JPS6034079B2 - Nuclear power plant output control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a condensed water atomic power plant (hereinafter referred to as a BWR power plant).

), and particularly relates to a method of maintaining the reactor output at a predetermined value by compensating for the influence of xenone (chemical symbol: Xe), which has negative reactivity. FIG. 1 is a schematic diagram of a BWR power plant according to the present invention.

In the figure, the steam generated in the reactor 1 is transferred to the steam control valve 10.
The steam is sent to the turbine 2 via the steam, where the heat energy possessed by the steam is converted into rotational energy for the turbine, and the generator 3 generates electricity. The steam is then converted to water in a condenser 4, which is then pumped into the reactor 1 by a condensate pump 5 and a feed water pump 7.
water is returned to the country as a water supply. This feed water is heated in a feed water heater 6 using extracted steam from the turbine 2 as a heating fluid. The reactor power of such a nuclear reactor 1 is usually adjusted by changing the insertion position of the control rod 9 or by changing the rotational speed of the recirculation pump 8 to change the recirculation flow rate. Control device 12 Recirculation flow rate control device 13
is a device that controls the device tread position or recirculation flow rate to a predetermined target value Ra or Wa. Further, the turbine control device 14, which is one of the main control devices, detects the turbine inlet pressure PT and the turbine speed NT so as to constantly maintain a balance between the reactor output of the reactor 1 and the load of the generator 3. The opening degree of the steam control valve 10 is adjusted to control the turbine steam flow rate. In a BWR power plant configured as described above, a typical conventional example of the process of starting up the furnace output from zero to the rated value is as follows.

FIG. 2 is a power control diagram of a known nuclear reactor showing the relationship between the recirculation flow rate W and the reactor power Q, as well as the position or pattern of the control rods. In this figure, if point ○ is the state before startup, first, the reactor output Q is kept at zero and only the recirculation flow rate W is increased, and after reaching the state at point A, the control rods are gradually withdrawn, and the reactor output Q to the state of point B. Thereafter, the recirculation flow rate W is increased to raise the furnace output Q to reach point C, which is the state of rated continuous operation, and this state is connected. In this rated operating condition, the recirculation flow rate W
is set for 100% flow rate, and the control rod insertion position (or insertion pattern) is set for 100% output.

Reactor startup requires 10 to 100 hours of operation, and the recirculation flow rate and control rod operations are performed in a predetermined order, and when all these operations are completed, the reactor is controlled so that it reaches the rated operating state point C mentioned above. be done. On the other hand, when a nuclear reactor is started, the amount of xenone (also called xenone poisoning) in the reactor, which has negative reactivity, changes.

For this reason, the reactor output is at the rated state (Fig. 2C) upon completion of startup.
Even if the recirculation flow rate and the control pole position are controlled in a predetermined order so that the recirculation flow rate and the control pole position are controlled in a predetermined order so that the amount of xenone changes, the reactor output gradually changes and becomes stable at, for example, point D in FIG. 2. Therefore, it is necessary to perform an operation to return to point C by controlling the reactor output at an appropriate time after a series of operations for startup are completed. However, at what point in Figure 2 the reactor output becomes stable depends on the operating process, etc., and the rate of change in Zenon varies, so it is difficult to compensate for load changes due to Zenon during the startup process. . There are three typical conventional methods for compensating for output changes due to the Zenon effect.

The first method is to maintain the rated output by manipulating the control rods, the second method is to maintain the rated output by manipulating the recirculation flow rate W (point C' in Figure 2), Method 3 reduces the recirculation flow rate once to bring it to point E, then inserts and withdraws the control rod to trace points F and B, and during this time cancels Zenon's bulging action and returns to point C. This is a method of putting it into a state. Among these, the first method, that is, the method of withdrawing the control rods, is for operational reasons that it is preferable to not operate the control rods as much as possible due to nuclear and thermal constraints such as fuel in the range where the reactor output is high. The second method, that is, the method of increasing the recirculation flow rate, has not been adopted due to safety reasons such as vibration of the nuclear reactor. The third method, that is, the method of significantly increasing or decreasing the furnace output, is mainly adopted. The third method is the first method implemented in a low output region. For the third method, which significantly increases or decreases the furnace power,
The furnace output Q is reduced to several tens of percent from the rated value, and then increased again to the rated value, forming a loop. However, if the cancellation of the turret effect is insufficient, it will take D, E, and B to reach point C in Figure 2. A loop similar to the trajectory of order C must be repeated. Furthermore, according to this method, the reactor output has to be changed significantly in consideration of the Zenon poisoning effect, and moreover, it is necessary to vary the reactor output slowly and rapidly over time, so it is easy to operate by controlling the control system or the recirculation flow rate. However, it also has drawbacks such as a long start-up time to reach the rated output and an inability to supply stable power to the power grid. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling the output of a nuclear power plant, which can compensate for the poisonous effect of Zenon through simple operations and shorten the time required to increase the reactor output to a set output.

The present invention can control the reactor output by changing only the temperature of the feed water without changing the position of the control rods or the recirculation flow rate, and moreover, this can sufficiently follow slow changes such as the Zenon effect. This is a reactor power control method that is characterized by the fact that changes in the reactor power due to the Zenon effect after the set power is reached are compensated for by controlling the feed water temperature. Hereinafter, a specific embodiment of the present invention will be described with reference to FIGS. 3 to 5.

Note that the same parts and elements as in FIGS. 1 and 2 are given the same reference numerals. It is already known that the output of a BWR also changes depending on the temperature of the water supply.

In other words, reduce (or increase) the feed water temperature under steady-state operating conditions.
As a result, the amount of voids in the reactor decreases (increases), the reactivity increases (decreases) due to the void reactivity effect, and the output increases (decreases). The present invention is an output control method that utilizes this phenomenon, particularly a method that compensates only for changes in output using the Zenon effect. An example of this is shown in FIG. The difference from the conventional configuration is that a feed water temperature control device 15 is newly installed, which compares the target value Qa of the furnace output, for example, the main steam flow rate, with the current value Q, and adjusts the extraction control valve 1 until they match.
1 is controlled to adjust the amount of heating to the water supply and adjust the temperature of the water supply. In this case, the feed water temperature control device 15 is designed to simplify the control by eliminating mutual interference with the control system control or recirculation flow rate control, and for the purpose of the present invention to cancel only the xenon effect. The feed water temperature control is prevented from operating during operation or recirculation flow rate control, or when reactor output fluctuates due to an accident or the like. In other words, feed water temperature control is performed only when Zenon compensation is required. A specific example of the feed water temperature control device 15 used in this embodiment is shown in FIG. The comparator 20 calculates the difference between the target value Qa and the current value Q of the furnace output, and if this difference is positive (or negative), the regulator 21 decreases (or increases) the opening degree of the air control valve 11. Lower (raise) the supply water temperature to make the output deviation (Qa-Q) equal to zero. In addition, in the device 15, in order to prevent the feed water temperature control device of the present invention from operating when the control rod is operated or when performing recirculation flow rate control, the OR gate 25, the relay coil 26, and the relay A contact 27 is provided, and when the recirculation flow rate control or control pole operation is performed by these, a signal is issued to the OR gate 25, and the OR gate 25 excites the relay coil 25 to open the relay contact 27. . Furthermore, if the deviation of the reactor output (Qa-Q) increases due to causes other than the Zenon effect, such as an accident, reactor safety may be compromised if the feed water temperature Tv is changed too much to reduce this deviation. Therefore, in FIG. 4, a dead zone 22 is provided, and when the water supply temperature TwP exceeds a predetermined width, a signal is sent to the OR gate 25 to open the relay contact 27. On the other hand, the sensitivity of the reactor output Q to changes in the feed water temperature TwF, aQ/6TwF, is mainly influenced by the feed water temperature T. The solid line in FIG. 5 is an example in which the sensitivity is normalized when the feed water temperature TwF is equal to the saturated water temperature Two of the reactor. From the figure, in order to stably control the reactor output by controlling the feed water temperature to compensate for the Zenon effect, the gain K of the regulator 21 of the feed water temperature control device 15 of this embodiment must be adjusted according to the feed water temperature TwF. I know what I need to fix. Therefore, the device 15 automatically corrects this gain K to the reciprocal of the sensitivity 6Q/aTwF, as indicated by the dotted line in FIG.
The overall sensitivity is constant regardless of the water supply temperature. The control method of this embodiment will be explained using FIG. 3 and FIG. 4, taking the time of nuclear reactor startup as an example. When increasing the reactor output to the rated output, first the recirculation flow rate control device 13 increases the rotational speed of the recirculation pump 8 to increase the recirculation flow rate to point A in FIG. The recirculation flow rate is maintained at point A, and the control rod 9 is withdrawn from the core by the control rod control device 12 to increase the reactor power Q to point B in FIG. When the reactor output Q reaches point B, the withdrawal of the control rod 9 is stopped. Thereafter, the recirculation flow rate is increased to bring the furnace output Q to point C, which is the rated operating state. When point C is reached, stop increasing the recirculation flow rate. After reaching point C, the relay contact 27 remains closed because control control and recirculation flow rate control are not performed. Although the furnace output Q begins to decrease due to the Zenon's effect as described above, the decrease in the furnace output Q can be compensated for by the action of the feed water temperature control device 15. That is, the deviation (Qa-Q) between the measured furnace output Q and the target value Qa of the furnace output is input to the regulator 21. Since the input deviation is a negative value, the regulator 21
The amount of citron vapor supplied to the feed water heater 6 is reduced by reducing the ratio of the citron air control valve 11. Therefore, the feed water temperature decreases, so the amount of voids in the reactor decreases, and the reactor output Q increases as described above. Such an operation makes it possible to compensate for changes in furnace power due to the Zenon lid effect. Further, if the reactor output fluctuates due to an accident or the like, the feed water temperature control according to this embodiment is essentially unnecessary.

F is an output output when the reactor output fluctuates due to an accident or the like, and opens the contact 27 via the OR gate 25 and the coil 26. The output F can be an output from an accident detection relay in a BWR power plant or a command to stop the water supply temperature by a BWR operator. Therefore, the feed water temperature control device in this embodiment can compensate for changes in reactor output due to Zenon. Further, according to this embodiment, the safety of the nuclear reactor is improved, and moreover, stable electric power can be supplied even during load following operation in which the reactor output changes significantly periodically. According to the present invention described above, the Zenon reed effect can be compensated for by simply adding a simple control such as feed water temperature control, and the time required to increase the reactor output to the set output can be significantly shortened.

The power control operation for increasing the reactor power to the set power is easy. In addition, in the present invention, when controlling the feed water temperature by changes in the reactor power, the steam flow rate is taken as the reactor power in the above explanation, but other factors such as neutron east in the reactor, which are equivalent to the reactor power, are used. may be used as the furnace output.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a schematic configuration of a BWR power plant according to the present invention, Fig. 2 is an output control diagram for explaining a nuclear reactor startup method, and Fig. 3 is a diagram showing the relationship between the present invention and a conventional example. FIG. 4 is a block diagram of a feed water temperature control device showing an embodiment of the present invention, and FIG. 5 is a diagram illustrating the sensitivity of reactor output change to feed water temperature. Explanation of symbols 1... Nuclear reactor, 2... Turbine, 3... Generator, 4... Condenser, 5... Condensate pump, 6... ...Feed water heater, 7...Water pump 8...Recirculation pump, 9...Control lever, 10...Steam control Valve, 11...
Yuzu control valve, 12... Control control device, 13.
...Recirculation flow rate control device, 14...Turbine control device, Ra...Target value of control lever position, Wa...
...Target value of recirculation flow rate, PT...Twin inlet pressure, NT...Turbine speed, 20...
...Comparator, 21...Adjuster, 22...
・Dead zone, 25...Order gate, 26...Relay coil, 27...Relay contact, K...Gain output diagram Fig. 3 *2 Fig. 4 Fig. S diagram

Claims (1)

[Claims] 1. Raise the reactor power to a predetermined value by a control rod withdrawal operation, and increase the reactor power to a set output exceeding the predetermined value by increasing the recirculation flow rate; After the reactor power reaches the set value, when the reactor power decreases from the set power due to the poisonous effect of Zenon, the temperature of the feed water supplied to the reactor is increased to reduce the reactor power to the A method of controlling the output of a nuclear power plant to increase it to a set value. 2. The output control method for a nuclear power plant according to claim 1, wherein the feed water temperature is controlled while the control rods and the recirculation flow rate control are stopped.