JP2019152618A - Exposure reduction method - Google Patents

Abstract

To provide an exposure reduction method capable of reducing the exposure amount of a worker, compared with the conventional art, by keeping the elution amount of cobalt from a material of a supply and condensate system at a low level without requiring part replacement.SOLUTION: A supply and condensate system includes a hydrogen injection device 32 and a corrosion potential sensor 25. During operation, the corrosion potential sensor 25 measures the corrosion potential of a member formed of a material containing cobalt, of members used in a contact state with a coolant disposed in the supply and condensate system of a BWR plant 100A. The amount of reducer injected into the coolant is controlled so that the measured potential keeps -0.2 Vvs.SHE or less.SELECTED DRAWING: Figure 1

Description

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

  For the purpose of reducing corrosion of parts exposed to high-temperature water, reducing stress corrosion cracking, lowering the corrosion potential, and reducing the amount of hydrogen injected into high-temperature water to lower the corrosion potential. Is formed of an alloy selected from the group consisting of carbon steel, alloy steel, stainless steel, nickel-base alloy, and cobalt-base alloy, and provides a reducing species that combines with oxidizing species in high temperature water; It also describes forming the part with a platinum group metal catalyst layer.

JP-A-5-148673

  For example, a boiling water nuclear power plant (hereinafter referred to as a BWR (Boiling Water Reactor) plant) has a nuclear reactor with a built-in core in a reactor pressure vessel (hereinafter referred to as an RPV (Reactor Pressure Vessel). Yes. 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 fission of the nuclear fuel material in the fuel assembly loaded in the core, and a part thereof becomes steam. This steam is led from the RPV to the turbine and rotates the turbine. The steam exhausted from the turbine is condensed in a condenser to become water.

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

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

  However, even if the above-described corrosion countermeasures are taken, it is inevitable that a very small amount of metal impurities remain in the coolant. Among the feed and condensate systems, especially from the high pressure condensate pump, the low pressure feed water heater, the feed water pump, the high pressure condensate heater, and the feed water drain system on the downstream side of the condensate filtration device and the condensate desalination device Metal impurities that elute as corrosion products are also slightly present 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 rod cause a nuclear reaction by irradiation of neutrons released by fission of nuclear fuel material in the fuel rod, and become radionuclides such as cobalt 60, cobalt 58, chromium 51, manganese 54 and the like.

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

  The radioactive material contained in the coolant that has not been removed by the reactor purification system is in contact with the coolant of the structural member (eg, piping) of the BWR plant while circulating in the recirculation system together with the coolant. It accumulates in the oxide film formed. The accumulated radioactive material is a cause of radiation exposure of workers who perform maintenance and inspection work for the BWR plant.

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

  For this reason, there is a technique of removing radioactive substances accumulated on the material surface together with the oxide film by applying a chemical decontamination technique while the plant is stopped. Chemical decontamination as an example thereof is a technique for removing an oxide film containing a radionuclide from the surface of a structural member. However, after restarting the plant operation, the radioactive material reattaches and accumulates as the oxide film is formed again, so it is necessary to perform chemical decontamination every time it is stopped, which takes time and cost. There is a problem.

  In contrast, a method of reducing the adhesion of radionuclides to the surface by forming a ferrite film on the surface of the piping that contacts the coolant, or chemical removal of the surface of the structural members of the nuclear power plant while the nuclear power plant is shut down. There is a method in which platinum is adhered to the surface of the ferrite film when dyeing is performed and a ferrite film is formed on the surface. Patent Document 1 described above describes a method of depositing platinum on the surface of the latter ferrite film. By these methods, it is possible to suppress the amount of radionuclide incorporated into the surface of piping or the like.

  However, although the above-described conventional technology is described as removing radionuclides accumulated on the surface of piping or the like, or suppressing adhesion / accumulation of radionuclides on the surface of piping or the like, cobalt that is activated is described. There is no mention of reducing the amount in the coolant. For this reason, it became clear by examination of the present inventors that there is room for further reducing the exposure dose of the workers.

  Moreover, when reducing the amount of cobalt contained in the material in the above-described prior art, there is a problem that parts that have already been used have to be replaced, which requires much labor and cost.

  Here, the method of injecting the noble metal as in Patent Document 1 attaches on the surface of the pipe in the middle when added from upstream, and the controllability of the concentration in the reactor is lowered, so that the feed water system pipe relatively close to the reactor is used. Need to be injected. Therefore, since it adheres only around the furnace, such as in the furnace and the recirculation system, and does not adhere to the feed and condensate system piping, it has been clarified by the present inventors that there is room for further improvement.

  Furthermore, in the prior art, it is described that the corrosion of the cobalt base alloy is suppressed by reducing the corrosion potential, thereby suppressing the adhesion of cobalt, but the amount of decrease in the corrosion rate due to the potential decrease cannot be evaluated. It has been clarified by the present inventors 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 to solve the above problems, and the problem to be solved by the present invention is to reduce the amount of cobalt eluted from the material of the feed and condensate system without replacing parts. It is an object of the present invention to provide an exposure reduction method capable of reducing the exposure amount of a worker as compared with the conventional case by controlling to the above.

  The present invention includes a plurality of means for solving the above-mentioned problems. To give an example, the exposure reducing method in a boiling water nuclear power plant is a supply and condensate system of the boiling water nuclear power plant. Among the members used in contact with the coolant provided in the plate, the corrosion potential of the member made of a material containing cobalt is -0.2 Vvs. It is characterized by maintaining control below SHE.

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

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

  Embodiments of the exposure reducing method of the present invention will be described below with reference to the drawings.

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

  Among radionuclides such as cobalt 60, cobalt 58, chromium 51, manganese 54, etc., it is known that cobalt 60 is the main factor of the increase in 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 that occurs when cobalt 59 is irradiated with neutrons. Cobalt 59, which is the basis of this cobalt 60, elutes into the coolant from cobalt-based alloys such as stellite used for valve bodies and 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 contains about 0.2% cobalt as an impurity. Therefore, the cobalt 59 is eluted not only from the cobalt base alloy but also from stainless steel or high nickel alloy.

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

  In order to reduce the dissolution amount of cobalt 59, the present inventors have examined whether it can be achieved by grasping and controlling the corrosion environment strength formed by the coolant.

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

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

  Therefore, the present inventors evaluated the correlation between the corrosion potential and the cobalt elution amount by measuring the polarization curve. As a typical material containing cobalt, cobalt-based alloy Stellite No. No. 6 was selected, and in the pure water of 553K 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. By controlling and maintaining below SHE (standard hydrogen electrode standard), the elution amount of cobalt from stellite is +0.2 Vvs. It became clear that it can be reduced to 1/20 or less of SHE.

  From this knowledge, a means for reducing the corrosion potential and a means for evaluating the corrosion potential are provided for the feed and condensate water system, and the potential is set to -0.2 Vvs. By controlling and maintaining below SHE, it is clear that the elution amount of cobalt eluting from the cobalt-containing material to the coolant in any part of the feed and condensate system can be controlled and maintained at a low level. It became.

  That is, if the amount of cobalt 59 eluted from the material in the system to the coolant is reduced, the total amount of cobalt 60 that is activated in the vicinity of the reactor core is naturally reduced, so that the accumulated amount of radionuclide on the pipe surface may be reduced. This can reduce the exposure of workers.

  The present invention has been made based on the above findings.

<Example 1>
A first embodiment of the exposure reducing 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 suitably 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, steam generated by boiling the coolant in the reactor core 13 drives the turbine 6 through the main steam system 5 to generate electric power.

  The steam that exits the turbine 6 is condensed in the condenser 7, and this condensed water flows through the condensate system 1 as condensate. This condensate passes through the low-pressure feed water heater 10, the feed water pump 12, and the high-pressure feed water heater 11 and returns to the RPV 3 through the feed water system 2 as feed water.

  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 FIG. 2 shows an example without a jet pump. A residual heat removal system 33 is connected to the recirculation system 4.

  Most of the coolant that has not become steam is separated from the steam at the top of the RPV 3 and flows below the RPV 3 through the downcomer 14 around the core 13. The coolant that has flowed downward flows into the recirculation system 4 and is returned again to the core 13 by the recirculation pump 4a.

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

  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 demineralizer 18. The coolant purified by the furnace purification system demineralizer 18 is supplied to the feed water system 2 through a pipe 17c connected to the feed water system 2, mixed with the feed water, and returned to the RPV 3.

  In an emergency, a high pressure spray system 40 for injecting pure water stored in a suppression chamber 41 connected to the reactor containment vessel 42 into the RPV 3 is installed.

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

  The condensate system 1 is composed of a condenser 7, a condensate pump 8, a condensate demineralizer 9, pipes connecting the respective devices, and valves and joints provided in the pipes.

  Further, an off-gas system 28 is connected to the condenser 7. The off-gas system 28 is provided with a steam extractor 27 and a recombiner 30. An oxygen injection device 29 is connected to a pipe between the condenser 7 and the steam extractor 27 of the off-gas system 28.

  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 pipes connecting these devices, and valves and joints provided in the pipes.

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

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

  The furnace purification system 17 is constituted by a heat exchanger 17a, a furnace purification system pump 17b, a furnace purification system demineralizer 18, and pipes connecting these devices, and valves and joints provided in the pipes. .

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

  Also 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 a pipe constituting the bottom drain 16. The bottom drain 16 is provided with a corrosion potential sensor (not shown) for measuring the corrosion potential of the coolant.

  Also to the main steam system 5, a water quality measuring device (not shown) is connected to piping 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 quality of the condensed water generated by condensing the steam. Furthermore, a dose rate monitor 26 for measuring the dose rate of the main steam system is also installed in the main steam system 5.

  The quality of the feed water (dissolved oxygen concentration, dissolved hydrogen concentration, pH, conductivity, etc.) is measured on-line by the water quality measurement device 20a by reducing and cooling the feed water collected from the sampling pipe 19.

  The water quality of the coolant is measured online by the water quality measuring device 20b after the coolant collected from the sampling pipe 21 is depressurized and cooled. In the case of a coolant, since the corrosion potential is also measured by a corrosion potential sensor (not shown), 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 decompressed 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 conditions of a temperature from room temperature to about 50 ° C. and a pressure from atmospheric pressure to about 5 atm by reducing and cooling the water. .

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

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

  As described above, the material constituting these members contains cobalt and is 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 as a means for reducing the corrosion potential with respect to the coolant. As the reducing agent, gaseous hydrogen or a gas or liquid containing hydrogen is mainly used.

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

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

  In the present embodiment, in addition to the adjustment of the hydrogen injection amount, a hydrogen injection device 32 is installed as a means for reducing the corrosion potential in the inlet side pipe of the low-pressure feed water heater 10 in the feed and condensate system. In addition, the corrosion potential sensor 25 is installed on the downstream side of the hydrogen injection device 32.

  In addition, the corrosion potential of the piping, joints, and valves constituting the condensate system 1 and the feed water system 2, and further the corrosion potential of the low pressure feed water heater 10 and the high pressure feed water heater 11 are continued by the corrosion potential sensor 25 during the operation of the BWR plant 100A. Measure automatically.

  Then, in order to reduce the exposure of workers working in the BWR plant 100A, the measured corrosion potential of these members is -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 threshold value (−0.2 V vs. SHE), the amount of reducing agent injected is increased.

  Thereby, the amount of cobalt 59 eluted from the above-mentioned member containing cobalt, which is installed downstream of the low-pressure feed water heater 10 in the supply and condensate water system, into the coolant due to corrosion is reduced and engaged. Reduce the amount of radiation exposure.

  The corrosion potential sensor 25 which is a means for evaluating the corrosion potential in this embodiment can have a known configuration, for example, using a zirconia diaphragm as described in JP-A-2003-4887. 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. By applying these measurement / analysis means, the corrosion potential of the desired part is evaluated.

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

  The amount of reducing agent injected can be adjusted manually by the operator, or automatically adjusted by the control device, or 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 and condensate system, etc. It is desirable to control by adjusting by any method of semi-automatic adjustment combining manual adjustment of the above and automatic adjustment by the control device.

  Further, in this embodiment, during operation of the BWR plant 100A, a coolant is collected from one or more systems such as the sampling pipes 19 and 21, and the main or temporary water quality measuring devices 20a and 20b and a pH meter are used. The impurity component concentration in the coolant, particularly the cobalt concentration, is measured. Alternatively, coolant is taken from one or more systems such as sampling pipes 19 and 21 at regular intervals or as necessary, and the concentration of cobalt 59 in the coolant is measured using an inductively coupled plasma mass spectrometer or flameless atomic absorption. Quantify with analytical instrument. As a result, when the measured concentration of cobalt 59 exceeds a predetermined value, it is desirable to increase the hydrogen injection amount so that the cobalt concentration in the coolant does not exceed the predetermined concentration.

  Next, the effect of the present embodiment will be described.

  The exposure reducing method in the BWR plant 100A according to the first embodiment of the present invention described above is that the hydrogen injection device 32 and the corrosion potential sensor 25 are installed in the feed and condensate system, and the BWR plant is operated by the corrosion potential sensor 25 during operation. Of the members used in contact with the coolant provided in the 100A feed and condensate system, the corrosion potential of a member made of a material containing cobalt is measured, and the measured potential is -0.2 Vvs. . The amount of reducing agent injected into the coolant is controlled so as to maintain SHE or lower.

  As a result, the amount of cobalt eluting into the coolant due to corrosion from the surface in contact with the coolant of the material containing cobalt among the members constituting the feed and condensate system of the BWR plant 100A is reduced to a lower level than before. It can be controlled and maintained. For this reason, the density | concentration of the cobalt 59 in a coolant can be reduced compared with the past, and the quantity of the cobalt 60 produced | generated by receiving neutron irradiation on the fuel surface can be reduced. Accordingly, since the amount of cobalt 60 re-eluting from the fuel surface into the coolant can be reduced, the surface of the piping is transferred to a system such as a recirculation system or a reactor water purification system accompanying the coolant flow. The amount of cobalt 60 accumulated in the battery can be reduced, and the exposure dose of workers can be reduced compared to the conventional case.

  Moreover, replacement of members is unnecessary, and it is possible to suppress an increase in labor and cost. In particular, reducing the cobalt content in the material of the member is a great disadvantage in terms of cost, but according to the present invention, there is no need to use such a special material. Has the advantage of being very large.

  Further, the cobalt-containing material is at least one of stellite, stainless steel, and high nickel alloy, and the member made of the cobalt-containing material is a pipe, a valve, a heater, or a joint. By using at least one of them, effective measures can be taken against the main cobalt elution source, and the concentration of cobalt 59 in the coolant can be reduced more effectively than before. Can do.

  Furthermore, by using at least one of hydrogen, hydrazine, and ethanol as the reducing agent, effective hydrogen can be effectively supplied as a reducing agent into the coolant, and the target member can be more easily obtained. Has a corrosion potential of -0.2 Vvs. The maintenance control can be performed so as to be equal to or lower than SHE.

  Further, water quality measuring devices 20a and 20b are further installed in the feed and condensate 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. Thus, by controlling the amount of the reducing agent injected into the coolant, the corrosion potential of the target member is more reliably −0.2 Vvs. The reducing agent can be injected into the coolant so as to be equal to or lower than SHE, and the concentration of cobalt 59 in the coolant can be further effectively reduced as compared with the conventional case.

  The corrosion potential was measured and the measured potential was -0.2 Vvs. The members to be maintained below SHE are not limited to the pipes, joints, and valves constituting the condensate system 1 and the feed water system 2, and are not limited to the low pressure feed water heater 10 and the high pressure feed water heater 11, and the heat exchanger of the furnace purification system 17 17a and the piping, valves, and joints constituting the furnace purification system 17 were also measured for corrosion potential, and the measured potential was -0.2 Vvs. It can be set as the object of the object which maintains SHE or less.

<Example 2>
An exposure reduction method according to embodiment 2, which is another preferred embodiment of the present invention, will be described with reference to FIG. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The same applies to the following embodiments.

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

  In this embodiment, during operation of the BWR plant 100B, hydrogen is injected into the feed and condensate system using the hydrogen injection device 32, and the corrosion potential of the target member is continuously measured using the corrosion potential sensor 25. The corrosion potential is -0.2 Vvs. The point of controlling the amount of hydrogen injected into the coolant so as to maintain the SHE or lower is the same as the exposure reduction method of the first embodiment.

  In this embodiment, further, during the reactor shutdown, platinum is injected into the coolant in the feed and condensate system using the noble metal injection device 31, and the low pressure feed water heater 10, the high pressure feed water heater 11, and the system Platinum is adhered to the surface of the cobalt-containing material used in contact with the coolant in the supply and condensate system, such as existing valves.

  The step of injecting platinum into the feed and condensate system using the noble metal injection device 31 is not limited to when the reactor is stopped, and may be performed during the operation of the reactor, during construction, or during the test operation / startup test.

  The noble metal injection apparatus 31 is an apparatus for injecting, for example, an aqueous solution in which platinum is dissolved in water in a chemical form of hydroxide or nitric acid compound into the coolant, so that platinum is introduced into the coolant and cooling including platinum. Platinum introduced into the coolant adheres to the surface of a structural member (for example, recirculation piping, core partition wall, etc.) that contacts the material.

  In addition, the noble metal to introduce | transduce is not restricted to platinum (Pt), In addition to platinum, gold (Au), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), It can be at least any one or more elements.

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

  In the exposure reducing method according to the second embodiment of the present invention, substantially the same effect as the exposure reducing method according to the first embodiment described above can be obtained.

  Further, a hydrogen injection device 32, a noble metal injection device 31, and a corrosion potential sensor 25 are installed in the feed and condensate system, and the corrosion potential of the member is measured by the corrosion potential sensor 25 during the operation of the BWR plant 100B. Applied potential is -0.2 Vvs. By controlling the amount of the reducing agent injected into the coolant so as to maintain the SHE or less, the catalyst layer of the noble metal can be provided on the surface of the target member by injecting the noble metal into the coolant. Because of 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, so that the concentration of cobalt 59 in the coolant can be reduced more effectively than in the first embodiment. Compared to, it can be reduced.

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

  In addition, when the precious metal is injected at least one of BWR plant 100B construction, trial operation / startup test, furnace shutdown, and operation, platinum is effectively applied to the surface of the structural member. , The corrosion potential on the surface of the structural member can be kept low, and the amount of cobalt 59 eluted can be reduced.

  The location where the noble 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 feed water heater 10 as shown in FIG. In this case, since most of the precious metal injected by the condensate demineralizer 9 is removed, it is desirable that the condensate demineralizer 9 is located downstream.

<Example 3>
The exposure reduction method of Example 3 of this invention is demonstrated.

  Since the structure of the BWR plant in which the exposure reducing method of the present embodiment is suitably implemented is substantially the same as that of the BWR plant 100A shown in FIG. 2, the description will be given 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 the SHE or lower is the same as the exposure reduction method of the first embodiment.

  In the present embodiment, a noble metal is further included as a component element in a member composed of a material containing cobalt, that is, a pipe, a valve, a heater, and a joint. Thereby, similarly to the form of Example 2, a noble metal catalyst layer is provided on the surface of the target member, and the corrosion potential on the surface of the structural member is kept low compared to the conventional case.

  As a method of adding a precious metal to the structural member, electrolytic / electroless plating, vapor deposition, meat on the surface of the target member used for valves / piping in the feed and condensate system during the operation stop period of the BWR plant 100A. A layer containing platinum is formed on the surface of the target member by any one or more of various methods such as adding platinum to the repair material.

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

  In the present embodiment, the noble metal contained as a component element in the member composed of a material containing cobalt is also one or more of gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium as in the second embodiment. It is desirable to use these elements.

  In the present embodiment, noble metal injection using the noble metal injection apparatus 31 as in the second embodiment is unnecessary because the effect of the noble metal injection has already been obtained.

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

  As in the exposure reduction method of the third embodiment of the present invention, the hydrogen injection device 32 and the corrosion potential sensor 25 are installed in the feed and condensate system, and noble metal is used as a component made of a material containing cobalt. The corrosion potential of the member was measured by the corrosion potential sensor 25 during operation, and the measured potential was -0.2 Vvs. By controlling the amount of the reducing agent injected into the coolant so as to maintain the SHE or lower, substantially the same effect as the exposure reducing method of Example 2 described above can be obtained.

  In addition, the method of adding a noble metal to the member is to form a layer containing the noble metal on the surface of the member by at least one of electroless plating, electrolytic plating, vapor deposition, and overlaying. There is no need to unnecessarily contain a noble metal in the material, and the amount of expensive noble metal used can be reduced to reduce costs.

<Example 4>
The exposure reduction method of Example 4 of this invention is demonstrated using FIG.

  As shown in FIG. 4, in the BWR plant 100C in which the exposure reduction method of the present embodiment is suitably 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 to inject the reducing agent from the upstream side of the condensate pump 8.

  Other configurations / operations are substantially the same configurations / operations as the BWR plant 100A of the first embodiment and the exposure reduction method, and the details are omitted.

  The exposure reducing method according to the fourth embodiment of the present invention can provide substantially the same effect as the exposure reducing method according to the first embodiment.

  In addition, the form which provides a hydrogen injection apparatus in the upstream from the condensate pump 8 like a present Example is not restricted to the form of Example 1, In the form of Example 2 or Example 3, it is the same. A hydrogen injection device can be provided further upstream.

  Furthermore, the location where the hydrogen injection device is provided is not limited to the form of the present embodiment or embodiment 1, and may be any location of the feed and condensate system, but the corrosion potential measured in the present invention is effectively −0. 2Vvs. In order to maintain the SHE or lower, it is desirable to provide in the condensate system 1 corresponding to the upstream side in the system as in the first embodiment or the present embodiment.

<Others>
In addition, this invention is not limited to said Example, Various modifications are included. The above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. For example, although the present invention has been described as being applied to a feed water condensate system, it is also suitable to apply to a feed water heater drain system.

  Further, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

1 ... Condensation system 2 ... Water supply system 3 ... RPV
DESCRIPTION OF SYMBOLS 4 ... Recirculation system 4a ... Recirculation pump 5 ... Main steam system 6 ... Turbine 7 ... Condenser 8 ... Condensate pump 9 ... Condensate demineralizer 10 ... Low-pressure feed water heater 11 ... High-pressure feed water heater 12 ... Feed water Pump 13 ... Core 14 ... Downcomer 15 ... Reactor lower plenum 16 ... Bottom drain 17 ... Reactor purification system 17a ... Heat exchanger 17b ... Reactor purification system pump 18 ... Reactor purification system demineralizers 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 (12)

A method for reducing exposure in a boiling water nuclear power plant,
Of the members used in contact with the coolant provided in the supply and condensate system of the boiling water nuclear power plant, the corrosion potential of the member made of a material containing cobalt is -0.2 Vvs. An exposure reduction method characterized by maintaining control below SHE. In the exposure reduction method of Claim 1,
In the supply and condensate system, a reducing agent injection device and a corrosion potential measurement device are installed,
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 so as to maintain SHE or less. In the exposure reduction method of Claim 2,
A precious metal injection device is further installed in the feed and 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 a reducing agent injected into the coolant so as to maintain SHE or less and injecting a noble metal into the coolant. In the exposure reduction method of Claim 2,
An exposure reducing method, comprising: containing a noble metal as a component element in a member composed of the cobalt-containing material of the feed and condensate system. In the exposure reduction method of Claim 2,
A water quality measuring device is further installed in the feed and condensate system,
The cobalt concentration in the coolant is measured by the water quality measuring device during the operation of the boiling water nuclear power plant, and the reducing agent injected into the coolant is measured 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 of Claim 1,
The material containing cobalt is at least one of stellite, stainless steel, and high nickel alloy. In the exposure reduction method of Claim 1,
The member comprised with the said cobalt containing material is made into at least any one or more among piping, a valve, a heat exchanger, a heater, and a coupling. The exposure reduction method characterized by the above-mentioned. In the exposure reduction method of Claim 2,
The exposure reducing method, wherein the reducing agent is at least one of hydrogen, hydrazine, and ethanol. In the exposure reduction method of Claim 3 or 4,
The exposure reducing method, wherein the noble metal is at least one of gold, platinum, palladium, rhodium, iridium, ruthenium, and osmium. In the exposure reduction method of Claim 3,
The exposure reduction method, wherein the precious metal is injected at least one of the following periods: during construction of the boiling water nuclear power plant, during trial operation / startup test, during reactor shutdown, and during operation. In the exposure reduction method of Claim 4,
The method for containing the noble metal in the member is to form the noble metal-containing layer on the surface of the member by at least one of electroless plating, electrolytic plating, vapor deposition, and overlaying. A method for reducing exposure. In the exposure reduction method of any one of Claims 1 thru | or 11,
The corrosion potential of the member made of the material containing cobalt is -0.2 Vvs. An exposure reduction method characterized in that the amount of cobalt 59 eluted into the coolant in the system by corrosion is reduced by maintaining and controlling below SHE.

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