JPH06167596A - Corrosion suppression method and device for reactor primary system structure material - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to prevent corrosion of a BWR primary system constituent material and to reduce radioactivity accumulation of the BWR primary system, which in turn reduces employee exposure. [Structure] A method and an apparatus for suppressing corrosion of a reactor primary system constituent material according to the present invention include a hydrogen injection mechanism 16 for injecting hydrogen into system water of a boiling water reactor primary system, which is necessary for countermeasures against stress corrosion cracking. An iron injection mechanism (24) for measuring the radioactivity concentration in the system water and injecting iron into the system water so that the radioactivity concentration becomes a predetermined value or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inhibiting corrosion of a primary reactor system constituent material by injecting hydrogen into a BWR primary system as a countermeasure for suppressing corrosion of a boiling water reactor (hereinafter referred to as BWR) primary constituent material. Regarding the device.

[0002]

2. Description of the Related Art A nuclear reactor power plant coolant is in a state of high temperature and high pressure water, and a plant structural material is under extremely severe environmental conditions. Under the above conditions, the corrosion behavior of materials becomes an important issue, and stress corrosion cracking (hereinafter referred to as SCC) of austenitic stainless steel piping is of great concern inside and outside the BWR plant. Has become the target.

This phenomenon of SCC is generally considered to occur when three factors, namely, material, stress, and environment are superimposed. In the newly established BWR nuclear power plant, it is necessary to pay sufficient attention to the above three factors and prepare for stress corrosion cracking.

However, since it is difficult to take measures in terms of materials and stress in the existing nuclear power plant, it has been attempted to take measures from the environmental aspect. The dissolved oxygen concentration in the reactor water is the largest factor causing SCC on the environment side.

Since oxygen is generated in the core by radiolysis of water, it is unavoidable that about 200 to 300 ppb of oxygen is dissolved in the reactor water. At the reactor temperature (285 ° C), the dissolved oxygen around 200 ppb is a sufficiently significant level for SCC, and the control of the dissolved oxygen concentration is important for plant operation.

Therefore, as a countermeasure against SCC, a hydrogen injection technique into a nuclear reactor has been developed and is being put to practical use in some plants. This technique is intended to suppress the generation of oxidizing chemical species such as oxygen and hydrogen peroxide by injecting and dissolving a small amount of hydrogen in feed water. When the reactor water is made into an appropriate reducing atmosphere by hydrogen injection, the recombination reaction of oxygen and hydrogen peroxide with hydrogen in water is accelerated in the presence of radiation. An example of hydrogen injection technology in an existing plant (Dresden No. 2 reactor in the United States) will be described with reference to FIG.

This figure is a system diagram of a primary reactor system for hydrogen injection. That is, the steam generated in the core 1 works in the turbine 2 and is then guided to the condenser 3 where it is cooled and condensed to be condensed water. This condensate goes through a pump 4, a condensate purification system 5, a high-pressure condensate pump 6, a feed water heater 7,
The reactor pressure vessel 9 is heated and pressurized by the water supply pump 8.
Injected inside. In the figure, 10 is a recirculation pump of the nuclear reactor recirculation system, which forcibly recirculates the reactor water in the reactor pressure vessel 9 to increase the core flow rate.

Further, a reactor coolant purification system is branched from the reactor recirculation system, and reactor water is supplied to the reactor coolant purification pump 1.
1. After passing through the reactor coolant purification system regenerative heat exchanger 12 and the non-regeneration heat exchanger 13, after being purified by the reactor coolant purification system 14, it is returned to the water supply system.

In the primary system of the above construction, hydrogen is injected from the hydrogen injection mechanism 16 into the injection point 15 located downstream of the condensate purification system 5 and upstream of the high-pressure condensate pump 6. In many cases other than the illustrated existing plants, hydrogen is often injected from the injection point 15 described above.

FIG. 3 also shows a gas waste treatment system for the gas discharged from the condenser 3. The off-gas (gas) carried out from the condenser 3 is processed by the off-gas recombiner 19 via the air extractor 17 and the off-gas preheater 18, and reaches the gaseous waste treatment system through the off-gas condenser 20. The oxygen injection point 21 is normally located between the air extractor 17 and the off-gas preheater 18, and oxygen is injected from the oxygen injection mechanism 22.

FIG. 4 shows Dresden No. 2, Peach Bottom 3
Is a diagram showing the test results of the effect of reducing the dissolved oxygen concentration by hydrogen injection in the existing US plants such as No., Pilgrim, Fitzpatrick, etc., where the vertical axis is the dissolved oxygen concentration (ppb) in the sample reactor water collected by the recirculation system, The abscissa shows the concentration of dissolved hydrogen in the water supply (ppm).

From this figure, it is understood that although the oxygen concentration reducing effect differs depending on the plant, the dissolved oxygen concentration in the reactor water decreases as the hydrogen concentration in the feed water increases.

As is clear from the above, the fact that the concentration of dissolved oxygen in the reactor water can be lowered by hydrogen injection has been proved in actual equipment, and is effective as an SCC measure from the environmental aspect.

In this hydrogen injection technique, the oxygen and hydrogen generated by radiolysis in the core return to water by the recombination reaction, but the amount of hydrogen injected from the outside corresponds to excess hydrogen in the gaseous waste treatment system. Is discharged. This surplus hydrogen needs to be recombined in the gas waste treatment system for safety, and normally, oxygen is injected into the gas waste treatment system, and the excess hydrogen and the gas waste treatment system are injected in the off-gas recombiner 19. It is treated by reacting with oxygen. Thus, in the conventional hydrogen injection technique, hydrogen is injected from the water supply system on the one hand, and oxygen is injected on the other hand in the gaseous waste treatment system.

[0015]

It has already been shown in FIG. 4 that the concentration of dissolved oxygen in the reactor water is reduced when hydrogen is injected in the conventional BWR nuclear power generation facility. However, in the plant in which this hydrogen injection is carried out, in recent years, there has been a problem that the radioactivity concentration of Co-60 or the like in the reactor water increases. An example of this is shown in FIG.
That is, FIG. 5 shows that the Co-60 radioactivity concentration in the reactor water increased after the hydrogen injection was started in the new pressure tube type converter. The cause is considered as follows.

When hydrogen is injected into the BWR primary system in a reducing atmosphere, metal oxides (eg, iron oxides) are reduced with the passage of time, causing a change in chemical form. Now, when the metal element is represented by M, an example of the morphological change is represented as follows.

[0017]

[Equation 1] M ₂ ^III O ₃ → M ₃ O ₄ (M ^II O ・ M ₂ ^III O ₃ ) ... (1) where II: metal element having an oxidation number of divalent III: metal element having an oxidation number of trivalent

For example, in the case of an oxide of iron, Fe ₂ O ₃ (hematite) is predominant during normal operation, but part of it is converted to Fe ₃ O ₄ (magnetite) during hydrogen injection. . Magnetite has a higher solubility in high-temperature water than hematite, and hydrogen injection increases the tendency of iron oxide to dissolve. On the other hand, the radioactivity such as Co-60 or Co-58 is incorporated in the iron oxide or the corrosion oxide film because it is the same transition metal as Fe as the element. When the dissolved tendency of iron oxide increases during hydrogen injection, these radioactivity are also released into the reactor water, which causes a problem that the radioactivity concentration in the reactor water increases.

The present invention has been made based on the above circumstances, and an object thereof is to inject hydrogen into system water of a BWR primary system and iron into system water to prevent corrosion of a BWR primary system constituent material. In addition, it is an object of the present invention to provide a method and an apparatus for suppressing corrosion of a nuclear reactor primary system constituent material, which can suppress the accumulation of radioactivity in the BWR primary system and thus can reduce the radiation exposure of employees.

[0020]

In order to achieve the above object, in the present invention, an amount of hydrogen required for countermeasures against stress corrosion cracking is injected into system water of a boiling water reactor primary system, and this system water is injected. To provide a method for inhibiting corrosion of a reactor primary system constituent material, which comprises injecting an appropriate amount of iron into the system water so that the radioactivity concentration is measured to be below a predetermined value, and boiling water is provided. Injection means for injecting hydrogen necessary for countermeasures against stress corrosion cracking into system water of primary reactor system, iron injection means for injecting iron into the system water, and measuring means for measuring radioactivity concentration in the system water Provided is a device for suppressing corrosion of a reactor primary system constituent material, which further comprises, from the iron injecting means so that the radioactivity concentration measured by the measuring means becomes a predetermined value or less. Iron injection amount control device to control injection amount The providing corrosion inhibiting device of the reactor primary system configuration material characterized by comprising.

[0021]

With this configuration, in a nuclear power plant that is injecting hydrogen, the concentration of radioactivity in reactor water is constantly monitored, and if a rising tendency is observed, BW
Iron is injected into the R primary system. In a BWR plant, when a small amount of iron is injected when ionic radioactivity such as Co-60 or Co-58 is increased, iron takes a clad-like form, and thus captures an ionic radioisotope,
It is possible for itself to be filtered by the condensate purification system to reduce the radioactivity concentration in the reactor water. This makes it possible to prevent corrosion of the BWR primary system constituent material and prevent accumulation of radioactivity in the BWR primary system.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the embodiments shown in the drawings.

FIG. 1 is a system diagram showing a first embodiment of the present invention and a part of a primary reactor system for hydrogen injection and a gaseous waste treatment system. That is, in the reactor primary system, steam generated in the core 1 works in the turbine 2 and then the condenser 3
And is condensed and cooled in the condenser 3 to be condensed water.
This condensate is heated by a high-pressure condensate pump 6, a feedwater heater 7, and a feedwater pump 8 via a pump 4 and a condensate purification system 5.
It is pressurized and injected into the reactor pressure vessel 9. In the figure, 10 is a recirculation pump of the nuclear reactor recirculation system, which forcibly recirculates the reactor water in the reactor pressure vessel 9 to increase the core flow rate.

A reactor coolant purification system is branched from the reactor recirculation system, and reactor water is used as a reactor coolant purification pump 1.
1. After passing through the reactor coolant purification system regenerative heat exchanger 12 and the non-regeneration heat exchanger 13, after being purified by the reactor coolant purification system 14, it is returned to the water supply system.

In the primary reactor system having the above structure, hydrogen is injected from the injection point 15 located downstream of the condensate purification system 5 and upstream of the high-pressure condensate pump 6 from the hydrogen injection mechanism 16. In many cases, other than the illustrated existing plant, injection is performed from the injection point 15 described above.

In this hydrogen injection technique, it is necessary to recombine surplus hydrogen with a gas waste system (off-gas system). Normally, oxygen is injected into the gas waste treatment system,
In the off-gas recombiner, excess hydrogen and off-gas system injected oxygen are reacted and treated.

FIG. 1 also shows the configuration of the gaseous waste treatment system. The off gas discharged from the condenser 3 is treated by the off gas recombiner 19 after passing through the air extractor 17 and the off gas preheater 18. , Through the off-gas condenser 20 for gaseous waste treatment.

In such a BWR nuclear power plant, according to the present invention, as shown in FIG. 1, the iron injection in the feed / condensation system located at the downstream side of the condensate purification system 5, that is, in the place where the system pressure is the lowest in the feed / condensation system. From point 23, an appropriate amount of iron is injected through the iron injection device 24. This iron may be either soluble or insoluble. In addition, the water supply / condensation system iron injection point
As for 23, any point downstream of the condensate purification system 5 may be used. The amount of iron injection is determined by monitoring the radioactivity concentration in the reactor water, and it should be controlled so as not to exceed the radioactivity concentration before hydrogen injection.

Next, the operation of this embodiment having such a configuration will be described. Hydrogen is injected into the system water of the BWR primary system by the hydrogen injection mechanism 16. The radioactivity concentration in the reactor water of the BWR primary system is constantly monitored. If an increase in the reactor water radioactivity concentration is observed as a result of hydrogen injection into the system water, it is soluble or insoluble in the BWR primary system from the iron injection mechanism 24 via the feed / condensation system iron injection point 23. Sex iron is injected. In a BWR plant, when a small amount of iron is injected when iron-like radioactivity such as Co-60 or Co-58, which is the main cause of the increase in radioactivity concentration in reactor water, rises, iron forms a clad-like form. Ionic radioisotope C for collection
O-60 or Co-58 can be captured and filtered by the condensate purification system 5 to reduce the radioactivity concentration in the reactor water. This has been demonstrated in the BWR plant as a so-called Ni / Fe ratio control for controlling the ratio between the Ni ion concentration and the Fe clad concentration in the feed water to reduce the reactor water activity concentration.

As described above, according to this embodiment, hydrogen is injected into the system water of the BWR primary system, and iron is injected into the system water to prevent corrosion of the BWR primary system constituent material and to radiate the radiation in the BWR primary system. It is possible to prevent the accumulation of energy. Next, a second embodiment of the present invention will be described with reference to FIG.

In order to more appropriately inject iron into the BWR primary system, it is desirable to constantly monitor the radioactivity concentration in the reactor water and apply feedback. A second embodiment in consideration of this point is shown in FIG. In FIG. 2, the same parts as those in the first embodiment are designated by the same reference numerals, the description of the overlapping parts will be omitted, and only the essential parts will be described. That is, in this second embodiment, a water quality measuring device 25 is provided in the reactor coolant purification system, and the water concentration measuring device 25 constantly monitors the concentration of radioactive water in the reactor water, and this value does not deviate from the range during normal operation. So, iron injection amount control device 26
Injection of iron into the BWR primary system via. Also in the second embodiment, it is possible to obtain the same effect as that of the first embodiment.

[0032]

As described above, according to the method and the apparatus for suppressing corrosion of the reactor primary system constituent material according to the present invention,
Hydrogen is injected into the system water of the BWR primary system, and iron is injected into this system water to prevent corrosion of the BWR primary system constituent materials and suppress the accumulation of radioactivity in the BWR primary system, which in turn reduces the radiation exposure of employees. Can be achieved.

[Brief description of drawings]

FIG. 1 is a system diagram of a reactor primary system according to a first embodiment of the present invention.

FIG. 2 is a system diagram of a reactor primary system according to a second embodiment of the present invention.

FIG. 3 is a system diagram of a conventional primary reactor system.

FIG. 4 is a characteristic diagram showing reduction of oxygen concentration in reactor water by conventional hydrogen injection.

FIG. 5 is a characteristic diagram showing changes in soluble Co-60 radioactivity concentration in reactor water before and after conventional hydrogen injection.

[Explanation of symbols]

 1 ... Core 2 ... Turbin 3 ... Condenser 5 ... Condensate purification system 9 ... Reactor pressure vessel 16 ... Hydrogen injection mechanism 18 ... Off-gas preheater 24 ... Iron injection mechanism 25 ... Water quality measurement device 26 ... Iron injection amount Control device

Claims (3)

[Claims] 1. The amount of hydrogen required to prevent stress corrosion cracking is injected into the system water of the boiling water reactor primary system, the radioactivity concentration in the system water is measured, and this radioactivity concentration falls below a predetermined value. A method for inhibiting corrosion of a reactor primary system constituent material, which comprises injecting an appropriate amount of iron into the system water as described above. 2. Hydrogen injecting means for injecting hydrogen required for countermeasures against stress corrosion cracking into system water of a boiling water reactor primary system,
An apparatus for inhibiting corrosion of primary reactor system constituent materials, comprising: iron injection means for injecting iron into the system water; and measurement means for measuring a radioactivity concentration in the system water. 3. An iron injection amount control device for controlling the injection amount of iron from the iron injection device so that the radioactivity concentration measured by the measurement device becomes a predetermined value or less. Item 2. A corrosion inhibitor for a primary reactor constituent material according to Item 2.