JPH05209992A - Method for restraining shift of radioactive nitrogen to gaseous phase in primary cooling water system of direct cycle type reactor - Google Patents

Abstract

PURPOSE:To enable the shift of radioactive nitrogen to a gaseous phase to be restrained, and reduce the dose rate of a turbine system by adding a reagent having high capability of forming complex ions with ammonia to primary cooling water. CONSTITUTION:In a feed water system at the downstream side of a condenser 15, a reducing agent, for example, nitrogen is supplied from a reducing agent filling system 16 to a line between a condensate demineralizing unit 10 and a feed water pump 21, thereby reducing the concentration of dissolved oxygen in a primary cooling system. On the other hand, a reagent filling system 23 is provided in a recirculation system comprising a recirculation pump 6 and a reactor water purifying system 8, and concurrently with the filling of the reagent from the system 16, a reagent having the high capability of forming a complex with ammonia is supplied from the system 23 to the downstream outlet of a purifying system 8. According to this construction, the reagent is dissolved in the liquid phases of a reactor core 1, a mixing plenum 4, a downcomer 5 and a lower plenum 7. Consequently, the gaseous phase shift amount of radioactive nitrogen generated in the core 1 can be restrained, and the radiation dose of a main steam piping and the turbine system can be reduced.

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 technique for reactor water of a direct cycle reactor, and more particularly to a water quality control method for a reactor suitable for reducing the dose rate of a reactor turbine system.

[0002]

2. Description of the Related Art Intergranular stress corrosion cracking (hereinafter referred to as IGSCC) of a nuclear reactor structural material is said to occur when the three factors of material composition, stress, and water quality are in unfavorable states. Conventionally, reactor structural materials, especially SUS304 steel, have been subjected to heat treatment such as reduction of carbon content and residual stress relaxation, and have been operated on a sufficiently safe side from the viewpoint of IGSCC. As described above, the measures so far have been for the two factors of the material and the stress among the three factors of IGSCC, but in recent years, one of the third factors for the direct cycle reactor primary cooling system has been adopted. In order to reduce the amount of dissolved oxygen in the reactor water, hydrogen injection has been attempted as seen in JP-A-57-3086.

FIG. 2 is a diagram of a main system of a direct cycle reactor primary system such as a boiling water reactor (BWR) and an advanced converter (ATR), showing a conventional example of hydrogen injection.
In the figure, 1 is a reactor core, 2 is an upper plenum, 3
Is a water / water separator, 4 is a mixing plenum, 5 is a downcomer, 6 is a recirculation pump, 7 is a lower plenum, 8 is a reactor water purification system, 9 is a water heater, 10 is a condensate demineralizer, and 11A is a high pressure turbine. , 11B is a low-pressure turbine, 12 is a generator operated by these turbines, 13 is an off-gas treatment device, 14 is a rare gas hold-up, 15 is a condenser, 16
Is a reducing agent injection device, 17 is a water supply pipe, 18 is a main steam pipe, 19 is a recirculation pipe, 20 is a jet pump, 21 is a water supply pump, and 22 is a condensate pump.

In the conventional example of the direct cooling type reactor primary cooling system shown in FIG. 2, the reducing agent injection device 16 is provided upstream of the water supply pump 21 to inject hydrogen into the water supply system after the condenser.
Is arranged, and hydrogen injected from here is combined with oxygen generated as a result of radiolysis of water in the core, and the aim is to reduce the dissolved oxygen concentration in each part of the primary cooling system including the recirculation system 6.

However, hydrogen injection has a limit. That is, when hydrogen is injected, radioactive nitrogen-16, which is usually dissolved in water in the form of nitric acid or the like, is reduced to a gas, and the phenomenon occurs that the dose rate at the turbine system and at the site boundary is increased (in the example of the actual machine, It has been reported that the maximum increase of hydrogen injection amount is about 5 times with the increase of hydrogen injection amount.) This increase tends to keep a constant value up to a certain hydrogen concentration threshold value and to increase sharply from that threshold value. .. Therefore, the hydrogen injection amount has an upper limit, and conventionally, in the hydrogen injection operation in the direct cycle reactor, it was necessary to realize environmental mitigation with the hydrogen injection amount less than the upper limit.

On the other hand, the radiation dose rate of the turbine system can be reduced by injecting nitrous acid, NO gas, etc., in JP-A-1-102396, Japanese Patent Application No. 63-154767.
Is shown in. According to this method, basically, it is possible to reduce the concentration of dissolved oxygen by hydrogen injection without inviting an increase in the concentration of radioactive nitrogen in the turbine system. However, if the injection amount of nitrous acid or NO gas is too large, the concentration of radioactive nitrogen will decrease, but the concentration of dissolved oxygen will rise conversely, the conductivity of water will increase, and the amount of dissolved oxygen in the primary system will increase. There were some points that were difficult to control, such as the concentration distribution.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a controllable method capable of suppressing the transfer of radioactive nitrogen to the gas phase in a direct cycle nuclear power plant in order to reduce the dose rate of the turbine system. There is

[0008]

The present invention controls the water quality of the primary cooling system by adding a reagent having a large ability to form complex ions with ammonia to the primary cooling water of a direct cycle reactor. It suppresses the transfer of radioactive nitrogen to the gas phase.

This reagent should be selected according to the complex formation constant with ammonia at a high temperature in a nuclear reactor, but since there is almost no data at a high temperature, as a guideline, the room temperature (2
It is preferable to select a reagent such that the complex formation constant with ammonia at 5 ° C.) is at least the product of the number of ligands (ammonia) and 3.0. Here, the complex formation constant means a constant defined as follows. Ie chemical formula

[0010]

[Equation 1]

(Where M is a reagent, L is a ligand (ammonia in this case), MLn is a complex, and n is the number of ligands), the reagent concentration [M] in the chemical reaction for complex formation, the ligand concentration Determined from [L] and complex concentration [MLn]

[0012]

[Equation 2]

Is called a complex formation constant.

In the present invention, the gas phase transfer of radioactive nitrogen is reduced by using, as a reagent, a metal ion having a high ability to form a complex with ammonia or a water-soluble salt composed of these ions in the reactor primary cooling water. It is achieved by adding. Such reagents include palladium, cadmium,
Platinum, gold, mercury, cobalt ions or mixtures thereof or water-soluble salts thereof can be used. All of these are the above-mentioned standard, room temperature (25 ° C)
The condition that the complex formation constant with ammonia in the above formula is not less than the number of ligands × 3.0 is satisfied. Moreover, since these reagents have a regenerating action, addition at a very low concentration is effective.

The above-mentioned reagent has a regulated value (generally minus 30) for which the conductivity of reactor water is generally defined as a nuclear reactor.
It is necessary to add it at a concentration such that it does not exceed 0 mV (SHE)).
It may be added at a low concentration of the order of b. In the present invention,
Addition of such a low concentration also has the effect of preventing the transfer of radioactive nitrogen to the gas phase.

[0016]

[Action] The increase in the dose rate of the turbine system is due to the nuclear reaction of oxygen atoms in the cooling water with high-energy neutrons in the high neutron flux field of the core, which is activated by ¹⁶ O (n, p) ¹⁶ N to produce radioactive nitrogen.
This is due to the generation of ¹⁶ N, which is transferred to the main steam system in the gas phase. At the time of this nuclear reaction, the generated radioactive nitrogen-16 initially moves at high speed. However, when its kinetic energy is lost due to collision with another atom and the kinetic energy reaches several tens keV, it becomes a hot atom which is a neutral atom having high energy. The radioactive nitrogen-16 in the state of such a hot atom further interacts with surrounding water molecules, and mainly causes a hydrogen abstraction reaction. This process is so rapid that radioactive nitrogen-
The initial form when 16 occurs is ¹⁶ NH, ¹⁶ NH ₂ or ¹⁶ N
H ₃ or ¹⁶ N heated to escape the Hot atom reaction
You can think of it. These radioactive nitrogen compounds are
It reacts with the radiolysis products of water, undergoes oxidation or reduction, and undergoes a more complex process to change its chemical form. Of the resulting chemical forms, the gaseous one is ¹⁶ NH ₃ .
¹⁶ NO.

When the reducing agent (usually hydrogen is used) is injected into the reactor water and, as a result, the reactor water has a reducing atmosphere, the radioactive nitrogen-16 is mainly ¹⁶ NH in the reactor water.
Exists as ₃ . Here, the addition of a reagent which is effective to form the complex ion of ammonia in the reactor water, the ammine complex ion formation reaction, since the ¹⁶ NH ₃ is captured in the reagent as a non-volatile compounds, volatile ¹⁶ NH ₃ , ¹⁶
The amount of NO produced is reduced. Therefore, the dose rate of the turbine system is reduced.

When the reactor water is in a normal non-reducing atmosphere without reducing agent injection, the initial compound of radioactive nitrogen-16 ( ¹⁶ N, ¹⁶ NH, ¹⁶ NH ₂ or ¹⁶ NH ₃ ) is dissolved oxygen O. since oxidized by reaction with OH radicals generated by radiolysis of ₂ and water, the major chemical forms of the radioactive nitrogen -16 in the reactor water is nitrate ion ¹⁶ NO ₃ ^- or nitrite
¹⁶ NO ₂ ^- it is. The increase in the dose rate of the turbine system is mainly due to the reaction of these anions with the hydrated electron e ⁻ or H radical, which is the reducing species in the radiolysis products of water, to produce volatile ¹⁶ NO, which is mainly Due to being released into the vapor system. However, here, when a reagent as described above is added to the reactor water, NH _{3 is formed in} the course of various chemical processes in which the initial compound of radioactive nitrogen is converted into ¹⁶ NO ₃ ⁻ or ¹⁶ NO ₂ ^{−. 16} N forms an ammine complex with the reagent, increasing the stability in the aqueous phase. Further, in the reagent _{can, N 2 H 4, NH 2} OH, NO 2 - There are higher for complexation ability with, it can be expected the effect of stabilizing the water phase of ¹⁶ N by the complex formation .. Therefore, the addition of the reagent as described above is performed even when the reactor water is in a normal non-reducing atmosphere without injecting the reducing agent, as in the case where the reactor water is in the reducing atmosphere by the reducing agent injection. It has the effect of reducing the production of volatile chemical forms of radioactive nitrogen that migrate to the system.

Further, when the organic water such as the ion exchange resin or the turbine oil is mixed in the reactor water, the reactor water becomes a reducing atmosphere and the proportion of ¹⁶ NH _{3 in} the released chemical form increases. In this case, when a reagent as described above is added, ¹⁶
Since NH ₃ forms an ammine complex with the reagent and the stability in the aqueous phase is increased, the dose rate of the turbine system is reduced. That is, the addition of the above-mentioned reagent has an effect of preventing an increase in the turbine dose rate due to the mixing of a reducing substance such as an organic substance.

Radioactive nitrogen-16 forming an ammine complex
Is a non-radioactive oxygen-16, which decays with a half-life of 7.13 seconds.
become. This causes the ammine complex to dissociate and the reagent to recoordinate with another NH ₃ . Therefore, it is not necessary to constantly monitor the concentration of the reagent in the reactor water, and the amount derived from the mass balance considering the reactor water purification system (that is, the amount of the reagent removed in the reactor water purification system must be compensated for. While constantly injecting the reagent of (amount), the reactor water is appropriately inspected after referring to the dose rate of the turbine system, and the reagent may be additionally injected. However, the reagent is added in a concentration range in which the electrical conductivity of the reactor water does not exceed its regulated value (regulated value generally set in a nuclear reactor), but it is sufficient to add it in the order of ppb. Is. Further, by performing the reagent injection for an arbitrary period, the dose rate of the turbine system can be reduced only during that period. After the end of the period, if the reagent injection is stopped, the reagent is recovered by the reactor water purification system, so that there is no effect. Further, this turbine system dose rate reduction effect is effective even in an area with a low dose rate because it does not depend on the presence or absence of radiation.

As described above, by adding a reagent having a high ability to form a complex with ammonia or a reagent having an effect of generating a substance having a high ability to form a complex with ammonia to the direct cycle reactor primary cooling system ( Or, by using a structural material containing the metal and adding it by eluting from it), not only when the reducing agent is injected, but also during the normal operation when the reducing agent is not injected, an extremely small amount of the order of ppb. Can reduce the amount of radioactive nitrogen gas phase transfer.

[0022]

EXAMPLES The present invention will be described below with reference to examples. Figure 1
Is an example of a direct cycle reactor primary system to which the present invention is applied. Direct-cycle reactor primary cooling system condenser 15
In the subsequent water supply system, the condensate debasing 10 and the water supply pump 2
During the period 1, the reducing agent injection system 16 injects a reducing agent (hydrogen in this embodiment) to reduce the concentration of dissolved oxygen in the primary cooling system. On the other hand, a reagent injection system 23 is installed in a recirculation system composed of the recirculation pump 6 and the reactor water purification system 8, and at the same time when the reducing agent injection from the reducing agent injection system 16 is performed, the reagent injection system 2
A reagent is injected from 3 into the downstream outlet of the reactor water purification system 8. As the reagent, ions of palladium, cadmium, platinum, gold, mercury or cobalt or salts thereof or a mixture thereof are used. As a result, the reagent is dissolved in the liquid phase of the reactor core 1, the mixing plenum 4, the downcomer 5 and the lower plenum 7, and the transfer of radioactive nitrogen to the main steam pipe 18 is reduced. From the reagent injection system 23, the above-mentioned reagent having a high complex forming ability or an aqueous solution thereof is supplied. Hereinafter, the case where palladium ions are used as a reagent will be described as an example. At this time, the palladium ion concentration and the concentration ratio of ammonia in which one ammonia is coordinated to palladium and ammonia are expressed by the following equation at room temperature (25 ° C.). Since the data at high temperature is insufficient, the data at room temperature will be used here.

[0023]

[Equation 3]

Therefore, when the palladium ion concentration is 1 ppb, the concentration ratio of ammonia with one coordinated palladium and ammonia is 3.7 × 10 ⁴ , and about 100% of ¹⁶ N is retained in the reactor water. , Do not move to turbine system. Edge ¹⁶ retention of N into the reactor water with increasing temperature, although the more ¹⁶ N increases going to the turbine system, the number palladium ion concentration reactor water to suppress the migration of ¹⁶ N to the turbine system About ppb is sufficient.

With respect to the other reagents, similarly, a sufficient effect similar to that of several ppb to 100 ppb can be expected.

FIG. 3 shows the installation position of the reagent injection system 23.
It is an example in the case of changing from the recirculation system to the water supply system in. In FIG. 3, the reducing agent (hydrogen in this embodiment) is injected from the reducing agent injection system 16 into the water supply system. Since the reagent injection works more effectively in a reducing atmosphere, it is desirable to inject the reagent downstream of the reducing agent injection point, but even if not, the effect is sufficient. Also in FIG. 3, as in the case of FIG. 1, the reagent is dissolved in the liquid phase of the reactor core 1, the mixing plenum 4, the downcomer 5 and the lower plenum 7, and the action of radioactive nitrogen to the main steam pipe 18 is caused by the same action as described above. Migration is reduced. FIG. 4 and FIG. 5 are examples in which the reducing agent injection is not performed in FIGS. 1 and 3, respectively. Also in this case, as in the case of FIG. 1, the reagent is dissolved in the liquid phase of the reactor core 1, the mixing plenum 4, the downcomer 5 and the lower plenum 7, and the transfer of radioactive nitrogen to the main steam pipe 18 is reduced by the above-mentioned action. To be done. In particular, it has the effect of preventing an increase in turbine system dose rate due to the mixing of reducing substances such as organic substances.

FIG. 6 shows a water supply pipe 17 and a recirculation pipe 19.
This is an example of using a metal or a metal alloy thereof that forms a metal ion having a high complex formation ability with ammonia.
A metal or a metal alloy thereof that generates a metal ion having a high ability to form a complex with ammonia is eluted from the pipe, and a metal ion is generated in the liquid phase of the reactor core 1, the mixing plenum 4, the downcomer 5 and the lower plenum 7. By the same action as described above, the transfer of radioactive nitrogen to the main steam pipe is reduced.

FIG. 7 shows a metal or a metal alloy thereof which forms a metal ion having a high complex formation ability with ammonia, in a part or the whole of the structural material of the reactor core 1, the mixing plenum 4, the downcomer 5 and the lower plenum 7. It is an example in the case of using. A metal or a metal alloy thereof that generates a metal ion having a high ability to form a complex with ammonia is eluted from the above structural material, and similarly to FIG. 6, the liquid phase of the reactor core 1, the mixing plenum 4, the downcomer 5 and the lower plenum 7. Metal ions are generated in the slag, and the transfer of radioactive nitrogen to the main steam pipe is reduced by the same action as described above.

[0029]

As described above, according to the present invention, by adding a reagent having a high ability to form a complex with ammonia to the primary reactor cooling water, the amount of radioactive nitrogen gas phase transfer to the core can be suppressed. However, the radiation dose of the main steam pipe and the turbine system can be reduced. Therefore, the soundness and safety of the nuclear reactor are remarkably improved and the life of the nuclear reactor is prolonged, which is a great advantage in securing an energy source. Moreover, in the present invention, since the reagent injection can be performed not by the NO gas injection but by the liquid injection, the action of the reagent becomes uniform in the reactor primary cooling water, and the reagent injection is easily controlled, and The control of the reagent injection amount may be performed within the range in which the electric conductivity of the reactor water does not exceed the regulation value, and thus the troublesome control such as the conventional NO gas injection is not necessary.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention,

FIG. 2 is a conceptual diagram of a conventional example of a primary cooling system for a direct-cycle reactor in which hydrogen is injected,

FIG. 3 Injection system 2 of reagent having high ability to form complex with ammonia
The figure which shows the Example when changing the installation position of 3 from the recirculation system of FIG. 1 to a water supply system,

FIG. 4 is a diagram showing an embodiment in which no reducing agent is injected in FIG.

FIG. 5 is a diagram showing an embodiment in which no reducing agent is injected in FIG.

FIG. 6 is a diagram showing an example in which a metal or a metal alloy thereof that forms metal ions having a high complex formation ability with ammonia is used in the water supply pipe 17 and the recirculation pipe 19,

[FIG. 7] A metal or a metal alloy thereof that forms a metal ion having a high complex formation ability with ammonia is used as a part or the whole of the structural material of the reactor core 1, the mixing plenum 4, the downcomer 5 and the lower plenum 7. The figure which shows the Example in a case.

[Explanation of symbols]

1 ... Reactor core 2 ... Upper plenum 3 ... Steam separator 4 ... Mixing plenum 5 ... Downcomer 6 ... Recirculation pump 7 ... Lower plenum 8 ... Reactor water purification system 9 ... Water heater 10 ... Condensate demineralizer 11A ... High-pressure turbine 11B ... Low-pressure turbine 12 ... Generator 13 ... Off-gas treatment device 14 ... Rare gas hold-up device 15 ... Condenser 16 ... Reductant injection device 17 ... Water supply pipe 18 ... Main steam pipe 19 ... Recirculation pipe 20 ... Jet Pump 21 ... Water supply pump 22 ... Condensate pump 23 ... Reagent injection system

Front page continuation (72) Inventor Hidetoshi Karasawa 1168 Moriyama-cho, Hitachi-shi, Ibaraki Prefecture Energy Research Institute, Nitrate Manufacturing Co., Ltd.

Claims (5)

[Claims] 1. A direct cycle reactor primary cooling water having a complex formation constant with ammonia at room temperature which has a number of ligands of 3.0 and 3.0.
A method of suppressing the transfer of radioactive nitrogen to the gas phase in a direct cycle reactor primary cooling system, which comprises adding a reagent having a capacity of forming complex ions with ammonia, which is equal to or more than the product of 2. The direct cycle reactor primary cooling water is added with the reagent having a large ability to form complex ions with ammonia at a concentration within a range such that the electrical conductivity of the reactor water does not exceed the regulation value. 1. The method for suppressing the transfer of radioactive nitrogen to the gas phase in the direct cycle reactor primary cooling system according to 1. 3. As the reagent having a large ability to form a complex ion with ammonia, an ion of palladium, cadmium, platinum, gold, mercury, cobalt or a mixture thereof or a water-soluble salt thereof is used, which is directly cycled. The method for suppressing the transfer of radioactive nitrogen to a gas phase in a direct cycle reactor primary cooling system according to claim 1 or 2, wherein the method is injected into the reactor primary cooling water. 4. A metal or an alloy thereof, which elutes a metal ion having a function of forming a complex ion with ammonia, is used as a part or the whole of a structural material of a direct cycle reactor primary cooling system. The method for suppressing transfer of radioactive nitrogen to a gas phase in a direct cycle nuclear reactor primary cooling system according to claim 1. 5. The direct cooling type reactor primary cooling system is injected with a reducing agent such as hydrogen to reduce dissolved oxygen in the reactor water while adding the reagent having a large ability to form complex ions with ammonia. Claims 1, 2, characterized in that
The method for suppressing the transfer of radioactive nitrogen to the gas phase in the direct cycle reactor primary cooling system according to 3 or 4.