JPH01184308A - Nuclear power plant - Google Patents

Abstract

PURPOSE:To prevent a concentration of dissolved oxygen in feed water from being increased in case of recovering a drain and enable an amount of clad to be restricted by a method wherein a concentration of the dissolved oxygen in the drain to be stored in a drain tank is properly controlled and the drain is sent to a condensor and a water supplying unit. CONSTITUTION:A connection pipe 120 for connecting a drain tank 113 with a condensor 105 is arranged, a flow rate adjusting valve 119 is arranged in this connecting pipe. When the drain from the drain tank is sent to a condensor and a water supplying unit, a control device 118 is arranged for giving an opening or closing signal to the flow rate adjusting valve 119 in such a way as the concentration of the dissolved oxygen in the condensate and the feed water may not exceed a specified value. Due to this fact, the concentration of the dissolved oxygen in the drain which is high in the feed water heater is also controlled in the drain tank and fed into the condensor and the feed water, so that it is possible to restrict the increasing of the concentration of the dissolved oxygen in the condensate and the feed water. So, it is possible to prevent a corrosion crack of a stainless steel pipe around a reactor, and an increased clad caused by corrosion in the condensor and the feed water supplying pipe and the feed water heater.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a nuclear power plant equipped with a system for recovering feed water heater drain to condensate/feed water, and in particular, to This article relates to a nuclear power plant that aims to control dissolved oxygen concentration and reduce corrosion products (crud) in condensate and water supply.

(Conventional technology) In recent years, in order to improve efficiency in nuclear power plants, high-temperature feedwater heater drain is no longer collected in a condenser.

Condensate recovery systems that directly collect condensate water or water supply are widely used.

Generally, this type of nuclear power plant includes a nuclear reactor 1, a high-pressure turbine 2, a moisture separation heater 3, as shown in FIG.
, low pressure turbine 4, condenser 5, low pressure condensate pump 6, condensate desalination device 7, high pressure condensate pump 8, low pressure feed water heater 9, reactor feed water pump 10° high pressure feed water heater 11, etc. A circulation cycle returning to the nuclear reactor 1 is configured, and the steam generated in the nuclear reactor 1 drives each of the turbines 2 and 4 to operate a generator (not shown) to generate nuclear power. On the other hand, heating steam is sent from each turbine 2 and 4 to the low-pressure feedwater heater 9 and high-pressure feedwater heater 11 through the bleed pipe 12, and the feedwater is heated by this steam. The heated steam becomes drain after heat exchange,
It is stored in the drain tank 13. Drain stored in drain tank 13 is at high temperature.

Moreover, the low pressure feed water heater 9 drain flow rate is approximately 55% of the feed water flow rate.
%, the high pressure feed water heater 11 drain flow rate is 45% of the feed water flow rate.
%, and for the purpose of improving efficiency through heat recovery, it is sent to the water supply via the drain recovery pipe 15 by the drain pump 14, and is mixed with the water supply to be integrated.

The water is then returned to the reactor 1 via the feed water heaters 9 and 11.

In addition, non-condensable gas consisting of oxygen and hydrogen generated by radioactive decomposition of water in the reactor 1 enters each feedwater heater 9, 11 through the oil air pipe 12 along with heated steam, reducing thermal efficiency. Therefore, most of the non-condensable gas flows through the exhaust pipe 16.
It is discharged to the condenser 5 through the condenser 5. The amount of non-condensable gas exhausted to the condenser is always controlled to be constant by an orifice plate 17 installed in the middle of the exhaust pipe 16, and is normally 0.5% or 1% of the amount of oil vapor. has been done.

In BWR type nuclear power plants, etc., reactor 1
In order to reduce the activation products generated within the nuclear reactor 1, the amount of crud brought into the reactor 1 is strictly limited.

Therefore, in order to prevent the formation of crud due to corrosion from the condensate/water supply piping 18 made of carbon steel and each feed water heater 9.11, etc., dissolved oxygen in the water supply from the oxygen cylinder 19 is maintained within a controlled range of 20 to 200 ppb. Oxygen gas is usually injected to a concentration of 50 ppb or more. The amount of injected oxygen gas was set after the oxygen gas injection point. Dissolved oxygen meter 20
is controlled by.

(Problems to be Solved by the Invention) However, in a nuclear power plant equipped with such a conventional drain recovery system.

There was a problem in that the dissolved oxygen concentration in the drain differed depending on the amount of noncondensable gas discharged from each of the feed water heaters 9 and 11.

In other words, when the non-condensable gas exhaust amount is set to 0.5%, the oxygen gas in the non-condensable gas is dissolved into the drain, and the dissolved oxygen concentration becomes several thousand ppb.
corrosion is greatly suppressed and the amount of crud in the drain is reduced, but if the drain is collected into the water supply, 20 to 200 PP
The dissolved oxygen concentration in the feed water managed by b is 200ppb
As a result, the dissolved oxygen concentration in the reactor 1 water increases,
There is a concern that stress corrosion cracking may occur in the stainless steel piping (not shown) surrounding the reactor. On the other hand, when the non-condensable gas exhaust amount is set to 1.0%, the dissolution of oxygen gas into the drain is reduced, and the dissolved oxygen concentration becomes several tens of ppb, which causes the problem of an increase in the dissolved oxygen concentration of the feed water when recovering the drain. However, as the concentration of dissolved oxygen in the drain decreases, corrosion of each feed water heater 9.11 increases, and as a result, crud in the drain increases. , the amount of crud in the feed water after drain collection exceeds the limit value, causing a problem.

In response, there is an idea to automatically adjust the non-condensable gas exhaust amount instead of using a fixed method, but there are a total of 18 feed water heaters in the actual plant, and controlling all of them would be difficult from a technical standpoint as well as cost. It is also difficult. - Therefore, an object of the present invention is to provide a nuclear power plant in which the dissolved oxygen concentration in the water supply does not increase when drain is recovered, and the amount of crud can also be suppressed.

[Structure of the invention]

(Means for Solving the Problems) According to the present invention, the dissolved oxygen concentration of drain stored in a drain tank is suitably controlled, and the drain is sent to condensate/water supply. In other words, a nuclear reactor, a high pressure turbine, a low pressure turbine, a condenser, a low pressure feed water heater, a high pressure feed water heater, etc. are connected in series to form a circulation cycle, while the feed water heater drain is stored in a drain tank. ,
In a nuclear power plant equipped with a drain recovery system that feeds condensate water into the water supply, a connecting pipe is provided that connects the drain tank and the condenser, and a flow rate regulating valve is installed in this connecting pipe, so that the drain Drain from the tank condenses
Features (effects) characterized in that a control device is provided that gives an opening/closing signal to the flow rate regulating valve so that the dissolved oxygen concentration in the condensate/supply water does not exceed a certain value when it is sent to the water supply.During the operation of a nuclear power plant , the dissolved oxygen concentration in the drain is measured, and this value is compared with the existing condensate/supply water dissolved oxygen concentration value, and if the value in the drain is high, a If the opening degree of the flow rate regulating valve increases and the value in the drain is low, the opening degree will conversely decrease.

Therefore, the dissolved oxygen concentration in the drain, which was high inside the feed water heater, is controlled in the drain tank and sent to the condensate and feed water, making it possible to suppress increases in the dissolved oxygen concentration in the condensate and feed water. .

(Embodiment) Hereinafter, a preferred embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows the configuration of an embodiment of the present invention, and the reference numeral 101 shown in the figure is a nuclear reactor.

The nuclear power plant includes a nuclear reactor 101, a high pressure turbine 102, a moisture separation heater 103, a low pressure turbine 104,
Condenser 105, low pressure condensate pump 106, condensate desalination device 1
07. High pressure condensate pump 108. low pressure feed water heater 109,
It is connected to the nuclear reactor 101 via a reactor feed water pump 110 and a high pressure feed water heater 111 to form a closed circulation cycle. The steam generated in the nuclear reactor 101 is then transferred to a high pressure turbine 102. Next, low pressure turbine 1
04 to drive each turbine 102, 104,
A generator (not shown) is operated to generate electricity. After the steam that has done work in the turbines 102 and 104 is condensed into condensate in the condenser 105,
Suctioned by the low pressure condensate pump 106, the condensate desalination device 1
07, and the cladding is removed. After that, the reactor 1
01, and one cycle is completed. Additionally, in order to prevent the generation of crud due to corrosion from the condensate/water supply piping 124 made of carbon steel and the respective feed water heaters 109, 111, etc., dissolved oxygen from an oxygen cylinder 125 is added to the water supply. With a control range of 200ppb, typically 5o
Oxygen gas is injected so that it is at least ppb, and the amount of injected oxygen gas is controlled by a dissolved oxygen meter 126.

On the other hand, the low pressure feed water heater 109 and the high pressure feed water heater 1
11, heated steam is sent from each turbine 102 and 104 through an oil air pipe 112, and as a result of heat exchange between this steam and feed water, the feed water is heated, the steam is condensed, becomes drain, and is stored in a drain tank 113. be done. Drain stored in the drain tank 113.

For heat recovery, the drain pump 114 sends the water to the feed water via the drain recovery pipe 115, mixes it with the feed water, and then passes through each feed water heater 109, 111 to the reactor 10.
It is refluxed to 1.

In addition, each feed water heater 109, 111 includes a reactor 101.
Non-condensable gas consisting of oxygen and hydrogen generated by the radioactive decomposition of water in the condenser 105 mixes with the heated steam, reducing thermal efficiency, so most of the non-condensing gas is discharged to the condenser 105 through the exhaust pipe 116. be done. The amount of non-condensable gas exhausted to the condenser is kept constant at 0.5% of the amount of extracted steam by an orifice plate 117 provided in the middle of the exhaust pipe 116, and the amount of crud in the drain is kept low. Although,
The dissolved oxygen concentration is as high as several thousand ρPb.

Therefore, a dissolved oxygen control device 118 is provided in the drain tank 113 so that the dissolved oxygen concentration in the supplied water does not exceed a reference value even after drain collection. This dissolved oxygen control device 1
Reference numeral 18 includes a comparison circuit 122 and an arithmetic unit 123. Further, the drain tank 113 is provided with a connecting pipe 120 that communicates with the condenser 105, and a flow rate regulating valve 119 is connected to the connecting pipe 120.
to be placed. Furthermore, a dissolved oxygen meter 121 is attached to the drain recovery pipe 115.

Therefore, during operation of a nuclear power plant, the dissolved oxygen concentration in the drain is measured by the dissolved oxygen meter 121 attached to the drain recovery pipe 115, and the dissolved oxygen concentration in the condensate is measured by another dissolved oxygen meter 126. Ru.

The signals of each dissolved oxygen meter 121 and 126 are sent to a comparison circuit 12
2, and the comparison circuit 122 compares the dissolved oxygen concentrations of the two. Dissolved oxygen concentration in condensate is 20-200Pp
If the dissolved oxygen concentration in the drain is higher than this range, an output signal corresponding to the comparison deviation value is sent from the comparison circuit 122 to the calculation section 123, and further calculation is performed according to the signal. From part 123 to flow rate adjustment valve 1
A signal to increase the opening is sent to 19.

The opening degree of the flow rate regulating valve 119 increases. Flow rate adjustment valve 119
If the opening degree of the drain tank 113 and condenser 10 increases,
5 are in communication with each other through the communication pipe 120, the dissolved oxygen in the drain is reduced by the degassing effect of the condenser 105.

Furthermore, when the dissolved oxygen concentration in the drain is lower than the dissolved oxygen concentration in the water supply, the dissolved oxygen concentration in the drain increases by the operation opposite to the above.

In this way, after controlling the opening degree of the flow rate adjustment valve 119 so that the dissolved oxygen concentration in the drain becomes the same as the dissolved oxygen concentration in the condensate, the condensate is By sending condensate into the water supply, the dissolved oxygen concentration in the condensate/supply water can be reduced to 2 of the standard value.
It never exceeds 0 to 200 PPb and can always be kept constant. This prevents the problem of stress corrosion cracking of the stainless steel pipes (not shown) around the reactor when the standard value is exceeded, and the increase in crud due to corrosion of the condensate/feed water pipe 124 and each feed water heater 109, 111 when the standard value is below the standard value. It can be prevented. In addition, since the dissolved oxygen concentration in each feed water heater 109, 111 is maintained at a high level of several thousand PPb, there is very little crud in the drain, and it is possible to prevent crud from increasing in the feed water after drain recovery. I can do it.

〔Effect of the invention〕

As explained above, the present invention installs a dissolved oxygen control device in the drain recovery system, and brings the dissolved oxygen concentration in the drain to the condensate/feed water dissolved oxygen concentration range while maintaining the dissolved oxygen concentration inside the feed water heater in a high state. Because it is controlled, the dissolved oxygen concentration in the condensate and feed water does not change even if condensate is recovered as condensate and feed water, resulting in stress corrosion cracking of stainless steel piping around the reactor, condensate water piping, and water supply piping. Also, it is possible to prevent the increase in crud due to corrosion of the feed water heater. In addition, since the crud in the drain is kept low, it has the effect of suppressing the increase in crud in the water supply6.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of a nuclear power plant according to the present invention, and FIG. 2 is a system diagram showing a conventional nuclear power plant. lot...Nuclear reactor, 102...High pressure turbine, 103...Moisture separation heater, 104...Low pressure turbine, 105...Condenser, 106...
Low pressure condensate pump, 107...Condensate desalination device I, 10g
...High pressure condensate pump. 109...Low pressure feed water heater, 110...Reactor feed water pump, 111...High pressure feed water heater, 112...Bleed pipe. 113...Drain tank, 114...Drain pump, 115...Drain recovery piping, 116...Exhaust pipe. 117... Orifice plate, 118... Dissolved oxygen control device, 119... Flow rate adjustment valve, 120... Connecting pipe, 121.126... Dissolved oxygen meter, 122... Comparison circuit, 123... ...Arithmetic unit, 124...Condensate/water supply piping, 125...Oxygen cylinder. Agent Patent Attorney Noriyuki Chika Yudo Ken Daishimaru

Claims (1)

[Claims] In a nuclear power plant in which a nuclear reactor, high-pressure turbine, moisture separation heater, low-pressure turbine, condenser, low-pressure feedwater heater, high-pressure feedwater heater, etc. are connected in series to form a circulation cycle, the low-pressure and high-pressure A connecting pipe is provided so that a drain tank that stores the drain generated in the feed water heater communicates with the condenser, and a flow rate adjustment valve is installed in this connecting pipe, so that the drain from the drain tank is condensed and connected to the condenser. A nuclear power generation plant, characterized in that a control device is provided for giving an opening/closing signal to the flow rate regulating valve so that the dissolved oxygen concentration in the condensate/feed water does not exceed a certain value when the water is sent to the water supply.