JP2000352597A - Nuclear power plant and method for operating it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the inter-granular stress corrosion cracking(IGSCC) of a material composed mainly of stainless steel, control the behavior of the ACP in reactor water, improve the integrity of materials for a nuclear power plant and reduce radiation exposure dose equivalents by treating Cr contained in the material to stabilize the element on the surface of the material. SOLUTION: This nuclear power plant is equipped with a means 14 that detects the condition of the corrosion in piping or equipment on a primary system in the plant, a means that judges the condition of the shortage of Cr in a material in piping or equipment on the basis of a value detected by the means 14 and means 15 and 16 for stabilization treatment which supply a system of piping or equipment with a substance or a potential that retards the corrosion of the material by stabilizing Cr in it when the amount of the shortage of Cr in the material goes beyond or is projected to exceed a certain value by the means for judging the condition of the shortage of Cr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to suppress the stress corrosion cracking of primary materials of a nuclear reactor, and to reduce the concentration of radioactivity in the primary system of the reactor, and to reduce the concentration of radioactivity attached to the primary piping or equipment. The present invention relates to a nuclear power plant and an operation method thereof.

[0002]

2. Description of the Related Art In a nuclear power plant, high-temperature water is used as a coolant, and under severe environmental conditions, corrosion behavior of a material is an important problem.
As the corrosion behavior, Fe, Ni,
Elution of constituent metal elements such as Cr and Co, and stress corrosion cracking of heat-affected zones such as welds of austenitic stainless steel and nickel-based alloys, which are particularly problematic in boiling water nuclear power plants (hereinafter referred to as BWRs) (Stress Co
erosion cracking, hereafter "SCC"
2) must be considered.

It is said that this SCC event occurs when three factors, namely, material, stress, and environment, are superimposed. SCC of stainless steel in pure water at high temperatures and pressures, such as BWR reactor water,
stress corrosion cracking at crystal grain boundaries where r is apt to be unevenly distributed, that is, intergranular stress corrosion cracking (Intergranular Street).
ss Corrosion Cracking,
"IGSCC"), and the three factors are:
It is considered that (1) the formation of a Cr-deficient layer by the sensitization treatment, (2) the applied stress equal to or higher than the yield point, and (3) the supply of sufficient dissolved oxygen. By superimposing these three factors,
Corrosion locally progresses along the Cr-deficient layer.

[0004] As one of means for suppressing "supply of dissolved oxygen" which is an environmental factor, a hydrogen injection technique from a water supply system has been applied to BWR. However, since hydrogen injection shifts the oxidizing environment in the furnace toward the reducing side, the solubility of metal oxides present in the furnace increases, and activated corrosion products (Activated Corrosion Pro) serving as radiation sources are exposed.
(hereinafter referred to as “ACP”), so that the radioactivity concentration in the reactor water represented by Co-60 increases.

As a source of ACP, corrosion products (C
Orrosion Product (hereinafter referred to as "CP") adheres to the surface of the fuel cladding tube and becomes so-called "fuel clad" and is activated, while there is one where the structural material in the neutron field of the core is directly activated and eluted. It is generally said.

[0006] The ACP dissolved in the reactor water takes an ion form, is taken into the pipe outside the furnace and the oxide film of the equipment, and becomes an exposure radiation source during a periodic inspection of the nuclear power plant. In particular, in relatively new plants, the amount of iron clad brought in from the feedwater is reduced, so that the radioactivity behavior of this ion form is dominant.

Conventionally, Ni / Fe ratio control has been applied to reduce the radioactivity concentration of ACP in the ion form of BWR. This is a technique for confining the CP in the fuel cladding, and has conventionally achieved an effect of reducing the reactor water radioactivity concentration by about 1/5. However, when the Ni / Fe ratio control is performed, the tendency of radioactivity to adhere to the pipe is accelerated, so that the amount of radioactivity adhering to the pipe and equipment outside the furnace does not always decrease. In particular, in the latest BWR, the effect of reducing the reactor water radioactivity concentration is small, and an increase in the pipe dose rate is becoming a problem. One of the reasons why the effect of reducing the reactor water radioactivity concentration has been reduced is that Cr oxide may temporarily precipitate on the surface of the fuel cladding tube and dissolve the surrounding fuel cladding when it becomes unstable. Sex is suggested.

As a means of solving such a problem, what is called “high Ni control” as a substitute for the conventional Ni / Fe ratio control, which suppresses the introduction of Fe from zinc injection or feed water as much as possible, is promising. Each of these techniques aims at suppressing the tendency of radioactivity to adhere to pipes and equipment, and the reactor water radioactivity concentration is Ni / Fe
Although there is a possibility that it may increase compared to when performing ratio control,
It is considered that the amount of attached radioactivity itself is suppressed.

Further, at the time of hydrogen injection, the chemical form of radioactive nitrogen generated in the furnace becomes a reduced molecule represented by ammonia, so that the radioactive nitrogen is easily transferred from the furnace to the main steam, and the main steam system is formed. Increasing turbine system dose rates. Among radioactive nitrogen, N-16 generated from the O atom of the water molecule emits γ-rays having an energy of 6 to 7 MeV.
As a result, it is not only a radiation source in the turbine building, but also can affect the dose rate at the plant site boundary. N
In order to suppress the transfer amount of −16 to the main steam, it is a simple measure to suppress the hydrogen injection amount to be low. Therefore, the effect of the hydrogen injection may not reach all the materials in the furnace.

[0010]

As described above, BW
In high-temperature, high-pressure pure water containing dissolved oxygen, such as R reactor water, when stress is applied, Cr generated by sensitization
Local corrosion may progress along the depletion layer.

As a countermeasure, a hydrogen injection technique has already been applied from the environment side. However, the effect differs depending on the location of the material, the plant shape, and the like, and the oxidizing environment on the material surface in the furnace cannot be uniformly transferred to the reduction side. Secondary effects such as an increase in the dose rate on the surface of primary equipment and piping due to an increase in the ACP concentration in the reactor water, and an increase in the dose rate in the turbine system due to an increase in the concentration of radioactive nitrogen in the main steam have also been observed.

Regarding the increase in the ACP concentration, it is suggested that the Cr oxide temporarily adheres to the surface of the fuel cladding tube and then becomes unstable and dissolves, thereby dissolving the ACP adhering to the surroundings. Have been.

Further, as one source of Cr in the BWR reactor water, Cr elution due to corrosion of a feed water heater installed in a water supply system is considered, which is an obstacle in controlling the Cr concentration in the reactor water. Becomes

The present invention has been made in order to solve the above-mentioned problems, and performs a process for stabilizing Cr contained in a material (particularly, a crystal grain boundary portion) mainly in stainless steel on the material surface. Accordingly, it is an object of the present invention to suppress the IGSCC of the material, control the behavior of the ACP in the reactor water, improve the soundness of the material of the nuclear power plant, and reduce the exposure dose equivalent.

[0015]

[MEANS FOR SOLVING THE PROBLEMS] C of a nuclear power plant
The generation process of r is roughly classified into two: corrosion of stainless steel in a water supply system used for a feed water heater cooling pipe and corrosion of a furnace material containing Cr.

It is an object of the present invention to provide a nuclear power plant with a treatment for stabilizing Cr contained in these materials on the surface of the material and to employ an operation method for stabilizing Cr. This controls the corrosion behavior of the primary system of the nuclear power plant, suppresses local corrosion typified by IGSCC, suppresses the ACP concentration in the reactor water, controls the Cr concentration in the reactor water that affects the ACP behavior, and thus the primary By controlling the amount of radioactivity adhering to the system piping and equipment, it is possible to reduce the exposure dose during work and the amount of shielded objects installed.

In consideration of application of the present invention to an existing plant, a method of performing a surface treatment for stabilizing Cr on a material surface,
There are a method of controlling the metal concentration in water in contact with the material and a method of controlling an oxidizing environment in which Cr present on the surface can stably exist. It is effective to apply these alone or in combination.

[0018] The stabilization of Cr is performed by pre-filming, polishing, electroplating, electroless plating, anodic oxidation, flame spraying, plasma spraying, ion plating, sputtering, physical vapor deposition (forming a dense oxide film before starting the plant). (PVD), chemical vapor deposition (CVD), painting, lining, or a plurality of applications.

The concentration of metal in water in contact with a material is controlled by a method of removing a metal to be controlled by a purification system, a method of connecting an injection system to a plant, and an amount of corroded and eluted metal contained in the material. One of the following methods: adding the target metal to the surface of the material in advance to elute and release it,
Alternatively, it can be controlled by multiple applications.

The oxidizing environment is a method for connecting a system for injecting a redox agent of oxygen, hydrogen, and hydrogen peroxide to the plant, and a device for distributing non-condensable gas typified by a condenser and a drain tank. Can be controlled by any of the methods for changing the operating conditions of the above or by applying a plurality of methods. Further, the supply rate of the oxidizing or reducing agent supplied to the material surface may be changed by changing the linear flow velocity of the fluid to control the thickness of the diffusion layer, by changing the structure, or by changing the flow rate of the fluid. It can be controlled by application.

By stabilizing Cr in the material, the following five functions can be expected.

(1) The Cr-deficient layer existing along the grain boundaries can be stabilized, and the SCC of the material can be suppressed.

(2) By reducing the SCC sensitivity, the amount of hydrogen injection can be reduced, and preventive maintenance water chemistry with small secondary effects such as an increase in the primary system dose rate and an increase in the turbine system dose rate can be achieved. .

(3) A dense oxide film having the form of MCr ₂ O ₄ is formed on the surface of the material to suppress corrosion of materials in the furnace, thereby suppressing corrosion of primary piping and equipment, and adhering radioactivity. The amount can be reduced.

(4) Cr oxidation deposited on the fuel cladding tube surface
The chemical form of the material₂O ₃Not stable
MCr₂O₄To reduce the amount of Cr oxide dissolved
And the fuel containing ACP existing around the Cr oxide
Suppresses dissolution of material cladding and reduces ACP concentration in reactor water
it can.

(5) Cr elution from the heat transfer tube of the feed water heater can be suppressed, and the Cr concentration in the furnace water can be controlled to be low.
This makes it possible to easily control the Cr concentration in the reactor water, maintain the reactor water pH near neutrality, and reduce the ACP concentration in the reactor water.

The present invention has been made on the basis of the above viewpoints. According to the first aspect of the present invention, there is provided a corrosion state detecting means for detecting a corrosion state in piping or equipment of a primary system of a nuclear power plant, and the corrosion state detecting means. Cr deficiency state determining means for determining a Cr deficiency state in the material in the pipe or the device based on the detection value by the situation detecting means, and the Cr deficiency amount in the material exceeds a certain value by the Cr deficiency state determining means. Or when it is expected to exceed, Cr stabilization processing means for stabilizing Cr in the material and supplying a substance or an electric potential which suppresses corrosion of the material to the piping or the system of the equipment. To provide a nuclear power plant.

According to a second aspect of the present invention, in the nuclear power plant according to the first aspect, the corrosion state detecting means includes at least one of a metal concentration, an oxygen concentration, a hydrogen concentration, or a hydrogen peroxide concentration in water or a corrosion potential of a material surface. A nuclear power plant characterized by detecting one type.

According to a third aspect of the present invention, in the nuclear power plant according to the first aspect, the Cr stabilizing means includes a metal concentration, an oxygen concentration, a hydrogen concentration, or a hydrogen peroxide concentration in water or a corrosion potential of a material surface. There is provided a nuclear power plant characterized by controlling at least one type.

According to a fourth aspect of the present invention, there is provided a method of operating a nuclear power plant, characterized in that a treatment for stabilizing Cr in a material in the nuclear power plant is performed to suppress corrosion of the material.

According to a fifth aspect of the present invention, in the operating method of the nuclear power plant according to the fourth aspect, the treatment method for stabilizing Cr includes any one or more of a metal group consisting of Zn, Ni, Cr, Co, and Fe. Is added to the material surface in an amount larger than the base material composition ratio.

According to a sixth aspect of the present invention, in the operating method of the nuclear power plant according to the fifth aspect, the form of MCr ₂ O ₄ (M: Zn, Ni,
A method for operating a nuclear power plant, characterized by forming a compound of one or more of Fe and Co).

According to a seventh aspect of the present invention, in the operating method of the nuclear power plant according to the sixth aspect, the MCr ₂ O ₄
There are plating, painting, lining, spraying,
Provided is a method for operating a nuclear power plant, wherein one or more of surface treatments such as plating, prefilming, and polishing are used.

According to an eighth aspect of the present invention, in the operating method of the nuclear power plant according to the sixth aspect, the MCr ₂ O ₄
The present invention provides a method for operating a nuclear power plant, characterized by controlling the concentration of any one or a plurality of metals in water in contact with a material as a method of forming a nuclear power plant.

According to a ninth aspect of the present invention, in the operating method of the nuclear power plant according to the eighth aspect, as the metal concentration control, one or both of Zn and Ni concentrations in the reactor water are controlled to 0.3 to 100 ppb. A method for operating a nuclear power plant characterized by the above feature is provided.

In the present invention, the reason why the concentrations of Zn and Ni in the reactor water are controlled to 0.3 ppb or more is to sufficiently obtain the function of suppressing the expansion of the Cr-deficient layer by MCr ₂ O ₄ .
The reason why the upper limit is set to 1000 ppb is to take into consideration the effect on plant operation as a secondary effect.

According to a tenth aspect of the present invention, in the operating method of the nuclear power plant according to the eighth aspect, as the metal concentration control, Zn and Cr are simultaneously or alternately injected into a primary system, and Zn is added to the surface of the material. Provided is a method for operating a nuclear power plant, characterized by stabilizing an oxide containing iron and Cr.

According to an eleventh aspect of the present invention, in the operating method of the nuclear power plant according to the eighth aspect, as the metal concentration control, the Cr concentration in the reactor water is 5 ppb or more and the Zn concentration in the reactor water is
A method for operating a nuclear power plant, comprising controlling the concentration to 2 ppb or more and stabilizing an oxide containing Zn and Cr on a material surface.

Under these conditions, M
Cr ₂ O ₄ can be generated stably.

According to a twelfth aspect of the present invention, in the operating method of the nuclear power plant according to the fourth aspect, the method for stabilizing the Cr includes, as a corrosion potential on a material surface, an oxygen concentration in water, a hydrogen concentration in water, a hydrogen concentration in water. Provided is a method for operating a nuclear power plant, which controls one or more of hydrogen peroxide concentrations to control an oxidation-reduction environment.

According to a fourteenth aspect of the present invention, in the method for operating a nuclear power plant according to the twelfth aspect, the corrosion potential of the stainless steel exposed to the reactor water during operation is controlled as the control of the material surface corrosion potential. Is controlled to 0.1V or less.

In the present invention, the corrosion potential of 0.1 V or less is defined as a standard hydrogen electrode potential (Standard Hydrode).
gen Electrode (SHE). This makes it possible to suppress corrosion of stainless steel.

According to a fifteenth aspect of the present invention, in the method for operating a nuclear power plant according to the twelfth aspect, a plurality of the surface treatments, the control of the metal concentration, and the control of the oxidizing environment are performed to stabilize Cr in the material. A method for operating a nuclear power plant is provided.

According to a sixteenth aspect of the present invention, in the method for operating a nuclear power plant according to the twelfth aspect, the method for stabilizing the Cr includes controlling the concentration of MCr ₂ by controlling the metal concentration.
By controlling the oxidizing environment after O ₄ is formed,
Provided is a method for operating a nuclear power plant, wherein the concentration is controlled to 1 ppb or less.

Under the strong oxidizing environment and high temperature conditions where the dissolved oxygen concentration in the BWR primary system water is several hundred ppb (ppb is a unit indicating a concentration of 10 ^-9 ), Cr is mainly converted into hexavalent ions. Exists. Therefore, when corroding a material containing Cr such as stainless steel, the released Cr is unlikely to form a stable Cr compound on the surface, and its stabilization and control of the concentration in water have not been performed.

However, in recent years, especially in BWR plants, C
Attention has been paid to the r behavior, and some results of thermodynamic analysis in a Cr—H ₂ O system have been reported. FIG.
It shows the solubility of the oxide containing chromium at a reactor water temperature of R of 280 ° C., that is, the stability of the oxide. F
The oxide in the form of MCr ₂ O ₄ containing e, Ni, Co and Zn has a lower solubility than Cr ₂ O ₃ , and among them, ZnC
It can be seen that r ₂ O ₄ has the lowest solubility and is stable.

The stainless steel used for the BWR is austenitic, and contains Fe, Ni, and Cr as main components.
Since Co and Zn are contained as impurities, the surface is exposed to Fe, Ni, Cr, C
Chromium oxide containing o and Zn may be spontaneously generated. Under high-temperature water conditions, the stainless steel oxide film has a two-layer structure of a ferrite-based outer layer based on iron oxide and a chromite-based inner layer based on chromium oxide. When a dense chromium film is formed, diffusion of oxygen molecules into the base metal, stainless steel, can be suppressed, and the corrosion rate is reduced. Thereby, stress corrosion cracking and general corrosion are suppressed. In particular, ZnCr ₂ O ₄ is stable under both high and low oxygen partial pressure conditions, and is an ideal film from the viewpoint of suppressing corrosion.

The effect of covering the stainless steel with the ZnCr ₂ O ₄ film from the viewpoint of SCC is as follows.
By the formation of Cr ₂ O ₄ , the appearance of a new surface due to film destruction, which is one mechanism of crack propagation, can be suppressed, and the Cr film of the Cr-deficient layer having SCC sensitivity is formed into ZnCr ₂ O _4. Will reduce SCC susceptibility.

Further, ACP materials represented by Co-60
ZnCr from the viewpoint of adhesion to the material surface ₂O₄The effect of formation
Looking at the effect of suppressing Co-60 uptake by suppressing corrosion
In addition, Co-6 to spinel due to competition between Zn and Co
It is considered that there is also an effect of suppressing 0 uptake. Such a competition
The synergistic effect also applies to Ni, whose ionic radius is relatively close to Co.
In practice, the Ni concentration in the BWR reactor water is maintained at several ppb.
By doing so, the pipe dose rate could be kept low
Examples have been reported.

When chromium is stabilized on the material surface to reduce SCC susceptibility, the secondary effect of hydrogen injection, which is already adopted in some BWR plants as an SCC measure from an environmental point of view, can be reduced. Specifically, the hydrogen injection rate is controlled to a low level within the range where stabilized chromium does not destabilize, so that the turbine system dose rate does not increase,
In addition, it is possible to achieve water quality in which the ACP concentration in the reactor water does not increase.

On the surface of the fuel cladding tube of the BWR, ionic impurities are concentrated near the boiling point, and the concentrations of oxidizing species such as oxygen and hydrogen peroxide are considerably high. Therefore, near the surface of the fuel cladding tube, Cr present as hexavalent ions present in the reactor water may be concentrated, reduced, and precipitated as Cr ₂ O ₃ . However, since Cr ₂ O ₃ is unstable under high oxygen concentration conditions, it dissolves when it goes out of the condition of increasing the concentration due to boiling and returns to hexavalent ions. At the time of dissolving Cr ₂ O ₃ , the surrounding ferrite-based fuel clad is destabilized, ACP typified by Co-60 contained in the fuel clad is eluted, and the ACP concentration in the reactor water is increased. .

However, the dissolution of the fuel clad can be suppressed by changing the precipitation form to ZnCr ₂ O ₄ which is stable even under the condition of high oxygen concentration.
The concentration can be suppressed.

In the BWR, the carry-in of Fe from the water supply has been suppressed as much as possible for the purpose of reducing the exposure dose of the workers during the periodic inspection. This is because Fe has a low solubility under high-temperature water conditions and forms a clad, which becomes a medium for carrying ACP represented by Co-60 to the surface of the primary piping equipment. In BWRs that have started commercial operation relatively recently, the amount of Fe brought in from the feedwater has been reduced since the beginning of operation, and the main impurity in the reactor water is Cr. In high-temperature water, Cr exists as hexavalent ions and has oxidizing power.
It is desirable to control the concentration in water to be low. By controlling the concentration of water in the water to a low level, it is possible to suppress the chromium deposition on the surface of the fuel cladding tube, as described above.
The effect of suppressing the elution of the fuel clad by keeping H high is also obtained.

To reduce the chromium concentration in the reactor water, it is effective to reduce the chromium concentration in the feedwater, that is, to reduce the amount of chromium brought in from the feedwater, and it is important to suppress the generation of chromium due to corrosion of the heat transfer tubes of the high-pressure feedwater heater. is there. Chromium in the heat transfer tube material for high pressure feed water heaters is injected with a very small amount of hydrogen, a method of forming a preliminary oxide film, a method of reducing the linear flow velocity to increase the oxygen diffusion layer, and injecting oxygen from the water supply system. Stabilization can be achieved by any or more of the lower control methods.

[0055]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of a nuclear power plant and a method of operating the same according to the present invention will be described with reference to BWR
Will be described with reference to the drawings.

FIG. 1 is a system diagram illustrating a system configuration of a primary system of a BWR plant for explaining a first embodiment of the present invention.

In this plant, after the steam generated in the reactor 1 passes through the main steam system 2 and works in the turbine 3,
It is led to the condenser 4, cooled and condensed by the condenser 4, returned to water and condensed. This condensate is used as coolant,
The pressure is increased by a high-pressure condensate pump 7, a low-pressure feedwater heater 8, and a high-pressure feedwater heater 9 through a condensate purification system 6.
By 0, water is supplied to the reactor 1 through the water supply pipe.

On the other hand, the reactor water is supplied to the reactor recirculation pump 11.
A part or all of them are forcibly recirculating the reactor recirculation system 12, and a reactor coolant purification system 13 is provided branching from the reactor recirculation system 12. Regarding the reactor water quality, the reactor water sampling system 1 was used to determine the metal concentration, dissolved oxygen concentration, dissolved hydrogen concentration, and hydrogen peroxide concentration in the reactor water.
4 allows monitoring.

In this embodiment, a metal addition system 15 is installed at the outlet of the condensate purification system 6 to control the metal concentration downstream of the injection point, and a non-condensable gas addition system 16 is installed to oxidize the downstream of the injection point. Control the sexual environment. This allows
Stabilizes Cr in the heat transfer tube 17 of the high-pressure feed water heater 9, which is one of the main sources of Cr in the reactor water, and
Elution can be suppressed.

At the same time, while confirming by the reactor water sampling system 14 that the chromium concentration in the reactor water has been reduced, the metal addition system 15 is used to stabilize the chromium oxide on the material surface of the material in the reactor. Adjust the amount of metal added. This makes it possible to suppress the SCC, reduce the reactor water radioactivity concentration, and reduce the amount of radioactivity adhering to the primary system piping and equipment such as the reactor recirculation system 12, and work in the containment vessel 18 during the periodic inspection of the plant. Exposure dose at the time can be suppressed.

That is, in this embodiment, the reactor water sampling system 14 is applied as a corrosion state detecting means for detecting a corrosion state in the piping or equipment of the primary system of the nuclear power plant. Based on the value detected by the reactor water sampling system 14, a Cr deficiency state determination unit (not shown) determines the Cr deficiency state in the pipe or material in the equipment.

When the Cr deficiency in the material exceeds or is predicted to exceed a certain value by the Cr deficiency state determining means, the Cr in the material is stabilized in the piping or the system of the equipment to corrode the material. Supplies substances that suppress chromium
As the stabilizing means, a metal addition system 15 or a non-condensable gas addition system 16 is applied.

In the metal addition system 15, for example, one or more of a metal group consisting of Zn, Ni, Cr, Co, and Fe is applied, and the metal surface is added to the pipe or the material surface in the equipment based on the base material composition ratio. Is also added. By such a metal addition, a compound in the form of MCr ₂ O ₄ (M: one or a mixture of Zn, Ni, Fe, and Co) is formed on the material surface.

FIG. 2 shows the principle of suppressing SCC by stabilizing the Cr in the Cr deficient layer 19 of the heat affected zone having SCC sensitivity.

As shown in FIG. 2, Cr tends to be unevenly distributed at the crystal grain boundaries of the material, and this Cr exerts a tensile stress 20 on the material, and when sufficient oxygen is supplied, a crack at the grain boundary may occur. It melts out in the reactor water in the form of ions, and corrosion progresses in the Cr-deficient layer 19 to generate IGSCC.

[0066] However, in the present embodiment, for example, at the time of plant shutdown, or surface treated Cr-depleted layer surface during plant operation, a stable chromium compound layer such ZnCr ₂ O ₄ (e.g. ZnCr ₂ O ₄₎ 21 Form. Thereby, corrosion is suppressed and the progress of SCC is suppressed. As a method for forming the stable chromium compound layer 21, a method of controlling the metal concentration in water or an oxidizing environment during operation of the plant, and a method of performing surface treatment such as plating and plating when the plant is stopped can be considered. This treatment can be performed only on the weld heat affected zone or on the entire surface of the material in contact with the reactor water in the nuclear reactor 1.

FIG. 3 shows a second embodiment of the present invention.
The plant which performed the chromium stabilization process is shown.

In this embodiment, the main steam pipe radiation monitor 2
2. A feedwater sampling system 23 and a control device 24 are provided. Other configurations are the same as those of the first embodiment shown in FIG.

When a hydrogen injection system is installed as the non-condensable gas addition system 16 for the purpose of plant preventive maintenance,
The main steam pipe monitor 22 fluctuates according to the hydrogen injection amount, and an increase in the turbine system dose rate is detected at a high hydrogen injection amount.

By installing a zinc injection system as the metal addition system 15 and performing Cr stabilization processing during plant operation, Cr on the material surface in the reactor 1 is stabilized,
SCC sensitivity is reduced. In this case, the hydrogen injection amount can be reduced, and the control device 24 analyzes the water quality analysis results in the reactor water sampling system 14 and the feedwater sampling system 23 and the indicated values of the main steam pipe radiation monitor 22, and the metal addition system 15. Thus, it is possible to give feedback to the addition amount of the non-condensable gas addition system 16.

FIGS. 4A and 4B show the principle of the effect of suppressing corrosion by forming ZnCr ₂ O ₄ on the surface of stainless steel. In the untreated state shown in FIG. 4A, iron oxide and Cr ₂ are formed on the stainless steel surface as an inner oxide film.
Although O ₃ is formed, when exposed to water with high dissolved oxygen, Cr becomes ions and dissolves, so that the corrosion of the base material easily proceeds.

On the other hand, as schematically shown in FIG. 4B, when Zn is supplied according to the present embodiment and ZnCr ₂ O ₄ is generated in the oxide film, this is stable, and water with high dissolved oxygen Since it does not dissolve even when exposed to iron, the base material is coated in iron oxide and Zr, Cr ₂ O, and corrosion is suppressed.

FIG. 5 shows a third embodiment of the present invention.
An operation method of chromium-stabilized prefilming will be described.

In a boiling water reactor, boiling occurs on the surface of the fuel rod during normal power operation, so that substances contained in the reactor water adhere or precipitate on the surface of the fuel rod with the boiling. In the method described in the first or second embodiment, the metal is added from the water supply system of the reactor water. Therefore, during the period when the water is supplied to the reactor, that is, during the period when the fuel surface is boiling. This is a method of supplying metal. Therefore, a part of the supplied metal adheres or precipitates on the fuel surface.

For the purpose of stabilizing the chromium oxide on the fuel surface, which is one of the effects of the present invention, boiling of the fuel surface has an effect of amplifying the effect, but stress corrosion cracking of structural materials in the nuclear reactor. When the purpose is to add a metal for suppressing the addition of the metal, it is effective to add the metal under the condition that boiling does not occur in the nuclear reactor.

In the present embodiment, the supplied metal becomes an oxide on the surface of the structural material in the nuclear reactor and exceeds 100 ° C., which is a temperature at which the metal is effectively deposited, and is supplied during a period in which water is not supplied to the nuclear reactor. The chemical supply tank 26 and the chemical supply pump 25 provided at the outlet pipe of the reactor purification system 13 are
This is a method applied as a metal addition device to supply a metal element. The formation of chromium-containing oxides according to the invention requires 10
Temperatures below 100 ° C. are not effective at temperatures below 0 ° C.
It is specified above.

In this embodiment, the metal supply point is the outlet of the reactor purification system 13. However, the same effect can be expected even if the metal addition device is connected to piping or equipment connected to another reactor. it can.

[0078]

As described above, according to the present invention, by stabilizing Cr in structural materials of a nuclear power plant,
It can reduce the SCC susceptibility of the material and achieve preventive maintenance water chemistry with less side effects. In addition, by suppressing the corrosion of materials, it is possible to suppress the deposition of radioactivity on the primary system piping and equipment surfaces, maintain the radioactivity concentration in the reactor water low, and reduce the exposure dose during periodic plant inspections by reducing the dose rate. be able to.

From these facts, it is possible to improve the material integrity of the nuclear power plant and to reduce the exposure dose, so that a highly reliable nuclear power plant and its operating method can be obtained.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a first embodiment of a nuclear power plant according to the present invention.

FIG. 2 is a diagram showing the principle of stabilization of Cr in a Cr-deficient layer according to the present invention.

FIG. 3 is a system diagram showing a second embodiment of the nuclear power plant according to the present invention.

FIGS. 4A and 4B are principle diagrams showing a material corrosion suppression effect by forming ZnCr ₂ O ₄ .

FIG. 5 is a system diagram showing a third embodiment of the nuclear power plant according to the present invention.

FIG. 6 is a principle diagram showing the potential dependence of the solubility of Cr oxide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nuclear reactor 2 Main steam system 3 Turbine 4 Condenser 5 Condenser pump 6 Condensate purification system 7 High-pressure condensate pump 8 Low-pressure feedwater heater 9 High-pressure feedwater heater 10 Feedwater pump 11 Reactor recirculation pump 12 Reactor Circulation system 13 Reactor coolant purification system 14 Reactor water sampling system 15 Metal addition system 16 Non-condensable gas addition system 17 Heat transfer tube 18 Containment vessel 19 Cr-depleted layer 20 Tensile stress 21 Stable Cr compound layer 22 Main steam tube radiation monitor 23 Water supply sampling system 24 Controller 25 Chemical supply pump 26 Chemical supply tank

Claims (16)

[Claims] 1. A corrosive state detecting means for detecting a corrosive state in piping or equipment of a primary system of a nuclear power plant, and a Cr deficiency state in a material in said pipe or equipment based on a value detected by said corrosive state detecting means. Cr deficiency state determining means for determining whether the Cr deficiency amount in the material exceeds or is expected to exceed a predetermined value by the Cr deficiency state determining means. And a Cr stabilizing means for supplying a substance or a potential for suppressing corrosion of the material by stabilizing the material. 2. The nuclear power plant according to claim 1, wherein the corrosion state detecting means detects at least one of a metal concentration, an oxygen concentration, a hydrogen concentration or a hydrogen peroxide concentration in water, and a corrosion potential of a material surface. A nuclear power plant characterized in that: 3. The nuclear power plant according to claim 1, wherein the Cr stabilization processing means controls at least one of a metal concentration, an oxygen concentration, a hydrogen concentration, or a hydrogen peroxide concentration in water or a corrosion potential of a material surface. A nuclear power plant characterized by the fact that: 4. C in a material in a nuclear power plant
A method for operating a nuclear power plant, characterized in that corrosion of the material is suppressed by performing a treatment for stabilizing r. 5. The method for operating a nuclear power plant according to claim 4, wherein Z is a treatment method for stabilizing Cr.
A method for operating a nuclear power plant, comprising adding one or more of a metal group consisting of n, Ni, Cr, Co, and Fe to the surface of the material in an amount larger than a base material composition ratio. 6. The method for operating a nuclear power plant according to claim 5, wherein the addition of the metal causes the surface of the material to have an MC value.
A method for operating a nuclear power plant, comprising forming a compound in the form of r ₂ O ₄ (M: one or a mixture of Zn, Ni, Fe and Co). 7. The method for operating a nuclear power plant according to claim 6, wherein the MCr ₂ O ₄ is formed by:
A method for operating a nuclear power plant, comprising using one or more of surface treatments of plating, painting, lining, thermal spraying, plating, prefilming, and polishing. 8. The method for operating a nuclear power plant according to claim 6, wherein the MCr ₂ O ₄ is formed by:
A method for operating a nuclear power plant, comprising controlling the concentration of any one or a plurality of metals in the water group in contact with a material. 9. The method for operating a nuclear power plant according to claim 8, wherein the control of the metal concentration comprises the step of:
Either or both of the n and Ni concentrations are 0.3 to 100
A method for operating a nuclear power plant, wherein the method is controlled to ppb. 10. The method for operating a nuclear power plant according to claim 8, wherein, as said metal concentration control, Zn and Cr are simultaneously or alternately injected into a primary system, and an oxidation containing Zn and Cr on the surface of the material surface. A method for operating a nuclear power plant, characterized by stabilizing a product. 11. The method for operating a nuclear power plant according to claim 8, wherein the metal concentration control is performed in a reactor water.
A method for operating a nuclear power plant, comprising controlling an r concentration of 5 ppb or more and a Zn concentration of furnace water to 2 ppb or more to stabilize an oxide containing Zn and Cr on a material surface. 12. The method for operating a nuclear power plant according to claim 4, wherein the method for stabilizing the Cr includes:
A method for operating a nuclear power plant, comprising controlling one or more of a corrosion potential of a material surface, an oxygen concentration in water, a hydrogen concentration in water, and a hydrogen peroxide concentration in water to control a redox environment. 13. The method for operating a nuclear power plant according to claim 12, wherein elution of Cr from a material surface is suppressed by controlling the oxidation-reduction environment. 14. The method for operating a nuclear power plant according to claim 12, wherein, as the control of the material surface corrosion potential, the corrosion potential of stainless steel exposed to reactor water during operation of the nuclear power plant is 0.1 V or less. A method for operating a nuclear power plant, comprising: 15. The method for operating a nuclear power plant according to claim 12, wherein the surface treatment, the metal concentration control, and the oxidizing environment control are performed to stabilize Cr in the material. How the plant operates. 16. The method for operating a nuclear power plant according to claim 12, wherein the method for stabilizing the Cr includes controlling the oxidizing environment after forming MCr ₂ O ₄ by controlling the metal concentration to thereby control the Cr in the reactor water. A method for operating a nuclear power plant, wherein the concentration is controlled to 1 ppb or less.