JPH039297A - Period trip monitor device - Google Patents

Abstract

PURPOSE:To adequately prevent the rapid increase of reactor output by disposing a fission chamber for which U<235> is used as a neutrom detector and a gammaray detector for which the U<235> is not used adjacently to this fission chamber. CONSTITUTION:The period trip monitor device has the fission chamber 11, the gamma ray detector 12, the fission chamber 11 and a side area measuring instrument 9. The monitor device 10 is connected to this wide area measuring instrument 9. The signal contributed only by the neutron flux detected by subtracting the signal by the gamma ray detector for which the U<235> is not used from the signal by the fission chamber for which the U<235> is detected. The period is evaluated by the signal of only the change in the neutron flux and a trip signal can be emitted without receiving the influence of the noise of the gamma rays even when the neutron flux changes abruptly. The generation of a delay in the time to the trip is, therefore, obviated.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention measures the reactor power from the neutron flux in the startup system region and the intermediate system region in the reactor pressure vessel, and The present invention relates to a period trip monitoring device that generates a control rod withdrawal prevention signal or a scram signal when a transient phenomenon such as an abnormal increase in average output or local output occurs.

(Prior art) Generally, the neutron flux level in a nuclear reactor has a wide measurement range, for example, a boiling water reactor has an 11-digit measurement range, and it is technically difficult to measure it with a single measurement method. . For this reason, conventionally, a combination of three measuring means has been used.

The first measurement method is in the low neutron flux range (start-up region), in which the reactor power is proportional to the count rate.
The neutron flux level is measured by determining the counting rate by counting the low range 6 digits using the pulse counting method. The second measurement means is based on the intermediate neutron flux range (intermediate region), and is measured using the Campbell method, focusing on the fact that in this region the reactor output is proportional to the root mean square value of the fluctuation component of the output signal.

That is, it is measured by the square of the effective value of the AC component of the detector output signal. The third measurement means is based on a high neutron flux range (output region), and focuses on the fact that the reactor output is proportional to the direct current in this region, and measures the direct current from the detector.

In recent years, wide-area measurement devices have been developed that measure pulse measurement and Campbell method measurements using the same device, and the startup region and intermediate region are measured together as one measurement region (startup intermediate region). It became possible to do so.

Furthermore, the methods of handling the above-mentioned measuring means when used as a safety system for a nuclear reactor are also different. Generally, the time T required for the output to increase by e (the base of the natural logarithm) is defined as a period, and is used as an index of output change. In the intermediate startup region, this period is monitored, and if this period exceeds a certain value, a control rod withdrawal prevention signal or reactor emergency shutdown (hereinafter referred to as scram) signal is output.

On the other hand, in the output region, when the output instruction value exceeds a certain value, for example, 120% of the rated output, a scram signal is output. Here, in the startup intermediate range, a sudden increase in output is prevented, and in the output range, the rated output is monitored to ensure the safety of the reactor.

Next, a period trip monitoring device used in the startup intermediate region will be explained. Note that the safety device used in the output region is not directly related to the present invention and will not be described in detail.

FIG. 4 is a block diagram of a conventional period trip monitoring device in the startup intermediate region.

The period trip monitoring device includes a wide-area measuring device 9 that measures the reactor output in the intermediate region of startup, and a monitoring device 10 that outputs a trip signal 8 for preventing control rod withdrawal or for scram based on the reactor output signal from the wide-area measuring device 9. It is equipped with

The wide-area measurement device 9 includes a neutron flux detector 1, a wide-area amplifier 2, a wide-area processing circuit 3, and a switch 4 installed in the nuclear reactor.

Among these, the neutron flux detector 1 uses a fission ionization chamber using U235. The wide-area amplifier 2 separates the output signal of the neutron flux detector 1 into frequency bands, and has a pulse amplifier to which a high frequency component is input and a Campbell system amplifier to which an intermediate frequency component is input. The wide area processing circuit 3 includes a starting output processing circuit that discriminates the pulse height of the output of the pulse amplifier, measures the counting rate, and outputs a starting signal, and an intermediate output processing circuit that takes the square mean of the output signal of the Campbell amplifier, smooths it, and outputs it as an intermediate signal. It has a circuit. The switch 4 allows the intermediate signal to pass when the counting rate of the starting signal is equal to or higher than a preset value, and on the other hand, allows the starting signal to pass when the starting signal is less than the set value.

On the other hand, the monitoring device IO converts the reactor output signal φ from the wide-area measurement device 9 into a signal φ through the amplifier 5 and the low-pass filter 6, compares the reactor output signal φ and the O signal φ with the comparator 7, and outputs the reactor output signal φ. When the signal φ is larger than the signal φ, the control rod withdrawal prevention signal 3 or the scram trip signal 8 is output.

Here, the relationship a between the reactor output signal φ and the signal φ is The relationship is expressed by the following formula.

dφa(1)+λφ(t) =λGφo(t) =i
l)t Here, φo(t): Input signal to the control rod system or scram system monitoring device 10 φa(1): Signal passed through the amplifier 5 and low-pass filter 6 (φa in FIG. 4) G: Amplifier Gain λ of 5: Reciprocal of time constant of low-pass filter 6 Equation (1) can be solved analytically as the neutron flux increases with period τ: φa (1) = G・φo(0)・[λ et / r + λ+1 /τ 1/r −1°t] ...(2) Given by λ+1/τ.

t/τ (φo (t) =φo(0)e) and t=
Utilizing the fact that φa=φ0 in (2), RC=(G-1)·τ (3) is obtained, and the relationship between the time constant RC and the gain G of the low-pass filter 6 is given. Therefore, when RC and G are set in this monitoring device 10, a period τ is given, and if it is desired to issue a control rod withdrawal prevention signal or a scram signal in a certain period (for example, 10 seconds), the corresponding RC and G All you have to do is set a combination of .

For example, if RC = 40 seconds and G = 5 seconds, the trip setting period τ will be τ = 10 seconds from equation (3), and if the reactor output increases in a period shorter than 10 seconds, trip signal 8 will be issued. . FIG. 5 shows an example of a response when the control rod withdrawal prevention setting period is 20 seconds, the scram setting period is 10 seconds, and the neutron flux of the reactor increases at 9 seconds. Reference numeral 30 indicates the reactor output signal φ of the switching device 4 shown in FIG. 4, and reference numeral 31 indicates the gain of the amplifier 5 and the time constant of the low-pass filter 6, which are components of the monitoring device IO, for the scram setting period of 10 seconds. The reference numeral 32 indicates the signal when the gain and time constant are set for the control rod withdrawal prevention setting period of 20 seconds.

A control rod withdrawal prevention signal is generated at the intersection 33, and a trip signal is generated at the intersection 34.

(Problem to be solved by the invention) As mentioned above, in the startup region, the wave height of γ-ray noise is smaller than that of pulses caused by neutrons, so it is only necessary to select pulses with a certain height or higher using a wide-area processing circuit, but in the intermediate region, Since it is measured in the form of a current signal, the influence of gamma rays becomes a problem. That is, if gamma ray noise is mixed, the response characteristics to changes in neutron flux will deteriorate. Figure 6 shows the case where there is no γ-ray noise when there is step-like reactivity input, and
The response characteristics will be shown by taking as an example the case where the γ-ray noise is 40% of the neutron flux signal. In FIG. 6, the reactor output signal when there is no gamma ray noise is designated as 35, and the monitoring device 10
The signal passed through the amplifier 5 and the low-pass filter 6, which are the components of
indicates the intersection of That is, it indicates the trip occurrence point. On the other hand, γ
If the reactor output signal when the line noise is 40% of the neutron flux signal is denoted by 38, the response to that signal after passing through the amplifier 5 and the low-pass filter 6 is a signal denoted by 39, If the intersection of 38 and 39 is indicated by 40, a trip will occur at the point 40. Therefore, due to the incorporation of gamma ray noise, the trip occurrence point is delayed from code 37 to code 40, and the output continues to increase during this time, causing an abnormal temperature rise in the fuel and impairing the integrity of the fuel. There is.

The present invention has been made to solve these problems, and improves the responsiveness of neutron flux changes to appropriately prevent output increases even in response to gamma ray noise without delaying the trip time. An object of the present invention is to provide a period trip monitoring device that can perform period trip monitoring.

[Structure of the Invention] (Means for Solving the Problems) The present invention sequentially connects a neutron detector, a wide-area amplifier, a wide-area processing circuit, and a switching device installed in a nuclear reactor to generate a reactor output signal. A period trip monitoring device comprising: a wide area measurement device; and a monitoring device that outputs a trip signal by passing the reactor output signal through an amplifier and a low-pass filter and outputting a trip signal when the reactor output signal is larger than the trip signal. A fission ionization chamber using U235 as the neutron detector and a gamma ray detector not using U235 are arranged adjacent to the fission ionization chamber, and the U235 is detected from the signal from the fission ionization chamber using U235. It is characterized in that it is connected to an arithmetic processing circuit that subtracts the signal from a gamma ray detector that does not use.

(Function) U235 is detected from the signal from the fission ionization chamber using U235.
By subtracting the signal from a gamma ray detector that does not use neutron flux, it is possible to detect a signal that only contributes to the neutron flux. Therefore, even when there is a sudden change in neutron flux, the period can be evaluated using only the signal of the change in neutron flux without being affected by gamma ray noise, and a trip signal can be issued, so there is no delay in the time until trip. There isn't.

(Embodiment) An embodiment of a period trip monitoring device according to the present invention will be described with reference to FIGS. 1 to 3.

The period trip monitoring device in this embodiment includes a nuclear fission ionization chamber 11 using U235 installed inside the nuclear reactor,
Consists of a gamma ray detector 12 that does not use U235, an arithmetic processing circuit I3 that processes signals from the fission ionization chamber 11 and the gamma ray detector 12, a wide area amplifier 2, a wide area processing circuit 3, and a switch 4. It is equipped with a wide area measuring device 9, and a monitoring device 10 is connected to this wide area measuring device 9.

On the other hand, the monitoring device 10 converts the reactor output signal φ from the wide-area measurement device 9 into a signal φ through the amplifier 5 and the low-pass filter 6, and outputs the reactor output signal φ.

The comparator 7 compares the signal φ and the reactor output signal φ.
When is larger than the signal φ, a control rod withdrawal drive signal or a scram trip signal 8 is output.

Next, the operation of the period trip monitoring device having such a configuration will be explained.

FIG. 2 shows an example of signal changes in the intermediate region when there is a sudden increase in output due to control rod withdrawal.

In the figure, a signal from a fission ionization chamber using U235 is indicated by reference numeral 15. Further, a signal from a γ-ray detector that does not use U235 is indicated by reference numeral 16. Even if there is a sudden increase in output, the change in γ rays is gradual, so the reference numeral 16 does not change vaguely. From the signal (code 15) from the nuclear fission ionization chamber, γ
The line detector signal (reference numeral 16) is subtracted by the arithmetic processing circuit 12. The subtracted signal is indicated by reference numeral 17 in FIG. The signal (reference numeral 17) output from this arithmetic processing circuit 12 becomes an input to the wide area amplifier 2 and finally becomes an output signal of the wide area measuring device 9.

Also in this embodiment, the amplifier 5 and the low-pass filter 6
The signal φ] from the wide area measurement device 9 is the signal φ
The relationships of equations (1), (2), and (3) shown in the prior art section hold true.

Therefore, since the signal φ from the wide-area measurement device 9 is a signal consisting only of the neutron flux component with the γ-ray noise component removed, the trip time generated by the monitoring device 10 does not include the delay time due to the γ-ray noise. It has become.

FIG. 3 shows the response when the γ noise component is not compensated for by the signal of the γ-ray detector without using U235, that is, using the reference numeral 15 in FIG. 2, and when it is compensated according to this embodiment, that is, the The response characteristics using reference numeral 17 in the figure are also shown. In the figure, the reactor output signal in the absence of gamma ray noise is indicated by 21, the signal passed through the amplifier 5 and low-pass filter 6, which are components of the monitoring device 10, is indicated by 22, and 23 is the same as 21. 22 intersection points are shown. That is, it indicates the trip occurrence point.

On the other hand, if the reactor output signal when gamma ray noise is mixed into the neutron flux signal is designated by code 18, then the response obtained by passing the amplifier 5 and the low-pass filter 6 for that signal is a signal of code 19, which is coded 18. If the intersection of 18 and 19 is indicated by 20, a trip will occur at the point 20. That is, reference numeral 20 indicates a trip when the γ-ray noise component is not deleted, and reference numeral 23 indicates a trip point when the γ-ray noise component is eliminated and the trip point is based on a signal of only a change in neutron flux. As is clear from FIG. 3, it is recognized that the trip point is shortened from 20 to 23 in this embodiment.

In this way, according to this embodiment, the period can be evaluated using only the neutron flux component signal from which the γ-ray noise component in the intermediate region has been removed, so that there is no delay in the trip salt time due to the γ-ray noise. This makes it possible to appropriately prevent a sudden increase in reactor power.

[Effects of the Invention] According to the present invention, when the reactor output increases for a period smaller than the trip setting period, the trip salt due to the γ-ray noise can be reduced even in the intermediate region where the ratio of the γ-ray noise component to the neutron flux signal is large. It is possible to output a trip signal without delaying the output time, appropriately prevent this output increase, and ensure the health of the fuel.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining one embodiment of the period trip monitoring device according to the present invention, FIG. 1 is a block diagram thereof, and FIG. 2 is a diagram showing the neutron flux signal and γ in the intermediate region.
Figure 3 is a characteristic diagram showing an example of a radiation noise component. Figure 3 shows an example of the response of the reactor output signal and trip signal when there is a step-like reactivity injection, with and without the gamma ray noise component. Fig. 4 is a block diagram showing a conventional period trip monitoring device, Fig. 5 is a characteristic diagram showing response examples of the reactor output signal and trip signal of the conventional device, and Fig. 6 shows gamma ray noise FIG. 6 is a characteristic diagram showing a response example explaining that the trip time is delayed due to the delay in the trip time. 8...Trip signal 9...Wide area measuring device IO...Monitoring device 11...Fission ionization chamber 12...γ-ray detector 13...Arithmetic processing circuit (8733) Agent Patent attorney Inomata Yoshiaki (and others)
1 person) 1...Neutron flux detector 2...Wide area amplifier 3...Wide area processing circuit 4...Switcher 5...Amplifier 6...Low pass filter 7...Comparator fence Figure 'i 4th cabinet map

Claims (1)

[Claims] A neutron detector, a wide-area amplifier, a wide-area processing circuit, and a switching device installed in the reactor are connected in sequence, and a wide-area measurement device generates a reactor output signal, and the reactor output signal is tripped through an amplifier and a low-pass filter. as a signal for
A period trip monitoring device comprising: a monitoring device that outputs a trip signal when the reactor output signal is larger than the trip signal; a nuclear fission ionization chamber using U^2^3^5 as the neutron detector; , A gamma ray detector that does not use U^2^3^5 is placed adjacent to this fission ionization chamber, and an arithmetic processing circuit that subtracts the signal from the gamma ray detector from the signal from the fission ionization chamber is connected. A period trip monitoring device characterized by: