WO1996022605A1

WO1996022605A1 - Nuclear power plant and method for operating the same

Info

Publication number: WO1996022605A1
Application number: PCT/JP1995/000040
Authority: WO
Inventors: Naoto Uetake; Hideyuki Hosokawa; Makoto Nagase
Original assignee: Hitachi, Ltd.
Priority date: 1995-01-18
Filing date: 1995-01-18
Publication date: 1996-07-25
Also published as: JP3179500B2

Abstract

A metallic ion easily forming a corundum construction is continuously left in a primary system cooling water during the operation of a nuclear reactor so as to prevent the deposition on the internal surface of a primary system cooling water piping of a divalent cobalt ion of cobalt-60 or cobalt-58 which is a main constituent of a radioactive nuclide which deposits on the piping when it forms a ferrite containing cobalt, thereby making it possible to securely reduce the dose of the piping.

Description

Specification

Nuclear plant and its operation method

The present invention relates to a plant operating method, and more particularly to a plant operating method suitable for a nuclear plant using light water or heavy water as a coolant, and a nuclear plant implementing the plant. Background art

In a nuclear power plant, radionuclides generated by neutron irradiation in a nuclear reactor adhere to the primary cooling system piping, etc., and cause workers to be exposed to radiation during regular inspections. For this reason, various methods are being studied to prevent the attachment of radionuclides to pipes.

As one of such methods, Japanese Patent Application Laid-Open No. 62-24195 discloses a technique in which a stable preliminary oxide film is formed on the inner surface of a pipe in advance under a certain condition. However, this method has a disadvantage that the effect of pre-oxidation decreases with time because the oxide film grows even during the operation of the reactor. Further, the pre-oxidation treatment has a disadvantage that it takes time.

On the other hand, a technique for injecting zinc (Zn) into reactor water to prevent radionuclides from adhering to piping is described in Japanese Patent Application Laid-Open No. 60-201295. However, in this method, the injected zinc may be activated to generate Zn — 65 (half-life 244), which may increase the pipe dose. As a countermeasure, JP-A-63-172999 discloses a method of using zinc in which Zn-64, which is a parent nuclide of Zn-65, is reduced by isotope separation. However, this method has high cost of isotopic separation and is economically problematic.

SUMMARY OF THE INVENTION An object of the present invention is to reliably reduce the dose of piping at a low cost and to achieve an effect. P

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a sustainable nuclear plant and its operating method.

The above object is achieved by continuously injecting a metal whose oxide has a corundum structure into primary cooling water during reactor operation.

First, the mechanism of attachment of radionuclides to the piping of a nuclear plant will be explained. Fig. 3 schematically shows this adhesion mechanism. Of the radionuclides in the reactor water, the problem at the time of routine inspection is the radioisotopes of Co-58 and C0-60 cobalt, which have relatively long elimination periods. Most of these radionuclides exist as cobalt divalent ions in reactor water. On the surface of stainless steel used as piping, iron elutes from the base material through the oxide film due to corrosion and becomes iron divalent ions. This iron divalent ion is oxidized by dissolved oxygen in water to form iron trivalent ions. ',' Because the solubility of iron trivalent ion is extremely low, it becomes oxide solid again and becomes a pipe surface. To be deposited.

At this time, if divalent metal ions are present in the vicinity, part of iron trivalent ions is ferrite, a spinel-type oxide containing divalent metal ions.

(XF e ₂ 〇 ₄ , X is a divalent metal ion). If the divalent metal I on is not present, Matthew Bok to an oxide of corundum - deposited as _{_{(α F e 2 0 3)}} . Here, the spinel means structure oxide represented by the chemical formula XY ₂ 〇, Formula Zeta ₂ 0 ₃ and corundum

(Ζ means a trivalent metal ion).

Ferrites are mainly composed of nickel ferrite formed by the reaction with nickel ions, which are the divalent metal ions that are the most abundant in the reactor water. Causes nuclides to adhere to pipes. Since zinc ions are also divalent ions, the ability to form ferrite is relatively low, and their stability is relatively low, so they dissolve immediately upon precipitation, and as a result, the amount of adhesion as a fluoride decreases. I do.

However, this is not the only way to prevent precipitation as ferrite: iron has been found to be ferrite when metal ions that are likely to form corundum oxide coexist with iron as a result of studies by the inventors. It has been found from new findings that precipitation is difficult to occur, and that precipitation as a hematite, which is a corundum oxide, is likely to occur.

This is thought to be due to the following reasons. That is, in the initial stage of precipitation, microparticles of hematite are precipitated from the iron trivalent ions on the pipe surface. Since the precipitated hematite has a corundum structure, trivalent metal ions forming a corundum-type oxide having a crystal structure similar to this are likely to adhere to the pipe surface. Adhesion trivalent metal Ion who is corundum oxides on the pipe surface (Z _z 0 _3, Z is a metal ion of trivalent) so stably precipitated, to Matthew I bind to divalent metal ions in the water as It can be prevented from changing to ferrite.

As a result, precipitation of cobalt-containing ferrite on the pipe surface can be suppressed as much as possible, so that attachment of radionuclides to the pipe can be suppressed, and the pipe dose can be reliably reduced.

Metal ions forming such corundum-type oxides include aluminum trivalent ion, gallium trivalent ion, chromium trivalent ion, titanium trivalent ion, vanadium trivalent ion, iron trivalent ion, and rhodium trivalent ion. Etc. Of these, iron trivalent ions are a source of the ferrite described above, and are therefore not preferred as the implanted metal of the present invention. In addition, titanium trivalent ion, vanadium trivalent ion and rhodium trivalent ion do not have very good stability of corundum-type oxides. Aluminum trivalent ions, gallium trivalent ions, and chromium trivalent ions, which have good stability of the random type oxide, are preferred. In addition, chromium trivalent ions do not have good stability in the reactor water and immediately change to chromate ions (corresponding to chromium hexavalent ions). It must be shared with a reducing agent that reduces chromium trivalent ions or used in a reducing atmosphere.

On the other hand, if metal ions added to the reactor water are activated in the reactor core, they will remain in the hematite, which is a random-type oxide, and adhere to the pipes, causing an increase in pipe dose. Therefore, it is necessary to select metal ions to be added that do not have such a problem of secondary radionuclide generation.

Fig. 8 shows the nuclear properties of metals that easily become corundum-type oxides in comparison with zinc. As shown in Fig. 8, chromium has a relatively long half-life of the generated nuclide produced by activation (27.8 days). (2.24 minutes, G a is 14.1 hours)

Therefore, if aluminum or gallium is used, nuclides with a long half-life will not be produced by neutron activation. In the case of aluminum and gallium, the cost is very low because isotope separation is not required and the abundance as a resource is large. In particular, aluminum has a short half-life of product nuclides, and high-purity aluminum can be obtained at low cost. In addition, since aluminum has already been detected in the reactor water, injection does not cause any new problems.

Also, chromium can be adequately applied to brands where a half-life of less than one month is acceptable. Furthermore, titanium, vanadium, and rhodium have sufficiently short half-lives of 5.76 minutes, 3.75 minutes, and 42.3 seconds, respectively. If acceptable, enough Applicable to

The injection amount may be controlled so that the ratio with respect to the concentration of divalent metal ions contributing to the precipitation of ferrite is a certain value or more (at least 1 or more). In practice, the main component of divalent metal ions in the reactor water is The ratio of nickel ions to metal ions to be implanted may be used as an index. If the injection amount is too large, the service life of the primary cooling water purification device containing ion-exchange resin etc. will be shortened, so the injection amount must be as small as possible within the effective range. It is also possible to directly measure the dose of piping that causes exposure, and control the amount of injection based on the rate of increase. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing a first embodiment in which the present invention is applied to a boiling water nuclear power plant.

FIG. 2 is a diagram showing an aluminum electrolytic device of the first embodiment. Fig. 3 is a diagram illustrating the mechanism of attachment of radionuclides to piping in a nuclear plant.

FIG. 4 is a diagram for explaining the mechanism of precipitation of corundum-type oxide on the piping of a nuclear power plant.

FIG. 5 is a diagram showing a change over time in the amount of radioactivity adhering to a pipe. FIG. 6 is a diagram showing a second embodiment in which the present invention is applied to a boiling water nuclear power plant.

FIG. 7 is a diagram showing a third embodiment in which the present invention is applied to a pressurized water nuclear power plant.

FIG. 8 is a diagram showing nuclear properties of a metal that easily becomes a corundum oxide. BEST MODE FOR CARRYING OUT THE INVENTION

Fig. 1 shows a first embodiment of the present invention applied to a boiling water nuclear power plant: Nuclear fuel 25, turbine 21, condenser ί, condensate purifier 23 , Feed water heater 24, recirculation system 26, reactor water purification device 27, aluminum injection device, etc.

The steam exiting the turbine 21 is returned to liquid by the condenser 22, and the condensate exiting the condenser 22 is removed by the condensate purification device 23. The condensate purified by the condensate purifier 23 is ripened by the feed water ripener 24. ',' At that time, metal corrosion products are generated due to the corrosion of the piping of the feed water ripener 24. This is brought into the furnace together with the water supply.

The metal corrosion product brought into the reactor adheres to the surface of the boiling part of the fuel rod of nuclear fuel 2δ, where it is activated by irradiation with neutrons generated by the fission of nuclear fuel 25, resulting in radionuclide Become. Some of the radionuclides generated on the surface of the nuclear fuel 25 are eluted again into the reactor water. Of the radionuclides eluted in the reactor water, some are removed by the reactor water purifier 27, while the remainder is oxidized as the oxidation of the pipe surface progresses while circulating through the recirculation system 26. It is taken in and causes an increase in the pipe dose rate.

In order to prevent such radionuclides from adhering to the pipe, in this embodiment, an aluminum solution tank 29 and an aluminum injection pump 28 were provided as an aluminum injection device, and a condensate purification device 23 and a feedwater heater 24 were provided. During this period, aluminum is injected continuously or intermittently during operation of the reactor. In this way, the continuous presence of aluminum ions that easily form a corundum structure in the reactor water allows the divalent cobalt ions, cobalt-60 and cobalt-158, which are the main nuclides to be exposed, to be exposed. Since it is possible to prevent the formation of the cobalt-containing light and adhere to the inner surface of the pipe, it is possible to surely reduce the dose of the pipe. The aluminum to be injected is supplied to the aluminum solution tank 29 in the form of a suspension of aluminum hydroxide, and is injected at a rate such that the aluminum concentration in the reactor water becomes about 50 ppb. As another form of aluminum to be injected, there is a method using an aluminum electrolytic device 33 as shown in Fig. 3: In this device, a metal aluminum electrode 31 is placed on the anode side of a DC power supply, and platinum is placed on the cathode side. The electrode 32 is connected to generate a solution containing aluminum ions to be implanted by electrolysis. This aluminum electrolytic device 33 can be used in place of the aluminum solution tank 29.

Cobalt-58, a radionuclide, was added to a loop device that circulates high-temperature water simulating reactor water conditions, and zinc ions were continuously injected so that the zinc ion concentration in the reactor water simulator became 5 O ppb. In the case where the aluminum ion concentration in the reactor water simulator was kept at 5 O ppb, aluminum ions were continuously injected, and when the reactor water simulator was not implanted, the cobalt ion was transferred to stainless steel piping. Fig. 4 shows an example of measuring the amount of adhesion of No. 8. From FIG. 4, it can be seen that the presence of aluminum ions in the simulated reactor water reduces the amount of cobalt-158 adhering to the pipe surface to the same extent as the presence of zinc ions.

Other forms of aluminum to be injected include aqueous solutions, solutions with organic solvents, and suspensions with water using aluminum organometallic compounds such as aluminum ethoxide, aluminum isopropoxide, and aluminum lactate. Or in the form of a suspension with an organic solvent. When these organoaluminum compounds are injected into the furnace, they decompose due to the high temperature conditions and irradiation, and some of them are present in the reactor water as aluminum ions.

In this embodiment, an example in which the aluminum concentration in the reactor water is about 5 O ppb has been described. As a guideline, the concentration of divalent metal ions in the reactor water, which is the source of ferrite, should be higher than the standard. Nickel ions can be considered as the main component of the divalent metal ion in the reactor water. Therefore, if the aluminum concentration is controlled to be equal to or higher than the nickel concentration, the pipe dose can be reduced. Specifically, it is known that the nickel concentration in the reactor water is about 2 to 3 ppb during the start-up operation of the reactor, and about 0.2 to 0.3 ppb during the commercial operation of the reactor (during normal operation). Therefore, it is sufficient to control the aluminum concentration in the reactor water according to such an operation state.

Next, a second embodiment in which the present invention is applied to a boiling water nuclear power plant will be described with reference to FIG. This embodiment differs from the first embodiment shown in FIG. 1 in that an element analyzer 51 for analyzing the aluminum concentration in the reactor water and an aluminum injection pump 2 based on the analysis results of the element analyzer 51 are provided. That is, a control device 53 that controls the motor 8 is provided.

In this embodiment, in order to continuously monitor and monitor the aluminum concentration in the reactor water in order to prevent the aforementioned radionuclide from adhering to the piping, a sampling line 50 is provided upstream of the reactor water purification device 27. The aluminum concentration is analyzed by an elemental analyzer 51 such as an ion chromatograph or ICP-MS, and a signal corresponding to the aluminum concentration is transmitted to the controller 3. The control device 53 controls the aluminum injection pump 28 based on the signal corresponding to the aluminum concentration and the amount of change thereof, so that the aluminum solution tank 29 is controlled so that the aluminum concentration in the reactor water falls within a predetermined range. Control the aluminum injection speed.

By such control, in addition to the effects obtained in the first embodiment, it is possible to prevent aluminum from being brought into the reactor pressure vessel in an amount more than necessary to suppress the adhesion of radionuclides to pipes. You can also.

In the second method for controlling the aluminum injection amount according to the present embodiment, FIG. The elemental analyzer 51 analyzes both the aluminum concentration and the nickel concentration in the reactor water and sends signals corresponding to the aluminum concentration and the nickel concentration to the controller 53. In this case, the controller 53 The concentration ratio between aluminum and nickel in the water is determined, and based on this concentration ratio, the aluminum injection pump 28 is controlled, and the aluminum injection speed from the aluminum solution tank 29 is controlled so that the concentration ratio falls within a predetermined range. Control.

With such control, the concentration ratio of aluminum and nickel in the reactor water can be adjusted within a predetermined range, effectively preventing cobalt from adhering to the piping, and minimizing the injection amount of aluminum. it can.

In the third method for controlling the aluminum injection amount according to the present embodiment, the surface dose rate of the recirculation system 26 is measured by the radiation measuring device 55 shown in FIG. 6, and the control device 53 is adapted to this surface dose rate. The corresponding signal is input from the radiation measurement device 55, and the rate of change of the surface dose rate is determined based on this signal. If the rate of change becomes too large beyond the predetermined allowable range, the controller 53 controls the aluminum injection pump 28 to increase the amount of aluminum injected from the aluminum solution tank 29. .

With such control, it is possible to effectively suppress the adhesion of cobalt to the piping and to minimize the amount of aluminum to be injected. The location where the surface dose rate is measured may be other than the recirculation system 26, for example, the upstream side of the reactor water purification device 27.

Next, a third embodiment in which the present invention is applied to a pressurized water nuclear power plant will be described with reference to FIG. This plant consists of a pressure vessel 60, a pressurizer 62, a nuclear fuel 63, a steam generator 64, a purifier 65, a boric acid water injection system 66, a dilute water injection system 67, and an aluminum injection system 68 Etc.

In the present embodiment, the primary cooling water 61 is pressurized by the pressurizer 62 so as not to boil. This primary cooling water 6 1 is used for nuclear fuel 6 3 in pressure vessel 60. The water that has been ripened and heated by heat is subjected to heat exchange in the steam generator 64, and the heat is passed to the secondary cooling water 69 and returned to the pressure vessel # 0 again. At this time, a part of the primary system cooling water 61 is guided to the reactor water purification system, and impurities are removed by the purification device G5. The steam generated by the steam generator 64 is used for power generation in the turbine 21, and is returned to water by the condenser 22. In the pressurized water reactor, the reaction of the nuclear fuel 63 is controlled using both the flow rate of the primary cooling water 61 and the concentration of boric acid in the primary cooling water 61. On the downstream side, a borate water injection system 6 G and a dilution water injection system G 7 are connected.

Due to such a configuration, in the pressurized water reactor, radionuclides adhere to the piping in contact with the primary cooling water 61 and cause exposure. In order to prevent this radionuclide from adhering to the pipe, in this embodiment, an aluminum injection system 68 is provided, and the injection position for the primary cooling water 61 is provided between the purification device 65 and the pressure vessel 60. Inject aluminum continuously or intermittently during reactor operation.

In this way, the continuous presence of aluminum ions that easily form a corundum structure in the reactor water makes it possible to obtain the divalent cations of cobalt 160 and cobalt 588, which are the main nuclides for exposure. Since the cobalt ions can form a ferrite containing the cobalt and prevent the cobalt ions from adhering to the inner surface of the pipe, the pipe dose can be reliably reduced:

Also in this embodiment, as described in the first and second embodiments, as a form of the aluminum to be injected, a suspension of aluminum hydroxide, an aluminum organometallic compound, or the like can be used. Also, the primary system cooling water was sampled from a position other than between the purifier 65 and the aluminum injection position to measure the concentration of elements such as aluminum nickel, and the amount of aluminum injection was determined based on the measurement results. The amount of aluminum injected is kept to a minimum and the dose rate of piping is reduced by configuring a control system that controls can do.

It should be noted that in the above embodiment, the force described in the example in which aluminum is used as the metal to be injected. In addition to this, even if gallium or chromium is used, the effect of reducing the dose rate of the pipe can be obtained. Industrial applicability

According to the present invention, there is no need for pre-oxidation, etc., the effect is continuous, and the cost can be reduced, and the dose to the pipe can be surely reduced without adverse effects such as secondary radionuclide production. A method of operating a nuclear power plant and a nuclear power plant can be provided.

Claims

The scope of the claims

1. In a nuclear power plant using light or heavy water as a coolant, an injection means for injecting a metal having an oxide having a corundum structure into the coolant;

Control means for controlling the injection means so as to continuously inject the metal into the coolant during operation of the nuclear reactor.

2. In claim 1,

A concentration measuring unit for measuring a concentration of the metal in the coolant, wherein the control unit controls the concentration of the metal from the injecting unit so that the metal concentration measured by the concentration measuring unit falls within a predetermined range. A nuclear power plant characterized by controlling the amount of metal injected.

3. In Claim 1,

Concentration measurement means for measuring the concentration of the metal in the coolant and Nigger ';

The nuclear power plant, wherein the control means controls an injection amount from the pouring means so that a ratio of a metal concentration and a nickel concentration measured by the concentration measuring means falls within a predetermined range. .

4. In claim 1,

A dose rate measuring means for measuring a surface dose rate of the coolant pipe, wherein the control means controls an injection amount from the injection means based on the surface dose rate measured by the dose rate measuring means. Atomic cabrant characterized by the following-

5. In Claim 4,

The dose rate measurement unit measures a surface dose rate of a recirculation pipe for recirculating the coolant or a purification pipe for purifying the coolant. Nuclear power plant.

6. At a nuclear power plant equipped with a purification device that purifies the primary cooling water of the reactor,

An injection means connected to a primary cooling water pipe downstream of the purification device, wherein an oxide injects a metal having a corundum structure into the primary cooling water; and Control means for controlling the injection means so as to inject the cooling water into primary cooling water.

7. The nuclear power plant plan according to any one of claims 1 to 6, wherein the metal is injected at least in any form of a metal atom, a metal ion, or a metal compound. Uru.

8. A nuclear power plant according to any one of claims 1 to 6, wherein the metal is at least one of aluminum, gallium, and chromium.

9. In the operation of nuclear power plant using light or heavy water as coolant,

A method for operating a nuclear power plant, comprising continuously injecting metal having a corundum structure in oxide into reactor water during operation of a nuclear reactor.

1 〇. In Claim 9,

A method for operating a nuclear power plant, comprising: measuring a concentration of the metal in the coolant; and controlling an injection amount of the metal such that the measured metal concentration falls within a predetermined range.

1 1. In claim 9,

Nuclear power, wherein the concentration of the metal and the nickel concentration in the coolant are measured, and the injection amount of the metal is controlled so that the ratio of the measured metal concentration to the nickel concentration is within a predetermined range. How to operate the brand.

1 2. In claim 9,

A method for operating a nuclear power plant, comprising: measuring a surface dose rate of a pipe of the coolant; and controlling an injection amount of the metal based on the measured surface dose rate.

1 3. In the operation method of a nuclear plant equipped with a purification device that purifies the primary cooling water of a nuclear reactor,

2. A method for operating an atomic cabulin, comprising continuously injecting a metal whose oxide has a corundum structure into primary cooling water downstream of the purification device during operation of the reactor.

14. In any one of claims 9 to 13,

A method for operating a nuclear power plant, wherein the metal is injected at least in any form of a metal atom, a metal ion, or a metal compound;

1 δ. In any one of claims 9 to 13,

The method for operating a nuclear power plant, wherein the metal is at least one of aluminum, gallium, and chromium.