JPS59193398A - Reactor power distribution monitoring device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a nuclear reactor power distribution monitoring device for monitoring the power distribution of a nuclear reactor.

[Technical background of the invention]

Nuclear reactors must monitor the current state of their core performance in order to maintain their health and provide the necessary performance. For this purpose, a process control old computer is generally used. The process control 51 computer calculates the power distribution within the core by manually inputting the core current data.

Here, the core current data includes, for example, the 31 numerical values of the thermal neutron flux measuring device placed in the gap (hereinafter referred to as iJ) of each fuel assembly, the total core power, the coolant flow rate, the control rod flow rate, etc. It consists of the counts of the measuring device that measured the position, etc.

The calculated power distribution within the core is one of the essential parameters required to monitor the health of the reactor.

The power distribution within the core obtained by this process control computer is completely dependent on the counts of the thermal neutron flux measuring device. If all thermal neutron flux measuring instruments are in normal condition, the calculated output distribution will be extremely close to the actual output distribution.

FIG. 1 shows a part of the thermal neutron flux measuring instrument installed in the reactor core. Inside the reactor, a large number of fuel assemblies (hereinafter referred to as bundles) 12 constituting the reactor core 11 are arranged as a whole in a conical shape ξ, and the control rods 13 cause a relatively rapid anti-L[ A conduit 15 is placed in the center of the string 14 surrounded by a handle 112.

In the conduit 15 in the IJ sink 4 shown in the figure, a thermal neutron flux measuring device 16 is fixed at a predetermined position in the axial direction of the reactor core 11, but other thermal neutron flux measuring devices (not shown) are
It is designed to be able to move within the conduit 15. The latter thermal neutron flux measuring device can count thermal neutron flux at any location in the axial direction. In the following description, the former measuring instrument will be referred to as a fixed measuring instrument, and the latter measuring instrument will be referred to as a mobile measuring instrument.

In some cases, the conduit 15 in the string 14 may be damaged due to water flow, etc.
When a curvature occurs in the string 14, this results in a widthwise displacement of these gauges within the string 14. Generally, the thermal neutron flux is not flat within the string 14,
It has a convex distribution shape upward in the core 11. Therefore, if these measuring instruments were to deviate from each other, Ushiko Higashi would no longer be able to obtain accurate counts.

When such a situation occurs, 31 numerical values having different values will be input into the process control computer as data at positions where exactly the same count values should originally be given. As a result, the correct power distribution of the reactor may not be obtained, which may have an unfavorable effect on the health of the fuel and the operating rate of the reactor.

[Purpose of the invention]

In view of the above circumstances, an object of the present invention is to provide a reactor power distribution monitoring device that can obtain the correct power distribution of the reactor even if the measuring device deviates from the center position of the string. do.

[Structure of the invention]

In the present invention, a γ-ray flux measuring device that measures T-ray flux at approximately the center position of the spring, and a γ-ray flux measuring device that controls this r-ray flux measuring device are used.
The reactor power distribution monitoring device is equipped with a radiation flux measurement device and a gamma ray flux count correction device that corrects the T-ray count value obtained by this device based on the temporal change in output at the measurement set point using a predetermined physical model. The reactor power distribution will be monitored using the average power of the fuel rods determined based on the corrected counts.

Since the T-ray bundle generally has a flat distribution within the string, the count value hardly changes even if the conduit within the string curves, and an accurate output distribution can be calculated.

〔Example〕

The present invention will be described in detail with reference to Examples below.

FIG. 2 shows a one-cylinder reactor power distribution monitoring device of the present invention. In the reactor power distribution monitoring device 21, three types of measuring instruments are arranged: a fixed thermal neutron flux measuring instrument 16, a moving T-ray flux measuring instrument 22, and a core current data measuring instrument 23.

The thermal neutron flux measuring device 16 is the above-described fixed measuring device,
It is used to constantly monitor the output of the nuclear reactor 21. T
The flux measuring device 22 is a measuring device used in place of the conventional moving type thermal neutron flux measuring device, and is used to determine the output distribution periodically or as necessary. Used for calibrating fixed measuring instruments that only have a few points. In this nuclear reactor, the T-ray flux measuring device 22 uses a detection device that utilizes the phenomenon of ionization of waste caused by T-rays. The core current data measuring device 23 is located at 4 in the cooling shrine.
This is a measuring device used to measure flow rate, pressure inside the reactor, temperature at the inlet and outlet, control rod position, etc.

The count value 24 outputted from the thermal neutron flux measuring device 16 and the core current state data 25 outputted from the core current state data measuring device 23 are collected in a data sampler 26 and sent to the subsequent device 2.
After the processing is performed in steps 7 to 29, the data is output to the input/output device 31. These device parts will be explained in detail later.

Now, the T-ray flux measuring device 32 performs control such as applying a predetermined voltage to the T-ray flux measuring device 22, and then outputs a signal 33.
get. The output signal 33 is counted by an internal counter, and the count value 3 of the T-ray flux in each string in the core 11 is calculated.
4 is supplied to the T-ray flux word number correction device 35.

The T-ray flux count correction device 35 performs a correction of the number Q\34 using a predetermined physical model. The number of gamma rays measured is (a) due to prompt T-rays due to nuclear fission, which is directly proportional to the current output, and (V-7) delayed T-rays due to past fission products.
Considering that it is the sum of the linear values, the correction model is generally known as )U(, and is expressed by the quadratic equation.

...(1) Fl (f(t'), t) −αf(
t')q(t-t')... (2) Here, g(t) is the count at time t of each measurement set point, f(t
) is the output at time t of each measurement set point, a is the prompt T-ray conversion coefficient corresponding to the output at time t of each measurement set point, C is the detection efficiency of the T-ray flux measuring device 22, h (f(t '), t) is the time t of each measurement set point
α is the residual amount of the delayed T line at time t corresponding to the output at time t′, and α is the delayed T line corresponding to the output at time t′ of each measurement set point.
The linear transformation coefficient, q is the delayed r-ray time distribution function.

Therefore, the emitted γ-ray af(t) corresponding to the current output is:
It is expressed by the following equation using the count g (t, ).

(3) The count value 36 after being corrected as shown in equation (3) by the T-line east/old number correction device 35 is manually input to the data sampler 26. This numerical value 36 obtained using the γ-ray flux measuring device 22
is sent to the fuel rod average power conversion device 27 in the vicinity of the numerical measurement set point along with the core current state data 25 obtained by the core current data measuring device 23 .

Correction word 1 Numerical measurement set point proximity fuel rod average output conversion device 2
At the end, using the built-in conversion formula, the manually inputted count value 36 and core current status data 25 are converted to the average output of the adjacent fuel rods at the nominal measurement set point t7. The conversion formula is as follows.

PARi,=CAR,,・T:, ...(4)
where 1 is the number of the axial measurement set point, `` is the number of the string, T:, is the corrected count value at the ) j position, PΔR1j is the adjacent fuel rod average power at the IJ position, CARij is the 1'' position is the coefficient for converting the corrected count value in to the average output of adjacent fuel rods. Further, in the apparatus of this embodiment, a total of 16 fuel rods, 4 of which are closest to the conduit 15 in each bundle 12, are selected as adjacent fuel rods. This means that these adjacent fuel rods contribute more than 70% of the T-ray flux to the T-ray flux measuring device 22, and the reactor power distribution can be calculated more accurately than when the number of fuel rods is less than this. This is because it becomes possible.

Equation 4) has a format similar to that used in conventional reactor power distribution monitoring equipment, and in conventional systems using this equation, the thermal neutron flux measuring device is placed in the center of the
It has a handle system.

Then, for example, by the two-dimensional diffusion method, the count value of the thermal neutron flux measuring device for the rated output and the average output of the J2f fuel contact rods near this measuring device are determined, and by taking the ratio of these, the average output of the adjacent fuel rods is calculated. .

When using a gamma ray flux measuring device, the thermal neutron count used in equation (4) is replaced by the gamma ray count. In other words, in the method newly used in the present invention,
Using the enrichment of each fuel rod, the concentration of burnable poisons such as Gd, the average void fraction, and the burnup, (a) Fuel using the unit cell two-dimensional fuel Hayabusa coalescence nuclear constant calculation that is normally performed for the rated output. From the output distribution of the rod and (b) T-ray transport calculation, calculate the count value of the gamma-ray flux measuring device for the rated output.

Then, the coefficient CΔR is determined by taking the ratio of the γ-ray count value for the rated output and the average output of adjacent fuel rods near the γ-ray flux measuring device determined by the two-dimensional diffusion calculation method of the four-handle system.

Correction count value measurement set point adjacent fuel rod average output conversion device 27
Adjacent fuel rod average power at the measurement set point determined by 3
8 is supplied to a fuel assembly average output calculation device 28.

In the fuel assembly average power calculation device 28, the measurement set point 4 fuel assembly average power 39 is determined in the same manner as in the conventional reactor power distribution monitoring device, and the fuel assembly average power 39 is calculated in the measurement set point fuel assembly power calculation device 29. supply The measured set point fuel assembly output calculation device 29 calculates the measured set point bundle output 41. Measurement setpoint bundle output 41 is provided to input/output device 31 . The output section of the input/output device 31 is equipped with a CRT and a line printer, and outputs the core power distribution.

The measurement set point bundle output 41 is also provided to a thermal limit value calculation device 42 if necessary. Thermal limit value calculation device 42
calculates various thermal limits to ensure fuel integrity.

On the other hand, the input section of the input/output device 31 outputs a calculation instruction signal 43 in order to obtain necessary data such as the reactor power distribution. The calculation instruction signal 43 is output periodically, for example, once every hour, and is supplied to the data sampler 26 and the correction side numerical measurement set point adjacent fuel rod average power conversion device 27, and is used to transfer data and perform core power distribution. Start calculation.

Of course, the reactor Zyte operator can also generate a total of nine instruction signals 43 at desired times as needed to determine the reactor power distribution.

The reactor power distribution monitoring device described below uses both the thermal neutron flux measuring device 16 and the γ-ray flux measuring device 22 as described above. Among these, several thermal neutron flux measuring devices 16 are fixedly installed in each string for monitoring the power inside the reactor, and constantly obtain numerical values.

The γ-ray flux measuring device 22 is employed as a mobile measuring device in this embodiment, and is used for calibrating the output distribution determined by the fixed thermal neutron flux measuring device 16. The mobile gamma ray flux measuring device 22 is used when the output distribution changes significantly, such as when the control rod insertion pattern changes, and
While moving in the axial direction within the IJ ring, count values are given at multiple points.

Therefore, the gamma ray flux count cannot always be bundled, but in this regard, the effective gamma ray flux count is determined by the following method.

That is, the numerical values of both the fixed thermal neutron flux measuring device 16 and the moving gamma ray flux measuring device 22 at the same measurement point do not match due to the difference in detection efficiency of the measurement target. However, it is possible to obtain a coefficient for each measurement point using the thermal neutron flux measuring device 16 so that the two coincide with each other. Therefore, the gamma ray flux count value at each measurement set point at each point in time is calculated by multiplying the current count value of the thermal neutron flux measuring device 16 in the IJ by this coefficient, and By interpolating the difference between the count value of the γ-ray flux measuring device 22 at the point in time closest to the present time at the position where 16 is installed, γ
It can be determined by adding it to the count value of the flux measuring device 22.

In other words, like the reactor power distribution monitoring device of this embodiment,
Even if the types of the fixed measuring instrument and the mobile measuring instrument are different, no problem will occur because the correction coefficient of the fixed measuring instrument is calculated for the count value of the mobile measuring instrument. Of course, in this example, the r-ray flux measuring device is used as a mobile measuring device that serves as a reference for each measurement set point, and the T-ray flux is measured, so even if the measuring device's position deviates from the center position of 31 numbers are accurate. Therefore, the accuracy of the reactor power distribution monitoring device will be significantly improved. In this way, sufficient accuracy can be obtained by using the T-ray flux measuring device only as a mobile measuring device. Depending on the device, it is also possible to use an r-ray flux measuring device as both a fixed type and a mobile type measuring device.

〔Effect of the invention〕

As described above, according to the reactor power distribution monitoring device of the present invention,
The position of the measuring device in the conduit during the
Even if the IJ song deviates from the center position, the use of the T-ray flux measuring device will allow a more accurate count value to be obtained, and a more accurate reactor power distribution will be stably obtained than when using a thermal neutron flux measuring device. I can do it.

In the present invention, since a T-ray flux measuring device is used, it is necessary to convert the value on the T-ray side to the average output of the fuel rods near the measurement set point. However, this is based on the conventional two-dimensional calculation of the 4-node system, which measures the average output of the fuel rods near the set point, the fuel rod enrichment at each node/job, the concentration of burnable poisons such as Gd, and the average void ratio. It can be easily obtained using the T-ray count value related from the burnup and burnup, and is comparable to conventional devices.

[Brief explanation of the drawing]

FIG. 1' is a perspective view showing the main parts of the core of a nuclear reactor, and FIG. 2 is a block diagram of a reactor power distribution monitoring system according to an embodiment of the present invention. 11... Core, 12... Fuel assembly/body (handle), 14...
...String, 16...Fuel assembly measuring device (fixed type measuring device),
21...Nuclear reactor, 22...T-ray flux measuring device (mobile measuring device), 27
... Correction coefficient value measurement set point adjacent fuel rod average power conversion device, 28 ... Fuel assembly average power calculation device, 29.
...Measurement set point fuel assembly output calculation device, 35.
...T-ray flux counting correction device. Applicant Japan Atomic Energy Corporation Representative Patent Attorney Umeo Yamauchi

Claims (1)

[Scope of Claims] 1. A gamma-ray flux allJ determiner that measures gamma-ray flux at a measurement set point located at the center of a gap surrounded by four fuel assemblies in a core in which a large number of fuel assemblies are arranged; T-ray flux count correction means for correcting the gamma-ray count value obtained from the gamma-ray flux measuring device based on the temporal change in output at the measurement set point using a predetermined physical model; and a corrected count value measurement set point adjacent fuel rod average output conversion means for converting into an average output of a plurality of fuel rods adjacent to the measurement set point loaded in the four fuel assemblies using a relational expression. A nuclear reactor power distribution monitoring device characterized by: 2. The corrected count value measurement set point adjacent fuel rod average output conversion means converts the output to the average output of each of the four fuel rods closest to the measurement set point of the fuel assembly, for a total of 16 fuel rods. A nuclear reactor power distribution monitoring device according to claim 1. 3. A mobile measuring device in which the gamma-ray flux measuring device measures gamma-ray flux while moving in the axial direction of the core in the central position of the gap surrounded by four fuel assemblies in the core in which many fuel assemblies are arranged. A nuclear reactor power distribution monitoring device according to claim 1, characterized in that: 4. A mobile gamma-ray flux measuring device that measures gamma-ray flux while moving in the axial direction of the core in the central position of a gap surrounded by four fuel assemblies in a core in which a large number of fuel assemblies are arranged. 2. The reactor power distribution monitoring device according to claim 1, wherein the reactor power distribution monitoring device is both a fixed measuring device installed at a predetermined position in the axial direction of the fuel assembly at the central position.