JP6921020B2 - Exposure reduction method - Google Patents

Description

The present invention relates to a method for reducing the exposure of workers in a nuclear power plant.

Patent Document 1 aims to reduce the corrosion of parts exposed to high-temperature water, reduce stress corrosion cracking, reduce the corrosion potential, and reduce the amount of hydrogen injected into high-temperature water to reduce the corrosion potential. Is formed of an alloy selected from the group consisting of carbon steels, alloy steels, stainless steels, nickel-based alloys and cobalt-based alloys, and provides reducing chemical species that combine with oxidizing chemical species in hot water. It is also described that the component is formed so as to have a catalyst layer of a platinum group metal.

Japanese Unexamined Patent Publication No. 5-148674

For example, a boiling water reactor (hereinafter referred to as a BWR (Boiling Water Reactor) plant) has a nuclear reactor having a built-in core in a reactor pressure vessel (hereinafter referred to as an RPV (Reactor Pressure Vessel)). There is. In such a BWR plant, pure water is used as a reactor coolant.

The coolant supplied to the core by the recirculation pump (or internal pump) is heated by the heat generated by the fission of the nuclear fuel material in the fuel assembly loaded in the core, and part of it becomes steam. This steam is guided from the RPV to the turbine to rotate the turbine. The steam discharged from the turbine is condensed by the condenser to become water.

This water is supplied to the RPV again as water supply through the condensate system. In the water supply, metal impurities are removed by a condensate filtration device and a condensate desalination device provided in the condensate system in order to suppress the generation of radioactive corrosion products in the RPV.

In such a condensate system, a non-corrosive alloy such as stainless steel and a nickel-based alloy with less corrosion is used for the structural member in contact with the coolant. Further, a cobalt-based alloy such as Stellite (registered trademark) having excellent wear resistance is used for the sliding member in contact with the coolant such as the valve body of the valve, the pin of the control rod, and the roller. By using these members, the formation of corrosion products that are the source of radionuclides in the coolant is suppressed.

However, even if the above-mentioned corrosion countermeasures are taken, it is inevitable that a very small amount of metal impurities remain in the coolant. In addition, among the condensate system, especially from the high-pressure condensate pump, low-pressure water supply heater, water supply pump, high-pressure condensate heater, and drain system on the downstream side of the condensate filtration device and condensate desalination device. There is also a small amount of metallic impurities eluted as a corrosion product in the coolant.

Some metal impurities that are not removed even if the above-mentioned corrosion countermeasures are taken adhere to the surface of the fuel rods in the core as metal oxides. The metal impurities adhering to the fuel rods cause a nuclear reaction by irradiation with neutrons emitted by the nuclear fission of the nuclear fuel material in the fuel rods, and become radionuclides such as cobalt-60, cobalt58, chromium 51, and manganese 54.

Some of these radionuclides are eluted as ions in the coolant depending on the solubility of the oxides taken in, or re-released into the coolant as an insoluble solid called a clad.

The radioactive material contained in the coolant that was not removed by the reactor purification system is the surface that comes into contact with the coolant of the structural members (for example, piping) of the BWR plant while circulating in the recirculation system together with the coolant. Accumulates in the oxide film formed in. The accumulated radioactive material causes radiation exposure of workers who perform maintenance and inspection work on BWR plants.

Here, the exposure dose of the worker is controlled so as not to exceed the specified value for each worker. In recent years, this regulation value has been lowered, and it has become necessary to reduce the exposure dose of each worker as much as possible.

Therefore, there is a technique of applying chemical decontamination technology while the plant is stopped to remove the radioactive substances accumulated on the surface of the material together with the oxide film. As an example, chemical decontamination is a technique for removing an oxide film containing radionuclides from the surface of a structural member. However, after restarting the operation of the plant, radioactive substances reattach and accumulate with the formation of the oxide film again, so it is necessary to perform chemical decontamination every time the plant is stopped, which is troublesome and costly. There is a problem.

On the other hand, a method of forming a ferrite film on the surface of the pipe that comes into contact with the coolant to reduce the adhesion of radionuclides to the surface, and chemical removal of the surface of the structural members of the nuclear power plant while the operation of the nuclear power plant is stopped. There is a method of adhering platinum to the surface of the ferrite film when dyeing and forming a ferrite film on the surface thereof. The above-mentioned Patent Document 1 describes a method of adhering platinum to the surface of the latter ferrite film. By these methods, it is possible to suppress the amount of radionuclides taken into the surface of pipes and the like.

However, although it is described that the above-mentioned prior art removes radionuclides accumulated on the surface of pipes and the like, or suppresses the adhesion and accumulation of radionuclides on the surface of pipes and the like, the activated cobalt There is no mention of reducing the amount in the coolant. Therefore, it has been clarified by the studies by the present inventors that there is room for further reduction of the exposure dose of workers.

Further, in the case of reducing the amount of cobalt contained in the material in the above-mentioned prior art, there is a problem that parts already used must be replaced, which requires a lot of labor and cost.

Here, in the method of injecting a precious metal as in Patent Document 1, if it is added from the upstream, it adheres to the pipe surface in the middle and the controllability of the concentration in the reactor is lowered, so that the water supply system pipe relatively close to the reactor is used. Need to inject. Therefore, it has been clarified by the studies by the present inventors that there is room for further improvement because it adheres only to the inside of the furnace, the recirculation system, etc., and does not adhere to the water supply / recovery system piping.

Further, in the prior art, it is described that the corrosion of the cobalt-based alloy is suppressed by lowering the corrosion potential to suppress the adhesion of cobalt, but the amount of decrease in the corrosion rate due to the lowering of the potential cannot be evaluated. The study by the present inventors has revealed that the amount of cobalt elution cannot be controlled to a low level and there is a position for further improvement.

The present invention has been made for the above-mentioned problems, and the problem to be solved by the present invention is to reduce the elution amount of cobalt from the material of the water supply / recovery system to a low level without replacing parts. It is an object of the present invention to provide an exposure reduction method capable of reducing the exposure dose of a worker as compared with the conventional one by controlling the radiation dose.

The present invention includes a plurality of means for solving the above problems. For example, it is an exposure reduction method in a boiling water reactor, and is a condensate system of the boiling water reactor. A member made of a cobalt-containing material among the members used in a state where a reducing agent injection device, a corrosion potential measuring device, and a water quality measuring device are installed and in contact with the provided coolant. Corrosion potential of -0.2V vs. It was maintained and controlled below SHE, and the corrosion potential of the member was measured by the corrosion potential measuring device during the operation of the boiling water nuclear power plant, and the measured potential was −0.2 Vvs. The amount of reducing agent injected into the coolant is controlled so as to maintain SHE or less, and the cobalt concentration in the coolant is measured and measured by the water quality measuring device during the operation of the boiling water reactor. It was characterized in that the amount of the reducing agent injected into the coolant was controlled so that the cobalt concentration did not exceed a predetermined concentration.

According to the present invention, it is possible to control the elution amount of cobalt from the material of the condensate system to a low level without replacing parts, and it is possible to reduce the exposure dose of workers as compared with the conventional case. .. Issues, configurations and effects other than those mentioned above will be clarified by the description of the following examples.

It is a figure which showed the measurement result of the current-potential curve of a cobalt-based alloy clarified by the present inventors. It is a figure which showed the outline of the primary cooling system of the BWR plant of Example 1 of this invention. It is a figure which showed the outline of the primary cooling system of the BWR plant of Example 2 of this invention. It is a figure which showed the outline of the primary cooling system of the BWR plant of Example 4 of this invention.

Hereinafter, examples of the exposure reduction method of the present invention will be described with reference to the drawings.

First, the background to the present invention will be described below with reference to FIG.

Among the radionuclides such as cobalt-60, cobalt58, chromium 51, and manganese 54, it is known that cobalt-60 is the main factor for increasing the dose rate of the piping and equipment of the primary cooling system of BWR.

Cobalt-60 is produced by a nuclear reaction of ⁵⁹ Co (n, γ) ⁶⁰ Co, which is generated when cobalt 59 is irradiated with neutrons. The cobalt-59, which is the basis of the cobalt-60, elutes into the coolant from a cobalt-based alloy such as stellite used for a valve body or the like.

Further, since nickel contains cobalt as an impurity, not only high nickel alloys but also stainless steel containing nickel such as austenitic stainless steel also contains about 0.2% cobalt as an impurity. Therefore, cobalt 59 is eluted not only from cobalt-based alloys but also from stainless steel, high nickel alloys, and the like.

As described above, it is known that cobalt is often eluted from the condensate system, particularly the valve and the water supply heater. The chemical components of the material elute into the coolant as ions or insoluble particles due to corrosion from the piping and corrosion and sliding of the valves and the like. Therefore, it is desired from the viewpoint of labor and cost to reduce the amount of cobalt-59 elution transferred from the cobalt-containing material of the condensate system into the coolant without replacing parts.

In order to reduce the amount of cobalt-59 eluted, the present inventors investigated whether it could be achieved by grasping and controlling the corrosive environmental strength formed by the coolant.

The corrosive environmental strength is determined by various parameters related to the coolant, but in the case of BWR, it is represented by the concentration of an oxidizing agent such as oxygen contained in the coolant. This corrosive environmental strength is represented by a corrosive potential that can be actually measured under the temperature and pressure of the coolant. When the corrosive environment strength is high, the corrosive potential is high, and when the corrosive environment strength is low, the corrosive potential is low.

Therefore, in order to control the elution amount of cobalt 59 eluted from the cobalt-containing material to a low level, it is necessary to grasp the corrosion potential and reduce the elution amount. Furthermore, it is necessary to understand what kind of corrosion potential and what kind of cobalt elution amount will be.

Therefore, the present inventors evaluated the correlation between the corrosion potential and the amount of cobalt elution by measuring the polarization curve. As a typical material containing cobalt, the cobalt-based alloy Stellite No. No. 6 was selected, and in pure water at 553 K and 8 MPa, which is a typical coolant temperature, Stellite No. 6 was selected. The corrosion rate was measured as the current density while scanning the potential of 6. The result is shown in FIG.

As a result, as shown in FIG. 1, the potential was changed to −0.2 Vvs. By controlling and maintaining below SHE (standard hydrogen electrode standard), the amount of cobalt eluted from stellite can be increased to +0.2 Vvs. It was clarified that it can be reduced to 1/20 or less of the case of SHE.

Based on this finding, the potential was set to -0.2 Vvs. It is clear that by controlling and maintaining below SHE, it is possible to control and maintain a low level of the amount of cobalt that elutes from the cobalt-containing material to the coolant at any part of the condensate system. It became.

That is, if the amount of cobalt-59 eluted from the system material into the coolant is reduced, the total amount of cobalt-60 activated near the core is naturally reduced, so that the amount of radionuclides accumulated on the pipe surface can also be reduced. It can be done, and by extension, the exposure dose of workers can be reduced.

The present invention is based on the above findings.

<Example 1>
Example 1 of the exposure reduction method of the present invention will be described with reference to FIG. FIG. 2 is a system diagram of a primary cooling system of a BWR plant that preferably implements the exposure reduction method of the present invention that reduces the exposure dose of workers.

In the BWR plant 100A as shown in FIG. 2, the steam generated by boiling the coolant in the core 13 of the nuclear reactor drives the turbine 6 through the main steam system 5 to generate electric power.

The steam discharged from the turbine 6 is condensed by the condenser 7, and this condensed water flows through the condensate system 1 as condensate. This condensate returns to RPV3 through the water supply system 2 as water supply through the low-pressure feed water heater 10, the feed pump 12, and the high-pressure feed water heater 11.

Further, the coolant is circulated in the recirculation system 4 by the recirculation pump 4a. In the case of a plant having a jet pump, there is a jet pump in the downcomer 14, but in FIG. 2, a plant without a jet pump is listed. A residual heat removing system 33 is connected to the recirculation system 4.

Most of the coolant that did not turn into steam is separated from the steam at the top of the RPV3 and flows below the RPV3 through the downcomer 14 around the core 13. The coolant that has flowed downward flows into the recirculation system 4, and is returned to the core 13 by the recirculation pump 4a.

The coolant reduced by the generation of steam is replenished by the supply of water supply.

In order to purify the coolant, a part of the coolant is removed from the recirculation system 4 and the bottom drain 16 of the reactor lower plenum 15 and sent to the reactor purification system 17. In the furnace purification system 17, impurity ions in the coolant are removed by the furnace purification system desalinator 18. The coolant purified by the furnace purification system desalting device 18 is supplied to the water supply system 2 via the pipe 17c connected to the water supply system 2, mixed with the water supply, and returned to the RPV3.

Further, in an emergency, a high-pressure spray system 40 for injecting pure water stored in the suppression chamber 41 connected to the reactor containment vessel 42 into the RPV3 is installed.

As shown in FIG. 2, the primary cooling system of the BWR is composed of an RPV 3, a main steam system 5, a turbine 6, a condensate system 1, a water supply system 2, a recirculation system 4, a furnace purification system 17, and the like.

The condensate system 1 is composed of a condensate 7, a condensate pump 8, a condensate desalinator 9, and a pipe connecting each of these devices, and valves and joints provided in the pipe.

Further, an off-gas system 28 is connected to the condenser 7. A steam extractor 27 and a recombination device 30 are installed in the off-gas system 28. Further, an oxygen injection device 29 is connected to the pipe between the condenser 7 of the off-gas system 28 and the steam extractor 27.

The feed water system 2 is composed of a low-pressure feed water heater 10, a high-pressure feed water heater 11, a feed water pump 12, and a pipe connecting each of these devices, and valves and joints provided in the pipe.

Further, a water quality measuring device 20a for measuring the water quality of the feed water is connected to a pipe between the high pressure feed water heater 11 and the RPV 3 via a sampling pipe 19.

Further, a corrosion potential sensor 25 for measuring the corrosion potential of the water supply is installed in the water supply system 2.

The furnace purification system 17 is composed of a heat exchanger 17a, a furnace purification system pump 17b, a pipe for connecting the furnace purification system desalinator 18 and each of these devices, and valves and joints provided in the pipe. ..

Further, a water quality measuring device 20b for measuring the water quality of the cooling material in the furnace purification system 17 is connected to a pipe constituting the furnace purification system 17 via a sampling pipe 21.

As for the bottom drain 16, a water quality measuring device (not shown) for measuring the water quality of the coolant other than the corrosion potential is connected to the piping constituting the bottom drain 16. Further, the bottom drain 16 is provided with a corrosion potential sensor (not shown) for measuring the corrosion potential of the coolant.

Also in the main steam system 5, a water quality measuring device (not shown) is connected to the pipes constituting the main steam system 5 via a sampling pipe (not shown). The water quality measuring device connected to the main steam system 5 measures the water quality of the condensed water generated by condensing the steam. Further, the main steam system 5 is also provided with a dose rate monitor 26 for measuring the dose rate of the main steam system.

The water quality of the water supply (dissolved oxygen concentration, dissolved hydrogen concentration, pH, conductivity, etc.) is measured online by the water quality measuring device 20a by depressurizing and cooling the water supply collected from the sampling pipe 19.

The water quality of the coolant is measured online by the water quality measuring device 20b by depressurizing and cooling the coolant collected from the sampling pipe 21. In the case of a coolant, the corrosion potential is also measured by a corrosion potential sensor (not shown), so both the oxygen concentration and the hydrogen peroxide concentration can be quantified.

In the main steam system 5, the steam extracted from the sampling pipe is condensed, the condensed water is depressurized and cooled, and the water quality is measured online by a water quality measuring device.

As described above, the water quality measuring devices 20a, 20b and the like measure the water quality under the conditions of a temperature of about 50 ° C. from room temperature and a pressure of about 5 atm from atmospheric pressure by depressurizing and cooling the water. ..

In the present invention, the system composed of the condensate system 1 and the condensate system 2 is referred to as a condensate system.

Among the feed water supply systems and the like, the low-pressure feed water heater 10 and the high-pressure feed water heater 11 constituting the feed water system 1 and the water supply system 2 are mainly composed of stainless steel or a high nickel alloy. Further, the valves constituting the water recovery system 1 and the water supply system 2 are mainly composed of stellite in the valve body and stainless steel in other parts.

As described above, the materials constituting these members contain cobalt and are in contact with the coolant. In order to reduce the amount of cobalt-59 eluted from these members, there is a method of injecting a reducing agent into the coolant as a means for reducing the corrosion potential. As the reducing agent, mainly gaseous hydrogen or a gas or liquid containing hydrogen is used.

Here, during the operation of the BWR plant 100A, the hydrogen concentration of the coolant in the furnace and the condensate system is reduced by the oxidation reaction on the pipe surface. In addition, a part of the oxidizing agent is reduced to water.

Therefore, using the main or temporary water quality measuring devices 20a and 20b and the pH meter installed in the sampling pipes 19 and 21, the change in the concentration of impurity components in the cooling material when the cooling material is not collected. The accompanying coolant conductivity, pH change, and dissolved hydrogen concentration are monitored, and hydrogen is injected so that the predetermined concentration is maintained in the furnace.

In this embodiment, in addition to adjusting the amount of hydrogen injected, a hydrogen injection device 32 is installed in the pipe on the inlet side of the low-pressure water supply heater 10 in the water supply / recovery system as a means for reducing the corrosion potential. Moreover, the corrosion potential sensor 25 is installed on the downstream side of the hydrogen injection device 32.

Then, the corrosion potentials of the pipes, joints, valves, the low-pressure feed water heater 10 and the high-pressure feed water heater 11 constituting the condensate system 1 and the water supply system 2 are continuously measured by the corrosion potential sensor 25 during the operation of the BWR plant 100A. Measure.

Then, in order to reduce the exposure of the workers working in the BWR plant 100A, the measured corrosion potentials of these members were -0.2 Vvs. The amount of reducing agent injected into the coolant is controlled by the hydrogen injection device 32 so as to be maintained below SHE.

For example, when the measured corrosion potential exceeds the above threshold (-0.2V vs. SHE), the injection amount of the reducing agent is increased.

As a result, the amount of cobalt 59 eluted by corrosion from the above-mentioned cobalt-containing member installed downstream of the low-pressure feed water heater 10 in the feed water supply system is reduced and engaged. Reduce the exposure dose of the person.

The corrosion potential sensor 25, which is a means for evaluating the corrosion potential in this embodiment, can have a known configuration, and for example, using a zirconia diaphragm as described in Japanese Patent Application Laid-Open No. 2003-48887. , A corrosion potential sensor for measuring the corrosion potential of a member in high temperature and high pressure water can be used. Further, a simulation method for analyzing the corrosion potential in the structural member of the nuclear power plant, as described in JP-A-2000-121780, can be used. These measuring and analyzing means are applied to evaluate the corrosion potential of a desired site.

In this embodiment, the reducing agent injected into the coolant by the hydrogen injection device 32 is preferably at least one or more of hydrogen, hydrazine, and ethanol. Of these reducing agents, it is desirable to inject hydrogen in the form of a gas and inject hydrazine and ethanol in liquid form.

As for the injection amount of the reducing agent, the flow rate supplied from the hydrogen injection device 32 connected to the inlet pipe of the low-pressure feed water heater 10 to the feed water supply / recovery system or the like is manually adjusted by the worker, automatically adjusted by the control device, or the worker. It is desirable to control by adjusting by either method of semi-automatic adjustment that combines manual adjustment and automatic adjustment by the control device.

Further, in this embodiment, during the operation of the BWR plant 100A, coolant is sampled from one or more systems such as sampling pipes 19 and 21, and a permanent or temporary water quality measuring device 20a, 20b and a pH meter are used. , Measure the concentration of impurity components in the coolant, especially the concentration of cobalt. Alternatively, the coolant is sampled from one or more systems such as sampling pipes 19 and 21 at regular intervals or as needed, and the concentration of cobalt 59 in the coolant is inductively coupled plasma mass spectrometer or frameless atomic absorption spectrometry. Quantify with an analytical instrument. As a result, when the measured concentration of cobalt 59 exceeds a predetermined value, it is desirable to increase the amount of hydrogen injected to control the concentration of cobalt in the coolant so that it does not exceed the predetermined concentration.

Next, the effect of this embodiment will be described.

In the exposure reduction method in the BWR plant 100A of the first embodiment of the present invention described above, the hydrogen injection device 32 and the corrosion potential sensor 25 are installed in the water supply / recovery system, and the BWR plant is operated by the corrosion potential sensor 25 during operation. Among the members used in contact with the coolant provided in the 100A water supply / recovery system, the corrosion potential of the member made of a cobalt-containing material was measured, and the measured potential was -0.2V vs. .. The amount of reducing agent injected into the coolant is controlled so as to maintain SHE or less.

As a result, the amount of cobalt that elutes from the surface of the cobalt-containing material that constitutes the water supply / condensate system of the BWR plant 100A from the surface in contact with the coolant into the coolant due to corrosion is reduced to a lower level than before. Can be controlled and maintained. Therefore, the concentration of cobalt-59 in the coolant can be reduced as compared with the conventional case, and the amount of cobalt-60 generated by neutron irradiation on the fuel surface can be reduced. Therefore, since the amount of cobalt-60 re-eluting from the fuel surface into the coolant can be reduced, it shifts to a system such as a recirculation system or a furnace water purification system along with the flow of the coolant, and the surface of the pipes. The amount of cobalt-60 accumulated in the fuel can be reduced, and the exposure dose of workers can be reduced as compared with the conventional case.

In addition, it is not necessary to replace the members, and it is possible to suppress an increase in labor and cost. In particular, reducing the content of cobalt in the material of the member is a great disadvantage in terms of cost, but according to the present invention, since it is not necessary to use such a special material, there are advantages in terms of labor and cost. Is very large, and has the advantage.

Further, the cobalt-containing material is at least one of stellite, stainless steel, and high nickel alloy, and the member composed of the cobalt-containing material is among pipes, valves, heaters, and joints. By using at least one of them, effective measures can be taken against the main cobalt elution sources, and the concentration of cobalt 59 in the coolant can be reduced more effectively than in the past. Can be done.

Further, by setting the reducing agent to at least one or more of hydrogen, hydrazine, and ethanol, it is possible to effectively supply hydrogen as a reducing agent into the coolant, and the target member can be more easily supplied. Corrosion potential is -0.2V vs. It can be maintained and controlled so as to be SHE or less.

Further, water quality measuring devices 20a and 20b are further installed in the water supply and recovery system, and the cobalt concentration in the coolant is measured by the water quality measuring devices 20a and 20b during operation, and the measured cobalt concentration does not exceed the predetermined concentration. By controlling the amount of the reducing agent injected into the coolant, the corrosion potential of the target member can be more reliably reduced to -0.2 Vvs. The reducing agent can be injected into the coolant so as to be SHE or less, and the concentration of cobalt 59 in the coolant can be more effectively reduced as compared with the conventional case.

The corrosion potential was measured, and the measured potential was −0.2 Vvs. The target members that maintain SHE or less are not limited to the pipes, joints, and valves that make up the water recovery system 1 and water supply system 2, and also the low-pressure feed water heater 10 and high-pressure feed water heater 11, but the heat exchanger of the furnace purification system 17. Corrosion potentials were also measured for the pipes, valves, and joints constituting 17a and the furnace purification system 17, and the measured potentials were −0.2 Vvs. It can be a member to be maintained below SHE.

<Example 2>
The exposure reduction method of Example 2, which is another preferred embodiment of the present invention, will be described with reference to FIG. The same reference numerals are shown in the same configurations as in the first embodiment, and the description thereof will be omitted. The same applies to the following examples.

As shown in FIG. 3, in the BWR plant 100B in which the exposure reduction method of the present embodiment is preferably implemented, in addition to the configuration of the BWR plant 100A of the first embodiment, the precious metal injection device 31 is located downstream of the hydrogen injection device 32. It is a connected configuration.

In this embodiment, hydrogen is injected into the water supply / recovery system using the hydrogen injection device 32 during the operation of the BWR plant 100B, and the corrosion potential of the target member is continuously measured and measured using the corrosion potential sensor 25. The corrosion potential was -0.2V vs. The point of controlling the amount of hydrogen injected into the coolant so as to maintain SHE or less is the same as the exposure reduction method of Example 1.

In this embodiment, platinum is further injected into the coolant in the condensate system using the precious metal injection device 31 while the reactor is shut down, so that the low pressure water supply heater 10, the high pressure water supply heater 11, and the system Platinum is attached to the surface of the cobalt-containing material used in the water supply / condensate system in contact with the coolant, such as the existing valves inside.

The step of injecting platinum into the condensate system using the precious metal injection device 31 is not limited to the reactor shutdown, and may be performed during the reactor operation, construction, test run / start-up test.

The noble metal injection device 31 is, for example, a device that injects an aqueous solution of platinum dissolved in water in the chemical form of a hydroxide or a nitrate compound into a coolant, whereby platinum is introduced into the coolant and cooling containing platinum is performed. The platinum introduced into the coolant adheres to the surface of the structural member (for example, recirculation system piping, core partition wall, etc.) that comes into contact with the coolant.

The precious metal to be introduced is not limited to platinum (Pt), and among gold (Au), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os), in addition to platinum. It can be at least one or more elements.

Other configurations / operations are substantially the same as those of the exposure reduction method of the first embodiment described above, and details will be omitted.

The exposure reduction method of Example 2 of the present invention also has almost the same effect as the exposure reduction method of Example 1 described above.

Further, a hydrogen injection device 32, a noble metal injection device 31, and a corrosion potential sensor 25 are installed in the water supply / recovery system, and the corrosion potential of the member is measured and measured by the corrosion potential sensor 25 during the operation of the BWR plant 100B. The applied potential is -0.2V vs. By controlling the amount of the reducing agent injected into the coolant and injecting the noble metal into the coolant so as to maintain SHE or less, the catalyst layer of the noble metal can be provided on the surface of the target member. Due to the presence of this catalyst layer, the corrosion potential on the surface of the structural member can be suppressed to a lower level, and the amount of cobalt-59 eluted can be reduced. Therefore, the concentration of cobalt-59 in the coolant can be increased more effectively than in Example 1. It can be reduced in comparison.

Further, by using at least one or more of gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium as the noble metal, an effective effect of suppressing the growth of stress corrosion cracking can be obtained.

Further, by setting the time for injecting the precious metal to at least one of the construction of the BWR plant 100B, the test run / start-up test, the furnace shutdown, and the operation, platinum can be effectively injected into the surface of the structural member. Can be attached, the corrosion potential on the surface of the structural member can be suppressed low, and the elution amount of cobalt 59 can be reduced.

The location where the precious metal injection device 31 is provided is not limited to the downstream side of the hydrogen injection device 32 and the upstream side of the low-pressure water supply heater 10 as shown in FIG. 3, but is installed on the upstream side of the condensate desalting device 9. In this case, most of the precious metal to be injected is removed by the condensate desalinator 9, so it is desirable to use the condensate desalinator 9 on the downstream side.

<Example 3>
The exposure reduction method of Example 3 of the present invention will be described.

Since the structure of the BWR plant in which the exposure reduction method of this embodiment is preferably implemented is substantially the same as that of the BWR plant 100A shown in FIG. 2, it will be described with reference to FIG.

In this example, the measured corrosion potential was -0.2 Vvs. The point of controlling the amount of hydrogen injected into the coolant so as to maintain SHE or less is the same as the exposure reduction method of Example 1.

In this embodiment, a noble metal is further contained as a component element in a member composed of a cobalt-containing material, that is, a pipe, a valve, a heater, and a joint. As a result, a noble metal catalyst layer is provided on the surface of the target member as in the second embodiment, and the corrosion potential on the surface of the structural member is suppressed to be lower than in the conventional case.

As a method of incorporating a precious metal into a structural member, electrolytic / electroless plating, thin film deposition, and meat are used on the surface of the target member used for valves and pipes of the water supply / recovery system during the shutdown period of the BWR plant 100A. A platinum-containing layer is formed on the surface of the target member by any one or more of various methods such as addition of platinum to the filling repair material.

In addition to this, there is a method of manufacturing the target member using a base material to which a noble metal is added in advance.

In this example, the noble metal contained as a component element in the member composed of the cobalt-containing material is also one or more of gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium, as in Example 2. It is desirable to use the element of.

In this embodiment, since the effect of injecting the precious metal has already been obtained, it is not necessary to inject the noble metal using the noble metal injection device 31 as in the second embodiment.

Other configurations / operations are substantially the same as those of the exposure reduction method of the first embodiment described above, and details will be omitted.

As in the exposure reduction method of Example 3 of the present invention, the hydrogen injection device 32 and the corrosion potential sensor 25 are installed in the water supply / recovery system, and a noble metal is contained in a member made of a cobalt-containing material. It is contained as an element, and the corrosion potential of the member is measured by the corrosion potential sensor 25 during operation, and the measured potential is −0.2 Vvs. By controlling the amount of the reducing agent injected into the coolant so as to maintain SHE or less, almost the same effect as the exposure reduction method of Example 2 described above can be obtained.

In addition, the method of incorporating a noble metal into a member is a method of forming a layer containing a noble metal on the surface of the member by at least one or more of electroless plating, electrolytic plating, thin film deposition, and overlay. It is not necessary to unnecessarily contain precious metals in the material, and the amount of expensive precious metals used can be reduced to reduce costs.

<Example 4>
The exposure reduction method of Example 4 of the present invention will be described with reference to FIG.

As shown in FIG. 4, in the BWR plant 100C in which the exposure reduction method of the present embodiment is preferably implemented, the upstream side of the condensate pump 8 in the condensate system 1 of the BWR plant 100A of the first embodiment shown in FIG. A hydrogen injection device 32A is provided in the water reactor so that the reducing agent is injected from the upstream side of the condensate pump 8.

Other configurations and operations are substantially the same as those of the BWR plant 100A of the first embodiment and the exposure reduction method described above, and details thereof will be omitted.

The exposure reduction method of Example 4 of the present invention also has almost the same effect as the exposure reduction method of Example 1 described above.

The mode in which the hydrogen injection device is provided on the upstream side of the condensate pump 8 as in this embodiment is not limited to the mode of the first embodiment, and the condensate pump 8 is also provided in the second and third embodiments. A hydrogen injection device can be provided on the upstream side.

Further, the place where the hydrogen injection device is provided is not limited to the embodiment of the present embodiment and the first embodiment, and may be any place of the water supply / recovery system, but the corrosion potential measured effectively in the present invention is −0. 2V vs. In order to maintain SHE or less, it is desirable to provide it in the condensate system 1 corresponding to the upstream side in the system as in Example 1 and this example.

<Others>
The present invention is not limited to the above examples, and includes various modifications. The above-mentioned examples have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. For example, although the present invention has described an example applied to a feed water system, it is also preferable to apply the present invention to a feed water heater drain system.

It is also possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add / delete / replace a part of the configuration of each embodiment with another configuration.

1 ... Water restoration system 2 ... Water supply system 3 ... RPV
4 ... Recirculation system 4a ... Recirculation pump 5 ... Main steam system 6 ... Turbine 7 ... Condenser 8 ... Condenser pump 9 ... Condensation desalting device 10 ... Low pressure water supply heater 11 ... High pressure water supply heater 12 ... Water supply Pump 13 ... Core 14 ... Downkama 15 ... Reactor lower plenum 16 ... Bottom drain 17 ... Reactor purification system 17a ... Heat exchanger 17b ... Reactor purification system pump 18 ... Reactor purification system condenser 19, 21 ... Sampling pipes 20a, 20b ... Water quality measuring device 25 ... Corrosion potential sensor (corrosion potential measuring device)
26 ... Dose rate monitor 31 ... Precious metal injection device 32, 32A ... Hydrogen injection device (reducing agent injection device)
100A, 100B, 100C ... BWR plant

Claims (10)

This is an exposure reduction method for boiling water nuclear power plants.
A reducing agent injection device, a corrosion potential measuring device, and a water quality measuring device are installed in the condensate system of the boiling water nuclear power plant.
Among the members used in contact with the provided coolant, the corrosion potential of the member composed of the cobalt-containing material is −0.2 Vvs. Maintain and control below SHE ,
During the operation of the boiling water nuclear power plant, the corrosion potential of the member was measured by the corrosion potential measuring device, and the measured potential was −0.2 Vvs. The amount of reducing agent injected into the coolant is controlled so as to maintain SHE or less.
During the operation of the boiling water reactor, the cobalt concentration in the coolant is measured by the water quality measuring device, and the reducing agent to be injected into the coolant so that the measured cobalt concentration does not exceed a predetermined concentration. An exposure reduction method characterized by controlling the amount. In the exposure reduction method according to claim 1,
A precious metal injection device was further installed in the condensate system.
During the operation of the boiling water nuclear power plant, the corrosion potential of the member was measured by the corrosion potential measuring device, and the measured potential was −0.2 Vvs. An exposure reduction method characterized by controlling the amount of reducing agent injected into the coolant and injecting a noble metal into the coolant so as to maintain SHE or less. In the exposure reduction method according to claim 1,
An exposure reduction method characterized by containing a noble metal as a component element in a member of the water supply / condensate system made of the cobalt-containing material. In the exposure reduction method according to claim 1,
An exposure reduction method characterized in that the cobalt-containing material is at least one of stellite, stainless steel, and a high nickel alloy. In the exposure reduction method according to claim 1,
An exposure reduction method characterized in that the member made of the cobalt-containing material is at least one or more of a pipe, a valve, a heat exchanger, a heater, and a joint. In the exposure reduction method according to claim 1,
An exposure reduction method characterized in that the reducing agent is at least one or more of hydrogen, hydrazine, and ethanol. In the exposure reduction method according to claim 2 or 3,
An exposure reduction method characterized in that the noble metal is at least one or more of gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium. In the exposure reduction method according to claim 2,
An exposure reduction method characterized in that the time for injecting the precious metal is at least one of the construction of the boiling water reactor, the trial run / start-up test, the shutdown of the furnace, and the operation. In the exposure reduction method according to claim 3,
As a method for incorporating a noble metal into the member, a layer containing the noble metal is formed on the surface of the member by at least one or more of electroless plating, electroplating, thin film deposition, and overlay. An exposure reduction method characterized by this. In the exposure reduction method according to any one of claims 1 to 9,
The corrosion potential of the member made of the cobalt-containing material is −0.2 Vvs. An exposure reduction method characterized by reducing the amount of cobalt-59 eluted into the coolant in the system due to corrosion by maintaining and controlling it below SHE.

Images