JPH0894793A - Start up method for natural circulation boiling water reactor - Google Patents

Abstract

PURPOSE: To prevent the occurrence of instable flow phenomenon in reactor start up and enable starting up reactor stably. CONSTITUTION: At core 2 outlet, a pressure gauge 25 and a temperature meter 26 are placed and at lower part of chimney 3 above the core 2, a pressure gauge 27 and a temperature meter 28 are placed so as to calculate the saturation pressure from the pressure gauges 25 and 27 and the temperature meters 26 and 28. When the core outlet becomes saturation state, the opening of a turbine bypass valve 19 or turbine control valve 11 is controlled to decrease the pressure in the pressure vessel so that the pressure in the lower part of the chimney 3 becomes the saturation pressure calculated from the temperature meter in the chimney 3 lower part. Besides, by controlling the withdrawal of the control rod 24 and increasing the reactor power, the chimney 3 part is quickly made to saturation state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for starting a natural circulation boiling water reactor in which a circulating flow rate of a coolant is secured by a difference in static head inside and outside the core.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional natural circulation boiling water reactor, in which 1 is a reactor pressure vessel (hereinafter,
It will be referred to as a pressure vessel).
And a cylindrical chimney 3 surrounding the reactor core 2 is installed, and a downcomer 4 is formed between the chimney 3 and the pressure vessel 1. Above the chimney 3 is a steam dome portion 5 in the upper plenum.

The cooling water 6 naturally circulates in the downcomer 4, the lower plenum 7, the core 2 and the chimney 3. The steam generated in the core 2 passes through the main steam pipe 8, flows through the main steam isolation valve 9, the turbine steam stop valve, and the turbine steam control valve 11 and is sent to the turbine 12. The steam after having worked in the turbine 12 flows through the water supply pipe 16 connected to the water supply pump 14 and the water supply stop valve 15 after being condensed in the main condenser 13, and is supplied to the pressure vessel 1 as cooling water. It has become.

A main steam drain pipe 18 having a main steam drain valve 17 is connected between the inlet side of the main steam isolation valve 9 and the main condenser 13, and the inlet side of the turbine stop valve 10 and the main condenser are connected. Turbine bypass pipe having turbine bypass valve 19 between 13 and
20 connected.

A drain pipe 21 which is a part of a coolant purification system is provided at the bottom of the pressure vessel 1, and the reactor water 6 extracted by the drain pipe 21 is heated by an electric heater or the like. The reactor water 6 sent to the exchanger 22 and heated therein is returned from the water injection pipe 23 and the water supply pipe 16 to the downcomer 4.

A control rod 24 is inserted into and removed from the core 2 to control the output of the core 2. Therefore, in the conventional natural circulation boiling water reactor having the above-mentioned configuration, the cylindrical chimney 3 surrounding the core 2 in the pressure vessel 1, the outer peripheral portion of the chimney 3 and the pressure vessel 1 are arranged.
The downcomer 4 is surrounded by and serves as a flow path for water as a coolant, and the coolant is circulated by using the ascending force of the buoyancy of water and steam in the chimney 3 and the water head pressure in the downcomer 4 as a driving force.

The method of starting the natural circulation boiling water reactor is as follows. First, the reactor water is heated to 80 ° C. by the heat exchanger 22 or decay heat. After evacuating the main condenser 13, the main steam drain valve 17 is opened to perform deaeration operation to remove impurities from the cooling water. After that, the control rod 24 is pulled out to make the reactor critical, and while the output is slowly increased, the temperature of the cooling water is raised and simultaneously the reactor pressure is increased.

[0008]

When the natural circulation boiling water reactor is started up, an unstable heat-hydraulic phenomenon may occur. The conditions under which this unstable flow phenomenon occurs are when the reactor pressure in the pressure vessel is low, the natural circulation flow rate is low, the core is saturated, and the chimney is in a subcooled state.

In the natural circulation boiling water reactor, in order to secure the natural circulation flow rate, the chimney 3 which is considerably high above the core 2 is used.
have. Assuming that the height of this chimney 3 is, for example, 10 m, its head pressure is 1 ata, the steam dome 5 part is atmospheric pressure, and the reactor water temperature is 100 ° C., the outlet of the reactor core 2, that is, the lower part of the chimney 3 Subcool degree is 20
It can be as high as ℃.

When the output of the nuclear reactor is increased, the temperature of the core portion where steam is generated first rises. Chimney 3
Since no heat is generated inside, the high temperature water flowing into the chimney 3 from the core mixes with the surrounding low temperature water, and the fluid temperature inside the chimney 3 is lower than that of the core, and remains in the subcooled state. When the power is further increased, the core is saturated at the outlet and voids are generated.

However, since the inside of the chimney 3 is still in a low temperature subcool state, this void disappears in the chimney 3. As a result, the subcooled water in the chimney 3 flows into the reactor water, causing flow vibration and output vibration. In natural circulation boiling water reactors, it is necessary to adopt a startup method that prevents the occurrence of such unstable flow phenomena.

FIG. 6 shows changes in main parameters when the natural circulation boiling water reactor is started, and FIG. 7 shows changes in fluid temperature in the core and chimney at that time. In FIG. 7, reference numeral 1 is the channel inlet water temperature, 2 is the upper plenum water temperature, 3 is the channel outlet, 4 and 5 are the saturation temperatures at the channel outlet and the upper plenum, t1 is the boiling delay time at a constant pressure, t
2 is the boiling delay time at the upper end of the channel, and t3 is the boiling delay time at the upper plenum. Here, the channel corresponds to the chimney 3 and the upper plenum corresponds to the steam dome 5.

As the reactor power increases, the reactor power and cooling water temperature increase. As you can see from Figure 7,
During this temperature rising process, a saturated state is first created at the core outlet and voids are generated. Next, the inside of the chimney 3 becomes saturated. The period in which the core is saturated and the chimney is in the subcool state is 1 hour at t3, and an unstable flow phenomenon may occur during this period.

Such an unstable flow phenomenon does not occur when the reactor pressure increases. Therefore, for example, Japanese Patent Laid-Open No. 5-
In the method for starting a natural circulation boiling water reactor as disclosed in Japanese Patent No. 72387, the water supply pipe 14 is used as shown in FIG.
A pressure tank 17 is installed in the pressure vessel 1 to pressurize the pressure vessel 1 from outside the pressure vessel 1 to increase the reactor pressure, and then the cooling water in the pressure vessel is changed from a single-phase flow state to a two-phase flow state. By doing so, the occurrence of unstable flow phenomenon is prevented. However, this starting method has a problem that it is not practical because the pressure tank 17 needs to be provided.

The present invention has been made to solve the above problems, and shortens the period in which an unstable flow phenomenon may occur at the time of starting a natural circulation boiling water reactor, thereby causing the unstable flow phenomenon. Another object of the present invention is to provide a method for starting a natural circulation boiling water reactor, which prevents the above-mentioned problems and enables stable start-up of the reactor.

[0016]

According to the present invention, a pressure gauge and a thermometer are installed at the core outlet, and a pressure gauge and a thermometer are installed below the chimney.
The saturation pressure is calculated from the thermometer, and the turbine bypass valve or turbine control valve is opened so that the pressure at the lower part of the chimney becomes the saturated pressure calculated from the thermometer at the lower part of the chimney when the core outlet becomes saturated. It is characterized by adjusting the pressure to reduce the pressure in the pressure vessel, or adjusting the withdrawal of control rods to increase the reactor power.

[0017]

[Action]

(1) A pressure gauge and a thermometer are installed at the core outlet, and a pressure gauge and a thermometer are installed at the lower portion of the chimney, and the saturation pressure is calculated from the thermometer. When the core outlet becomes saturated, the pressure at the lower portion of the chimney is the chimney. The main steam isolation valve is opened and the opening of the turbine bypass valve is adjusted to reduce the pressure in the pressure vessel so that the saturated pressure calculated from the lower thermometer is reached.

(2) The unstable flow phenomenon at the time of startup is when the core outlet is saturated and the lower part of the chimney is in the subcool state. The lower part of the chimney can be saturated by adjusting the turbine bypass valve.

(3) As a result, the period during which the unstable flow phenomenon may occur can be shortened, and the reactor can be stably started up. In addition, the lower part of the chimney can be saturated by adjusting the withdrawal of the control rod and increasing the reactor output.

(4) The main steam isolation valve and the turbine stop valve are opened so that the pressure in the lower portion of the chimney becomes the saturated pressure calculated by the thermometer in the lower portion of the chimney when the core outlet is saturated, and the turbine control is adjusted. Adjust the valve opening to reduce the pressure in the pressure vessel. When the core outlet is saturated, the control rod withdrawal is adjusted to increase the reactor output and saturate the chimney quickly so that the pressure below the chimney reaches the saturation pressure calculated from the thermometer below the chimney. Put in a state.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a method for starting a natural circulation boiling water reactor according to the present invention will be described with reference to FIG. FIG. 1 is a schematic system diagram showing a natural circulation boiling water reactor, a turbine system, and a feed water system for explaining the present embodiment.

In FIG. 1, a core 2 in which a large number of fuel assemblies are loaded in a pressure vessel 1 and control rods 24 are inserted and removed.
, A cylindrical chimney 3 is installed so as to surround the core 2, and a downcomer 4 is formed between the chimney 3 and the pressure vessel 1. Above the chimney 3 is a steam dome portion 5 in the upper plenum. The cooling water 6 in the pressure vessel 1 naturally circulates in the downcomer 4, the lower plenum 7, the core 2 and the chimney 3. The reactor power is adjusted by the control rod 24.

The steam generated in the core 2 flows out from the main steam pipe 8, flows through the main steam isolation valve 9, the turbine steam stop valve, and the turbine steam control valve 11 and is sent to the turbine 12. Turbine
The steam after driving the generator at 12 and working is the main condenser
After the water is condensed at 13, it flows through a water supply pipe 16 to which a water supply pump 14 and a water supply stop valve 15 are connected, and is returned to the pressure vessel 1 as cooling water.

Between the inlet side of the main steam isolation valve 9 and the main condenser 13, a main steam drain pipe 18 having a main steam drain valve 17 is branched and connected from the main steam pipe 8, and the turbine is also connected. Between the inlet side of the steam stop valve 10 and the main condenser 13, a turbine bypass pipe 20 having a turbine bypass valve is branched and connected from the main steam pipe 8.

On the outlet side of the core 2, a core outlet pressure gauge 25 and a core outlet thermometer 26 are installed, and the chimney 3 above the core 2 is installed.
A lower chimney pressure gauge 27 and a lower chimney thermometer are installed in the lower part of the, and these pressure gauges 25, 27 and thermometers 26, 28 are connected to a controller 27 to input respective signals. Meanwhile, the controller
The output signal of 27 is output to the main steam isolation valve 9 and the turbine bypass valve 19.

Here, the turbine stop valve 10, the turbine control valve 11 and the feed water stop valve 15 are closed, and the main steam isolation valve 9, the main steam drain valve 17 and the turbine bypass valve 19 are open. .

However, in the initial stage of start-up, which is the object of this embodiment, the steam generated in the core flows to the main condenser 13 through the main steam drain pipe 18. In a state where the reactor pressure is 0.5 MPa or more, which is outside the scope of the present invention, the steam generated in the core 2 flows to the main condenser 13 after passing through the main steam isolation valve 8 and then the turbine bypass valve 19. .

A pressure gauge 25 and a thermometer 26 are provided at the outlet of the core 2, a pressure gauge 27 and a thermometer 28 are provided below the chimney 3, and a pressure gauge,
A controller 29 for calculating the saturated pressure from a thermometer is installed. The controller 29 compares the pressure at the outlet of the core 2 with the saturation pressure calculated from the thermometer, and determines that the core outlet is saturated when the former value and the latter value become equal.

Further, the lower pressure of the chimney 3 is compared with the saturated pressure calculated from the thermometer, and when the former value and the latter value become equal, it is determined that the lower part of the chimney 3 is saturated. . When the controller 29 determines that the core outlet is saturated, the main steam isolation valve 9 is fully opened, and the opening degree of the turbine bypass valve 19 is controlled to control the chimney 3
Adjust so that the bottom of is saturated. According to the present embodiment, the period during which an unstable flow phenomenon may occur can be shortened, and the reactor can be stably started up.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals, and the description of the overlapping parts will be omitted. The second embodiment is different from the first embodiment in that the turbine bypass valve 19 and the water stop valve 15 are closed, the main steam isolation valve 9, the turbine steam stop valve 10, the turbine control valve 11 and the main steam drain valve 17 are closed.
Is open. The output signal of the controller 29 is input to the main steam isolation valve 10, the turbine steam stop valve 10 and the turbine steam control valve 11.

In the second embodiment, when the controller 29 determines that the core outlet has become saturated, the main steam isolation valve 9 and the turbine stop valve 10 are fully opened, and the opening degree of the turbine control valve 11 is changed. It controls and adjusts so that the lower part of the chimney 3 may be saturated. As a result, the period during which the unstable flow phenomenon may occur at the time of starting the reactor can be shortened.

Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment differs from the first embodiment in that only the main steam drain valve 17 is opened and all other valves 9, 10,
19 and 15 are closed. The other parts are the same as those in the first embodiment, and the description thereof will be omitted.

In the third embodiment, the withdrawal of the control rod 24 is controlled to increase the reactor power, and the lower portion of the chimney 3 is adjusted to be saturated. This has the same effect as that of the first embodiment.

FIG. 4 shows the chimney lower temperature and core outlet temperature of the present invention described in FIGS. 2 to 3 and the conventional example in comparison with each other in relation to temperature and time from start-up. As is apparent from FIG. 4, according to the embodiment of the present invention,
The period T3 during which the unstable flow phenomenon may occur at the time of starting the natural circulation boiling water reactor can be shortened, and the stable start-up of the reactor becomes possible.

[0035]

According to the present invention, a pressure gauge and a thermometer are installed at the core outlet, and a pressure gauge and a thermometer are installed below the chimney, and the saturation pressure is calculated from the thermometer, and the core outlet becomes saturated. At times, adjust the opening of the turbine bypass valve or turbine control valve so that the pressure under the chimney reaches the saturation pressure calculated from the thermometer under the chimney, and lower the pressure in the pressure vessel, or Adjusting the withdrawal and increasing the reactor power.

As a result, the lower part of the chimney can be quickly saturated, and as a result, the conditions under which this unstable flow phenomenon occurs (the core outlet is saturated and the chimney part is unsaturated) are satisfied. This can be avoided, and the period during which the unstable flow phenomenon may occur can be shortened.

[Brief description of drawings]

FIG. 1 is a system diagram for explaining a first embodiment of a method for starting a natural circulation boiling water reactor according to the present invention.

FIG. 2 is a system diagram for explaining a second embodiment of a method for starting a natural circulation boiling water reactor according to the present invention.

FIG. 3 is a system diagram for explaining a third embodiment of a method for starting a natural circulation boiling water reactor according to the present invention.

FIG. 4 is a characteristic diagram showing the effects of the present invention and the conventional example in comparison with each other in the relationship between temperature and time from startup.

FIG. 5 is a system diagram for explaining a method for starting a conventional natural circulation boiling water reactor.

FIG. 6 is a characteristic diagram showing changes in main parameters of a conventional natural circulation boiling water reactor.

7 is a characteristic diagram showing changes in coolant temperature in the core and chimney in FIG.

[Explanation of symbols]

1 ... Reactor pressure vessel, 2 ... Reactor core, 3 ... Chimney, 4 ... Downcomer, 5 ... Steam dome part, 6 ... Cooling water, 7 ... Lower plenum, 8 ... Main steam pipe, 9 ... Main steam isolation valve, 10 ... Turbine steam stop valve, 11 ... Turbine steam control valve, 12 ... Turbine, 13 ... Main condenser, 14 ... Water pump, 15 ... Water stop valve,
16 ... Water supply pipe, 17 ... Main steam drain valve, 18 ... Main steam drain pipe, 19 ... Turbine bypass valve, 20 ... Turbine bypass pipe, 21 ... Drain pipe, 22 ... Heat exchanger, 23 ... Water injection pipe, 24 ...
Control rod, 25 ... Core outlet pressure gauge, 26 ... Core outlet thermometer, 27
… Chimney bottom pressure gauge, 28… Chimney bottom thermometer, 29…
Controller.

Claims (5)

[Claims] 1. A method for starting a natural circulation boiling water reactor, comprising a chimney in a pressure vessel, a reactor core arranged in the chimney, holding cooling water in the chimney, and generating steam inside. When the temperature of the cooling water in the pressure vessel is raised, the outlet of the core is in a saturated state, and the period in which the chimney is in an unsaturated state is shortened, or
Alternatively, when the core outlet is saturated, the reactor pressure is reduced to maintain the chimney in a saturated state, the core outlet is in a saturated state, and the chimney is in an unsaturated state. A method for starting a natural circulation boiling water reactor characterized by shortening the period. 2. When the outlet of the core becomes saturated, the reactor output is increased to maintain the inside of the chimney in a saturated state, the outlet of the core is in a saturated state, and the inside of the chimney is not yet saturated. The method for starting a natural circulation boiling water reactor according to claim 1, characterized in that the period of the saturated state is shortened. 3. The method for starting a natural circulation boiling water reactor according to claim 1, wherein the reduction of the reactor pressure is performed by opening a main steam isolation valve and adjusting and controlling an opening of a turbine bypass valve. . 4. The method for starting a natural circulation boiling water reactor according to claim 1, wherein the reduction of the reactor pressure is performed by opening a main steam isolation valve and adjusting and controlling an opening of a turbine control valve. . 5. The method for starting a natural circulation boiling water reactor according to claim 1, wherein the increase of the reactor power is controlled by adjusting the pulling out of the control rod.