CN106653131A - Method for separating boron and radionuclides from radioactive wastewater by lengthening flow channels - Google Patents

Abstract

The invention discloses a method for separating boron and radionuclides in radioactive waste water with lengthened flow channels, which includes: 1) setting up a membrane stack, in which several anodes and cathodes are alternately arranged, and adjacent anodes and cathodes constitute An electric field, a cation exchange membrane and an anion exchange membrane are set between the anode and the cathode to form the cathode chamber, the anode chamber and the fresh water chamber; 2) Fill the anode chamber, the cathode chamber and the fresh water chamber with ion exchange resin; 3) The membrane stacks are connected in series The cathode chamber, the anode chamber and the fresh water chamber inside constitute three flow channels, and radioactive waste water is passed into these three flow channels, the borate ions in the fresh water chamber migrate to the anode chamber under the action of the electric field, and the nuclide ions in the fresh water chamber migrate to the anode chamber. To the cathode chamber, thereby separating boron and radioactive nuclides in the radioactive wastewater in the freshwater chamber; during the separation process, the ratio of the average concentration of boron in the anode chamber and the freshwater chamber under the same electric field is controlled to be no more than 35.

Description

A method for separating boron and radionuclides in radioactive waste water with lengthened flow channel

technical field

The invention relates to the field of radioactive waste water treatment, in particular to a method for separating boron and radionuclides in radioactive waste water by using an extended flow channel.

Background technique

In traditional pressurized water reactor nuclear power plants, boron is used for reactive chemical compensation control, and the adjustment of boron concentration is completed by chemical volume control system (referred to as chemical volume system). During the operation of the power plant, a large amount of boron-containing waste liquid is produced due to the frequent operation of boron adjustment and chemical discharge. The discharged boron waste liquid is concentrated and purified by the boron recovery system, and then reused in the power plant.

The boron recovery system was canceled in the design of the AP1000 nuclear power plant in the United States, and the boron in the coolant effluent was basically discharged into the receiving water body of the plant site environment.

Boric acid has acute toxicity, chronic toxicity and reproductive toxicity, and entering into the water body will affect the ecological environment and human health. Since the dilution capacity of the circulating cooling water of inland power plants is much smaller than that of coastal power plants, and the receiving water body is a precious fresh water resource, inland power plants need to strictly control the content of boron in the discharged waste liquid.

At present, the processes that can be used to remove boron mainly include evaporation, chemical precipitation, ion exchange, and reverse osmosis. Evaporation is the boron removal process adopted by the boron recovery system of the second-generation plus nuclear power plant. It has the advantages of mature technology and rich experience in engineering operation, but the disadvantages are large floor area, high energy consumption, and high activity of radionuclides in the concentrated solution; Boron has a high decontamination factor, but the ion exchange resins currently on the market have a low working exchange capacity for boron, and a large amount of waste resin will be generated in the treatment of boron-containing waste liquid; reverse osmosis is the main method for removing boron in seawater desalination. Process, in order to ensure the efficiency of boron removal, reverse osmosis boron removal needs to adjust the pH value of the boron solution inlet water, because boric acid is a monobasic weak acid, a large amount of alkali needs to be added to adjust the pH value, causing secondary pollution, and the reverse osmosis membrane will have nuclides and boron At the same time, the interception will also cause the accumulation of radionuclides on the concentrated water side. At the same time, the interception effect of reverse osmosis on boric acid is much lower than that of other ions, which constitutes a contradiction between the decontamination factor of boron and the concentration multiple. When the concentration ratio is increased, the decontamination factor of boron by reverse osmosis decreases. In a typical reverse osmosis system, when the recovery rate reaches over 80%, the removal rate of boron is less than 30%.

In the treatment of boron-containing radioactive waste liquid, there may be different requirements. In addition to the separation requirements of boron, there may also be requirements for the separation of radionuclides. The method provided by the present invention can separate boron-containing radioactive wastewater into three streams: a stream with low boron content and low radioactive content; a stream with high boron content and low radioactive content; and a stream with low boron content and high radioactive content . In addition, any two of the above three liquid streams can also be blended to meet different separation requirements.

Contents of the invention

In view of the problems existing in the prior art, the object of the present invention is to provide a method for separating boron in radioactive waste water with lengthened flow channel, and to separate boron-containing radioactive waste water into three liquid streams: liquid streams with low boron content and low radioactive content ; high boron content, low radioactive content streams and low boron content; high radioactive content streams.

To achieve the above object, the technical scheme of the present invention is as follows:

A method for separating boron and radionuclides in radioactive waste water with lengthened flow channels, the method comprises the following steps:

Step 1) set up a membrane stack, in which a plurality of anodes and cathodes at a certain distance are arranged alternately, an electric field is formed by adjacent anodes and cathodes, and an electric field is arranged between the anodes and cathodes of the electric field A cation exchange membrane and an anion exchange membrane perpendicular to the direction of the electric field, the cation exchange membrane is close to the cathode, and forms a cathode chamber with the cathode, and the anion exchange membrane is close to the anode, forms an anode chamber with the anode, and the cation exchange A fresh water chamber is formed between the membrane and the anion exchange membrane;

Step 2) filling the anode chamber with a strongly acidic cation exchange resin, filling the cathode chamber with a strongly basic anion exchange resin, and filling the fresh water chamber with a mixed ion exchange resin;

Step 3) Cathode chambers in series, anode chambers in series, and freshwater chambers in series constitute three flow paths, and radioactive waste water is introduced into these three flow paths, and the borate ions in the freshwater chambers migrate to the anode chambers under the action of an electric field, and the borate ions in the freshwater chambers Nuclide ions migrate to the cathode chamber, thereby separating boron and radionuclides from radioactive wastewater in the freshwater chamber;

During the separation process, the ratio of the average concentration of boron in the anode chamber and the fresh water chamber in the same electric field is controlled not to be greater than 35.

Further, the ratio of the average concentration of boron in the anode chamber and the fresh water chamber in the same electric field is controlled not to be greater than 20.

Further, adjust the pH value of the radioactive wastewater entering the step 3) to above 9.

Further, in the step 3), the radioactive waste water flows in the fresh water chamber opposite to that in the anode chamber and the cathode chamber, and is perpendicular to the direction of the electric field.

Further, the inflow water of the flow channel connected in series with the anode chamber and the flow channel connected in series with the cathode chamber is taken from the effluent water of the flow channel connected in series with the fresh water chamber.

Further, after passing through a predetermined number of said anode chambers, the radioactive waste water with boron concentration lower than that of the anode chamber is passed into the next anode chamber to control the ratio of the average concentration of boron in the anode chamber and the fresh water chamber in the same electric field .

The method for separating boron and radionuclides in radioactive waste water of the present invention utilizes boric acid as a monobasic weak acid, and the boron-containing radioactive waste liquid first enters the fresh water chamber, and under the action of the electric field, the borate ions existing in the form of ions in the water continue along the cathode to the The direction of the anode migrates into the anode chamber, so the content of boric acid in the effluent of the anode chamber increases. Most of the radionuclides exist in the form of cations. The radionuclides in the fresh water chamber migrate into the cathode chamber along the direction from the anode to the cathode. Since the cations cannot pass through the anion exchange membrane and the anions cannot pass through the cation exchange membrane, the anode chamber Neither cations nor anions from the cathode compartment can enter the fresh water compartment. The final result is that a liquid flow with high boron content and low radioactive content flows out of the effluent of the anode chamber; a liquid flow with low boron content and high radioactive content flows out of the effluent of the cathode chamber; a liquid flow with low boron content and low radioactive content flows out of the effluent of the fresh water chamber. flow.

It should be noted that in the separation process, the ratio of the average concentration of boron in the anode compartment to the average concentration of boron in the fresh water compartment must be controlled, and the ratio should not be greater than 35, preferably not greater than 20.

Raising the pH value of radioactive wastewater can improve the effect of boron separation.

Description of drawings

Fig. 1 is the schematic diagram of the membrane stack in the separation radioactive waste water of boron and radionuclide of lengthening flow passage among the present invention;

Fig. 2 is a schematic diagram of introducing radioactive waste water into the membrane stack shown in Fig. 1 .

detailed description

The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

For ease of description, spatially relative terms such as "upper," "lower," "left," and "right" may be used herein to describe the relationship of one element or feature relative to another element or feature shown in the figures. It will be understood that the spatial terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "lower" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative specifications used herein interpreted accordingly.

As shown in Fig. 1 and Fig. 2, the method for boron and radionuclide in the separation radioactive waste water of a kind of lengthening flow path of the present invention, this method has utilized boric acid as monobasic weak acid, and there is following dissociation equilibrium in water:

Since the vast majority of radionuclides exist in the form of cations, it is possible to separate boron and nuclide ions based on the difference in the charging properties of the ions.

As shown in Figure 1 and Figure 2, the method comprises the following steps:

Step 1) Set up a membrane stack, in which two anodes 1 and two cathodes 2 are arranged alternately, with a certain distance between the anodes 1 and cathodes 2, and adjacent anodes 1 and cathodes 2 form an electric field, A cation-exchange membrane 3 and anion-exchange membrane 4 perpendicular to the direction of the electric field are set between the anode 1 and the cathode 2 of the electric field, the cation-exchange membrane 3 is close to the cathode 2, and a cathode chamber 7 is formed between the cathode 2, and the anion-exchange membrane 4 is close to the anode 1, and forms an anode chamber 6 with the anode 1, and forms a fresh water chamber 5 between the cation exchange membrane 3 and the anion exchange membrane 4;

Step 2) Fill the strong acidic cation exchange resin in the anode chamber 6, fill the strong basic anion exchange resin in the cathode chamber 7, and fill the fresh water chamber 5 with doped strong acidic cation exchange resin and strong basic anion exchange resin mixed ion exchange resin;

Step 3) The cathode chamber 7, the anode chamber 6 and the fresh water chamber 5 in the membrane stack are respectively connected in series to form three flow paths, and the radioactive waste water is passed into these three flow paths, wherein the radioactive waste water is passed into the fresh water chamber 5 from the A end, and passes through three After four fresh water chambers 5 flow out from the D end, part of the water flowing out from the D end is passed into the anode chamber 6 and the cathode chamber 7 from the E end and the F end, and the water passed into the anode chamber 6 passes through three anode chambers 6 Flow out from the B end, the water passed into the cathode chamber 7 flows out from the C end after passing through three cathode chambers 7, the borate ions in the fresh water chamber 5 move to the anode 1 under the action of the electric field, and after passing through the anion exchange membrane 4 Migrating to the anode chamber 6, the nuclide ions in the fresh water chamber 5 move to the cathode 2 under the action of the electric field, and migrate to the cathode chamber 7 through the cation exchange membrane 3, thereby separating boron and radioactive nuclei in the radioactive waste water in the fresh water chamber 5 white;

During the separation process, the ratio of the average concentration of boron in the anode chamber 6 and the fresh water chamber 5 in the same electric field is controlled to be no more than 35, preferably no more than 20. The specific control method can be after passing through a predetermined number of anode chambers 6, pass into the next anode chamber 6 the radioactive waste water with boron concentration lower than this anode chamber 6, to control the anode chamber 6 and the fresh water chamber 5 of the same electric field The ratio of the average concentration of boron.

It is also possible to adjust the pH value of the radioactive waste water entering the step 3) to above 9 to increase the separation effect. For example: at 20°C, in a 500mg/L boric acid solution, the percentage of boron content in the form of ions in the total amount of boron under different pH conditions is as follows (Table 1):

pH of the solution 5.29 7 9.24 11 B(OH) ₄ ^- the percentage of total boron, % 0.011 0.572 50 98.3

It can be seen from Table 1 that when the pH value is not adjusted at room temperature, the degree of dissociation of boric acid in water is very low, so the conductivity of high-concentration boric acid is not strong. The pH value of the radioactive waste water passed into the cathode chamber and the anode chamber is above 9, which can increase the separation effect.

The specific experimental data (Table 2) are given below:

*ND means not detected. Cs ⁺ , Co ²⁺ and Sr ²⁺ were detected by Plasma Quad 2plus ICP-MS instrument, and the detection limits were 1, 2 and 5 ng/L, respectively.

In the test results given in Table 2, among all the effluents from the fresh water chamber and the effluent from the cathode chamber, only one water sample detected extremely low concentrations of Co ²⁺ , and none of Cs ⁺ , Sr ²⁺ , or Co ²⁺ was detected in the other water samples. Detected, this shows that the low concentration nuclide ions in the influent water can be fully purified in the invented device. The concentrations of Cs ⁺ , Sr ²⁺ , and Co ²⁺ detected in the effluent of the anode chamber were all low. Through the material balance calculation, it can be found that none of the Cs ⁺ , Sr ²⁺ , and Co ²⁺ in this test reached the material balance. The reason is that most of Cs ⁺ , Sr ²⁺ , and Co ²⁺ stay in the cathode chamber. Due to the low concentration of Cs ⁺ , Sr ²⁺ , and Co ²⁺ in the feed water and the cation exchange resin filled in the cathode chamber has a large adsorption capacity for nuclide ions, it takes a long time for the cathode chamber to reach a steady state ( tens to hundreds of hours).

Claims (6)

1. it is a kind of lengthen runner separate radioactive wastewater in boron and radionuclide method, it is characterised in that the method comprises the steps：

Step 1）Membrane stack is set, anode and negative electrode that several keep at a certain distance away are arranged alternately in the membrane stack, one electric field is constituted by the adjacent anode and the negative electrode, one cation exchange membrane and anion exchange membrane perpendicular to direction of an electric field is set between the anode and negative electrode of the electric field, the cation exchange membrane is near negative electrode, cathode chamber is constituted between the negative electrode, the anion exchange membrane is near anode, anode chamber is constituted between the anode, freshwater room is constituted between cation exchange membrane and anion exchange membrane；

Step 2）Storng-acid cation exchange resin is filled in the anode room, in the negative electrode room strong-base anion-exchange resin is filled, mixture iron exchange resin is filled with the fresh water room；

Step 3）Series cathode room, series connection anode chamber, series connection freshwater room constitute three runners, radioactive wastewater is passed through into this three runners, borate ion in freshwater room is migrated to anode chamber in the presence of electric field, radionuclide ion in freshwater room is migrated to cathode chamber, so as to separate boron and radionuclide in fresh water room in radioactive wastewater；

In separation process, anode chamber of the control in same electric field is not more than 35 with the ratio of the mean concentration of boron in freshwater room.

2. the method for claim 1, it is characterised in that the anode chamber of the control in same electric field is not more than 20 with the ratio of the mean concentration of boron in the freshwater room.

3. the method for claim 1, it is characterised in that adjust and enter the step 3）In radioactive wastewater pH value to more than 9.

4. the method for claim 1, it is characterised in that the step 3）Described in radioactive wastewater flow in the freshwater room with the anode chamber and the cathode chamber flow direction conversely, and perpendicular to the direction of the electric field.

5. the method for claim 1, it is characterised in that the runner of the runner of the anode chamber of having connected and the cathode chamber of having connected enters the water outlet that water takes from the runner of the freshwater room of having connected.

6. the method for claim 1, it is characterized in that, the ratio of the mean concentration of boron in the anode chamber of same electric field and freshwater room is controlled boron concentration behind the anode chamber of predetermined quantity, is passed through in next anode chamber less than the radioactive wastewater of the anode chamber.