JPH10111286A - Evaluation of water quality of reactor water of nuclear reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control reactor water with high accuracy by calculating the relation between the corrosion current density and crack developing speed of a required region by simulation calculation. SOLUTION: An operation condition is hourly inputted to an operation apparatus 7 and water quality is calculated at every time and place by radiolysis analysis. Reactor water from the bottom of a pressure container 1 turned toward a reactor water purifying system 9 or a recirculating system 2 is guided to a sampling line 15 and diissolved oxygen, dissolved hydrogen, conductivity and pH are measured by a water quality measuring part 8 to be taken in the operation apparatus 7 and the calculated result is approximately corrected. The electrochemical reaction of stainless steel and a nickel base alloy is performed in high temp. pure water by using the result of radiolysis analysis and, from the data base of current density and a crack advancing speed, the crack developing speed of the structure at each region in the pressure container 1 is evaluated. When the calculated crack advance speed does not satisfy a control reference, a water quality control device 6 is operated by the operation apparatys 7. For example, hydrogen may be injected from the water quality control apparatus 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the remaining life of a reactor structural material, such as stress corrosion cracking prevention, and more particularly to the selection of a material and an atom suitable for preventing corrosion damage to equipment in a boiling water reactor pressure vessel 1. It relates to a furnace cooling water management method.

[0002]

2. Description of the Related Art Since the advent of nuclear reactors, higher safety has always been required. In recent years, there has been a demand for a technology that operates for as long as possible while maintaining safety. Therefore, there is a high interest in accurately evaluating a stress corrosion cracking (SCC) environment of structural components in an aging furnace. The material S at each part in the furnace
As a method of evaluating the CC behavior, for example, Japanese Patent Application Laid-Open No. 5-100087 discloses a method of estimating a corrosive environment in a furnace and controlling water quality. Japanese Patent Application Laid-Open No. Hei 6-34786 describes a method of evaluating a corrosive environment in the form of an effective oxygen concentration and estimating a remaining life from a crack growth rate of a material.

[0003]

In the prior art, the corrosive environment for SCC is evaluated based on the effective oxygen concentration and corrosion potential. However, the effective oxygen concentration does not take into account the difference in the chemical properties of oxygen and hydrogen peroxide, but merely performs stoichiometric treatment when hydrogen peroxide is decomposed into oxygen.
Literature (Y. Wada et al. “Radiolytic Environments arou
nd RPV Internalsof BWR ”, Proc. Int'l Sym. Plant Ag
ing and Life Predictions of CorrodibleStructures,
May 15-18, 1995, Sapporo, Japan, JSCE, (1995). As shown in the above, the corrosion potential of oxygen and hydrogen peroxide behaves differently when arranged by effective oxygen. On the other hand, the corrosion potential considered to be effective as a corrosion
Not enough as an evaluation index. Literature (Anzai et al., Co
rrosion Science, 36 , 1201 (1994)), the corrosion potential does not change with respect to the concentration of hydrogen peroxide in a region where the concentration of hydrogen peroxide is as high as about 1 ppm. Therefore, in the corrosion potential, the crack growth rate in a region where a high concentration of hydrogen peroxide is generated by the radiolysis of water, such as the core 12, cannot be evaluated within the conventional theoretical range. Even if the crack growth rate is measured directly using a sensor, it is necessary to treat the crack based on a theoretical basis in order to evaluate the crack growth rate in places where sensors cannot be installed or under arbitrary conditions. Become.

[0004] It is an object of the present invention to provide an appropriate method for managing the reactor water by calculating the crack growth rate of an arbitrary part of a structure in a furnace by simulation.

[0005]

A feature of the water quality evaluation method according to the present invention is that a current density is used in a simulation as an index for obtaining a crack growth rate. RN Parki
As shown in ns, CorrosionScience, 20 , 147 (1980), the following relationship is established between the crack growth rate Vt and the current density Ia.

[0006]

Vt = IaM / zF ρ (Equation 1) where M is atomic weight, z is electric charge, F is Faraday constant, ρ
Is the density.

However, in a high temperature pure water environment such as a nuclear reactor environment, various solvents are not contained unlike the experiment of Parkins, and the existence of oxygen and hydrogen peroxide itself is a condition of the oxide film on the surface of the metal material. Is considered to change

[0008]

Vt = f (Ia) (Equation 2) It is necessary to treat this as a general function of the current density. It is difficult to know the current density inside the reactor,
It is necessary to obtain the current density reflecting the state of the film by simulation.

A feature of the water quality evaluation method according to claim 2 is that stainless steel and a nickel-based alloy are used as structures of a nuclear reactor.

The characteristic of the water quality evaluation method according to the present invention is characterized in that the corrosion current density is an absolute value of Ia or Ic when the current density Ic generated by the cathodic reaction and the current density Ia generated by the anodic reaction satisfy the relationship of Ia + Ic = 0. It is to be taken.

The calculation of the corrosion current density by simulation is performed according to the following procedure as shown in FIG.

First, the radiolysis is calculated using the operating conditions of the nuclear reactor, that is, the reactor water flow rate, the feed water flow rate, the temperature distribution, the dose rate distribution, and the like. For the calculation method of radiolysis, see Ibe et al., Nucl. Sci. Technol., 23, 11 (1
986). Electrochemical calculations are performed using the oxygen, hydrogen, and hydrogen peroxide concentrations at each point of the reactor structure obtained by radiolysis calculation as inputs. Details are provided by Wada. According to this method, the current density generated by the electrochemical reaction on the metal surface is calculated according to the chemical species concentration at each point. In addition, when an electrochemical reaction of a chemical species occurs, a current density generated by a metal dissolution reaction was also considered. FIG. 2 is a plot of the absolute values of the anode current density and the cathode reaction current density with respect to the potential. As shown in the figure, when the anode current density and the cathode current density are calculated by sweeping the potential, the current density is given as the corrosion current density at a potential at which the total current density entering and exiting the metal surface is apparently zero.

Further, the potential at this time is the corrosion potential. From the current density calculated in this way, the reactor structure is identified using the relational expression between the crack growth rate and the current density obtained in an environment simulating reactor water under various conditions in the laboratory in advance. The stress corrosion cracking environment at the position is evaluated using the crack growth rate as an index.

The following calculations were performed to find the relationship between current density and crack growth rate. The experimental data obtained by Anzai et al. Was used. The test environment has a conductivity of 0.07μ
S / cm, 750 ° C after solution treatment at 1050 ° C
SU sensitized at × 100 minutes + 500 ° C × 24 hours
S304 stress intensity factor of a compact tension (CT) test piece was 25~27MPa · m ⁰ · ^5. Using the oxygen, hydrogen peroxide and hydrogen concentrations under the test conditions given in this paper,

[0015]

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[0016]

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[0017]

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[0018]

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In consideration of the electrochemical reaction described above, the cathode current density was calculated from the electrochemical reaction of oxygen and hydrogen peroxide, and the anode current density was calculated from the electrochemical reaction of hydrogen. Also
The elution current density of the metal was considered as the anode current density from the polarization curve of SUS304. For these calculations, see Wada
This is the same as the method for calculating the corrosion potential described in US Pat.

The current density obtained by the procedure of the present invention and the Anzai
FIG. 3 is a plot of the crack growth rate obtained by the present inventors. According to this figure, it can be seen that the crack growth rate, which could not be arranged by the corrosion potential, can be arranged by the current density if the properties on the material side are the same in each case of the oxygen system and the hydrogen peroxide coexisting system.

A feature of the method for managing water quality of a reactor water according to claim 4 is that a crack growth rate at a specific portion is calculated by using the water quality evaluation method according to claim 1, and based on a predetermined reference value,
Implement measures to reduce the rate of crack growth. FIG. 4 explains the concept of the water quality management method of the fourth aspect. According to the water quality evaluation method of the first aspect, a crack growth rate of a structure at one or a plurality of positions in a nuclear reactor is evaluated. For example, it is determined whether the absolute value exceeds the crack growth speed set in advance as a management standard or how many times the relative value has increased. If the determination conditions are not satisfied, the water quality control device 6 is operated to change the reactor water quality. After operating the water quality control device 6, the crack growth speed is evaluated again, and the operation of the water quality control device 6 and the evaluation of the crack growth speed are repeated until the determination condition is satisfied.

A feature of the method for managing water quality of a reactor water according to claim 5 is that hydrogen is injected as a measure for reducing the crack growth rate in claim 4.

A feature of the reactor water quality management method of claim 6 is that the reactor water conductivity is reduced by increasing the flow rate of the reactor water purification system 9 as a measure for reducing the crack growth rate in claim 4.

The feature of the nuclear reactor management method according to claim 7 is that the crack growth rate is estimated by using the reactor water quality evaluation of claim 1, and at the same time, the crack growth rate is actually measured and compared. Evaluate the effect on the crack growth sensor 14,
It is to estimate the environment inside the reactor.

A feature of the nuclear reactor management method according to claim 8 is that the in-reactor environmental condition estimated in claim 7 is a gamma ray or neutron ray dose rate in the reactor.

FIG. 5 explains the concept of the water quality management method of claim 7. First, the crack growth rate of a structure at one or a plurality of positions in a nuclear reactor is measured by a crack growth sensor 14 set under given conditions. Subsequently, the crack growth rate is evaluated by the water quality evaluation method according to claim 1 based on the setting conditions of the crack growth sensor 14. If the crack growth sensor 14 is not affected by the furnace environment, it should show the same value as the calculation result by feeling only the effect of the reactor water quality. If the crack growth sensor 14 is completely sensitized and is no longer affected by radiation, and if the crack growth rate is reduced, it is considered that the stress has fluctuated due to irradiation. Therefore, if the stress intensity factor at which the crack growth rate coincides is determined by simulation, the irradiation amount in the furnace is estimated from a database of stress fluctuation due to irradiation.
If the crack growth sensor 14 is set with a certain sensitization while keeping the stress constant, the dose rate in the furnace is calculated by reading the change in the sensitization from the crack growth rate in the same manner. Alternatively, the degree of sensitization of a nearby structure is calculated in the same manner.

According to the method for evaluating the water quality of reactor water according to the first aspect, the concentration of the chemical species dissolved in the reactor water does not take the form of the effective oxygen concentration, but the mutual relationship between the concentration and the metal surface as the current density. It is possible to handle in consideration of both effects.

According to the method for evaluating the water quality of the reactor water according to the second aspect, the effects of the first aspect can be obtained and the evaluation can be performed in accordance with the material used as the reactor structural material. According to the method for evaluating the water quality of a reactor water according to claim 3, the effect of claim 1 can be obtained, and information of the corrosion potential can be considered when calculating the corrosion current density. Can be accurately evaluated.

According to the method for controlling water quality of a reactor water according to the fourth aspect, even when a plurality of oxidizing components such as oxygen and hydrogen peroxide are mixed, as long as a database in a laboratory system is available, Since the change in the SCC environment of the reactor structure can be detected with high accuracy by combining the current density with the theoretical calculation, fine water quality control is possible.

According to the method for managing water quality of a reactor water according to the fifth aspect, the effect of the fourth aspect can be obtained, and the concentration of oxidizing components in the reactor water can be reduced by hydrogen injection, thereby alleviating the SCC environment. It is.

According to the method for managing water quality of a reactor water according to the sixth aspect, the effect of the fourth aspect can be obtained, and the increase in the crack growth rate due to the deterioration of the electric conductivity can be controlled.

According to the nuclear reactor management method of claim 7,
It is possible to estimate the in-furnace environmental factors that are difficult to measure directly in the furnace, and the accuracy of the SCC environment simulation in the furnace is further improved.

According to the nuclear reactor management method of claim 8,
The effect of claim 7 is obtained, and the dose rate distribution in the furnace can be estimated.

[0034]

FIG. 6 shows an embodiment of the water quality management method of the present invention.

Description will be made using a case where the reactor is a boiling water reactor. The reactor is composed of typical equipment such as a pressure vessel 1, a recirculation system 2, a turbine 3, a condenser 4, a condensate purification system 5, a reactor water purification system 9, a water supply system 10, a jet pump 11, and a reactor core 12. Shall be At this time, the system using the reactor water quality management method of the present invention includes three elements: a water quality control device 6, an arithmetic unit 7, and a water quality measurement unit 8. In the pressure vessel 1, there are a jet pump 11, a reactor core 12, etc., and various temperature distributions, reactor water velocity distributions and radiation dose rate distributions are obtained. As a result, the concentration of chemical species components in the reactor water also depends on the location in the reactor. It changes in various ways. In addition, the flow rate of the recirculation system 2 and the flow rate of the water supply system 10 fluctuate due to power control in the reactor core 12 throughout the operation period of the nuclear reactor, as well as the difference in conditions depending on the location. Therefore, these operating conditions are fetched into the arithmetic unit 7 from time to time, and time- and location-dependent water quality is calculated by radiolysis analysis. The reactor water from the bottom of the pressure vessel 1 toward the reactor water purification system 9 and the reactor water from the recirculation system 2 are guided to a sampling line 15 drawn out of the pressure vessel 1. Sampling line 15
The dissolved oxygen, dissolved hydrogen, conductivity, and pH are measured by a water quality measurement unit 8 provided in The calculation result is corrected based on the water quality data taken in as appropriate.
Using the results of the radiolysis analysis, the electrochemical reaction of stainless steel or nickel-based alloy in high-temperature pure water was calculated, and from the database of the current density and crack growth rate as shown in FIG. To evaluate the crack growth rate of the structure at At this time, the water quality factor that cannot be obtained from the radiolysis calculation during the operation of the reactor and that affects the crack growth rate is electrical conductivity. The crack growth rate is dependent on the electrical conductivity, and it is described in Japanese Unexamined Patent Publication No. Hei 6-34786 that the speed increases with high electrical conductivity. 7. Read the appropriate database corresponding to the measured conductivity. This database may be one that has been fitted to an analytical expression in advance, or one that has been subjected to numerical processing by an interpolation method or the like in the arithmetic unit 7 as appropriate. When the calculated crack growth rate does not satisfy the management standard, the water quality control device 6 is operated by the arithmetic device 7. For example, hydrogen may be injected from the water quality control device 6.

FIG. 7 shows another embodiment of the water quality management method of the present invention. FIG. 6 shows a case where the water quality measuring unit 8 installed in the sampling line 15 is installed in the recirculation system 2 to measure the water quality environment in the furnace.

FIG. 8 shows another embodiment of the water quality management method of the present invention. The system using the reactor water quality management method of the present invention includes an arithmetic unit 7 and a water quality measurement unit 8. The arithmetic unit 7 directly controls the reactor water purification system 9.
If the management standard is not observed, the flow rate to the reactor water purification system 9 is increased to lower the conductivity and reduce the crack growth rate.

FIG. 9 shows another embodiment of the water quality management method of the present invention. A system using the reactor water quality management method of the present invention includes a water quality control device 6, an arithmetic unit 7, and a water quality measurement unit 8. If the calculated crack growth rate does not satisfy the management standard, the water quality control device 6 is switched to the arithmetic device 7
To operate. For example, hydrogen may be injected from the water quality control device 6.

At the same time, by increasing the flow rate to the reactor water purification system 9, the conductivity is reduced and the crack growth rate is reduced. By increasing the flow rate to the reactor water purification system 9 simultaneously with the hydrogen injection, the current density can be further reduced and the crack growth rate can be reduced. Rather than increasing the flow rate to the reactor water purification system 9, rather than bypassing the recirculation system 2 and returning a large amount of reactor water flowing through the recirculation system 2 to the water supply system 10, the oxidizing component concentration is reduced by hydrogen injection. Since the reactor water flows above the jet pump 11, the hydrogen injection effect on the bottom of the pressure vessel 1 is improved, and the hydrogen injection effect is expected further above the jet pump 11.

FIG. 10 shows an embodiment of a method for managing an influential factor on the SCC environment in a nuclear reactor according to the present invention. For simplicity, assuming that the reactor is a boiling water reactor, a pressure vessel 1, a recirculation system 2, a turbine 3, a condenser 4, a condensate purification system 5, a reactor water purification system 9, a water supply system 10, a jet The pump 11, the core 12, and the in-furnace instrumentation tube 13 are assumed to be constituted by typical devices. At this time, the system for measuring the dose rate in the reactor using the reactor management method of the present invention includes the arithmetic unit 7, the water quality measurement unit 8, and the crack loaded in the in-core instrumentation tube 13 of the core 12. It consists of a progress sensor 14. The arithmetic unit 7 receives the operating conditions of the nuclear reactor every moment, and calculates the crack growth rate at the crack growth sensor 14 under the conditions. If integrated over the measurement time, the total amount of crack propagation from the start of operation can be determined. In the crack propagation sensor 14, the core 12
Is measured for a certain period of time. The amount of crack growth in the crack growth sensor 14 is compared with the amount of crack growth obtained by calculation. Now, as the material side conditions of the crack growth sensor 14, those that change include the sensitization, the stress intensity factor, and the strain rate. When the reactor operates in a steady state and the water quality factors are all constant and known by calculation, as shown in FIG. 11, the material becomes sensitized by neutron irradiation, or the stress changes due to the change in the material properties, and the stress intensity factor increases. It deviates from the initial value. Therefore, if the relationship between the dose and the sensitization or stress change is determined in advance by the laboratory, the neutron dose can be estimated from a comparison between the calculated value of the crack growth rate and the actually measured value.

FIG. 12 shows an embodiment of the method for measuring the current density according to the present invention. When, for example, a certain welded portion 17 of the furnace internal structure 18 is selected for evaluating the SCC environment, the reference electrode 16, the counter electrode 20 and the sample electrode 2
1 is set. The sample electrode 21 was prepared so as to have the same metallurgical properties as the vicinity of the weld 17. It is assumed that the reference electrode 16, the counter electrode 20, and the sample electrode 21 are electrically connected to the arithmetic unit 7. It is assumed that the arithmetic unit 7 and the in-furnace structure 18 are both electrically connected through the ground 19. As shown in FIG. 13, the corrosion potential near the welding portion 17 is measured using the reference electrode 16. Sample electrode 2 at the same time
The corrosion potential of Sample No. 1 is measured with the reference electrode 16 to confirm that the corrosion environment in the vicinity of the sample electrode 21 and the welded portion 17 is the same.
Next, using the sample electrode 21, the reference electrode 16, and the counter electrode 20, the potential is swept toward the noble and base sides near the corrosion potential of the sample electrode 21, and the current density flowing between the sample electrode 21 and the counter electrode 20 at this time is set to the potential. Measure for The current density at the corrosion potential is estimated from the Tafel slope of the current density change near the corrosion potential, and this is defined as the current density obtained by the measurement.

[0042]

According to the present invention, the crack growth rate at each part of the reactor structure can be analyzed and evaluated by simulation, and an effective water quality control method for stress corrosion cracking can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a procedure for evaluating a crack growth rate at a certain location of a reactor structure.

FIG. 2 is a current density-potential diagram showing a relationship between an anode current density, a cathode current density, and a corrosion current density.

FIG. 3 is a graph showing a relationship between a crack growth rate obtained by an experiment and a current density obtained by an analysis using the experimental conditions as input.

FIG. 4 is an explanatory diagram showing a procedure for evaluating a crack growth rate at a certain location of a reactor structure and controlling reactor water quality based on the evaluation result.

FIG. 5 is an explanatory diagram showing a procedure for estimating another influencing factor in the reactor by actually measuring a crack growth rate at a certain location of the reactor structure and comparing the result with an analysis result.

FIG. 6 is a system diagram of an embodiment showing a water quality control method of the present invention.

FIG. 7 is a system diagram of an embodiment showing a water quality control method of the present invention.

FIG. 8 is a system diagram of an embodiment showing a water quality control method of the present invention.

FIG. 9 is a system diagram of an embodiment showing a water quality control method of the present invention.

FIG. 10 is a system diagram of an embodiment showing a method for estimating a water quality affecting factor of the present invention.

FIG. 11 is an explanatory diagram showing the effect of crack length and radiation irradiation.

FIG. 12 is an explanatory view showing a method of measuring a current density.

FIG. 13 is an explanatory diagram showing a method for determining a current density.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pressure vessel, 2 ... Recirculation system, 3 ... Turbine, 4 ... Condenser, 5 ... Condensate purification system, 6 ... Water quality control device, 7 ... Operation device, 8 ... Water quality measurement part, 9 ... Furnace water purification System, 10 ... water supply system,
11: jet pump, 12: core, 15: sampling line.

Claims (8)

[Claims] 1. A method for estimating the corrosive environment of reactor water exposed to a structure of a nuclear reactor, comprising the steps of: Arranged in water simulated reactor water, on the previously determined relationship between the growth rate of the crack and the corrosion current density generated in the test piece exposed to the simulated reactor water when the crack is growing, By calculating or measuring the corrosion current density flowing when the structure is in contact with the reactor water for each part where the corrosion environment is to be evaluated by measuring or actually measuring, it is possible to indicate the degree of the corrosion environment as the crack growth rate of the structure. Characteristic water quality evaluation method for reactor water. 2. The method according to claim 1, wherein the material constituting the structure is a stainless steel or nickel-based alloy. 3. The corrosion current density according to claim 1, wherein the corrosion current density is generated by a current density Ic generated by a cathodic reaction and an anodic reaction when a chemical species in the reactor water and a material constituting the structure form a hybrid potential. When the current density Ia is Ia +
A method for evaluating the water quality of reactor water, in which the absolute value of Ia or Ic when the relationship of Ic = 0 is taken. 4. A method for calculating a crack growth rate at a specific portion of the structure using the water quality evaluation method according to claim 1, and reducing the crack growth rate based on a predetermined reference value. Reactor water management method to implement. 5. The method according to claim 4, wherein the measure for reducing the crack growth rate is hydrogen injection. 6. The reactor water management method according to claim 4, wherein the measure for reducing the crack growth rate is a decrease in reactor water conductivity by increasing a flow rate of the reactor water purification system. 7. The method of claim 1, wherein a crack growth rate of a specific portion of the structure is calculated, and a crack growth speed of the specific portion is actually measured. Reactor management method that estimates the environment inside the reactor by comparing measured values. 8. The method according to claim 7, wherein the factor estimated as the environment inside the reactor is a gamma ray or a neutron dose rate.