JPS5910888A - Core stability monitoring device of bwr type reactor - 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 The present invention relates to a core stability monitoring system for a boiling water nuclear reactor.

[Technical background of the invention and its problems]

Normally, boiling water reactors operate by controlling both the control rods and the core flow rate to increase or decrease the reactor output, but under certain conditions, the reactor core and Canopling of thermal-hydraulic dynamics may cause the core to become unstable. Therefore, the current situation is to change the reactor power and core flow rate within the ranges set in advance through design calculations. On the other hand, if the above-mentioned stability can be constantly measured and monitored, it will not only be useful for the safe operation of a nuclear power plant, but also the conventional operating range can be expanded, leading to more efficient operation of an atomic coupler.

Conventionally, the equipment for measuring core stability is as follows:
A method has been proposed in which artificial disturbance is applied to the plant and evaluation is made from the response, and a method in which the power spectrum density of the fluctuating component of the neutral r-flux signal is determined in a steady state and the stability is evaluated from that butter. However, it is a device that calculates stability after measuring data of a certain length, and is not a device that measures stability online sequentially.

In addition, there is an online sequential monitoring device based on an autoregressive model, but it is complicated and a simpler and more direct device is desired.

[Purpose of the invention]

The present invention has been made based on the circumstances mentioned above, and an object of the present invention is to obtain a core stability monitoring device that can sequentially monitor core stability online.

1. Summary of the Invention In the present invention, the above is achieved by analyzing the fluctuation component of a neutron flux signal that is always obtained in a steady state.

Examples of the invention] The present invention will now be described in detail.

The fluctuation component of the neutral P flux signal obtained from the plant is expressed as X(t
), its Fourier transform is given by the following equation (1).

This calculation uses a fast Fourier transform algorithm (if the data is x(t+(N-1)△t) ~
When N points are collected every second, T=N△ can be performed in real time at intervals of seconds. The self-power spectral density (APSD) corresponding to equation (1) is determined by linear equation (2).

Furthermore, in order to monitor core stability, it is necessary to average this APSD over a certain period of time. .

In the present invention, the above-mentioned averaging operation is performed sequentially as follows.

That is, the APSD of book F is at time t, t −'+r,
is obtained sequentially every -2T... However, due to the fear, the averaged APSDPj(f) is calculated using the following equation (8).

Pt(r)-tun(f)+-(Pj(f)-Pj(f))
・・・・・・(3) Note that the formula (B) r4+ M corresponds to the number of times of this averaging operation, and ′α is used to adjust this value.
One for special changes in Replant] Two sets of APSDPt
The followability of (f) can be changed. If the value of M is small, the followability improves, but the accuracy of PI(f) deteriorates, and conversely, if the value of M is large, the followability deteriorates and the accuracy of Pt(f) improves. In consideration of such characteristics, the present invention uses the following method to change M as needed to improve followability to changes in plant characteristics.

First, a change in the operating conditions of the plant is detected from the slope of the signal X(t). That is, where α is a threshold.

When this change is detected, the above-mentioned M is successively changed from 1 to M as shown in Fig. 1 every time the time advances by T seconds, thereby improving the followability of the above-mentioned APSD calculation when the operating conditions of the plant change. There is.

Next, a method for determining the reduction [1] ratio and resonance frequency, which are measures of core stability, from the APSDPj(f) will be described.

Normally, in this APSD, there is a resonance peak indicative of core stability around 03 to 0.5 Hz, and the shape of this peak is expressed by the following approximate equation (5).

This approximate formula and the actual APSD are A, ζ, and 8 in 1 set.

By adjusting, a good match can be obtained. This is performed according to the principle of the nonlinear least squares method, which is evaluated as follows: A, ζ+JR that minimizes the function is found (a). Among the parameters thus determined, ζ is called the attenuation rate, and is connected to the width reduction ratio as shown in the following equation (7).

DR=e-2"(/h ding and-......
(7) The words 1 and 1 are calculated by Pi at a time interval of every T seconds.
It is executed every time (f) is obtained one after another, and the determined width reduction ratio DR and resonance frequency -f□ are output. Here, the formula (6
) is the resonance peak/lt+, which indicates core stability.
Since + varies depending on the operating conditions of Zoran 1, it is most effective to give it as follows.

/ m a x - / RO + △f / min "" / R (+ - △f where /no is the peak frequency of A P S D P, (f), △
f is a design parameter that specifies the width of the fitting band.

FIG. 2 shows an example of APSD performed in this manner and the approximation formula (5) after fitting.

FIG. 3 is a block diagram of one embodiment of the present invention.

The neutron flux signal obtained from the original T reactor is sent to a trigger detection device 1 and a Fourier transform device 2.

The Fourier transform device 2 performs Fourier transform on the fluctuation component of the neutron flux signal according to equation (1), and sends this to the power spectral density sequential calculation device 3.

- On the other hand, the trigger detection device 1 detects a disturbance in the plant based on equation (4) and changes the weight of APSD sequential calculation. The power spectral density sequential calculation device 3 sequentially calculates A P SD based on the output of the trigger detection device 1 and the output of the Fourier transform device 2 based on equation (8).

The stability analyzer 4 applies equation (5) to the APSD obtained as described above to obtain the attenuation ratio and resonance frequency.

The calculated values of the power spectral density sequential calculation device 3 and the calculated values of the stability estimating device 4 are not only their current values, but also retroactive values (a fleeting value is stored in the storage device 5 and displayed on the display device 5). 6 to display the trend.

Note that when the width reduction ratio obtained by the stability estimating device 4 exceeds a predetermined value, the alarm device 7 generates an alarm to alert the operator.

] According to the device of the present invention having the configuration described in (2) above, the trend display of the power spectrum density, attenuation ratio, and resonance frequency is displayed on the display device 6, so that the operator can effectively know the changes in the above and 11 etc. online. , core stability can be monitored.

〔Effect of the invention〕

As is clear from the above, according to the present invention, core stability can be constantly monitored online, and atomic coupler/
This not only contributes to the safe operation of nuclear reactors, but also enables the operating range of the nuclear reactor to be expanded compared to the conventional method, and enables efficient plant operation.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a weight change method for APSD sequential calculation, FIG. 2 is a diagram showing an APSD fitting sequence, and FIG. 3 is a diagram of an embodiment of the present invention. It is a lock diagram. 1--Trigger detection device, 2--Fourier transform device, 3-Power spectral density sequential calculation device, 4-Stability estimation device, 5--Storage device, 6--Display device, 7--Warning device application Agent Patent Attorney Gobe Kikuchi

Claims (1)

[Claims] The power is controlled by a Fourier transform device that performs Fourier transform of the fluctuating component of the neutron flux signal of a boiling water nuclear reactor, a trigger detection device that detects disturbances in the reactor, and the output of the Fourier transform device and the weight given by the trigger detection device. A power spectral density sequential calculation device that sequentially calculates spectral density in real time, and a quadratic transfer function model applied to the output of this power spectral density sequential calculation device to calculate the reduction ratio and resonance frequency that indicate core stability. A stability estimation device to be obtained, a storage device for storing power spectral density, attenuation ratio, and resonant frequency, and a display device for constantly displaying temporal changes in each of these quantities; 1. A reactor core stability monitoring device for a boiling water reactor, comprising: an alarm device that issues an alarm when an alarm occurs.