JPH05172985A - Reactor water environment monitoring system - Google Patents

Abstract

(57) [Summary] (Corrected) [Structure] Equipment for accurately measuring the amount of radioactive substances adhering to the surface of the material that comes into contact with reactor water during plant operation, and direct water quality and corrosion under the environment of reactor water. Facility for monitoring the environment Radioactive substance amount monitoring piping 2
6. Corrosion environment monitoring The pressure vessel 36 improves the reliability of plant operation management. [Effect] By accurately measuring the rise behavior of the plant dose rate during plant operation, contributing to the reduction of the radiation dose received by workers during regular inspection work, and by providing the reactor water environment monitoring equipment with high temperature sensors, Contributes to maintaining the soundness of plant materials.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a system for monitoring the amount of radioactive nuclides accumulated in materials that come into contact with reactor water in a nuclear power plant, and contributes to reducing the amount of radiation received by a plant periodic inspection worker. Concerning the system to do.

In addition, it provides an effective system for monitoring the corrosive environment of materials in contact with reactor water under the same high temperature and high pressure environment as reactor water by using various monitoring sensors, and contributes to the reliability of plant constituent materials. Concerning the system to do. The present invention relates to a system in which the above two high temperature and high pressure facilities are combined as a reactor water environment monitoring facility.

[0003]

2. Description of the Related Art This is provided at the time of inspecting various pipes / equipment, which is regularly performed during the operation of a nuclear power plant. The source of the radiation dose received by this worker is generated by the combustion of the reactor fuel, as the corrosion products accumulated with the cooling water inside the reactor adhere to the fuel inside the reactor or the surface of the structural materials inside the reactor. It is generated when a part of it is activated by the irradiation of neutrons.

Further, a part of the corrosion product adhered to the fuel or the internal structural material is redissolved in the reactor water and circulates together with the reactor water. Therefore, a certain amount of radioactive material is contained in the reactor water, and it accumulates little by little on the surface of the constituent materials that come into contact with the reactor water during the plant operation period.
The radiation dose rate on the surface of piping and equipment gradually increases.

In order to suppress the increase in the radiation dose rate, in a boiling water nuclear power plant, in order to keep the concentration of radioactive substances existing in the reactor water low, Hitachi commentary vol. 7
0, No. 4, 417 (1988), various measures have been taken. One of the measures is ⁶⁰ Co (half-life of about 5.2 years) after activation, which reduces the generation of Co, which makes a large contribution to the radiation dose of the plant.
Stainless steel and Inconel materials with a reduced Co content have been used. Furthermore, in order to reduce the amount of corrosion products that flow into the reactor, the condensate purification system is dualized with a filter and a demineralizer to enhance the purification capacity. Furthermore, by injecting iron into the water supply system and forming complex oxides of Co and Ni with iron such as NiFe ₂ O ₄ or CoFe ₂ O _{4 on} the fuel surface in the reactor, corrosion formation adhered to the fuel We have also adopted an operation that suppresses the re-elution of radioactive substances from materials.

Further, in the plant trial operation stage after the construction of the plant, a treatment for forming a protective film on the material surface in contact with the reactor water to reduce the accumulation rate of radioactive substances during the plant operation period (pre-filming treatment) is performed. Has been done.

As a result of these various measures, reduction of radioactive substances in nuclear reactor water can be achieved, and the amount of radioactive substances adhering to the piping and equipment of the plant has also been reduced.

On the other hand, although a certain amount of reduction in the plant line is being achieved, efforts for further reduction have always been made. Furthermore, in the future, it may be difficult for an engineer who carries out regular inspections of nuclear power plants to take corrective measures against the increase in the number of plants, further reducing the plant dose rate, and There is a demand for planning the radiation dose that workers receive during regular inspections. To plan the radiation dose that workers receive during regular inspections (hereinafter referred to as regular inspections), it is necessary to predict in advance the amount of radioactive material that accumulates on the inner surfaces of pipes and equipment during regular inspections. or,
In order to accurately predict the amount of radioactive material accumulated at the time of regular inspection, it is effective to accurately monitor the amount accumulated on the material surface in contact with the reactor water during the plant operation period.

The contents monitored so far in the boiling water nuclear power plant will be described below with reference to FIG.

FIG. 2 shows a plant configuration of a boiling water nuclear power plant. The steam generated by the combustion of the nuclear fuel loaded in the reactor 1 is guided to the high-pressure turbine 3 and the low-pressure turbine 4 through the main steam pipe 2 to perform work. The steam after the work is re-condensed in the condenser 5, passes through the condensate pipe 6, the condensate pump 7, the condensate filter 8, the condensate demineralizer 9 and the condensate booster pump 10 to supply water. Be led to. In the water supply system, the cooling water passes through the water supply pipe 11 and the water supply pump 12, is heated by the water supply heater 13, and then returns to the nuclear reactor 1. On the other hand, the reactor water circulates in the two series of recirculation system constituted by the recirculation pump 14 and the recirculation system pipe 15. In addition, part of the reactor water is the reactor purification system pump 1
After passing through 6 and the reactor cleaning system piping 17 to be purified by the reactor cleaning equipment 18, it joins the water supply system piping 11 and returns to the reactor 1. In the meantime, by using the ion exchange resin in the reactor cleaning equipment 18, 60
Since it is necessary to cool it to ℃ or below,
Cooling at 9. Further, for monitoring the water quality of the reactor water, sampling piping systems 20 and 21 that branch from the recirculation system piping 15 and the reactor cleaning system piping 17 and can sample the system water are provided. These sampling systems use conductivity meters and pH meters that cannot be measured at high temperature and high pressure (280 ° C, 70 kg / cm ² ) of the reactor.
The sampling water cooler 22 is provided to measure the water quality after cooling.

Here, it is difficult to measure the amount or dose rate of radioactive substances adhering to the inner surfaces of pipes and equipment in contact with the reactor water and under the environment of high temperature and high pressure.

Therefore, in this case, a place outside the containment vessel, which is in contact with high-temperature and high-pressure reactor water and which can measure the amount of radioactive substances adhering to the inner surface, has been selected and measured. Specifically, the reactor purification system pump 16 is provided in the reactor purification system pipe 17 branched from the reactor recirculation pipe 15 shown in FIG.
And the heat exchanger 19 of the reactor cleaning system.
For the measurement of radioactive substances, a method has been used in which the energy of γ-rays emitted when the radioactive substances attached to the inner surface of the pipe are disintegrated is detected by a semiconductor detector to determine the nuclide and the attached amount.

[0013]

In the latest boiling water nuclear power plant, the system configuration of the reactor cleaning system, which was measured during the operation period, was changed as shown below.

Since the reactor cleaning system pump 16 is in the same high temperature and high pressure water environment as the reactor water, there is no amount of radioactive material attached, and the amount of radiation received by the operator at the time of overhauling the pump during regular inspection is low. It was relatively high. For this reason, in recent plants, the position of the pump has been moved to the downstream side in FIG. 2 in order to reduce the radiation dose received by the operator of the pump inspection work. Along with this, the radiation dose received by the pump inspector has been reduced to 1/5 or less of the conventional radiation dose. Along with the change in the position of the reactor purification system pump 16, the length of the pipe from the branch portion of the recirculation system pipe to the reactor purification system heat exchanger 19 is shortened. As a result, a short half-life nuclide ¹⁶ N (half-life: 7.14 seconds, γ
(Ray: 6.13 Mev), the intensity of γ-rays is relatively large, and it is becoming difficult to identify γ-rays from radioactive substances adhering to the inner surface of the pipe. further,
In a plant where the reactor cleaning system piping goes out of the containment unit 23 and is directly connected to the reactor cleaning system heat exchanger, the contribution of ¹⁶ N γ-rays reaches ten times that of the conventional one, and it adheres to the inner surface of the piping. There is a situation where the γ-rays of existing radioactive materials cannot be identified. Such a situation leads to a decrease in the prediction accuracy of the plant dose rate at the time of regular inspection, and the planning for reducing the radiation dose received by the worker at the time of inspection work becomes low, and improvement is desired.

Furthermore, the reactor cleaning system piping of the boiling water nuclear power plant is carbon steel piping, which is different from stainless steel materials such as recirculation piping which has the greatest effect on the atmospheric radiation dose rate in the containment vessel. Radioactive substances have the property of being incorporated into the oxide film formed on the surface of the material, and the amount of film formed under the same reactor water environment differs depending on the material (corrosion rate is different). Depends on the material. Therefore, the amount of radioactive substances deposited on the inner surface of the reactor cleaning system and carbon steel pipe was measured, and the amount of radioactive substances deposited on the stainless steel material surface was estimated from empirical values.

In this respect as well, it is desired to improve the prediction accuracy of the plant dosimeter at the time of regular inspection by monitoring the amount of radioactive substances deposited for each material.

On the other hand, in recent years, the need for direct measurement in a high temperature and high pressure environment as a water environment monitoring sensor for nuclear reactor water has been indicated, and various high temperature sensors have been developed.

Specifically, the conductivity sensor (Y. Asakura an
d S.Uchida, J.Nucl, Sci.Technol, 24 , 632 (1987), pH sensors (DDMachonald, et al J.Solution Chomistry 17 , 7
19 (1988), Dissolved oxygen sensor (N.Nakayamma, et al j.Nuc
l, Sci.Technol, 21 , 476, (1984)) and others are being developed. Furthermore, as a facility for monitoring the corrosive environment such as stress corrosion cracking of structural materials inside the reactor, a corrosion potential sensor (A. Molander, 1911JAIF International Conterence on
Water Chomistry in Nuclear Powor Plants, 361 (199
1)) and corrosion rate sensor (Sugimoto, Hosoya, anticorrosion technology, 34 ,
63 (1985)) and the like have been developed.

It is desired to provide a system to which these high temperature sensors are applied in an actual plant to monitor the water quality of the reactor water and the corrosive environment, and to improve the reliability.

[0020]

[Means for Solving the Problems] In order to monitor the amount of radioactive substances adhering to the inner surface of plant piping equipment during the operation of a boiling water nuclear power plant, a new high temperature and high pressure reactor water is used. It is effective to install equipment for immersing various material test pieces in reactor water and measuring the amount of radioactive substances adhering to the material surface during the plant operation period. In addition, since high-temperature and high-pressure reactor water is introduced, it is necessary to consider equipment beforehand so that problems such as leakage of cooling water will not occur. Specifically, it is desirable that the test piece that measures the amount of radioactive material attached is a piping material that has the same quality control as the reactor system. It is effective to monitor the amount. Furthermore, the amount of radioactive material that adheres to the inner surface of the pipe can be quantified by measuring the γ-rays that pass through the pipe wall from the outside of the pipe for each energy with a semiconductor detector. It is also effective in terms of reduction.

Furthermore, present only in plant operation, hinder γ ray measurement from the radioactive material of the pipe inner surface attachment ¹⁶
The removal of the effects of N nuclides can be done by setting the system configuration so that the passage of reactor water to the monitoring system can be stopped only during measurement.
The measurement accuracy can be improved. In addition, when installing a new monitoring system under high temperature and high pressure, in the same system,
By adding various high temperature sensors that can directly measure the water quality environment or the corrosion environment of reactor water under high temperature and high pressure,
The efficient use of equipment and the use of the data obtained as described above can greatly improve the reliability of plant management.

[0022]

By adopting the present invention in a nuclear power plant, the following plant management purposes can be easily achieved.

By providing a facility for monitoring the accumulated amount of radioactive substances, it becomes possible to easily monitor the change with time of the radioactive substances adhering to the material surface in contact with the reactor water even during plant operation. As a result, it is possible to improve the accuracy of predicting the atmospheric radiation dose rate in the containment vessel and the radiation dose rate received by various workers at the time of regular inspection. In particular, as a result of monitoring the amount of radioactive substances deposited, if the amount of radiation is large and it is expected that the amount of radiation received by workers will increase, by increasing the number of shielding materials or preparing remote automatic inspection equipment in advance, It is possible to prevent a delay in the inspection process or an obstacle such as an abnormal increase in the radiation dose rate received by the worker.

Furthermore, by adding a water quality environment monitoring facility using a high temperature sensor to the above facility, the environment of the reactor water can be grasped more clearly than in the present situation. As a result, fluctuations in the amount of radioactive substances deposited, fluctuations in the corrosive environment of materials in contact with reactor water, etc. can be detected early, and water quality improvement operations can be carried out early, contributing to the maintenance of plant soundness.

[0025]

EXAMPLE An example of equipment for monitoring the amount of radioactive substances adhering to the surface of a material in contact with reactor water will be described with reference to FIG.

In order to guide the reactor water as it is at high temperature and high pressure to the monitoring system, it may be branched by piping of the reactor recirculation system, or branched on the reactor or upstream of the system heat exchanger 19. It is possible. In practice, assuming that the system is isolated due to an abnormality on the reactor or the system, and reactor water cannot be sampled, as shown in FIG. 1, the pipe 25 and the pipe 25 and the pipe 26 are connected from both systems. It is desirable to provide. The reactor water led to the monitoring system is led to a monitoring unit in which pipes 26 of the same quality as the reactor constituent material such as carbon steel, stainless steel or Inconel are connected by welding or the like. Monitoring section piping 26
Is in the same environment as the material inside the containment vessel that comes into contact with the reactor water during the opening and closing of the reactor water, so the amount of radioactivity deposited is almost the same. Due to the accumulation of radioactive materials in the monitoring section,
Since the surface dose rate of the monitoring pipe also increases, it is desirable to isolate it by the shield 30 in advance.
Further, the measurement of the radioactive substance adhering to the inner surface of the pipe 25 is performed in a state where the monitoring equipment inlet valves 26 and 28 are closed and the above contribution is eliminated. Further, the gamma ray energy measurement by the semiconductor detector 29 is performed through the hole 31 provided in the shield 30. Further, in order to measure the regions of various materials separately, it is effective to add a kisque 32 that can be moved vertically or horizontally to the semiconductor detector. Also,
The reactor water that has passed through the monitoring pipe 26 is cooled by the cooler 3
After cooling in 3, it is effective to return to the inlet side of the reactor cleaning system pump and reduce the amount of waste liquid generated.

FIG. 3 shows an example of the reactor water monitoring system configuration in which the piping dose rate monitoring equipment and the water quality high temperature monitoring equipment are combined.

The reactor water is led through the pipes 24 and 25, and further led through the pipe 34 to various high temperature center portions 35 and a pressure vessel 36 for monitoring the material corrosion environment. The reactor water that has passed through this measuring device passes through the cooler 33 and the reactor cleaning system pump 1 as in the piping dose monitoring equipment.
Return to the entrance side of 6. The water quality sensor under high temperature and high pressure
High temperature conductivity meter, high temperature pH meter, high temperature dissolved oxygen meter,
Provide a high temperature dissolved hydrogen meter, etc.

The corrosive environment of the material is monitored by immersing the material test piece in a pressure vessel and measuring the corrosion potential of the material by a corrosion potential meter 39 or by measuring the corrosion resistance. By adding a load to the total test piece and the immersed test piece by the application adding device 38 to add a facility capable of performing an accelerated test of stress corrosion cracking, it becomes possible to monitor a corrosive environment under a reactor water environment. By adding these monitoring facilities, subtle changes in reactor water can be detected quickly, and the reliability of water quality management can be improved and the integrity of the plant can be easily maintained.

FIG. 4 shows an example of space-saving monitoring equipment when it is difficult to add a high temperature sensor unit in the embodiment shown in FIG. 3 due to a problem in installation space. By incorporating various water quality high temperature sensors in the pipe dose rate monitoring pipe 35, the water quality sensor installation space can be omitted. Especially, the material test piece to be measured by the corrosion potential meter and the corrosion rate meter for corrosion monitoring can be substituted by the monitoring pipe, which is a great advantage in terms of equipment cost.

[0031]

By adopting the present invention, it becomes possible to accurately monitor the amount of radioactive substances adhering to the material surface in contact with reactor water during plant operation. As a result, it is possible to investigate the cause and make an early examination and implementation of the improvement operation should a change occur in the plant dose rate increase rate. further,
When the plant radiation rate rises, it becomes easier to prepare in advance such as shielding enhancement measures for the regular inspection work, and the planning of the radiation dose received by the workers involved in the regular inspection work improves.

Further, by adding the reactor water monitoring using the high temperature sensor and the corrosive environment monitoring equipment, the reliability of the reactor water environment under the present room temperature environment can be greatly improved.

[Brief description of drawings]

FIG. 1 is a system diagram of an example of equipment for accurately monitoring the amount of radioactive substances adhering to the material surface in contact with reactor water in a reactor water environment.

FIG. 2 is a system diagram showing a configuration of a boiling water nuclear power plant and a system configuration change of a reactor cleaning system.

FIG. 3 is a system diagram showing an example of equipment for monitoring the amount of radioactive substances deposited in a reactor water environment and equipment for monitoring the water quality environment of reactor water using a high temperature sensor.

FIG. 4 is a system diagram showing an embodiment in which a facility for monitoring the amount of radioactive substances deposited in a reactor water environment and a high temperature sensor are incorporated to save space.

[Explanation of symbols]

16 ... Reactor cleaning system pump, 26 ... Radioactive substance adhesion amount monitoring piping, 29 ... Semiconductor detector, 30 ... Shield,
35 ... High temperature sensor, 36 ... Corrosion environment monitoring pressure vessel, 37 ... Corrosion electrometer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G21C 17/003 7808-2G G21C 17/00 GDB E

Claims (5)

[Claims] 1. A facility for guiding the reactor water of a nuclear power plant in a high-temperature and high-pressure state, and providing equipment for monitoring the amount of radioactive elements in the reactor water adhering to the surfaces of pipes and equipment in contact with the reactor water. Reactor water environment monitoring system. 2. Reactor water of a nuclear power plant is introduced under high temperature and high pressure conditions, and at least one of electrical conductivity, pH, dissolved oxygen concentration, dissolved hydrogen concentration, and corrosion potential at high temperature is set to high temperature. A reactor water environment monitoring system that is equipped with equipment for measuring at high pressure. 3. A facility for guiding reactor water of a nuclear power plant at a high temperature and high pressure state and measuring the corrosion effect of pipes / equipment existing in the reactor water environment with a material immersed in the actual reactor water environment. A reactor water environment monitoring system characterized by the provision of 4. The facility for monitoring the amount of radioactive elements adhering to the material surface according to claim 1, wherein the reactor water is flown into a pipe made of a material forming the reactor, and the radioactive substance adhering to the inner surface of the pipe is radioactive. A nuclear water environment monitoring system that measures the amount of nuclides by measuring the gamma rays emitted from radionuclides with a semiconductor detector. 5. The method for measuring the corrosive environment of the reactor internal material according to claim 3, wherein stress corrosion cracking is measured by applying stress to a material test under the reactor water environment, and under the reactor water environment. A reactor water environment monitoring system that employs one or more methods of electrochemically measuring the corrosion resistance of immersed material test pieces or measuring the corrosion potential of the material surface.