Method for concentrating radionuclide in liquid effluent of nuclear power plant

Abstract

The invention discloses a method for concentrating radionuclides in liquid effluent of a nuclear power plant, which comprises the following steps: S1, mixing the liquid effluent of the nuclear power plant and a nuclide carrier liquid, performing primary electrodialysis, and ending the primary electrodialysis when the conductivity of a concentrated solution reaches a target conductivity to obtain a primary concentrated solution; and S2, carrying out second-stage electrodialysis on the first-stage concentrated solution, and when the voltage of the concentrated solution reaches a target voltage, ending the second-stage electrodialysis to obtain a second-stage concentrated solution. According to the method for concentrating the radionuclide in the liquid effluent of the nuclear power plant, the nuclide ions with unknown concentration in the liquid effluent of the nuclear power plant are concentrated to a certain multiple through electrodialysis treatment by utilizing the electrification property of the nuclide ions in the liquid effluent of the nuclear power plant and combining an electrodialysis technology; the actual concentration of the nuclide ions in the liquid effluent can be conveniently detected, the method is environmentally friendly and efficient, and the problems that a traditional evaporation method is low in nuclide ion concentration efficiency, long in consumed time and the like are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear power liquid effluent detection, in particular to a method for concentrating radioactive nuclides in liquid effluent of a nuclear power plant. Background Art

[0002] With the development of nuclear power and the increasing emphasis on the ecological environment, regulation of radioactivity in liquid effluents from nuclear power plants has become increasingly stringent. However, due to the lack of corresponding standards for monitoring radioactivity levels in liquid effluents, nuclear power plants generally rely on direct sampling and measurement. This method has high detection limits and large measurement uncertainties, making the results unfavorable for regulating radionuclide emissions. Furthermore, as a means of regulating emissions, monitoring liquid effluents from nuclear power plants often requires rapid measurement. Therefore, from the perspective of nuclear power plant emissions and regulation, rapid effluent measurement, while ensuring sufficiently low detection limits, is particularly important.

[0003] Currently, nuclear power plant effluent monitoring utilizes two methods: online monitoring and sampling and analysis. The former only provides qualitative measurement of total radioactivity, lacking the ability to perform radionuclide analysis. It is generally used for early warning and has a very limited role. The latter, on the other hand, requires analysis of collected samples in an effluent laboratory to quantify radionuclide concentrations and to calculate nuclear power plant emissions. Because effluent sampling and analysis involves a complex and lengthy pre-processing process, laboratory analysis has long relied on manual analysis, resulting in low efficiency. Furthermore, the equipment configuration is relatively simple, with minimal automation, necessitating the urgent need for new technologies.

[0004] As a new and highly applicable advanced membrane separation technology, electrodialysis utilizes the selective permeability of ion exchange membranes to generate an electrodialysis-driven process, achieving the selective separation of ions in solution. It has broad application prospects, offering advantages such as high efficiency and energy saving, ease of operation, ease of integration with other technologies, and environmental friendliness. It provides a new solution for detecting radionuclide concentrations in nuclear power plant effluents. However, there are currently few reports on the concentration of radionuclide ions from liquid effluents of nuclear power plants using electrodialysis. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for enriching radioactive nuclides in liquid effluent from a nuclear power plant.

[0006] The technical solution adopted by the present invention to solve the technical problem is to provide a method for enriching radioactive nuclides in liquid effluent from a nuclear power plant, comprising the following steps:

[0007] S1. mixing the liquid effluent from the nuclear power plant and the nuclide carrier liquid and performing a first-stage electrodialysis. When the conductivity of the concentrated liquid reaches a target conductivity, the first-stage electrodialysis is terminated to obtain a first-stage concentrated liquid.

[0008] S2. The primary concentrated solution is subjected to secondary electrodialysis. When the voltage of the concentrated solution reaches the target voltage, the secondary electrodialysis is terminated to obtain a secondary concentrated solution.

[0009] In some embodiments, the nuclide carrier liquid is a mixed liquid containing nuclides, and the nuclides include chromium, manganese, cobalt, nickel, zinc and strontium, and the concentration of each element is 0.09-0.11 mg / mL.

[0010] In some embodiments, the volume of the nuclide carrier liquid is 0.1% or less of the volume of the liquid effluent of the nuclear power plant.

[0011] In some embodiments, the target conductivity is a conductivity that determines that the nuclide ions are concentrated at least 10 times on average;

[0012] The target voltage is a voltage at which the nuclide ions are determined to be concentrated 20 times or more on average.

[0013] In some embodiments, step S1 includes:

[0014] S1.1. Pass liquid effluent from the nuclear power plant and a nuclide carrier liquid into the desalination chamber of a primary electrodialysis membrane stack, pass a nitrate solution or a dilute acid solution into the concentrating chamber of the primary electrodialysis membrane stack, and pass a strong electrolyte solution into the anode and cathode chambers of the primary electrodialysis membrane stack;

[0015] The volume of the solution in the desalination chamber is greater than the volume of the solution in the concentrating chamber;

[0016] S1.2. Direct current is applied to the anode and cathode plates at opposite ends of the primary electrodialysis membrane stack;

[0017] Under the action of direct current, the nuclide ions in the desalination chamber migrate from the desalination chamber to the concentrating chamber through the cation exchange membrane of the first-stage electrodialysis membrane stack, and the chloride ions and other anions in the desalination chamber migrate to the concentrating chamber through the anion exchange membrane of the first-stage electrodialysis membrane stack;

[0018] S1.3. Obtain the concentrated liquid from the concentrating chamber to obtain a primary concentrated liquid.

[0019] In some embodiments, step S2 includes:

[0020] S2.1. Pass the primary concentrate into the desalination chamber and the concentrating chamber of the secondary electrodialysis membrane stack, respectively, and pass a strong electrolyte solution into the anode chamber and the cathode chamber of the secondary electrodialysis membrane stack;

[0021] The volume of the primary concentrate flowing into the desalination chamber of the secondary electrodialysis membrane stack is greater than the volume of the primary concentrate flowing into the concentrating chamber;

[0022] S2.1. Direct current is applied to the anode and cathode plates at opposite ends of the secondary electrodialysis membrane stack;

[0023] Under the action of direct current, the nuclide ions in the desalination chamber of the secondary electrodialysis membrane stack migrate from the desalination chamber to the concentration chamber through the cation exchange membrane, and the chloride ions and other anions in the desalination chamber migrate to the concentration chamber through the anion exchange membrane;

[0024] S1.3. Obtain the concentrated liquid from the concentration chamber to obtain a secondary concentrated liquid.

[0025] In some embodiments, the strong electrolyte solution is a sodium sulfate solution with a concentration of 0.2 mol / L to 0.4 mol / L.

[0026] In some embodiments, the current density of the applied direct current in the primary electrodialysis is 20 mA / cm 2 ~50mA / cm 2 , or the applied constant voltage is 10V to 30V;

[0027] In the secondary electrodialysis, the current density of the applied direct current is 20 mA / cm 2 ~50mA / cm 2 .

[0028] In some embodiments, the primary electrodialysis membrane stack and the secondary electrodialysis membrane stack have the same structure, both comprising a dialysis module, an anode plate and a cathode plate disposed on opposite sides of the dialysis module;

[0029] The dialysis module includes a plurality of cation exchange membranes and a plurality of anion exchange membranes, which are alternately arranged to define an anode chamber, a cathode chamber, a plurality of concentrating chambers, and a plurality of desalination chambers in the electrodialysis membrane stack;

[0030] The anode chamber is located between the anode plate and the adjacent cation exchange membrane, the cathode chamber is located between the cathode plate and the adjacent anion exchange membrane, and a plurality of the concentration chambers and a plurality of the desalination chambers are located between the anode chamber and the cathode chamber and are arranged alternately.

[0031] In some embodiments, in the primary electrodialysis and the secondary electrodialysis, the linear velocity of the liquid flow is controlled to be 2 cm / s to 10 cm / s.

[0032] In some embodiments, the method for enriching radioactive nuclides in liquid effluent from a nuclear power plant further comprises the following steps:

[0033] S3. Calculate the nuclide ion recovery rate:

[0034] Under initial conditions, liquid effluent from nuclear power plants was sampled and the concentration of each nuclide ion was measured by inductively coupled plasma mass spectrometry. Combined with the volume of the liquid effluent from the nuclear power plant, the total amount of each nuclide ion before enrichment was calculated.

[0035] After the secondary electrodialysis is completed, the secondary concentrated solution is sampled and the concentration of each nuclide ion is measured by inductively coupled plasma mass spectrometry. Combined with the volume of the secondary concentrated solution, the total amount of each nuclide ion after concentration is calculated.

[0036] The recovery rate of each nuclide ion was calculated based on the total amount of each nuclide ion before and after concentration.

[0037] The beneficial effects of the present invention are as follows: utilizing the charge of nuclide ions in the liquid effluent of a nuclear power plant, combined with electrodialysis technology, the nuclide ions of unknown concentration in the liquid effluent of a nuclear power plant are concentrated to a certain multiple through electrodialysis treatment, thereby facilitating the detection of the actual concentration of nuclide ions in the liquid effluent. This method is green, environmentally friendly and highly efficient, and avoids the problems of low efficiency and long time consumption in the concentration of nuclide ions by traditional evaporation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0039] Figure 1 It is a schematic structural diagram of the electrodialysis membrane stack in the present invention;

[0040] Figure 2 This is a schematic diagram of the radionuclide enrichment effect in Example 1 of the present invention;

[0041] Figure 3 This is a schematic diagram of the radionuclide enrichment effect in Example 2 of the present invention;

[0042] Figure 4 Schematic diagram of the radionuclide enrichment effect in Example 3 of the present invention. DETAILED DESCRIPTION

[0043] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0044] The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant of the present invention comprises the following steps:

[0045] S1. mixing the liquid effluent from the nuclear power plant and the nuclide carrier liquid and performing a first-stage electrodialysis. When the conductivity of the concentrated liquid reaches a target conductivity, the first-stage electrodialysis is terminated to obtain a first-stage concentrated liquid.

[0046] S2. The primary concentrated solution is subjected to secondary electrodialysis. When the voltage of the concentrated solution reaches the target voltage, the secondary electrodialysis is terminated to obtain a secondary concentrated solution.

[0047] In particular, given that the nuclide content in the liquid effluent of a nuclear power plant is at a trace level, a nuclide carrier liquid is added to increase the nuclide content in order to achieve better concentration and facilitate subsequent recovery rate calculations. Furthermore, the volume of the added nuclide carrier liquid is much smaller than the volume of the liquid effluent of the nuclear power plant, thereby minimizing the impact on the volume change of the liquid effluent of the nuclear power plant. Preferably, the volume of the nuclide carrier liquid is 0.1% or less of the volume of the liquid effluent of the nuclear power plant.

[0048] The nuclide carrier liquid is a mixed liquid containing nuclides, including chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn) and strontium (Sr), etc. The concentration of each element is 0.09-0.11 mg / mL.

[0049] The base liquid of the nuclide carrier liquid is nitric acid solution or hydrochloric acid solution.

[0050] In primary electrodialysis, the end of the primary electrodialysis (effectively, the primary concentration) is determined by the change in conductivity. The conductivity corresponds to the conductivity of the entire concentrate. Therefore, by setting the target conductivity, it is determined that after the primary electrodialysis, the average concentration of the nuclides is 10-fold or greater. In other words, this 10-fold or greater concentration factor represents the average concentration of all nuclides in the concentrate.

[0051] In secondary electrodialysis, voltage changes are used to determine the end of the secondary electrodialysis (effectively, secondary concentration). This voltage corresponds to the voltage of the entire concentrate. Therefore, by setting the target voltage, it is determined that after secondary electrodialysis, the average concentration of the nuclides ions is 20-fold or greater. In other words, this 20-fold or greater concentration factor represents the average of all nuclides in the concentrate.

[0052] Both the primary electrodialysis and the secondary electrodialysis are realized by electrodialysis membrane stacks. The electrodialysis membrane stack for realizing the primary electrodialysis is the primary electrodialysis membrane stack, and the electrodialysis membrane stack for realizing the secondary electrodialysis is the secondary electrodialysis membrane stack. The two have the same structure.

[0053] refer to Figure 1 The electrodialysis membrane stack for primary and secondary electrodialysis structurally includes a dialysis module, an anode plate 10 and a cathode plate 20 disposed on opposite sides of the dialysis module. The anode plate 10 is used to connect to the positive pole of a power supply, and the cathode plate 20 is used to connect to the negative pole of a power supply.

[0054] The dialysis module includes several cation exchange membranes 11 and several anion exchange membranes 12. The several cation exchange membranes 11 and several anion exchange membranes 12 are arranged alternately, and with the flow channel separators and sealing gaskets, define the anode chamber 101, the cathode chamber 102, several concentration chambers 103 and several desalination chambers 104 in the electrodialysis membrane stack.

[0055] The anode chamber 101 is located between the anode plate 10 and the adjacent cation exchange membrane 11, the cathode chamber 102 is located between the cathode plate 20 and the adjacent anion exchange membrane 12, and a plurality of concentration chambers 103 and a plurality of desalination chambers 104 are located between the anode chamber 101 and the cathode chamber 102 and are arranged alternately.

[0056] The adjacent concentrating chamber 103 and the desalting chamber 104 are used as a group of treatment chambers. In a preferred embodiment, the dialysis module has ten groups of treatment chambers by alternately arranging a plurality of cation exchange membranes 11 and a plurality of anion exchange membranes 12 .

[0057] Combine Figure 1 In the electrodialysis membrane stack shown, in some embodiments, the primary electrodialysis in step S1 includes the following steps:

[0058] S1.1. The liquid effluent from the nuclear power plant and the nuclide carrier liquid are introduced into the desalination chamber of the first-stage electrodialysis membrane stack, the nitrate solution or dilute acid solution is introduced into the concentrating chamber of the first-stage electrodialysis membrane stack, and the strong electrolyte solution (as the electrode liquid) is introduced into the anode chamber and cathode chamber of the first-stage electrodialysis membrane stack.

[0059] The strong electrolyte solution uses a sodium sulfate solution with a concentration of 0.2 mol / L to 0.4 mol / L.

[0060] The volume of the solution in the desalination chamber is greater than that in the concentration chamber. The initial pH of the solution in the desalination chamber is controlled to be 1-4.

[0061] In the first-stage electrodialysis, each ion migrates in the form of hydrated ions. At the same time, affected by the membrane structure, current density and solution pH, the radionuclide ions migrate from the large-volume desalination chamber to the small-volume concentration chamber and are concentrated.

[0062] S1.2. Direct current is applied to the anode and cathode plates at opposite ends of the first-stage electrodialysis membrane stack. The current density of the applied direct current is 20 mA / cm 2 ~50mA / cm 2 , or the applied constant voltage is 10V~30V.

[0063] Due to the charge of radionuclide ions, under the action of the electric field generated by direct current, radionuclide ions in the desalination chamber migrate from the desalination chamber to the concentration chamber through the cation exchange membrane of the first-stage electrodialysis membrane stack. Chloride ions and other anions in the desalination chamber migrate to the concentration chamber through the anion exchange membrane of the first-stage electrodialysis membrane stack. Other anions refer to anions in the solution other than chloride ions.

[0064] The conductivity of the solution in the desalination chamber is measured by a built-in conductivity meter. When the conductivity reaches the target conductivity, it is determined that the radionuclide ions are concentrated at least 10 times on average, and the first-stage electrodialysis is terminated.

[0065] S1.3. Obtain the concentrated liquid from all the concentration chambers to obtain a primary concentrated liquid.

[0066] In the first-stage electrodialysis, the linear velocity of the liquid flow in each chamber is controlled by a peristaltic pump to be 2 cm / s to 10 cm / s.

[0067] Combine Figure 1 In the electrodialysis membrane stack shown, in some embodiments, the secondary electrodialysis in step S2 includes the following steps:

[0068] S2.1. The primary concentrate is introduced into the desalination chamber and the concentration chamber of the secondary electrodialysis membrane stack respectively, and a strong electrolyte solution is introduced into the anode chamber and the cathode chamber of the secondary electrodialysis membrane stack.

[0069] The volume of the primary concentrate flowing into the desalination compartment of the secondary electrodialysis membrane stack is greater than the volume of the primary concentrate flowing into the concentrating compartment. Alternatively, the volume of the primary concentrate flowing into the desalination compartment of the secondary electrodialysis membrane stack may account for 70% to 95% of the total volume of the primary concentrate. Alternatively, the volume ratio of the primary concentrate flowing into the desalination compartment of the secondary electrodialysis membrane stack to the primary concentrate flowing into the concentrating compartment may be 10:1.

[0070] The strong electrolyte solution used in the secondary electrodialysis is a sodium sulfate solution with a concentration of 0.2 mol / L to 0.4 mol / L.

[0071] S2.1. Direct current is applied to the anode and cathode plates at opposite ends of the secondary electrodialysis membrane stack; the current density of the applied direct current is 20 mA / cm 2 ~50mA / cm 2 .

[0072] Under the action of the electric field generated by direct current, the radionuclides in the desalination chamber of the secondary electrodialysis membrane stack migrate from the desalination chamber to the concentration chamber through the cation exchange membrane, and the chloride ions in the desalination chamber migrate to the concentration chamber through the anion exchange membrane.

[0073] In secondary electrodialysis, each ion migrates in the form of hydrated ions. At the same time, affected by the membrane structure, current density and solution pH, the radionuclide ions migrate from the large-volume desalination chamber to the small-volume concentration chamber and are concentrated.

[0074] The voltage of the concentrated liquid in the concentration chamber is measured by a built-in voltmeter. When the voltage reaches the target voltage, it is determined that the radionuclide ions are concentrated to 20 times or more on average, and the secondary electrodialysis is terminated.

[0075] S1.3. Obtain the concentrated liquid from all the concentration chambers to obtain a secondary concentrated liquid.

[0076] In some embodiments, the method for enriching radionuclides in liquid effluent from a nuclear power plant further comprises the following steps:

[0077] S3. Calculate the nuclide ion recovery rate.

[0078] The specific steps of nuclide ion recovery are as follows:

[0079] S3.1. Under initial conditions (before electrodialysis begins), sample the liquid effluent from the nuclear power plant and measure the concentration of each nuclide ion using an inductively coupled plasma mass spectrometer. Combined with the volume of the liquid effluent from the nuclear power plant, the total amount of each nuclide ion before enrichment is calculated.

[0080] Among them, the sampling volume of liquid effluent from nuclear power plants is 0.1mL~1mL, which is diluted to 1ug / L~100ug / L and then measured by inductively coupled plasma mass spectrometry.

[0081] S3.2. After the completion of the secondary electrodialysis, the secondary concentrated liquid is sampled and the concentration of each nuclide ion is measured by inductively coupled plasma mass spectrometry. Combined with the volume of the secondary concentrated liquid, the total amount of each nuclide ion after concentration is calculated.

[0082] The sampling volume of the secondary concentrate is 0.1 mL to 1 mL, which is diluted to 1 ug / L to 100 ug / L and then measured by inductively coupled plasma mass spectrometry.

[0083] S3.3. Calculate the recovery rate of each nuclide ion based on the total amount of each nuclide ion before and after concentration.

[0084] In combination with the above steps S1 to S3, the present invention uses two-stage electrodialysis and finally uses an inductively coupled plasma mass spectrometer to determine that the nuclide ion recovery rate can reach more than 90%.

[0085] The present invention will be further described below by means of specific examples.

[0086] Example 1:

[0087] 20,000 mL of liquid effluent from a nuclear power plant and 10 mL of a carrier solution (a mixture containing the nuclides chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), and strontium (Sr) at a concentration of 0.1 mg / mL) are introduced into the desalination chamber of the first-stage electrodialysis. 250 mL of a low-concentration nitric acid solution is introduced into the concentration chamber. The anode and cathode chambers are connected in series, and 500 mL of a (0.2-0.4) mol / L Na2SO4 aqueous solution is introduced as a strong electrolyte solution. During the electrodialysis process, the first-stage electrodialysis is operated at a constant voltage of 20 V. The first-stage electrodialysis is stopped when the conductivity of the concentration chamber begins to decrease and the operating current drops sharply. The first-stage concentrate obtained from the first-stage electrodialysis is used as the feed solution for the desalination chamber of the second-stage electrodialysis for further concentration. The operation is performed at a constant current density of 30 mA / cm2 , set the current to 5.67 A, and set the voltage upper limit to 20 V. When the secondary electrodialysis operating voltage reaches 20 V, the electrodialysis is terminated.

[0088] As the number of electrodialysis stages increases, the concentration of nuclides ions increases step by step. In the first stage of electrodialysis, the maximum concentration of chromium, manganese, cobalt, nickel, zinc and strontium is 8.4 times, 11.7 times, 11.7 times, 11.7 times, 7.6 times and 18.7 times. In the second stage of electrodialysis, the maximum concentration of chromium, manganese, cobalt, nickel, zinc and strontium is 13.5 times, 17.6 times, 17.1 times, 16.3 times, 12.0 times and 31.1 times. The concentration changes of each nuclide ion in the first stage of electrodialysis and the second stage of electrodialysis are as follows: Figure 2 As shown, Figure 2 The left part of the curve is the primary electrodialysis stage, and the right part of the curve is the secondary electrodialysis stage.

[0089] The above shows that the radionuclide ions in the desalination chamber can be concentrated to about 10 times by the first-stage electrodialysis, and to about 15 times by the second-stage electrodialysis. This method can be used to detect the actual concentration of radionuclide ions in the liquid effluent of nuclear power plants.

[0090] Example 2:

[0091] 25,200 mL of nuclear power plant liquid effluent and 10 mL of carrier solution (a mixture containing chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), and strontium (Sr) at a concentration of 0.1 mg / mL) were introduced into the primary electrodialysis desalination chamber. The pH was adjusted to 3-4 with nitric acid. 180 mL of low-concentration nitric acid solution was introduced into the concentrating chamber. The anode and cathode chambers were connected in series, and 500 mL of a 0.3 mol / L aqueous Na₂SO₄ solution was introduced as a strong electrolyte. The cation exchange membrane was CMX, manufactured by Astom, Japan, and the anion exchange membrane was AMX, manufactured by Astom, Japan. The linear velocity of each solution flowing through the membrane stack was 2 cm / s. The primary electrodialysis was operated at a constant voltage of 10 V. The primary electrodialysis process was terminated when the conductivity in the concentrating chamber began to decrease and the operating current dropped sharply. The primary concentrate obtained from the primary electrodialysis process was divided into two sections according to a specific volume ratio (desalination chamber solution volume > concentrating chamber solution volume), and these two sections were used as the feed solutions for the secondary electrodialysis chamber and the concentrating chamber, respectively. Constant current operation was performed with a current density of 20 mA / cm², a current setting of 3.78 A, and a voltage upper limit of 25 V. Electrodialysis was terminated when the secondary electrodialysis operating voltage reached 25 V.

[0092] As the number of electrodialysis stages increases, the concentration of nuclides ions increases step by step. In the first stage of electrodialysis, the maximum concentration of chromium, manganese, cobalt, nickel, zinc and strontium is 8.7 times, 11.2 times, 11.5 times, 13.1 times, 7.6 times and 15.8 times. In the second stage of electrodialysis, the maximum concentration of chromium, manganese, cobalt, nickel, zinc and strontium is 17.0 times, 19.8 times, 20.2 times, 20.1 times, 22.5 times and 28.2 times. The concentration changes of each nuclide ion in the first stage of electrodialysis and the second stage of electrodialysis are as follows: Figure 3 As shown, Figure 3 The left part of the curve is the primary electrodialysis stage, and the right part of the curve is the secondary electrodialysis stage.

[0093] The above shows that the radionuclide ions in the desalination chamber can be concentrated to about 11 times by the first stage of electrodialysis, and to about 20 times by the second stage of electrodialysis. This method can be used to detect the actual concentration of radionuclide ions in the liquid effluent of nuclear power plants.

[0094] Example 3:

[0095] 25,200 mL of nuclear power plant liquid effluent and 10 mL of a carrier solution (a mixture containing chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), and strontium (Sr) at a concentration of 0.1 mg / mL) were introduced into the primary electrodialysis desalination chamber. An appropriate amount of nitric acid was added to bring the solution's initial pH to 1-3 (conductivity ~30 mS / cm). 180 mL of a low-concentration sodium nitrate solution was introduced into the concentration chamber. The anode and cathode chambers were connected in series, and 500 mL of a 0.3 mol / L aqueous Na₂SO₄ solution was introduced as a strong electrolyte. The cation exchange membrane used was CMX, produced by Astom Corporation of Japan, and the anion exchange membrane was AMX, produced by Astom Corporation of Japan. The linear velocity of each solution flowing through the membrane stack was 2 cm / s. The primary electrodialysis was operated at a constant current density of 30 mA / cm⁻¹. 2 , the current is set to 5.67A, and the voltage upper limit is set to 30V. When the primary electrodialysis operating voltage reaches 30V, it stops. The primary concentrate obtained by the primary electrodialysis is divided according to a certain volume ratio (the volume of the desalination chamber solution > the volume of the concentration chamber solution), and used as the desalination chamber and the concentration chamber feed solution of the secondary electrodialysis for electrodialysis. Constant current operation, the current density is 40mA / cm 2 , set the current to 7.56 A, and set the voltage upper limit to 30 V. When the secondary electrodialysis operating voltage reaches 30 V, the electrodialysis is terminated.

[0096] As the number of electrodialysis stages increases, the concentration of nuclides ions increases step by step. In the first stage of electrodialysis, the maximum concentration of chromium, manganese, cobalt, nickel, zinc and strontium is 11.5 times, 12.4 times, 12.3 times, 12.1 times, 12.7 times and 14.5 times. In the second stage of electrodialysis, the maximum concentration of chromium, manganese, cobalt, nickel, zinc and strontium is 20.4 times, 19.2 times, 18.6 times, 18.4 times, 19.7 times and 22.8 times. The concentration changes of each nuclide ion in the first stage of electrodialysis and the second stage of electrodialysis are as follows: Figure 4 As shown, Figure 4 The left part of the curve is the primary electrodialysis stage, and the right part of the curve is the secondary electrodialysis stage.

[0097] The above shows that the first-stage electrodialysis can concentrate the nuclide ions in the desalination chamber to about 12 times, and the second-stage electrodialysis can concentrate them to about 20 times, with a recovery rate of over 90%. This method can be used to detect the actual concentration of nuclide ions in the liquid effluent of nuclear power plants.

[0098] As can be seen from the above, the present invention utilizes the charge of radionuclide ions in liquid effluent from nuclear power plants and the ordered arrangement of electrodialysis membrane stacks (alternating anion exchange membranes and cation exchange membranes) to concentrate radionuclide ions of unknown concentration in liquid effluent from nuclear power plants to a certain concentration factor (secondary electrodialysis can achieve a concentration factor exceeding 20 times, with a concentration efficiency exceeding 90%) through electrodialysis, facilitating detection of the actual concentration of radionuclide ions in the effluent. The present invention is simple to implement and poses no environmental risk. It also operates stably, consumes relatively little energy, and achieves a high concentration factor. It is a green, environmentally friendly, and highly efficient method with significant industrial application value.

[0099] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for enriching radioactive nuclides in liquid effluent from a nuclear power plant, characterized in that: The following steps are involved: S1. mixing the liquid effluent from the nuclear power plant and the nuclide carrier liquid and performing a first-stage electrodialysis. When the conductivity of the concentrated liquid reaches a target conductivity, the first-stage electrodialysis is terminated to obtain a first-stage concentrated liquid. S2. The primary concentrated solution is subjected to secondary electrodialysis. When the voltage of the concentrated solution reaches the target voltage, the secondary electrodialysis is terminated to obtain a secondary concentrated solution.

2. The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant according to claim 1, characterized in that: The nuclide carrier liquid is a mixed liquid containing nuclides, wherein the nuclides include chromium, manganese, cobalt, nickel, zinc and strontium, and the concentration of each element is 0.09-0.11 mg / mL.

3. The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant according to claim 1, characterized in that: The volume of the nuclide carrier liquid is 0.1% or less of the volume of the liquid effluent of the nuclear power plant; The target conductivity is a conductivity for determining that the nuclide ions are concentrated at least 10 times on average; The target voltage is a voltage at which the nuclide ions are determined to be concentrated 20 times or more on average.

4. The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant according to claim 1, characterized in that: Step S1 includes: S1.

1. Pass liquid effluent from the nuclear power plant and a nuclide carrier liquid into the desalination chamber of a primary electrodialysis membrane stack, pass a nitrate solution or a dilute acid solution into the concentrating chamber of the primary electrodialysis membrane stack, and pass a strong electrolyte solution into the anode and cathode chambers of the primary electrodialysis membrane stack; The volume of the solution in the desalination chamber is greater than the volume of the solution in the concentrating chamber; S1.

2. Direct current is applied to the anode and cathode plates at opposite ends of the primary electrodialysis membrane stack; Under the action of direct current, the nuclide ions in the desalination chamber migrate from the desalination chamber to the concentrating chamber through the cation exchange membrane of the first-stage electrodialysis membrane stack, and the chloride ions and other anions in the desalination chamber migrate to the concentrating chamber through the anion exchange membrane of the first-stage electrodialysis membrane stack; S1.

3. Obtain the concentrated liquid from the concentrating chamber to obtain a primary concentrated liquid.

5. The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant according to claim 4, characterized in that: Step S2 includes: S2.

1. Pass the primary concentrate into the desalination chamber and the concentrating chamber of the secondary electrodialysis membrane stack, respectively, and pass a strong electrolyte solution into the anode chamber and the cathode chamber of the secondary electrodialysis membrane stack; The volume of the primary concentrate flowing into the desalination chamber of the secondary electrodialysis membrane stack is greater than the volume of the primary concentrate flowing into the concentrating chamber; S2.

1. Direct current is applied to the anode and cathode plates at opposite ends of the secondary electrodialysis membrane stack; Under the action of direct current, the nuclide ions in the desalination chamber of the secondary electrodialysis membrane stack migrate from the desalination chamber to the concentration chamber through the cation exchange membrane, and the chloride ions and other anions in the desalination chamber migrate to the concentration chamber through the anion exchange membrane; S1.

3. Obtain the concentrated liquid from the concentration chamber to obtain a secondary concentrated liquid.

6. The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant according to claim 5, characterized in that: The strong electrolyte solution is a sodium sulfate solution with a concentration of 0.2 mol / L to 0.4 mol / L.

7. The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant according to claim 5, characterized in that: In the first stage electrodialysis, the current density of the applied direct current is 20 mA / cm 2 ~50mA / cm 2 , or the applied constant voltage is 10V to 30V; In the secondary electrodialysis, the current density of the applied direct current is 20 mA / cm 2 ~50mA / cm 2 .

8. The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant according to claim 5, characterized in that: The first-stage electrodialysis membrane stack and the second-stage electrodialysis membrane stack have the same structure, both comprising a dialysis module, an anode plate and a cathode plate arranged on opposite sides of the dialysis module; The dialysis module includes a plurality of cation exchange membranes and a plurality of anion exchange membranes, which are alternately arranged to define an anode chamber, a cathode chamber, a plurality of concentrating chambers, and a plurality of desalination chambers in the electrodialysis membrane stack; The anode chamber is located between the anode plate and the adjacent cation exchange membrane, the cathode chamber is located between the cathode plate and the adjacent anion exchange membrane, and a plurality of the concentration chambers and a plurality of the desalination chambers are located between the anode chamber and the cathode chamber and are arranged alternately.

9. The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant according to any one of claims 1 to 8, characterized in that: In the primary electrodialysis and the secondary electrodialysis, the linear velocity of the liquid flow is controlled to be 2 cm / s to 10 cm / s.

10. The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant according to any one of claims 1 to 8, characterized in that: The method for enriching radioactive nuclides in liquid effluent from a nuclear power plant further comprises the following steps: S3. Calculate the nuclide ion recovery rate: Under initial conditions, liquid effluent from nuclear power plants was sampled and the concentration of each nuclide ion was measured by inductively coupled plasma mass spectrometry. Combined with the volume of the liquid effluent from the nuclear power plant, the total amount of each nuclide ion before enrichment was calculated. After the secondary electrodialysis is completed, the secondary concentrated solution is sampled and the concentration of each nuclide ion is measured by inductively coupled plasma mass spectrometry. Combined with the volume of the secondary concentrated solution, the total amount of each nuclide ion after concentration is calculated. The recovery rate of each nuclide ion was calculated based on the total amount of each nuclide ion before and after concentration.

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