JPS59216095A - System water recirculation circuit in atomic 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] [Technical Field of the Invention] The present invention relates to a system water circulation system of a nuclear power plant,
In particular, the present invention relates to a system water circulation system of a nuclear power plant suitable for preventing the generation of corrosion products in the system water circulation system of a nuclear power plant.

[Technical background of the invention and its problems]

In a nuclear power plant equipped with a boiling water reactor, corrosion products such as rust are generated on the inner surfaces of condensate and water supply pipes in the system water circulation system, and these corrosion products flow into the reactor pressure vessel. This corrosion product that has flowed into the reactor pressure vessel becomes radioactive and circulates, which poses the problem of contaminating the entire system water circulation system and potentially increasing the radiation dose to operators and others.

Therefore, oxygen is dissolved in the system water at a predetermined concentration to form a stable oxide film on the inner surface of the pipe to prevent the generation of corrosion products such as rust.

Conventionally, oxygen was supplied to the system water only downstream of the condensate desalination equipment, but not upstream. In other words, a stable oxide film is formed only on the inner surface of the piping on the downstream side of the condensate desalination equipment, and the corrosion products generated inside the piping on the upstream side of the condenser are removed by the condensate desalination equipment. No special countermeasures were taken other than the use of condensate desalination equipment.

However, the removal of corrosion products in this condensate demineralizer is actually not complete, and only about 50 to 70% is removed.

The remaining corrosion products, which account for 50% of the total, flow into the reactor pressure vessel, become activated, and circulate within the system. Therefore, an unexpected situation may occur in which the degree of contamination of the entire system water circulation system of a nuclear power plant increases, and the exposure dose of operators and the like may increase.

[Purpose of the invention]

The present invention has been made in consideration of the above points, and includes:
The purpose of the present invention is to provide a system water circulation system for a nuclear power plant that can reduce the exposure of operators, etc. in the nuclear power plant.

[Summary of the invention]

In order to achieve the above object, the system water circulation system of a nuclear power plant according to the present invention guides steam generated in a nuclear pressure vessel to a turbine to do work, and condenses the steam that has done this work in a condenser. An oxygen gas injection device for injecting oxygen gas into the upstream system water is provided on the upstream side of the desalination device in a system water circulation system of a nuclear power plant in which condensed water is returned to the nuclear pressure vessel via a desalination device. An oxide film is also formed inside the piping on the upstream side of the desalination equipment to prevent the generation of corrosion products in this piping and reduce the introduction of corrosion products into the reactor pressure vessel. It is something to do.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram showing an embodiment of the system water circulation system of a nuclear power plant according to the present invention.

In the figure, reference numeral 1 denotes a reactor pressure vessel housed in a reactor containment vessel 2. Steam generated in this reactor pressure vessel 1 is led to a high-pressure turbine 5 via a main steam pipe 3. Work is done, and the steam that has done the work passes through a moisture separator 7 and is introduced into a low pressure turbine 9. High pressure turbine5. The steam introduced into the low-pressure turbine 9 does work in both of these turbines 5 and 9, and is arranged coaxially with both turbines 5 and 9 to generate a generator 11.
Rotate at high speed.

A condenser 13 is connected to the low pressure turbine 9.

Steam led from the low-pressure turbine 9 is condensed in the condenser 13 and becomes condensate, which is stored in a hot well 15 provided at the lower part of the condenser 13.

The condensate in the hot well 15 passes through a condensate low-pressure pump 17 and a condensate filtration device 19, which are sequentially installed in a condensate pipe 16.
The condensate is guided to the condensate desalination device 21, where it is treated and desalted. Thereafter, the water is returned to the reactor pressure vessel 1 via a high-pressure condensate pump, a feedwater heater 5, and a feedwater pump n, which are sequentially arranged in the condensate drain and the water supply pipe η.

On the other hand, the steam that has done work in the low-pressure turbine is condensed and deaerated in the condenser 13, and this deaerated non-condensable gas (hereinafter referred to as "off gas") is transferred to the condenser 13. It is guided to the connected off-gas system.

The off-gas contains krypton, xenon, and argon activated within the reactor pressure vessel 1, as well as large amounts of oxygen gas and hydrogen gas generated by activation decomposition of reactor water.

The off-gas system includes an air extractor 4, a steam jet pump 31, a gas preheater, and a re-supply unit 35, which are sequentially arranged from the upstream side. Wave decay tank 43. It consists of a filter 45 and an active field up device.

The air extractor 4 is directly connected to the condenser 13,
The off-gas in the condenser 13 is extracted. Thereafter, the off-gas is guided to the gas preheater by the steam jet pump 31 and heated. Furthermore, in the refeeder section, oxygen and hydrogen gas in the components of the off-gas are converted to water by a catalyst,
Off-gas volume is reduced. This volume-reduced off-gas is then led to an attenuation filter 43, where short half-life nuclides are attenuated before filter 45. It passes through the active hold-up device 47 and is sent to the exhaust stack, from which it is discharged into the atmosphere. Furthermore, an oxygen gas injection device 51 is disposed between the air extractor 4 and the hot well 15 of the condenser 13. That is, this oxygen gas injection device 51 includes a flow rate adjustment mechanism 53 and a main valve 55, which are arranged sequentially from the upstream side.
．． and an oxygen injection nozzle 57.

FIG. 2 is a circuit diagram showing the oxygen gas injection device of FIG. 1, and the same members as those in FIG. 1 are given the same reference numerals and the explanation thereof will be omitted.

As shown in FIG. 2, the pressure of the off-gas is measured by a pressure gauge 59 inside the flow rate adjustment mechanism, and then guided to the flow meter B via six branch pipes 61. The off-gas flow rate is measured in the field. A needle valve part is arranged in the branch pipe 61 on the downstream side of the flow meter field, and the pressure gauge 5
The off-gas flow rate is controlled based on the measured values from 9 and the flow meter.

Each branch pipe 61 is extended and connected to the three condensers 1.
One pair is connected to each hot well 15 of No. 3.

Further, each branch pipe 61 is provided with the above-mentioned main valve 5. This original valve is a globe valve, etc., and the flow rate adjustment mechanism 5
3 does not operate normally, this prevents abnormal supply of off-gas into the hot well 15.

Further, each branch pipe 61 extends inside the hot well 15 through the hot well body plate 67, as shown in FIG. The branch pipe 61 in the hot well 15 is further branched and fixed to the hot well bottom plate 71 via an oxygen gas injection nozzle 57 attached to each end thereof and a support stand 91 to be described later. Reference numeral 73 in FIG. 3 indicates a hot well roof.

FIG. 4 is a half-sectional view showing the oxygen gas injection nozzle, and FIG. 5 is a side view showing the attached state of the oxygen gas injection nozzle.

The oxygen gas injection nozzle 57 includes a base pipe 75 and a foam tube 77.
and an end plate 79. The base pipe 75 has a substantially T-shape, and the end of the branch pipe 61 can be attached to the inflow end 81. Still, both outflow ends 83 of the base pipe 75
A foam tube 77 is fitted and fixed to the.

This foam tube 77 has a double tube structure, and the inner tube 85 has a large number of through holes 87 formed therein. Further, the outer cylinder 89 is formed of porous sintered metal, and off-gas bubbles are formed by the numerous holes of about 5 μm in the outer cylinder 89. moreover,
End plates 79 are fitted to both ends of the foam tube 770.

As shown in FIG. 5, a support stand 91 having a concave cross-section is fixed to the hot well bottom plate. This support stand 91
The concave portion 93 extends perpendicularly to the flow direction of the condensate in the hot well 15. The base pipe 75 and foam tube 77 of the oxygen gas injection nozzle 57 are fitted into the recessed portion 93 and fixed by the band 95. As a result, the oxygen gas injection nozzle 57 has its longitudinal direction perpendicular to the flow direction of the condensate in the hot well 15, making it possible to inject off-gas into the condensate over a wide range.

Next, the effect will be explained.

The off-gas in the condenser 13 extracted by the air extractor 4 is
Needle valve 65 of oxygen gas injection device 51 (see Figure 2)
The flow rate is adjusted by , and the oxygen gas is guided to the oxygen gas injection nozzle 57 via the main valve I. The off-gas guided to the oxygen gas injection nozzle 57 is passed through the foam tube 77 of the oxygen gas injection nozzle 57.
The bubbles are made into air bubbles and injected into the condensate in the hot well 15. The dissolved oxygen concentration of the condensate in the hot well 15 increases due to the oxygen in the injected off-gas. As a result, condensate piping 16. Condensate low pressure pump 17. An oxide film is formed on each inner wall of the condensate filter to prevent the formation of corrosion products.

Here, FIG. 6 is a graph obtained through experiments to determine the relationship between corrosion formation rate and dissolved oxygen concentration. In this experiment, water with a conductivity of 0.5 μB/cm or less and a temperature of 32°C was circulated in a large closed-loop waterway, a test piece with a surface area of 20.1 r (material: 5B46) was introduced, and oxygen gas was further injected. Second, the corrosion products generated on the test pieces were measured by varying the flow rate of circulating water. Here, the flow rate of circulating water is 3.5 m/s e 1. (1m/s, 0
．． 42m/s t 0025m/s In each case in Fig. 6, solid line A1 covered line B1
Each is indicated by a dashed dotted line C and a dashed dotted line.

According to this graph, it can be seen that when the dissolved oxygen concentration reaches around 100 ppd, the corrosion products decrease rapidly regardless of the above-mentioned circulation flow rate of water.

According to the above embodiment, the inflow of corrosion products into the reactor pressure vessel 1 is reduced due to the reduction in corrosion products, and the contamination of the system water circulation system of the nuclear power plant is prevented, thereby reducing the exposure of operators, etc. It has the effect of being able to reduce

FIG. 7 is a graph showing the relationship between the amount of oxygen gas injected and the dissolved oxygen concentration when oxygen gas was injected into the condensate in the hot wells in three condensers.

In addition, the oxygen solubility is about 2-.

According to this graph, the dissolved oxygen concentration in the condensate is
00 ppd requires 200t/m under standard conditions.
It is necessary to inject IR oxygen gas for a predetermined period of time. Therefore, considering this ratio, a large amount of oxygen gas of 8640 rrl is required under standard conditions every day (one month), and a storage facility for this must be provided.

However, according to the above embodiment, this large amount of oxygen gas is continuously obtained by dividing it from the air extractor 4, so there is no need to store oxygen.

Since oxygen gas is a combustion-enhancing gas, this is extremely beneficial in terms of the safety of nuclear power plants. Also,
Another effect is that costs can be reduced.

In addition, according to the above-mentioned embodiment, explanation has been made regarding the case where oxygen gas is injected into the condensate in the hot well 15 in the water tank 13, but the condensate from the condenser 13 to the condensate desalination device It may also be injected into the pipe 16, condensate filtration device 17, etc. during drainage.

In addition, in the above embodiment, the air extractor 29 in the off-gas line
Although the explanation has been given on a device that separates the off-gas from the off-gas system, it may also be a device that separates the off-gas from a 31° gas preheater or the like.

〔Effect of the invention〕

As described above, according to the system water circulation system of a nuclear power plant according to the present invention, oxygen gas is injected into the upstream system water upstream of the desalination equipment in the system water circulation system of the nuclear power plant. Since the equipment was installed,
It is possible to form an oxide film in the piping on the upstream side of the desalination equipment and prevent the generation of corrosion products in the piping, thereby reducing the amount of corrosion products flowing into the reactor pressure vessel. It is possible to reliably reduce the radiation exposure of nuclear reactor power plant operators.

Further, when the oxygen gas is obtained by off-gas that is branched from the off-gas system, there is no need to provide a storage facility for storing a large amount of oxygen in the nuclear reactor power plant, which has the effect of being extremely favorable in terms of plant safety.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment of the system water circulation system of a nuclear power plant according to the present invention, FIG. 2 is a circuit diagram showing the oxygen gas injection device of FIG. 1, and FIG. 3 is a reproduction of FIG. 4 is a half sectional view showing the oxygen gas injection nozzle shown in FIG. 3, and FIG. 5 is a side view showing the installation state of the oxygen gas injection nozzle shown in FIG. 4. FIG. 6 is a graph showing the relationship between corrosion formation rate and dissolved oxygen concentration, and FIG. 7 is a graph showing the relationship between oxygen gas injection amount and dissolved oxygen concentration. 1... Nuclear reactor pressure vessel, 5... High pressure turbine, 9...
...Low pressure turbine, 13...Condenser, 15...Hontowell, 16...Condensate piping, 21...Condensate desalination equipment, %...Off gas system, 4...Air extractor, 51.
...Oxygen gas injection device, 53...Flow rate adjustment mechanism, 55
... Main valve Mi57 ... Oxygen gas injection nozzle.

Claims (1)

[Claims] 1. Steam generated in the reactor pressure vessel is guided to a turbine to do work, and the steam that has done work is condensed in a condenser to form condensate, and the reactor pressure is reduced through a desalination device. A nuclear power generation plant characterized in that, in a system water circulation system of a nuclear power plant that is returned to a container, an oxygen gas injection device for injecting oxygen gas into the upstream system water is provided upstream of the desalination device. Systemic water circulation system. 2. Claim 1, wherein the upstream system water of the desalination device is condensate stored in a hot well in the condenser.
The system water circulation system of the nuclear power plant described in Section 1. 3. The nuclear power plant according to claim 1 or 2, wherein the oxygen gas is oxygen gas contained in off-gas of an off-gas system that discharges off-gas generated in a condenser. Systematic water circulation system. 4. The nuclear power plant system according to claim 3, wherein the off-gas is incorporated into the off-gas system and is separated from an air extractor connected to the condenser. water circulation system. 5. The oxygen gas injection device includes a flow rate adjustment mechanism connected to the air extractor to adjust the pressure and flow rate of off-gas from the air extractor, and a flow rate adjustment mechanism from the flow rate adjustment mechanism to the hot well of the condenser. an oxygen gas injection nozzle provided at a tip of the extending branch pipe to bubble off gas from the flow rate adjustment mechanism and inject it into the condensate in the hot well; and an oxygen gas injection nozzle in the branch pipe. A system water circulation system for a nuclear power plant according to claim 4, characterized in that it has a main valve disposed between the flow rate regulating mechanism and the flow control mechanism to prevent the inflow of excessive off-gas.