Chemical decontamination process for accelerating pressurized water reactor nuclear power plant primary circuit equipment component

Abstract

The invention discloses a chemical decontamination process for accelerating a pressurized water reactor nuclear power station primary circuit equipment component. According to the method, in the mode of externally applying direct-current voltage, current flows through the surface of a metal part of loop equipment to promote precipitation of surface metal oxide, meanwhile, under the action of citric acid, DTPA and sodium ascorbate, dissolution of a metal oxide film is accelerated, then the oxidation action of KMnO4 and HNO3 is used for converting insoluble trivalent chromium into soluble hexavalent chromium, and the hexavalent chromium can be separated out from the surface of the metal part of the loop equipment. Therefore, removal of the metal oxide film is promoted, efficient removal of the metal oxide film within a short time is achieved, and the method has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical decontamination of nuclear power plant components, and in particular relates to a chemical decontamination process for accelerating primary circuit equipment components of a pressurized water reactor nuclear power plant. Background Art

[0002] Nuclear power is a clean energy source with the characteristics of stability, high efficiency and scalability. Pressurized water reactors have become the main type of new nuclear power reactors in my country due to their compact structure, small size, high power density, high average burnup, low escape of radioactive fission products, good power self-stabilization and self-adjustment characteristics, high safety and reliability. During the operation of nuclear reactors, the core will produce and gradually accumulate activated corrosion products, and pass through the entire primary circuit with the coolant as a carrier. The surface of the equipment in contact with the primary circuit coolant will form a metal oxide film with radioactive nuclides under the action of high temperature and high pressure. These oxide films will cause radiation hazards to equipment maintenance personnel and system operators.

[0003] The use of chemical decontamination technology can effectively remove the simulated oxide film on the surface of the equipment to be repaired. The chemical decontamination process currently used is generally an alternating process of potassium permanganate oxidation and reduction cleaning. The purpose of potassium permanganate oxidation is to convert the trivalent chromium in the oxide film into soluble hexavalent chromium, and the purpose of reduction cleaning is to dissolve the oxide film so that elements such as Fe, Ni, and Cr enter the cleaning solution. The time for chemical decontamination of equipment is relatively long, generally more than 24 hours, and there is also the disadvantage of large dosage of reagents, which also requires the primary circuit equipment to shorten the time as much as possible during the maintenance process, which also means that a more efficient chemical decontamination process is needed to treat the primary circuit equipment. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0006] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a process for accelerating the chemical decontamination of primary circuit equipment components of a pressurized water reactor nuclear power plant.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The primary circuit equipment components are placed in an electrolytic cell containing citric acid detergent, the primary circuit equipment components are connected to the negative pole of the DC adjustable power supply I, the electrolytic cell is connected to the negative pole of the DC adjustable power supply I, the DC adjustable power supply I is turned on, and the negative pole polarization auxiliary cleaning and flushing are performed;

[0009] The flushed primary circuit equipment components are transferred to an electrolytic cell containing an acidic potassium permanganate oxidant, the primary circuit equipment components are connected to the positive electrode of the DC adjustable power supply II, the electrolytic cell is connected to the positive electrode of the DC adjustable power supply II, the DC adjustable power supply II is turned on, and the positive electrode polarization auxiliary oxidation treatment is performed for cleaning;

[0010] Repeat the above two steps alternately until the oxide layer on the surface of the primary circuit equipment components is completely removed.

[0011] As a preferred scheme of the chemical decontamination process for the primary circuit equipment components of the accelerated pressurized water reactor nuclear power plant described in the present invention, the citric acid detergent is composed of 0.3% to 2.0% citric acid, 0.1% to 0.5% DTPA, 0.1% to 0.2% sodium ascorbate and deionized water.

[0012] As a preferred solution of the chemical decontamination process for the primary circuit equipment components of the accelerated pressurized water reactor nuclear power plant described in the present invention, the pH value of the citric acid detergent is adjusted to 2-3 with ammonia water, and the temperature is 80-85°C.

[0013] As a preferred scheme of the chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant described in the present invention, the acidic potassium permanganate oxidant is composed of 1.0% to 1.5% nitric acid, 1.0% to 1.5% potassium permanganate and deionized water, and the temperature is 80 to 85°C.

[0014] As a preferred solution of the chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant described in the present invention, the material of the electrolytic cell is 304L or 316L stainless steel.

[0015] As a preferred solution of the chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant described in the present invention, the voltage of the DC adjustable power supply I is set to 2.0-2.5V.

[0016] As a preferred solution of the chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant described in the present invention, the voltage of the DC adjustable power supply I is set to 2.25-2.5V.

[0017] As a preferred solution of the chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant described in the present invention, the time for the negative electrode polarization auxiliary cleaning is 5 to 7 minutes.

[0018] As a preferred solution of the chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant described in the present invention, the voltage of the DC adjustable power supply II is set to 0.1-0.5V.

[0019] As a preferred solution of the chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant described in the present invention, the time of the positive electrode polarization auxiliary oxidation treatment is 3 to 5 minutes.

[0020] Beneficial effects of the present invention:

[0021] (1) In the present invention, under the action of an external DC voltage, an electric current is caused to flow through the surface of a metal component of a primary circuit device, and a viscous layer is formed on the surface along with the precipitation of surface metal oxide. The viscous layer is thin at the raised parts of the metal surface, and thick at the recessed parts. The current is concentrated on the raised parts with low resistance, so that the parts are preferentially dissolved, thereby accelerating the removal of the metal oxide layer, greatly improving the chemical decontamination efficiency of the primary circuit equipment components of an accelerated pressurized water reactor nuclear power plant, shortening the chemical decontamination time, and being able to achieve efficient removal of the metal oxide film in a relatively short time.

[0022] (2) The present invention adopts a chemical decontamination process to accelerate the chemical decontamination of the primary circuit equipment components of a pressurized water reactor nuclear power plant. By applying an external voltage, the dissolution of the metal oxide film is accelerated by combining the effects of citric acid, DTPA and sodium ascorbate, and KMnO is alternately reacted with the decontamination process to accelerate the dissolution of the metal oxide film. 4 , HNO 3 The oxidation action converts the insoluble trivalent chromium into soluble hexavalent chromium, thereby promoting the removal rate of the oxide film.

[0023] (3) The present invention adopts a lower chemical cleaning agent concentration to dissolve the oxide film, thereby reducing the amount of chemicals used. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0025] Figure 1 This is a schematic diagram of electrolytic decontamination of a circuit equipment component in Example 1 of the present invention.

[0026] Figure 2 These are macroscopic photographs of the simulated oxide film on the surface of the ZG06Cr13Ni4Mo sample in Example 1 of the present invention before and after dissolution.

[0027] Figure 3This is the microscopic surface morphology and EDS analysis diagram of the simulated oxide film on the surface of the ZG06Cr13Ni4Mo sample in Example 1 of the present invention before dissolution.

[0028] Figure 4 The sample surface photograph and surface scanning (EDS) diagram after the simulated oxide film on the surface of the ZG06Cr13Ni4Mo sample in Example 1 of the present invention is dissolved.

[0029] Figure 5 This is a graph showing the change in current value with applied voltage when the 04Cr13Ni4Mo sample in Example 1 of the present invention is cathodically polarized in citric acid + DTPA detergent.

[0030] Figure 6 These are macroscopic photographs of the simulated oxide film on the surface of the 04Cr13Ni4Mo sample in Example 2 of the present invention before and after dissolution.

[0031] Figure 7 This is a diagram showing the effect of simulated oxide film removal on the surface of 04Cr13Ni4Mo when alkaline potassium permanganate is used as the electrolyte in Comparative Example 3 of the present invention.

[0032] Figure 8 These are macroscopic photographs of the simulated oxide film on the surface of the 022Cr19Ni10 sample in Example 3 of the present invention before and after dissolution. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0036] The materials used in this experiment are the primary circuit waste heat removal pump and guide vane materials (ZG06Cr13Ni4Mo, 04Cr13Ni4Mo, 022Cr19Ni10) of the Hualong One unit of the Changjiang Nuclear Power Plant.

[0037] The present invention detects the content of metal oxide film by taking a sample surface photo and surface scanning (EDS). The radiation dose is formed when the metal material reacts with the radiation medium in the primary circuit to form oxides during operation. The corrosion dose of the metal material is positively correlated with the amount of the oxide film of the metal material. The present invention indirectly detects the radiation dose by detecting the content of the metal oxide film and the oxygen element.

[0038] The oxide film prefabrication method of the primary circuit component in the present invention is: placing a waste heat discharge pump impeller material sample in a high temperature and high pressure test bench for oxide film prefabrication, the water chemical conditions in the high temperature and high pressure test bench are 1000 mg / L of boric acid, 2.2 mg / L of lithium hydroxide, oxygen concentration less than 1 μg / L, hydrogen concentration 25-30 mL / kg, and obtaining a sample with an oxide film after 1000 hours at 190°C.

[0039] Example 1

[0040] This embodiment provides a chemical decontamination process for accelerating the chemical decontamination of primary circuit equipment components in a pressurized water reactor nuclear power plant.

[0041] 1) The ZG06Cr13Ni4Mo sample with oxide film is placed in a 304L stainless steel electrolytic cell filled with citric acid detergent (0.3% citric acid + 0.2% DTPA + 0.1% sodium ascorbate, pH = 3, temperature 85°C), the sample is connected to the negative electrode of the DC adjustable power supply, and the electrolytic cell is connected to the negative electrode of the DC adjustable power supply, as shown in the schematic diagram Figure 1 As shown, the DC adjustable power supply is turned on to 2.5V, the sample is subjected to negative polarization auxiliary cleaning for 5 minutes, and then the sample is rinsed with water;

[0042] 2) Transfer the sample to a solution containing an acidic potassium permanganate oxidant (1.0% KMnO 4 +1.0%HNO 3 , 85°C) in a 304L stainless steel electrolytic cell, the sample is connected to the positive electrode of a DC adjustable power supply, the electrolytic cell is connected to the positive electrode of the DC adjustable power supply, the DC adjustable power supply is turned on to 0.25V, the sample is subjected to positive polarization auxiliary oxidation treatment for 5 minutes, and then the sample is cleaned;

[0043] 3) Repeat steps 1) and 2) twice, and finally perform step 1). After judging the metallic luster of the sample through macroscopic visual inspection, perform surface and surface scanning (EDS) to confirm and determine the O content on the metal surface. The surface oxide layer of the ZG06Cr13Ni4Mo sample is completely removed.

[0044] The total time for removing the oxide film on the surface of the ZG06Cr13Ni4Mo sample is 35 minutes. The macroscopic photos of the surface oxide film of the ZG06Cr13Ni4Mo sample before and after removal are shown in Figure 2, see the microscopic photos before and after removal Figure 3 , Figure 4 It can be seen that the matrix of oxide particles (iron and chromium oxides) completely covers the original ZG06Cr13Ni4Mo material, with a thickness of about 276nm before removal; after removal, the cross-sectional photos and ESD surface scan results show that no oxygen element is detected, indicating that the decontamination process can completely remove the simulated oxide film on the surface of the sample.

[0045] Figure 5 The relationship between voltage and current during the electrolytic decontamination process of citric acid + DTPA detergent in step 2) is shown in Figure 2. When the voltage exceeds 2.25V, bubbles are precipitated on the surface of the sample, and the decontamination effect of the solution is improved. In order to achieve the electrolytic decontamination effect in citric acid + DTPA detergent, the voltage should be controlled to be greater than 2.25V.

[0046] Comparative Example 1

[0047] The difference between this comparative example and Example 1 is that the DC adjustable power supply is turned off, and the oxide film on the surface of the ZG06Cr13Ni4Mo sample is removed, specifically:

[0048] The ZG06Cr13Ni4Mo sample with oxide film was cleaned in citric acid cleaning agent (0.5% citric acid + 0.1% sodium ascorbate, pH = 3, temperature 85°C), potassium permanganate oxidation cleaning solution (1.0% KMnO 4 +1.0%HNO 3 , 85℃) were cleaned alternately, first with citric acid and then with potassium permanganate oxidation. Cleaning was done for 4 hours in each cleaning agent, for a total of 20 hours, and the oxide film on the surface of the sample could be completely removed.

[0049] The time for removing the oxide film on the surface of the ZG06Cr13Ni4Mo sample in Example 1 is only 35 minutes, which is greatly reduced compared with the oxide film removal time in Comparative Example 1.

[0050] Comparative Example 2

[0051] The difference between this comparative example and Example 1 is that the DC adjustable power supply is turned off, and the other operation steps are the same as those in Example 1, and the cleaning time of each cleaning agent is 5 minutes, and the cleaning is carried out alternately for a total of 35 minutes.

[0052] The metal oxide layer basically maintains a gray-black state, the appearance of the oxide film does not change, the metal color is not exposed, and the oxide layer cannot be removed.

[0053] Example 2

[0054] This embodiment provides a chemical decontamination process for accelerating the chemical decontamination of primary circuit equipment components in a pressurized water reactor nuclear power plant.

[0055] 1) Place the 04Cr13Ni4Mo sample with an oxide film in a 304L stainless steel electrolytic cell filled with a citric acid detergent (1.5% citric acid + 0.5% DTPA + 0.1% sodium ascorbate, pH = 2, temperature 85°C), connect the sample to the negative electrode of a DC adjustable power supply, connect the electrolytic cell to the negative electrode of the DC adjustable power supply, turn on the DC adjustable power supply to 2.0V, perform negative polarization auxiliary cleaning on the sample for 5 minutes, and then rinse the sample with water;

[0056] 2) Transfer the sample to a solution containing an acidic potassium permanganate oxidant (1.0% KMnO 4 +1.0%HNO 3 , 85°C) in a 304L stainless steel electrolytic cell, the sample is connected to the positive electrode of a DC adjustable power supply, the electrolytic cell is connected to the positive electrode of the DC adjustable power supply, the DC adjustable power supply is turned on to 0.5V, the sample is subjected to positive polarization auxiliary oxidation treatment for 5min, and then the sample is cleaned;

[0057] 3) Repeat steps 1) and 2) twice, and then perform step 1) at the end.

[0058] Figure 6 The macroscopic photos of the simulated oxide film on the surface of the 04Cr13Ni4Mo sample before and after dissolution show that the sample has a metallic luster through macroscopic visual inspection, and the oxide layer on the surface of the sample is completely removed through visual inspection. EDS spectrum shows that the sample surface does not contain oxygen after cleaning, further proving that the oxide film has been 100% removed.

[0059] Comparative Example 3

[0060] This comparative example uses alkaline potassium permanganate and citric acid detergent to treat the components of the primary circuit of the pressurized water reactor nuclear power plant, specifically:

[0061] 1) Place the 04Cr13Ni4Mo sample with an oxide film in a 304L stainless steel electrolytic cell filled with a citric acid detergent (1.5% citric acid + 0.5% DTPA + 0.1% sodium ascorbate, pH = 2, temperature 85°C), connect the sample to the negative electrode of a DC adjustable power supply, connect the electrolytic cell to the negative electrode of the DC adjustable power supply, turn on the DC adjustable power supply to 1.5V, perform negative polarization auxiliary cleaning on the sample for 5 minutes, and then rinse the sample with water;

[0062] 2) Transfer the sample to a solution containing alkaline potassium permanganate oxidant (1.0% KMnO 4+1.0% NaOH, 85°C) electrolytic cell, the sample is connected to the positive electrode of the DC adjustable power supply, the 304L stainless steel electrolytic cell is connected to the positive electrode of the DC adjustable power supply, the DC adjustable power supply is turned on to 0.5V, the sample is subjected to positive polarization auxiliary oxidation treatment for 5min, and then the sample is cleaned;

[0063] 3) Repeat steps 1) and 2) twice, and then perform step 1) again.

[0064] Through macroscopic visual inspection, the layout of the oxide film on the sample surface is still dark gray, such as Figure 7 As shown, the oxide film in some areas was not completely removed.

[0065] Example 3

[0066] This embodiment provides a chemical decontamination process for accelerating the chemical decontamination of primary circuit equipment components in a pressurized water reactor nuclear power plant.

[0067] 1) Place the 022Cr19Ni10 sample with an oxide film in a 304L stainless steel electrolytic cell filled with a citric acid detergent (1.2% citric acid + 0.6% DTPA + 0.1% sodium ascorbate, pH 2, temperature 85°C), connect the sample to the negative electrode of a DC adjustable power supply, connect the electrolytic cell to the negative electrode of the DC adjustable power supply, turn on the DC adjustable power supply to 1.5V, perform negative polarization auxiliary cleaning on the sample for 5 minutes, and then rinse the sample with water;

[0068] 2) Transfer the sample to a solution containing an acidic potassium permanganate oxidant (1.0% KMnO 4 +1.0%HNO 3 , 85°C) in an electrolytic cell, the sample is connected to the positive electrode of a DC adjustable power supply, the 304L stainless steel electrolytic cell is connected to the positive electrode of the DC adjustable power supply, the DC adjustable power supply is turned on to 0.4V, the sample is subjected to positive polarization auxiliary oxidation treatment for 5min, and then the sample is cleaned;

[0069] 3) Repeat steps 1) and 2) twice, and then perform step 1) again.

[0070] Figure 8 The macroscopic photos of the simulated oxide film on the surface of the 022Cr19Ni10 sample before and after dissolution show that the oxide layer on the surface of the sample is completely removed. According to the EDS spectrum, the sample surface does not contain oxygen after cleaning, which further proves that the oxide film is completely removed.

[0071] Comparative Example 4

[0072] The difference between this comparative example and Example 3 is that the lemon detergent does not contain DTPA, and the other decontamination process steps are the same as those in Example 3.

[0073] The oxide film layout on the surface of the 022Cr19Ni10 sample is still dark gray, and the oxide film in some areas has not been completely removed.

[0074] In summary, in the present invention, under the action of an external DC voltage, an electric current is made to flow through the surface of a metal component of a primary circuit device, and a viscous layer is formed on the surface along with the precipitation of surface metal oxides. The viscous layer is thin at the raised parts of the metal surface, and thick at the concave parts. The current is concentrated on the raised parts with low resistance, so that the parts are preferentially dissolved, which accelerates the removal of the metal oxide layer, greatly improves the chemical decontamination efficiency of the components of the primary circuit equipment of the accelerated pressurized water reactor nuclear power plant, shortens the chemical decontamination time, and can achieve efficient removal of the metal oxide film in a relatively short time. The present invention adopts a chemical decontamination process for the components of the primary circuit equipment of the accelerated pressurized water reactor nuclear power plant, and accelerates the dissolution of the metal oxide film by means of an external voltage, while combining the effects of citric acid, DTPA and sodium ascorbate, and alternately accompanies the removal of KMnO 4 , HNO 3 The oxidation action converts the insoluble trivalent chromium into soluble hexavalent chromium, thereby promoting the removal rate of the oxide film.

[0075] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A chemical decontamination process for accelerating the chemical decontamination of primary circuit equipment components of a pressurized water reactor nuclear power plant, characterized in that: include, The primary circuit equipment components are placed in an electrolytic cell containing citric acid detergent, the primary circuit equipment components are connected to the negative pole of the DC adjustable power supply I, the electrolytic cell is connected to the negative pole of the DC adjustable power supply I, the DC adjustable power supply I is turned on, and the negative pole polarization auxiliary cleaning and flushing are performed; The flushed primary circuit equipment components are transferred to an electrolytic cell containing an acidic potassium permanganate oxidant, the primary circuit equipment components are connected to the positive electrode of the DC adjustable power supply II, the electrolytic cell is connected to the positive electrode of the DC adjustable power supply II, the DC adjustable power supply II is turned on, and the positive electrode polarization auxiliary oxidation treatment is performed for cleaning; Repeat the above two steps alternately until the oxide layer on the surface of the primary circuit equipment components is completely removed.

2. The chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant according to claim 1, characterized in that: The citric acid detergent consists of 0.3% to 2.0% citric acid, 0.1% to 0.5% DTPA, 0.1% to 0.2% sodium ascorbate and deionized water.

3. The chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant according to claim 2, characterized in that: The pH value of the citric acid detergent is adjusted to 2-3 by using ammonia water, and the temperature is 80-85°C.

4. The chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant according to claim 1, characterized in that: The acidic potassium permanganate oxidant is composed of 1.0% to 1.5% nitric acid, 1.0% to 1.5% potassium permanganate and deionized water, and the temperature is 80 to 85°C.

5. The chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant according to claim 1, characterized in that: The electrolytic cell is made of 304L or 316L stainless steel.

6. The chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant according to claim 1, characterized in that: The voltage of the DC adjustable power supply I is set to 2.0-2.5V.

7. The chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant according to claim 6, characterized in that: The voltage of the DC adjustable power supply I is set to 2.25-2.5V.

8. The chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant according to claim 1, characterized in that: The time for the negative electrode polarization auxiliary cleaning is 5 to 7 minutes.

9. The chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant according to claim 1, characterized in that: The voltage of the DC adjustable power supply II is set to 0.1-0.5V.

10. The chemical decontamination process for accelerating the primary circuit equipment components of a pressurized water reactor nuclear power plant according to claim 1, characterized in that: The time of the positive electrode polarization auxiliary oxidation treatment is 3 to 5 minutes.

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