JPH0221553B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for monitoring and controlling a coolant flow rate in a boiling water nuclear reactor.

(Prior art) In general, the power distribution of the fuel rods in the core of this type of nuclear reactor changes in a variety of ways, so setting a limit value for the calorific value distribution of the fuel rods prevents all possible abnormal transient operations in the power distribution. This is done on the assumption that the output distribution (design output distribution) has sufficient margin to include the output.

That is, the operation of a nuclear reactor is usually sufficiently flat, as evidenced by the relationship between the design power distribution curve and the typical power distribution curve of an actual reactor, such as the example shown in the graph of FIG. The system is operated with an output distribution with a sufficient margin.

That is, to explain the calorific value and distribution margin of a fuel rod using a formula, the boiling transition starting power in the design power distribution curve shown in the graph of Fig. 1, that is, the critical power (CP), and the actual fuel assembly The limit power ratio of the fuel assembly (hereinafter simply referred to as the limit power ratio) defined from the actual power distribution curve according to the output (CP
R.) is expressed as CPR=CP/ABP.

However, ABP indicates the output of the actual target fuel assembly.

Further, the above-mentioned critical power (CP) is calculated by an empirical formula using parameters such as the coolant flow rate, core temperature, voids and power distribution, and reactor pressure.
In other words, the above critical power ratio (CPR) is an index that indicates the thermal margin until the fuel assembly reaches boiling transition, and is the lowest among the critical power ratios (CPR) for each fuel assembly in the core. This is called the Minimum Critical Power Ratio (MCPR).

In this way, in actual nuclear reactor operation, the minimum critical power ratio operating control value (OLMCPR) is set so that the above-mentioned minimum critical power ratio (MCPR) does not reach boiling transition even during abnormal transient operation of the reactor.
The reactor is operated by adjusting the output level and core flow rate to a value that does not fall below. In setting this minimum output ratio operation control value (OLMCPR), the first
A design power distribution curve, shown in the graph of the figure, has been used, which has been shown by experiment to give a critical power ratio that is smaller than the power distribution typically found in practice.

On the other hand, conventionally, one means of output adjustment in this type of reactor operation is to keep the control rods constant during normal operation and adjust the flow rate of the core coolant, but the above OLMCPR setting Due to the assumption of the power distribution in this case, the flow rate adjustment range is reduced, which reduces the degree of freedom in reactor operation. For example, when adjusting the reaction change due to the advance of fuel in the above-mentioned nuclear reactor by the core flow rate, the reduction in the output adjustment range will shorten the operating period during which reactivity compensation can be performed due to the flow rate change.
As a result, in order to avoid thermal shock to the fuel as much as possible, it is necessary to reduce the output and change the position of the control rods frequently.

On the other hand, when the output is changed significantly, such as in load following operation, it is necessary to compensate for changes in Zenon reactivity to maintain the output at the planned level, but it is necessary to maintain the output at the planned level by Control rod operations should be avoided as much as possible, and reactor operating operations should be controlled by adjusting the core cooling flow rate, which results in favorable output changes in terms of fuel rod integrity.For this purpose, the range of coolant flow rate adjustment should be widened. It is preferable.

(Problems to be Solved by the Invention) However, in relation to the design power distribution, the coolant flow rate adjustment range of conventional nuclear reactors uses a power distribution that is uniformly set in the steady state of the reactor.
In addition, since the coolant flow rate control range is determined by determining the minimum critical power ratio operation control value (OLMCPR) at each predetermined operating point, there is more margin than necessary during actual reactor operation. As a result, the degree of freedom in reactor operation is severely restricted. In other words, in Figure 3, which shows the relationship between thermal output and core flow rate in the operating range of a nuclear reactor, when the reactor is at the operating point of 105% of the rated output and 100% flow rate, the curve suddenly changes due to abnormal transient operation. shows the curve showing the relationship between core thermal output and core flow rate when the core flow rate is reduced, and the boundary of the area included by 100% rated power. The operating control value of the minimum output ratio (OLMCPR) was set from several operating points on the curve, including at 105% of the rated output and 100% flow rate, assuming that abnormal transient operation occurs. It is something. An example of the power distribution used in this setting is shown in the graph of FIG. The operating range of a normal nuclear reactor is limited to the region included in the curve, regardless of the margin of the minimum critical power ratio (MCPR) relative to the above-mentioned OLMCPR. This results in the imposition of unnecessary safety on the nuclear reactor, which has disadvantages such as the degree of freedom in reactor operation being significantly hindered.

In order to solve the above-mentioned difficulties, the present invention expands the degree of freedom of operation by controlling the range in which the flow rate of the coolant can be adjusted using thermal restriction conditions, increases the range of adjustment of the flow rate of the coolant, and The present invention provides a method for monitoring and controlling a coolant flow rate with the aim of improving operational efficiency while ensuring reliability and safety.

[Structure of the invention]

(Means for Solving the Problems and Their Effects) The present invention provides flow rate monitoring of each detection value detected by a neutron flux detector, a flow rate detector, and a temperature detector provided in the core of a boiling water reactor. The flow rate monitoring device determines the axial power distribution of each fuel assembly from each detected value and the insertion position of the control rod in the core, and from this power distribution the limit of each fuel assembly is determined. The output ratio is calculated and the recirculation pump is linked with a signal calculated by comparing the minimum limit output ratio, which is the minimum value of the limit output ratio of each fuel assembly, with the operation control value of this minimum limit output ratio. By controlling the flow rate of coolant by operating the core flow rate control device, the application of automatic operation is greatly expanded.

(Example) Hereinafter, the present invention will be described with reference to an illustrated example.

2 to 4, reference numeral 1 denotes a light water type nuclear reactor (pressure vessel), and a core 1a in this reactor 1 includes fuel rods (constituting a fuel assembly) 2 and various A control rod 3 is installed, and the control rod 3 is movable up and down by a control rod drive device 4 installed below the reactor 1.
Further, a water intake pipe 6 connected to a water supply pump 5 is provided in the middle of the reactor 1, and a water intake pipe 6 is provided in the middle of the reactor 1.
A main steam pipe 8 connected to a turbine 7 is provided at the upper part of the main steam pipe 8 . Furthermore, this turbine 7 has
A generator 9 is directly connected, and the rotation of this turbine 7 allows the generator 9 to generate electricity. Furthermore, a condenser 10 is attached to the turbine 7, and the steam that has finished its work in the turbine 7 is condensed in the condenser 10.
The water is supplied to the water supply pump 5.

On the other hand, a coolant discharge pipe 12 of the recirculation pump 11 is provided at the lower part of the reactor 1, and a reflux pipe 13 of the recirculation pump 11 is connected to the upper part of the discharge pipe 12. . Further, a core flow rate control device 14 is connected to the recirculation pump 11, and the core flow rate control device 14 can control the recirculation pump 11 and adjust the discharge flow rate of the coolant. There is. Furthermore, a plurality of neutron flux detectors 15, a flow rate detector 16, and a temperature detector 17 are attached to the core 1a of the nuclear reactor 1, and each of the neutron flux detectors 15, flow rate detector 16, and temperature detector The device 17 has each lead wire 15a, 16a, 17
It is connected to the flow rate monitoring device 18 through a.
Further, the control rod drive control device 4 is connected to the flow rate monitoring device 18 through a lead wire 19, and the flow rate monitoring device 18 is connected to the core flow rate control device 14 through a lead wire 20 to determine the limit power ratio. They are connected in such a way that they can transmit the flow rate control signal calculated by.

Therefore, during normal operation of the nuclear reactor, each of the neutron flux detectors 15, flow rate detector 16, and temperature detector 17
Each signal detected by each lead wire 15a, 16a,
17a to the flow rate monitoring device 18;
Here, the heat balance due to the axial power distribution of each fuel assembly at the control rod position of the reactor core is determined,
Now the critical power ratio (CPR) of each fuel assembly
Calculate each of the determined critical output ratios (C.
Minimum critical power ratio (MCP), which is the minimum value of PR)
R.) and the operating limit value of the minimum critical output ratio (OLMC
The core flow rate control signal calculated by comparison with PR) is passed through the lead wire 20 to the core flow rate control device 1.
4, which controls the operation of the recirculation pump 11 and adjusts the flow rate of the coolant.

On the other hand, when the control rod drive control device 4 is driven, the position of the control rods 2 in the core 1a is displaced, so the displacement of the control rods 3 is transmitted to the flow rate monitoring device 18 through the lead wire 19. For example, the process amount is calculated by a separately installed process calculator, and based on this, each of the above-mentioned limit output ratios is newly calculated, and the above-mentioned minimum limit output ratio is determined from each of the above-mentioned limit output ratios. This minimum limit power ratio is compared with the operation control value of the minimum limit power ratio, and this calculated signal is used to adjust the core flow rate control device 14 through the lead wire 20.

Next, the present invention will be described in connection with an operating range limit curve using a design power distribution that sets an operating range on the high power, low flow rate side based on the core flow rate and thermal output shown in FIG.

That is, as an example, when the reactor is operating at 95% of the rated output and MCPR = 1.28, changes in the core reactivity can be controlled not by the fuel rods 3 but by adjusting the core flow rate. When attempting to compensate, the operating point is 71, as shown in Figure 3, and this is the reactivity compensation operation by reducing the core flow rate to perform constant output operation, that is, operating point 7.
1 → 72, or power increase operation due to increase in core flow rate, that is, operating point 71 → 73, but the minimum critical power ratio (MCPR) is
Looking at the relationship with the core flow rate, as shown in the graph of Fig. 4, each combined operation point 81→82 or 81→
83. This is calculated by the flow rate monitoring device 18 according to the present invention, and thereby the fourth
As shown in the figure, the core flow rate adjustment width (range) is limited between operating points 84→85.

This core flow rate adjustment range can be significantly increased compared to conventional systems of this type.

On the other hand, it is also possible to predict how the minimum critical power ratio (MCPR) will change when the core flow rate changes. It is done in the same way as a critical power ratio (CPR) calculation by a process calculator. That is, when the fuel rod output and the core flow rate change simultaneously, that is, in the operation prediction such as operating point 71 → 73 in FIG. 3, in the calculation method, the fuel rod output and the core flow rate are By changing the relationship from operating point 71 to 73 in Figure 3, the critical output ratio (CP
R.) By calculating the above operating point 73
Calculate the minimum critical power ratio (MCPR) of and obtain the MCPR of operating point 73. Also, as shown in operating points 71→72 in Figure 3, the output of the fuel rods does not change,
On the other hand, even in operations where only the core flow rate changes, it is possible to predict the MCPR at the operating point 72 in the same way.

Furthermore, as another means of predicting MCPR, we can empirically determine the change in MCPR per change in fuel rod output and the change in MCPR per change in core flow rate based on past operating records of nuclear reactors. , it can also be calculated quickly by storing this in advance and multiplying it by the difference between the output at the operating point to be predicted and the current output or core flow rate.

〔Effect of the invention〕

As described above, according to the present invention, the neutron flux detector 15 and the flow rate detector 16 provided in the core 1a
The detected values detected by the temperature detector 17 are sent to the flow rate monitoring device 18, and the axial power distribution of the fuel assembly is determined by the flow rate monitoring device 18 based on these detected values and the insertion position of the control rod in the core. is calculated, and each limit output ratio is calculated, and the recirculation pump 11 is controlled using a calculated signal that compares the minimum limit output ratio obtained from this limit output ratio with the operation control value of this minimum limit output ratio.
By controlling the flow rate of coolant by operating the core flow rate control device 14 that moves automatically, the scope of application of automatic operation can be greatly expanded, and the operating rate of the nuclear power plant can be improved. Can be done.

[Brief explanation of drawings]

Figure 1 is a graph showing the design power distribution curve of a nuclear reactor and a typical power distribution curve of an actual reactor;
The figure is a diagram showing the coolant flow rate control method according to the present invention, Figure 3 is a graph showing the operating range of operating points in the design power distribution curve according to the present invention, and Figure 4 is a graph showing changes in the operating point of the reactor. FIG. DESCRIPTION OF SYMBOLS 1... Nuclear reactor, 1a... Core, 2... Fuel rod, 3... Control rod, 4... Control rod drive device, 5... Water supply pump, 7
...Turbine, 11...Recirculation pump, 14...Core flow rate control device, 15...Neutron flux detector, 16...Flow rate detector, 17...Temperature detector, 18...Flow rate monitoring device.

Claims (1)

[Claims] 1 Send each detection value detected by the neutron flux detector, flow rate detector, and temperature detector installed in the core of the boiling water reactor to the flow rate monitoring device, and transmit the detected values and the control rods inside the core. The axial power distribution of each fuel assembly is determined from the insertion position of the fuel assembly using a flow rate monitoring device, and the critical output ratio of each fuel assembly is calculated from this output distribution. A signal calculated by comparing the minimum critical power ratio, which is the minimum value of the critical power ratio, with the operation control value of this minimum critical power ratio is used to operate the core flow control device linked to the recirculation pump to control the flow rate of the coolant. A method for monitoring and controlling a coolant flow rate, comprising: