JP2006010705A - Control rod drawing monitoring device, and control rod controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To draw a control rod without reducing reactor power when the amount of neutron fluctuation increases, and to prevent drawing of the control rod in local power increase in the reactor core. <P>SOLUTION: This monitoring device and this controller comprise a digital filter 6 that is connected with an amplifier and has a finite length impulse response (FIR). They also comprise an adjusting means 4 that inputs signals from an average power monitor 10 and an LPRM power average processor 3, sets the gain of an amplifier 5 to one when the reactor core average neutron flux is lower than the local average neutron flux, adjusts the gain of the amplifier 5 so that the reactor core average neutron flux becomes equal to the local average neutron flux when the reactor core average neutron flux is the local average neutron flux or higher, and sets the reactor core average neutron flux in each delay element Z<SP>-1</SP>of the digital filter 6 as an initial value. They also comprise a comparing means 7 for outputting a control rod drawing prevention signal when the power from the digital filter 6 exceeds the set level. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a control rod pull-out monitoring device and a control rod control device, and is particularly suitable for application to a boiling water reactor (referred to as BWR), and is it possible to pull out a control rod during the power operation of the reactor? The present invention relates to a control rod pull-out monitoring device and a control rod control device that determine whether or not based on a neutron flux.

  The BWR loads a large number of fuel assemblies in the core. These fuel assemblies have a plurality of fuel rods filled with nuclear fuel. In the conventional BWR, the average value of the local outputs of the neutron detectors located around the control rod selected as the extraction target during the power operation of the reactor is obtained, and the set value of the reactor power determined by the core flow rate and the above A control rod withdrawal monitoring device is applied that compares a local power average value and outputs a control rod withdrawal prevention signal to the control rod control means when the local power average value exceeds the set value of the reactor power. Yes. For example, if a control rod is pulled out accidentally, the fuel rod may be damaged due to a local increase in power in the core. However, the control rod withdrawal monitoring device outputs a control rod withdrawal prevention signal, thereby Prevent damage.

  By the way, in the operation of the BWR, the reactivity of the core decreases as the nuclear fuel material burns. Therefore, the coolant flow rate (core flow rate) supplied to the core is increased to compensate for the decrease in the reactivity, and the reactor output is increased. Hold constant. When the core flow rate reaches the maximum value, the decrease in reactivity cannot be compensated and the reactor power cannot be maintained at the rated power (100% power). Therefore, it is necessary to increase the reactor power by pulling out the control rod. In order to maintain the integrity of the fuel rods in the nuclear reactor, in order to prevent the reactor power from exceeding the rated power, the control rod is not pulled out near the rated power.

  When performing control rod drawing operation, the reactor power is sufficiently reduced by decreasing the core flow rate, and then the control rod drawing operation is performed.After that, the core flow rate is increased to bring the reactor power to the rated output. Raised. However, in order to reduce the reactor power once, the equipment utilization rate of the BWR plant is lowered, which is not desirable. Moreover, it is not preferable from any aspect such as a decrease in the core flow rate, an increase in the burden on the operator for the increase rod operation, and an increase in disturbance to the power system due to a decrease in the reactor output.

  Therefore, the number of times of pulling out the control rod while reducing the reactor power is preferably as small as possible.

  In recent years, from the viewpoint of effective utilization of uranium resources and ensuring energy security, plutonium utilization plans (pulthermal) in light water reactors are being promoted step by step. In the future, about 1/3 of the fuel assemblies loaded in the reactor core at the boiling water nuclear power plant in operation, the fuel assemblies containing mixed oxides (MOX) of uranium and plutonium (MOX) It is planned to be a fuel assembly). The remaining 2/3 is a fuel assembly (referred to as a uranium fuel assembly) that does not contain a mixed oxide of uranium and plutonium but contains uranium oxide at the time of manufacture. Furthermore, it is planned that all fuel assemblies in the core will be MOX fuel assemblies.

  The MOX fuel assembly differs from the uranium fuel assembly in that it contains plutonium at the time of manufacture of the fuel assembly. Plutonium has a smaller delayed neutron ratio and a larger neutron absorption cross section than uranium. That is, the amount of change in output when the amount of voids in the coolant changes is large. This means that the void coefficient is large, and the amount of neutron fluctuation at the time of high reactor power output becomes large. It was newly found that the fluctuation amount is ± 5% or more at the rated output by the evaluation by simulation.

  Even in the core (MOX fuel core) loaded with the MOX fuel assemblies, it is desirable to perform the control rod pull-out operation without reducing the reactor power as described above. As described above, in this core, the amount of neutron fluctuation changes by ± 5% or more of the rated power at the time of high reactor power output. The control rod pull-out monitoring device is a logic that prohibits the control rod pull-out operation when the output of the neutral detector exceeds 105%. For this reason, even if an attempt is made to pull out the control rod without reducing the reactor power, the pulling out of the control rod is prohibited due to neutron fluctuation. That is, in the MOX fuel core, control rod extraction is prohibited due to neutron fluctuation, and it becomes impossible to perform control rod extraction operation without reducing the reactor power.

  In a conventional BWR loaded with a uranium fuel assembly in the core, the generated plutonium accumulates in the fuel assembly as the number of operating cycles increases, and the void coefficient increases. Also, in the first half of one operating cycle, the core flow rate is lowered to increase the amount of voids, so that plutonium is actively accumulated in the fuel assembly, and in the second half of the operating cycle, the void amount is reduced and accumulated by increasing the core flow rate. Spectral shift operation is performed to increase the utilization rate of nuclear fuel by burning plutonium. In the first half and second half of the operation cycle, the reactor power is maintained at the rated power by the combined use of control rod operation and core flow rate control. When the spectrum shift operation is performed, the amount of neutron fluctuation is higher in the first half of the operation cycle (when the above core flow rate is low) than in the second half of the operation cycle. There is no ban. However, if a highly enriched fuel assembly is loaded, the operation cycle progresses, or the operation cycle period itself becomes longer, the void coefficient increases and the amount of neutron fluctuation increases. There is a possibility that the standard value of the pull-out monitoring device exceeds 105%. As a result, there arises a problem that control rod withdrawal at the time of high reactor power is prohibited by the control rod withdrawal monitoring device.

  It is an object of the present invention to control rods that can be pulled out without lowering the reactor power when the amount of neutron fluctuation increases, and to prevent the rods from being pulled out against a local increase in power in the core. An object of the present invention is to provide a drawing monitoring device and a control rod control device.

In order to achieve the above object, a control rod pull-out monitoring device of the present invention includes a plurality of local output monitors for inputting neutron flux signals output from each neutron detector string arranged in the core, and the local output monitors. The average power monitor that calculates the core average neutron flux using the neutron flux signal that is the output of the connected local power monitor, and the neutron flux signals of multiple neutron detectors that measure the neutron flux around the control rod that performs the extraction operation An LPRM output average processor for obtaining a local average neutron flux, an amplifier connected to the LPRM output average processor for amplifying the local average neutron flux, an input signal connected to the amplifier and delayed by a filter operation period A value obtained by multiplying a plurality of output delay elements Z ⁻¹ by a current input signal x (t) by a weighting factor a ₀ and past input signals x (t−1), x (t−2),. A digital filter of finite impulse response (FIR) that outputs y (t) obtained by adding a value obtained by multiplying (tk) by a weighting coefficient by the adder 30 as an output signal, the average output monitor, When a signal from the LPRM output average processor is input and the core average neutron flux is lower than the local average neutron flux, the gain of the amplifier is set to 1, and when the core average neutron flux is greater than or equal to the local average neutron flux Adjusting the gain of the amplifier so that the core average neutron flux is equal to the local average neutron flux, and adjusting the core average neutron flux as an initial value for each delay element Z- ¹ of the digital filter; Comparing means for outputting a control rod pull-out prevention signal when the output from the digital filter exceeds a set level.

In addition, an infinite-length impulse response (IIR) digital filter which is connected to an amplifier and has a loop in which a part of the operation result is fed back to the input and circulated, and signals from the average output monitor and the LPRM output average processor When the core average neutron flux is lower than the local average neutron flux, the gain of the amplifier is set to 1. When the core average neutron flux is equal to or greater than the local average neutron flux, the core average neutron flux and the local average neutron Adjusting the gain of the amplifier so that the bundles are equal, adjusting means for setting 0 as an initial value to the delay element Z ^-1 of the digital filter, and when the output from the digital filter exceeds a set level And a comparison means for outputting a control rod pull-out prevention signal.

Also, a plurality of local output monitors that input neutron flux signals output from each neutron detector string arranged in the core, and a neutron flux signal that is connected to the local output monitor and output from the local output monitor. An average output monitor for calculating the core average neutron flux, and a plurality of delay elements Z ^-1 for outputting the input signal to each of the local output monitors after being delayed by a filter operation cycle, and a weighting factor for the current input signal x (t) A value obtained by multiplying a ₀ by a value obtained by multiplying a past input signal x (t−1), x (t−2),..., x (t−k) by a weighting coefficient is obtained by the adder 30. The neutron flux of a plurality of neutron detectors connected to each other through a finite impulse response (FIR) digital filter that outputs the output y (t) as an output signal and that measures the neutron flux around the control rod performing the extraction operation During local average using signal An LPRM output average processor for obtaining a neutron flux; an amplifier connected to the LPRM output average processor for amplifying the local average neutron flux; and signals from the average output monitor and the LPRM output average processor; When the average neutron flux is lower than the local average neutron flux, the gain of the amplifier is set to 1. When the core average neutron flux is greater than or equal to the local average neutron flux, the core average neutron flux is equal to the local average neutron flux. And adjusting means for adjusting the gain of the amplifier and comparison means for outputting a control rod pull-out prevention signal when the output from the amplifier exceeds a set level.

According to the present invention, the values of the weight coefficients a _{0 to} a _k of the digital filter of finite impulse response (FIR) and the values of the weight coefficients α ₁ and β ₁ of the digital filter of infinite impulse response (IIR) The frequency component above the fluctuation frequency can be suppressed by adjusting the characteristic of the low-pass filter. In addition, when the selection control rod information for the control rod to be extracted this time is input, the initial value of the delay element Z ^-1 can be set to the value of the core average neutron flux, and when the digital filter selects the extraction control rod for the input signal Can output a low frequency signal following the input signal.

Further, the low-pass filters 6 _{1 to} 6 _N are not arranged between the local output monitors LPRM-1 to LPRM-N and the average output monitor APRM, and the response until the core average neutron flux reaches the set value and the scram is generated. The time is 90 ms or less, and there is an effect that safety is extremely high.

  For this reason, when the amount of neutron fluctuation increases, the control rod can be pulled out without reducing the reactor power, and the control rod can be prevented from being pulled out against a local increase in power in the core.

  A control rod pull-out monitoring device which is a preferred embodiment of the present invention will be described below with reference to FIG.

  First, an outline of a BWR plant to which this embodiment is applied will be described. The BWR plant includes a reactor pressure vessel 13, a plurality of fuel assemblies (not shown) loaded on the core in the reactor pressure vessel 13, and a plurality of controls inserted between the fuel assemblies to control the reactor output. A bar 15 is provided. The control rod drive mechanism 16 is provided on each of these control rods 15. The control rod drive mechanism 16 includes a motor 18 and an electromagnetic brake 19 for stopping the rotation, and converts the rotation amount of the motor 18 into linear motion to drive the control rod 15 in the vertical direction. . The position of the control rod 15 in the core height direction is detected by the position detector 17. The core is a MOX fuel core in which uranium fuel assemblies and MOX fuel assemblies are mixed.

  By pulling out the control rod 15 from the core by driving the motor 18, the reactor power is increased. Cooling water 14 supplied into the core by driving a recirculation pump (not shown) is heated by heat generated by the splitting of nuclear fuel material while rising in the fuel assembly to become steam. The steam is sent through a main steam pipe 31 to a turbine (not shown). The reactor power can also be controlled by controlling the core flow rate with a recirculation pump. As the core flow rate increases, the reactor power increases.

  A plurality of neutron detector strings 12 are arranged in the water gap between the fuel assemblies in which the control rods 15 are not inserted. One cell is constituted by four fuel assemblies surrounding one control rod 15, and one neutron detector string 12 is arranged at one corner of the cell. In the neutron detector string 12, as shown in FIG. 2, four neutron detectors A, B, C and D for measuring neutron fluxes at different heights are arranged. When these neutron detector strings 12 are grouped into one quadrant of the core horizontal section divided into four quadrants, one neutron detector string 12 is arranged at the corner of each cell. In FIG. 2, the neutron flux at the other three corner positions of the cell is detected by each neutron detector in the neutron detector strings 12A, 12B and 12C arranged in a quadrant different from the quadrant where the neutron detector string 12 is located. Detected by devices A to D.

  The control rod withdrawal monitoring device of this embodiment includes a control rod withdrawal monitoring device 1, N local output monitors (LPRM-1 to LPRM-N) and an average output monitor (APRM) 10. The control rod drive mechanism control device includes a control rod operation monitoring device 21 and a control rod controller 22.

When the core flow rate reaches the maximum value and the reactor power cannot be maintained at the rated output due to the increase of the core flow rate, the control selected by the input of the operation command 20 by the operator from the operation panel (not shown). The pulling operation of the rod 15 is executed. Based on the input operation command 20, the control rod operation monitoring device 21 controls a command for pulling out one control rod to be pulled out (a plurality of control rods when operated in the gang mode) to the target position. Output to the bar controller 22. The control rod operation monitoring device 21 also has information (selection control rod information 25) indicating the position (position in the horizontal cross section of the core) of the one control rod (or a plurality of control rods) selected based on the operation command 20. ) Is output to the LPRM output averaging processor 3 described later.

  The control rod controller 22 takes in the control rod position from the position detector 17 of the corresponding control rod 14, outputs a control command to the control rod driving device 23, and executes control to pull out the corresponding control rod to the target position. . When a control command is input, the control rod driving device 23 causes the motor 18 to apply the voltage of the power supply 24 in order to rotate the motor 18 in a direction corresponding to the control rod driving direction. At this time, the electromagnetic brake 19 is released and the motor 18 rotates. When the control rod 15 is pulled out to the target position, the control rod controller 22 stops outputting a control command, and the control rod driving device 23 cuts off the power supply to the motor 18 and the electromagnetic brake 19. The motor 18 stops and the control rod 15 is held at the target position by the braking force of the electromagnetic brake 19. The reactor power will rise and be maintained at the rated power.

Next, the control rod withdrawal monitoring device 1 will be described. The output signals of the neutron detectors A to D in each neutron detector string 12 are LPRM-1, LPRM, which are local output monitors (LPRM).
LPRM-2,..., LPRM-N are input to the corresponding monitor. One LPRM is connected to one neutron detector. LPRM-1, LPRM-2,..., LPRM-N inputs the neutron flux signal measured by the corresponding neutron detector, and deteriorates the sensitivity of the neutron detector (caused by depletion of uranium applied to the detector) ), Correction processing to suppress the influence of high frequency electrical noise of about 10 Hz or more, gain processing to correspond to the reactor output, etc., and a neutron flux signal corresponding to the reactor output Output each.

  The APRM 10 calculates and outputs the core average neutron flux (the average value of the reactor output) using the neutron flux signals that are the outputs of LPRM-1, LPRM-2,..., LPRM-N. The control rod withdrawal monitoring device 1 includes OR gate means 9 for inputting the output signals of the control rod withdrawal monitoring devices 2A and 2B and the control rod withdrawal monitoring devices 2A and 2B.

The control rod pull-out monitoring device 2A includes an LPRM output average processing device 3, an adjusting means 4, an amplifier 5, a low-pass filter 6, a comparator 7 and a determination criterion setting device 8. The low-pass filter 6 is a digital filter called a finite impulse response (FIR) shown in FIG. The delay element Z ^-1 delays the input signal by the filter calculation cycle and outputs it. a _{0 to} a _k are weighting factors, and 30 is an adder. The FIR filter of FIG. 3 is also called a non-recursive filter, and a value obtained by multiplying a current input signal x (t) by a weighting factor a ₀ and past input signals x (t−1), x (t−2), ..., X (t−k) multiplied by a weighting coefficient is added by the adder 30 and y (t) obtained is output as an output signal. The characteristics of the low-pass filter 6 are determined by the values of the weighting factors a _{0 to} a _k .

As the low-pass filter 6, a digital filter called an infinite length impulse response (IIR) shown in FIG. 4 may be used. The IIR filter in FIG. 4 is also called a recursive filter, and a loop is formed in which a part of the operation result is fed back to the input and circulated. The characteristics of the low-pass filter 6 are determined by the values of the weighting factors α ₁ and β ₁ .

  The control rod withdrawal monitoring device 2B has the same configuration as the control rod withdrawal monitoring device 2A. The control rod withdrawal monitoring device 2A performs control rod withdrawal monitoring on the neutron flux signals of the neutron detectors A and C. The control rod extraction monitoring device 2B performs control rod extraction monitoring on the neutron flux signals of the neutron detectors B and D. Since the control rod withdrawal monitoring device 2A and the control rod withdrawal monitoring device 2B perform the same operation, the operation of the control rod withdrawal monitoring device 2A will be described in detail below.

  The output signal of each LPRM that inputs the neutron flux signals of the neutron detectors A and C is input to the LPRM output averaging processor 3. The LPRM output average processing device 3 also receives selection control rod information 25. The LPRM output averaging processor 3 includes neutron detectors A and C in the four neutron detector strings around the control rod 15 at the position designated by the selected control rod information 25 (for example, the neutron detector string in FIG. 2). The neutron detectors A and C) in 12, 12A, 12B, and 12C are selected, and the local average neutron flux that is the average of these signals is calculated using the neutron flux signals that are the outputs of these neutron detectors. To do. The local average neutron flux is input to the amplifier 5. Since the output increase due to the control rod drawing is small at the outermost periphery in the furnace, the output signals of the neutron detectors A and C in the three or two neutron detector strings are used in this portion of the control rod drawing.

  The adjusting unit 4 has functions of a gain adjusting unit and a filter initial value setting unit. The function of the gain adjusting means in the adjusting means 4 will be described. The gain adjusting means in the adjusting means 4 adjusts the gain of the amplifier 5 to 1 when the core average neutron flux output from the APRM 10 is lower than the local average neutron flux output from the LPRM output average processing device 3. That is, in this case, the local average neutron flux is directly output from the amplifier 5 and input to the low-pass filter 6.

  When the core average neutron flux is greater than or equal to the local average neutron flux, the gain adjusting means in the adjusting means 4 calculates a gain that makes the core average neutron flux equal to the local average neutron flux, and this gain is obtained. The gain of the amplifier 5 is adjusted. The amplifier 5 amplifies the local average neutron flux using the adjusted gain and outputs it to the low-pass filter 6. The gain of the amplifier 5 is fixed and not changed until the next control rod to be extracted is selected.

  Since the gain adjusting means in the present embodiment performs the gain adjustment described above, when the control rod 15 at a position where the neutron flux level is low is selected, this control rod 15 is selected when the value of the selected control rod 15 is high. Thus, the possibility of fuel rod damage due to the extraction of the control rod 15 having a high value can be prevented. For this reason, the safety | security of a fuel rod increases. The gain adjusting means is also necessary for setting the initial value of the low-pass filter 6.

  The low-pass filter 6 is for passing a neutron flux signal, which is an output of LPRM-1 or the like indicating a local output increase of the core, and suppressing fluctuations in the neutron flux included in the output of the neutron detector. The low-pass filter 6 suppresses a frequency component higher than the fluctuation frequency (for example, 0.2 Hz) included in the output signal of the amplifier 5 and outputs a low-frequency signal including a frequency component smaller than the fluctuation frequency.

  The comparator 7 compares the level of the low frequency signal from the low-pass filter 6 with the determination reference value set in the determination reference setting unit 8. As shown in FIG. 5, the determination reference value set in the determination reference setting unit 8 has three determination reference values linked to the core flow rate. The three determination reference values are a normal position serving as an upper limit level alarm threshold value, an intermediate position serving as an intermediate level alarm threshold value, and a low position serving as a low level alarm threshold value. The comparator 7 compares the level of the low frequency signal with the three determination reference values, and outputs an alarm when the level of the low frequency signal exceeds each determination reference value. When the level of the low frequency signal exceeds the determination reference value for the normal position, the comparator 7 outputs a control rod pull-out prevention signal 9a. Since the core flow rate is 90% or more at the rated output, the control rod withdrawal prevention signal 9a is output when the level of the low frequency signal exceeds 105%.

  When at least one of the control rod withdrawal prevention signal 9a from the control rod withdrawal monitoring device 2A and the control rod withdrawal prevention signal 9b from the control rod withdrawal monitoring device 2B is input to the OR gate means 9, an output is output from the OR gate means 9. The control rod withdrawal prevention signal 9c is input to the control rod operation monitoring device 21. Based on the control rod withdrawal prevention signal 9c from the control rod operation monitoring device 21, the control rod controller 22 instructs the control rod drive device 23 to stop withdrawal in order to prevent further withdrawal of the drawn control rod. Is output. The control rod drive device 23 stops the supply of electric power to the motor 18 of the control rod drive mechanism 16 that operates the corresponding control rod based on this control command. In this way, when the control rod withdrawal prevention signal 9c is output, the withdrawal of the corresponding control rod is stopped.

Note that the LPRM output averaging processing device 3 of the control rod withdrawal monitoring device 2B includes the neutron detectors B and D (in the four neutron detector strings around the control rod 15 at the position specified by the selection control rod information 25). For example, using the neutron flux signals that are the outputs of the neutron detectors B and D) in the neutron detector strings 12, 12A, 12B, and 12C of FIG. 2, the local average neutron flux that is the average of these signals is calculated. To do. Since the output increase due to the control rod drawing is small at the outermost periphery in the furnace, the output signals of the neutron detectors B and D in the three or two neutron detector strings are used in this portion of the control rod drawing.

Since the low-pass filter 6 includes the delay element Z ⁻¹ , the current and past local average neutron flux (the output signal of the amplifier 5) is handled. When the output signal of the amplifier 5 is applied to the low-pass filter 6, the output of the delay element Z- ¹ is generally zero. For this reason, the level of the low-frequency signal that is the output of the low-pass filter 6 gradually increases from zero and follows the local average neutron flux that is the output of the amplifier 5. Until the level of the low frequency signal follows the local average neutron flux, which is the output of the amplifier 5, it is lower than the criterion reference value at the positive position. Therefore, in a situation where the output of the control rod withdrawal prevention signal 9a is actually required. However, there arises a problem that the comparator 7 does not output the control rod withdrawal prevention signal 9a. This is because the initial value of the delay element Z ⁻¹ is zero. Therefore, when the selection control rod information 25 is input, the adjusting means 4 sets the initial value of the delay element Z ⁻¹ as the core average neutron flux value output from the APRM 10. The initial value of each delay element Z ⁻¹ may be set to the core average neutron flux value output from the APRM 10 (or the local average neutron flux value output from the amplifier 5), for example.

In the IIR filter of FIG. 4, when the initial value of the delay element Z ⁻¹ is zero, the input signal is output as it is as the output signal, so the initial value of the delay element Z ⁻¹ may remain zero. Further, as the low-pass filter, the output of the FIR filter of FIG. 3 connected to the IIR filter of FIG. 4 may be used. In this case as well, the initial value of each delay element Z ⁻¹ of the FIR filter is, for example, the core average What is necessary is just to set to the value of the local average neutron flux which is the value of a neutron flux or the output of amplifier 5.

When the initial value setting process of each delay element Z ⁻¹ is not performed, the low-pass filter 6 is level with respect to the input signal (characteristic I in FIG. 6) when the initial value of the delay element Z ⁻¹ is zero. A low-frequency signal (characteristic II in FIG. 6) that gradually rises from zero is output, or the value of the local average neutron flux that is the output of the amplifier 5 for the fuel assembly adjacent to the previously extracted control rod is the delay element When Z- ¹ remains, this value is used as an initial value, and a low-frequency signal is output from an initial value different from that for the fuel assembly adjacent to the control rod that is pulled out this time. On the other hand, when the filter initial value setting means in the adjusting means 4 inputs the selection control rod information 25 for the control rod to be extracted this time, the initial value of each delay element Z ^-1 is set to the value of the core average neutron flux. When the initial value setting process is executed, the low-pass filter 6 is a low-frequency signal (characteristic III in FIG. 6) that follows the input signal from the time when the extraction control rod is selected for the input signal (characteristic I in FIG. 6). Is output.

In this embodiment, the filter initial value setting means in the adjustment means 4 further has the following functions. When the filter initial value setting means determines that the local average neutron flux that is the output of the LPRM output average processing device 3 is higher than the core average neutron flux that is the output of the APRM 10 when the selection control rod information 25 is input, The value of the local average neutron flux is set as the initial value of the delay element Z- ¹ . The filter initial value setting means sets the value of the core average neutron flux as the initial value of each delay element Z- ¹ when it is determined that the local average neutron flux is equal to or less than the core average neutron flux.

When the filter initial value setting means does not have such a function, the following problem occurs. That is, when the output of the LPRM output average processing device 3 is higher than the output of the APRM 10, the gain of the amplifier 5 is not changed, so that the signal input to the low-pass filter 6, that is, the output of the LPRM output average processing device 3 is the delay element. The level is higher than the initial value of Z- ¹ . When the control rod is pulled out in such a state, the output level of the LPRM output averaging processing device 3 is increased, and the level of the low frequency signal becomes equal to or higher than the determination reference value (105%) of the normal position. Since the initial value of the delay element Z ⁻¹ is lower than the output level of the LPRM output averaging processing device 3, the device 7 outputs the control rod pull-out prevention signal 9 a even later. The prevention of the output delay of the control rod withdrawal prevention signal 9a is performed by the initial stage of the delay element Z ^-1 based on the magnitude relationship between the local average neutron flux and the core average neutron flux, which are the outputs of the LPRM output average processor 3 described above. The filter initial value setting means may have a value setting function.

In the present embodiment, the output of the LPRM output averaging processing device 3 and the filter initial value setting means
Since the initial value of the delay element Z ⁻¹ is set according to the magnitude relationship of the output of the APRM 10, the level of the output signal of the amplifier 5 that is always input first to the low-pass filter 6 when the control rod is pulled out. It is possible to perform the filter operation of the input signal with the same value as the initial value. For this reason, it is possible to prevent the output of the low-pass filter 6 from being delayed unnecessarily, and to prevent the output delay of the control rod extraction prevention signal 9a from the comparator 7. There is no delay in the output of the control rod withdrawal prevention signal 9c from the control rod withdrawal monitoring device 1, and the withdrawal of the corresponding withdrawal control rod can be prevented in a short time.

  In the present embodiment, the gain of the amplifier 5 is adjusted based on the output of the gain adjusting means, and the output of the amplifier 5 is input to the low-pass filter 6 to suppress the frequency component above the fluctuation frequency. Therefore, in the MOX fuel core, Even if the local average neutron flux that is the output of the amplifier 5 exceeds the criterion value for the positive position due to the increase in the neutron fluctuation amount at the high reactor power, for example, at the rated power, the neutron fluctuation amount It is possible to prevent the control rod from being pulled out due to the increase. For this reason, when the amount of neutron fluctuation increases, the operation of reducing the reactor power is not performed by reducing the core flow rate, that is, the control rod 15 is pulled out at the rated power to compensate for the decrease in the reactor power accompanying the combustion of nuclear fuel. it can. Further, in this embodiment, when the local average neutron flux increases due to a local increase in power in the core and the level of the low frequency signal of the low-pass filter 6 exceeds the determination reference value of the normal position, the corresponding control is performed. Pulling out the rod can be prevented.

  Since the control rods for maintaining the rated output can be pulled out without reducing the reactor output, the equipment utilization rate of the BWR plant can be improved and the burden on the operator can be reduced. The present embodiment also has an effect of suppressing an increase in disturbance to the power system.

  In this embodiment, not only a BWR plant having a MOX fuel core but also a BWR plant having a core loaded with uranium fuel assemblies and not loaded with MOX fuel assemblies, in which spectrum shift operation is performed, and enrichment The present invention can also be applied to a BWR plant equipped with a core in which a high-grade uranium fuel assembly is loaded and the amount of neutron fluctuation at the rated power increases.

  A control rod pull-out monitoring apparatus according to another embodiment of the present invention will be described below with reference to FIG. This embodiment differs from the embodiment shown in FIG. 1 in the location of the low-pass filter, and the adjusting means 4 has a function of gain adjusting means and does not have a function of filter initial value setting means. The other configuration of this embodiment is the same as that of the embodiment of FIG.

The low pass filter ₆₁ to the LPRM-1, the low-pass filter 6 ₂ The LPRM-2, ......, a low-pass filter 6 _N are respectively connected to the LPRM-N. The configuration of the low-pass filters 6 ₁ , 6 ₂ ,..., 6 _N is the same as the configuration of the low-pass filter 6 in FIG. For this reason, in this embodiment, regardless of whether or not the extraction control rod is selected, the output signals of LPRM-1 to LPRM-N are always individually similar to the low-pass filter 6 of FIG. A filtering process is performed. Therefore, the filter initial value setting means in the embodiment of FIG. In this embodiment, the initial value setting process described above for each low-pass filter is not required, and, as in the embodiment of FIG. 1, when the amount of neutron fluctuation increases, the reactor power reduction operation is not performed by reducing the core flow rate. Thus, it is possible to compensate for a decrease in the reactor power accompanying the combustion of nuclear fuel due to the withdrawal of the control rod 15. Further, in this embodiment, when the local average neutron flux increases due to the local increase in power in the core, the corresponding control rod can be prevented from being pulled out.

In the embodiment of FIG. 7, the adjusting means 4 is the core average neutron flux and the local average neutron flux when the core average neutron flux as the output of the APRM 10 becomes equal to or greater than the local average neutron flux as the output of the LPRM output average processor 3. And the gain of the amplifier 5 is calculated. However, in the embodiment of FIG. 7, since the low-pass filters 6 _{1 to} 6 _N are provided at the input stage of the LPRM output average processing device 3, the output of the LPRM output average processing device 3 is a signal that is delayed in time from the output of the APRM 10. Thus, the calculation of the gain is complicated.

  For this reason, it takes a lot of time to calculate the gain, the output of the control rod pull-out prevention signal 9c is delayed, and the safety margin may be reduced. This problem can be solved by the embodiment shown in FIG.

  FIG. 8 shows a control rod pull-out monitoring apparatus according to another embodiment of the present invention. In this embodiment, the control rod pull-out monitoring device 2A is newly provided with an LPRM output average processing device 3 ', and the adjusting means 4 receives the output of the LPRM output average processing device 3' instead of the output of the LPRM output average processing device 3. That is to input. Also in this embodiment, the control rod withdrawal monitoring device 2B has the same configuration as the control rod withdrawal monitoring device 2A. The LPRM output average processing device 3 ′ receives the outputs of LPRM-1 to LPRM-N as they are, and, like the LPRM output average processing device 3, 4 around the control rod 15 at the position designated by the selection control rod information 25. The neutron detectors A and C in the neutron detector string of the body are selected and the local average neutron flux is calculated using the outputs of these neutron detectors. The adjusting means 4 is a gain that makes the core average neutron flux equal to the local average neutron flux when the core average neutron flux that is the output of the APRM 10 is lower than the local average neutron flux that is the output of the LPRM output average processing device 3 '. And the gain of the amplifier 5 is adjusted so that the calculated gain is obtained. The adjustment means 4 sets the gain of the amplifier 5 to 1 otherwise. The output signal of the LPRM output average processing device 3 is amplified by the amplifier 5 whose gain is adjusted as described above. Other operations in this embodiment are the same as those in the embodiment of FIG.

  In this embodiment, by newly providing an LPRM output averaging processing device 3 ', the gain of the amplifier 5 can be calculated easily and at a higher speed than in the embodiment of FIG. It can be shortened. This embodiment can also obtain the effects produced in the embodiment of FIG.

Incidentally, the embodiment of FIGS. 7 and 8 receives the output of the LPRM-1~LPRM-N to APRM10 and the low-pass filter 6 ₁ to 6 _N. However, in the embodiment of FIGS. 7 and 8, the outputs of LPRM- ₁ to LPRM- _N are input to the low-pass filters 6 _{1 to} 6 _N , and the outputs of the low-pass filters 6 _{1 to} 6 _N are APRM 10 and the LPRM output averaging processor. When the number 3 is entered, the following problem occurs.

  Although not shown, the APRM 10 outputs a scram trip signal to a reactor protection system (not shown) when the average core neutron flux exceeds the scram set value. Based on this trip signal, the reactor protection system opens an electromagnetic valve provided in a line connected to an accumulator filled with high-pressure water. The high pressure water in the accumulator is supplied into the control rod drive mechanism 16 to rapidly insert the control rod 15 into the reactor core. As a result, the BWR is scrammed.

It is required from the viewpoint of safety that the response time until the core average neutron flux reaches the set value and the scram is generated is 90 ms or less. For this reason, if the low-pass filters 6 _{1 to} 6 _N having a large time constant are provided between the LPRM-1 to LPRM-N and the APRM 10, the scram response time of 90 ms or less is not satisfied. 7 and 8, the low pass filters 6 _{1 to} 6 _N are not arranged between the LPRM-1 to LPRM-N and the APRM ₁₀ until the core average neutron flux reaches the set value and the scram is generated. The response time is 90 ms or less, and the safety is extremely high.

  Another embodiment of the present invention will be described below with reference to FIG. In this embodiment, the control rod pull-out monitoring device 1 is replaced with the control rod pull-out monitoring device 1A in the embodiment of FIG. 1, and a switching command switch 32 is further provided. The control rod withdrawal monitoring device 1 </ b> A includes control rod withdrawal monitoring devices 2 </ b> A and 2 </ b> B in the same manner as the control rod withdrawal monitoring device 1. The control rod withdrawal monitoring devices 2A and 2B of the control rod withdrawal monitoring device 1A have a changeover switch 33. The changeover switch 33 is connected to the output terminals of the amplifier 5 and the low-pass filter 6 and is connected to the input terminal of the comparator 7.

  The connection state of the changeover switch 33 is controlled by the changeover command switch 32. The changeover switch 33 has a first contact that is normally open and a second contact that is normally closed. FIG. 9 shows a state in which the output signal of the amplifier 5 is input to the comparator 7 through the second contact in the normal state. For this reason, the output of the low-pass filter 6 is not input to the comparator 7. If the switching command switch 32 is closed, the first contact is closed and the second contact is opened, so that the output of the low-pass filter 6 is output to the comparator 7, but the output signal of the amplifier 5 is the comparator. 7 is not input. That is, either the output of the amplifier 5 or the output of the low-pass filter 6 is selected by the switch command switch 32 and input to the comparator 7. The power supply 34 </ b> A and the resistor 35 are provided to output a switching command signal to the switching switch 33 when the switching command switch 32 is closed.

Further, the display 34 can monitor the state of the changeover command switch 32, that is, which of the output of the amplifier 5 or the output of the low-pass filter 6 is being output to the comparator 7. As will be described later, this makes it possible for the plant operator to easily recognize whether or not the low-pass filter 6 is working to suppress neutron fluctuation according to the plant state. This indicator 34 is attached to a central control panel that can be operated and monitored by a plurality of operators, and it is easy and common to determine whether or not the low-pass filter 6 is operated by a plurality of operators to suppress neutron fluctuation. By recognizing, the reliability of operation monitoring can be further improved. The display 34 is supplied with necessary power from the power source 34B.

  Neutron fluctuation is about ± 3% when the rated power (100% output) of the reactor is up to about 1/3 of the replacement fuel is MOX fuel, and ± 5 when everything in the core is MOX fuel. % Or more. Since the control rod withdrawal monitoring device 1A has a logic that prohibits the control rod withdrawal operation when the neutron output exceeds 105%, when about 1/3 of the replacement fuel is the core of the MOX fuel, Neutron fluctuation does not prevent the control rod from being pulled out, but if the entire core is MOX fuel, the control rod is prevented from being pulled out by neutron fluctuation. The low-pass filter 6 is used to pass an LPRM output signal indicating a local increase in power of the core and suppress fluctuations in the neutron output signal, but involves a time delay. If there is a time delay, the control rod withdrawal prevention determination is delayed accordingly.

It is necessary to secure a safety margin in consideration of this delay time. However, if the low-pass filter 6 is used, the margin is slightly reduced. In the case where up to about 1/3 of the replacement fuel is a MOX fuel core, the neutron output signal does not exceed 105%. In this case, the output signal of the amplifier 5 is controlled by controlling the changeover switch 33. The safety margin can be further improved by outputting to the comparator 7 and comparing with the determination reference value.

  When everything in the core is MOX fuel, the neutron fluctuation is ± 5% or more. In this case, the changeover switch 33 is controlled so that the output signal of the low-pass filter 6 is output to the comparator 7 and compared with the determination reference value to prevent the control rod from being pulled out due to neutron fluctuation. It is possible to improve the facility utilization rate of plant operation. The same applies to the case where the amount of neutron fluctuation increases due to the spectrum shift operation. When the neutron output becomes 105% or more of the reference value of the control rod pull-out monitoring device, the changeover switch 33 is controlled to control the low pass. The output signal of the filter 6 is output to the comparator 7 and compared with the determination reference value, so that it is possible to prevent the control rod from being pulled out due to neutron fluctuation.

  The neutron output, which is the output signal of APRM10, is output to the operation monitoring panel (not shown), so that the changeover switch 33 can be easily operated by operating the changeover command switch 32 based on this indicated value. Is possible. Moreover, since the neutron output which is an output signal of APRM10 is not shown, but is taken into the core performance calculator, it is determined whether or not the neutron output exceeds 105%, and this determination result is displayed on the display device, It is possible to easily control the changeover switch 33 by operating the changeover command switch 32 based on the result output to a printer or the like.

  The comparator 7 compares the output of the changeover switch 33 with the determination reference value from the determination reference setting unit 8, and when the output of the changeover switch 33 is larger than the determination reference value 8, it prevents the control rod from being pulled out. A control rod pull-out prevention signal 9a is output. The control rod withdrawal prevention signal 9a is output to the control rod operation monitoring device 21 via the OR gate means 9, and the control rod withdrawal operation is prohibited.

Even though the low-pass filter 6 is not supposed to work, if the switch command switch 32 is accidentally touched and switched, and the low-pass filter 6 is activated, even if it is time to prevent the control rod from being pulled out. It is conceivable that the control rod pull-out prevention determination is delayed and the safety is lowered. In order to solve such a problem, it is assumed that the switching command switch 32 operates with a double action (for example, a switch that can be switched only after the switch lever is pulled up).

  The control rod pull-out monitoring device 1A can also be achieved by a computer, that is, software processing, and its processing flow is as shown in FIG.

  First, in step 1, various signals such as LPRM output signals are captured. Next, in step 2, the average of the LPRM signal around the selected control rod is calculated. In step 3, the LPRM average value around the selected control rod selected in step 2 is compared with the APRM output value input in step 1, and a gain for amplifying the LPRM average value is calculated. The furnace average value (APRM output value) output from the average power monitor 10 is compared with the above-mentioned LPRM average value. When the furnace average value is higher than the LPRM average value, the above-mentioned LPRM average value is compared with the furnace average value. The gains are determined so as to be equal. If the gains are low, the gain is set to 1. However, the determined gain is fixed until a new control rod is selected.

  In step 4, the LPRM average value selected in step 2 is multiplied by the gain selected in step 3. In step 5, it is determined whether or not the switch command switch 32 is ON (closed state). If not, go to step 7. If ON, go to Step 6. In step 6, for example, the FIR filter (low-pass filter) shown in FIG.

If the switch command switch 32 is not turned on, it is determined in step 7 whether the value obtained in step 4 is higher than the determination reference value (reference value in FIG. 5). If the switching command switch 32 is ON, it is determined in step 7 whether the value after the filtering process in step 6 is higher than the comparison reference value (reference value in FIG. 5). In either case, if the value is higher than the comparison reference value, the process proceeds to step 8. If it is lower than the comparison reference value, the process ends. In step 8, a control rod withdrawal prevention signal is output. These processes are periodically executed at a predetermined cycle.

  As described above, when the amount of neutron fluctuation at the time of high output increases, it is possible to prevent the prevention of control rod pull-out, and when the neutron output increases due to the local increase in power in the core. It is possible to prevent the control rod from being pulled out.

  Although APRM10 is not illustrated, when the average neutron output value (reactor average value) exceeds a predetermined value, a trip signal for scram is output to the reactor protection system. It is required for safety that the time from when the average neutron output value becomes equal to or greater than a predetermined value to cause scram is 90 ms or less. For this reason, if a low-pass filter having a large time constant is provided between LPRM-1 to LPRM-N and APRM10, there is a problem that the scram response 90 ms is not satisfied. Therefore, taking such a configuration is not allowed for safety.

It is a block diagram of a control rod pull-out monitoring device which is a preferred embodiment of the present invention. It is explanatory drawing which shows the arrangement | positioning relationship between the control rod and the neutron detector in the core in the reactor pressure vessel of FIG. It is a detailed block diagram of the low pass filter (FIR filter) of FIG. It is a block diagram of the IIR filter which is another Example of a low-pass filter. It is a characteristic view which shows the relationship between a core flow volume and a control rod pull-out prevention determination reference value. It is explanatory drawing which shows the input signal and output signal in the low-pass filter of FIG. It is a block diagram of the control-rod pulling-out monitoring apparatus which is another Example of this invention. It is a block diagram of the control-rod pulling-out monitoring apparatus which is another Example of this invention. It is a block diagram of the control-rod pulling-out monitoring apparatus which is another Example of this invention. It is a flowchart which shows the software processing flow of the control-rod extraction monitoring apparatus of FIG.

Explanation of symbols

1, 2A, 2B ... Control rod drawing monitoring device, 3 ... LPRM output average processing device, 4 ... Adjusting means (gain adjusting means, filter initial value setting means), 5 ... Amplifier, 6 ... Low pass filter, 7 ... Comparator, 8 ... Criteria setting device, 9 ... OR gate means, 10 ... Average output monitor (APRM), 12, 12A, 12B, 12C ... neutron detector string, 13 ... reactor pressure vessel,
DESCRIPTION OF SYMBOLS 15 ... Control rod, 16 ... Control rod drive mechanism, 18 ... Motor, 21 ... Control rod operation monitoring device, 22 ... Control rod controller, 25 ... Selection control rod information, 32 ... Switch command switch, 33 ... Switch, A , B, C, D: Neutron detector, LPRM-1, LPRM-2, LPRM-N ... Local output monitor, Z- ¹ ... Delay element.

Claims (3)

A plurality of local output monitors that input neutron flux signals output from each neutron detector string arranged in the core, and a core average using the neutron flux signals that are connected to the local output monitor and output from the local output monitor An average output monitor for calculating the neutron flux, an LPRM output averaging processor for obtaining a local average neutron flux using neutron flux signals of a plurality of neutron detectors for measuring the neutron flux around the control rod for performing the extraction operation, and the LPRM An amplifier connected to an output average processor for amplifying the local average neutron flux, and a plurality of delay elements Z ^-1 connected to the amplifier and outputting an input signal delayed by a filter operation cycle, are supplied to the current input signal x (t ) Multiplied by the weighting factor a ₀ and the past input signals x (t−1), x (t−2),..., X (t−k) multiplied by the weighting factor are added by the adder 30. Add The finite-length impulse response (FIR) digital filter that outputs the output y (t) as an output signal, and the signals from the average output monitor and the LPRM output average processor are input, and the core average neutron flux is the local average neutron. The gain of the amplifier is adjusted to 1 when it is lower than the flux, and the gain of the amplifier is adjusted so that the core average neutron flux is equal to the local average neutron flux when the core average neutron flux is equal to or greater than the local average neutron flux. And adjusting means for setting the core average neutron flux as an initial value in each delay element Z ^-1 of the digital filter, and outputting a control rod pull-out prevention signal when the output from the digital filter exceeds a set level. And a control rod pull-out monitoring device. A plurality of local output monitors that input neutron flux signals output from each neutron detector string arranged in the core, and a core average using the neutron flux signals that are connected to the local output monitor and output from the local output monitor An average output monitor for calculating the neutron flux, an LPRM output averaging processor for obtaining a local average neutron flux using neutron flux signals of a plurality of neutron detectors for measuring the neutron flux around the control rod for performing the extraction operation, and the LPRM An infinite-length impulse response (IIR) digital circuit comprising an amplifier connected to an output average processor for amplifying the local average neutron flux, and a loop connected to the amplifier and a part of the operation result fed back to the input. A signal from the filter, the average power monitor and the LPRM power average processor is input, and the core average neutron flux is locally When the average neutron flux is lower than the average neutron flux, the gain of the amplifier is set to 1. When the core average neutron flux is equal to or higher than the local average neutron flux, the gain of the amplifier is set so that the core average neutron flux is equal to the local average neutron flux. And adjusting means for setting 0 as an initial value to the delay element Z ^-1 of the digital filter and a comparison for outputting a control rod pull-out prevention signal when the output from the digital filter exceeds a set level And a control rod pull-out monitoring device. A plurality of local output monitors that input neutron flux signals output from each neutron detector string arranged in the core, and a core average using the neutron flux signals that are connected to the local output monitor and output from the local output monitor The average output monitor for calculating the neutron flux, and the plurality of delay elements Z ^-1 that output the input signal to each of the local output monitors after being delayed by the filter operation period, and the weighting factor a ₀ for the current input signal x (t). Obtained by multiplying the past input signals x (t−1), x (t−2),..., X (t−k) by a weighting coefficient by the adder 30. The neutron flux signals of a plurality of neutron detectors that measure the neutron flux around the control rod that is connected through a finite impulse response (FIR) digital filter that outputs y (t) as an output signal. Use local average neutron flux An LPRM output average processor to be obtained, an amplifier connected to the LPRM output average processor to amplify the local average neutron flux, signals from the average output monitor and the LPRM output average processor are input, and the core average neutron flux Is less than the local average neutron flux, the amplifier gain is 1, and when the core average neutron flux is greater than or equal to the local average neutron flux, the amplifier is set so that the core average neutron flux is equal to the local average neutron flux. A control rod pull-out monitoring device comprising adjusting means for adjusting the gain of the control rod and comparison means for outputting a control rod pull-out prevention signal when the output from the amplifier exceeds a set level.

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