Method for mitigating corrosive environments of boiling water reactor, and nuclear power plant

Abstract

To provide a method for mitigating corrosive environments of boiling water reactor capable of increasing the amount of precious metals supplied to a reactor pressure vessel by suppressing the adhesion of precious metals to chemical injection pipes and other pipes compared to conventional methods when injecting precious metals into a boiling water reactor, and a nuclear power plant.SOLUTION: The method for mitigating corrosive environments of a boiling water reactor includes a step of simultaneously injecting hydrogen and precious metals into the water supplied to the reactor pressure vessel 1. In the step of injection, the oxidant is injected into chemical injection pipings 8 and 8A so that the molar ratio of hydrogen to oxygen in the chemical solution flowing through chemical injection pipings 8 and 8A connected to piping that supplies water to the reactor pressure vessel 1 is less than 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for mitigating the corrosive environment of a boiling water nuclear reactor and to a nuclear power plant. [Background technology]

[0002] Patent Document 1 describes a method for mitigating the corrosive environment in a boiling water reactor, which mitigates the corrosive environment inside the reactor pressure vessel by injecting hydrogen and a precious metal compound into the water supplied to the reactor pressure vessel during power generation operation of a boiling water nuclear power plant having the reactor pressure vessel. The method describes injecting hydrogen into the water supplied to the reactor pressure vessel, and injecting a precious metal compound into water in a system in which the concentration of oxygen or hydrogen peroxide exceeds the equivalent concentration of hydrogen that chemically reacts to turn into water.

[0003] Non-Patent Document 1 discloses a phenomenon in which an increase in the differential pressure in a chemical injection pipe occurs as a result of the deposition of platinum compounds. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-181350 A [Non-patent literature]

[0005] [Non-Patent Document 1] BWRVIP-62 Rev. 1 Pre-RAI Submittal Meeting, BWRVIP Presentation to NRC Three White Flint North, MD, July 18, 2014 (US NRC Report No. ML14205A603) Summary of the Invention [Problem to be solved by the invention]

[0006] In a boiling water reactor (BWR), it is necessary to suppress stress corrosion cracking (SCC) in the reactor internals installed inside the reactor pressure vessel and the system piping connected to the pressure vessel. The reactor internals and system piping are made of stainless steel, low alloy steel, carbon steel, nickel-based alloy, etc. Although these materials have excellent corrosion resistance, there is a risk of SCC initiation and progression due to the overlap of material factors, stress factors, and environmental factors.

[0007] When a nuclear reactor is operating, high-temperature, high-pressure cooling water comes into contact with reactor internal structures and system piping. The cooling water contains oxygen and hydrogen peroxide produced by radiolysis of water. It is known that the higher the oxygen and hydrogen peroxide concentrations in the cooling water, the more pronounced the occurrence and progression of SCC. Reducing the oxygen and hydrogen peroxide concentrations in the cooling water is known to be effective in suppressing SCC, as it alleviates environmental factors.

[0008] Measures to suppress SCC include hydrogen injection and precious metal injection. Hydrogen injection is a technique in which hydrogen gas is injected into the cooling water, causing a recombination reaction between oxygen and hydrogen peroxide and hydrogen, turning it back into water. Precious metal injection is a technique in which a solution containing a precious metal compound is injected into the cooling water, causing the precious metal to adhere to the surface of the material that comes into contact with the cooling water. Precious metals such as platinum, rhodium, and palladium catalyze the recombination reaction.

[0009] In BWRs, precious metal injection may be performed while the reactor is in operation (hereinafter referred to as "in-operation precious metal injection"). For in-operation precious metal injection, a low-concentration solution of platinum compound is used. Sodium hexahydroxoplatinate (Na2Pt(OH)6) is used as the platinum compound. The platinum compound solution is injected into the cooling water through a chemical injection pipe. The chemical injection pipe is connected to the system piping of the feedwater system.

[0010] The solution of precious metal compounds is injected into the cooling water through the chemical injection pipe, and then supplied together with the cooling water to the reactor pressure vessel, etc. The solution of precious metal compounds is turned into a colloidal solution of oxides by exposure to gamma rays, and the precious metals are attached to the surfaces of the reactor internals and system piping. Hydrogen is also injected at the same time as the precious metals are injected. Hydrogen gas is injected into the cooling water upstream of the chemical injection pipe, and then supplied together with the cooling water to the reactor pressure vessel, etc.

[0011] When hydrogen is injected, oxygen and hydrogen peroxide are consumed by recombination reactions inside the reactor pressure vessel and in the system piping. This reduces the oxygen and hydrogen peroxide concentrations in the cooling water, making it difficult for intergranular corrosion to progress and suppressing SCC in the reactor internals and system piping. When precious metals are injected, the recombination reaction is catalyzed, so SCC can be suppressed with a small amount of hydrogen. Generally, 1 μg / cm of precious metals is injected on the surface of the material. 2 When the above amount of platinum is adhered, a sufficient SCC suppression effect is obtained.

[0012] It is known that when precious metals are injected, excessive reduction and precipitation of the precious metals occurs near the outlet of the chemical injection pipe. If the cooling water into which a solution of a precious metal compound is injected is at a high temperature of 190°C or higher, the precious metal compound will be thermally decomposed. Also, if the cooling water has a high hydrogen concentration, reduction of the precious metal ions will occur. In particular, the cooling water is likely to become hot and have a high hydrogen concentration near the outlet of the chemical injection pipe, making it a place where precious metals are likely to precipitate. Therefore, there is a risk that the flow resistance of the chemical injection pipe will increase or the chemical injection pipe will become clogged when precious metals are injected. This causes a problem that the injection efficiency of the precious metals decreases and the amount of precious metals supplied to the reactor pressure vessel will decrease (see Non-Patent Document 1).

[0013] Patent Document 1 describes a technique for injecting a precious metal compound into water in a system in which the concentration of oxygen or hydrogen peroxide exceeds the equivalent concentration relative to the concentration of hydrogen that chemically reacts to form water.

[0014] As described in Patent Document 1, when an aqueous solution of sodium hexahydroxoplatinate is injected into water in a system in which the concentration of oxygen or hydrogen peroxide exceeds the equivalent concentration of hydrogen that chemically reacts to form water, the amount of platinum compounds precipitated due to the reduction reaction and thermal decomposition reaction by hydrogen is reduced in the water supply system piping and in the vicinity of the connection between the chemical injection piping and the system piping.

[0015] Specifically, an oxygen injection device is installed in the piping between the outlet of the purification device of the reactor coolant purification system and the heat exchanger, and a precious metal injection device is further installed in the piping downstream of the oxygen injection device. This creates a system in which precious metal compounds are injected into cooling water whose oxygen concentration exceeds the equivalent of the hydrogen concentration, and it is said that the reduction of precious metal ions by hydrogen can be suppressed, thereby reducing the risk of precious metal precipitation and piping blockage.

[0016] When applying precious metal injection during operation as described in Non-Patent Document 1, if an aqueous solution of sodium hexahydroxoplatinate is injected into the feedwater system piping, the thermal decomposition reaction of sodium hexahydroxoplatinate and the reduction reaction of platinum ions by hydrogen contained in the cooling water may cause some platinum compounds to precipitate in the feedwater system piping and in the vicinity of the feedwater system piping connections of the chemical injection piping, resulting in a decrease in the amount of precious metal supplied to the reactor pressure vessel.

[0017] An object of the present invention is to provide a method for mitigating the corrosive environment of a boiling water reactor, which is capable of suppressing adhesion of precious metals to chemical injection piping and other piping when injecting precious metals into a boiling water reactor, as compared to conventional methods, and of increasing the amount of precious metal supplied into the reactor pressure vessel, and a nuclear power plant. [Means for solving the problem]

[0018] The present invention includes a number of means for solving the above problems. One example of the present invention includes a step of simultaneously injecting hydrogen and a precious metal into water to be supplied to a reactor pressure vessel, and in the injecting step, an oxidizer is injected into a chemical injection pipe connected to a pipe through which the water to be supplied to the reactor pressure vessel flows, so that the molar ratio of hydrogen to oxygen in the chemical flowing through the chemical injection pipe is less than 2. Effect of the Invention

[0019] According to the present invention, when injecting precious metals into a boiling water reactor, adhesion of the precious metals to the chemical injection pipes and other pipes can be suppressed compared to the conventional art, and the amount of precious metals supplied into the reactor pressure vessel can be increased. Other objects, configurations and effects will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic configuration diagram showing a nuclear power plant according to a first embodiment. [Diagram 2] 1 is a graph showing the relationship between the time from the start of platinum injection and the increase in differential pressure due to clogging of the chemical injection piping. [Diagram 3] FIG. 1 is a block diagram showing a preferred hydrogen peroxide injection device of the present invention. [Figure 4] FIG. 1 is a block diagram showing a preferred oxygen injection device of the present invention. [Diagram 5] FIG. 1 is a schematic diagram illustrating the relationship between the vortex penetration depth flowing in from the water supply system piping and the oxidant injection point into the chemical injection piping. [Figure 6] 1 is a graph showing the relationship between the flow velocity of a water supply system piping and the ratio of the vortex penetration depth to the inner diameter of the chemical injection piping. [Figure 7] 1 is a graph showing the relationship between the inner diameter of a chemical injection pipe and the oxidizing agent concentration required to suppress deposition of precious metals. [Figure 8] 1 is a graph showing the relationship between the feed water hydrogen concentration and the oxidizing agent concentration required for suppressing deposition of precious metals. [Figure 9] FIG. 1 is a schematic configuration diagram showing a nuclear power plant according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, the embodiment of the method for mitigating the corrosive environment of a boiling water reactor and the nuclear power plant of the present invention will be described with reference to the drawings. In the drawings used in this specification, the same or similar reference numerals are used to designate the same or corresponding components, and the repeated description of these components may be omitted.

[0022] <Example 1> A method for mitigating a corrosive environment in a boiling water reactor and a nuclear power plant according to a first embodiment of the present invention will be described with reference to FIGS.

[0023] First, the overall configuration of a boiling water nuclear power plant will be described with reference to Fig. 1. Fig. 1 shows the configuration of the nuclear power plant of this embodiment.

[0024] A boiling water nuclear power plant 100 shown in FIG. 1 includes a reactor pressure vessel 1, a turbine 3, a condenser 4, a feedwater system, and the like.

[0025] A reactor core (not shown) loaded with a plurality of fuel assemblies is disposed inside the reactor pressure vessel 1. The fuel assemblies include a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel material. A plurality of internal pumps (not shown) are provided at the bottom of the reactor pressure vessel 1. A main steam system piping 2 connected to the reactor pressure vessel 1 is connected to a turbine 3.

[0026] The feedwater system has a configuration in which a condensate filtration and demineralization device 12, a feedwater pump 13, and a feedwater heater 14 are installed in this order from the condenser 4 toward the reactor pressure vessel 1 in feedwater system piping 5 that connects the condenser 4 and the reactor pressure vessel 1. The turbine 3 is installed above the condenser 4 and is connected to the turbine 3.

[0027] Cooling water in the reactor pressure vessel 1 is pressurized by an internal pump and supplied to the reactor core. The cooling water supplied to the core is heated by heat generated by nuclear fission of the nuclear fuel material in the fuel rods. Part of the heated cooling water becomes steam. This steam has moisture removed in a steam separator (not shown) and a steam dryer (not shown) installed inside the reactor pressure vessel 1, and is then guided from the reactor pressure vessel 1 through the main steam system piping 2 to the turbine 3, causing it to rotate. A generator (not shown) connected to the turbine 3 rotates, generating electricity.

[0028] The steam discharged from the turbine 3 is condensed into water in a condenser 4. This water is supplied as feedwater to the reactor pressure vessel 1 through a feedwater system piping 5. The feedwater flowing through the feedwater system piping 5 has impurities removed by a condensate filtering and demineralizing device 12, and is pressurized by a feedwater pump 13. The feedwater is heated in a feedwater heater 14, and is led into the reactor pressure vessel 1 through the feedwater system piping 5.

[0029] When applying the precious metal injection technology during operation, hydrogen gas is injected into the feedwater flowing through the feedwater system piping 5 by the hydrogen injection device 11 installed in the feedwater system piping 5 between the condensate filtration demineralizer 12 and the feedwater pump 13. This controls the hydrogen concentration of the feedwater to 0.2 to 0.5 ppm.

[0030] In this embodiment, the precious metal injection device 9 is installed upstream of a chemical injection pipe 8 connected to a portion of the feedwater system piping 5 from the feedwater heater 14 to the junction with the reactor pressure vessel 1, through which water with a hydrogen to oxygen molar ratio of 2 or more flows as water to be replenished to the reactor pressure vessel 1, and injects sodium hexahydroxoplatinate or platinum oxide colloid into the chemical flowing through the chemical injection pipe 8.

[0031] The hydrogen peroxide injection device 10A and the oxygen injection device 10B are devices for injecting an oxidant so that the molar ratio of hydrogen to oxygen in the chemical solution flowing through the chemical solution injection piping 8 is less than 2, and are installed in the chemical solution injection piping 8 at a position from the precious metal injection device 9 to the junction with the water supply system piping 5.

[0032] Here, we will explain the effect of hydrogen concentration on the reduction reaction of sodium hexahydroxoplatinate, a platinum compound. Patent Document 1 shows the effect of hydrogen concentration on the adhesion of platinum compounds in carbon steel piping, and it is known that the amount of platinum attached to the carbon steel increases with increasing hydrogen concentration.

[0033] Next, the results of tests conducted to determine the water quality conditions that cause platinum to adhere to and block chemical injection piping will be explained with reference to Figure 2.

[0034] Figure 2 shows the change over time in the pressure difference between the upstream and downstream sides of the platinum compound injection point under various water chemistry conditions, for carbon steel piping. In Figure 2, the horizontal axis represents the time from the start of platinum compound injection, and the vertical axis represents the pressure difference between the upstream and downstream sides of the platinum compound injection point. In other words, the higher the pressure difference on the vertical axis, the more platinum adheres to the chemical injection piping, and the more likely it is that the chemical injection piping will become clogged.

[0035] When a platinum compound was injected into a carbon steel pipe with an inner diameter of 0.5 mm, clogging of the carbon steel pipe occurred within 30 minutes of injection in water quality conditions with a hydrogen concentration of 160 ppb and an oxygen concentration of 90 ppb, regardless of temperature conditions between 80 and 220°C. In addition, the time it took for the differential pressure to rise to 1.0 MPa tended to be shorter as the temperature increased. On the other hand, in water quality conditions with a hydrogen concentration of 0 ppb and an oxygen concentration of 90 ppb, no increase in differential pressure occurred, even at the high temperature condition of 220°C.

[0036] Based on these test results, it became clear that the amount of platinum compound precipitation can be reduced under water chemistry conditions in an oxidizing atmosphere where the molar concentration of oxygen relative to hydrogen is in excess.

[0037] In this way, in the present invention, an oxidizing agent is added to the chemical injection pipe 8 connected to the pipe through which the cooling water supplied to the reactor pressure vessel 1 flows, and the chemical containing a precious metal compound is injected while controlling the water quality in the chemical injection pipe 8 so that the molar ratio of hydrogen to oxygen is less than 2.

[0038] As the oxidizing agent to be injected into chemical injection pipe 8 from hydrogen peroxide injection device 10A and oxygen injection device 10B, oxygen or hydrogen peroxide is suitable.

[0039] As shown in reaction formula (1), oxygen and hydrogen react in a molar ratio of 1:2 to produce water. Therefore, in order to create an oxidizing atmosphere inside the chemical injection piping, the molar ratio of hydrogen to oxygen must be less than 2. 2H2+ O2→ 2H2O ··· Reaction equation (1)

[0040] In addition, hydrogen peroxide decomposes to produce water and oxygen, as shown in reaction formula (2). Since the molar ratio of hydrogen peroxide to oxygen produced by the decomposition of hydrogen peroxide is 2:1, the molar ratio of hydrogen to hydrogen peroxide must be less than 1 in order to create an oxidizing atmosphere inside the chemical injection piping. 2H2O2 → 2H2O + O2... Reaction equation (2)

[0041] From the above, by adding an oxidizing agent to the chemical injection pipe so as to satisfy inequality (3), the inside of the chemical injection pipe can be made into an oxidizing atmosphere, and the reduction and precipitation of precious metal compounds can be suppressed. Note that, because hydrogen peroxide decomposes to produce oxygen as shown in reaction equation (2), inequality (3) can be rewritten as inequality (3)'.

[0042] Therefore, controlling the water quality in the chemical injection pipe so that the molar ratio of hydrogen to oxygen is less than 2 is effective in reducing the amount of precious metals that precipitate. [O2] + 2[H2O2] > 2[H2] ···(3) [O2] > 2[H2] ···(3)'

[0043] Fig. 3 shows hydrogen peroxide injection device 10A that injects hydrogen peroxide as an oxidizing agent. In Fig. 3, hydrogen peroxide injection device 10A includes chemical tank 17 filled with hydrogen peroxide solution, valve 22, oxidizing agent injection piping 21A, flow meter 18, pump 19, and valve 23.

[0044] Valves 22 and 23 are opened and pump 19 is started to inject hydrogen peroxide solution from chemical tank 17 into chemical injection pipe 8. The flow rate is adjusted by pump 19 and is confirmed by flow meter 18.

[0045] Alternatively, chemical tank 17 may be filled with a chemical solution containing hydrogen peroxide and a precious metal compound, and the mixture of hydrogen peroxide and the precious metal compound may be injected into chemical injection pipe 8.

[0046] Fig. 4 shows an oxygen injection device 10B when injecting oxygen as an oxidizing agent. In Fig. 4, a cylinder 20 filled with oxygen and a chemical injection pipe 8 are connected by an oxidizing agent injection pipe 21B. In the oxidizing agent injection pipe 21B, a pressure reducing regulator 24, a flow meter 18, and a valve 25 are installed in that order from the cylinder 20 on the upstream side.

[0047] Pressure reducing regulator 24 and valve 25 are opened to inject oxygen from cylinder 20 into chemical injection pipe 8. The flow rate of oxygen gas is adjusted by pressure reducing regulator 24 and is confirmed by flowmeter 18.

[0048] Hereinafter, a method of injecting an oxidizing agent into the chemical injection pipe 8 when the technique of injecting precious metals during operation is applied will be described with reference to FIG.

[0049] The cooling water flowing in the water supply system piping 5 has a high flow velocity of several m / s, whereas the chemical flowing in the chemical solution injection piping 8 has a low flow velocity of several to several tens of cm / s. Therefore, the cooling water containing hydrogen flows as a vortex 26 from the water supply system piping 5, which has a fast flow, to the chemical solution injection piping 8, which has a slow flow.

[0050] Therefore, it is important to control the concentration of the oxidant injected into the chemical injection pipe 8 so that twice the product of the amount of chemical injected from the chemical injection pipe 8 to the water supply system piping 5 and the molar concentration of oxygen in the chemical is greater than the product of the amount of cooling water flowing from the water supply system piping 5 into the chemical injection pipe 8 and the molar concentration of dissolved hydrogen in the cooling water.

[0051] Here, Fig. 6 shows the relationship between the flow velocity of the feedwater system piping 5 and the ratio of the penetration depth of the vortex to the inner diameter of the chemical injection piping 8. In Fig. 6, the conditions for calculating the oxidant concentration are the inner diameter of the feedwater system piping 5 of 0.5 m, the feedwater flow rate of 3800 t / h, the flow velocity in the feedwater system piping 5 of 5.3 m / s, the inner diameter of the chemical injection piping 8 of 0.03 m, and the chemical injection flow rate of 0.5 L / min.

[0052] As shown in Figure 6, the penetration depth of the vortex into chemical injection piping 8 is 10 to 16 times the inner diameter of chemical injection piping 8, and the chemical flowing inside chemical injection piping 8 is diluted several hundred times by the infiltrating cooling water.

[0053] At this time, it is necessary to inject an oxidizing agent into the chemical injection pipe 8 so that the molar concentration of oxygen is 0.5 times, or the molar concentration of hydrogen peroxide is 1 time, relative to the molar concentration of dissolved hydrogen contained in the infiltrating cooling water.

[0054] Figure 7 shows the relationship between the inner diameter of the chemical injection pipe 8 and the oxidant concentration required to suppress the adhesion of precious metals. In Figure 7, the conditions for calculating the oxidant concentration are as follows: inner diameter of the feedwater system pipe 5 is 0.5 m, feedwater flow rate is 3800 t / h, flow velocity in the feedwater system pipe 5 is 5.3 m / s, inner diameter of the chemical injection pipe 8 is 0.03 m, and chemical injection flow rate is 0.5 L / min.

[0055] As is clear from FIG. 7, since the inner diameter of the chemical injection pipe 8 in an actual boiling water nuclear power plant is 2 to 3 cm, it is necessary to inject an oxidizer into the chemical injection pipe 8 at a concentration of 300 to 1000 ppm for oxygen, or 500 to 2500 ppm for hydrogen peroxide, depending on the inner diameter of the chemical injection pipe 8.

[0056] Figure 8 shows the relationship between the dissolved hydrogen concentration in the cooling water flowing through the feedwater system piping 5 and the oxidant concentration required to suppress precious metal adhesion. In Figure 8, the conditions for calculating the oxidant concentration are as follows: inner diameter of the feedwater system piping 5 is 0.5 m, feedwater flow rate is 3800 t / h, flow velocity in the feedwater system piping 5 is 5.3 m / s, inner diameter of the chemical injection piping 8 is 0.03 m, and chemical injection flow rate is 0.5 L / min.

[0057] As shown in FIG. 8, when applying the precious metal injection technology during operation, the dissolved hydrogen concentration in the feedwater system piping 5 is controlled to 0.2 to 0.3 ppm, so it is necessary to inject an oxidant into the chemical injection piping 8 at a concentration of 500 to 1500 ppm for oxygen or 1000 to 2500 ppm for hydrogen peroxide.

[0058] If oxygen levels are 0.8 ppm or higher, there is a risk of pitting corrosion in the carbon steel chemical injection pipe 8. Therefore, it is necessary to quickly react the high-concentration oxidant injected into the chemical injection pipe 8 with the dissolved hydrogen contained in the cooling water that has entered the chemical injection pipe 8.

[0059] Therefore, as shown in Figure 5, it is effective to inject the oxidant into the chemical injection pipe 8 at a depth position in the chemical injection pipe 8 that corresponds to the maximum penetration depth of vortex 26 containing dissolved hydrogen that penetrates from the feedwater system piping 5 into the chemical injection pipe 8.

[0060] Based on the flow velocity in the feedwater system piping 5 of an actual boiling water nuclear power plant and the inner diameter of the chemical injection piping 8, the penetration depth of the vortex is 10 to 16 times the inner diameter D of the chemical injection piping 8, so it is effective to connect the oxidizer injection piping 21A, 21B to the chemical injection piping 8 at a position 10 to 16 times the inner diameter D from the junction with the feedwater system piping 5.

[0061] Next, the effects of this embodiment will be described.

[0062] The corrosive environment mitigation method of the present embodiment 1 described above includes a step of simultaneously injecting hydrogen and a precious metal into the water to be supplied to the reactor pressure vessel 1. In the injection step, an oxidizing agent is injected into the chemical injection pipe 8 connected to the pipe through which the water to be supplied to the reactor pressure vessel 1 flows so that the molar ratio of hydrogen to oxygen in the chemical flowing through the chemical injection pipe 8 is less than 2.

[0063] According to the present invention, when injecting precious metals into a boiling water reactor, even if a backflow occurs from a connected pipe with a large diameter and a high flow rate, a reducing atmosphere is prevented from forming inside the chemical injection pipe 8, and thus adhesion of precious metals to the chemical injection pipe 8 and other pipes can be suppressed, thereby suppressing an increase in flow resistance and blockage of the flow paths of the chemical injection pipe 8 and other pipes. Accordingly, the amount of precious metals injected into the cooling water in the reactor pressure vessel can be increased compared to the conventional method.

[0064] Furthermore, since the chemical injection pipe 8 is connected to a pipe through which water with a hydrogen to oxygen molar ratio of 2 or more flows, the effect of suppressing precipitation in the system where hydrogen or precious metals are injected can be further improved.

[0065] Furthermore, by controlling the concentration of the oxidizing agent injected into the chemical injection piping 8 so that twice the product of the amount of the chemical injected into the piping through which the water supplied to the reactor pressure vessel 1 flows from the chemical injection piping 8 and the molar concentration of oxygen in the chemical is greater than the product of the amount of water flowing into the chemical injection piping 8 and the molar concentration of dissolved hydrogen in the piping through which the water supplied to the reactor pressure vessel 1 flows, the precipitation of precious metals can be reduced more efficiently.

[0066] In addition, by setting the position at which the oxidizer is injected into the chemical injection piping 8 to a position equivalent to the penetration depth of the vortex that penetrates into the chemical injection piping 8 from the piping through which the water supplied to the reactor pressure vessel 1 flows, precipitation in the chemical injection piping 8 can be more effectively suppressed.

[0067] <Example 2> Second Embodiment A method for mitigating a corrosive environment in a boiling water reactor and a nuclear power plant according to a second embodiment of the present invention will be described with reference to Fig. 9. Fig. 9 is a diagram showing the configuration of a nuclear power plant according to this embodiment.

[0068] The boiling water nuclear power plant 100A of this embodiment shown in FIG. 9 is different from the boiling water nuclear power plant 100 of the first embodiment in that the chemical injection piping 8A is connected to a reactor coolant purification system piping 6 that purifies the coolant of the reactor pressure vessel 1.

[0069] The reactor coolant purification system has a configuration in which a purification system pump 15, a regenerative heat exchanger 16, a non-regenerative heat exchanger (not shown), and a reactor coolant purification device 7 are installed in this order in reactor coolant purification system piping 6, which is arranged to extract a portion of the cooling water from the reactor pressure vessel 1 and join the feedwater system piping 5 midway. The reactor coolant purification system piping 6 is connected to the feedwater system piping 5 downstream of the feedwater heater 14.

[0070] A part of the cooling water in the reactor pressure vessel 1 flows into the reactor coolant purification system piping 6 by driving the purification system pump 15, and is cooled in the regenerative heat exchanger 16 and the non-regenerative heat exchanger, and then purified in the reactor coolant purification device 7. The purified cooling water is heated in the regenerative heat exchanger 16, and is returned to the reactor pressure vessel 1 as feed water via the reactor coolant purification system piping 6 and the feed water system piping 5.

[0071] When applying the precious metal injection technique during operation, the hydrogen injection device 11 operates to inject hydrogen into the cooling water flowing in the feed water system piping 5, and the hydrogen concentration is controlled to 0.2 to 0.5 ppm.

[0072] On the other hand, since hydrogen is not injected into the cooling water flowing through the reactor coolant purification system piping 6, the hydrogen concentration in the reactor coolant purification system piping 6 is lower than that in the feedwater system piping 5. Therefore, by connecting the chemical injection piping 8A to the reactor coolant purification system piping 6, there is an advantage in that the concentration or amount of the oxidizing agent injected into the chemical injection piping 8A can be reduced.

[0073] Furthermore, when the chemical injection pipe 8A is connected to the feedwater system pipe 5 as in the first embodiment, the piping distance from the precious metal injection point to the reactor pressure vessel 1 is shorter than when it is connected to the reactor coolant purification system pipe 6. This reduces the amount of precious metal adhering to the surface of the feedwater system pipe 5 before the injected precious metal compound is introduced into the reactor pressure vessel 1, which has the advantage of improving the efficiency of precious metal injection into the reactor pressure vessel 1.

[0074] The chemical solution injection pipe 8A according to this embodiment can be used in various plants in which a solution of a metal compound is injected into system piping.

[0075] The other configurations and operations are almost the same as those of the method for mitigating a corrosive environment in a boiling water reactor and the nuclear power plant in the first embodiment described above, and therefore details are omitted here.

[0076] Even in the case where the chemical injection pipe 8A is connected to the reactor coolant purification system pipe 6 for purifying the coolant of the reactor pressure vessel 1 as in the method for mitigating a corrosive environment for a boiling water reactor and a nuclear power plant according to the second embodiment of the present invention, substantially the same effects as those of the method for mitigating a corrosive environment for a boiling water reactor and a nuclear power plant according to the first embodiment described above can be obtained.

[0077] <Other> Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and various modifications are possible within the scope of the present invention. For example, the present invention is not necessarily limited to those having all the configurations of the above-mentioned embodiments. It is possible to replace a part of the configuration of a certain embodiment with another configuration, add a part of the configuration of a certain embodiment to another form, or omit a part of the configuration of a certain embodiment. [Explanation of symbols]

[0078] 1...Reactor pressure vessel 2...Main steam system piping 3. Turbine 4…Condenser 5…Water supply system piping 6...Reactor coolant purification system piping 7...Reactor coolant purification equipment 8,8A…Chemical injection piping 9…Precious metal injection device 10A…Hydrogen peroxide injection device (oxidizer injection device) 10B...Oxygen injection device (oxidizer injection device) 11...Hydrogen injection device 12...Condensate filtration and demineralization equipment 13…Water supply pump 14…Feed water heater 15...Purification system pump 16…Regenerative heat exchanger 17...Chemical tank 18...Flowmeter 19…Pump 20…Cylinder 21A, 21B...Oxidizer injection pipe 22, 23, 25…Valves 24…Reducing pressure adjusting valve 26...Whirlpool 100,100A...Boiling water nuclear power plant

Claims

1. co-injecting hydrogen and a precious metal into water supplied to a reactor pressure vessel; In the step of injecting, an oxidizing agent is injected into a chemical injection pipe connected to a pipe through which water supplied to the reactor pressure vessel flows, so that a molar ratio of hydrogen to oxygen in the chemical flowing through the chemical injection pipe is less than 2. Methods for mitigating corrosive environments.

2. The method for mitigating a corrosive environment according to claim 1, Hydrogen peroxide or oxygen is injected as the oxidizing agent. Methods for mitigating corrosive environments.

3. The method for mitigating a corrosive environment according to claim 1, The chemical injection pipe is connected to a pipe through which water flows, the molar ratio of which is 2 or more relative to oxygen. Methods for mitigating corrosive environments.

4. The method for mitigating a corrosive environment according to claim 1, The concentration of an oxidizing agent injected into the chemical injection pipe is controlled so that twice the product of the amount of the chemical injected from the chemical injection pipe into a pipe through which water supplied to the reactor pressure vessel flows and the molar concentration of oxygen in the chemical is greater than the product of the amount of water flowing into the chemical injection pipe and the molar concentration of dissolved hydrogen in the pipe through which the water supplied to the reactor pressure vessel flows. Methods for mitigating corrosive environments.

5. The method for mitigating a corrosive environment according to claim 1, The position where the oxidizer is injected into the chemical injection pipe is set to a position corresponding to the penetration depth of a vortex penetrating into the chemical injection pipe from a pipe through which water supplied to the reactor pressure vessel flows. Methods for mitigating corrosive environments.

6. The method for mitigating a corrosive environment according to claim 1, As the precious metal, sodium hexahydroxoplatinate or platinum oxide colloid is injected. Methods for mitigating corrosive environments.

7. A reactor pressure vessel; The turbine, A condenser; a water supply system piping for supplying water from the condenser to the reactor pressure vessel; A chemical injection pipe connected to a pipe through which water supplied to the reactor pressure vessel flows; and an oxidant injection device for controlling the molar ratio of hydrogen to oxygen in the chemical solution flowing through the chemical solution injection pipe to be less than 2. Nuclear power plant.

8. The nuclear power plant according to claim 7, The chemical injection pipe is connected to the water supply pipe. Nuclear power plant.

9. The nuclear power plant according to claim 7, The chemical injection pipe is connected to a purification system pipe for purifying the coolant of the reactor pressure vessel. Nuclear power plant.

10. The nuclear power plant according to claim 7, The oxidant injected from the oxidant injection device is either hydrogen peroxide or oxygen. Nuclear power plant.

11. The nuclear power plant according to claim 7, The apparatus further includes a hydrogen injection device for injecting hydrogen into the water flowing through the water supply system piping. Nuclear power plant.

12. The nuclear power plant according to claim 7, The apparatus further includes a precious metal injection device for injecting sodium hexahydroxoplatinate or platinum oxide colloid into the chemical solution flowing through the chemical solution injection pipe. Nuclear power plant.

Images