KR100423749B1 - Purification apparatus and method for primary cooling water of nuclear power plant using electrodeioniztion process - Google Patents

Abstract

The present invention relates to an electrodeionization (EDI) apparatus and method for purifying a reactor primary coolant, and more particularly, to removing hydroxide metal ions in the reactor primary coolant using an electrodeionization process. By controlling the charging order of the ion exchange material and the composition of the electric deion stack to prevent the precipitation of ions, the problem of generating waste ion exchange resins is fundamentally solved, unlike conventional methods using only ion exchange resins. Unlike the electric deionization process, which has been used exclusively in the manufacturing field, since metal ions do not form complexes by reacting with hydroxide ions, it is possible to prevent rapid deterioration of the device due to complex precipitation, thereby maximizing purification efficiency and removing efficiency. The present invention relates to a method for ensuring reliability. Then, in order to recover the boron as a reactivity control material in the concentrate obtained in the process, the electrodialysis and electrodeionization process are carried out. In the electrodeionization process, a weak ion species such as boron are charged by filling the water decomposition suppression network in a necessary position. The present invention relates to a method for reducing waste and operating costs by recovering with high efficiency.

Description

Reactor primary cooling water purification apparatus and method using an electric deionization process {Purification apparatus and method for primary cooling water of nuclear power plant using electrodeioniztion process}

The present invention relates to a reactor primary cooling water purification apparatus and method using an electrodeionization (EDI) process, and more particularly, in the removal of metal ions in the reactor primary cooling water using an electrodeionization process, By controlling the packing order and ion deion stack composition of the ion exchange material in order to prevent the precipitation of the complex, the problem of waste ion exchange resin generation is fundamentally solved, unlike the conventional method using only ion exchange resin. Unlike the electric deionization process, which has been used only in the field of ultrapure water, metal ions do not form complexes by reacting with hydroxide ions, which prevents the rapid deterioration of the device due to complex precipitation, thus maximizing purification efficiency and removal efficiency. It is about how to ensure the reliability of. Then, in order to recover the boron as a reactivity control material in the concentrate obtained in the process, the electrodialysis and electrodeionization process are carried out. In the electrodeionization process, a weak ion species such as boron are charged by filling the water decomposition suppression network in a necessary position. The present invention relates to a method for reducing waste and operating costs by recovering with high efficiency.

Conventional light-water reactors use ion exchange resins most often for primary system cooling water purification. The ion exchange resin method has the advantages of low facility cost, excellent decontamination effect and low operating cost. Since the treatment of ion exchange resins currently used has not been established, most of them have been stored in nuclear power plants for a long time or solidified with cement. In the case of solidifying waste resins using solid fires such as cement, the risk of radiation exposure is always exposed to nuclear power workers, and the radioactivity of waste resins is not only related to the technical problems of solidification itself but also to the handling of solidified wastes and securing storage space. There are difficulties, and there is a high possibility of swelling, limit of volume reduction, and leaching of metal components.

Electrodeionization process is a mixing process in which ion exchange material (ion exchange resin or ion exchange fiber, etc.) is filled in the desalination chamber of an electrodialysis apparatus. Has the effect of reducing the environmental burden on wastewater treatment. In addition, since the ion exchange material used in the electrodeionization device acts only as an ion transfer medium, the ion exchange material can be used continuously without replacement, thereby fundamentally solving the problem of generating the waste ion exchange resin.

Electrodeionizers have only been applied to ultrapure water production since it was first commercialized by Miloreore Co. in 1987, and the US Filter's electrodeionization system applied to the Edison plant in Southern California, USA Only applied to Make up Water treatment.

In the case of inflow water containing metal ions such as primary cooling water, when a commercially available electric deionization device is applied, hydroxide ions and metal ions generated by ionization of water in a stack react to form a hydroxide complex. These deposits increase the electrical resistance and form polarization. Therefore, the electric deionization device filled with the mixed cation exchange resin mixed with the existing cation exchange resin and the anion exchange resin cannot continuously process the influent containing the metal ions such as the primary cooling water. For this reason, there are no examples of applying the electrodeionization process to the purification of the reactor primary cooling water.

Boron, on the other hand, is a reactivity regulator and operates at a very high concentration of 1200 ppm at the beginning of the core and at 30 ppm or less at the end of the core, when the activity of the reactor is weakened. At present, the apparatus used for the removal of boron from the primary cooling water is an anion exchange resin filled in the form of hydroxide ions. Boron recovery process is not used, but the following recovery process is considered. At the end of the core, boron anion exchange resin substituted with hydroxide ions to remove boron is used again at the beginning of the core. However, due to the selectivity of the ion exchange resin, it is difficult to obtain an anion exchange resin filled with boron only at the end of the core. As other radioactive metal ions are charged together, further studies are needed to increase the boron selectivity of ion exchange resins.

Accordingly, the present inventors stably purify the primary cooling water by changing the charging method of the ion exchange material in the existing electric deionizer in order to improve the disadvantage of the ion exchange resin method used in the purification of the primary reactor primary cooling water. It has been found that the environmental burden for wastewater treatment can be reduced. In addition, by recovering boric acid contained in the electro-deionized concentrated water, a method of reducing waste generation and operating costs was completed.

Accordingly, an object of the present invention is to replace an existing ion exchange resin process, which is a primary cooling water purification process of a nuclear reactor, with an electrodeionization process, to secure process reliability and stability, and to provide an environment-friendly process.

1 is a system diagram of a process for purifying a reactor primary cooling water by applying an electrodeionization method.

FIG. 2 is a schematic diagram of a process for purifying reactor primary cooling water using three sequential electrodeionization stacks without formation of hydroxide complexes.

FIG. 3 is a detailed view of a stack capable of desalting / concentrating in one electrodesorption stack unlike FIG. 2.

4 is a detailed view of an electrodeionization stack capable of purifying the reactor primary cooling water using a bipolar membrane.

FIG. 5 is a detailed diagram of an electrodeionization stack configuration of multi cell pairs.

6 is a schematic diagram of a boron recovery process.

7 is a detailed view of boron removal and recovery.

[Description of Symbols for Main Parts of Drawing]

100: pretreatment device 110: heat exchanger

120: pH adjustment tank 121: acid tank for pH adjustment

122: pH tank base tank 130: precision filtration device

200: electrical deionization (EDI) device 210: electrical deionization stack (stack)

211 desalination chamber 212 concentration chamber

213: cation exchange membrane 214: anion exchange membrane

215 bipolar membrane 216 water decomposition suppression network

220: power supply device 230: electrode liquid tank

240: EDI desalting tank 250: EDI concentrate tank

300: electrodialysis apparatus

According to the present invention, a desalting chamber is formed by filling an ion exchange material between a cation exchange membrane and an anion exchange membrane, and a concentration chamber is mounted on both sides of the desalting chamber from the exchange membrane, and the desalting chamber and the concentration chamber are disposed between the cathode and the anode. An electric deionization apparatus comprising a deion stack,

In one electrodeion stack, the cation exchange material, the anion exchange material, and the mixed ion exchange material of the cation and anion are sequentially filled from the inlet side of the treated water in the desalination chamber.

In addition, the apparatus is equipped with a bipolar membrane in the center of the desalting chamber in a single electrodeionization stack, and the cation exchanger is filled at the inlet side of the desalting chamber based on the membrane, and the anion exchanger on the opposite side thereof. It may be made of a form filled with a passage connecting the two ion exchange material layers.

In addition, the apparatus comprises three electrodeionization stacks, an electrodeionization stack filled with only cation exchange material, an electrodeionization stack filled with only anion exchange material, and an electrodeionization stack filled with mixed ion exchange material only. It may be made in a form arranged sequentially.

The metal ions in the reactor primary cooling water can be removed through a process of introducing the treated water into the desalination chamber and introducing the concentrated water into the concentration chamber while applying a voltage to the electric deionization apparatus.

In addition, the concentrated water obtained through the above process includes not only metal ions but also weak ionic species such as boron. In the present invention, electroporation and electrodeionization are performed as a method for recovering boron. The electric deionization apparatus for recovering boron is different from the apparatus for removing metal ions, and is configured as follows. In the electric deionizer,

1) cation exchange material and anion exchange material are sequentially charged from the treated water inlet side of the desalting chamber, 2) between cation exchange material and anion exchange membrane, between anion exchange material and cation exchange membrane, and cation exchange material and anion exchange A water decomposition inhibiting layer is mounted between the materials.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

Figure 1 shows a schematic diagram of a process for purifying the reactor primary cooling water by applying the electric deionization method. The reactor primary cooling water discharged from the reactor inlet pipe is maintained below 60 ° C., which is a temperature suitable for operation of the ion exchange resin tower via the heat exchanger 110. The reactor primary cooling water should be operated at pH 6.9 to 7.4 to minimize the deposition of fuel cladding and the minimization of zircaloy oxidation by the clad. In order to minimize the pH associated with the output of the reactor, the pH is adjusted through the pH adjustment tank 120 having the pH adjustment acid tank 121 and the base tank 122, and then suspended in the precision filtration device 130 except the dissolved impurities. The solids will be removed. The liquid waste concentrated by the microfiltration device is discharged to the waste treatment system and the microfiltration treatment water is introduced into the electric deionizer 200. The electric deionization apparatus 200 includes an electric deionization stack 210, an electric deionization power supply device 220, an electrode liquid tank 230, a desalination liquid tank 240, and a concentrate liquid tank 250. The liquid waste concentrated by the electric deionizer is sent to the boron recovery process (FIG. 6). The primary coolant replenishment water flows into the electrodeionization desalting liquid tank 240 and is sent to the reactor inlet tube as the electrodeionization treatment water. Accordingly, the electrodeionized desalination tank 240 performs the same role as the volume control tank (VCT) of the existing reactor chemistry and volume control system (CVCS).

FIG. 2 shows a schematic diagram of a process for purifying the reactor primary cooling water using three sequential electrodeion stacks 210 without formation of hydroxide complexes. Hydroxide and metal ions generated by ionization of water react to form a hydroxide complex in an electrodeionized stack filled with a conventional cation exchange material (ion exchange resin or ion exchange fiber, etc.) and a mixed ion exchange resin mixed with anion exchange material. do. Therefore, the reactor primary cooling water is introduced into the electrodeionization stack filled with only the cation exchange material to remove metal ions, and the treated water containing only hydrogen ions and anions is stored in the storage tank. In addition, the negative ions are removed by flowing into the electrodeionization stack filled with only the anion exchange material. As a result, the treated water collected in the storage tank is mostly metal ions and anions are removed to form ultrapure water of 1 ㏁-cm or more. In this case, the ion form of the anion exchange material should take an ion form other than hydroxide ion. This is because in the case of the hydroxide ion, the hydroxide complex may be formed by reacting with a trace amount of metal ions contained in the treated water of the electrodeionized stack filled with the cation exchange material. The third electrodeionized stack is filled with a mixed phase ion exchanger mixed with cation and anion exchanger to remove trace metal ions and anions from the treated water of the first and second electrodeionized stacks, and the pH of the treated water Keep it neutral.

FIG. 3 is a detailed view of a stack capable of desalting / concentrating in one electrodesorption stack unlike FIG. 2. In the cell deionization stack of one cell pair, the deionization chamber 211 of the electric deionization is first charged with cation exchange material, followed by anion exchange material, and finally mixed ion exchange material. Cobalt ions with the largest impact of radiation exposure in the reactor primary cooling water are shown. Cobalt ions pass through the cation exchange membrane 213 to the cathode under an electric field and move to the concentration chamber 212. Hydrogen ions and hydroxide ions are generated by ionization of water between the desalination chamber 211 and the concentration chamber 212. This is because ionization of water occurs due to the opposite charge between the cation exchange material and the anion exchange membrane. Only primary nitrate ions and hydrogen ions are present in the reactor primary cooling water passing through the cation exchange material. Even in the layer filled with the cation exchange material, a small amount of nitrate ions are removed through the anion exchange membrane 214. In the layer filled with anion exchange material, nitrate ions are removed and ionization of water occurs due to the opposite charge between the anion exchange material and the cation exchange membrane. Hydrogen ions generated in the layer filled with the cation exchange material and hydroxide ions generated in the layer filled with the anion exchange material react with each other to form water.

4 is a detailed view of an electrodeionization stack capable of purifying the reactor primary cooling water using a bipolar membrane. The bipolar membrane 215 is a membrane that generates hydrogen ions and hydroxide ions under an electric field. Cobalt ions with the largest impact of radioactive exposure in the reactor primary cooling water are described. Cobalt ions in the reactor primary coolant flow into the desalination chamber 211a filled with only the cation exchange material and move to the concentration chamber 212. The primary coolant passing through the desalination chamber 211a is the desalination chamber filled with only the anion exchange material. Flows into 211b. Hydrogen ions generated in the desalting chamber 211a react with hydroxide ions generated in the desalting chamber 211b to form water. It can be seen that the same as the principle described in the electrodeionization stack of FIG.

FIG. 5 is a detailed diagram of an electrodeionization stack configuration of multi cell pairs. The cell pair consisting of the desalination chamber 211 and the concentration chambers 212 on both sides thereof is connected to the cathode and the anode more than two times to form a stack of multi cell pairs. The enrichment room is to be equipped with one additional compartment. 3 and 4 correspond to the case where the electrical deionization stack is one cell pair, and when the cell pair is increased, as shown in FIG. 5, the four compartments electrical deionization stack (concentration chamber 1, desalination chamber, and concentration chamber) 2, cell structure of concentration room 3). This is because, in the case of the 2-room electrodeionization stack, the hydroxide ions and the cobalt ions moved from both desalting chambers to the concentration chamber react to form a hydroxide complex. Therefore, in the case of the four-room electrodeionization stack, the complex was not formed by suppressing the mixing of the hydroxide ions and the cobalt ions moved in the desalination chamber.

In addition, when using a bipolar membrane, as shown in FIG. 4, there are two desalination chambers 211a and 211b. In this case, in order to apply the electrodeionization stack having multiple cell pairs, a 5-room electrodeionization stack in which cell structures of concentration chamber 1, desalination chamber, desalting chamber, concentration chamber 2, and concentration chamber 3 are repeated is required.

6 is a schematic diagram of a boron recovery process. Here, the electrodialysis apparatus 300 treats the concentrated solution that has undergone the electrodeionization process of FIG. 1 to the optimum treatment range of the electrodeionization apparatus 200. Electrodialysis devices are not used to treat electrical conductivity up to 1 kW / cm because of their high electrical resistance, and electrodeionization devices are used to treat water to be treated with electrical conductivity 1 kW / cm or less. Therefore, by sequentially going through the electrodialysis and electrodeionization process to treat ions other than boron, and to recover the boron. Here, the electrodeionization apparatus 200 is an electrodeionization apparatus filled with a water decomposition inhibiting layer.

Figure 7 shows a detailed view of the boron removal and recovery, (a) the principle of boron removal is anion ionization of water due to the opposite charge of the cation exchange membrane 213 and the anion exchange material in the layer filled with anion exchange material anion There is a sharp rise in pH locally in the exchange material. Boric acid is ionized by such a rise in pH, and moves to the concentration chamber 212 through the anion exchange membrane 214 and is removed. (b) The boron recovery principle utilizes the property that boric acid does not ionize at a pH of 9 or lower, and the water decomposition inhibiting layer 216 is filled between the ion exchange material ionized with water and the ion exchange membrane to form a diffusion boundary layer like electrodialysis. Let's do it. At this time, the water decomposition inhibiting layer 216 uses a plastic-based net, and the thickness thereof is preferably 80 nm to 2 mm. That is, the water decomposition inhibiting layer 216 is an inhibitor layer for suppressing a bipolar interface, and suppresses ionization of water to prevent local pH rise of the ion exchange material, thereby preventing boric acid from being ionized. .

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by Examples.

Example 1

In order to explain the principle of the primary cooling water purification of the reactor of the electric deionized stack in which the cation exchange material, the anion exchange material, and the mixed ion exchange material were arranged sequentially, the separation experiment was conducted sequentially to remove the removal efficiency and energy consumption of the ion exchange material. And the like. The microfiltration treated water was introduced into three electrodeionized stacks arranged in sequence. The primary cooling water of the reactor contains radioactive corrosion products such as cobalt, nickel, iron, silver, boron, and chromium as the power generation cycle is repeated, and conducts electrodeionization experiments centering on cobalt ions having the greatest effect of exposure. It was. At this time, the concentration of cobalt ion used was 10 mg / L. The cation exchange membrane used in the experiment was CMX (manufactured by Tokuyama Co., Japan), the anion exchange membrane was used by AMX (manufactured by Tokuyama Co., Japan), and the ion exchange material was IRN-77 strongly acidic cation exchange resin, IRN-78 steel. Basic anion exchange resin (manufactured by Rohm and Haas Co.) was used. Current density was 1.7 mA / cm 2, effective film area 80 cm 2, and continuous operation for 22 hours under constant current conditions. The experimental results are summarized in Table 1.

Measurement result of electric deionized stack filled with ion exchange resin Electrodeion Stack Cobalt ion removal efficiency (%) Nitrate removal efficiency (%) Energy Consumption (kWh / ton) One Electrodeionization with Cation Exchange Resin 99.9 27.9 0.9 2 Electrodeionization with anion exchange resin 96 99.9 0.5 3 Electrodeionization with Mixed Ion Exchange Resin 99.4 98.7 1.5

The concentration of cobalt ion decreased from the initial 10 mg / L to three electrodeionization stacks sequentially and then decreased to a low concentration of 1 ppb.

Example 2

Purification experiments were carried out using an electrodesorption stack filled with cation exchanger, anion exchanger and mixed ion exchanger in one cell, and the removal efficiency and energy consumption of the ion exchanger were compared. Electrodeionization experiments were carried out around cobalt ions with the greatest effect of exposure. The initial concentration of cobalt ions and the ion exchange membrane and ion exchange resin used in the experiment are the same as in Example 1. For the ion exchange fiber, AMPS strong acid cation exchange fiber, PLEXIMON strong basic anion exchange fiber (manufactured by Institute Textile De France) was used. One stack was charged with a cation exchange resin, an anion exchange resin, and a mixed ion exchange resin in this order, and the current density was 3.3 hours / cm 2, an effective membrane area of 80 cm 2, and continuous operation for 25 hours under constant current conditions. In the case of the electric deionized stack filled with ion exchange fibers, the cation exchange fibers and the anion exchange fibers were sequentially charged 1: 1, and operated continuously for 7 hours at a current density of 2.7 mA / cm 2, an effective membrane area of 80 cm 2, and constant current. The experiment results are summarized in Table 2.

Measurement Result of Electrodeionized Stack with Ion Exchange Resin and Ion Exchange Fiber Electrodeion Stack Cobalt ion removal efficiency (%) Current efficiency (%) Energy Consumption (kWh / ton) Electrodeionization with Ion Exchange Resin 99 30 2 Electrodeionization with ion exchange fiber 99 23.2 3.5

Example 3

In order to recover the boron ion as a reactivity control material, the electrodialysis process and the electrodeionization process were sequentially applied to observe the recovery rate and the energy consumption. When the concentration of the electrodeionizer was 10 times the concentration of the desalination solution, it was used as the influent of the recovery process. The concentrate of the electrodeionization device, which is the influent of the recovery process, exhibited about 4000 dl / cm including ions such as cobalt ions, iron, nickel, silver, boron, and chromium. The ion exchange membrane and ion exchange resin used in the experiment were the same as in Example 1. Polypropylene mesh (mesh size: 43.5 × 43.5 strands per inch, Naltex, Nalle Plastics, Inc.) used as a water decomposition suppressor was mounted at a thickness of 0.013 ", current density 2.3 mA / ㎠, effective film area 80 ㎠ In the constant current conditions, continuous operation was carried out, and the experimental results are summarized in Table 4.

Measurement result of boron recovery process as reactivity control material Boric acid recovery (%) Current efficiency (%) Energy Consumption (kWh / ton) Boron Recovery Process 94 20 4.2

As a result of investigating the recovery of boron according to the change of current density, it was 94% at 2.3 mA / ㎠ and decreased to 43% with increasing current density. As the current density increases, the diffusion boundary layer is formed in the network and the ion exchange membrane installed to suppress the water decomposition of the electrodeionization device.

As described above, the method of removing metal ions and recovering boron from the reactor primary cooling water according to the present invention by the electrodeionization process by changing the charging method of the ion exchange material in the existing electrodeionization apparatus, waste treatment It can innovatively reduce the burden and protect workers from the risk of radiation exposure, and can help secure competitiveness by reducing operational and maintenance costs of nuclear power plants in terms of economy and industry. Therefore, in the context of strengthening regulations on environmental pollution through green rounds in international trade, the application of the clean deionization process, which is a clean technology, will generate economic profits in the industrial field where the ion exchange resin law was applied. By applying the electrodeionization process to water, sewage, and wastewater containing metal ions, it is possible to create more applications.

Claims (9)

An ion exchange material is filled between the cation exchange membrane 213 and the anion exchange membrane 214 to form a desalination chamber 211, and a concentration chamber 212 is mounted on both sides of the desalination chamber from the exchange membrane. In the reactor primary cooling water purifier using an electric deionization device including an electric deionization stack 210 is disposed between the cathode and the anode, A reactor characterized in that the cation exchange material, the anion exchange material, and the mixed ion exchange material of the cation and anion are sequentially filled from the inlet side of the desalination chamber 211 in the deionization chamber 211. Primary Cooling Water Purifier. An ion exchange material is filled between the cation exchange membrane 213 and the anion exchange membrane 214 to form a desalination chamber 211, and a concentration chamber 212 is mounted on both sides of the desalination chamber from the exchange membrane. In the reactor primary cooling water purifier using an electric deionization device including an electric deionization stack 210 is disposed between the cathode and the anode, In one electrodeionization stack, a bipolar membrane 215 is mounted in the center of the desalination chamber, and based on the membrane, a cation exchanger is charged at the inlet side of the desalination chamber, and an anion exchanger is opposite to the membrane. A reactor primary coolant purification apparatus characterized by being filled with a passage connecting two layers of ion exchange material. An ion exchange material is filled between the cation exchange membrane 213 and the anion exchange membrane 214 to form a desalination chamber 211, and a concentration chamber 212 is mounted on both sides of the desalination chamber from the exchange membrane. In the reactor primary cooling water purifier using an electric deionization device including an electric deionization stack 210 is disposed between the cathode and the anode, The apparatus consists of three electrodeionization stacks, an electrodeionization stack filled with cation exchange material only, an electrodeionization stack filled with anion exchange material only, and an electrodeionization stack filled with mixed ion exchange material in sequence. Reactor primary coolant purification apparatus, characterized in that arranged. According to any one of claims 1 to 3, wherein the cell pair consisting of the desalination chamber and the enrichment chambers on both sides are connected two or more layers between the cathode and the anode to form a stack of multi cell pairs (cell stack), Reactor primary cooling water purification apparatus, characterized in that the concentration chamber is additionally installed one by one between the cell pair. In the reactor primary cooling water purification method for removing impurity ions in the treated water by flowing the treated water into the desalination chamber while applying a voltage to the electric deionizer, Reactor primary cooling water purification method comprising the step of passing the water to be treated in the arrangement of the ion exchange material in the apparatus of claim 1, claim 2 or claim 3. In the reactor primary cooling water purification method for removing impurity ions in the treated water by flowing the treated water into the desalination chamber while applying a voltage to the electric deionizer, Reactor primary cooling water purification method comprising the step of using the apparatus of claim 4. An ion exchange material is filled between the cation exchange membrane 213 and the anion exchange membrane 214 to form a desalination chamber 211, and a concentration chamber 212 is mounted on both sides of the desalination chamber from the exchange membrane. In the reactor primary cooling water purifier using an electrodeionization device disposed between the cathode and the anode, 1) cation exchange material and anion exchange material are sequentially charged from the treated water inlet side of the desalting chamber, 2) between cation exchange material and anion exchange membrane, between anion exchange material and cation exchange membrane, and cation exchange material and anion exchange Reactor primary cooling water purifier, characterized in that the water decomposition suppression layer 216 is mounted between the materials. The reactor primary coolant purification apparatus according to claim 7, wherein the water decomposition inhibiting layer (216) comprises a plastic-based net having a thickness of 80 nm to 2 mm. In the reactor primary cooling water purification method, A process of treating up to an ion concentration of 1 ms / cm or less suitable for an electrodeionization process using an electrodialysis method, A method for purifying the reactor primary cooling water, comprising the step of recovering the weak ion species in the water to be treated using the purifier of claim 7 or 8.