JPH03128497A - Method for supplying iron clad into reactor coolant - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION Field of Industrial Application The present invention relates to a method for supplying iron cladding into the reactor coolant of a boiling water nuclear power plant.

(Prior technology) In recent years, boiling water nuclear power plants have adopted highly corrosion-resistant metal materials for the liquid contact parts of each system, greatly reducing the generation of corrosion products compared to the past, and reducing the amount of iron in the water supply system. A so-called low cladding plant has been developed that can reduce the cladding concentration to an extremely low concentration (1 ppb or less). However, such a low cladding blunt has the following problems due to the low iron cladding concentration.

That is, generally, at the start of operation of a boiling water nuclear power plant, nickel ions are eluted due to initial corrosion of stainless steel feed water heaters and the like, and are brought into the reactor water system from the feed water system. In conventional plants, the concentration of iron cladding in the water supply system is high, so these iron claddings react with the generated nickel ions to produce complex oxides such as nickel spinel, and these oxides are deposited on the surface of the fuel cladding tube. Fixed by boiling concentration phenomenon. In addition, ionic radioactivity (mainly Co-58, Co-[io
) also migrates in much the same way as nickel ions, and most are fixed on the fuel surface as oxides.

However, in the above-mentioned low cladding blunt, sufficient iron cladding to react with the generated nickel ions does not exist before or after the start of plant operation, resulting in an environment in which iron cladding is insufficient. Therefore, excess nickel ions remain in the reactor water, and their concentration increases due to concentration (up to
It has been reported that Equation 1) I) b).

Also, the concentration of ionic radioactivity in the reactor water becomes extremely high during this period. This is because all of the generated radioactivity cannot be fixed in the fuel cladding as oxides, but remains in the reactor water as ions. Ionic radioactivity in the reactor water is incorporated into the corrosion film that is generated as piping materials in the wetted parts of the primary system corrode, but when the radioactivity concentration is high, the amount of radioactivity that is incorporated into the film increases. As a result, the radiation dose rate (pipe dose rate) on the pipe surface increases. Furthermore, when the pipe dose rate increases, the air dose in the working environment of the plant increases, leading to an increase in the exposure dose (manrem) of various workers.

For this reason, in low cladding plants, in order to fix nickel ions generated before and after the start of operation as composite oxides on the fuel surface, the insufficient iron cladding is systematically introduced into the primary system, increasing the radioactivity concentration in the reactor water. Water quality management is being carried out to suppress this.

There are two specific methods for introducing iron cladding into the primary system: bypass operation of the condensate prefilter (CF) and injection of simulated iron cladding. The bypass operation of the water prefilter will be explained first.

As shown in Fig. 2, in a low-clad boiling water nuclear power plant, steam generated in a reactor 1 and worked in a high-pressure turbine 2 and a low-pressure turbine 3 is condensed in a condenser 4. is purified by two systems, a condensate prefilter 5 and a condensate demineralizer (CD) 6, and then circulated back to the reactor 1 via the feedwater heater 7.

Further, the condensate prefilter 5 is provided with a bypass path 8, and by bypassing all or part of the condensate through this bypass path 8, a crud load is applied to the condensate demineralizer 6. . Since the condensate demineralizer 6 was originally installed to remove ionic impurities, a portion of the crud passes through the condensate demineralizer 6. In other words, by intentionally reducing the purification ability of the iron cladding,
This is a method to increase the concentration of iron cladding in the system.

The graph in Figure 3 shows an example of data in which the radioactivity concentration of Co-58, one of the ionic radioactivity in reactor water, was significantly reduced by bypass operation of the condensate prefilter 5 in an actual plant. It shows.

As shown in this graph, in the two plants, the concentration of Co-58 gradually increased immediately after continuous operation, and the concentration of Co-58 increased to about 1.5
X to "μC1/ml. In the two plants, bypass operation of the condensate prefilter 5 was started at that point, so the radioactivity concentration decreased rapidly and stabilized immediately after that. This is because The iron cladding brought into the system by bypassing the condensate prefilter 5 reaches the reactor water and generates composite oxides with ionic components in the reactor water, and due to the boiling concentration phenomenon on the fuel rod surface, the iron cladding enters the cladding tube. Due to being fixed.

However, in this method, a crud load is applied to the condensate demineralizer 6 by bypassing the condensate prefilter 5, so that the condensate demineralizer 6 is slightly contaminated. In order to purify the condensate demineralizer 6, it is necessary to backwash and regenerate the ion exchange resin constituting the condensate demineralizer 6, which generates waste and requires an enormous amount of effort.

Additionally, there are reports of secondary failures due to bypass operation of the condensate prefilter 5, such as loss of flow balance among the several condensate demineralizers 6. Furthermore, condensate demineralizer 6
Since it uses an iron cladding that leaks, there are problems such as difficulty in controlling the concentration.

On the other hand, in a method of injecting iron cladding (simulated cladding) generated outside the system as a substitute for iron cladding naturally generated in the plant, an iron injection device 10 connected to the downstream side of the condensate demineralizer 6 is used to Generate iron cladding and inject it.

FIG. 4 shows an example of an iron injection device 10. In this iron injection device, pure water introduced from the MUWP (meaning a pure water line in a plant) is degassed in a mass deaerator 11. Thereafter, carbon dioxide gas (Co2) is introduced into the carbon dioxide gas container 12 and blown into the degassed pure water inside the carbon dioxide gas container 12. This is because the electrolytic voltage is high in pure water (it is difficult for electricity to flow), so carbon dioxide gas is blown into the water to generate carbonate ions, making it easier for electricity to flow. Next, the water containing carbon dioxide gas is sent to an electrolytic cell 13, where iron ions are generated by electrolysis of carbon steel.

The generated iron ions are then sent to the clad aging tank 14 on the downstream side, where they are oxidized by air blowing and turned into particles (clad). The water containing the iron cladding is then injected into the system by the pump 15. Note that if iron ions are directly injected into the system, they will stick to each piping from the injection point to the injection target point (reactor water), so the generated iron ions are made into cladding.

In such a method, a large iron injection device 10 that requires a clad aging tank 14 in addition to an electrolytic cell 13 must be installed within the nuclear power plant.

In addition, such an iron injection device 10 requires complicated maintenance and management (constant monitoring of the amount of iron cladding generated, electrode maintenance, adjustment, replacement, etc.), but since it is located inside a nuclear power plant, such troubles are minimized as much as possible. should be prevented;
It was also necessary to have a system in place that could immediately respond in the event of an outbreak.

(Problems to be Solved by the Invention) As mentioned above, the conventional method of supplying iron cladding into the reactor coolant has the problem of a large amount of trouble and work involved in injection of iron cladding in a boiling water nuclear power plant. However, there was a problem in that it was difficult to stably supply the desired amount of iron cladding.

The present invention has been made in response to such conventional circumstances, and can significantly reduce troubles and workload related to iron cladding injection in boiling water nuclear power plants compared to conventional methods, as well as reduce reactor cooling. The present invention aims to provide a method for supplying iron cladding into a nuclear reactor coolant, which can stably supply a desired amount of iron cladding into the reactor coolant.

[Configuration of the Invention (Means for Solving the Problems) In other words, the present invention provides a method for supplying iron cladding to the reactor coolant of a boiling water nuclear power plant outside the boiling water nuclear power plant. Manufacture, concentrate,
The method is characterized in that the concentrated iron cladding is then transported to the boiling water nuclear power plant, diluted, and supplied into the reactor coolant.

(Function) In the method for supplying iron cladding into a nuclear reactor coolant of the present invention having the above configuration, it is possible to downsize the equipment installed in a boiling water nuclear power plant compared to the conventional method, and to reduce the trouble and work involved. - can be significantly reduced. In addition, if the iron cladding is tested before being transported to the plant, the amount of iron in the iron cladding is accurately quantified, and its characteristics are thoroughly investigated, the desired amount of iron cladding can be transferred into the reactor coolant. can be stably supplied.

(Example) Hereinafter, details of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a low cladding boiling water nuclear power plant, and in the figure, reference numeral 1 indicates a boiling water reactor. Steam generated in the boiling water nuclear reactor 1 and subjected to work in the high-pressure turbine 2 and low-pressure turbine 3 is condensed in the condenser 4 and becomes condensate.

This condensate is then transferred to a condensate prefilter 5 and a condensate demineralizer 6.
The water is purified by the following two systems, and is then circulated back to the boiling water reactor 1 via the feed water heater 7.

Furthermore, an iron clad storage tank 33 equipped with a stirring mechanism 32 for preventing precipitation of iron clad is connected to the downstream side of the condensate demineralizer 6 via an iron clad injection pump 31.

In this embodiment method, iron cladding is produced outside the boiling water nuclear power plant using a device such as that shown in Figure 4, concentrated, and then transported into the boiling water nuclear power plant for dilution. It is stored in an iron clad storage tank 33 together with water (pure water), and is injected into the reactor coolant by an iron clad injection pump 31 while being stirred by a stirring mechanism 32.

That is, according to the method of this embodiment, the electrolytic iron generation part in the conventional iron injection device 10 as shown in FIG. 4 is separated from the ferrous input part, and only iron injection is carried out in the boiling water nuclear power plant . Therefore, since the equipment installed in a boiling water nuclear power plant basically consists of only the iron clad storage tank 33 and the iron clad injection pump 31, troubles and workload related to iron clad injection in the boiling water nuclear power plant can be avoided. can be significantly reduced compared to conventional methods. In addition, if the iron cladding is tested before being transported to the plant, the amount of iron in the cladding is accurately determined, and its characteristics are thoroughly investigated, it is possible to stably supply the desired iron cladding. Can be done.

[Effects of the Invention] As explained above, the method for supplying iron cladding into the reactor coolant of the present invention can significantly reduce the trouble and amount of work involved in iron cladding injection in a boiling water nuclear power plant compared to the conventional method. It is possible to reduce the amount of iron cladding and to stably supply a desired amount of iron cladding into the reactor coolant.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic configuration of a boiling water nuclear power plant for explaining a method according to an embodiment of the present invention, and FIG. 2 is a diagram showing a schematic configuration of a boiling water nuclear power plant for explaining a conventional method. , FIG. 3 is a graph showing changes in the radioactive concentration of Co-58, and FIG. 4 is a diagram showing the configuration of an example of a conventional iron injection device. 1... Boiling water reactor 2...
・・・・・・・・・High pressure turbine 3・・・・・・・・・
...Low pressure turbine 4...Condenser 5...Condensate prefilter (CF) 6
・・・・・・・・・Condensate demineralizer (CD) 7...
......Water heater 31...
Iron clad injection pump 32... Stirring mechanism

Claims (1)

[Claims] (1) In supplying iron cladding into the reactor coolant of a boiling water nuclear power plant, the iron cladding is manufactured and concentrated outside the boiling water nuclear power plant, and then the concentrated iron cladding is supplied to the boiling water nuclear power plant. A method for supplying iron cladding into a nuclear reactor coolant, the method comprising transporting the iron cladding to a nuclear power plant, diluting it, and supplying it into the reactor coolant.