxide layer on the surface of a stainless steel pipeline or the inner wall of a reactor vessel in a nuclear facility decommissioning project, and the oxide layer is rich in radioactive nuclides.

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