JP6144480B2 - Zinc injection method and zinc injection device - Google Patents

Description

  The present invention relates to a zinc injection method and a zinc injection device, and more particularly to a zinc injection method and a zinc injection device suitable for zinc injection into reactor water in a reactor pressure vessel of a boiling water nuclear power plant.

  For example, a boiling water nuclear power plant (hereinafter abbreviated as a BWR plant) includes a nuclear reactor having a reactor pressure vessel (referred to as RPV) in which a core loaded with a plurality of fuel assemblies is disposed. I have. The reactor water supplied to the core by the recirculation pump (or internal pump) is heated by the heat generated by the fission of nuclear fuel material in the fuel assembly loaded in the core, and a part thereof becomes steam. This steam is led from the RPV to the turbine and rotates the turbine. The steam exhausted from the turbine is condensed in a condenser to become water. This water is supplied to the RPV as feed water. In order to suppress the generation of radioactive corrosion products in the RPV, mainly metal impurities contained in the feed water are removed by a filtration and desalting apparatus provided in the feed water pipe.

  In addition, since the corrosion product that is the source of the radioactive corrosion product is generated from the water contact portion of the BWR plant component such as RPV and recirculation piping, the main component of the BWR plant is corroded. Stainless steel and nickel-based alloys such as nickel-based alloys are used. The RPV made of low alloy steel has a built-in stainless steel on the inner surface to prevent the RPV low alloy steel from coming into direct contact with the reactor water. Reactor water is cooling water present in the RPV. Furthermore, a part of the reactor water is purified by a filtration and desalination apparatus of a reactor purification system connected to the RPV to positively remove metal impurities that are slightly present in the reactor water.

  However, even if the above-mentioned corrosion countermeasures are taken, it is unavoidable that very few metal impurities are contained in the reactor water, so some metal impurities are contained in the fuel assembly as metal oxides. Adhere to the surface of the fuel rod. Impurities (for example, metal elements) adhering to the surface of the fuel rod cause a nuclear reaction by irradiation of neutrons released by fission of nuclear fuel material in the fuel rod, and radioactive materials such as cobalt 60, cobalt 58, chromium 51 and manganese 54 are emitted. Become a nuclide.

  These radionuclides remain mostly attached to the fuel rod surface in the form of oxides. However, some radionuclides are eluted as ions in the reactor water depending on the solubility of the incorporated oxide, or re-released into the reactor water as an insoluble solid called a clad. The radioactive material contained in the reactor water is removed by the reactor purification system connected to the RPV. However, since the amount of reactor water treated by the reactor water purification system is only a few percent of the feed water flow rate, the radioactive substances in the reactor water cannot be completely removed. The radioactive material remaining in the reactor water is accumulated on the surface of the BWR plant in contact with the reactor water while circulating in the recirculation system connected to the RPV together with the reactor water. As a result, the radiation emitted from the surface of the component member causes radiation exposure of workers engaged in the periodic inspection work in the periodic inspection of the BWR plant.

  The exposure dose of the employee is managed so that it does not exceed the prescribed value for each person. In recent years, this specified value has been reduced, and it has become necessary to reduce the exposure dose of each person as much as possible.

  Therefore, various methods for reducing the adhesion of radionuclides to the surface of the piping in contact with the reactor water and methods for reducing the concentration of radionuclides in the reactor water have been studied.

  As one of such methods, metal ions such as zinc coexist in the reactor water, and a dense oxide film containing zinc is formed on the inner surface of the piping and the surface of the structure in contact with the reactor water. A method for suppressing the incorporation of radionuclides such as cobalt 60 and cobalt 58 into the oxide film is described in JP-A-58-79196.

  Also, in Japanese Patent No. 3344608, carbon dioxide gas is introduced into an aqueous solution in a zinc dissolution tank to produce an aqueous solution saturated with carbon dioxide, and zinc (for example, zinc oxide) is added to the aqueous solution in the zinc dissolution tank. It is described that this zinc is dissolved in an aqueous solution saturated with carbon dioxide. The produced aqueous solution containing zinc ions is supplied into the RPV.

JP 58-79196 A Japanese Patent No. 3344608

  When preparing zinc ions, there is a method of dissolving a zinc salt and a zinc compound or zinc metal with an acid and an alkali. In either case, since a counter anion or counter cation having a charge opposite to that of zinc ions is also brought into the reactor water, a chemical form with little influence on the reactor water and components is desired. As one such chemical form, in Japanese Patent No. 3344608, zinc ions are prepared by dissolving a zinc compound (for example, zinc oxide powder) using carbonated water.

  In the zinc injection method described in Japanese Patent No. 3344608, zinc is dissolved in an aqueous solution saturated with carbon dioxide gas generated in a zinc dissolution tank, and an aqueous solution containing zinc ions is generated. The zinc concentration is lowered. When an aqueous solution having a low zinc concentration is injected into the RPV reactor water, for example, the effect of suppressing the attachment of radionuclides to the surface of the reactor internal structure and the pipe inner surface connected to the RPV is reduced.

  An object of the present invention is to provide a zinc injection method and a zinc injection apparatus capable of further increasing the zinc ion concentration of an aqueous carbonate solution containing zinc ions injected into a reactor pressure vessel.

  The feature of the present invention that achieves the above-described object is that carbon dioxide gas is injected into a carbonic acid aqueous solution existing in the carbon dioxide gas dissolving region to dissolve the carbon dioxide gas in the carbonic acid aqueous solution. The gas dissolution region and the closed loop including the zinc dissolution region where the solid substance containing zinc exists are circulated, and the zinc contained in the solid material is moved from the carbon dioxide dissolution region to the zinc dissolution region by the circulation in the zinc dissolution region. Dissolved in the supplied carbonic acid aqueous solution, the carbonic acid aqueous solution containing dissolved zinc was supplied to the carbon dioxide dissolving region by circulation, and the carbonic acid aqueous solution containing zinc in the carbon dioxide dissolving region was connected to the reactor pressure vessel To supply to the reactor pressure vessel through piping.

  Since the carbonic acid aqueous solution containing zinc is circulated in the closed loop including the carbon dioxide dissolving region and the zinc dissolving region, the zinc contained in the solid substance is dissolved in the carbonic acid aqueous solution every time it passes through the zinc dissolving region. The ion concentration can be further increased. For this reason, the zinc ion concentration of the reactor water in the reactor pressure vessel can also be increased in a shorter time.

  Preferably, the first flow rate of the aqueous carbonate solution supplied to the zinc dissolving region when the zinc concentration of the aqueous carbonate solution is smaller than the set zinc concentration is such that the zinc flow rate in the zinc dissolving region is reached when the zinc concentration of the aqueous carbonate solution reaches the set zinc concentration. It is desirable to make it faster than the second flow rate of the aqueous carbonate solution supplied.

  According to the present invention, it is possible to further increase the zinc ion concentration of the aqueous carbonate solution containing zinc ions injected into the reactor pressure vessel.

It is a block diagram of the zinc injection | pouring apparatus used for the zinc injection | pouring method of Example 1 which is one preferable Example of this invention. It is explanatory drawing of the zinc ion implantation method into the reactor pressure vessel in a boiling water nuclear power plant using the zinc injection apparatus shown in FIG. It is explanatory drawing which shows the relationship between the zinc melt | dissolution density | concentration in carbonate saturated melt | dissolution water, and pH. It is a characteristic view which shows the relationship between the linear flow rate of carbonated water, and the thickness of the diffusion layer of carbonated water formed on the surface of zinc oxide. It is a characteristic view which shows the relationship between the dissolution time of zinc oxide by carbonated water and zinc concentration. It is a characteristic view which shows the relationship between the zinc concentration in carbonic acid saturated water, and electrical conductivity. It is a block diagram of the zinc injection | pouring apparatus used for the zinc injection | pouring method of Example 2 which is another suitable Example of this invention. It is a block diagram of the zinc injection | pouring apparatus used for the zinc injection | pouring method of Example 3 which is another suitable Example of this invention.

  In Japanese Patent No. 3344608, as described above, zinc ions are prepared by dissolving a zinc compound (for example, zinc oxide powder) using carbonated water. Carbon dioxide is bubbled into the water in the zinc dissolution tank from the bottom of the zinc dissolution tank to generate carbonated water, and the zinc compound is dissolved in the same zinc dissolution tank and stirred to generate zinc ions. can do. When carbon dioxide gas is bubbled into water to which a zinc compound is added, an equilibrium reaction of carbonate ions represented by the formulas (1), (2), and (3) occurs.

CO ₂ (g) = CO ₂ (aq); K _H = [CO ₂ (aq)] / P _CO2 = 0.034 (at 25 ° C.) (1)
CO ₂ (aq) + H ₂ O = HCO ₃ ⁻ + H ⁺ ; K ₁ = [HCO ₃ ⁻ ] [H ⁺ ] / [CO ₂ (aq)] = 4.45 × 10 ⁻⁷ (2)
HCO ₃ ⁻ = CO ₃ ²⁻ + H ⁺ ; K ₂ = [CO ₃ ²⁻ ] [H ⁺ ] / [HCO ₃ ⁻ ] = 4.69 × 10 ⁻¹¹ (3)
In addition to these three equilibrium equations, the ionic product of water [H ⁺ ] [OH ⁻ ] = 10 ⁻¹⁴ , the total pressure 101.3 kPa, and the water vapor pressure of water at 25 ° C. of 8.44 kPa, When the charge balance equation is solved, the pH is 3.91.

[OH ⁻ ] + [HCO ₃ ⁻ ] +2 [CO ₃ ²⁻ ] = [H ⁺ ] (4)
When zinc is dissolved in the carbonated water, each equilibrium reaction of zinc ions represented by the formulas (5) to (9) is added.

Zn ²⁺ + OH ⁻ = Zn (OH) ⁺ ; K _Zn1 = [Zn (OH) ⁺ ] / ([Zn ²⁺ ] [OH ⁻ ]) = 2.04 × 10 ⁶ (5)
Zn ²⁺ + 2OH ⁻ = Zn (OH) ₂ ; K _Zn2 = [Zn (OH) ₂ ] / ([Zn ²⁺ ] [OH ⁻ ] ² ) = 1.55 × 10 ¹¹ (6)
Zn ²⁺ + 3OH ⁻ = Zn (OH) ₃ ⁻ ; K _Zn3 = [Zn (OH) ₃ ⁻ ] / ([Zn ²⁺ ] [OH ⁻ ] ³ ) = 2.04 × 10 ¹⁴ (7)
[Zn ²⁺ ] + [CO ₃ ^2- ] = [ZnCO ₃ ]; K _ZnC = [ZnCO ₃ ] / ([Zn ²⁺ ] [CO ₃ ^2- ])) 2.00 × 10 ³ (8) )
[Zn ²⁺ ] + [HCO ₃ ⁻ ] = [ZnHCO ₃ ⁺ ]; K _ZnHC = [ZnHCO ₃ ⁺ ] / ([Zn ²⁺ ] [HCO ₃ ⁻ ]) = 7.08 (9)
The charge balance formula with zinc and the mass balance formula of zinc are shown below.

[Zn] _T = [Zn ²⁺ ] + [Zn (OH) ⁺ ] + [Zn (OH) ₂ ] + [ZnCO ₃ ] + [ZnHCO ₃ ⁺ ] (10)
[H ⁺ ] +2 [Zn ²⁺ ] + [Zn (OH) ⁺ ] + [ZnHCO ₃ ⁺ ] = [OH ⁻ ] + [HCO ₃ ⁻ ] +2 [CO ₃ ²⁻ ] (11)
FIG. 3 shows the results of determining the relationship between the total zinc concentration [Zn] _T and pH using the equations (1) to (11). Based on FIG. 3, it can be seen that the pH increases as the concentration of zinc increases and the concentration increases. This zinc concentration is the saturated dissolution concentration of zinc, and the difference from the actual zinc concentration in the solution is the driving force, and the dissolution rate of zinc is expressed by the Nernst-Noyes-Whitney's equation, which represents the dissolution rate of solids of the following equation: Can do.

Here, c is the solute concentration (ppm), t is the dissolution time (h), A is the solute surface area (cm ² ), D is the diffusion coefficient (cm ² / h), c _s is the solute saturation concentration (ppm), V Is the amount of solution (cm ³ ), and δ is the thickness of the diffusion layer (cm).

The amount of solution V is determined by the size of the dissolution apparatus, and the solute surface area A is a value determined by the amount of solid material containing zinc charged in the apparatus. Similar to the saturated solute concentration c _s , the diffusion coefficient D is a value determined by the temperature and the type of solid substance. On the other hand, the diffusion layer thickness δ is the diffusion layer thickness of carbonated water formed on a solid material containing zinc, and has a property that the faster the relative speed of the solid material and carbonated water, the thinner.

  The inventors obtained this relationship by experiment and obtained the results shown in FIG. As can be seen from FIG. 4, when the flow rate of carbonated water is increased, the thickness of the diffusion layer formed on the surface of the solid substance containing zinc is rapidly reduced, and the rate of decrease is slow above a certain flow rate. The thickness of the diffusion layer formed on the surface of the solid material at a flow rate of 5500 cm / h is about 1/3 compared to the thickness of the diffusion layer formed on the surface of the solid material at a flow rate of 124 cm / h. Based on Formula (12), it turns out that the dissolution rate of the solid substance containing zinc is also tripled. If this is utilized, the operation of increasing the flow rate of carbonated water when the zinc concentration of carbonated water is low and decreasing the flow rate when the zinc concentration increases will be possible.

  The effect of suppressing the Co-60 adhesion by zinc occurs when the zinc concentration in the reactor water is 2 to 10 ppb. In order to obtain this effect, for example, a zinc concentration of feed water of about 0.2 ppb is required in a BWR plant of the 1.1 million kW class. Since the feed water flow rate supplied to the reactor pressure vessel is about 6400 t / h, the injection rate of zinc into the feed water is 1.3 g / h. When one operation cycle is set to one year, the amount of zinc used in this operation cycle is 11.4 kg, and when zinc is supplied by zinc oxide, the amount of zinc oxide required is 14.2 kg. If the zinc oxide in the zinc dissolution unit is filled in the zinc dissolution tank during the periodic inspection of the nuclear power plant, the raw material zinc oxide is supplied into the dissolution tank during operation of the nuclear power plant. do not have to.

  Examples of the present invention reflecting the above-described examination results will be described below.

  A zinc injection method according to embodiment 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS. The zinc injection method of the present embodiment is applied to a boiling water nuclear plant (hereinafter referred to as a BWR plant).

First, a schematic configuration of this BWR plant to which the zinc injection method of the present embodiment is applied will be described with reference to FIG. The BWR plant includes a nuclear reactor 26, a turbine 34, a condenser 35, a recirculation system, a nuclear reactor purification system, a water supply system, and the like. The nuclear reactor 26 installed in the nuclear reactor containment vessel 32 has a nuclear reactor pressure vessel (hereinafter referred to as RPV) 27 containing a core 28, and a jet pump 29 is installed in the RPV 27. The core 28 is loaded with a plurality of fuel assemblies (not shown). Each fuel assembly includes a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel material. The recirculation system includes a recirculation pump 30 and a stainless steel recirculation pipe 31, and the recirculation pump 30 is installed in the recirculation pipe 31. The water supply system is connected to a water supply pipe 36 connecting the condenser 35 and the RPV 27, from the condenser 35 to the RPV 27, a condensate pump 37, a condensate purification device 38, a low pressure feed water heater 40, a feed water pump 39, and a high pressure. The feed water heater 41 is installed in this order. A hydrogen injection device 49 is connected to the water supply pipe 36 between the condenser 35 and the condensate pump 37. Reactor water cleanup system is installed in a clean system pipe 43 to contact the recirculation pipe 31 and the water supply pipe 36, cleaning system pump 45, the regenerative heat exchanger 46, a non-regenerative heat exchanger 47及BiKiyoshi apparatus 48 Configured. The purification system pipe 43 is connected to the recirculation system pipe 31 upstream from the recirculation pump 30.

  Cooling water (hereinafter referred to as “reactor water”) in the RPV 27 is pressurized by the recirculation pump 30, passes through the recirculation system pipe 31, and from the nozzle (not shown) of the jet pump 29 to the bell mouth (not shown) of the jet pump 29. ) The reactor water present around the nozzle is also sucked into the bell mouth by the action of the jet flow jetted from the nozzle. Reactor water discharged from the jet pump 29 is supplied to the core 28 and heated by heat generated by fission of nuclear fuel material in the fuel rods. Part of the heated reactor water becomes steam. The steam is guided from the RPV 27 through the main steam pipe 33 to the turbine 34 to rotate the turbine 34. A generator (not shown) connected to the turbine 34 is rotated to generate electric power. The steam discharged from the turbine 34 is condensed by the condenser 35 to become water.

This water is supplied into the RPV 27 through the water supply pipe 36 as water supply. The feed water flowing through the feed water pipe 36 is boosted by a condensate pump 37, impurities are removed by a condensate purification device 38, further boosted by a feed water pump 39, and heated by a low pressure feed water heater 40 and a high pressure feed water heater 41. . Extracted steam extracted from the main steam pipe 33 and the turbine 34 by the extracted pipe 42 is supplied to the low-pressure feed water heater 40 and the high-pressure feed water heater 41, respectively, and serves as a heating source for the feed water.

  The water brought into the reactor core as the feed water is irradiated with radiation generated as a result of nuclear fission of the nuclear fuel material and undergoes radiolysis to produce oxidizing species such as hydrogen peroxide and oxygen. This oxidizing chemical species raises the corrosion potential of the components in contact with the reactor water. Therefore, as an environmental mitigation measure against stress corrosion cracking, hydrogen is injected into the feed water from the hydrogen injection device 49, and this hydrogen and an oxidizing agent are reacted to reduce the oxidizing agent concentration and lower the corrosion potential. Yes. The operation performed while injecting hydrogen into this water supply is called hydrogen injection water quality operation (HWC: Hydrogen Water Chemistry), and the conventional operation without hydrogen injection is called normal water quality operation (NWC: Normal Water Chemistry). Although it is desirable to continue the operation for decreasing the corrosion potential by hydrogen injection during the operation, it may be interrupted, and at this time, the corrosion potential becomes high.

  A part of the reactor water flowing in the recirculation system pipe 31 flows into the purification system pipe 43 by the drive of the purification system pump 45 and is purified by the purification device 48. The purified reactor water is returned to the RPV 27 through the purification system pipe 43 and the water supply pipe 36.

  The BWR plant is stopped after the operation in one operation cycle is completed. After this shutdown, a periodic inspection is performed on the BWR plant. After this periodic inspection is completed, the BWR plant is started again. During this periodical inspection, some fuel assemblies in the core 28 are replaced with new fuel assemblies. That is, a part of the fuel assembly in the core 28 is taken out from the RPV 27 as a spent fuel assembly, and a new fuel assembly having zero burnup is loaded into the core 28.

  The zinc injection device 1 used in the zinc injection method of the present embodiment is connected to the feed water pipe 36 between the condensate purification device 38 and the low-pressure feed water heater 40 via the zinc injection pipe 21. Details of the zinc injection device 1 will be described with reference to FIG. The zinc injection apparatus 1 includes a zinc dissolution tank (second dissolution tank) 2 that forms a zinc dissolution area therein, a carbon dioxide dissolution tank (first dissolution tank) 4 that forms a carbon dioxide dissolution area therein, and a carbon dioxide supply It has a device 13. The other end of the pipe 7 whose one end is connected to the bottom of the carbon dioxide dissolution tank 4 is connected to the bottom of the zinc dissolution tank 2. One end of the pipe 8 is connected to the top of the zinc dissolution tank 2, and the other end of the pipe 8 is connected to the top of the carbon dioxide gas dissolution tank 4. A closed loop is formed by the carbon dioxide gas dissolution tank 4, the pipe 7, the zinc dissolution tank 2 and the pipe 8. A circulation pump 6 and a flow meter 12 are provided in the pipe 7. A water level meter 10 and a conductivity meter 11 are provided in the carbon dioxide gas dissolution tank 4.

  The zinc dissolution tank 2 is filled with a granular solid containing zinc. The granular solid is set to a size that does not easily flow due to the flow of the carbonic acid aqueous solution 24 pressurized by the circulation pump 6. Examples of such a solid include a cylindrical sintered body of zinc oxide (diameter 1 cm, height 1 cm) or metal zinc sphere (diameter 1 cm).

Carbon dioxide supply apparatus 13 includes a diffuser tube 5, carbon dioxide supply piping 15 and the carbon dioxide cylinder 14. The air diffuser 5 is formed with a large number of ejection holes and is arranged at the bottom in the carbon dioxide dissolution tank 4. Carbon dioxide supply piping 15 is connected to the diffuser tube 5 and the carbon dioxide cylinder 14. Valve 16 is provided in the carbon dioxide gas supply piping 15.

  The zinc injection pipe 21 is connected to the pipe 7 upstream of the circulation pump 6 and further connected to the water supply pipe 36. An injection pump 20 and a flow meter 22 are provided in the zinc injection pipe 21. The control device 23 is connected to the water level meter 10, the conductivity meter 11, and the flow meters 12 and 22 by signal lines.

  The zinc injection method of the present embodiment using the zinc injection device 1 will be specifically described below.

The pump 18 is driven based on a control command output from the control device 23, and makeup water is supplied from the makeup water source 17 to the carbon dioxide gas dissolution tank 4 through the makeup water pipe 19. The water level signal measured by the water level gauge 10 is input to the control device 23. When the control device 23 determines that the carbon dioxide gas dissolution tank 4 is full based on the water level signal from the water level gauge 10, the control device 23 stops driving the pump 18 and supplies the makeup water to the carbon dioxide gas dissolution tank 4. Is stopped.

  After the carbon dioxide gas dissolution tank 4 is full, the control device 23 opens the valve 16. Carbon dioxide gas in the carbon dioxide cylinder 14 is supplied to the diffuser pipe 5 through the carbon dioxide supply pipe 15 and is released from the diffuser pipe 5 into the water of the carbon dioxide dissolution tank 4. The released carbon dioxide is dissolved in the water in the carbon dioxide dissolution tank 4. The carbon dioxide gas not dissolved in the water rises in the carbon dioxide dissolution tank 4 and is discharged from the carbon dioxide dissolution tank 4 to the vent pipe 9.

The carbon dioxide gas supplied to the carbon dioxide gas dissolution tank 4 is dissolved in water from the interface with water by the reaction of the formula (1), and becomes CO ₂ (aq). Subsequently, the equilibrium reactions of the formulas (2) and (3) occur, and hydrogen carbonate ions (HCO ₃ ⁻ ) and carbonate ions (CO ₃ ²⁻ ) are generated. The pressure of the carbon dioxide dissolution tank 4 is atmospheric pressure (101.3 kPa), and the vapor phase portion contains 8.44 kPa of saturated water vapor at 25 ° C. in addition to carbon dioxide. The pH of the carbon dioxide dissolved water is calculated using the relationship between the equilibrium constants of equations (1) to (3) and equation (4). When the dissolution of carbon dioxide into water reaches equilibrium, the carbon dioxide dissolution tank 4 The pH of the aqueous carbonate solution 24 becomes 3.91.

  As the pH of the aqueous carbonate solution 24 in the carbon dioxide dissolution tank 4 decreases, the conductivity of the aqueous carbonate solution 24 increases. When this pH approaches pH 3.91 of saturated carbonated water, the increase in the conductivity of the aqueous carbonate solution 24 in the carbon dioxide gas dissolution tank 4 is saturated. The saturation of the increase in conductivity is determined, for example, when the conductivity of the carbonic acid aqueous solution 24 generated in the carbon dioxide dissolution tank 4 does not show an increasing tendency for 10 minutes or more.

The conductivity meter 11 measures the conductivity of the carbonic acid aqueous solution 24 in the carbon dioxide gas dissolution tank 4. When the controller 23 inputs the conductivity measured by the conductivity meter 11 and determines that the increase in the conductivity of the carbonic acid aqueous solution 24 in the carbon dioxide dissolution tank 4 is saturated based on the input conductivity, the controller 23 circulates. A drive start signal is output to the pump 6. Thereby, the circulation pump 6 is driven, and the aqueous carbonic acid solution 24 in the carbon dioxide dissolution tank 4 is supplied to the zinc dissolution tank 2 through the pipe 7.

  More than the amount consumed in one operation cycle of the BWR plant, for example, 30 kg or more of zinc oxide pellets (solid substance containing zinc) 3 is filled in the zinc dissolution tank 2 in advance. Instead of zinc oxide, any of zinc carbonate, basic zinc carbonate, and metallic zinc can be used. The zinc oxide pellet 3 is set to a size that does not float at the flow rate of the aqueous carbonate solution 24 rising in the zinc dissolution tank 2. For this reason, the magnitude | size of the zinc oxide pellet 3 shall be 5 mm or more in particle size, for example. This is because, when the zinc oxide previously filled in the zinc dissolution tank 2 is a fine powder, the zinc oxide rides on the flow of the aqueous carbonic acid solution 24 and remains in a state of not being dissolved. It is injected into the water supply pipe 36 through the pipe 21. For this reason, there is a possibility that the zinc injection pipe 21 may be clogged by zinc oxide that does not dissolve, and it is not preferable for managing the zinc concentration of the reactor water in the RPV 27.

  The aqueous carbonic acid solution 24 supplied from the carbon dioxide gas dissolution tank 4 into the zinc dissolution tank 2 rises in contact with the zinc oxide pellets 3 among the many zinc oxide pellets 3 filled in the zinc dissolution tank 2. . The rising low pH carbonic acid aqueous solution 24 dissolves the zinc oxide pellets 3, and the zinc contained in the zinc oxide pellets 3 is ionized and eluted into the carbonic acid aqueous solution 24. The dissolution reaction of the zinc oxide pellet 3 at this time is represented by the formula (13).

ZnO + H ⁺ + H ₂ O = Zn ²⁺ + 2OH ⁻ (13)
As a result, an aqueous carbonate solution containing zinc ions (injected water containing zinc ions) 24 is generated in the zinc dissolution tank 2 . In the aqueous carbonate solution containing zinc ions, the equilibrium relations of the equations (4) to (9) are established, and the equation (10) that is a charge balance equation and the equation (11) that is a mass balance equation of zinc are established. By using the relational expressions of Expression (1) to Expression (11), the relationship between the total zinc concentration [Zn] _T of the aqueous carbonate solution and the pH of the aqueous carbonate solution as shown in FIG. 3 is obtained.

  As shown in FIG. 3, the elution of zinc in the zinc dissolution tank 2 causes the pH of the aqueous carbonate solution 24 in the zinc dissolution tank 2 to change to the neutral side, and the degree of zinc elution into the aqueous carbonate solution 24 is suppressed. . The aqueous carbonate solution 24 containing zinc ions is discharged from the top of the zinc dissolution tank 2 to the pipe 8 and supplied to the carbon dioxide dissolution tank 4 through the pipe 8. The carbonic acid aqueous solution 24 containing zinc ions supplied to the carbon dioxide dissolving tank 4 is mixed with the carbonic acid aqueous solution 24 in the carbon dioxide dissolving tank 4, pressurized by the circulation pump 6, and introduced into the zinc dissolving tank 2 through the pipe 7. . The aqueous carbonate solution 24 containing zinc ions comes into contact with the zinc oxide pellets 3 in the zinc dissolution tank 2, and the zinc contained in the zinc oxide pellets 3 is ionized and eluted into the aqueous carbonate solution 24 as described above. For this reason, the density | concentration of the zinc ion of the carbonic acid aqueous solution 24 containing a zinc ion increases.

  The aqueous carbonate solution 24 containing zinc ions in the zinc dissolution tank 2 circulates in a closed loop formed by the carbon dioxide dissolution tank 4, the pipe 7, the zinc dissolution tank 2 and the pipe 8. The circulation of the aqueous carbonate solution 24 containing zinc ions increases the zinc ion concentration of the aqueous carbonate solution 24 each time the aqueous carbonate solution 24 passes through the zinc dissolution tank 2 filled with the zinc oxide pellets 3. The concentration of zinc ions in the aqueous carbonic acid solution 24 circulating in the closed loop will eventually reach a saturation concentration. By circulating the carbonic acid aqueous solution 24 in the closed loop including the zinc dissolution tank 2 filled with the zinc oxide pellets 3, the carbonic acid aqueous solution 24 in which the concentration of zinc ions is increased to near the saturation concentration can be easily obtained.

  The inventors examined the dissolution rate of zinc dissolved in the aqueous carbonate solution 24 from the zinc oxide pellet 3 at this time using a test apparatus having the configuration shown in FIG. This test apparatus is a miniaturized version of the zinc injection apparatus 1 shown in FIG. The amount of water used is 10 liters, and 770 g of zinc oxide pellets filled in the zinc dissolution tank. Further, in this test apparatus, the makeup water pipe 19 provided with the pump 18 and the zinc injection pipe 21 provided with the injection pump 20 provided in the zinc injection apparatus 1 are removed.

The temperature of the water in the carbon dioxide dissolution tank was set to 30 ° C., and carbon dioxide was bubbled into the water from the diffuser tube to generate an aqueous carbonate solution in the carbon dioxide dissolution tank. When the increase in the conductivity of the aqueous carbonate solution was saturated, the circulation pump was driven to supply the aqueous carbonate solution in the carbon dioxide dissolution tank to the zinc dissolution tank filled with zinc oxide pellets. FIG. 5 shows the relationship between the supply time of the aqueous carbonate solution to the zinc dissolution tank at this time and the zinc concentration of the aqueous carbonate solution. Based on the characteristics of FIG. 5, the zinc concentration of the aqueous carbonate solution in the zinc dissolution vessel has reached the saturation concentration when about 20 hours have elapsed since the start of the supply of the aqueous carbonate solution to the zinc dissolution vessel. I understand. Based on the rhombus plot (experimental value) and the equation (12) shown in FIG. 5, the diffusion rate coefficient D of the dissolved zinc, the thickness of the diffusion layer δ formed on the surface of the zinc oxide pellet, the saturation solubility c of zinc _s was obtained by fitting, and the change over time in the zinc concentration calculated using these values was shown by a solid line in FIG.

  A similar experiment was performed by changing the flow rate of the aqueous carbonate solution, and the relationship between the obtained thickness δ of the diffusion layer and the flow rate of the aqueous carbonate solution was determined. As a result, when the flow rate of the aqueous carbonate solution changed, the thickness δ of the diffusion layer changed as shown in FIG. According to FIG. 4, it can be seen that the diffusion layer thickness δ decreases as the flow rate of the aqueous carbonate solution increases, and the dissolution rate of zinc increases as the diffusion layer thickness δ decreases from equation (12). For example, the thickness of the diffusion layer when the flow rate is 124 cm / h is about 0.13 cm, which is about three times as large as the diffusion layer thickness of 0.034 cm when the flow rate of the aqueous carbonate solution is 5500 cm / h. As a result, the dissolution rate of zinc when the flow rate of the aqueous carbonate solution is 124 cm / h is reduced to 1/3 of the dissolution rate of zinc when the flow rate of the aqueous carbonate solution is 5500 cm / h. Therefore, the faster the flow rate of the aqueous carbonate solution in contact with the zinc oxide pellets, the faster the zinc concentration of the aqueous carbonate solution reaches the saturation solubility. When the zinc concentration reaches near the saturation solubility, it is desirable to reduce the load of the circulation pump 6 by lowering the rotational speed of the circulation pump 6 to reduce the flow rate of the aqueous carbonate solution in the zinc dissolution tank.

  The zinc injection method of the present embodiment using the zinc injection device 1 will be further described using the characteristics shown in FIGS. When the total amount of the carbonic acid aqueous solution 24 circulating in the closed loop of the zinc injection device 1 is 200 kg and the linear flow rate of the carbonic acid aqueous solution 24 is 5500 cm / h, the zinc concentration of the carbonic acid aqueous solution 24 is 350 ppm close to the saturation solubility in about 10 hours. To reach. Therefore, when the control device 23 determines that the carbonic acid concentration of the carbonic acid aqueous solution 24 bubbling carbon dioxide gas has reached the carbonic acid saturation concentration based on the conductivity measured by the conductivity meter 11, the zinc dissolution tank 2 is used. The circulation pump 6 is driven so that the linear flow rate of the aqueous carbonate solution 24 becomes 5500 cm / h.

  FIG. 6 shows the characteristics obtained by experiments by the inventors and showing the relationship between the zinc concentration in the carbonated aqueous solution 24 saturated with carbonic acid and the conductivity of the carbonated aqueous solution 24. This characteristic shown in FIG. 6 is stored in advance in a memory (not shown) of the control device 23. The control device 23 obtains the zinc concentration of the aqueous carbonate solution 24 using the conductivity of the aqueous carbonate solution 24 measured by the conductivity meter 11, and when the zinc concentration reaches, for example, 350 ppm, the rotational speed of the circulation pump 6 is determined. The flow rate of the aqueous carbonate solution 24 flowing through the zinc dissolution tank 2 is controlled to be lowered to, for example, 124 cm / h. In the initial stage of zinc dissolution in the zinc dissolution tank 2, it is preferable to dissolve zinc in the aqueous carbonate solution 24 earlier because zinc can be injected into the RPV 27 earlier. However, once the zinc concentration of the aqueous carbonic acid solution 24 reaches the saturation solubility, it is desirable to reduce the linear flow rate to lower the zinc dissolution rate and save the driving power of the circulation pump 6.

  When it is determined that the zinc concentration of the aqueous carbonate solution 24 has reached 350 ppm, the control device 23 outputs an activation signal for the infusion pump 20. The infusion pump 20 is activated by this activation signal. When the injection pump 20 is started, the carbonic acid aqueous solution 24 having a zinc concentration of 350 ppm discharged from the carbon dioxide dissolution tank 4 is injected into the water supply pipe 36 through the zinc injection pipe 21. The carbonic acid aqueous solution 24 having a zinc concentration of 350 ppm is mixed into the feed water flowing through the feed water pipe 36. Further, the control device 23 determines that the zinc concentration of the feed water supplied to the RPV 27 based on the zinc concentration of the carbonated aqueous solution 24 to be injected and the flow rate (feed water flow rate) of the feed water flowing in the feed water pipe 36 is a predetermined value, for example, 0.2 ppb. The injection amount of the carbonic acid aqueous solution 24 into the water supply pipe 36 is controlled so as to be (set zinc concentration). Since the feed water flow rate is 6400 t / h in the BWR plant of 1.1 million kW, the control device 23 injects the carbonate aqueous solution 24 having a zinc concentration of 350 ppm based on the zinc concentration of the carbonate aqueous solution 24 to be injected, the feed water flow rate, and the set zinc concentration. The amount is calculated as 3.5 kg / h, and the rotation speed of the injection pump 20 is controlled so that the injection amount of the aqueous carbonate solution 24 becomes this value. In the carbonic acid aqueous solution 24, zinc is ionic.

The aqueous carbonate solution 24 containing zinc ions injected into the water supply pipe 36 is mixed with the water supply in the water supply pipe 36, and the water supply containing the zinc ions is supplied to the RPV 27. Zinc ions contained in the feed water are mixed into the reactor water in the RPV 27. Reactor water containing zinc ions circulates in the RPV 27 and flows in pipes connected to the RPV 27 (for example, the recirculation system pipe 31 and the purification system pipe 43). If the carbonic acid aqueous solution 24 containing zinc ions is continuously injected into the water supply pipe 36, the water level in the carbon dioxide gas dissolution tank 4 is lowered. For this reason, water is replenished from the makeup water source 17 into the carbon dioxide gas dissolution tank 4. For example, the control device 23 that has input the water level of the carbon dioxide gas dissolution tank 4 measured by the water level gauge 10 determines that the water level of the carbon dioxide gas dissolution tank 4 is based on this water level out of the retained water amount 200 kg of the carbon dioxide gas dissolution tank 4. When it is determined that the water level has been lowered to the lower limit set water level of the carbon dioxide gas dissolution tank 4 in a state where 10% is injected into the water supply pipe 36, an activation signal of the pump 18 is output. The pump 18 is activated, and the water from the makeup water source 17 is supplied to the carbon dioxide dissolution tank 4 through the makeup water pipe 19. When the control device 23 determines that the water level measured by the water level gauge 10 has reached the upper limit set water level indicating a full water state by supplying makeup water, it outputs a stop signal for the pump 18 . At this time, the drive of the pump 18 is stopped.

By supplying makeup water to the carbon dioxide dissolution tank 4, the zinc concentration of the aqueous carbonate solution 24 in the carbon dioxide dissolution tank 4 is lowered, and the conductivity of the aqueous carbonate solution 24 is also lowered. The control device 23 determines that the zinc concentration of the aqueous carbonic acid solution 24 in the carbon dioxide dissolution tank 4 obtained based on the conductivity measured by the conductivity meter 11 is lower than the saturation concentration of zinc, for example, 280 ppm, which is a 20% decrease. When it is determined that the rotation has occurred, the rotational speed of the circulation pump 6 is increased. The linear flow rate of the aqueous carbonate solution 24 rising in the zinc dissolution tank 2 is increased to 5500 cm / h, and the time required for the zinc ion concentration of the aqueous carbonate solution 24 to reach the saturated zinc concentration is shortened. In a period in which the zinc concentration of the aqueous carbonate solution 24 is lower than the saturation concentration of zinc, the controller 23 controls the driving of the injection pump 20 so that the zinc concentration of the aqueous carbonate solution 24 injected into the feed water can be maintained at 0.2 ppb. This can be dealt with by increasing the injection rate and increasing the injection amount of the aqueous carbonate solution 24. For example, when the zinc concentration of the aqueous carbonate solution 24 is 280 ppm, the control device 23 calculates the injection amount of the aqueous carbonate solution 24 to the water supply pipe 36 as 4.6 kg / h, and the injection amount of the aqueous carbonate solution 24 is this value. The drive of the infusion pump 20 is controlled so that

The flow rate of the aqueous carbonate solution 24 supplied to the zinc dissolution tank 2 measured by the flow meter 12 is input to the control device 23. Control unit 23, corresponding to the saturation concentration of zinc carbonate aqueous solution 24 stores a flow rate (set flow rate) of the carbonate aqueous solution 24 to be supplied to the zinc dissolving tank 2, based on the flow rate inputted from the flow meter 12 Then, it is confirmed whether the flow rate of the aqueous carbonate solution 24 supplied to the zinc dissolution tank 2 has reached the set flow rate. Further, the flow rate measured by the flow meter 22 is also input to the control device 23. The control device 23 adjusts the rotation speed of the injection pump 20 based on the flow rate input from the flow meter 22 and the zinc concentration of the aqueous carbonate solution 24 determined using the conductivity measured by the conductivity meter 11, and the water supply pipe The injection amount of the carbonic acid aqueous solution containing zinc injected into 36 is controlled.

  As described above, in this embodiment, the carbon dioxide gas is dissolved in the carbon dioxide dissolution tank 4, the zinc is dissolved by the carbon dioxide solution 24 in the zinc dissolution tank 2, and the carbon dioxide dissolution tank of the carbon dioxide solution 24 in which zinc ions are dissolved. 4 and by recirculation to the zinc dissolution tank 2, a zinc carbonate aqueous solution 24 having a zinc concentration close to the saturation concentration of zinc is prepared, this zinc-containing carbonate aqueous solution is injected into the feed water, and the amount of water reduced by this injection is reduced. The supply of water containing zinc ions is supplied to the RPV 27 by repeating the operation of the zinc injection device 1 for supplying water to the carbon dioxide dissolution tank 4 to make up for it in one operation cycle of the BWR plant.

  In this embodiment, the aqueous carbonate solution 24 containing 350 ppm of zinc ions is injected into the feed water at 3.5 kg / h, which corresponds to a supply rate of 1.2 g / h of zinc ions. Assuming that one operation cycle is 10,000 h, the consumption amount of the solid substance containing zinc is 12 kg for zinc and 15 kg for zinc oxide. In this embodiment, 30 kg of zinc oxide pellets 3 are supplied to the zinc dissolution tank 2 during the periodic inspection before the start of the BWR plant, so there is no need to replenish zinc ion raw materials during plant operation, It is possible to operate the zinc injection device 1 continuously.

  In this embodiment, the aqueous carbonate solution 24 containing zinc ions generated as described above in the zinc injection device 1 is injected into the water supply pipe 36, and the supply water containing zinc ions is supplied to the reactor water in the RPV 27. It is possible to reduce the amount of radioactive cobalt attached to the inner surfaces of the piping through which the reactor water flows, such as the system piping 31 and the purification system piping 43. For this reason, the radiation exposure of the worker at the time of the work of the periodic inspection can be reduced.

  According to the present embodiment, the carbonic acid aqueous solution 24 in the carbon dioxide dissolution tank 4 is circulated in the closed loop including the zinc dissolution tank 2 filled with the zinc oxide pellets 3 and the carbon dioxide dissolution tank 4, so that the RPV 27 containing zinc ions is contained. The zinc ion concentration of the carbonic acid aqueous solution (injected water) 24 injected into the can be increased. For this reason, the zinc ion concentration of the reactor water in the RPV 27 can be increased in a shorter time.

In this embodiment, since the flow rate of the carbonic acid aqueous solution 24 supplied from the carbon dioxide dissolving tank 4 to the zinc dissolving tank 2 through the pipe 7 can be adjusted, the zinc ion concentration of the carbonic acid aqueous solution 24 is increased to the set zinc ion concentration. The time required can be shortened. Moreover, after the zinc ion concentration of the carbonic acid aqueous solution 24 increases to the set zinc ion concentration, the flow rate of the carbonic acid aqueous solution 24 in the zinc dissolution tank 2 can be adjusted to be slow. As a result, the load on the circulation pump 6 that supplies the aqueous carbonate solution 24 from the carbon dioxide dissolution tank 4 to the zinc dissolution tank 2 can be reduced, and the power consumed by the circulation pump 6 can be reduced.

  In the present embodiment, the dissolution of carbon dioxide and the dissolution of zinc are performed in separate dissolution tanks, that is, the carbon dioxide aqueous solution 24 is generated by the dissolution of carbon dioxide in the carbon dioxide dissolution tank 4, and this is dissolved in the zinc dissolution tank 2. Since zinc is dissolved using the carbonic acid aqueous solution 24, the carbonic acid concentration of the carbonic acid aqueous solution 24 generated by dissolving carbon dioxide gas can be easily adjusted, and the carbonic acid aqueous solution 24 containing a predetermined concentration of zinc ions can be easily generated. Can be done.

  In this embodiment, since the conductivity meter 11 is installed in the carbon dioxide gas dissolution tank 4, the carbon dioxide concentration of the aqueous carbonic acid solution 24 generated in the carbon dioxide gas dissolution tank 4 based on the measured conductivity value of the conductivity meter 11. Can be easily confirmed. The aqueous carbonic acid solution 24 having a set carbonic acid concentration can be supplied to the zinc dissolution tank 2 filled with the zinc oxide pellets 3, and the zinc can be efficiently dissolved in the zinc dissolution tank 2. In this embodiment, since the zinc ion concentration of the aqueous carbonate solution 24 is obtained based on the measured conductivity value of the conductivity meter 11, the zinc ion concentration of the aqueous carbonate solution 24 can be obtained with high accuracy. For this reason, the zinc ion concentration injected into the reactor water in the RPV 27 can be adjusted to a predetermined concentration. The measured value of the conductivity meter 11 can be used to calculate the carbonic acid concentration and the zinc concentration of the aqueous carbonic acid solution 24.

  While the carbonated water solution 24 containing a predetermined concentration of zinc ions is poured into the feed water, makeup water is supplied to the carbon dioxide gas dissolution tank 4 and the carbonated water solution 24 is supplied to the zinc dissolution tank 2. Water can be continuously poured into the water supply.

  In the present embodiment, injection of carbon dioxide into the carbon dioxide dissolution tank 4, determination of stoppage, determination of the zinc concentration of the aqueous carbonate solution, adjustment of the flow rate of the aqueous carbonate solution 24 supplied to the zinc dissolution tank 2, and the water supply pipe 36 The control device 23 controls the injection amount of the aqueous carbonate solution 24 containing zinc ions, the supply and stop of the makeup water, and the valve 16. However, some or all of these control operations are performed by the operator. Can also be done. However, it is desirable to use the control device 23 as much as possible from the viewpoint of reducing the burden on the operator.

  The zinc injection device 1 is connected to the purification system pipe 43 downstream of the purification device 48 instead of the water supply pipe 36, and the aqueous carbonate solution 24 containing zinc ions generated by the zinc injection device 1 is purified downstream of the purification device 48. You may inject | pour into the piping 43. FIG. The aqueous carbonate solution 24 containing zinc ions injected into the purification system pipe 43 downstream of the purification device 48 is supplied into the RPV 27 through the water supply pipe 36.

  A zinc injection method according to embodiment 2, which is another preferred embodiment of the present invention, will be described with reference to FIG. The zinc injection method of the present embodiment is applied to a boiling water nuclear plant (hereinafter referred to as a BWR plant).

A zinc injection apparatus 1A used in the zinc injection method of this embodiment will be described with reference to FIG. The zinc injection apparatus 1A essentially has a dissolution tank 25 in which the zinc dissolution tank 2 and the carbon dioxide gas dissolution tank 4 are integrated in the zinc injection apparatus 1 used in the first embodiment. One end of the pipe 7 provided with the circulation pump 6 and the flow meter 12 is connected to the bottom of the dissolution tank 25, and the other end of the pipe 7 is connected to the top of the dissolution tank 25. The dissolution tank 25 has a configuration in which the zinc dissolution tank 2 and the carbon dioxide dissolution tank 4 are integrated. The dissolution tank 25 is filled with the zinc oxide pellets 3 and below the zinc dissolution area 52. A positioned solution storage area 50 is formed. The other end of the pipe 7 is connected to the dissolution tank 25 above the zinc dissolution region 52. The makeup water pipe 19 is connected to the dissolution tank 25 above the zinc dissolution region 52. A pressure gauge 51 is connected to the dissolution tank 25 by a pipe provided with an exhaust valve (not shown). A carbon dioxide supply device 13 </ b> A installed in place of the carbon dioxide supply device 13 does not have the diffuser pipe 5 but has a carbon dioxide supply pipe 15 and a carbon dioxide cylinder 14. Other configurations of the zinc injection device 1A are the same as those of the zinc injection device 1 described above. The solution storage area 50 corresponds to the carbon dioxide dissolution tank 4 in the first embodiment, and the zinc dissolution area 52 corresponds to the zinc dissolution tank 2 in the first embodiment. The carbon dioxide gas supply pipe 15 is connected to the dissolution tank 25 and communicates with a space formed between the solution storage area 50 and the zinc dissolution area 52 in the dissolution tank 25.

  The zinc injection method of the present embodiment using the zinc injection device 1A will be described below. The control device 23A outputs an opening signal of the valve 16. The valve 16 is opened by the output of the open signal, and the carbon dioxide in the carbon dioxide cylinder 14 is injected into the dissolution tank 25 through the carbon dioxide supply pipe 15. This carbon dioxide gas is also filled between the zinc oxide pellets 3 in the zinc dissolution region 52 in the dissolution tank 25. After the carbon dioxide gas is filled into the dissolution tank 25, the exhaust valve is closed by a close signal output from the control device 23A. When the pressure in the dissolution tank 25 measured by the pressure gauge 51 becomes a value higher than the set atmospheric pressure, for example, 1.5 atmospheric pressure, the control device 23A closes the valve 16 by outputting a closing signal. Since water does not exist in the solution storage region 50 when the valve 16 is closed, the injected 1.5 atmospheric pressure carbon dioxide gas exists in the entire dissolution tank 25 including the solution storage region 50 and the zinc dissolution region 52. .

After the valve 16 is closed, the control device 23 </ b> A outputs an activation signal to the pump 18. The pump 18 is driven, and water is supplied from the make-up water source 17 into the dissolution tank 25 through the make-up water pipe 19. The water supplied from the make-up water pipe 19 is sprayed in a shower shape toward the zinc dissolving region 52 from an injection nozzle (not shown) provided at the top in the dissolution tank 25 and connected to the make-up water pipe 19. The The sprayed water is poured onto the zinc oxide pellets 3 in the zinc dissolution region 52 and forms a water film on the surface of each zinc oxide pellet 3 present at the upper end of the zinc dissolution region 52. The carbon dioxide gas previously filled in the dissolution tank 25 is dissolved in the water film formed on the surface of the zinc oxide pellets 3, and the pH of each water film is lowered. The surface of the zinc oxide pellet 3 begins to dissolve due to a decrease in the pH of the water film. Since water is continuously sprayed from the spray nozzle, this water film dissolves the carbon dioxide in the gas phase and zinc contained in the zinc oxide pellets 3, while passing through the surface of each zinc oxide pellet 3. It flows down toward the lower end of the dissolution region 52. Eventually, the water film in which carbon dioxide gas and zinc are dissolved becomes a carbonic acid aqueous solution 24 containing zinc ions, and falls from the zinc dissolution region 52 to the solution storage region 50. Since the circulation pump and the injection pump 20 are not driven, the carbonated aqueous solution 24 containing the dropped zinc ions is stored in the solution storage region 50.

  When the water level in the solution storage region 50 measured by the water level meter 10 is input to the control device 23A, and the control device 23A determines that the measured water level has reached the upper limit set water level in the solution storage region 50, The control device 23 </ b> A stops the pump 18 and stops the supply of water from the makeup water pipe 19 to the dissolution tank 25. When the solution storage region 50 becomes full, a space is formed between the liquid surface of the aqueous carbonate solution 24 containing zinc ions and the lower end of the zinc dissolution region 52 formed in the solution storage region 50.

  When the level of the aqueous carbonate solution 24 containing zinc ions in the dissolution tank 25 reaches the upper limit set water level, the control device 23 activates the circulation pump 6. The aqueous carbonate solution 24 containing zinc ions in the solution storage region 50 is pressurized by the activation of the circulation pump 6, and is guided to the injection nozzle at the top of the dissolution tank 25 through the pipe 7. Carbonic acid aqueous solution 24 containing zinc ions is sprayed in a shower shape from the spray nozzle toward each zinc oxide pellet 3 located at the upper end of the zinc dissolution region 52. While the carbonated aqueous solution 24 containing the injected zinc ions descends along the surface of each zinc oxide pellet 3 in the zinc dissolution region 52, the carbon dioxide gas existing in the gas phase portion of the zinc dissolution region 52 is dissolved and oxidized. Zinc contained in the zinc pellet 3 is dissolved. The carbonic acid aqueous solution 24 containing zinc ions descending along the surface of each zinc oxide pellet 3 while the respective concentrations of carbonic acid and zinc are increased falls from the zinc dissolution region 52 toward the solution storage region 50. The zinc concentration of the aqueous carbonate solution 24 containing zinc ions falling into the solution storage area 50 is higher than the zinc concentration of the aqueous carbonate solution 24 containing zinc ions ejected from the ejection nozzle.

  The aqueous carbonate solution 24 containing zinc ions in the solution storage region 50 flows by the circulation pump 6 so that the linear flow velocity in the pipe 7 is 5500 cm / h. For this reason, the descending speed of the carbonic acid aqueous solution 24 containing zinc ions ejected from the ejection nozzle and descending in the zinc dissolution region 52 along the surface of each zinc oxide pellet 3 is also increased. The dissolution rate of zinc in the carbonic acid aqueous solution 24 containing sucrose increases.

  The aqueous carbonate solution 24 containing zinc ions includes a solution storage area 50 in the dissolution tank 25, a pipe 7, a zinc dissolution area 52 in the dissolution tank 25, and a solution storage area 50 in the dissolution tank 25 by driving the circulation pump 6. Circulate in a closed loop. By continuing such circulation of the aqueous carbonate solution 24 containing zinc ions, the zinc concentration of the aqueous carbonate solution 24 containing zinc ions increases. When the circulation of the carbonic acid aqueous solution 24 is continued, the carbon dioxide gas in the dissolution tank 25 is dissolved in the carbonic acid aqueous solution 24 containing zinc ions as described above, so that the pressure in the dissolution tank 25 gradually decreases.

  The control device 23 opens the valve 16 when the input pressure measured by the pressure gauge 51 becomes, for example, 1.2 atmospheres. Carbon dioxide gas is supplied from the carbon dioxide cylinder 14 through the carbon dioxide supply pipe 15 into the dissolution tank 25, and the controller 23 opens the valve 16 so that the pressure in the dissolution tank 25 is maintained at 1.5 atm. To control.

  When the circulation of the aqueous carbonate solution 24 containing zinc in the closed loop is continuously performed, the zinc concentration of the aqueous carbonate solution 24 containing zinc existing in the solution storage region 50 increases, and the conductivity of the aqueous carbonate solution 24 is increased. Rises. The conductivity of the aqueous carbonate solution 24 is measured by the conductivity meter 11, and the measured conductivity is input to the control device 23. The control device 23 obtains the zinc concentration of the carbonic acid aqueous solution 24 in the solution storage region 50 using the input conductivity, and reduces the rotational speed of the circulation pump 6 when the zinc concentration reaches a saturation concentration, for example, 350 ppm. . Thereby, the flow rate of the aqueous carbonate solution 24 flowing in the pipe 7 is reduced to, for example, 124 cm / h, and the flow rate of the aqueous carbonate solution 24 containing zinc ions descending along the surface of the zinc oxide pellet 3 in the zinc dissolution region 52 is slow. Become. Accordingly, the dissolution rate of zinc from the zinc oxide pellet 3 into the aqueous carbonate solution 24 containing zinc ions decreases.

  Furthermore, when the zinc concentration of the aqueous carbonic acid solution 24 in the solution storage area 50 reaches 350 ppm, the control device 23 activates the infusion pump 20. The aqueous carbonate solution 24 in the solution storage area 50 having a zinc concentration of 350 ppm is pressurized by the injection pump 20 and injected into the feed water flowing through the feed water pipe 36 through the zinc injection pipe 21. Supply water containing zinc ions is supplied into the RPV 27 from the supply water pipe 36. Similarly to the first embodiment, the control device 23 calculates the injection amount of the carbonated aqueous solution 24 having a zinc concentration of 350 ppm into the feed pipe 36 based on the zinc concentration, the feed water flow rate and the set zinc concentration of the carbonated aqueous solution 24 to be injected, The rotation speed of the injection pump 20 is controlled so that the injection amount of the carbonic acid aqueous solution 24 becomes the calculated value.

  When the water level in the solution storage area 50 is lowered to the lower limit set water level due to the injection of the aqueous carbonate solution 24 containing zinc ions in the solution storage area 50 into the water supply pipe 36, the makeup water is supplied to the makeup water as in the first embodiment. By supplying into the dissolution tank 25 through the pipe 19, the water level in the solution storage area 50 is recovered to the upper limit set water level.

  This example can obtain the remaining effects except for the effect obtained by performing dissolution of carbon dioxide gas and dissolution of zinc in separate dissolution tanks among the effects produced in Example 1. In the description of each effect in the first embodiment, the carbon dioxide dissolution tank 4 corresponds to the solution storage area 50 in this embodiment, and the zinc dissolution tank 2 corresponds to the zinc dissolution area 52.

  In the present embodiment, since the zinc dissolution region 52 and the solution storage region 50 are arranged in the dissolution tank 25, the pipe 8 connecting the zinc dissolution tank 2 and the carbon dioxide gas dissolution tank 4 in the first embodiment is not necessary. Furthermore, in this embodiment, the inlet of the carbon dioxide gas into the dissolution tank 25 is in the gas phase, and the air diffuser 5 is not installed. In this embodiment, since carbon dioxide gas is not blown into water, the dissolution efficiency of carbon dioxide gas in water is lowered, but the zinc oxide pellets 3 filled in the zinc dissolution region 52 can be used as an alternative to rahisling, The gas-liquid contact area can be enlarged. For this reason, the fall of the melt | dissolution efficiency to the water of a carbon dioxide gas can be suppressed.

  A zinc injection method according to embodiment 3, which is another preferred embodiment of the present invention, will be described with reference to FIG. The zinc injection method of the present embodiment is applied to a boiling water nuclear plant (hereinafter referred to as a BWR plant).

  A zinc injection apparatus 1B used in the zinc injection method of this embodiment will be described with reference to FIG. In the zinc injection device 1B, the diffuser pipe 5 in the zinc injection device 1 used in the first embodiment is arranged in the bottom of the solution storage region 50 in the zinc injection device 1A used in the second embodiment. The carbon dioxide gas supply pipe 15 of the supply device 13A is connected. Other configurations of the zinc injection device 1B are the same as those of the zinc injection device 1A. The dissolution tank (third dissolution tank) 25 has a configuration in which the zinc dissolution tank 2 and the carbon dioxide dissolution tank 4 in Example 1 are integrated.

  In the present embodiment, as in the first embodiment, carbon dioxide is bubbled from the air diffuser 5 to the aqueous carbonate solution 24 to dissolve the carbon dioxide in the aqueous carbonate solution 24. In this embodiment, the carbon dioxide gas released from the air diffuser 5 is dissolved in the aqueous solution 24 in the solution storage area 50. The solution storage area 50 in the present embodiment is a carbon dioxide dissolution area where the carbon dioxide is dissolved in the aqueous carbonate solution 24. Each action produced by the zinc injection method of Example 2 also occurs in this example. In this embodiment, the carbon dioxide gas released from the air diffuser 5 and not completely dissolved in the aqueous carbonate solution 24 in the solution storage area 50 rises to above the liquid level in the solution storage area 50, It is dissolved in the aqueous carbonate solution 24 descending along the surface of the zinc oxide pellet 3.

  The aqueous carbonate solution 24 having a zinc concentration of 350 ppm in the solution storage area 50 is injected into the feed water flowing through the feed water pipe 36 by driving the injection pump 20 and mixed into the reactor water in the RPV 27.

  In the present embodiment, each effect produced in the second embodiment can be obtained.

  Examples 1 to 3 can be applied to a pressurized water nuclear plant.

  DESCRIPTION OF SYMBOLS 1,1A, 1B ... Zinc injection | pouring apparatus, 2 ... Zinc dissolution tank, 3 ... Zinc oxide pellet, 4 ... Carbon dioxide dissolution tank, 5 ... Aeration pipe, 6 ... Circulation pump, 7, 8 ... Piping, 10 ... Water level meter, DESCRIPTION OF SYMBOLS 11 ... Conductivity meter, 13 ... Carbon dioxide supply device, 14 ... Carbon dioxide gas cylinder, 19 ... Supply water piping, 20 ... Injection pump, 21 ... Zinc injection piping, 23, 23A ... Control device, 26 ... Reactor, 27 ... Atom Reactor pressure vessel, 28 ... core, 31 ... recirculation piping, 33 ... main steam piping, 34 ... turbine, 35 ... condenser, 36 ... feeding piping, 39 ... feed pump, 49 ... hydrogen injection device, 50 ... solution Storage area, 51 ... pressure gauge, 52 ... zinc dissolution area.

Claims (9)

Injecting carbon dioxide into a carbon dioxide aqueous solution present in the carbon dioxide dissolution region to dissolve the carbon dioxide gas in the carbon dioxide aqueous solution,
Before SL carbon dioxide dissolution zone, and by driving the pump device provided in a closed loop comprising zinc dissolution zone the solid material is present, including zinc, the carbonate solution in the carbonic acid gas dissolving region is circulated in the closed loop,
The zinc contained in the solid substance is dissolved in the aqueous solution of carbonic acid supplied from the carbon dioxide dissolution region to the zinc dissolution region by the circulation in the zinc dissolution region,
Before SL carbon dioxide dissolved in the region, a carbonate aqueous solution containing the zinc dissolved, was supplied to the reactor pressure vessel through pipe connected to the reactor pressure vessel,
The carbonic acid aqueous solution containing the dissolved zinc discharged from the zinc dissolving region is supplied to the carbon dioxide dissolving region by the circulation, and mixed with the carbonic acid aqueous solution present in the carbon dioxide dissolving region,
Supplying the aqueous carbonate solution containing the dissolved zinc mixed with the aqueous carbonate solution in the carbon dioxide dissolution region to the zinc dissolution region;
By controlling the pump device based on the zinc concentration of the carbonated aqueous solution containing the dissolved zinc, the flow rate of the carbonated aqueous solution supplied to the zinc-dissolved region is changed to change the solid substance in the zinc-dissolved region from the solid substance. A zinc injection method characterized by controlling the dissolution rate of the zinc in an aqueous carbonate solution . A first flow rate of the carbonic acid aqueous solution in which the zinc concentration of the carbonate aqueous solution is supplied to the zinc dissolution zone when less than the set concentration of zinc, the zinc concentration of the carbonate aqueous solution to the set concentration of zinc 2. The zinc injection method according to claim 1, wherein the zinc injection method is made faster than the second flow rate of the aqueous carbonate solution supplied to the zinc dissolution region when the first and second zinc dissolution regions become. When the water level in the carbon dioxide gas dissolution zone is lowered to the lower limit set water level by supplying the carbonated aqueous solution containing dissolved zinc circulated in the closed loop to the reactor pressure vessel, water is introduced into the carbon dioxide gas dissolution zone. The zinc injection method according to claim 1 or 2 , wherein replenishment is performed. 4. The zinc injection method according to claim 3 , wherein when the water level in the carbon dioxide dissolution region rises to an upper limit set water level, supply of the water to the carbon dioxide dissolution region is stopped. Measuring the conductivity of the carbonate aqueous solution, using the conductivity which is measured to calculate the zinc concentration of the carbonate aqueous solution, the supply to the zinc dissolution region based on the calculated zinc concentrations The zinc injection method according to claim 1, wherein the flow rate of the aqueous carbonate solution is controlled.   The injection of the carbon dioxide gas is performed on the aqueous solution of carbonic acid in the carbon dioxide gas dissolution region formed in the first dissolution tank, and the zinc dissolution region formed in the second dissolution tank is dissolved in the zinc. The method for injecting zinc according to claim 1, wherein the method is performed within the inside.   The carbon dioxide gas is injected into the carbonic acid aqueous solution in the carbon dioxide gas dissolution region formed in the dissolution tank, and the zinc is dissolved in the zinc dissolution region formed in the dissolution tank. The zinc injection method according to claim 1. A first dissolution tank for forming a carbon dioxide gas dissolution region in which a carbonic acid aqueous solution exists , a carbon dioxide supply device for supplying carbon dioxide gas to the carbon dioxide dissolution region, and a zinc dissolution region in which a solid substance containing zinc exists a second dissolution tank is formed, the saw including a first dissolution tank and the second dissolving tank, a closed loop for circulating the carbonate solution between said first dissolution tank and the second dissolving tank, in the closed loop A pump device provided to supply the carbonic acid aqueous solution in the carbon dioxide dissolution region to the zinc dissolution region, and a pipe connected to the carbon dioxide aqueous solution containing the zinc in the carbon dioxide dissolution region to a reactor pressure vessel a carbonate solution injection device for injecting, said carbon dioxide supply unit for supplying carbon dioxide dissolution zone into carbon dioxide, said pump apparatus from the first dissolving tank upon supply of the carbonate solution of the the second dissolving tank By driving and controlling the pump device based on the zinc concentration of the aqueous carbonate solution containing zinc, the flow rate of the aqueous carbonate solution supplied to the zinc dissolution region is changed, and the zinc in the zinc dissolution region is changed. And a control device for controlling a dissolution rate of the zinc from the solid substance contained in the aqueous carbonate solution . A third dissolution tank in which the carbon dioxide dissolution area and the zinc dissolution area disposed above the carbon dioxide dissolution area are disposed, and the first dissolution tank and the second dissolution tank are integrated; The zinc injection device according to claim 8 .

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