JPH049277B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method of operating a boiling water nuclear power plant, and in particular, a method suitable for preventing stress corrosion cracking of austenitic stainless steel in the primary system of a nuclear reactor. This article relates to a method for degassing dissolved oxygen in reactor water during reactor startup.

[Background of the invention]

Regarding the conventional degassing operation method at reactor startup, the dissolved oxygen concentration in the reactor water in the reactor pressure vessel is
An operating method is known in which the reactor output is increased after degassing to about 200 ppb or less. One method is to evacuate the inside of the reactor vessel using an inert gas, and the other is to evacuate the reactor under vacuum using the vacuum level of the main condenser of the turbine. The former method requires equipment for filling inert gas and equipment for extracting it, resulting in high costs, so it is not used much except in some plants. On the other hand, the latter method is being put into operation because it can be easily implemented by using existing vacuum equipment.
However, since the operating method utilizes the vacuum level of the main condenser, the reactor startup time will be longer, reducing the plant's equipment operating rate and causing a loss in power generation, so operation has to be continued. The drawback was that it did not provide any benefits. Among the conventional techniques, the operation-related equipment and operation method of the vacuum degassing method will be explained with reference to FIG. When degassing the dissolved oxygen in the reactor water 24 in the reactor vessel 1, first, the steam generated in the in-house boiler (H・B) is passed through the valve 17 through the pipe 18 to the high-pressure turbine 7 and the low-pressure turbine 8. Perform a ground seal. At the same time, in order to increase the vacuum in the main condenser 9, the air in the main condenser is pumped through the exhaust gas pipe 11 to the vacuum pump 12.
As a result, it is released into the main exhaust stack 13. When the vacuum capacity of the vacuum pump is reached, the starting ejector 14 is started to create a higher vacuum and parallel operation is performed. Thereafter, the vacuum pump 12 is stopped, and the vacuum is raised and maintained only by the starting ejector. In this case, the exhaust gas can be discharged to the main exhaust stack via the activated carbon adsorption tower. In this state, after sealing the reactor vessel, the main steam drain valve isolation valves 21 and 22 are opened, and the MS drain valve 23 is opened, thereby disconnecting the main condenser 9 and the reactor. The vessel 1 is brought into communication and the high vacuum of the main condenser is used to create a negative pressure in the reactor vessel gas phase section 25, thereby achieving degassing of the reactor water 24. Thereafter, the main steam isolation valves 3, 4 and 5 valves 6, 10 are opened to start the reactor and begin to raise the reactor water temperature.

In addition, when starting up, in order to equalize the temperature of the reactor water 24 and enhance the deaeration effect, the recirculation pump 20 is operated to stir the reactor water.

Note that when steam starts to be generated in the nuclear reactor, the evaporator 19 sends the generated steam to the pipe 18 to perform ground sealing of the turbine. At this stage, the valve 17 is closed.

The above driving operation is shown in Fig. 2. At the same time as the condenser vacuum pump is started, the vacuum begins to rise along the curve A line. After stopping the vacuum pump, open the MS drain valve and increase the vacuum inside the reactor vessel along curve B. Dissolved oxygen in the reactor water is degassed by maintaining a vacuum in the reactor vessel for approximately 3 hours. When the dissolved oxygen concentration in the reactor water falls below 200 ppb, the mode switch is activated and the control rods begin to be withdrawn, the reactor water temperature rises along curve C and the reactor output increases.

In the above operation, it takes about 5.5 seconds from starting the vacuum pump to turning on the mode switch.
It takes time. Of this time, 3 hours is the time required to raise the vacuum in the main condenser. This time was a drawback of the prior art, causing a reduction in the operating rate of the nuclear reactor.

[Purpose of the invention]

The purpose of the present invention is to reduce the operational time loss associated with the conventional vacuum degassing operation method by raising the vacuum of the main condenser and the reactor vessel at the same time. The purpose of this invention is to provide an operating method that shortens the start-up operation time and increases plant availability.

[Summary of the invention]

In order to achieve the above object, the present invention provides a boiling water nuclear reactor having a reactor vessel, a turbine, and a main condenser, in which the main condenser and the gas phase part of the reactor vessel are connected, and then the main In addition to creating negative pressure in the condenser, the coolant purification system of the reactor recirculation system is operated in conjunction with the operation of the reactor recirculation pump that stirs the reactor water in the reactor vessel, and purified water is pumped into the reactor vessel. Dissolved oxygen in the reactor coolant is removed by spraying it into the gas phase of the reactor, and then the reactor is started up and the output of the reactor is increased.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIG. The prior art and equipment are similar, and only the differences in procedure will be described. After confirming that the system configuration around the reactor pressure vessel and around the turbine has been completed, the main steam isolation valves 3, 4, and 5 are opened, the turbine bypass valve 10 is opened, and in-house steam is supplied from the pipe 18. Perform shaft sealing of the turbine gland. The vacuum pump 12 is started, and vacuum raising of the main condenser 9, the turbines 7 and 8, the main steam piping 2, and the reactor vessel gas phase section 25 is started at the same time. As the vacuum pump rises, the reactor vessel gas phase section 25 becomes under negative pressure, and the air in the gas phase section is purged. When the capacity of the vacuum pump 12 reaches its capacity limit, the starting ejector 14 is started to create an even higher vacuum. At this point, the vacuum pump stops, and the startup ejector alone raises the vacuum. At this point, the reactor vessel gas phase has reached a high vacuum of approximately 50 to 120 mmHgabs, and the supersaturated oxygen in the reactor water 24 gradually turns into gas, and the gas phase section 25 is degassed. It takes about two hours for the vacuum inside the reactor vessel and the supersaturated dissolved oxygen in the reactor water to reach concentration equilibrium. There is no need for further deaeration operations, and the dissolved oxygen concentration in the reactor water has already been reduced to below 200 ppb, so the reactor mode switch is turned on and control rod withdrawal begins.

When the temperature of the reactor water reaches 100° C. or more, steam is generated and the turbine bypass valve 10 is closed to start increasing the pressure of the reactor, pressurizing the reactor vessel 1 and raising the temperature. From this point on, the MS drain isolation valve 21,
22 is opened, and the MS drain valve 23 is opened to allow air to relax in the main steam pipe and discharge steam drain to the main condenser. In this case, operate according to the specified output increase procedure.

The above operating procedure is shown in FIG. As soon as the condenser vacuum pump starts, the condenser vacuum begins to rise according to curve A'. At the same time, the degree of vacuum in the reactor vessel also increases along curve B'. After starting the vacuum pump, deaeration of oxygen from the reactor water will be completed in about 2 to 3 hours, and the reactor will start up.

After that, the control rod was pulled out and the pressure was applied upward.
Output increases. Through this operation, as shown in Figure 4, the dissolved oxygen in the reactor water is vacuum degassed from the concentration of 5 ppm at atmospheric saturation to 0.2 ppm, that is, 200 ppb or less, and then the temperature is increased during startup. As a result, the equilibrium value G during rated operation is reached along curve D. With this degassing operation, the reactor can be started without passing through the stress corrosion cracking susceptibility region F of the austenitic stainless steel that constitutes the reactor primary system, and the integrity of the pressure boundary of the reactor can be maintained. In addition, if deaeration operation is not performed, curve E
This is not preferable because it has the following characteristics.

Now, the effects of the present invention include not only achieving the effect of degassing the upper air, but also making it possible to significantly shorten the start-up time when starting up the nuclear reactor, as shown in FIG. The critical path of the reactor startup process is the time between starting the condenser vacuum pump and starting the reactor mode switch. With the conventional technology, it took about 2.5 hours to raise the vacuum in the main condenser and about 3 hours to raise the vacuum in the reactor pressure vessel, for a total of 5.5 hours to start the reactor. On the other hand, according to the operation of the present invention, it was possible to raise the vacuum of the main condenser and the reactor vessel at the same time, so the time from starting the vacuum pump to starting the mode switch could be shortened to about 3 hours. In the case of a 1100MWe class plant, this 3hr reduction will result in an economic benefit equivalent to approximately 20.9 million yen per startup. If the plant is started up twice a year, the life of the plant is
Over a period of 30 years, it can bring about an economic effect of approximately 1.25 billion yen.

Another embodiment of the present invention will be explained with reference to FIG. Only the points that are different from those described in the embodiments of the present invention will be shown. Raising the vacuum of the main condenser 9 and the reactor pressure vessel 25 is started at the same time. Main condenser vacuum requirement is 90mmHgabs for turbine startup condition.
This value can be achieved by increasing the vacuum until the reactor pressure reaches the rated pressure. On the other hand, the degree of vacuum in the reactor pressure vessel needs to be raised to high vacuum as soon as possible, and reactor water must be degassed in a short time. Therefore, the present invention operates the reactor recirculation pump 20 and stirs the reactor water at the same time as the vacuum rises in the main condenser and reactor vessel. The purified circulating water is sprayed into the gas phase section of the reactor pressure vessel, increasing the gas-liquid contact area and enhancing the vacuum degassing effect. The reactor water taken out from the piping 26 is passed through the regenerative heat exchanger 28 and the non-regenerative heat exchanger 29 by the CUW pump 27.
The water purified by the purifier 30 is sprayed into the gas phase from the top spray nozzle 34 by opening the valve 33 through the pipe 32. By performing this operation, the time for dissolved oxygen in the reactor water to reach 200 ppb or less is shortened, so the reactor startup mode switch can be turned on quickly, and the startup time can be further shortened. In plants where the reactor vessel top spray nozzle is not connected to the CUW system, this can be done via the residual heat removal (RHR system) top spray nozzle. In this case,
Just start the RHR system pump and run it in top spray mode.

According to one embodiment of the present invention, the spray degassing effect of reactor water can reduce the degassing time, which is effective in shortening the start-up time.

Another embodiment of the present invention will be described with reference to FIG.
The present invention is an operating method that takes preventive measures into consideration in the unlikely event that the fuel in the reactor water is damaged. First, the presence or absence of fuel damage can be clearly determined by analyzing the nuclide in the reactor water while the plant is shut down. In this case, the vacuum rise in the reactor pressure vessel and main condenser is
Separately, the gas in the reactor pressure vessel should be treated in a gaseous radioactive waste treatment system.

Furthermore, before reactor startup, a nuclide analysis of the reactor water was carried out.
If the presence of rare gas is at background level, there is no problem by raising the vacuum of the reactor pressure vessel and the turbine main condenser at the same time. However, during the vacuum degassing operation, substances dissolved in the reactor water
It is necessary to consider the case where the gas comes out as a non-condensable gas. To this end, in another embodiment of the present invention, the vacuum pump 12 first increases the vacuum in the main condenser.
rises with At the same time, main steam line 2 and valves 3 and 4
5 and the turbine bypass valve 10 are opened to purge the gas phase air in the reactor pressure vessel.

In order to monitor radioactivity during the air purge, a sampling nozzle is provided at the reactor pressure vessel outlet of the main steam pipe 2 and guided to a radioactivity monitoring device 37 via a pipe 35 for continuous monitoring.

If radioactivity is detected, an alert is issued to the operator and the signal is used to activate the main steam isolation valve (MSIV).
3 and 4 are provided with an interlock for quick closing. When the MSIV is closed, vacuum degassing of the reactor pressure vessel cannot be achieved, so the vacuum in the main condenser 9 is increased first, the start-up ejector 14 enters independent operation, and the gas processing equipment 16 having an activated carbon adsorption tower is activated. After the MS drain isolation valves 211 and 22 are opened, the MS drain valve 2 is opened.
After the jogging operation in step 3, the MSIV is opened, the turbine bypass valve 10 is opened, and the vacuum rise in the reactor is resumed.

According to this embodiment, it is possible to prevent radioactive gas from being directly released into the stack, and vacuum deaeration of the reactor is achieved, so that the integrity of the boundary of the reactor primary system is ensured, and at the same time, It can prevent the release of radioactivity in the unlikely event.

〔Effect of the invention〕

According to the present invention, since the start-up time of the nuclear reactor can be shortened, the plant availability rate can be improved and the plant can be operated economically.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the system related to the operation of the present invention, Fig. 2 is a characteristic diagram explaining the vacuum degassing operation of the prior art, and Fig. 3 is a line diagram explaining one embodiment of the present invention. 4 is a characteristic diagram explaining the degassing effect of the present invention, FIG. 5 is a diagram explaining the effect of the prior art and the present invention, and FIG. 6 is a system diagram of another embodiment of the present invention. ,
FIG. 7 is a system diagram of still another embodiment of the present invention. 1... Reactor vessel, 9... Condenser, 12... Vacuum pump, 14... Starting ejector, 3, 4... Main steam isolation valve, 23... MS drain valve, 34... Top spray nozzle, 37... Radioactivity monitoring device , B... Reactor vessel vacuum degree, D... Reactor water dissolved oxygen concentration.

Claims (1)

[Claims] 1. In a boiling water reactor having a reactor vessel, a turbine, and a main condenser, the main condenser and the gas phase portion of the reactor vessel are communicated, and then the main condenser is brought into negative pressure. At the same time, in conjunction with the operation of the reactor recirculation pump that stirs the reactor water in the reactor vessel, the coolant purification system of the reactor recirculation system is operated to spray purified water into the gas phase part of the reactor vessel. A method of operating a nuclear reactor, characterized in that dissolved oxygen in a reactor coolant is removed while the reactor is being operated, and then the reactor is started up and the output of the reactor is increased.