JPS61205897A - Nuclear power plant - 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] [Field of Application of the Invention] The present invention relates to water quality control for reducing the surface dose rate of sub-system piping within a nuclear power plant, and relates to iron cladding of the water supply system of a boiling water reactor. This invention relates to a nuclear power plant suitable for optimally controlling the amount of nonferrous metal ions and reducing the dose rate.

[Background of the invention]

Ionic or insoluble corrosion products are generated due to corrosion of piping, pumps, valves, etc. used in the water supply system of nuclear power plants, e.g. . The corrosion products brought in adhere to the fuel rods and become radioactive corrosion products when irradiated with neutrons. Some of the radioactive corrosion products are re-eluted into the cooling water, or
Detach. For example, Mn, Ni, and Co are transformed by neutron irradiation into radioactive corrosion products with long half-lives such as "Mn,""Co," and "Co," respectively.

These radioactive corrosion products adhere to the surfaces of recirculation system piping and the like while circulating in the secondary cooling water system. For this reason, the ft5t rate on the piping surface increases, which increases the radiation exposure of workers when performing maintenance and inspection of the nuclear reactor.

Narrow side of piping #! As a method for reducing the total quantity rate, it has been proposed to suppress the generation of corrosion products in the water supply system and to suppress the adhesion of radioactive corrosion products to the piping surface.

Conventionally, the generation of corrosion products, especially Co-? As a method for reducing Ni elution, Japanese Patent Application Laid-Open No. 59-89775 proposes a method of forming an oxide film on the surface of stainless steel in advance.

However, recent results have shown that simply suppressing the generation of corrosion products is not sufficient.

Furthermore, in order to suppress the adhesion of radioactive ions to the structural materials of nuclear power plants, JP-A-58-79196 discloses that the amount of metal ions in the coolant is measured with a conductivity meter, and the measured value is Based on Mn.

A method has been proposed in which non-ferrous metal ions such as Ni and Ni are injected into the coolant. The present invention suppresses the production and elution of radioactive ions on the surface of fuel rod cladding tubes by controlling the water quality of the water supply system. It is.

[Purpose of the invention]

An object of the present invention is to provide a nuclear power plant that is equipped with a water quality control method and device necessary to effectively reduce the surface dose rate of primary piping in a nuclear power plant.

[Summary of the invention]

The Fe concentration in the water supply system of a boiling water nuclear power plant is N i
As a result of analyzing the phenomenon that when the temperature is extremely low compared to 78 degrees, the Ico radioactivity concentration in the reactor water increases (even when the Fe concentration is higher than the Ni concentration), it was found that the iron cladding and after-arc ion concentrations were balanced at a constant ratio. It has been found that the increase in 51Co radioactivity can be effectively suppressed by reducing it, leading to the discovery of the present invention.

The nuclear power plant of the present invention is a nuclear power plant whose main components include a nuclear reactor, a turbine, a condenser, a low-pressure feedwater heater, a high-pressure feedwater heater, and each piping connecting these.
Based on the means for measuring the amount of iron cladding in the reactor feed water, the means for measuring the nonferrous metal ions f containing at least Co and Ni in the reactor feed water, and the measurement results by each of the above means, It must be equipped with a means to increase or decrease the amount of iron cladding or non-ferrous metal ions so that the iron content ratio of the cladding becomes 2 to 8 (weight ratio).
ff: Characterized.

[Embodiments of the invention]

Corrosion products produced by corrosion damage to structural materials consist of water-soluble ions and insoluble metal oxides, the latter commonly referred to as cladding. The main component of the cladding is pe, which is hemamate (α-Fe*Os) in rising water reactors with an oxidizing atmosphere, magnetite (Feas4), and niakel ferrite in pressurized water reactors with a reducing atmosphere. (NiFezO4), etc.

The present inventors investigated the characteristics of a high temperature filter using hematite particles. At 285C, flow rate 1t/
Figure 2 shows the relationship between the differential pressure that occurs when water containing hematite particles is passed for one hour at λ and the concentration of hemamate particles in the flowing water. Pore diameter 0.45μ as a maintenance plant
A glass filter was used as the fiber layer filter.

When fluid is filtered through a membrane filter, all particles larger than the pore size of the filter are captured on the surface of the filter. In contrast, in fiber layer filters, particles are trapped not only on the surface but also on the interior.

In the case of a membrane filter, particles are captured on the surface, so the captured particles in the first layer will block the pore size of the filter. Therefore, the differential pressure across the filter increases rapidly. The differential pressure at this time is proportional to the particle concentration in the fluid and the flow rate, and does not depend on the shape of the particles as long as the particles are larger than the pore size of the filter. Since the trapped particles in the second and subsequent layers can be treated as a powder-filled bed, the differential pressure generated by the trapped particles in the second and subsequent layers depends on the shape of the particles. In this way, when a membrane filter is used, the relationship between differential pressure and particle concentration is in two stages as shown in FIG.

In the case of a fibrous layer filter, particles are trapped on the surface and inside the filter, so that the differential pressure across the filter resulting from particle trapping is proportional to the particle concentration in the fluid and the flow rate.

From the above experimental results, when using a membrane filter with a pore size of 0.45 μm, particles with a particle size of 0.45 μm or more, that is, iron cladding, can be collected by passing 1 ton of water up to a concentration of 10 ppb of iron cladding at the differential pressure of the filter. Can be measured with good sensitivity. By using a fiber layer filter, iron cladding of top per billion or higher can also be quantified.

At this time, if the water flow rate is increased, the differential pressure will also increase, so the measurement accuracy can be improved. Filters are selected depending on the concentration of iron cladding in the water supply.

To find the absolute iron concentration from the differential pressure, proceed as follows.

First, a calibration curve showing the relationship between differential pressure and iron cladding concentration as shown in FIG. 2 is created. Now, assuming that the water flow rate Vt/h and the water flow time are the differential pressure generated in time as PKt/-, the iron cladding amount w pp can be calculated from the differential pressure P using a calibration curve as shown in Figure 2.
Find b. The iron clan is hematite (α-Pe*Oa
), then the iron content WF − in the iron cladding is
(g) can be found using the following formula.

,”,Wr,=vVVt(g) Nizo as an ionic corrosion product in the water supply.

Cu", Mn"°, Co2'", Mg"° zn! +
etc., but these behave similarly in reactor water, and by neutron irradiation, l1lC□, 64C11, respectively.
Cu, s4Mn.

6°Produces radioactive nuclides such as Co, ``Mg, ''・Zn, etc.

Cr exists in the form of CrO4''-.

The electrical conductivity can be expressed as the sum of the electrical conductivities of various ions as shown in the following equation.

K = AM"CM" + Aom-Co +i-
+ΣA+C+ where A: limit equivalent ionic conductivity C: ion concentration limit equivalent ionic conductivity (the magnitude of the ionic conductivity varies depending on the ion) has temperature existence. The ultimate ionic conductivity for the above cationic corrosion products is (54
±1) It is almost the same as Ω-1d1mol-1, and it is thought that the size will be about the same even at high temperatures. Now, the anions are converted into OH ions by a high temperature anion filter. According to the law of conservation of charge, the same amount of OH ions as the cations of the corrosion product were generated.

Accordingly, the conductivity of cations/ions is sensitized by the conductivity of OH ions. In other words, the conductivity of pure water! 12o, the conductivity Kl due to the positive ions and the same amount of OH- ions is determined by the following equation.

+ =Kab Kg2゜=ΣΔtCI+ Aog-C'oi- Here, K*b "Measured conductivity C'O!l-: OH generated by the anion filter
-Ion concentration (=ΣC+) In this way, the nonferrous metal ion concentration can be determined from the conductivity of 1. Figure 3 shows Co(OH)t and N1(OH)
) shows the results of measuring the electrical conductivity at 285C of z. The ultimate equivalent ionic conductivity at high temperature is larger than that at room temperature, and given the OH ion, the third
The electrical conductivity due to the nonferrous metal ions shown in the figure is about an order of magnitude higher than the value at room temperature.

If the pH of the feed water is not neutral, correction is required accordingly.

When the pH of the feed water is acidic, the anions are converted to OH ions by the anion filter, so no correction is necessary, but when the pH of the feed water is alkaline, the ion-conducting carbon content due to alkali metals is corrected. Must. Since the amount of alkali metal ions can be determined from the pH of the water supply, the nonferrous metal ion concentration can be determined more accurately by providing a pH meter and sending its signal to the controller 16 for correction.

Figure 4 shows the ratio of FeI and Ni ion concentration in the water supply (
This figure shows the surface dose rate of piping relative to the weight ratio) based on actual data. From this figure, it can be seen that the optimal range of the ratio (weight ratio) between the iron content of the iron cladding in the water supply and the l'Ji ion concentration is 2 to 8. Iron content and Co
Ratio (weight ratio) of the concentration of ionic corrosion products such as ions K
The same is true for the optimal range. An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows the basic system of the water supply system of a boiling water nuclear power plant to which the present invention is applied. In Figure 1, 1 is a turbine, 2 is a condenser, 3 is a condensate pump, 4 is a condensate demineralizer, 5 is a feed water pump, 6 is a low pressure feed water heater, 7 is a boost pump, 8 is a high pressure water feed Heater, 9 is nuclear pressure vessel, 10.11 is valve, 1
2 is a high temperature filter, 13 is a differential pressure gauge, 14 is a high temperature anion filter, 15 is a high temperature conductivity gauge, 16 is a controller, 1
7゜18.19 is a valve, 20 is a high temperature clad filter,
21 is a high temperature cation filter.

In FIG. 1, the difference from a conventional boiling water nuclear power plant is that a high-temperature filter 12, a differential pressure gauge 13, a high-temperature anion filter 14,
A branch line consisting of a high temperature conductivity gauge 15 and a valve 10° 11 is attached, and a high temperature clad filter 20 and a high temperature cation are connected between the point where one end is connected to the water supply line and the high pressure water supply heater 8 and the branch line. Filter 21, valves 17, 18
19 and the point where the controller 16 is provided.

In this embodiment, the water quality of the water supply system is controlled by the following steps. First, the differential pressure between both ends of the high temperature filter 12 is measured using the differential pressure gauge 13. This measured value is sent as a signal to the controller 16.

The signal sent from the differential pressure gauge 13 is processed by the controller 16. At this time, the amount of iron in the iron cladding is calculated and determined from the differential pressure using the method described above.

Next, in the high temperature anion filter 14, the anions are converted to OH ions. After that, high temperature conductivity level 1
At 5, the conductivity is measured and the signal is sent to the controller 16.

A metal hydroxide or the like is used as the high temperature anion filter. With this filter, HCos-, H
Even if anions such as 81ts- are present, they are converted to OH ions, making it easy to convert the cation concentration from the conductivity.

The signal sent from the high-temperature conductivity liver 15 is processed by the controller 16. At this time, the nonferrous metal ion concentration of the corrosion product is determined by calculation using the relationship shown in FIG.

Using the previously determined iron content, the ratio (weight ratio) of the iron content to the nonferrous metal ions is determined. The quality of the water supply is controlled so that the value of this ratio falls within a predetermined range.

If the ratio of iron to non-ferrous metal ions calculated by the controller 16 is less than 2, the signal from the controller 16 causes the valve 1 to
9 is opened, and non-ferrous metal ions in the water supply are removed by the high temperature cation filter 21.

When the weight ratio falls within a predetermined range, the valve 19 is closed by a signal from the controller 16.

The high temperature cation filter 21 uses metal oxide.

If the ratio of iron content to non-ferrous metal ions calculated by the controller 16 is greater than 8, the valve 17 opens in response to a signal from the controller 16, and the iron cladding in the water supply reaches the high temperature cladding filter=20. It will be removed. When the weight ratio falls within a predetermined range, a signal from the controller 16 causes the valve 17 to close.

High temperature clad filter 20 is the same as high temperature filter 12.

In this way, the surface dose rate of the plant piping is reduced, and maintenance and inspection as described above is facilitated. Furthermore, it becomes easier to handle radioactive solid waste generated by repairing structural materials, etc.

Embodiment 2 will be explained with reference to FIG.

In Example 1, when the ratio of the iron content of the iron cladding to the amount of nonferrous metal ions deviated from a predetermined range, the quality of the water supply was controlled by removing the iron cladding or nonferrous metal ions in the water supply. A similar effect can be achieved by installing a bypass line in the condensate demineralizer 4 and opening and closing the valve 17 in response to a signal from the controller 16. However, the amount of iron cladding and non-ferrous metal ions brought into the reactor is larger than in Example 1, and the effect is correspondingly smaller.

Embodiment 3 will be explained with reference to FIG.

In Example 1, by removing iron cladding and nonferrous metal ions, and in Example 2, by adjusting the amount of iron cladding and nonferrous metal ions removed by the condensate demineralizer.
The water quality of the water supply was controlled. In this embodiment, when the ratio of the iron content of the iron cladding to the nonferrous metal ion content is less than 2, the iron cladding is injected into the outlet of the condensate demineralizer 4 through the cladding injection device 22. When the weight ratio is greater than 8, metal ions are implanted by the metal ion implanter 23. The valves 17 and 18 are opened and closed by signals from the controller 16.

The metal ions injected from the metal ion implantation device 23 behave in the same way as Co ions and Ni ions in the furnace, and may be Cu ions, Mg ions, Zn ions, etc., which have short half-lives even when activated. desirable.

The effect of this embodiment is reduced by the amount of iron cladding introduced into the reactor.

Example 4t - The seventh factor will be explained.

In Example 1, by removing iron cladding and nonferrous metal ions, in Example 2, by adjusting the amount of iron cladding and nonferrous metal ions removed by the condensate demineralizer,
In Example 3, the quality of the water supply was controlled by implanting iron cladding and non-ferrous metal ions. In this example, when the weight ratio is smaller than 2, iron cladding is injected as in Example 3. When the weight ratio is greater than 8, the iron cladding is removed by the cladding filter 20. The valves 17 and 18 are opened and closed by signals from the controller 16.

The effect of this embodiment becomes smaller as the amount of iron cladding brought into the reactor increases.

In this example, the ionic corrosion products were measured using a high-temperature conductivity sensor, but the concentration of individual ions may also be measured using a high-temperature ion sensor.

〔Effect of the invention〕

According to the present invention, the ratio (weight ratio) of the amount of iron in the iron cladding to the amount of nonferrous metal ions in the water supply can be kept within the range of 2 to 8, making it possible to keep the surface dose rate of the piping extremely low. can.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration when the present invention is implemented, FIGS. 2 to 4 are diagrams showing data on which the idea of the present invention is based, and FIGS. 5 to 7 are diagrams showing another example of the present invention. It is a figure showing an example. 1... Turbine, 2... Condenser, 3... Condensate pump, 4... Condensate demineralizer, 5... Water supply pump, 6...
・Low pressure feed water heater, 7... Boost pump, 8... High pressure feed water heater, 9... Reactor pressure vessel, 10... Valve,
11...Valve, 12...High temperature filter, 13...
Differential pressure gauge, 114... High temperature anion filter, 15.
...High temperature conductivity meter, 16...Controller, 17...Valve,
18... Valve, 19... Valve, 2o... High temperature clad filter, 21... High temperature cation filter, 22
...Iron cladding injection device, 23...Metallic hematite tk degree (BiPb) Note 3 Co, N (51/l (BiPb) Print I + figure

Claims (1)

[Claims] 1. In a nuclear power plant whose main components are a nuclear reactor, a turbine, a condenser, a low-pressure feedwater heater, a high-pressure feedwater heater, and each piping connecting these, the amount of iron cladding in the reactor feedwater , a means for measuring the amount of non-ferrous metal ions containing at least Co and Ni in the reactor feed water, and a means for measuring the amount of non-ferrous metal ions containing at least Co and Ni in the reactor feed water, and based on the measurement results by each of the above-mentioned means, the ratio of the iron content of the iron cladding to the amount of non-ferrous metal ions is 2 A nuclear power plant characterized by comprising means for increasing or decreasing the amount of iron cladding or the amount of nonferrous metal ions so that the weight ratio becomes 8 to 8 (weight ratio). 2. The nuclear power plant according to claim 1, wherein the means for measuring the amount of iron cladding is a filtration device equipped with a differential pressure gauge and having a function of measuring the amount of cladding by measuring the differential pressure. 3. The nuclear power plant according to claim 1 or 2, wherein the means for measuring the amount of nonferrous metal ions is a conductivity meter. 4. A means for providing a bypass line between the high-pressure feedwater heater and the reactor and measuring the amount of iron cladding on the bypass line;
3. The nuclear power plant according to claim 1, further comprising means for measuring the amount of nonferrous metal ions and means for increasing or decreasing the amount of iron cladding or the amount of nonferrous metal ions. 5. A means for providing a bypass line between the high-pressure feedwater heater and the reactor and measuring the amount of iron cladding on the bypass line;
4. The nuclear power plant according to claim 3, further comprising means for measuring the amount of nonferrous metal ions and means for increasing or decreasing the amount of iron cladding or the amount of nonferrous metal ions. 6. A bypass line is provided between the high-pressure feedwater heater and the reactor, and a means for measuring the amount of iron cladding and a means for measuring the amount of non-ferrous metal ions are provided on the bypass line to connect the condenser to the high-pressure feedwater heater. 3. The nuclear power plant according to claim 1 or 2, further comprising means for increasing or decreasing the amount of iron cladding or the amount of nonferrous metal ions during the process. 7. A bypass line is provided between the high-pressure feedwater heater and the reactor, and a means for measuring the amount of iron cladding and a means for measuring the amount of non-ferrous metal ions are provided on the bypass line to connect the condenser to the high-pressure feedwater heater. 4. The nuclear power plant according to claim 3, further comprising means for increasing or decreasing the amount of iron cladding or the amount of nonferrous metal ions during the process.