JPH09222495A - Hydrogen injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the velocity of crack propagation in reactor bottom material by controlling the hydrogen concentration in a water supply system so that corrosion potential and dose rate in the main steam line are kept within specific ranges. SOLUTION: The measurement of corrosion potential at a reactor bottom is done with a corrosion potential electrode 11a and monitoring is done with a data acquisition device 11b. When the corrosion potential is less than -0.1V, the opening of a valve 30 is reduced to reduce the injection rate of hydrogen from a hydrogen injection system 54 into water supply systems. On the contrary, when the corrosion potential is -0.1V or higher and 0.1 V or lower, the opening of the valve 30 is maintained. When the corrosion potential is larger than 0.1V, the opening of the valve 30 is increased to increase the hydrogen injection rate from the system 54 to the water supply system 54. By the above operation, the hydrogen injection rate is properly controlled so that the corrosion potential at the reactor bottom material is to be between -0.1V and 0.1V.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiling water nuclear power plant, and more particularly to a boiling water nuclear power plant equipped with a system suitable for mitigating a corrosive environment of materials in a nuclear reactor by hydrogen injection.

[0002]

2. Description of the Related Art Hydrogen peroxide, hydrogen molecules, and oxygen molecules are generated by radiolysis of water in a nuclear reactor during operation of a boiling water nuclear power plant, and 1/2 of the hydrogen peroxide concentration is added to the oxygen concentration. The effective oxygen concentration defined by the above value increases. It is known that when the effective oxygen concentration rises, the corrosion potential, which is an index showing the degree of the corrosive environment of the metal material, rises, which affects SCC (stress corrosion cracking) of the material and increases its sensitivity. On the other hand, it has been found by actual measurement or analysis that this effective oxygen concentration varies depending on the position inside the reactor. Especially, in the bottom area of the reactor, C
Since there is a structure such as an RD (control rod drive mechanism) housing or an ICM (reactor instrumentation tube) housing,
It is important to mitigate the corrosive environment of materials in this area.

As a conventional example, the corrosion potential, the dissolved oxygen concentration, and the dissolved hydrogen of reactor water are measured, and the amount of hydrogen injection into the reactor water supply system is controlled based on these measured values, thereby Japanese Patent Publication No. 63-19838 describes an operation method for suppressing the radiolysis of water and reducing the concentration of dissolved oxygen in the nuclear reactor. In this publication, when hydrogen is injected into the reactor primary cooling water to regulate the dissolved oxygen concentration, corrosion potential, etc., and SCC of the stainless steel material is prevented, the corrosion potential of the stainless steel in the primary cooling water, the primary cooling water The dissolved oxygen concentration and dissolved hydrogen concentration were measured, and the corrosion potential was -0.25V
The hydrogen injection amount is controlled so that the dissolved oxygen concentration is −0.6 V, the dissolved oxygen concentration is 10 ppb to 50 ppb, and the dissolved hydrogen concentration is 150 ppb or less.

In this example, the target range for which the effect of hydrogen injection is expected is not clear. Further, it is described with the idea of completely preventing the occurrence of SCC. Furthermore, no consideration is given for application such as the fact that the dose rate rise of the main steam system, which is one of the disadvantages of hydrogen injection, is not considered.

On the other hand, similarly, in Japanese Patent Laid-Open No. 6-174891, the measurement of the radioactivity concentration of the main steam system, the corrosion potential and the dissolved oxygen concentration are measured in the core part and the recirculation system to obtain the minimum required hydrogen injection amount. However, the target range in which the effect of hydrogen injection is expected is not clear. In addition, it is described in consideration of completely preventing the generation of SCC (reducing the corrosion potential to −0.23 V or less), and does not describe reduction of a certain limit of the crack growth rate. It is known from the conventional knowledge that a large amount of hydrogen injection of 1 ppm or more is required to reduce the corrosion potential of the core to −0.23 V or less. Therefore, in this case, the hydrogen injection amount is relatively large and the dose rate of the main steam system is likely to increase.

[0006]

As described above, in order to reduce the corrosion potential of the stainless steel in the primary cooling water to -0.25 V or less by injecting hydrogen, as shown in FIG. It is necessary to set the hydrogen concentration to 0.4 ppm or more. On the other hand, as shown in FIG. 8, it is known that the dose rate of the main steam system sharply rises when the hydrogen concentration of the water supply system exceeds about 0.4 ppm.

Therefore, Japanese Patent Publication No. 63-19838 and Japanese Patent Laid-Open No. 6-17
In the conventional technology as disclosed in Japanese Patent No. 4891, the corrosive environment in the reactor cannot be mitigated unless a large amount of hydrogen that increases the dose rate of the main steam system is injected. Further, in the prior art, since the corrosion potential, the dissolved oxygen concentration and the dissolved hydrogen concentration are measured in the primary reactor cooling system, the water quality environment at the bottom of the reactor is not accurately monitored.

Further, the corrosion potential of the prior art is measured by attaching electrodes to an autoclave as shown in FIG. 12 and using water in the autoclave.

The corrosion potential of the material is calculated by reading the potential difference between the reference electrode 30 and the sample electrode 31 with a potentiometer 33 and converting it with a corrosion potential measuring plate 34. The flow velocity of water flowing in the autoclave is generally very low, on the order of 0.1 cm / sec, and the corrosion potential in such a low flow velocity region is much lower than the actual flow velocity in the furnace. In addition, since it takes time to reach the autoclave, components such as hydrogen peroxide that contribute to the corrosion potential decompose at high temperatures and disappear, resulting in poor measurement accuracy. Therefore, when evaluating the corrosion potential of a material, there arises a problem in the reliability of the measured value.

From the above viewpoint, when mitigating the corrosive environment at the bottom of the reactor by hydrogen injection, the corrosive environment data such as the corrosion potential of the material at the bottom of the reactor or the effective oxygen concentration of reactor water is It is necessary to measure accurately by different methods to control the optimum hydrogen injection amount.

An object of the present invention is to reduce the rate of crack growth (a phenomenon caused by corrosion or deterioration of the material surface) of the reactor bottom material without increasing the dose rate of the main steam system. A hydrogen injection system for a boiling water nuclear power plant and its control method.

[0012]

The first means for achieving the above object is to measure the corrosion potential of the reactor bottom material,
Obtain the crack growth rate of the reactor bottom material from the measured corrosion potential, measure the dose rate of the main steam system, and supply water so that the corrosion potential and the dose rate of the main steam system are within the specified range. Controlling the hydrogen concentration of the system.

The second means is to obtain the concentration of the oxidizer (oxygen, hydrogen peroxide, etc.) in the reactor from the hydrogen concentration of the feed water system, and to obtain the corrosion potential of the reactor bottom material from this value. It is to measure the dose rate of the main steam system and control the hydrogen concentration of the water supply system so that the corrosion potential and the dose rate fall within a predetermined range.

In the first means, the correlation between the crack growth rate of the reactor bottom material and the corrosion potential is obtained in advance, and the dose rate of the main steam system is determined from the measured corrosion potential of the reactor bottom material based on this correlation. The hydrogen concentration of the feed water system is controlled so that the corrosion potential of the material at the bottom of the reactor reaches a predetermined value within the range where does not rise.

In the second means, the correlation between the hydrogen concentration in the feed water system and the corrosion potential at the bottom of the reactor is obtained in advance, and the range in which the dose rate in the main steam system does not rise from the hydrogen concentration in the feed water system based on this correlation. The hydrogen concentration of the feed water system is controlled so that the corrosion potential of the reactor bottom material becomes a predetermined value.

By setting the amount of hydrogen injection into the water supply system based on the previously determined correlation as described above, the corrosive environment at the bottom of the nuclear reactor can be directly improved within the previously determined range. It is possible to properly control the water quality for the equipment at the bottom of the reactor, reduce the crack growth rate of the material at the bottom of the reactor without increasing the dose rate of the main steam system, and eventually the boiling water type. The life of the nuclear power plant can be extended.

Overseas Literature BWR Water Chemistry Gideline
s−1993 Revision, NP TR−103515, EPRI, Feburary 1994,
As shown in Fig. 2-10, when the corrosion potential of the stainless steel material is lowered to 0.1 V or less, the crack growth rate of the stainless steel is 150 mils / yr. (Fig. 6).

This is because the corrosion potential at the bottom of the reactor in a normal plant is based on the literature ('Draft Proceeding of International
Symposium on Plant Aging and Life Prediction of Cor
rodible Structure ', BVI08, SAPPORO JAPAN, May 1995
), The crack growth rate of the stainless steel material at the bottom of the reactor can be reduced to 1/100% of the normal case by setting the corrosion potential to 0.1 V or less.
It can be reduced to 2 or less. This makes it possible to determine that the design is effective.

Further, as shown in FIG. 9, if the corrosion potential is lowered too much, the dose rate of the main steam system may increase.
Further, if the dissolved oxygen concentration is too low, there is a concern that it may be a cause of the corrosion limit of the carbon steel material. By setting the amount of hydrogen injection into the feedwater so that the corrosion potential of the reactor bottom is -0.1 V or more and 0.1 V or less, without increasing the dose rate of the main steam system, The crack growth rate can be reduced.

On the other hand, the corrosion potential at the bottom of the reactor is set to -0.1V.
To 0.1V to 0.1V, the hydrogen concentration of the water supply system should be 0.1
It can be seen from FIG. 7 that the control may be performed within the range of 1 ppm to about 0.4 ppm.

Therefore, the dose rate of the main steam system is adjusted by setting the hydrogen concentration according to the characteristics of each plant so that the hydrogen concentration in the feed water is within the range of about 0.1 ppm to about 0.4 ppm. The crack growth rate of the reactor bottom material can be reduced without raising it.

[0022]

Embodiments of the present invention will be described below.

First, a first embodiment of the present invention will be described with reference to FIGS.
It is described using 0.

FIG. 1 shows a boiling water nuclear power plant according to a first embodiment of the present invention. In the boiling water nuclear power plant, the steam generated from the nuclear reactor 1 is directly sent to the turbine 2 and is condensed into water by the condenser 2a below the turbine. After that, the condensed water is brought into the furnace through the condensate purification device 3 and the feed water heater 4. Further, in the nuclear reactor system, a nuclear reactor recirculation system (PLR) 51 is provided with a nuclear reactor coolant purification system 52, which is purified by the filter demineralizer 6 and then returned to the nuclear reactor. A reactor bottom drain line system 53 for draining the reactor water is provided at the bottom of the reactor. The water supply system 50 is equipped with hydrogen injection equipment 54. This hydrogen injection facility 54 is provided with pipes P20, P21 and valve 3 for connecting the hydrogen supply source 12 to the water supply system 50.
It has a line composed of 0 and 0.

Details of the corrosion potential electrode portion 11a in FIG. 1 are shown in FIG.

As shown in the figure, the electrode parts 30 and 31 are 0.1
Since it is directly immersed in the reactor bottom drain water with a high flow rate of about 3 m / sec, the electrode is directly immersed in the high-velocity reactor water in the vicinity of the bottom of the reactor and hydrogen peroxide remains relatively. By measuring the position, it is possible to accurately grasp the corrosive environment at the bottom of the reactor.

As described above, the accuracy of measurement is remarkably improved as compared with the conventional measurement technique such as an autoclave.

A method of controlling the hydrogen injection amount will be described below.

The corrosion potential at the bottom of the nuclear reactor is measured by the board 11a and is monitored by using the data collecting device 11b. When the corrosion potential is less than -0.1 V, the opening degree of the valve 30 is reduced to reduce the amount of hydrogen injected from the hydrogen injection equipment 54 into the water supply system. On the other hand, when the corrosion potential is −0.1 V or more and 0.1 V or less, the opening degree of the valve 30 is maintained. On the other hand, when the corrosion potential is greater than 0.1 mV, the opening degree of the valve 30 is increased to increase the amount of hydrogen injected from the hydrogen injection equipment 54 into the water supply system.

By the above operation, the proper amount of hydrogen injection is controlled so that the corrosion potential of the reactor bottom material is not less than -0.1V and not more than 0.1V.

Next, the concept and effect of the control method of the boiling water nuclear power plant in this embodiment will be described.

In the nuclear reactor, hydrogen peroxide and oxygen are generated by the radiolysis of water, the reactor water becomes an oxidizing atmosphere, and the corrosiveness surrounding the reactor internal structure increases. Fig. 2 shows the water quality distribution in the reactor by analysis based on radiolysis of water. As can be seen from FIG. 2, the water quality in the furnace depends on the parts inside the furnace, and the effective oxygen concentration greatly differs depending on each region in the furnace. However, the reactor bottom is characterized by a relatively large reduction effect, and the present invention utilizes this feature.

On the other hand, as shown in FIG. 3, the corrosion potential, which is an index of the material corrosion environment, increases with the effective oxygen concentration.
Responses to hydrogen peroxide and oxygen are different, and it is reported in the above-mentioned literature that the hydrogen peroxide atmosphere exhibits a higher corrosion potential than the oxygen atmosphere.

Hydrogen peroxide is a very unstable substance at high temperature. Therefore, as shown in FIG. 4, as the distance from the bottom of the furnace to the measurement point becomes longer, the hydrogen peroxide generated in the furnace is decomposed and the conversion rate to oxygen becomes larger, and as a result, the corrosion potential becomes Get lower.

FIG. 5 shows the difference in hydrogen injection effect on the corrosion potential near the bottom of the reactor. It was found that the response of the corrosion potential near the bottom of the reactor varies greatly depending on the measurement position.

The present invention is based on the above findings,
When evaluating the corrosive environment in a nuclear reactor, it is necessary to consider the measurement point. When evaluating the corrosion potential of the reactor bottom material, the corrosion potential of the reactor bottom can be accurately obtained by analysis by bringing the measurement point of the corrosion potential as close as possible to the reactor bottom. Therefore, it is desirable to install the corrosion potential electrode 11a, which is the measurement point of the corrosion potential in FIG. 1, as close to the reactor bottom as possible by installing it on the upstream side of the reactor bottom drain system.

Further, JP-A-6-174891 describes that the corrosion potential is measured at the core part, but the measurement at this position is not necessarily affected by the water quality but is directly affected by irradiation, so that it is not always necessary to measure the corrosion potential at the bottom of the reactor. Does not reflect water quality. Therefore, it is necessary to measure the corrosion potential on the upstream side of the reactor bottom drain system as shown in the present invention.

On the other hand, when the water quality at the bottom of the reactor is controlled by injecting hydrogen to mitigate the corrosive environment, the SCC at the bottom of the reactor is suppressed and the positive and negative effects such as the main steam system dose rate are reduced. It is important to understand the control range of the corrosion potential after considering both sides.

FIG. 6 shows the relationship between the corrosion potential and the crack growth rate of stainless steel obtained from the experimental data and analysis reported in the above literature. In addition, the regions of corrosion potential and crack growth rate of the reactor bottom stainless steel in an ordinary plant are also shown. In an ordinary plant, the corrosion potential of stainless steel at the bottom of a nuclear reactor is about 0.2 V, and the crack growth rate is 300 mils / yr.-400 mils / yr. Therefore, when the corrosion potential of stainless steel is lowered to 0.1 V or less by injecting hydrogen, the crack growth rate is 150 mils.
/ Yr. 1 in the normal case where hydrogen drops below and hydrogen is not injected
It is understood that it is possible to reduce the crack growth rate to / 2 or less.

FIG. 7 shows the correlation between the hydrogen concentration in the water supply system and the corrosion potential of the stainless steel at the bottom of the reactor, which was obtained by analysis targeting an average 800 MWe class BWR in terms of electric output reported in a later document. FIG. 8 shows the correlation between the hydrogen concentration in the water supply system and the main steam system dose rate.

Further, the electric output is from 500 MWe class to 110
When the BWR of 0 MWe class is different, or when the reactor type is different, the water quality response due to hydrogen injection is different, so it is considered that there is a difference of about several tens of percent in the corrosion potential, but basically the idea of the present invention is Applicable.

Further, in the 800 MWe class BWR, it was found from FIGS. 7 and 8 that the correlation between the corrosion potential of the stainless steel at the bottom of the reactor and the main steam dose rate is as shown in FIG.

According to FIG. 9, a typical 800 MWe class BW
In the case of R, the corrosion potential of stainless steel at the bottom of the reactor is −
It can be seen that the dose rate of the main steam system starts to rise at 0.1 V or lower, and the main steam dose rate becomes twice or more the value in the normal case when the corrosion potential becomes −0.2 V or lower.

Based on the above, the concept of the operating method of this embodiment will be described with reference to the flowchart shown in FIG. That is, when mitigating the in-reactor corrosive environment by injecting hydrogen, positive effects such as a decrease in the corrosion potential of the stainless steel at the bottom of the reactor due to hydrogen injection and the dose rate of the main steam system due to hydrogen injection The hydrogen injection amount is set while considering the opposite polar surfaces of negative effects such as increase. The positive effect is a delay in the SCC crack growth of the structural material present in the reactor bottom region, which lowers the corrosion potential of the reactor bottom material to below 0.1 V in order to improve the SCC resistance life. On the other hand, it is necessary to suppress the rise in the dose rate of the main steam system, which is a concern due to the influence of hydrogen injection, and in order to do so, it is necessary to keep the corrosion potential at -0.1 V or higher. Based on the above idea, by injecting an optimum amount of hydrogen, the crack growth rate of the reactor bottom material can be reduced without increasing the dose rate of the main steam system. According to the first embodiment of the present invention described above, in a boiling water nuclear power plant, the corrosion potential of the outer surface of the CRD housing or the outer surface of the ICM housing existing in the reactor bottom region can be accurately grasped and controlled. The amount of hydrogen most suitable for alleviating the corrosive environment can be mitigated by using hydrogen, and thus the soundness of the structure in the reactor bottom region can be maintained and the life can be extended.

Next, as a second embodiment of the present invention, a case of automatically controlling the setting of the hydrogen injection amount will be described. FIG. 11 is a system diagram of a boiling water nuclear power plant according to the second embodiment of the present invention.

In addition to the plant of the first embodiment, the plant of the second embodiment has a hydrogen injection system 55 provided with a controller 13 for automatically controlling the water quality at the bottom of the nuclear reactor.

The automatic control operation method will be described below. The opening of the valve 30 is controlled according to the electric signal output from the control device 13, and the control device 13 inputs the corrosion potential of the reactor bottom measured by the corrosion potential electrode 11a from the corrosion potential meter. It The control device 13 generates and outputs an electric signal for controlling the opening degree of the valve 30, so that the corrosion potential of the bottom of the reactor can be directly monitored and controlled.

Even by the above-described automatic control, the corrosion potential of the reactor bottom material is controlled to be -0.1 V or more and 0.1 V or less, and the same effect as that of the first embodiment can be obtained.

Also, by using the correlation value between the hydrogen concentration of the water supply system and the corrosion potential of the reactor bottom material, which was previously obtained by a test or analysis, the hydrogen concentration of the water supply system can be controlled without depending on the measurement of the corrosion potential. The effect of can be achieved.

[0050]

According to the present invention, the corrosive environment of the equipment existing in the reactor bottom region such as the CRD housing or the ICM housing can be mitigated without increasing the main steam system dose rate.

[Brief description of drawings]

FIG. 1 is a system diagram of a boiling water nuclear power plant according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the water quality distribution in the reactor obtained by analysis.

FIG. 3 is a characteristic diagram showing a correlation between effective oxygen concentration and corrosion potential of stainless steel.

FIG. 4 is a characteristic diagram showing the influence on the corrosion potential of stainless steel due to the difference in measurement points.

FIG. 5 is a characteristic diagram showing the difference in the hydrogen injection effect on the corrosion potential of stainless steel due to the difference in measurement points.

FIG. 6 is a characteristic diagram showing the effect of corrosion potential on the crack growth rate of stainless steel.

FIG. 7 is a characteristic diagram showing the correlation between the hydrogen concentration in the water supply system and the corrosion potential of the stainless steel at the bottom of the reactor.

FIG. 8 is a characteristic diagram showing the correlation between the hydrogen concentration in the water supply system and the main steam system dose rate.

FIG. 9 is a characteristic diagram showing a correlation between a corrosion potential of stainless steel at the bottom of a nuclear reactor and a main steam system dose rate.

FIG. 10 is a flow sheet showing the concept of setting the hydrogen injection amount.

FIG. 11 is a system diagram showing a boiling water nuclear power plant according to a second embodiment of the present invention.

FIG. 12 is an explanatory view showing a conventional autoclave type corrosion potential measuring device.

FIG. 13 is an explanatory view showing a corrosion potential measuring device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor, 2 ... Turbine, 3 ... Condensate purification device, 4 ... Feed water heater, 5 ... Purification system heater, 6 ... Filtration desalination device, 11a
... Corrosion potential electrode, 11b ... Data collection device, 12 ... Hydrogen supply source, 13 ... Control device, 50 ... Water supply system, 51 ... Reactor recirculation system, 52 ... Reactor coolant purification system, 53 ... Reactor bottom drain System, 54 ... Hydrogen injection equipment.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Okano 3-1, 1-1 Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Hidefumi Ibe 7-2, Omika-cho, Hitachi-shi, Ibaraki No. 1 Incorporated company Hitachi, Ltd. Power & Electric Machinery Development Headquarters (72) Inventor Noriyuki Ohnaka 7-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory

Claims (3)

[Claims] 1. In a boiling water nuclear power plant, the corrosion potential of the reactor bottom material and the dose rate of the main steam system are measured so that the corrosion potential and the dose rate of the main steam system fall within a predetermined range. A hydrogen injection system characterized by controlling the concentration of hydrogen injected into a water supply system. 2. The hydrogen injection system according to claim 1, wherein the hydrogen concentration is controlled so that the corrosion potential of the reactor bottom material is not less than −0.1V standard hydrogen electrode potential and not more than 0.1V. 3. The hydrogen concentration of the water supply system according to claim 1, wherein the correlation value between the hydrogen concentration of the water supply system and the corrosion potential of the material at the bottom of the reactor, which is previously obtained by a test or an analysis, is used, and the hydrogen concentration of the water supply system is Controlling hydrogen injection system.