JPH08262186A - Method for controlling water quality of boiling water reactor plant - Google Patents

Abstract

PURPOSE: To reduce the occurrence of radioactivity emitted into a reactor water and at the same time reduce the adhesion of radioactivity onto a reactor outer pipe or an equipment by controlling Ni and Zn metal ion concentration in the reactor water to each specific range. CONSTITUTION: The metal ion concentration of Ni and Zn in a reactor water is controlled to 2-10 and 3-15ppb ranges, respectively. When the Ni ion concentration in the reactor water is equal to or less than 2ppb, the reactor water is supplied from a metal ion injection device 23 installed in a water supply system. On the other hand, when the Ni ion concentration is equal to or more than 10ppb, a flow adjustment valve 9 of a bypass line 10 of a hollow string film water-return filter 7 is opened, the ion exchange resin in the water return desalting device 8 is loaded with iron generated in the water return system, the Ni ion concentration of the reactor water is controlled to a specific concentration range by increasing the amount of leak iron. Zn is supplied from the metal ion injection device 23 installed in a water supply system. An automatic ion chromatography analyzer 25 installed in the reactor water system measures the metal ion concentration of Ni and Zn in the reactor water to see whether it is within a proper range or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water quality control method for a boiling water nuclear reactor plant, which aims to reduce material corrosion and radioactivity in the boiling water nuclear power plant.

[0002]

2. Description of the Related Art In a boiling water nuclear reactor plant, N is used to reduce the concentration of ⁶⁰ Co and ⁵⁸ Co ions in reactor water.
Zn injection is carried out for the purpose of controlling the i / Fe ratio and suppressing the adhesion of ⁶⁰ Co and ⁵⁸ Co ions to the outer core piping, but these water quality control methods have advantages and disadvantages.

When the Ni / Fe ratio is controlled, the concentration of ⁶⁰ Co and ⁵⁸ Co ions in the reactor water is 1/2 to 1
It is reduced to about / 5. However, due to the decrease in the Ni ion concentration in the reactor water, the deposition rate of ⁶⁰ Co and ⁵⁸ Co on the out-of-core piping equipment increases by 2 to 8 times, which does not necessarily lead to the reduction of radioactivity in the out-core piping.

Recently, fuel cladding tubes having high corrosion resistance have been applied to actual plants. Along with this, Ni
A remarkable increase in the ⁶⁰ Co ion concentration in the reactor water after controlling the / Fe ratio was observed. As one of the factors, it is known that a small amount of Cr deposit accelerates the elution of ⁶⁰ Co from the fuel clad.

On the other hand, when only the concentration of Zn ions in the reactor water is increased by injecting Zn, the adhesion of ⁶⁰ Co and ⁵⁸ Co ions to the outer core piping, which mainly contains oxygen, is suppressed. Corrosion of SUS304 steel, which is used in the core where the corrosive environment exposed to oxyhydrogen is severe, and Inconel (Ni-based alloy) and stellite (Co-based alloy) used in the furnace, increase. Radioactivity generation from core structural materials increases.

[0006]

In recent years, an austenitic stainless steel having a surface smoothed and a surface Cr content increased in order to reduce the radioactivity adhering to the outer core pipe has a Ni / Fe ratio. It is used under controlled conditions (reactor water Ni ion concentration: 0.2 ppb). However, initially, the adhesion of radioactivity is smaller than that of conventional pickled or mechanically polished stainless steel piping, but there is a problem that the adhesion of radioactivity is increased in the long term.

Further, in order to reduce the corrosion of the fuel spring material and suppress the generation of ⁶⁰ Co and ⁵⁸ Co ions, a Ni-base alloy that has been age hardened in the atmosphere is being adopted. However, under the condition that the Ni / Fe ratio was controlled, Zn
When the injection is performed, there is a problem that the outer layer NiFe ₂ O ₄ and the inner layer chromium oxide, which are formed by age hardening treatment in the atmosphere, are peeled off with high corrosion resistance.

Further, the corrosion rate of materials used in the furnace in an actual plant and the generation and transfer rate of radioactivity cannot be evaluated directly from plant data due to its complicated behavior, and it cannot be evaluated by a laboratory test. Corrosion rate and simple F
It has been evaluated by the behavior analysis model based on the basic test of Co behavior conducted by _{e-Ni (Co) -H 2} O system.
However, although the standard behavior can be estimated from these analysis results, no knowledge about the difference in data between plants is obtained.

The present inventors have investigated the influence of water quality on the Ni / Fe ratio control and the radioactivity generation and migration behavior during Zn water injection, such as stainless steel (Fe base alloy), inconel (Ni base alloy) and stellite (Co base alloy). result of examining the corrosion behavior of), Ni / Fe under the conditions Ni concentration in the reactor water is decreased to 0.2ppb by ratio control, NiFe ₂ O ₄ or Ni-based alloys and Co-based alloy which is formed on the outer layer of stainless steel It was found that the oxides of NiO and CoO formed on the surface layer of were unstable.

When Zn is implanted at a low Ni concentration of 0.2 ppb, the increase in corrosion of SUS304 steel used in the core and Ni-based alloy (Co-based alloy) used in the reactor is NiFe formed on the surface of these materials
Oxide and ZnFe ₂ O _4, and their oxides by Zn implantation crystal forms are different because of the oxide of ZnO of ₂ O ₄ Ya NiO (CoO) was found to be unstable.

Further, regarding metals and radionuclides suitable for evaluating the corrosion rate of materials used in the reactor, from the corrosion data of stainless steel, inconel and stellite used in the primary reactor system, Cr and ⁵¹ respectively. It was found that it is a main source of Cr and Co ions, and almost all of it is released to the reactor water in proportion to the amount of corrosion, and thus it is suitable for a tracer. Further, as for Cr and ⁵¹ Cr, the adhesion as fuel clad and the adhesion to the outside of the core are small, and almost all of them are removed by the reactor water purification system.

The present invention has been made in order to solve the above problems, and pays attention to the generation and transfer behavior of radioactivity based on the corrosion behavior of materials, and reduces the generation of radioactivity released into reactor water,
An object of the present invention is to provide a water quality control method for a boiling water reactor plant, which can reduce the adhesion of radioactivity to the out-of-core piping and equipment.

[0013]

According to the present invention, the metal ion concentrations of Ni and Zn in reactor water are set to 2 to 10 and 3, respectively.
In addition to controlling within the range of up to 15 ppb, it is characterized by neutral and pure water as the basic water quality control both during normal operation and during hydrogen injection.

According to the present invention, a Ni-base alloy, which is age-hardened in the atmosphere under the condition that the water quality is controlled to be within the range of 2 to 10 and 3 to 15 ppb in the reactor water, is used as the spring member. It is characterized by using the fuel to be used.

The present invention is a reactor water recirculation system piping of austenitic stainless steel electrolytically polished under the condition that the water quality is controlled within the range of 2 to 10 and 3 to 15 ppb for the metal ion concentration of Ni and Zn in the reactor water. Is used.

The present invention provides carbon steel or low alloy steel for pipes and equipment of a reactor system under the condition that the water quality is controlled within the range of 2 to 10 and 3 to 15 ppb, respectively, for the concentration of Ni and Zn in reactor water. Is used.

The present invention is a hollow fiber membrane condensate filter for purifying the total amount of condensate that suppresses the amount of iron inflowing from the feed water into the condensate system as much as possible (in order to reduce the iron concentration to 0.1 ppb or less) in order to increase the concentration of Ni ions in the reactor water. Is provided to suppress.

The present invention is characterized in that when the metal ion concentrations of Ni and Zn in the reactor water are as low as 2 and 3 ppb or less, respectively, the metal ions are injected into the feed water or the reactor water system in order to control the concentration within a predetermined range. And

In the present invention, the Ni ion concentration in the reactor water is 1
When it is higher than 0 ppb, the iron load on the condensate desalination equipment filled with the ion exchange resin is increased by bypassing the hollow fiber membrane condensate filter installed in the condensate system, and the iron retention from the feed water to the reactor is increased. The Ni ion concentration in the reactor water was increased to 10p
It is characterized by controlling to pb or less.

The present invention is characterized in that a flow rate adjusting valve is provided in the bypass line in order to quantitatively perform the iron loading. The present invention is characterized by connecting an automatic ion chromatographic analyzer to the sampling pipe of the reactor water purification system in order to measure the metal ion concentrations of Ni and Zn in the reactor water.

The present invention feeds back measured values of the metal ion concentrations of Ni and Zn in the reactor water to a metal ion implanter provided on the downstream side of the condensate demineralizer to automatically set an appropriate dose. A control device is provided.

According to the present invention, the Cr ion concentration in the reactor water is measured using the automatic ion chromatographic analyzer,
The feature is that the ⁵¹ Cr ion concentration in the reactor water is measured by an automatic γ-ray nuclide analyzer.

According to the present invention, the ion concentration of ⁵¹ Cr, ⁵⁸ Co, ⁶⁰ Co, etc. in reactor water is measured by using the automatic γ-ray nuclide analyzer, and the reactor water in the reactor water recirculation system or reactor water purification system is also measured. The feature is that the radioactivity of ⁵¹ Cr, ⁵⁸ Co, ⁶⁰ Co, etc. adhering to the piping of the system is measured by an automatic γ-ray nuclide analyzer.

The present invention relates to the changes in the generation and transfer of material corrosion and radioactivity due to the relation with the data of metals, impurities and other dissolved chemical species obtained from the measurement of water quality obtained from the automatic ion chromatograph and the factors thereof. It is characterized in that the relationship with the water quality is evaluated by an analyzer.

[0025]

The present invention provides water quality conditions for suppressing corrosion of various corrosion resistant materials such as stainless steel (Fe-based alloy), inconel (Ni-based alloy) and stellite (Co-based alloy) used in boiling water reactors. As a basic rule, the metal ion concentrations of Ni and Zn are both increased.

Generally, as shown in the potential-pH diagram of FIG.
With the water quality standard of BWR of pH = 5.6 ± 0.2, NiFe ₂
O ₄ and NiO are zinc oxides, ZnF
It can be seen that the stable region is wider and more stable than e ₂ O ₄ and ZnO.

Therefore, the Ni concentration in the reactor water is 2 ppb or more and Z
When the concentration of n-ions is about the same, NiFe ₂ O _{4 and} ZnFe ₂ O ₄ and Inconel (N
NiO is formed more predominantly than ZnO on the surface of (forming an iO film).

In this case, the Ni ion concentration in the reactor water when the Ni / Fe ratio is controlled is higher than 0.2 ppb by a factor of 10 or more, so that NiFe ₂ O ₄ and NiO are stabilized. Therefore, it is recognized that the corrosion of these corrosion resistant materials is reduced to 1/3 or less as shown in FIG.

Further, since NiO has the same crystal structure as CoO and substantially the same lattice constant, by increasing the Ni ion concentration in the reactor water, the corrosion of stellite (which forms a CoO film) is also reduced to about 1/3. .

The upper limit of Ni ions was determined experimentally as the concentration at which NiO did not precipitate on the surface of the fuel film tube. Since NiO has an oxide similar to CoO, it has a large uptake of Co and its solubility is about 100 times larger than that of NiFe ₂ O ₄ , so it is easily dissolved and unstable. Therefore, it becomes a source of ⁶⁰ Co.

The upper limit of Zn ion was determined from the relation between effect and economy. The lower limit value was determined as a concentration range in which the corrosion of various corrosion resistant materials is suppressed to about 1/3 of the conventional water quality Ni / Fe ratio control.

In order to increase the concentration of Ni ions in the reactor water, it is necessary to reduce the amount of iron carried into the reactor from the feed water as much as possible. That is, the iron brought into the reactor from the water supply easily adheres to the fuel and easily reacts with the Ni ions in the reactor water.
e ₂ O ₄ is produced. Since iron ions that have diffused through the inner layer coating and reached the outer surface due to corrosion of stainless steel, etc. have a low solubility, they react with Ni ions in the reactor water to form NiFe ₂ O ₄
Generate

When the Ni ion concentration in the reactor water is higher than the predetermined concentration,
If the amount of Ni generated is excessive compared to iron, the amount of iron brought into the reactor from the water supply system is increased. On the contrary, when the Ni ion concentration in the reactor water is low and the amount of Ni generated is insufficient, it is necessary to make up by injection. On the other hand, Zn is less reactive with iron than Ni, and the reaction with iron is negligible when the concentration of Ni is 0.2 ppb or more, which is the solubility of NiFe ₂ O ₄ .

However, it reacts with the chromium oxide in the corrosion film of the corrosion resistant material to form ZnCr ₂ O ₄ . Since Zn does not reach the predetermined reactor water concentration due to the occurrence of corrosion of the primary reactor material, it is necessary to supplement the amount removed by the reactor water purification system by injection and the amount taken into the corrosion coating of the corrosion resistant material by injection. .

Regarding the analytical evaluation of material corrosion and the generation and transfer behavior of radioactivity, Cr and ⁵¹ Cr in an actual plant, which had not been paid attention so far, were focused on. It was found that the corrosion rates of stainless steel and Inconel can be roughly estimated from the ion concentrations of Cr and ⁵¹ Cr in the reactor water. Furthermore, by correlating the material corrosion rate with the generation and transfer rate of radioactivity, the plant data show that ⁶⁰ Co and ⁵⁸ Co
The balance between the generation and migration of Cr and ⁵¹ Cr is evaluated.

It can be expected that by increasing the metal ion concentrations of Ni and Zn in the reactor water to 2 and 3 ppb or more, respectively, the material corrosion is reduced due to the strengthening of the corrosion film and the behavior similar to that of Ni is exhibited.

Corrosion-resistant materials such as stainless steel (Fe-based alloy), inconel (Ni-based alloy) and stellite (Co-based alloy) used in boiling water nuclear reactors and carbon steel are subject to corrosion as shown in FIG. It can be suppressed to about / 3.

In the case of stainless steel, Ni is the outer layer of NiF.
This is because e ₂ O ₄ is stabilized and Zn strengthens the inner chromite layer by the formation of ZnCr ₂ O ₄ . As a result, the effect of suppressing the radioactivity due to electropolishing did not decrease over time.

For Inconel, Ni strengthens NiO and Zn further stabilizes the chromium oxide by forming ZnCr ₂ O ₄ . Also, in the case of the fuel spring material which was age-hardened in the atmosphere, NiFe ₂ O _{4 in the} outer layer was stabilized and no increase in corrosion due to peeling of the film was observed.

For stellite, Ni strengthens CoO and Zn stabilizes the chromium oxide by the formation of ZnCr ₂ O ₄ . In the case of carbon steel, the effect of inhibiting corrosion was confirmed for both Ni and Zn. The film showing the anticorrosion property of carbon steel is considered to be Fe ₃ O ₄ , but NiF
It is considered that corrosion is suppressed by the formation of e ₂ O ₄ and ZnFe ₂ O ₄ .

In the case of low alloy steel, the synergistic effect of Ni and Zn has been confirmed in stainless steel and carbon steel, and it is presumed that there is a corrosion inhibiting effect.
In addition, the synergistic effect of Ni and Zn on the inhibition of material corrosion was confirmed even in the water quality of hydrogen injection. Compared with the water quality conditions during normal operation, the effect of Zn addition tends to be slightly greater than that of Ni, but Ni and Zn in the reactor water
Corrosion inhibition close to 1/4 was observed in the range of metal ion concentrations of 2 to 10 and 3 to 15 ppb, respectively.

A similar synergistic effect between Ni and Zn was also found for inconel and stellite. However, it was not possible to quantitatively clarify the corrosion rate of the fuel spring material that had been age-hardened in the atmosphere, because the hydrogen injection significantly reduced the corrosion rate and was close to the lower limit of the weight loss measurement.

From the above results, ⁶⁰ Co released directly into reactor water due to corrosion of the core structural material under the water quality condition during normal operation.
And the amount of ⁵⁸ Co generated is reduced to about 1/3. In addition,
When using a fuel spring material that has been age hardened in the atmosphere, it can be reduced to 1/10 or less.

On the other hand, with respect to the fuel clad, if the amount of iron feedwater brought in is reduced to about 1/3 of the conventional amount, the amount of NiFe ₂ O ₄ , which is a production source of ⁶⁰ Co, can be reduced to 1/3 or less. Further, the Ni ion concentration in the reactor water is significantly increased compared to the Co ion concentration, and the amount of Co generated is reduced to about 1/3 as the corrosion amount of the corrosion resistant material of the reactor system is reduced. Can be expected to be reduced.

Therefore, the amount of Co deposited, which is the source of ⁶⁰ Co, is greatly reduced to 1/3 or less. Further, the concentration of chromium is also reduced by reducing the amount of deposited clad and the amount of chromium generated in the furnace due to the reduction of material corrosion, and the introduction of Zn also suppresses the unstable formation of CoCr ₂ O ₄ .

The pH of the reactor water can be controlled from normal weak acidity to weak alkalinity by increasing the metal ion concentrations of Ni and Zn in the reactor water and decreasing the chromium ion concentration accompanying the inhibition of corrosion of the corrosion resistant material in the reactor. Therefore, the solubility of NiFe ₂ O ₄ which is the main component of the fuel-adhering clad is reduced, and the elution of ⁶⁰ Co contained in the fuel-adhering clad can be greatly reduced to about 1/10.

Further, the amount of corrosion coating of stainless steel on the surface of the out-core piping equipment where the radioactivity of ⁶⁰ Co and ⁵⁸ Co is incorporated is reduced, and the incorporation of Co into ferrite and chromite is suppressed, and the radioactivity per unit coating weight is reduced. The amount of uptake is also reduced. Therefore, the adhesion of radioactivity can be reduced to about 1/3.

From the above results, it was estimated that the radioactivity outside the core could be reduced to about 1/10 of the conventional value even if the ⁶⁰ Co and ⁵⁸ Co ions of the reactor water were not reduced by controlling the Ni / Fe ratio.

Further, by measuring the water quality of the reactor water and the radioactivity of the pipe outside the core, it is possible to analyze the relation between the corrosion of the material, the behavior of the radioactivity and the water quality, and to carry out the optimum water quality control and the exposure assessment during the regular inspection. Can be grasped in advance.

[0050]

EXAMPLE An example of a water quality control method for a boiling water reactor plant according to the present invention will be described with reference to FIGS. 3 is a system diagram for explaining the embodiment of the present invention.

In FIG. 3, reference numeral 1 is a reactor pressure vessel of a boiling water reactor, and in this reactor pressure vessel 1, a core 2 loaded with a large number of fuel assemblies is arranged. The steam outlet side of the reactor pressure vessel 1 is connected to a steam turbine 4 by a main steam pipe 3. The steam outlet side of the steam turbine 4 is a condenser 5
The condenser 5 is connected to the hollow fiber membrane condensate filtration device 7 via the condensate pump 6, and the hollow fiber membrane condensate filtration device 7 is connected to the condensate desalination device 8 filled with an ion exchange resin. Connected.

A bypass line 10 having a flow rate adjusting valve 9 is provided on the inlet / outlet side of the hollow fiber membrane condensate filtration device 7.
A low-pressure feed water heater 11, a feed water pump 12, and a high-pressure feed water heater 13 are sequentially connected on the downstream side of the condensate demineralizer 8.
The high-pressure feed water heater 13 is connected to the reactor pressure vessel 1 by a feed water pipe 14.

The reactor pressure vessel 1 is provided with a recirculation system pipe 15 for circulating the reactor water, and the recirculation system pipe 15 is provided with a reactor recirculation pump 16. Further, a reactor coolant purification system (C which connects the recirculation system pipe 15 and the water supply pipe 14)
A UW) pipe 17 is provided, and the reactor water purification system pipe 17 is provided with a heat exchanger 18, a CUW pump 19 and a filter desalting device 20.

One end of a metal ion implantation pipe 21 is connected to a pipe between the low-pressure feed water heater 11 and the feed water pump 12, and the metal ion implantation pump 22 and the metal ion implantation device are connected to the other end of the metal ion implantation pipe 21. 23 is connected. CUW pump 19
To the pipe between the filter and the desalinizer 20 and the reactor water sampling pipe 24
Is connected to one end, and the other end of the reactor water sampling pipe 24 is connected to an automatic ion chromatographic analyzer 25 and a radioactivity concentration measuring γ-ray nuclide analyzer 26.

The metal ion implantation device 23 and the automatic ion chromatographic analysis device 25 are electrically connected to the metal ion implantation control device 29 by signal lines 27 and 28. The recirculation system pipe 15 is provided with a γ-ray nuclide analyzer 30 for measuring the radioactivity attached to the pipe, and this γ-ray nuclide analyzer 30 is electrically connected to the material corrosion / radiation generation transfer behavior analysis device 32 by a signal line 31. This analyzer 32 is connected to the automatic ion chromatograph analyzer 25.
And γ-ray nuclide analyzer 26 for measuring radioactivity concentration are signal lines 33, 34
It is electrically connected by.

Since iron produced in the condensate system leaks from the condensate purification system, iron is mainly brought in from the water supply.
Normally, the condensate is purified by the hollow fiber membrane condensate filter 7 and controlled to 0.1 ppb or less.

Ni is corroded in the form of ions from Inconel, which is used in the high pressure feed water heater 13 in the high temperature section and the core 2 in the reactor pressure vessel 1, mainly in the fuel spring parts. A part of the generated Ni reacts with the iron adhered to the fuel and the iron generated by the corrosion of the stainless steel in the furnace and reacts with N.
iFe ₂ O ₄ is produced. The rest is removed by the reactor water purification system.

When the Ni ion concentration in the reactor water is 2 ppb or less, the water is supplied from the metal ion implanter 23 installed in the water supply system. On the other hand, in the case of 10 ppb or more, the hollow fiber membrane condensate filter 7
Open the flow control valve 9 of the bypass line 10 to increase the amount of leaked iron by loading iron generated in the condensate system into the ion-exchange resin in the condensate demineralizer 8 to increase the Ni ion concentration in the reactor water to a predetermined concentration. Control in range.

Zn is supplied from the metal ion implanter 23 installed in the water supply system. In addition, metal ion implanter
23 may be connected to a reactor such as a reactor water purification system or a reactor water recirculation system pipe instead of the water supply system.

Whether or not the Ni and Zn metal ion concentrations in the reactor water are within the proper range is measured by an automatic ion chromatography analyzer 25 installed in the reactor water system. The signal from this automatic ion chromatograph analyzer 25 is taken out, and the metal ion implanter 23
It does not matter even if the automatic control of.

The effect of this embodiment is that the chromate ion concentration is measured by the automatic ion chromatograph analyzer 25 installed in the reactor water system of FIG. 3 and the concentration of ⁵¹ Cr is measured by the gamma ray nuclide analyzer 26 for measuring the radioactivity concentration. Monitor. As a result, the corrosion state of the core structural material and the core structural material can be understood from the flow sheet shown in FIG.

FIG. 4 (a) is a flow chart showing the method of evaluating the corrosion rate of the corrosion resistant material in an actual plant. The method of evaluating the corrosion rate of Inconel from ⁵¹ Cr is shown in FIG. In the flow chart showing the evaluation method of
To evaluate the corrosion rate of stainless steel.

Stainless steel used in nuclear reactors (F
e-based alloy), inconel (Ni-based alloy), and stellite (Co-based alloy), the amount of corrosion of Cr depends on the contact area, content of Cr, corrosion rate and corrosion elution rate of Cr (corrosion elution of Cr). It can be calculated from the residual ratio of Cr in the corrosion coating to the total corrosion amount by the ratio of the amount of corrosion to the amount of corrosion of the metal base material, and is estimated to be approximately 100% for Inconel and Stellite and 88% or more for stainless steel). It is calculated.

The generation of ⁵¹ Cr from the core structural material is
The yield can be calculated by giving a neutron flux that can calculate the specific activity. Laboratory corrosion test results show that Cr and ⁵¹
It is known that the respective main sources of Cr are in-reactor stainless steel and fuel springs.

On the other hand, Cr and ⁵¹ Cr generated in the core and by the corrosion of the core structural material are present in the form of chromate ions and have high solubility, so that the amount of adhesion to the fuel and the amount of adhesion outside the core are small. Therefore, almost all is removed by the reactor water purification system.

Therefore, Cr and ^{51 in} FIGS.
The transfer amount (2) of Cr can be obtained from the removal amount of the reactor water purification system as a first-order approximation. Of course, the accuracy of the transfer amount (2) can be improved by knowing the fuel Cr deposition amount obtained from the analysis of the fuel clad and the ⁵¹ Cr deposition amount outside the core obtained from the radioactivity measurement.

FIG. 5 shows measurement of ion concentration of ⁶⁰ Co and ⁵⁸ Co of reactor water and ⁶⁰ C of radioactivity adhering to piping of reactor water recirculation system.
An evaluation flow of the generation and transfer behavior of ⁶⁰ Co obtained from o measurement is shown. Fig. 5 shows the relationship between material corrosion and radioactivity generation and transfer behavior and the data of metals, impurities, and other dissolved chemical species data obtained from other water quality measurements obtained from automatic ion chromatographic analyzers. Assess the relationship between changes in developmental shifts and the water quality that is the factor.

In this evaluation method, the sources of ⁶⁰ Co are the fuel clad and the core structure material, but ⁵⁸ Co showing the same chemical behavior with the isotope of ⁶⁰ Co is mainly the generation of the core structure material. This is a method of distinguishing the contribution of the ⁶⁰ Co generation source, focusing on.

The corrosion rate of the core structural material is evaluated from the balance between the generation and migration of ⁵¹ Cr shown in FIG. 4, and the amounts of ⁵¹ Cr, ⁵⁸ Co and ⁶⁰ Co generated from the core structural material can be calculated (1). Further, ⁶⁰ Co generation contribution of ions from the core structural material occupying the reactor water, than that reactor water ⁵⁸ Co ions are those generated from the core structural material, the reactor water ⁵⁸ Co ion concentration and reactor core structural member ⁶⁰ Product of Co and the rate of occurrence of corrosion of ⁵⁸ Co (2)
Calculated from

The difference between the measured value of ⁶⁰ Co in the reactor water and the contribution to the generation of the core structural material is the contribution to the generation from the fuel clad.
(3) Therefore, the amount of ⁶⁰ Co generated from the fuel clad is calculated by calculating the amount of ⁶⁰ Co generated from the core structure material (1) and the ratio of the contribution of the fuel clad and the core structure material to the ⁶⁰ Co ions of the reactor water. Indicated by the product.

On the other hand, the transfer amount (4) out of the core can be evaluated by the following equation (1). Radioactivity attached to piping (A: Bq / m
^The rate of increase in ² ) can be linked to the rate of increase in the amount of corrosion (m: g / m ² ) at the measurement site, that is, the corrosion rate, using the following formula. dA / dt = k · dm / dt · C (1) where k: proportional constant (m ³ / g) C: radioactivity concentration (Bq / m ³ ) The proportional constant k in the formula (1) is It is a factor of water quality.

The water quality changes depending on the concentration of oxidizing species during normal operation or hydrogen injection, Ni / Fe control, and the presence or absence of Zn injection. Further, the deposition of radioactivity outside the core is mainly made of stainless steel which forms a stable and thick film with a large contact area, and is mainly made of stainless steel on the pickled surface in the reactor.

Therefore, from the ⁶⁰ Co sum of (1) and (3) (total of core structure material and fuel clad), the removal amount of reactor water purification system (product of reactor water concentration, purification flow rate and removal rate) and (4) The difference in the adhesion amount to the stainless steel outside the reactor water (mainly the stainless steel inside the reactor) is evaluated from the balance as the amount transferred to the fuel clad.

By the γ-ray nuclide analyzer 26 for measuring the radioactivity concentration and the γ-ray nuclide analyzer 30 installed in the pipe of the reactor water recirculation or reactor water purification system shown in FIG. The radioactivity adhering to the pipe can be measured to determine the radioactivity adhering rate.

Generally, the corrosion rate of a recirculation system stainless steel pipe that has been subjected to a surface treatment such as electrolytic polishing is different from that of a pickled surface in a furnace having a large contact area. The corrosion rate of the stainless steel pipe of the recirculation system can be obtained in reverse from the above equation (1) using the measurement result of ⁶⁰ Co deposition amount of the pipe shown in FIG.

The ratio of the corrosion rates of the recirculation system stainless steel pipe subjected to the surface treatment such as electrolytic polishing and the out-of-core stainless steel shows the effect of electrolytic polishing itself. Further, by measuring the attached radioactivity of the carbon steel pipe of the reactor water purification system, the difference in the behavior of the attached radioactivity between the stainless steel and the carbon steel can be found.

Further, the generation and transfer behavior of radioactivity and the corrosion behavior of materials and the automatic ion chromatograph analyzer 25 shown in FIG.
The factors responsible for the change can be examined based on the relations between the ion concentrations of metals and impurities and the water quality data of other dissolved chemical species obtained from the measurement.

[0078]

EFFECTS OF THE INVENTION According to the present invention, for example, in order to reduce the exposure during the periodic inspection of a nuclear power plant, the corrosion of the core structural material is suppressed, and the elution of the radioactivity generated by being activated by being attached to the fuel is suppressed. As a result, it is possible to reduce the generation of radioactivity released into the reactor water and reduce the adhesion of radioactivity to the out-of-core piping and equipment made of carbon steel and austenitic stainless steel.

[Brief description of drawings]

FIG. 1 (a) is a Ni- layer for explaining the function of the present invention.
Fe-H ₂ O system potential -pH diagram showing the stability of, (b) potential also shown an Zn-Fe-H ₂ O system stability of -pH
Fig.

FIG. 2 is a characteristic diagram showing the water quality dependence of the corrosion rate of the corrosion resistant material, as in FIG.

FIG. 3 is a system system diagram for explaining an embodiment of the present invention.

FIG. 4 (a) is a flow chart showing a method for evaluating a corrosion rate of a corrosion resistant material in an actual plant for explaining an embodiment of the present invention, and FIG. 4 (b) is a flow chart showing a method for evaluating a structure outside the core. .

FIG. 5 is a flow chart showing an evaluation method of ⁶⁰ Co ion generation and transfer behavior in an actual plant for explaining an example of the present invention.

[Explanation of symbols]

1 ... Reactor pressure vessel, 2 ... Reactor core, 3 ... Main steam pipe, 4 ... Steam turbine, 5 ... Condenser, 6 ... Condensate pump, 7 ... Hollow fiber membrane condensate filter, 8 ... Condensate desalination Device, 9 ... Flow control valve, 10
… Bypass line, 11… Low pressure feed water heater, 12… Water feed pump, 13… High pressure feed water heater, 14… Water supply pipe, 15… Recirculation system piping, 16… Reactor recirculation pump, 17… Reactor coolant purification System piping, 18 ... Heat exchanger, 19 ... CUW pump, 20 ... Filtration demineralizer, 21 ... Metal ion injection piping, 22 ... Metal ion injection pump, 23 ... Metal ion injection device, 24 ... Reactor water sampling piping, 25 … Automatic ion chromatograph analyzer, 26… γ-ray nuclide analyzer for measuring radioactivity concentration, 27, 28, 31, 33, 34… Signal line, 29… Metal ion implantation control device, 30… γ for measuring radioactivity adhering to pipes Radionuclide analyzer, 32 ... Material corrosion / radioactivity generation migration behavior analyzer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G21D 1/00 GDBW GDBY

Claims (13)

[Claims] 1. A water quality control method for a boiling water reactor plant, characterized in that the metal ion concentrations of Ni and Zn in the reactor water are controlled in the ranges of 2 to 10 and 3 to 15 ppb, respectively. 2. A spring member made of a Ni-based alloy that has been age-hardened in the atmosphere under the condition that the water quality is controlled so that the metal ion concentrations of Ni and Zn in the reactor water are in the ranges of 2 to 10 and 3 to 15 ppb, respectively. The water quality control method for a boiling water reactor plant according to claim 1, wherein the fuel is used. 3. A reactor water recirculation system of austenitic stainless steel electrolytically polished under the condition that the water qualities of Ni and Zn in the reactor water are controlled within the ranges of 2 to 10 and 3 to 15 ppb, respectively. The water quality control method for a boiling water reactor according to claim 1, wherein a pipe is used. 4. Carbon steel or a low alloy for pipes and equipment of a reactor system under the condition that the water quality is controlled such that the metal ion concentrations of Ni and Zn in the reactor water are in the ranges of 2 to 10 and 3 to 15 ppb, respectively. The water quality control method for a boiling water reactor according to claim 1, characterized in that steel is used. 5. The amount of iron inflowing from the feed water is 0.1 ppb in terms of iron concentration in order to increase the Ni ion concentration in the reactor water and purify the condensate.
The water quality control method for a boiling water reactor according to claim 1, wherein the method is controlled by a condensate-type hollow fiber membrane condensate filter below. 6. When the metal ion concentrations of Ni and Zn in the reactor water are as low as 2 and 3 ppb or less, respectively, the metal ions are injected into the feed water or the reactor water system to control the concentration within a predetermined range. The water quality control method for a boiling water reactor plant according to claim 1. 7. When the concentration of Ni ions in the reactor water is as high as 10 ppb or higher, the iron load on the condensate desalination device that bypasses the condensate hollow fiber membrane condensate filter and is filled with ion exchange resin. The water quality control method for a boiling water reactor according to claim 1, wherein the Ni ion concentration in the reactor water is controlled to 10 ppb or less by increasing the amount of iron introduced from the feed water to the reactor. . 8. The water quality control method for a boiling water reactor according to claim 7, wherein a flow rate adjusting valve is provided in the bypass line to quantitatively perform the iron load. 9. A boiling water atom according to claim 1, wherein an automatic ion chromatographic analyzer is connected to the sampling pipe of the reactor water purification system in order to measure the metal ion concentrations of Ni and Zn in the reactor water. Reactor water quality management method. 10. A metal ion implantation control for feeding back measured values of metal ion concentrations of Ni and Zn in reactor water to a metal ion implantation device provided on the downstream side of a condensate desalination device to automatically set an appropriate implantation amount. The water quality control method for a boiling water reactor according to claim 1, further comprising a device. 11. The Cr ion concentration in the reactor water is measured by using the automatic ion chromatographic analyzer, and the ⁵¹ Cr ion concentration in the reactor water is measured by an automatic γ-ray nuclide analyzer. Water quality control method for boiling water reactor plant described 12. The ion concentration of ⁵¹ Cr, ⁵⁸ Co, ⁶⁰ Co, etc. in reactor water is measured using the automatic γ-ray nuclide analyzer, and the reactor system such as reactor water recirculation system or reactor water purification system is measured. The water quality control method for a boiling water reactor plant according to claim 1, wherein the radioactivity of ⁵¹ Cr, ⁵⁸ Co, ⁶⁰ Co, etc. adhering to the pipe of (1) is measured by an automatic γ-ray nuclide analyzer. 13. Due to changes in material corrosion and radioactivity generation and transfer due to changes in factors related to metals and impurities obtained from the automatic ion chromatograph and data of dissolved chemical species obtained from other water quality measurements. The water quality control method for a boiling water reactor plant according to claim 1, wherein a relation with a certain water quality is evaluated by an analyzer.