JP4420838B2 - Hydrogen injection method for nuclear power plant - Google Patents

Description

  The present invention relates to a method for injecting hydrogen into a nuclear power plant, and more particularly to a method for injecting hydrogen into a nuclear power plant that injects hydrogen into reactor water via a water supply system of a boiling water reactor (BWR).

  In recent years, with the increase in the operating years of nuclear power plants, events of deterioration and damage of the primary structural material of boiling water reactors have become apparent. For this reason, it is necessary to take measures to suppress these events and ensure the safe operation of the nuclear power plant for a long time.

  One example of deterioration and damage of the primary structural material of a boiling water reactor is stress corrosion cracking of materials such as stainless steel and nickel-base alloys.

  Stress corrosion cracking includes materials (materials that are sensitive to stress corrosion cracking), stress (high tensile stress such as welding residual stress), and water quality environment (water quality environment that includes oxidizing species such as chlorine, oxygen, and hydrogen peroxide). It is well known that it occurs when these three factors overlap (for example, see Non-Patent Document 1).

  Conventionally, in order to cope with the stress corrosion cracking as described above, hydrogen is injected into the reactor water through the water supply system of the boiling water reactor to reduce the dissolved oxygen concentration, hydrogen peroxide concentration, etc. in the reactor water, thereby improving the water quality. The environment is improved, and the corrosion potential (an index indicating the degree of the corrosive environment) of the primary structural material is lowered to reduce the sensitivity to stress corrosion cracking.

  For example, the corrosion potential, dissolved oxygen concentration and dissolved hydrogen concentration of the reactor water are measured, and hydrogen is injected into the reactor water through the water supply system of the boiling water reactor according to the measured values, and the dissolved oxygen concentration of the reactor water is In addition, it is known that the hydrogen peroxide concentration is reduced, the corrosion potential of the primary structural material made of stainless steel or the like is lowered, and the susceptibility to stress corrosion cracking is reduced (for example, patent document) 1).

  As another example, the corrosion potential at the bottom of the boiling water reactor or the dose rate of the main steam system is measured, and hydrogen is added to the reactor water via the feed water system of the boiling water reactor according to these measured values. Is used to reduce the dissolved oxygen concentration, hydrogen peroxide concentration, etc. of the reactor water, reduce the corrosion potential of primary structural materials made of stainless steel, etc., and reduce the susceptibility to stress corrosion cracking. It is known (for example, refer to Patent Document 2).

  By the way, in the hydrogen injection method having the above-described configuration, the sensitivity to stress corrosion cracking of the primary structural material of the boiling water reactor can be reduced by injection of hydrogen into the reactor water.

  However, since the nuclear power plant is continuously operated while injecting hydrogen continuously for a certain period (about 300 days), the amount of chromium oxide accumulated in the piping system increases.

  In addition, when hydrogen injection is stopped after continuous operation of the nuclear power plant, the chromium oxidation accumulated on the inner surface of the pipe is caused by a sudden change in the water quality environment of the reactor water from the reducing atmosphere to the oxidizing atmosphere. A large amount of chromium oxide accumulated on the inner surface of the piping is generated in the reactor water due to the leaching of substances in the reactor water as chromate ions and the generation of vortex on the outlet side of the reactor recirculation system (PLR) pump. Since it is discharged, irregularities are formed in the chromium oxide layer on the inner surface of the pipe.

Thereafter, when the hydrogen injection is resumed, the water quality environment of the reactor water changes from the oxidizing atmosphere to the reducing atmosphere, so that the radioactive substance concentration rapidly increases. In particular, a large amount of radioactive cladding adheres to the piping on the outlet side of the reactor recirculation system (PLR) pump, and the dose equivalent rate of that portion increases.
Reactor Water Chemistry Handbook (pp. 194-210), Japan Atomic Energy Society, Corona Japanese Patent Publication No. 63-19838 JP-A-9-222495

  The present invention has been made in view of the above-described conventional problems, and can reduce the susceptibility to stress corrosion cracking of the primary structural material of a boiling water nuclear reactor, thereby enabling safe operation over a long period of time. If the hydrogen injection is stopped for periodic inspection after injecting hydrogen into the reactor water for a certain period via the boiling water reactor water supply system, The accumulated chromium oxide is not expelled in a large amount by the vortex on the outlet side of the reactor recirculation system (PLR) pump and unevenness is formed on the chromium oxide layer on the inner surface of the pipe. When restarting hydrogen injection, even if the water quality of the reactor water changes from an oxidizing atmosphere to a reducing atmosphere, the concentration of radioactive materials does not increase rapidly and the dose equivalent rate does not increase. Of hydrogen It is an object to provide the incoming process.

  The present invention employs the following means in order to solve the above problems.

In other words, in one of the invention, a method of implanting hydrogen nuclear power plants to inject hydrogen into the reactor water through the water supply system of the nuclear reactor of a nuclear power plant, during operation of the nuclear power plant, the hydrogen The first period in which the injection is continued for 2 to 3 months, the second period in which the hydrogen injection is gradually reduced over 2 days, the third period in which the hydrogen injection is stopped for 2 to 3 days, and the hydrogen injection over 2 days By repeating the cycle consisting of the fourth period that increases stepwise, hydrogen is continuously injected and stopped for a certain period.

  According to the method of injecting hydrogen in a nuclear power plant according to the present invention, the sensitivity to stress corrosion cracking of the primary structural material of a boiling water reactor can be reduced by continuous hydrogen injection for a certain period.

  In addition, by stopping hydrogen injection after continuous injection of hydrogen for a certain period, chromium oxide accumulated in the piping system can be appropriately eluted in the reactor water, and chromium oxide into the piping system Can be reduced.

In another aspect of the invention, in the second period, for example, the hydrogen concentration of the feed water is set to 0.45 to 0.2 ppm on the day before stopping the hydrogen injection, and 0.2 to 0.2 on the day when the hydrogen injection is stopped. 0 ppm.

In the fourth period, the hydrogen concentration in the feed water is set to 0 to 0.2 ppm on the first day and is set to 0.2 to 0.45 ppm on the second day.

According to the method of injecting hydrogen in a nuclear power plant according to the present invention, the sensitivity to stress corrosion cracking of the primary structural material of a boiling water reactor can be reduced by continuous hydrogen injection for 2 to 3 months. Further, the chromium oxide accumulated in the piping system can be appropriately eluted in the reactor water, and the amount of chromium oxide accumulated in the piping system can be reduced. In addition , when hydrogen injection is stopped after continuous injection of hydrogen for a certain period (for example, 2 to 3 months), it is stopped while gradually changing the feedwater hydrogen concentration, for example, after stopping for 2 to 3 days. When the injection is resumed, the process shifts to continuous injection while changing the hydrogen concentration stepwise. Accordingly, it is possible to prevent the water quality environment of the reactor water from gradually changing from the oxidizing atmosphere to the reducing atmosphere or from the reducing atmosphere to the oxidizing atmosphere, and the radioactive substance concentration from being rapidly increased.

  According to the hydrogen injection method of the nuclear power plant according to the present invention, the susceptibility to stress corrosion cracking of the primary structural material of the boiling water reactor is reduced by continuous hydrogen injection for a certain period (for example, 2 to 3 months). Can be made. Therefore, safe driving can be ensured in the long term.

  In addition, after continuous injection of hydrogen for a certain period (for example, 2 to 3 months), chromium oxide accumulated in the piping system can be appropriately eluted in the reactor water by stopping the hydrogen injection. . Therefore, when a nuclear power plant is stopped and a periodic inspection is performed, a large amount of chromium oxide accumulated in the piping system is discharged, and irregularities are formed in the chromium oxide layer on the inner surface of the piping. Disappear.

  Furthermore, when the hydrogen injection is stopped after the continuous injection of hydrogen, the hydrogen concentration is stopped while changing the hydrogen concentration stepwise, and when the injection is restarted after the stop for two to three days, the hydrogen concentration is changed. Since it is configured to shift to continuous injection while changing in stages, the water quality environment of the reactor water can be gradually changed from the oxidizing atmosphere to the reducing atmosphere or from the reducing atmosphere to the oxidizing atmosphere. Therefore, the concentration of radioactive materials does not increase sharply due to changes in the water quality environment, and the dose equivalent rate of the piping system does not increase, so there is no impact on inspection work, and periodic inspections can be performed safely and easily. .

  Embodiments of the present invention will be described below.

  The method for injecting hydrogen in a nuclear power plant according to the present invention is applied to a nuclear power plant equipped with a boiling water reactor (BWR), and hydrogen is supplied to the reactor water through a feed water system of the boiling water reactor. Is configured to be injected.

  As shown in FIG. 1, the piping system of the boiling water nuclear power plant is composed of a main steam system piping 3 for sending steam generated in the core of the boiling water reactor 1 to the turbine 2a, and steam working in the turbine 2a. Is condensed in the condenser 2b, the condensate system pipe 5 for sending the condensate to the condensate demineralizer 4, the condensate demineralizer 4 from the condensate booster pump 12, the heater 13, and the feed pump 6 And a recirculation system pipe 9 for recirculating the cooling water in the boiling water reactor 1 by a recirculation pump 8. ing.

  As the primary structural material, those having excellent corrosion resistance, toughness, strength, weldability and the like are preferable. For example, various stainless steels, various carbon steels and the like are used. In addition, components such as the casing, impeller, and valve of the feed water pump 6 and the recirculation pump 8 are preferably excellent in corrosion resistance, toughness, strength, weldability, etc., and various stainless steels and various carbon steels are used. Is done.

  The hydrogen injection apparatus 10 is connected to, for example, a water supply system pipe 7 between the condensate demineralizer 4 and the feed water pump 6 in the piping system of the boiling water reactor 1 via a pipe 11. However, it is not limited to this location, and any location can be used as long as hydrogen can be injected into the water supply flowing through the water supply system pipe 7.

  Examples of the hydrogen injection device 10 include a device for reducing the pressure from a high-pressure gas cylinder to a predetermined pressure and injecting gaseous hydrogen into the feed water flowing through the water supply system pipe 7, and producing hydrogen by electrolysis of water. And an apparatus for injecting gaseous hydrogen into the feed water flowing through the feed water system pipe 7. However, it is not limited to these devices, and any device that can inject hydrogen into the water supply via the water supply system may be used.

  Then, during operation of the nuclear power plant equipped with the boiling water reactor 1 having the above-described configuration, the hydrogen injection device 10 injects hydrogen at a predetermined concentration into the feed water flowing through the feed water system pipe 7. As a result, the recombination reaction between the oxidizing substance such as oxygen and hydrogen peroxide generated by the radiolysis of water and hydrogen is promoted, and the concentration of the oxidizing substance in the reactor water is lowered.

  Then, after the hydrogen injection is continued for a certain period (for example, 2-3 months), the hydrogen injection is stopped, and after the stop period is 2-3 days, the hydrogen injection is restarted. In this case, hydrogen is stopped for 2 days, the hydrogen concentration is decreased stepwise, and hydrogen injection is started for 2 days, and the hydrogen concentration is increased stepwise. Such continuous injection of hydrogen for a certain period of time and stop of hydrogen injection are repeated, and when the time for periodic inspection comes, the operation of the nuclear power plant and hydrogen injection are completely stopped to Check the plant.

  In the method of injecting hydrogen in the nuclear power plant according to this embodiment configured as described above, hydrogen injection is continuously performed for a certain period (for example, 2 to 3 months). The density | concentration of the oxidizing substance of the furnace water of the furnace 1 can be reduced.

  Therefore, since the corrosion potential of the primary structural material can be lowered and the sensitivity to stress corrosion cracking can be reduced, safe operation of the nuclear power plant can be ensured for a long period of time.

  In addition, hydrogen injection is stopped after hydrogen injection is continuously performed for a certain period (2 to 3 months), so that chromium oxide accumulated in the piping system is appropriately eluted in the reactor water. Can do. Therefore, when hydrogen injection is completely stopped at the time of periodic inspection, a large amount of chromium oxide accumulated in the piping system is discharged, and irregularities are formed in the chromium oxide layer on the inner surface of the piping. Disappears.

  Further, when the hydrogen injection is stopped after the continuous injection of hydrogen, the hydrogen concentration is stopped while gradually changing the hydrogen concentration, for example, when the injection is restarted after the stop for 2 to 3 days. Therefore, the water quality environment of the reactor water can be gradually changed from the oxidizing atmosphere to the reducing atmosphere or from the reducing atmosphere to the oxidizing atmosphere. Therefore, the radioactive substance concentration does not increase rapidly due to changes in the water quality environment, and the dose equivalent rate of the piping system does not increase, so that the periodic inspection can be performed safely and easily without affecting the inspection work.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  Using the hydrogen injection method (after implementation) of the nuclear power plant according to the present invention and the conventional hydrogen injection method (before implementation) of the nuclear power plant, the dose equivalent rate, conductivity, chromic acid concentration, Co-60 ion Concentration and Co-60 cladding concentration were measured and compared, the results are shown below.

  First, measurement conditions for the case of using the conventional hydrogen injection method and the case of using the hydrogen injection method according to the present invention will be described.

  Measurement conditions in the case of using the conventional hydrogen injection method (before implementation) were set to 300 days for continuous hydrogen injection, and this was defined as one cycle. In addition, when hydrogen injection was started and stopped, the feed water hydrogen concentration was changed from 0 to 0.5 ppm and from 0.5 to 0 ppm in a short time.

  The measurement conditions in the case of using the hydrogen injection method of the present invention (after implementation) are as follows. One cycle is divided into six, and the hydrogen continuous injection days are 102 days, 67 days, 80 days, 106 days, 32 days, and 16 days. The hydrogen injection was stopped five times during one cycle. However, the number of days in one cycle of the conventional hydrogen injection method (before implementation) and the hydrogen injection method of the present invention (after implementation) are not the same for business reasons. In addition, when hydrogen injection is started, the hydrogen supply hydrogen concentration is set to 0 to 0.2 ppm on the first day and 0.2 to 0.45 ppm on the second day, and thereafter, for the predetermined number of days shown above. Hydrogen was continuously injected, and when hydrogen injection was stopped, it was set to 0.45 to 0.2 ppm on the day before the injection stop and 0.2 to 0 ppm on the stop day. Then, until the next injection, hydrogen injection was stopped for 2 days in order to stabilize the conductivity of the reactor water.

  FIG. 2 shows a conventional nuclear power plant hydrogen injection method (before implementation) and a nuclear power plant hydrogen injection method (after implementation) according to the present invention. (PLR) It is a figure which shows the measurement result of the dose equivalent rate of two places of A and B of pump outlet piping.

  As shown in FIG. 2, the dose equivalent rate (mSv / h) of the reactor recirculation system (PLR) pump outlet pipe is A: 2.1, B: 3.9 for the conventional hydrogen injection method (before implementation). Thus, the hydrogen injection method (after execution) according to the present invention is A: 0.6 and B: 0.6. The dose injection rate at the reactor recirculation system (PLR) pump outlet pipe is greatly reduced in the hydrogen injection method (after implementation) according to the present invention compared to the conventional hydrogen injection method (before implementation). Yes.

  Therefore, by setting the continuous injection period to about 100 days or less from the conventional about 300 days, it is possible to achieve a dose equivalent rate that does not affect the inspection work.

  Next, measurement results of Co-60 ion concentration and Co-60 clad concentration, which are radioactive materials, are shown when the feedwater hydrogen concentration is increased stepwise.

  FIG. 3 shows a conventional method for injecting hydrogen in a nuclear power plant (before implementation) and a method for injecting hydrogen in a nuclear power plant according to the present invention (after implementation). It is a figure which shows the change of Co-60 ion concentration in the reactor water at the time.

  As shown in FIG. 3, when the feedwater hydrogen concentration was increased to 0 to 0.5 ppm in a short time by the conventional hydrogen injection method, the Co-60 ion concentration (Bq / ml) was about 5.1. In the case where the feed water hydrogen concentration is increased stepwise by the hydrogen injection method according to the present invention, the Co-60 ion concentration is less than about 4.0 in all the continuous injection periods. Further, the Co-60 ion concentration from the start of hydrogen injection until the feedwater hydrogen concentration gradually increases until the feedwater hydrogen concentration reaches 0.45 ppm is substantially the same. Therefore, when the feedwater hydrogen concentration is increased stepwise, the Co-60 ion concentration in the reactor water becomes substantially constant, and the rapid elution of the Co-60 ion concentration is prevented, and the water environment in the reactor water changes rapidly. Can be mitigated.

  FIG. 4 shows a conventional method for injecting hydrogen in a nuclear power plant (before implementation) and a method for injecting hydrogen in a nuclear power plant according to the present invention (after implementation). It is a figure which shows the change of Co-60 clad density | concentration in the reactor water at the time.

  As shown in FIG. 4, when the feedwater hydrogen concentration was increased to 0 to 0.5 ppm in a short time by the conventional hydrogen injection method, the Co-60 cladding concentration (Bq / ml) was about 0.9. In the case where the feedwater hydrogen concentration is increased stepwise by the hydrogen injection method according to the present invention, the Co-60 clad concentration is less than about 0.3 in all the continuous injection periods. Further, the Co-60 cladding concentration from the start of hydrogen injection until the feedwater hydrogen concentration gradually increases until the feedwater hydrogen concentration reaches 0.45 ppm is substantially the same. Therefore, when the feedwater hydrogen concentration is increased step by step, the Co-60 cladding concentration in the reactor water becomes substantially constant, and the rapid elution of the Co-60 cladding concentration is prevented, and the water environment in the reactor water changes rapidly. Can be mitigated.

  From these results, when the feedwater hydrogen concentration is increased stepwise, the radioactive substance concentration in the reactor water is low and stable, so that a safe dose equivalent rate can be maintained.

  FIG. 5 shows the peak value of the conductivity in the reactor water when hydrogen injection is stopped, using the conventional hydrogen injection method for nuclear power plants (before implementation) and the hydrogen injection method for nuclear power plants according to the present invention (after implementation). It is a figure which shows the measurement result of the peak value of chromic acid concentration.

  As shown in FIG. 5, the peak value (uS / m) of conductivity in the reactor water is 20 for the conventional hydrogen injection method (before implementation), and 16 days after the hydrogen injection method (after implementation) according to the present invention. 8, 32 days are 8, 67 days are 9, 9, 80 days are 11, 11, 102 days are 11, and 106 days are 10.

  The peak value (ppb) of the chromic acid concentration in the reactor water is 20 for the conventional hydrogen injection method (before implementation), and 9 and 32 days for the 16th day of the hydrogen injection method (after implementation) according to the present invention. The 15th and 67th days are 19, the 80th day is 23, the 102nd day is 21, and the 106th day is 19.

  As the period of continuous hydrogen injection is shorter, the peak values of conductivity and chromic acid concentration in the reactor water tend to be smaller. Therefore, it is possible to reduce the peak values of conductivity and chromic acid concentration in the reactor water by shortening the continuous injection period.

  From these results, the intermittent operation in which hydrogen injection is stopped about once every about three months can reduce the amount of chrome oxide discharged, so that irregularities are formed in the chrome oxide layer on the inner surface of the pipe. Disappear.

It is the schematic system diagram which showed the piping system of the boiling water reactor which applied the hydrogen injection method of the nuclear power plant by this invention. Reactor recirculation system (PLR) pumps after one cycle operation using the conventional hydrogen injection method for nuclear power plants (before implementation) and the hydrogen injection method for nuclear power plants according to the present invention (after implementation) It is a figure which shows the measurement result of the dose equivalent rate of 2 places of A and B of exit piping. Furnace when hydrogen concentration of feed water is increased stepwise at the time of hydrogen injection using a conventional hydrogen injection method for nuclear power plant (before implementation) and a hydrogen injection method for nuclear power plant according to the present invention (after implementation) It is a figure which shows the change of Co-60 ion concentration in water. Furnace when hydrogen concentration of feed water is increased stepwise at the time of hydrogen injection using a conventional hydrogen injection method for nuclear power plant (before implementation) and a hydrogen injection method for nuclear power plant according to the present invention (after implementation) It is a figure which shows the change of Co-60 clad density | concentration in water. Furnace when hydrogen concentration of feed water is increased stepwise at the time of hydrogen injection using a conventional hydrogen injection method for nuclear power plant (before implementation) and a hydrogen injection method for nuclear power plant according to the present invention (after implementation) It is a figure which shows the change of Co-60 clad density | concentration in water.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Boiling water reactor 2a Turbine 2b Condenser 3 Main steam system piping 4 Condensate demineralizer 5 Condensation system piping 6 Feed water pump 7 Feed water system piping 8 Recirculation pump 9 Recirculation system piping 10 Hydrogen injection Device 11 Pipe 12 Condensate boost pump 13 Heater

Claims (3)

A method for injecting hydrogen into a nuclear power plant that injects hydrogen into reactor water via a nuclear reactor water supply system,
During the operation of the nuclear power plant,
A first period of 2 to 3 months of hydrogen injection,
A second period in which hydrogen injection is gradually reduced over 2 days,
A third period of stopping hydrogen injection for 2-3 days, and
Fourth period to increase hydrogen injection step by step over 2 days
By repeating the cycle consisting of
A method for injecting hydrogen into a nuclear power plant, characterized in that continuous injection and stop of hydrogen for a certain period are repeated. A method for injecting hydrogen in a nuclear power plant according to claim 1,
In the second period, the hydrogen concentration in the feed water is set to 0.45 to 0.2 ppm on the day before the hydrogen injection is stopped, and is set to 0.2 to 0 ppm on the day when the hydrogen injection is stopped.
A method of injecting hydrogen into a nuclear power plant. A method for injecting hydrogen in a nuclear power plant according to claim 1,
In the fourth period, the hydrogen concentration of feed water is 0 to 0.2 ppm on the first day, and 0.2 to 0.45 ppm on the second day.
A method of injecting hydrogen into a nuclear power plant.

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