JPH041599A - Reducing method for radioactive material of atomic energy power plant - Google Patents

Abstract

PURPOSE:To improve reliability for the control of iron density by injecting soluble iron salt in a method by which the density of a radioactive material in nuclear reactor water can be reduced by controlling the density of iron and nickel in supply water. CONSTITUTION:The supply of pure water to a dissolver 1 is performed by a supply water piping 21, and the supply and the stoppage of the supply water are performed with a valve 22. Also, it is possible to attach controllability to perform the adjustment of a water level by a water level meter 19, and to automatically close the valve 22 by an instruction for an upper limit water level, and to automatically open the valve by the instruction for a low limit water level. A diffusion tube 23 and a supply pipe 24 for nitrogen gas and carbon dioxide gas connected to the tube 23 are provided to obtain carbonic acid required for the dissolution of ferrous carbonic acid. The quantity of dissolution of the ferrous carbonic acid is adjusted by varying water carbonic acid density by the voltage division control of the carbon dioxide. In such a case, the quantity of dissolution can be stabilized by controlling the temperature of liquid by keeping constant by a humidifier 18 and a thermometer 20.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling the iron concentration in the feed water by injecting iron in order to reduce the radioactivity concentration in the reactor water in a boiling water nuclear power plant. , relates to a method for supplying a soluble iron salt that enables a stable supply of iron.

[Conventional technology]

The system organization of a boiling water nuclear power plant (hereinafter referred to as a BWR plant) is shown in Figure 2. 6 Cooling water inside the reactor turns into steam due to the heat generated from the uranium fuel in the reactor 1 and passes through the main steam pipe 2. Work is guided by Turbine 3. Thereafter, the steam becomes condensed water (condensate) in the condenser 4 and is sent to the feed water heater 6 by the condensate pump 5. Impurities such as corrosion products in this laparotomy water are purified by a condensate filtration device 7 and a condensate desalination device 8. The cooling water heated by the water supply turbine returns to the reactor 1 again.

On the other hand, the reactor water is constantly circulated within the reactor by the reactor recirculation system piping 9 and the pump 10, and a part of the reactor water is led to the reactor purification system 11, and is It is cooled by a heat exchanger 12 and purified by a purification device 13.

In general, the piping and pumps that make up a plant.

Corrosion products such as metal ion components and insoluble components are eluted from the constituent materials of heat exchangers and the like. Here, as mentioned above, most of the corrosion products generated in the turbine system on the upstream side of the condensate purification device are removed by the condensate filtration device 7 and the condensate desalination device 8, but the condensate purification device Corrosion products generated in the downstream water supply system 14 flow into the reactor without being purified.

Corrosion products brought into the reactor 1 adhere to and accumulate on the fuel surface as a result of boiling and evaporation of cooling water occurring on the fuel surface.

Some of the corrosion products attached to the fuel surface are irradiated with neutrons and become radioactive substances.

For example, corrosion products such as Ni and Go become radioactive substances with long half-lives such as 5δCo and 80CO by irradiation with neutrons. Some of the corrosion products that adhered to the fuel rods and became radioactive again.

or elutes into the cooling water (Jj'f reactor water).

Reactor coolant recirculation system that separates and circulates reactor water9. Alternatively, it adheres and accumulates on the inner surfaces of the equipment and piping of the reactor water purification system which purifies some of the impurities in the reactor water, becoming a radiation source. Here, when the concentration of radioactive substances in reactor water increases, the amount of radioactive substances that adhere and accumulate on the surfaces of constituent materials increases, and the radiation dose of equipment piping increases. As a result, the radiation dose received by workers when performing work such as inspecting equipment and piping will also increase.

Therefore, technology has been developed and applied to operate the plant while maintaining the radioactive material concentration in the reactor water as low as possible.

For example, in order to reduce the amount of Fe, which accounts for the majority of corrosion products, instead of conventional carbon steel piping, we use low-alloy steel or weather-resistant steel, which generates less corrosion products. Furthermore, in order to effectively remove the generated corrosion products, a dual type condensate purification device combining a filter 7 and a demineralizer 8 has been used.

In addition, in the water supply system 14 downstream of the condensate purification device, where newly generated corrosion products cannot be purified, oxygen gas is injected into the cooling water and allowed to coexist with the water to form a protective film on the surface of the material that has the effect of inhibiting corrosion. The generation of products has been suppressed.

On the other hand, measures are also being taken to use materials with low 59Co content and to reduce the long-half life and the amount of 60Co, which is a nuclide, generated.

Plants that have adopted such corrosion product reduction measures have been able to reduce the amount of corrosion products flowing into the reactor, but the radioactive material concentration in the reactor water remains stable at a higher level than before. This was the result.

As a result of examining this factor, we found that Ni and Go generated from stainless steel feed water heater tubes and reactor internal structural materials using stainless steel and Inconel materials.
This was thought to be due to the large decrease in the amount of Fe corrosion products compared to the amount of . In addition, as a result of partially bypassing the condensate purification equipment mentioned above and increasing the iron concentration in the water supply,
The concentration of radioactive materials in the reactor water decreased, proving that this assumption was correct. The Fe concentration in the feed water is determined by the Nj generated from the feed water heater tube and reactor internals.
A method of controlling the amount of Co and Co generated is currently being applied.

Furthermore, although it is possible to control the Fe concentration in the water supply by partially bypassing the condensate purification device described above, only the filter 7 can be bypassed among the duplex purification devices. This is necessary to prevent the seawater used as cooling water from mixing with the reactor water in the event that the cooling pipe of the condenser on the upstream side of the condensate purification system is damaged. This is because bypass operation of the condensate demineralizer 8 is not preferable. Therefore, control of the Fe concentration in the feed water by bypass operation of the condensate purification device results in bypass operation of only the filter on the upstream side, and operation via the desalination device installed on the downstream side.

In this case, the controllability of the Fe concentration in the feed water depends on changes in the iron removal performance of the demineralizer, which cannot be bypassed, and there is a problem in that it is difficult to control the concentration. From this point,
As a method to control the Fe concentration in the water supply, a method of directly injecting Fe into the water supply was disclosed in Japanese Patent Application Laid-Open No. 60-188.
No. 893, JP-A-61-79194, JP-A-62-8
No. 5897 and Japanese Unexamined Patent Publication No. 62-226099.

JP-A-60-188893, JP-A-61-79193
No., JP-A-62-226099 and JP-A-62-8
According to Publication No. 5897, the iron to be injected is iron ion, iron oxide, iron hydroxide, stainless steel and carbon steel that are brought into contact and corroded, iron fine powder, magnetite powder, or an iron electrode immersed in water. It has been shown that these are iron ions or iron particles generated by underwater discharge.

On the other hand, a report by Nishino et al. (Chemical Engineering Transactions, Vofl.

15(2), 276 (1989)), as shown in Table 1, amorphous iron hydroxide and γ-FeOOH react with Ni in the reactor water environment to produce NiFezO4.
However, a-FeOOH, a-Fezes and Fe5O
It is reported that a did not react with Ni.

From this report, it is considered desirable that the iron injected into the water supply system be iron ions or amorphous hydroxide, considering its reactivity with Ni in the reactor.

On the other hand, as shown in Figure 3, the injection efficiency of iron ions produced by electrolyzing an iron electrode in water or amorphous iron hydroxide was 30% as shown in Figure 3.
% and 80%, and it was confirmed that the injected iron remained in the injection pipe.

This poses a problem in that the injection pipe may become clogged with the injected iron during long-term operation.

[Problem to be solved by the invention]

The above conventional technology injects iron ions or amorphous hydroxide, which are highly reactive with Ni, into the feed water in the JV sub-reactor.
Although it is possible to reduce the concentration of radioactive substances in reactor water, there is a problem that these iron tend to adhere to the injection pipes, making it difficult to obtain sufficient injection efficiency.

Further, since iron adhering to the inside of the injection pipe has the possibility of clogging the injection pipe over a long period of time, it is necessary to periodically remove the iron inside the pipe. If it is difficult to periodically remove iron, it will increase equipment costs such as installing multiple pre-injection pipes, so improvements must be made. An object of the present invention is to provide an iron injection method that can inject iron and ignore iron adhesion to injection piping.

[Means to solve the problem]

In order to achieve the above object, the present invention investigated the solubility of various iron compounds in water and the adhesion characteristics to injection piping,
We investigated and selected the most effective method.

As a result, the present inventors found that by injecting using a soluble iron salt or by allowing anions to coexist in electrolytic iron, adhesion to the injection pipe can be almost ignored.

Moreover, in order to inject it as an aqueous solution, it is necessary that the solubility in water is high. When the paired anion species injected together with iron flow into the reactor, reactor constituent materials,
Alternatively, it is necessary that the influence of corrosion on the constituent materials inside the reactor is small.

Taking these points into consideration, the present inventors discovered that ferrous carbonate, which has a solubility of about 1 g/Ω (at 20°C) in carbon dioxide saturated water,
Or about 45g per 100g of water (at 20℃)
Ferrous nitrate or ferric nitrate, which has a solubility of Since the concentration is less than i Ppb and is a very small concentration, it is thought that there will be no influence.

Furthermore, in the case of carbonate ions, they are removed together with the steam as the cooling water boils inside the reactor, so they are not concentrated inside the reactor. On the other hand, nitrate ions have a low carryover rate into steam, so several tens of ρppb are present in the reactor.
It is thought that it is concentrated as a concentration of .

However, the test results shown in Figure 4 by V. E. Ruther et al. (Corrosion, VoQ44 (11),
(1988)), 100 ppb
Nitrate ion (NOs-) (1) Coexistence is borate ion (BO3g-) *chloride ion (CO), phosphate ion (PO48-).

Stress corrosion cracking compared to coexistence of sulfate ions (S042-),
Furthermore, there is no significant difference from the data for pure water, which has no effect on the acceleration of crack growth and does not contain any impurities.Therefore, it is concluded that there is no practical problem with the inflow of nitrate ions into the reactor. possible, but with lower priority than carbonates,
Applicable. Note that the test results by W, E, Ruther et al. are test results for sensitized materials, and in actual plants, measures such as adopting construction methods and materials that do not sensitize are taken, and anionic species Even if there is coexistence, it is judged that the margin is sufficiently maintained.

In addition, as a result of considering a method for adjusting the amount of water to be injected into cooling water such as water supply, it was determined that this method was preferable.

When injecting an aqueous solution of ferrous carbonate, in advance,
A process is required to dissolve ferrous carbonate in water containing carbon dioxide gas. To dissolve ferrous carbonate, there is a method in which water containing carbon dioxide gas is prepared in advance in a dissolution tank, and a predetermined amount of ferrous carbonate is added and dissolved to obtain a solution with a predetermined concentration. Nitrogen (N2) gas and carbonic acid (C
By adjusting the mixing ratio of OZ) gas, it is also possible to adjust the carbon dioxide concentration in water based on the correlation shown in Figure 5, and it is also possible to adjust the concentration of ferrous carbonate in water based on the correlation shown in Figure 6. .

Also, in the case of dissolving ferrous and ferric nitrate salts,
Since it has a high solubility in water, it is possible to adjust the iron concentration by adding a predetermined amount to the dissolution tank.

On the other hand, when using iron ions generated by electrolysis,
Injection efficiency can be improved by adding carbon dioxide gas, carbonate-containing water, or nitric acid-containing water after electrolytic iron is produced, and by injecting the iron in the presence of carbonate ions or nitrate ions.

On the other hand, although the above description was given regarding an inorganic salt, a method of injecting it as a water-soluble iron complex salt is also possible.

Iron complex salts include polyaminocarboxylic acids or oxycarboxylic acids as chelating agents. Since the stabilization constant of these iron complex salts is much higher than that of inorganic salts, it is possible to effectively reduce the adhesion of the injected iron into the injection pipe. Also, when these complex salts enter a nuclear reactor, they decompose into carbon dioxide gas.

It is determined that it will be removed along with the steam as ammonia, so there is no possibility that it will be concentrated as an impurity.

Furthermore, when water containing carbonate ions or nitrate ions is injected into the reactor, the pH of the reactor water shifts to the fIi side, albeit slightly.

In this case, the pH of the reactor water is assumed to be 50p with nitrate ions.
If pb were to exist, the minimum value would be approximately 6.1, but
BWR plant reactor water pH operational control range 5.6 to 8.
6 and does not pose an obstacle to plant operation.

However, in the case of BWR, it is desirable to maintain the cooling water neutral even when iron is injected, since the cooling water has been mainly managed using neutral water. Furthermore, Y
, Solmon (Int' 1 , Conf, onW
ator Chemistry of Nuclear
Reactor System BNES, 1977)
reported by.

As seen in the solubility data of magnetite in high-temperature water shown in FIG. 7, iron oxides in high-temperature water have a minimum solubility value on the alkaline water side.

This phenomenon is caused by the reaction of the injected iron with Ni.
Exo4 has a similar tendency, and the amount of elution of radioactive substances such as 6♂Co produced by activation of Ni can also be suppressed. Therefore, controlling the pH of reactor water by adding alkali chemicals together with iron is a more effective means of reducing the concentration of radioactive substances.

[Effect]

As shown in the present invention, when iron ions or amorphous hydroxide are implanted, by implanting them in coexistence with carbonate ions, nitrate ions, or chelating agents, the implantation efficiency is increased. As a result, it is possible to prevent the injection pipe from being blocked by the injected iron, and stable iron injection operation can be realized.

Furthermore, considering the need for long-term continuous operation, a large-capacity dissolving tank is required in the case of injection of ferrous carbonate or iron nitrate, but when combined with an electrolytic iron generator, injection The same effect as above can be achieved by first coexisting iron ions with carbonate ions, nitrate ions, or chelating agents, and then implanting them.

In addition, if a method is adopted in which alkaline chemicals are generated simultaneously with the injected iron, it becomes possible to stabilize the reactor water pH to neutral or alkaline side, and the Ni- or Co stabilized by the injected iron can be stabilized. The elution of can be suppressed. As a result, more effective suppression of radioactive materials in the reactor water can be achieved.

〔Example〕

Below, one embodiment of the present invention will be explained with reference to FIG.
The embodiment shown in the figure is an embodiment of a method for dissolving and injecting ferrous carbonate in water containing carbonate. The ferrous carbonate is dissolved in the dissolving tank 15. Packet containing ferrous carbonate in dissolving tank 1]6. Stirrer 17. Warmer 18. Water level gauge 19
and a thermometer 20. Pure water is supplied to the dissolution tank 1 through a supply water pipe 21, and a valve 22 is used to supply and stop the supply water. Further, the water level can be adjusted using a water level gauge 19, and a control facility may be provided in which the valve 22 automatically closes when the upper limit water level is indicated and automatically opens when the lower limit water level is indicated. In order to obtain the carbonic acid necessary for dissolving ferrous carbonate, a diffuser pipe 2 is installed at the bottom of the dissolving tank.
3 and nitrogen gas and carbon dioxide gas supply piping 24 connected thereto.
will be established. A nitrogen gas cylinder 25 is connected to the supply pipe 24. Pressure regulating valve 27 from carbon dioxide cylinder 26. A mixed gas of nitrogen gas and carbon dioxide gas is supplied through the flow meter 28.

As described above, the amount of ferrous carbonate dissolved is adjusted by changing the carbon dioxide concentration in water by controlling the partial pressure of carbon dioxide gas shown in FIGS. 5 and 6. In that case,
It is desirable to stabilize the amount of dissolution by controlling the temperature of the liquid in the dissolution tank to be constant using the warmer 18 and thermometer 20. The nitrogen gas and carbon dioxide gas supplied to the dissolving tank are discharged to the outside of the yarn through the exhaust pipe 24. In this case, the amount of carbonic acid dissolved can be controlled by using an inert gas such as helium gas or argon gas instead of nitrogen gas. The liquid whose iron concentration was adjusted using the method described above is filter 2.
5. Infusion pump 26. Flow control valve 27. Injection pipe 28,
Then, it is injected into the injection piping system 30 via the injection piping main valve 29.

Next, a second embodiment of the present invention will be described using FIG. 8. The embodiment shown in FIG. 8 is a case in which ferrous nitrate or ferric nitrate is dissolved and injected. The dissolving tank 15 contains a packet 16 containing iron nitrate. Stirrer 17. The equipment is equipped with a water level gauge 19°, a warmer 18, and a thermometer 20.

The operation of these facilities is similar to that shown in Example 1.

The liquid in the dissolution tank, which has been adjusted to a constant iron concentration, is passed through a filter 25 and an injection pump 26. Flow control valve 27. It is injected into the injection pipe 30 via the injection pipe 28 and the injection pipe main valve 29. The amount of iron injected is controlled by the iron concentration in the melting tank and the injection flow rate.

Next, a third embodiment of the present invention will be described using FIGS. 9 and 10. The embodiment shown in FIG. 9 includes an alkaline chemical tank 31 and a supply pump 32 to adjust the pH in the reactor water to neutral or slightly alkaline in the equipment for injecting ferrous carbonate shown in FIG. A supply pipe 33 and a valve 34 are added.

A fourth embodiment will be explained using FIG. 11. FIG. 11 shows a method of adding and implanting iron ions generated by electrolysis or carbonate ions to an amorphous iron hydroxide solution.

The supply of demineralized water used as electrolyte and injection water is supplied to the electrolytic iron generator through a supply pipe 35, and through a flow rate control valve 36. Then, use the flowmeter 37.

The feed water led to the Cox press-in raw water tank; 38 is heated by an electric heater 39, the water temperature is detected by a thermometer 40 and adjusted to a constant temperature, and the iron electrode 42 is electrolyzed in an electrolytic tank 41 on the downstream side. In order to obtain sufficient electrical conductivity, carbon dioxide gas is injected from the lower part of the CO2 injection raw water tank 38. The supply of carbon dioxide gas is performed using a plurality of carbon dioxide gas cylinders 43, and the carbon dioxide gas supply piping 44
．． Flowmeter 45. This is done via the flow control valve 46.

After adjusting the temperature and conductivity of the supplied water, the water is led to the lower part of the electrolytic cell through a transfer pipe 47, and is raised by 1 between the iron electrodes 42. Thereafter, a current is supplied to the iron electrode from the DC power supply 48, and electric ions are eluted into the electrolyte.

Furthermore, nitrogen gas is blown into the electrolytic solution from the lower part of the electrolytic cell 41 to perform operation while suppressing scale adhesion to the surface of the 7-iron electrode.1! The raw gas is supplied from a plurality of nitrogen gas cylinders 49 through a supply pipe 50° and a flowmeter 51. And, it is performed via the flow rate l1i1 regulating valve 52.

The electrolytic solution containing electrolytic iron moves to the reaction tank 53 by overflowing into the reaction tank from the upper part of the electrolytic tank via a barrier. Therefore, even if the water in the reaction tank runs out, the electrolytic tank 41. The electrolytic iron introduced into the reaction tank 53 can be prevented from running out of water in the CO2 injection raw water tank 38, and can prevent overheating of the heater or abnormal rise in the 1'f electrolysis voltage. The contained water is stirred by the stirrer 54, and is also fed from the carbon dioxide gas cylinder 43 mentioned above.
Carbon dioxide gas is supplied again to form an iron carbonate solution. C
ot press-in raw water tank: 38. Electrolytic tank 41 and reaction tank 53L
The supplied carbon dioxide gas and nitrogen gas are led to an exhaust duct inside the building and discharged through an exhaust pipe 55 provided in one part of the electrolytic cell and the reaction tank. Further, the water level of the reaction tank is adjusted by detecting it with a water level gauge 56 and lowering the water level from the injected water level to the taken out water level. : To prevent and.

On the other hand, the upper limit water level can be checked and controlled using a water level gauge, but it is also possible to adjust the setting of the overflow line 57 as shown in FIG. The injection gun made of iron carbonate has an injection pump of 58 degrees and an injection pipe of 59 degrees. Flow rate adjustment #
60. and the injection system piping 6 via the injection piping source valve 61.
3 injection system led to condensate demineralizer 8 shown in FIG.
and the reactor 1 population section, or the reactor purification system purification device t1. From a to the piping system of the reactor 1 population section may be used.

A fifth example of the embodiment will be explained using FIG. 2. In the embodiment shown in FIG. 12, a nitric acid supply facility is provided in the electrolytic iron production facility shown in FIG. 11. in particular,
In order to inject electrolytic iron coexisting with nitrate ions (NO3), a supply pump 6 is supplied from a nitric acid supply tank 63 to the reaction tank 53.
4. Flow meter 65. A sixth embodiment of the present invention, which is equipment for supplying a nitric acid solution through a flow rate control valve 66 and a supply pipe 67, will be described with reference to FIG. 13 and @FIG. The embodiment shown in FIGS. 13 and 14 is a method of injecting carbonate ions or nitrate ions coexisting into the electrolytic iron solution shown in FIGS. 11 and 12, and also In order to control this, equipment for adding alkaline chemicals has been added.

Addition of alkaline chemicals to the electrolytic iron solution is done in the alkaline chemical tank 31. This can be achieved by providing a liquid feeding pump 32, a flow meter 68, and a flow control valve 34.

〔Effect of the invention〕

According to the invention, the injection gun is attached within the injection pipe.

This prevents clogging of the piping, making stable iron injection possible and improving the reliability of iron concentration control in the injection system.

As a result, it becomes easier to stabilize the concentration of radioactive materials in the reactor water, which in turn contributes to reducing the dose rate received during plant inspections.7 Furthermore, by injecting alkaline chemicals together with the injection gun, It becomes possible to suppress the amount of elution of radioactive substances, and 1 rational water quality control can be achieved.

[Brief explanation of the drawings] Fig. 1 is a system diagram of an embodiment of the present invention, Fig. 2 is a general system diagram of BWR, and Fig. 3 is an actual measurement result of the adhesion rate of injected iron to the injection pipe. Figure 4 is an explanatory diagram showing the test results of the influence of anionic impurities on SCC, Figure 5 is an explanatory diagram showing the relationship between the carbon dioxide concentration in the gas phase and the dissolved concentration of carbonic acid in water, and Figure 6 is an explanatory diagram showing the relationship between the carbon dioxide concentration in the gas phase and the dissolved concentration of carbonic acid in water. The figure is an explanatory diagram showing the relationship between the carbonic acid concentration in water and the amount of dissolved ferrous carbonate. Figure 7 is an explanatory diagram showing the solubility of iron oxide in high-temperature water. Figure 8 is an explanatory diagram showing the relationship between the carbonate concentration in water and the amount of dissolved ferrous carbonate. Figure 8 is an explanatory diagram showing the solubility of iron oxide in high-temperature water. 9 and 10 are the system diagrams of the third embodiment of the present invention, FIG. 11 is the system diagram of the fourth embodiment of the present invention, and FIG. 12 is the system diagram of the fourth embodiment of the present invention. A system diagram showing the fifth embodiment, and FIGS. 13 and 14 are system diagrams showing the sixth embodiment of the present invention. 15...Dissolution tank, 16...Packet, 17...Agitator. 18... Warmer, 19... Water level gauge, 23... Diffusion pipe, 26... Injection pump, 31... Alkaline chemical tank, 38... COz injection raw water tank, 41... Electrolytic cell, 43... Carbon dioxide gas cylinder, 49... Nitrogen gas cylinder, 53... Reaction tank, 63... Nitric acid tank.

Claims (1)

[Claims] 1. By controlling the iron and nickel concentrations in the feed water of a boiling water nuclear power plant, the concentration of radioactive substances in the reactor water can be reduced, and the concentration of radioactive substances in the reactor water can be reduced according to changes in the nickel concentration in the feed water. A method for reducing radioactive substances in a nuclear power plant, which method comprises injecting soluble iron salt. 2. In claim 1, the soluble iron salt to be injected is at least one selected from ferrous nitrate, ferric nitrate, or ferrous carbonate. Method. 3. In a method of reducing the concentration of radioactive substances in reactor water by controlling the iron and nickel concentrations in the feed water of boiling water nuclear power plants, and injecting the necessary iron according to changes in the nickel concentration in the feed water. , A method for reducing radioactive substances in a nuclear power plant, characterized by injecting soluble iron salts and alkaline chemicals. 4. In claim 3, the soluble iron salt is one or more selected from ferrous nitrate, ferric nitrate, and ferrous carbonate, and the alkali chemicals are sodium hydroxide, lithium hydroxide, A radioactive material reduction method for nuclear power plants that selects one or more types of potassium hydroxide. 5. A method of reducing the concentration of radioactive materials in reactor water by controlling the iron and nickel concentrations in the feed water of boiling water nuclear power plants, and injecting the necessary electrolytic iron according to changes in the nickel concentration in the feed water. Reduction of radioactive substances in a nuclear power plant, characterized by injecting carbonate ions, nitrate ions, or both carbonate ions and nitrate ions in coexistence into an electrolytic iron solution produced by electrolyzing the iron electrode. Method. 6. The nuclear power plant according to claim 5, wherein the supply of carbonate ions coexisting in the electrolytic iron solution is selected from one or more of carbon dioxide gas, carbonic acid, sodium carbonate, potassium carbonate, and lithium carbonate. Radioactive substance reduction method. 7. In claim 5, the supply of nitrate ions coexisting in the electrolytic iron solution is selected from one or more of nitric acid, sodium nitrate, potassium nitrate, and lithium nitrate. Method. 8. A method of reducing the concentration of radioactive materials in reactor water by controlling the iron and nickel concentrations in the feed water of boiling water nuclear power plants, and injecting the necessary electrolytic iron according to changes in the nickel concentration in the feed water. , radioactivity in a nuclear power plant is characterized by injecting carbonate ions, nitrate ions, or both carbonate ions and nitrate ions together with an alkaline chemical into an electrolytic iron solution produced by electrolyzing an iron electrode. Substance reduction method. 9. In claim 8, the supply of carbonate ions to coexist in the electrolytic iron solution is provided by radioactive materials in a nuclear power plant where one or more types are selected from carbon dioxide gas, carbonic acid, sodium carbonate, potassium carbonate, and lithium carbonate. Reduction method. 10. The method for reducing radioactive substances in a nuclear power plant according to claim 8, wherein the supply of nitrate ions coexisting in the electrolytic iron solution is selected from among nitric acid, sodium nitrate, potassium nitrate, and lithium nitrate. 11. The method for reducing radioactive substances in a nuclear power plant according to claim 8, wherein the alkaline chemical coexisting in the electrolytic iron solution is selected from one or more of sodium hydroxide, lithium hydroxide, and potassium hydroxide. 12. A method of injecting the necessary iron according to changes in the nickel concentration in the feed water in order to reduce the concentration of radioactive substances in the reactor water by controlling the iron and nickel concentrations in the feed water of boiling water nuclear power plants. A method for reducing radioactive substances in a nuclear power plant, characterized by injecting a water-soluble iron complex salt. 13. The method for reducing radioactive substances in a nuclear power plant according to claim 12, wherein the water-soluble iron complex salt chelating agent to be injected is a polyaminocarboxylic acid or an oxycarboxylic acid. 14. In order to reduce the radioactive material concentration in reactor water by controlling the iron and nickel concentration in the feed water of boiling water nuclear power plants, a method of injecting electrolytic iron according to changes in the nickel concentration in the feed water. , A method for reducing radioactive substances in a nuclear power plant, characterized by injecting a chelating agent into an electrolytic iron solution produced by electrolyzing an iron electrode. 15. The method for reducing radioactive substances in a nuclear power plant according to claim 14, wherein the chelating agent coexisting in the electrolytic iron solution is polyaminocarboxylic acids or oxycarboxylic acids.