JPS6379099A - Feedwater dissolved oxygen regulator - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is used in a boiling water nuclear power plant to properly maintain the dissolved oxygen concentration in the feed water sent to a nuclear reactor, The present invention relates to a water supply dissolved oxygen regulating device suitable for preventing rust from forming on the inner surface of pipes, etc.

(Conventional technology) In boiling water nuclear power plants, water is treated so that the quality of the water supplied to the reactor is higher than the level required to reduce the chances of crud being transported to the reactor, or to eliminate it. Many efforts are made to maintain the dissolved oxygen concentration at an appropriate value through air treatment. This is because if crud, etc. are transported to the reactor together with the water supply, it becomes radioactive there, increasing the risk of radiation exposure to workers, and if the dissolved oxygen concentration exceeds a certain value, This is because it causes stress corrosion cracking in +14 material made of stainless steel. Therefore, not only the condensate but also the various types of trains generated in Plan 1~ are once collected in the condenser and degassed, and further water treatment is performed by the condensate purification device to maintain a certain water quality. .

In the past, feedwater heater condensate was typically collected in a condenser for this purpose, but instead, feedwater heater condensate has been collected for the purpose of improving the efficiency of the turbine cycle. Instead of directly returning the water to the condensate system or water supply system using a pump, a so-called feedwater heater drain pump-up method has been proposed and is attracting attention.

Hereinafter, as an example of this method, a method of returning the high-pressure feed water heating drain to the suction side of the feed water pump will be described with reference to the drawings.

In FIG. 2, hot air exiting a nuclear reactor (not shown) is sent to a high pressure turbine 1 where it is expanded and becomes low pressure steam which flows into a moisture separator reheater 2. Moisture in the steam is here removed by a moisture separator and roughly heated by a heater to become superheated steam that flows to the low pressure turbine 3. The steam is expanded again in the low-pressure turbine 3, further reduced in pressure, and guided to the condenser 4, where it is cooled by cooling water introduced from the outside and condensed to become condensed water. This condensate is extracted by a condensate pump 5 and sent to a condensate purifier 6. Solid matter, metal ions, etc. mixed in the condensate are removed by water treatment here, and the water is purified to the required quality.

The condensate is heated in a plurality of low-pressure feed water heaters 7 using extracted air from the low-pressure turbine 3, and is again compressed by the feed water pump 8 and sent as feed water to the high-pressure feed water heater 9, where it is heated by the high-pressure turbine 1.
heated by bleed air from At this time, the high pressure water heater 9
Heat exchange occurs between the feed water flowing through the drain and the steam, and the steam condenses and becomes drain. The drain generated in this high-pressure feed water heater 9, that is, the feed water heater drain, is each drained by a drain recovery pipe 1.
0 is collected in a drain tank 11, from which it is extracted by a drain pump 12, and directly injected into the suction side of the water supply pump 8 via a drain injection pipe 13. As a result,
The heat held by the feedwater heater drain is transferred to the feedwater,
A portion of the heat conventionally carried away by the cooling water when recovered in the condenser is recovered. In addition, the reference numeral 14 in the figure indicates a drain discharge pipe 15 for discharging the water heater 4 from which the feed water heater drains.
Each shows a cascade drain pipe.

(Problems to be Solved by the Invention) As described above, in a nuclear power plant, an upper limit is determined for the concentration of dissolved oxygen in condensate or feed water going to the reactor, and operation cannot be continued at a value exceeding this. When the feedwater heater drain pump-up method is adopted, since a large amount of PIim is dissolved in the feedwater heater drain, it is necessary to heat the feedwater heater drain in the drain tank 11 to degas it. It's normal. This prevents the dissolved oxygen concentration from increasing and keeps it at a desirable value without exceeding the upper limit.

However, if the plant is operated at a value lower than the rated output, that is, if it is operated at partial load or if it is not possible to inject feedwater heating condensate into the feedwater due to manual handling, etc., the condensate Alternatively, it is possible that dissolved oxygen in the water supply becomes insufficient. In other words, the proportion of the feed water heater drain injected into the feed water to the total water supply amount is about 30%, but the dissolved oxygen concentration in the feed water largely depends on the amount of dissolved oxygen in the feed water heater drain. You may end up losing almost the entire amount.

Dissolved oxygen decreases depending on the type of steel, such as stainless steel, but on the other hand, for components made of carbon steel, such as water pipes that lead water, a stable oxide film forms on the surface of the material. This means that there will be no formation of rust, which poses a problem.

If rust occurs in water supply pipes, etc., there is an increased risk that this will be transported to the nuclear reactor as crud in the future and become radioactive.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a water supply dissolved oxygen regulating device that maintains the dissolved oxygen concentration in the water supply within an appropriate range and prevents the occurrence of multi-legged crats in water supply pipes, etc. It is in.

1. Structure of the Invention (Means for Solving the Problems) The feed water dissolved oxygen regulating device of the present invention includes an oxygen storage device and an inlet pipe connecting the oxygen storage device and the downstream route of the condensate purification device. The installed control valve compares the detected dissolved oxygen concentration of condensate with a predetermined dissolved oxygen rate, and outputs a control signal that determines the valve opening of the control valve according to the deviation. The first adjusting means compares the detected dissolved oxygen concentration of the feed water flowing through the downstream path of the high-pressure feed water heater with a predetermined dissolved oxygen concentration, and adjusts the valve opening of the control valve according to the deviation. and a second regulating means for outputting a control signal that determines the flow rate of the control valve based on the flow m of the feed water heater drain flowing through the drain injection pipe connecting the drain tank and the suction side of the feed water pump. and means for switching from one adjustment means to the other adjustment means.

(Function) The concentration of dissolved oxygen in condensate and feed water is expected to be suppressed when considering the components inside the reactor as a consideration for stainless steel, which is highly susceptible to horn corrosion cracking. When considering condensate water and water supply system constituent materials, it is necessary to ensure a certain value or more so that an oxide film is formed on the inner surface of the constituent materials.

The present invention controls the dissolved oxygen concentration at each of these two points to a predetermined value, and the feed water heater drain is injected into the feed water through the drain injection pipe to the suction side of the water pump. During this period, the amount of oxygen dissolved in the feedwater heater drain is mainly monitored in the downstream path of the high-pressure feedwater heater, while when the feedwater heater drain injection is stopped, the amount of oxygen injected is mainly monitored. The valve 17n degree of the control valve that supplies the flying line from all sides is automatically controlled using the first control means and the second control means.

The flow m of the feedwater heater condensate through the condensate injection pipe is then checked and adjusted to a predetermined flow rate so that the switching of the two regulating means from one to the other and vice versa takes place automatically. A signal is issued to switch the contacts.

(Example) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, reference numeral 21 indicates an oxygen storage device configured as an oxygen supply source, and this oxygen storage device 21 and the downstream path of the condensate purification device 6 are connected by an oxygen injection pipe 22. A control valve 23 is provided in the path of the oxygen injection pipe 22 to adjust the injection oxygen ♀.

On the other hand, a first core element Q degree detector 24 is provided downstream of the position where the oxygen injection pipe 22 is connected, and the detected value is sent to a comparator 25 and compared with a set value. The signal is configured to be output to the regulator 26. Further, a second oxygen concentration detector 27 is installed downstream of the high-pressure feed water heater 9, and the value detected here is sent to a comparator 28 and compared with a set value. Furthermore, the regulation signals generated by the regulators 26 and 29 are transmitted to the drive unit (not shown) of the regulation valve 23 via the relay 30, respectively. .

In addition, the discharge level of the drain pump 12 of the drain injection pipe 13 is detected and the relay 30 is activated! A flow rate detector 31 is provided for detecting I-waste.

Note that each configuration other than the above is the same as the configuration shown in FIG. 2, and some are omitted from illustration.

In the above 1^1 configuration, while the feed water heater drain is being injected into the suction side of the feed water pump 8, the regulating valve 23 detects the dissolved oxygen concentration in the feed water with the second oxygen concentration detector 27, and detects the dissolved oxygen concentration in the feed water. The output and the set value are compared by a comparator 28, and a regulator 29
ijJ is controlled by a signal corresponding to the deviation. In this case, since the dissolved oxygen concentration in the feed water heater drain is relatively high, the control valve 23 is not opened very much, and therefore the amount of oxygen injected is almost no or only a small amount.

On the other hand, if it becomes impossible to inject the feed water heater drain into the feed water for some reason, the operation of the drain pump 12 is stopped and the flow rate of the feed water heater drain flowing through the drain injection pipe 13 is reduced. This decrease in flow rate is detected by the flow rate detector 31, and if the flow rate is lower than the set value, the relay 30 is activated and the control signal of the control valve 23 or the signal output from the two regulators is output from the regulator 26. signal.

Usually, dissolved i′ in the condensate extracted from the condenser 4! The number of 2 lines is small, and the first oxygen concentration detector 24 detects this and inputs it to the comparator 25. Since the lower limit of dissolved oxygen: 1 degree is specified as the setting value of the comparator 25, a signal to open the control valve 23 is outputted via the regulator 26, and oxygen is recovered from the oxygen storage device 21 through the oxygen injection pipe 22. Injected into the water. This increases the dissolved oxygen concentration in the condensate and brings it to the specified concentration.

In addition, after this, the water heater de! When the injection of water into the water supply starts again, the relay 30 is actuated by the output signal of the mountain flow detector 31, and the control signal of the control valve 23 changes from the output signal from the regulator 26 to the output signal from the regulator 29. Can be switched.

Furthermore, the same control as when the operation of the drain pump 12 is stopped is also performed during partial load. That is,
Since the injection of the feed water heater drain into the feed water is restricted at partial load, the flow [F] value detected by the flow mountain detector 31 becomes smaller than the set value, and the opening degree of the control valve 23 is adjusted. It is controlled by a signal output from the device 26.

[Effects of the Invention] As explained above, according to the present invention, it is possible to prevent the dissolved oxygen content in the feed water sent to the nuclear reactor from deviating from the appropriate range due to changes in operating conditions. Therefore, a large amount of crud is not generated in water supply pipes, etc., and the increase in radioactive materials due to activation of crud is suppressed, which is highly effective in eliminating the causes of radiation exposure accidents.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing an embodiment of the feedwater dissolved oxygen regulating device according to the present invention, and Fig. 2 is a diagram showing the main equipment of a nuclear power plant and its accompanying feedwater heater according to the prior art. It is a system diagram showing drain system connection. 4...Condenser 6...Condensate purification device 8...Water pump 9...High pressure Feed water heater 11...Drain tank 12...Drain pump 13...Drain injection pipe 21... Oxygen storage device 22... Oxygen injection pipe 23... Control valve 24... First oxygen concentration detector 25.2
8...Comparator 26.29...Adjuster 27...Second oxygen concentration detector 30...
......Relay 31...Flow rate detector Applicant Toshiba Corporation Representative Patent attorney Sasu Suyama - Figure 1

Claims (1)

[Claims] (1) An oxygen storage device, a control valve installed in an oxygen injection pipe connecting this oxygen storage device and the downstream route of the condensate purification device, and a predetermined control valve that controls the detected dissolved oxygen concentration in the condensate. a first regulating means that compares the dissolved oxygen concentration with the dissolved oxygen concentration and outputs a control signal that determines the valve opening of the regulating valve according to the deviation;
The detected dissolved oxygen concentration of the feed water flowing through the downstream path of the high-pressure feed water heater is compared with a predetermined dissolved oxygen concentration, and a control signal is output that determines the valve opening degree of the control valve according to the deviation. a second regulating means; and a control signal for the regulating valve is transmitted from the one regulating means to the other regulating means based on the flow rate of the feed water heater drain flowing through the drain injection pipe connecting the drain tank and the suction side of the feed water pump. A water supply dissolved oxygen regulating device comprising switching means.