JPS5916674B2 - Reactor power control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a reactor power control device for a reactor recirculation flow rate control system for a boiling water nuclear power plant.

■0 [Technical background of the invention and its problems] Conventionally, there are two types of reactor power control in boiling water nuclear power plants: one by operating one control rod, and the other by controlling two reactor recirculation flow rates. Different methods are used depending on the operating stage of the plant.

5. Except for adjusting fuel combustion conditions during plant start-up or long-term plant operation, a method based on reactor recirculation flow rate control is used during normal plant operation, and it is not necessary to change the output. This is done manually or automatically following requests from the power grid.

FIG. 1 shows a conventional reactor power control device that controls the reactor power in accordance with requests from the power system. This reactor output control device receives the power system response control circuit 1 and its output change request signal, and controls the increase or decrease of the reactor core flow rate by changing the speed of the recirculation pump or the opening degree of the flow rate adjustment valve of the recirculation loop. Reactor recirculation flow control unit 2 that outputs a request signal to operate the
and a reactor recirculation flow rate operation section 22. The operation of the power system response control circuit 1 is to detect frequency fluctuations in the power system, perform automatic frequency control operation (AFC operation) to control the output of the nuclear power plant in a direction to suppress the fluctuations, and plan power supply and demand distribution for the power system. The load setting 13 of the turbine generator is automatically set based on the intermediate supply command 12 based on the above, and consideration is given so that the plant output follows it. The deviation of the system frequency fluctuation from its target value is calculated, and this is combined with the load setting value to convert it into an appropriate required value of plant output, so that the actual reactor output can correspond to the required value. The turbine inlet pressure regulator output 14, which is an index, is subjected to a comparison calculation, and the output demand deviation signal, which is the result, is sent to the reactor recirculation flow rate control unit 2 via the output demand deviation limit 15.
A recirculation flow rate change request signal is applied to the recirculation flow rate operation unit 22 through the recirculation flow rate main controller 21 .
Changing the recirculation flow rate changes the core flow rate, and as the core flow rate changes, the neutron moderator density in the core changes, and the reactor thermal output changes accordingly, increasing the turbine generator power throughout the reactor process. Output changes. Through this process, the control system continues the follow-up operation until the output request deviation signal of the power system response control circuit 1 disappears. However, in recent years, as the operational experience of atomic couplets has increased, consideration has been required for operations that involve changes in reactor output from the perspective of preventing fuel damage, and considerations that are commensurate with the thermal state and thermal history of the fuel have been required. An automatic control system for reactor recirculation flow rate corresponding to this has not been established.

In other words, in the current operation that takes into account the prevention of nuclear fuel damage, changes in the thermal state of the reactor fuel are detected and corrections are made each time using process computers, which can sometimes involve trial and error. Nuclear reactor operation control that takes into account the prevention of nuclear fuel damage requires long calculations, and the work of making full use of process computers places an excessive burden on operators.

In addition, as the number of nuclear power plants increases in the future, it is expected that there will be an increasing demand for nuclear power plants to be integrated into the power grid and operated in response to the system, and the thermal restrictions necessary to prevent nuclear fuel damage will be taken into consideration. Output control automated operation of nuclear power plants is a problem that must be solved. In this way, in the conventional reactor power control system, in order to prevent damage to nuclear fuel, the output upper and lower limit limiters 21 installed in the recirculation flow rate main controller 21 are set at the maximum allowable value of the average power of the reactor core.
However, there was a problem in that no consideration was given to the operation commensurate with the thermal state and thermal history of the fuel in each part of the core mentioned above.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and is a nuclear reactor that follows and controls nuclear reactor output in response to requests from the power system while prioritizing damage prevention to nuclear fuel according to the thermal state and thermal history of the nuclear fuel. The purpose is to provide a furnace output control device.

[Summary of the invention]

In order to achieve this object, the nuclear reactor power control device according to the present invention includes a neutron flux detection means for detecting the neutron flux density in each region of the core of a nuclear reactor, and a neutron flux density detected by the neutron flux detection means. a calculation means for calculating the maximum linear power density in each region based on the above, a first power increase means for increasing the output in accordance with a request from the electric power system, and a rate of increase that is such that the nuclear fuel rods of the reactor are not destroyed. a second power increasing means for performing a thermal learning operation to thermally adapt the nuclear fuel rods by increasing the power in the nuclear fuel rods; and storing a maximum linear power density distribution indicating the maximum linear power density that each of the regions can reach. If the maximum linear power density in each region determined by the storage means and the calculation means is lower than the maximum linear power density distribution stored by the storage means, the output is increased by the first output increase means, and the Output control means for increasing the output by the second output increasing means when any of the maximum linear power densities in each region determined by the calculation means exceeds the maximum linear power density distribution stored by the storage means. When the output is increased by the second output increasing means and a thermal learning operation is performed, the maximum linear output density distribution stored in the storage means is changed to the maximum linear output reached by this thermal learning operation. The present invention is characterized by comprising an updating means for updating the density distribution.

[Embodiments of the invention]

Thermal Learning Operation Before explaining the embodiments of the present invention, problems related to prevention of damage to nuclear fuel and an operation method for preventing such problems will be described.

Changes in the power output of a nuclear reactor are brought about by changes in the heat output generated by the nuclear fission reaction of the fuel, but due to the structure of the fuel rod, there is a linear power density (the heat output generated per unit length of the fuel rod). When the threshold value is exceeded, the fuel pellets on the cylinder and the sheathing material surrounding them interact (hereinafter referred to as PCI) due to a sudden increase in the linear power density, and the degree of interaction exceeds a certain limit. It is known that this can cause fuel rod damage. However, as mentioned above, even if the linear power density of the fuel exceeds the threshold, it is possible to cause the fuel to experience a slow and predetermined power increase process, and then maintain that thermal power density distribution for a predetermined period of time after reaching the target state. to thermally blend the fuel pellets and cladding material. This operation process is called fuel thermal learning operation (hereinafter referred to as PC operation), and after it is achieved, the distribution of fuel linear power density at the time of achievement is stored in the process computer as a registered value (hereinafter referred to as PC envelope). Then, when the reactor power changes thereafter, the PC envelope becomes the maximum limit value for the linear power density at each part of the fuel core, and if it is within that thermal limit value, a relatively high speed linear power density can be achieved. It is known that nuclear fuel damage is unlikely to occur even if the reactor output is freely varied within the rate of increase limit. Outline of Nuclear Reactor Power Control Device FIG. 2 shows a nuclear reactor power control device according to an embodiment of the present invention.

As before, the power system response circuit 1 outputs an output demand deviation signal based on the frequency fluctuations of the six systems and the intermediate supply command, and the reactor recirculation flow rate control unit 2 outputs an output signal according to this output demand deviation signal. is input to the output control section 30. In-core output monitor system 3 taken into process computer 31
The measurement data of 2 is also taken into the dedicated computer 33, which is the central part of the control device of the present invention, which is connected to the process computer by a data bus (data signal transfer path).
3 calculates the distribution of the linear power density in each part of the fuel in the reactor core using various parameters necessary for calculating the linear power density of the fuel sent in advance from the process computer 31 based on the information.

The dedicated computer 33 performs necessary logical operations based on the monitoring results while referring to various information from the process computer 31, and outputs the results as a control command signal for the reactor recirculation flow rate. This command signal is sent to a reactor power control effect signal generator (hereinafter referred to as SPCD) 34, which converts it into a signal suitable for input to a conventional recirculation flow control system, and SPCD 34 generates the required operating signal. It is input to the recirculation flow rate operation section 22. The automatic follow-up circuit 36 may control the SP depending on the control command of the dedicated computer 33 during the above-mentioned AFC operation.
The output of the CD 34 and the output of the recirculation flow rate control system 2 are different from each other, and when the output of the SPCD 34 is switched to a control command that follows the output of the control system 2 due to changes in the thermal output distribution of the fuel from this state, This discrepancy causes disturbance, so this circuit is designed to avoid this, and SPCD controls the control system output only when the control system output is limited by a control command during AFC operation.
It operates to follow the output of 34. Specifically, the SPCD 34 is connected to the output side circuit of the recirculation flow rate main controller 21 shown in FIG.
It receives a reactor power control command signal based on the monitoring result of the thermal power density distribution of the fuel phase from the reactor, and adjusts the input signal of the upper control circuit according to this command signal. FIG. 3 shows the input paths for various output control command signals from the dedicated computer 33 and the circuit configuration of the SPCD 34.

The SPCD 34 compares the input signal from the recirculation flow rate controller 21 with its own output signal using a comparator 34A, and if there is a deviation between them, an increase/decrease determiner 34B determines whether the change is an increase or decrease request. , Logic Gate 34C
When the deviation is zero, that is, when the output of the SPCD 34 matches its input, no change signal is output. logic gate 34c
In addition to these change signals from the increase/decrease determiner 34B, three types of similar signals such as increase/decrease/retention are also added from the dedicated computer 33, and the signal from the dedicated computer 33 is always given priority at the input section. The circuit is set up so that it can be input. In addition to the change signal, the logic gate 34C receives a clock signal that triggers and operates the gate circuits for increase and decrease through the switching circuit 34D. A change signal is applied to increment/decrement counter 34E. This increment/decrement counter 34E starts accumulation when a change signal is applied, and in response to each increment/decrease change signal, addition/subtraction is applied to the output value held in the counter 34E until then using a clock signal. It is executed a number of times according to the pulse frequency of
The higher the pulse frequency of the clock signal, the higher the count rate, that is, the faster the output change rate of the counter 34E becomes.

The output value of the counter 34E is converted into an analog signal by a D/A signal converter 34F, and then passed through a power amplifier to generate an output signal. The clock signals are provided from a first internal clock 34F and a second internal clock 34G provided inside the SPCD 34, which generate pulse signals at a constant frequency per unit time, and from a clock signal generator of the dedicated computer 33.

The first internal clock 34F generates a high-frequency pulse signal so that the output signal can immediately respond to the input signal when there is a deviation between the input and output of the SPCD 34, and the second internal clock 34G responds to special commands from the dedicated computer 33. Generates a pulse signal with a predetermined frequency. Further, the clock signal generator of the dedicated computer 33 generates a pulse signal with a constant frequency or a variable frequency depending on the result of monitoring the thermal power density distribution of the fuel. Operation of the reactor power control device Next, the reactor power control device 30 according to the present invention having the above configuration.
Explain the operation.

First, the action of the dedicated computer command signal of the SPCD 34 is such that, as will be described later, one output signal always instantaneously follows the input signal (hereinafter referred to as input tracking mode) according to the monitoring result of the thermal output density of the fuel from the dedicated computer 33. ) and
The 2nd output signal operates to increase/decrease according to the clock signal from the computer 33 (hereinafter referred to as ramp change mode), and the 3rd output signal operates according to the command from the computer 33 regardless of the presence or absence of a deviation in the input/output signal. The operation is held (hereinafter referred to as change prevention mode), and the 4 output signals are decreased at a predetermined rate of change (hereinafter referred to as forced reduction mode) according to instructions from the computer 33, and in the end four types of operation are performed. conduct.

In FIG. 3, these output signals are input to the input following mode command output circuit 33A and the lamp change mode command output circuit 33A.
B. It is sent from the change prevention mode command output circuit 33C, the forced decrease mode command output circuit 33D, and the increase/decrease command output circuit 33E, and each output circuit is connected to the lamp output increase/decrease rate calculation circuit 33.
F and the PC creation mode circuit 33G.

A method for monitoring the thermal output distribution of nuclear fuel, and a method for monitoring the thermal output distribution of the fuel using the dedicated computer 33 for automating the above-mentioned PC operation and AFC operation that prioritizes nuclear fuel damage prevention, and a method for controlling the nuclear reactor output based on the monitoring method. The action of generating the signal is as follows.

In other words, in order to make these automated operations useful, one thing is to use a dedicated computer 33 to respond to changes in the reactor process.
The thermal power density distribution of the fuel must be monitored accurately, and the monitoring must be sufficiently traceable over time. As a measure to solve this problem, the dedicated computer 33 collects neutron flux detection data (hereinafter referred to as LPRM readings) at each location in the core to the extent that it can sufficiently track changes in the thermal power distribution of the core, which is expected to be the fastest during AFC operation. ), and based on the samples, it is necessary to calculate the linear power density distribution of the fuel in the reactor core in real time with the required accuracy using required parameters that have been previously taken in from the process computer 31. For this purpose, the dedicated computer 33 is equipped with an input channel for taking in data of LPRM readings by high-speed sampling, and is also provided with an approximate calculation program that processes the fuel linear power density distribution at high speed based on the data. Since means for importing process data into a computer by high-speed sampling are well known, a method for performing high-speed arithmetic processing using LPRM reading data will be described here.

In the core power monitoring system of a boiling water reactor, conventionally, as shown in FIGS. 4 and 5, neutron flux detectors (hereinafter referred to as LPRMs) 41 in the local core are located at four points in the axial direction of the core;
In terms of the core cross section, the linear power density of the fuel loaded in the four fuel assemblies 42 (several tens of fuel rods packed together and loaded into a prismatic storage container) is calculated by taking advantage of the symmetry of the core configuration. Responsible for monitoring distribution. In addition, in FIG. 5, 43 is a control rod. However, in order to monitor the linear power density distribution of fuel from conventional LPRM readings, first
When calibrating M, the continuous output distribution in the axial direction is monitored by scanning the movable in-core probe system (hereinafter referred to as TIP) in the LPRM guide tube arranged as shown in FIG. Store it as a base output distribution so that the reading at each position in the axial direction of the LPRM matches the TIP reading, and use the process computer 31 to calculate the LPR.
The axial output distribution is calculated by performing a correction calculation based on the deviation between the M reading value and the base output distribution, and the output distribution of the four fuel assemblies 4 is calculated.
Taking into account the cross-sectional power distribution in 2, each fuel is The maximum linear power density of the fuel is calculated for each axial position of the assembly 45, and is used to monitor the linear power density of the fuel at each position within the core.

However, in a boiling water reactor, the control rod pattern is constant, and when the reactor output is changed by changing the core flow rate due to recirculation flow rate control, the output in the upper part of the core gradually decreases as the core flow rate increases. Moreover, it is known that the power increases almost uniformly, and the degree to which parameters that change with changes in core flow rate, such as board distribution and channel flow rate, affect the local power distribution of each fuel assembly 42 is small.

Therefore, the simple calculation method according to the present invention divides each LPRM detector into four in the axial direction of the reactor core, and divides each detector into four adjacent ones in cross section.
A local area belonging to the fuel assembly 42 of the body is set as a unit to be monitored for the linear power density of the fuel, and each unit area (hereinafter LPRM
Calculate the conversion coefficient between the LPRM reading value and the maximum linear power density in the area (referred to as area), and store it once in the dedicated computer.From then on, the dedicated computer will use the conversion coefficient to calculate the LPRM reading value from time to time. The maximum linear power density in the above-mentioned LPRM region is monitored throughout the entire core.

As a result, the linear power density distribution of the fuel in the reactor core can be calculated using PRM readings and a simple calculation method in a very short amount of calculation processing time, making it possible to calculate the linear power density distribution of the fuel in the reactor core, which is necessary for automation of PC operation or AFC operation. It becomes possible to give real-time commands to the output control system.

Nuclear fuel monitoring data processing Figure 6 is a flowchart of calculation processing for giving automatic power control commands for the reactor using the dedicated computer 33 for PC operation and AFC operation based on the linear power density distribution monitoring of the fuel using the above-mentioned simple calculation method. show.

LP of each part of the core captured by high-speed sampling
The maximum linear power density (hereinafter referred to as LP) of each LPRM region is calculated from the RM reading value using the calculation method described above, and each LP
It is determined whether or not even one fuel linear power density threshold A (KW/Ft) that must be followed in the above-mentioned PC operation is exceeded when viewed in the entire core area. If all LPs are less than or equal to A, the control restriction on the recirculation flow rate control system is released,
An input follow-up mode command is given to the SPCD 34.

If even one LP exceeds A, it is determined whether the PC envelope is valid at that point based on information from the process computer, and if it is not valid, the automatic control mode of PC operation (
Issue a command (hereinafter referred to as PC creation mode). If the PC envelope is valid, each LP value is compared with the PC envelope (an upper limit value of linear power density, referred to as PCE) of each corresponding LPRM area based on information transferred from the process computer. However, all LPs are below PCE and the average thermal output AP of the core is the target output F for PC operation.
If it is below AP, an input follow-up mode command is given to the SPCD 34.

On the other hand, when AF reaches FAP, changes in the recirculation flow rate are prevented.

On the other hand, when the SPCD 34 is in the input follow-up mode, the output of the main controller 21 in FIG.
Since the main controller 21 is automatically set (contact A is closed), the reactor output is controlled in response to the power system.

In addition, if one or more of each LP exceeds the PCE, for the one with the largest excess, if it is within the allowable range β, the recirculation flow rate is prevented from changing in order to stop the reactor from rising. is given to the SPCD 34 only when the deviation polarity determination signal of the AFC control circuit is an increase request, and when it exceeds the width β, the AFC control circuit issues a command to reduce the recirculation flow rate at a predetermined speed (i.e., a forced flow rate reduction command). The deviation polarity determination signal is given to the SPCD 34 only when an increase is requested. Here, if the deviation polarity determination signal is a reduction request, an input follow-up mode command is given to the SPCD regardless of the magnitude of the excess.

If a flow rate change prevention or flow rate forced reduction command is output based on the monitoring results of fuel linear power density distribution during AFC operation,
Since the SPCD output does not follow the output of the main controller 21,
Depending on the change in the request signal from the power system response control circuit 1, it is assumed that the SPCD output and the output of the main controller 21 may show a large discrepancy, and in such a situation, the output control command is set to the input follow-up mode. When switched, it causes harmful disturbances to the reactor.

In order to avoid this, as shown in Fig. 6, a contact signal is output when the AND condition of the condition signal of either the flow rate change prevention or flow rate reduction command and the condition signal of AFC operation (automatic setting of the main controller 21) is established. The automatic tracking circuit 36 shown in FIG.
At the same time, the automatic follow-up circuit 36 is routed through the signal route, and the automatic follow-up circuit 36 operates so that the output of the main controller 21 immediately follows the output of the SPCD 34. This action prevents the occurrence of harmful disturbance when switching the mode of the output control command of the dedicated computer 33, so that the output control command of the dedicated computer 33 is faithfully transmitted to the recirculation flow rate operating section 2.
given to 2. Operation in the PC creation mode Next, the operation in the PC creation mode will be explained with reference to the flowchart shown in FIG.

For each LP that exceeds the above-mentioned A (KW/Ft), the average increase in unit time Δt suitable for PC operation monitoring is 2′,2;=2? J, which is the limit value 1 (KW/F
t/Hr), and determine whether it exceeds 1Vax.
(If j f → is less than I, it is determined that the reading value AP of the core average power monitor has not reached the reactor output FAP aimed at by PC operation, and the reactor output is gradually increased. A command is given to SPCD 34 to request an increase in the recirculation flow rate (ramp up mode).

If ΔLP-Max(-7〒-1) exceeds I, Max(+.) is set as the allowable limit value exceedance coefficient δ (>1, determined by taking into account fluctuations in the climbing speed). If it is less than δ・I, a command is issued to prevent the recirculation flow rate from changing, and if it exceeds δ・I, a command is issued to reduce the recirculation flow rate at a predetermined speed.
Give to PCD34.

Also, if Max (Nol product L) is less than the limit value 1, AP =
If it becomes FAP, it prevents changes in the recirculation flow rate and maintains the reactor output. Automation of AFC operation and automation of PC operation with priority given to prevention of nuclear fuel damage are realized by acting as a reactor power control command on SPCD 34 based on the monitoring of fuel linear power density distribution and its rate of increase by dedicated computer 33. The problem with the simple calculation method using the dedicated computer 33 mentioned above is that the monitoring of the linear power density of the fuel rods is not possible with the LPRM.
Based on the readings, only the four divisions in the axial direction of the core are targeted, and locally, the conversion value from the above-mentioned LPRM readings to the maximum linear power density of that LPRM region is calculated at the time of power distribution calibration by the process calculator 31. It is conceivable that the error may deviate to such an extent that it becomes a problem. Therefore, in order to monitor the linear power density with higher accuracy, it is necessary to use the conventional linear power density monitoring method performed by the process computer 31, that is, to perform a correction calculation based on the deviation between the base power distribution obtained during TIP scanning and the LPRM reading value. It is desirable to monitor four divisions in the axial direction of the core. Especially when PC envelope is not enabled.
In C operation, the change in the thermal power distribution of the reactor core is extremely gradual, so the corrective action of reactor power control based on the thermal power distribution monitoring results does not require a high-speed response, so the calculation processing time of the dedicated computer 33 may be long. do not have. Taking these circumstances into consideration, two types of thermal output distribution calculation methods are prepared in the dedicated computer 33. During PC operation, the same thermal output distribution monitoring method as the conventional process computer 31 is used, and when AFC operation is used, the calculation method is used. The above-mentioned simple calculation method is used, which may be somewhat inferior in accuracy depending on changes in the thermal power distribution, but the calculation processing for thermal power distribution monitoring is fast, and therefore the reactor power control can be quickly corrected. Other methods are also possible.

Taking advantage of the fact that the SPCD 34 is a signal generator that outputs an output signal that indicates increase/decrease polarity information and a rate of change proportional to the pulse signal frequency per unit time of the clock signal, Figure 8 shows the calculation in PC creation mode. A flowchart of a modification of the command method is shown. Furthermore, in FIG. 3, the signal path between the dedicated computer and the SPCD in this modified case is shown by a broken line. The feature of this modification is that the ramp rate of change in the output of the SPCD 34 during PC operation is variable in accordance with the rate of increase in the linear power density of the fuel.

In other words, ΔLP, the above-mentioned time integral value of the deviation between Max. In the case b) above, no clock signal is generated, and in the case c) above, the same clock signal as in the case a) is given to the SPCD 34 along with a decrease command.

The clock signal changes according to the calculation result at every time interval Δt, and the (n-1)th integral value is adopted at the nth time interval. With such a control system, it is expected that the output of the reactor will be increased more smoothly during PC operation. In FIG. 8, Ku and kD are the adjustment coefficients of the ramp change rate. [Effects of the Invention] As described above, according to the present invention, nuclear reactor output can be automatically controlled in accordance with requests from the power system while giving priority to preventing damage to nuclear fuel.

In particular, since the PC envelope can be automatically updated using the PC creation mode, it is possible to fully meet the output requirements from the power system, which is currently difficult to achieve, through automatic thermal learning operation. updated pc
Envelopes allow rapid response to subsequent requests for the same output.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional reactor power control system, Figure 2
The figure is a block diagram of a reactor power control device according to an embodiment of the present invention, FIG. 3 is a partially detailed block diagram of the same reactor power control device, and FIG. 4 is a graph showing the power distribution and PC envelope of the reactor. Figure 5 is a diagram showing the core configuration of a nuclear reactor, Figure 6 is a flowchart of monitoring data processing of nuclear fuel thermal output distribution, and Figures 7 and 8 are flowcharts each showing operations in PC creation mode. be. 1... Power system response control circuit, 2...
Reactor recirculation flow rate control unit, 21...Recirculation flow rate main controller, 22...Reactor recirculation flow rate operation unit,
30... Output control device, 31... Plant process computer, 32... Core output monitor system, 33... Dedicated computer, 34...・Reactor power control action signal generator, 41... Neutron flux detector, 42... Fuel assembly, 43...
...control rod.

Claims (1)

[Scope of Claims] 1. In a reactor power control device that controls the output of a nuclear reactor by adjusting the recirculation flow rate flowing into the core of a nuclear reactor based on a request from an electric power system, neutron flux detection means for detecting neutron flux density; calculation means for calculating the maximum linear power density in each region based on the neutron flux density detected by the neutron flux detection means; The first step to increase the output is
a second output increasing means for increasing the output at a rate of increase that does not destroy the nuclear fuel rods of the reactor and performing a thermal learning operation to thermally adapt the nuclear fuel rods; and each of the above-mentioned regions. storage means for storing a maximum linear power density distribution indicating the maximum linear power density that can be reached; and a maximum linear power density distribution in which the maximum linear power density in each region determined by the calculation means is stored by the storage means; If the output is lower, the output is increased by the first output increasing means,
If any of the maximum linear power densities in each region calculated by the calculation means exceeds the maximum linear power density distribution stored by the storage means, output control is performed to increase the output by the second output increasing means. and when a thermal learning operation is performed by increasing the output by the second output increasing means, the maximum linear power density distribution stored in the storage means is determined by the maximum line reached by the thermal learning operation. A nuclear reactor power control device comprising: updating means for updating the power density distribution. 2. In the apparatus according to claim 1, the calculation means calculates the maximum linear power density in each region by multiplying the neutron flux density detected by the neutron flux detection means by a predetermined conversion coefficient. Characteristic reactor power control device.