JPH08297195A - Radioactivity reducing method for nuclear power plant - Google Patents

Abstract

PURPOSE: To suppress the corrosion of the constituting members of a nuclear power plant and reduce radioactivity without being adversely affected by zinc 65 by injecting Zm having bivalent cations in the reactor cooling water, adjusting the pH value of the cooling water to a specific value, and injecting hydrogen into the reactor cooling water. CONSTITUTION: The pH of the cooling water is made alkaline when Zn is injected into the cooling water, then Zn is easily absorbed into an oxide film on the surfaces of constituting members, and the oxide film is made more stable. The effect on the corrosion suppression of the constituting members and the reduction of radioactivity becomes remarkable, and the quantity of the Zn required for the same effect can be reduced. The pH value is preferably set to the range of 7-9, more preferably to the range of 8-9. When hydrogen is injected, Zn and Cr form a stable composite compound ZnCY2 O4 in the oxide film on the surfaces of the constituting members, the oxide film becomes more stable, and the effect on the corrosion suppression of the constituting members and the reduction of radioactivity is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear power plant, and a method for suppressing corrosion of a metal component of a nuclear power plant in contact with a reactor cooling water containing a radioactive material to reduce radioactivity of the nuclear power plant. In particular, the present invention relates to a method for suppressing corrosion of a constituent member used in contact with a solution in which a radioactive substance is dissolved, such as a primary cooling system pipe, and a method for suppressing adhesion of the radioactive substance.

[0002]

2. Description of the Related Art Pipes, pumps, valves, etc. used in a primary cooling system of a BWR plant are made of stainless steel, stellite, etc. (hereinafter abbreviated as "components").

When these metals are used for a long time, they are corroded and damaged, and constituent metal elements are eluted into the reactor cooling water (hereinafter referred to as cooling water) and brought into the reactor.

Most of the eluted metal elements become oxides and adhere to the fuel rods and are irradiated with neutrons. As a result, cobalt 6
Radionuclides such as 0, cobalt 58, manganese 54, and chromium 51 are produced.

These radionuclides are re-eluted and float as ions or insoluble solid components (hereinafter abbreviated as cladding).

A part of it is removed by a demineralizer for purifying the reactor water, and the rest adheres to the surfaces of the constituent members while circulating in the primary cooling water system.

As a result, the dose rate on the surface of the constituent members becomes high, and there has been a problem of radiation exposure of workers during maintenance and inspection.

In order to reduce the amount of radioactive substances deposited, a method of suppressing the elution of the metal element that is the source has been proposed.

For example, there is a method of using a material having good corrosion resistance or a method of injecting oxygen into a water supply system to suppress corrosion of constituent members.

However, whichever method is used, it is not possible to sufficiently suppress the corrosion of the components of the primary cooling water system including the water supply system, and it is not possible to sufficiently reduce the radioactive substances in the primary cooling water. , The surface dose rate was increasing due to the deposition of radioactive materials on the components.

For this reason, for example, methods for reducing radioactivity in nuclear power plants have been proposed, such as those disclosed in Japanese Patent Laid-Open Nos. 61-95290 and 63-172999.

[0012]

Of the above-mentioned conventional techniques,
The one described in Japanese Patent Application Laid-Open No. 61-95290 suppresses the adhesion of cobalt 60 to the surfaces of the constituent members by injecting Zn. However, when Zn is injected, the adhesion of cobalt 60 to the surface of the constituent members is suppressed, but the natural Zn
Since zinc 64, which accounts for about 50% of the above, is irradiated with neutrons in a nuclear reactor and zinc 65 which is a radioisotope is generated, the dose rate of a nuclear power plant may be rather high.

Further, the one described in JP-A-63-172999 uses Zn-6 that isotope-separated to obtain Zn-6.
Although the increase in the dose rate due to No. 5 is suppressed, isotope-separated Zn is very expensive, and this method has a problem that the effect does not last unless Zn is continuously injected.

It is an object of the present invention to provide a method for suppressing corrosion of components of a nuclear power plant and reducing radioactivity without adversely affecting zinc 65.

[0015]

A method for reducing radioactivity in a nuclear power plant according to the present invention suppresses corrosion of metal components of the nuclear power plant that come into contact with the reactor cooling water containing radioactive substances, thereby suppressing the corrosion of the nuclear power plant. In the method for reducing radioactivity, the divalent cation Zn is injected into the reactor cooling water, and the pH value of the reactor water is adjusted to 7-9.

The method of reducing the radioactivity of a nuclear power plant according to the present invention is a method of reducing the radioactivity of a nuclear power plant by suppressing the corrosion of metal components of the nuclear power plant that come into contact with the reactor cooling water containing radioactive substances. Zn, which is a divalent cation, is injected into the reactor cooling water, the pH value of the reactor water is adjusted to 7 to 9, and hydrogen is injected into the reactor cooling water.

In the method for reducing radioactivity in a nuclear power plant of the present invention, the Zn concentration which is a divalent cation injected into the reactor water is adjusted according to the pH value, and the Zn concentration is set to 50 ppb or less. Is desirable.

The method of reducing radioactivity in a nuclear power plant of the present invention controls the hydrogen concentration in reactor water to 0 to 1000 ppb, and adjusts the pH.
Inject into the reactor water according to the value and hydrogen concentration of the reactor water 2
It is desirable to adjust the Zn concentration, which is a valent cation.

In the method for reducing radioactivity of a nuclear power plant of the present invention, it is desirable that the metal to be injected is isotope-removed zinc, which is a divalent cation except zinc 64.

In the method for reducing radioactivity of a nuclear power plant of the present invention, it is desirable that the metal to be injected be divalent cation Ni.

The method of reducing the radioactivity of a nuclear power plant according to the present invention is a method of reducing the radioactivity of a nuclear power plant by suppressing the corrosion of metal components of the nuclear power plant that come into contact with the reactor cooling water containing radioactive substances. , Hydrogen is injected into reactor cooling water, and Zn is a divalent cation
Is intermittently injected and the pH value of the reactor water is adjusted to 7-9.

[0022]

When injecting Zn into the cooling water, if the pH of the cooling water is made alkaline, Zn is more likely to be taken into the oxide film on the surface of the constituent member and stabilizes the oxide film.
The effect of suppressing corrosion of components and reducing radioactivity becomes remarkable,
A small amount of Zn is required to obtain the same effect.

At this time, the pH value is preferably in the range of 7 to 9, and more preferably in the range of 8 to 9.

When hydrogen is further injected, Zn forms a stable complex oxide Z with Cr in the oxide film on the surfaces of the constituent members.
The oxide film becomes more stable due to the formation of nCr ₂ O ₄ ,
The effects of suppressing corrosion of components and reducing radioactivity are increased. The formation of ZnCr ₂ O ₄ suppresses the re-elution of Zn into the cooling water. Therefore, even if the injection of Zn is stopped midway, the effects of suppressing adhesion and reducing radioactivity can be maintained for a long time.

The Zn concentration which is a divalent cation injected into the reactor water is adjusted according to the pH value, and the Zn concentration is adjusted to 50.
By setting the content to ppb or less, the Zn implantation amount can be reduced while maintaining the corrosion suppression and radioactivity reduction effects.

By controlling the hydrogen concentration in the reactor water to 0 to 1000 ppb and adjusting the Zn concentration, which is a divalent cation injected into the reactor water, in accordance with the pH value and the hydrogen concentration in the reactor water, further corrosion can be achieved. Z while maintaining suppression and radioactivity reduction effects
The n implantation amount can be reduced.

By using divalent cation isotope-removed zinc excluding zinc 64 as the metal to be injected, the effects of suppressing corrosion and reducing radioactivity can be enhanced.

Even if the metal to be injected is Ni, which is a divalent cation, the same effect as zinc can be obtained. When hydrogen is injected into the reactor cooling water and Zn, which is a divalent cation, is injected intermittently, the same effect can be obtained.

[0029]

【Example】

 (Example 1) An example of the present invention will be described below.

First, as data for examining the amount of corrosion,
Stainless steel was used. This stainless steel was immersed in high temperature water for 1000 hours, and the relationship between the corrosion amount, pH value and Zn concentration was investigated.

At this time, the dissolved oxygen concentration (DO) was set to 200 pp.
b (hereinafter referred to as water quality) and the temperature was 288 ° C.

The results of this experiment are shown in FIG. Here, the amount of corrosion is a relative value when the case where Zn is not injected at neutral is set to 1.

From the results shown in FIG. 1, it was found that the corrosion inhibiting effect of stainless steel became remarkable by controlling the pH value from neutral to alkaline at pH 8 and pH 9 under the Zn injection condition.

In particular, the effect obtained at a Zn concentration of 50 ppb in the case of neutrality is about 0.7 in relative corrosion, but p
In the case of H9, the Zn concentration that achieves the same effect is about 10 ppb, and it was found that the amount of injected Zn that achieves the same effect can be reduced.

Further, when the Zn concentration was 50 ppb and the pH was 9, the corrosion amount was less than 1/2 of the normal water quality, and it was found that the corrosion inhibiting effect of stainless steel was improved.

Next, the effect of reducing the amount of cobalt deposited was investigated.

In the above test, the relationship between the amount of cobalt 60 adhering to stainless steel, the pH value, and the Zn concentration was investigated in the presence of cobalt 60 ions.

The results are shown in FIG. Here, the adhesion amount of cobalt 60 is a relative value when the case where Zn is not injected at neutral is set to 1.

As shown in FIG. 2, with respect to the effect of reducing the amount of cobalt 60 deposited, the effects of alkalizing and Zn implantation show the same tendency as that of the amount of corrosion.

The effect is more remarkable than the amount of corrosion.
In the case of H9, the adhesion amount was halved when the Zn concentration was about 13 ppb, and the adhesion amount was reduced to 1/4 when the Zn concentration was about 4 ppb.

As described above, according to the present invention, the amount of deposited cobalt was reduced.

In the above test, the effect of Zn implantation for reducing the adhesion of cobalt 60 ions was shown as a relative value with 288 ° C., a dissolved oxygen concentration (DO) of 200 ppb and no Zn implantation as a reference value 1. It shows in Table 1.

[0043]

[Table 1]

In Table 1, cobalt 60 ion attachment is 1 /
The reduction conditions of 2 were summarized by the combination of pH value and Zn concentration.

According to this, the required concentration of Zn at pH 7 is 50 ppb, but at pH 8 it is 15 ppb and at pH 9 it is 5 ppb.
It can be seen that the effect of reducing ion attachment can be obtained.

As described above, according to the present embodiment, it is possible to improve the effect of reducing the adhesion of cobalt 60 and the effect of suppressing corrosion, and even if a small amount of Zn is injected, cobalt 60 can be provided as compared with the conventional case.
It was found that the effect of reducing the adhesion and the effect of suppressing corrosion can be expected, and the Zn injection amount can be reduced.

Although divalent cation Zn was injected in the above, similar results can be obtained by injecting isotope-removed zinc excluding zinc 64 or divalent cation Ni instead. It was

Example 2 The hydrogen concentration (DH) was changed in the same manner as in Example 1.

FIG. 3 shows the relationship between the amount of corrosion of stainless steel and the pH and Zn concentration when 1000 ppb of hydrogen was injected (hereinafter referred to as hydrogen injected water quality).

From FIG. 3, even under the hydrogen-injected water quality, the pH
It can be seen that when the value is adjusted to alkali, the Zn injection effect is increased with respect to the corrosion inhibition of stainless steel.

FIG. 4 shows the relationship between the amount of cobalt 60 adhering to the stainless steel and the pH value and Zn concentration in the test under the hydrogen-injected water quality in the presence of cobalt 60 ions.

At this time, the amount of cobalt 60 deposited was such that the hydrogen concentration (DH) was 1000 ppb and the dissolved oxygen concentration (DO) was 0.
It is a relative value with the amount of adhesion at ppb being 1.

It can be seen from FIG. 4 that the effect of reducing the amount of cobalt 60 deposited is similar to the effect of alkalizing and Zn implantation on the amount of corrosion, but a more remarkable effect is recognized.

Further, when comparing the normal water quality and the hydrogen-injected water quality, it can be seen that the effect of suppressing the adhesion of cobalt 60 is significantly higher in the hydrogen-injected water quality.

In the above test, Zn-implanted cobalt 6
0 ion adhesion reduction effect, 288 ℃, dissolved oxygen concentration 20
Table 2 shows relative values with 0 ppb and no Zn implantation as the reference value 1.

[0056]

[Table 2]

In Table 2, cobalt 60 ion attachment is 1 /
The reduction conditions of 2 are summarized by the combination of pH and Zn.

According to this, under the normal water quality of the temperature of 288 ° C. and the dissolved oxygen concentration of 200 ppb, the required concentration of Zn at pH 7 is 50 ppb. It becomes 5 ppb at pH 8 and 1 ppb at pH 9, and the effect of reducing the adhesion of cobalt 60 ions is obtained at a Zn concentration level which is significantly lower than that under normal water quality.

As described above, according to the present embodiment, it is possible to improve the effect of reducing the adhesion of cobalt 60 and the effect of suppressing corrosion, and even if a small amount of Zn is injected, the amount of cobalt 60 can be increased as compared with the prior art.
It was found that the effect of reducing the adhesion and the effect of suppressing corrosion can be expected, and the Zn injection amount can be reduced.

Although divalent cation Zn was injected in the above, similar results can be obtained by injecting isotope-removed zinc excluding zinc 64 or divalent cation Ni instead. It was

(Example 3) Next, an example of continuous injection and intermittent injection of Zn injection will be described.

FIG. 5 shows Co in stainless steel when Zn is injected intermittently in normal water quality and hydrogen injection water quality.
3 is a graph showing a change with time of the adhered amount of.

From FIG. 5, in the normal water quality, when the Zn injection is stopped, the adhered amount of Co increases rapidly, whereas
It can be seen that under the hydrogen injection conditions, the effect of suppressing Co deposition continues even after Zn injection is stopped.

From the above, in the Zn injection in the actual machine, intermittent operation such as injection every other day, injection for one week, or no injection for one week becomes possible instead of continuous injection, and the required amount of injected metal is reduced. Can be achieved.

Further, conventionally, when Zn implantation is stopped due to a failure of the Zn implanting device or the like, it is difficult to suppress the adhesion of Co, and no consideration has been given to an accident, but in the present invention, It was found that the effect of suppressing Co adhesion can be maintained even when Zn injection is stopped due to a failure of the Zn injection device or the like.

Although divalent cation Zn was injected in the above, similar results can be obtained by injecting isotope-removed zinc excluding zinc 64 or divalent cation Ni instead. It was

[0067]

As described above, according to the present invention, by making the pH value of the reactor cooling water alkaline and injecting Zn, it is possible to improve the effect of reducing the adhesion of cobalt 60 and the effect of suppressing corrosion. Therefore, it was found that the effect of reducing the adhesion of cobalt 60 and the effect of suppressing corrosion can be expected even with a small amount of Zn injection, and the Zn injection amount can be reduced.

Further, if hydrogen injection is also used, the effect is maintained even if Zn injection is stopped, so that the increase in radioactivity due to zinc 65 can be suppressed.

Further, even when the Zn implantation is stopped due to a failure of the Zn implantation apparatus or the like, the effect of suppressing Co adhesion can be maintained.

It was found that the same result was obtained by injecting isotope-removed zinc except for zinc 64 or Ni as a divalent cation.

[Brief description of drawings]

FIG. 1 is an embodiment of the present invention, the amount of corrosion, pH value and Z
The relationship of n concentration is shown.

FIG. 2 shows the relationship between the amount of deposited cobalt 60, the pH value, and the Zn concentration, which is an example of the present invention.

FIG. 3 is an embodiment of the present invention, the amount of corrosion, pH value and Z
The relationship of n concentration is shown.

FIG. 4 shows the relationship between the amount of cobalt 60 deposited, the pH value, and the Zn concentration, which is an example of the present invention.

FIG. 5 shows a change over time in the amount of Co deposited when Zn is intermittently injected.

[Explanation of symbols]

 1 ... Standard value.

Front Page Continuation (72) Inventor Hiroshi Yamauchi 7-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Kazuhiko Akamine 3-1-1, Saiwaicho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd., Hitachi Plant (72) Inventor, Koichi Yamane 3-1-1, Saiwaicho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd., Hitachi Plant

Claims (7)

[Claims] 1. A method for reducing radioactivity in a nuclear power plant, which suppresses corrosion of metal components of a nuclear power plant in contact with reactor cooling water containing a radioactive substance, and divalent cations in the reactor cooling water. Zn is injected and the pH value of the reactor water is adjusted to 7 to 9 to reduce the radioactivity in the nuclear power plant. 2. A divalent cation in the reactor cooling water in a method for reducing radioactivity in a nuclear power plant, which suppresses corrosion of metal components of the nuclear power plant that come into contact with the reactor cooling water containing radioactive substances. Zn is injected, the pH value of the reactor water is adjusted to 7 to 9, and hydrogen is injected into the reactor cooling water. A method for reducing radioactivity in a nuclear power plant. 3. The Zn concentration which is a divalent cation injected into the reactor water is adjusted in accordance with the pH value, and the Zn concentration is adjusted to 50.
ppb or less, Claim 1 or Claim 2 characterized by the above-mentioned.
Radioactivity reduction method for nuclear power plants described in. 4. The hydrogen concentration in the reactor water is controlled to 0 to 1000 ppb, and the Zn concentration which is a divalent cation injected into the reactor water is adjusted according to the pH value and the hydrogen concentration in the reactor water. The method for reducing radioactivity of a nuclear power plant according to any one of claims 1 to 3. 5. The method for reducing radioactivity of a nuclear power plant according to claim 1, wherein the metal to be injected is divalent cation isotope-removed zinc excluding zinc 64. The characteristic method of reducing radioactivity in nuclear power plants. 6. The method for reducing radioactivity of a nuclear power plant according to any one of claims 1 to 4, wherein the metal to be injected is divalent cation Ni. Noh reduction method. 7. A method for suppressing radioactivity of a nuclear power plant that is in contact with a reactor cooling water containing a radioactive substance, and injecting hydrogen into the reactor cooling water in a method of reducing radioactivity in a nuclear power plant, In addition, Zn, which is a divalent cation, is intermittently injected, and the pH value of the reactor water is adjusted to 7
A method for reducing radioactivity in a nuclear power plant, characterized by adjusting to ~ 9.