JPH0551117B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a neutron flux measuring device in a nuclear power plant.

[Technical background of the invention and its problems]

In boiling water nuclear power plants, the system is based on data such as the neutron flux and core water flow rate, pressure, and temperature measured by fixed neutron flux measurement devices installed in the reactor core for the purpose of monitoring the reactor core. Core performance calculations are being carried out using process computers. Accurate measurements of neutrons lead to accurate calculations of core power, which in turn provides a fuel health monitoring point. The sensitivity of fixed neutron flux measurement devices deteriorates because they are constantly irradiated within the reactor core. In order to compensate for this deterioration, fixed neutron flux measurements are calibrated by scanning the inside of the reactor core with a movable neutron flux measurement device at key points during operation.

In other words, the measurement values from the mobile neutron flux measurement device (later referred to as TIP) determine the accuracy of core performance calculations.
TIP inputs neutron flux signals by being driven by a drive device from top to bottom of the reactor core, but because the TIP is inserted and operated inside the thin guide tube inside the reactor core, the drive cable bends, etc. There is a hidden possibility that an error will occur in the absolute positioning of the direction. Conventionally, TIP scanning data is recorded using a pen recorder at the time of scanning signals, and whether or not axial positional deviation has occurred can be determined by using pen recorders installed at several locations in the axial direction of the reactor core. Neutrons are absorbed by a spacer, which is a type of reactor internal structure, and a "dent" DIP is created on the chart where the neutron flux is absorbed at the location of the spacer.Using this fact, positioning is performed visually. There is.

However, as it stands now, there is a possibility that individual reading errors may occur, and it is not possible to process it on-line, and it takes time to scan the entire core when starting up a nuclear power plant. ing. Gamma-ray TIP that uses gamma rays instead of conventional TIP that uses neutrons to improve the accuracy of current TIP measurement values
is increasingly being applied. This gamma ray TIP
is effective for correcting the radial deviation of the reactor inside the TIP guide tube, but the signal level is more than 2 orders of magnitude or weaker compared to the conventional type, making it inferior to the axial positioning of the spacer by dip. There is.

In order to eliminate individual reading errors, a technique disclosed in, for example, Japanese Patent Application Laid-Open No. 58-205894 has been proposed as a method of automatically correcting the axial deviation using a computer. The method disclosed in this publication first averages the measured values to remove noise, calculates the deviation based on the slope of the averaged output distribution shape, and then calculates the deviation before and after the calculated position. This is a method to correct the deviation.

However, with this method, it is difficult to actually specify the dip position, and the corrected output distribution shape may be distorted, so improvements are desired.

[Object of the Invention] An object of the present invention is to obtain a neutron flux measuring device that detects Dip using a computer and can correct the measured value with high accuracy.

[Summary of the invention] The raw data of neutron flux measured by a neutron flux measurement device is input into a process computer, and the singular point of the second-order difference value of the measured value is determined near the position of the actual neutron absorber (for example, a spacer). The deviation from the singular point of the quadratic approximation curve is determined for each neutron absorber, and all measured values are corrected using these average values.
This allows Dip detection to be performed with high precision, and the shape of the output distribution in the axial direction to be faithfully reproduced.

[Embodiments of the invention]

FIG. 1 shows the configuration of the present invention. A movable neutron flux measuring device 3 moves inside a neutron flux measuring device guide tube 2 installed in the reactor core 1 into a neutron flux measuring device driving device 4.
The neutron flux is measured while moving from the top to the bottom of the core at a constant speed. The measured signal is introduced into the process computer 6 via the process input/output device 5.

After the signal is appropriately processed by the input processing means 61, the measured value correction means 62 detects the DIP and corrects the deviation by the method described later, and then the corrected data is sent to the core performance calculation means 6.
3, quantities such as power distribution and flow rate distribution are calculated according to a predetermined method, and the results are sent to the output device 7 such as a typewriter or CRT via the output processing means 64 as necessary data of the reactor core. It is output and presented to the operator 8.

As shown in FIG. 2, if the neutron flux measuring device operates correctly as designed, the position of the dip should coincide with the position of the spacer, which is an internal structure of the reactor. However, if the measurement position of the neutron measurement device is incorrect due to a problem with the drive system, a measurement value like f _p (x) in FIG. 3 is obtained. Here, it is assumed that the neutron flux measuring device performs measurements at intervals of Δ. Here, if the original correct reading is f _c (x), it can be assumed that the deviation a is the same value for each spacer with good accuracy, so f _c (x) = f _p (x + a) ...( The relationship 1) holds true.

Up and down N△ centered on spacer position x=x _p
(Here, N is a constant, △ is the distance between the measured data of neutron flux measurements), that is, x = x _p + N △ to x = x _p
The second-order difference of the curve f _p (x) in the region between −N△ d(x _i )=f _p (x _i −△)−2f _p (x _i )+f _p (x _i +
△)……(2) Calculate x _p +N′△x _i x _p +N△ Let the next quantity be g(x _i ) g(x _p )=Max {d(x _i ) | x _p −NΔx _i x _p +NΔ} However, in order to eliminate abnormal spikes due to defective inputs, it is checked that the following condition is satisfied: O≦g(x _p )≦A (3).

If the formula is not satisfied, that value is removed as a defective value, and the same operation is repeated for the remaining measurement points excluding the coordinates where that value occurs. Here, g(x _p ) is f _p in the vicinity of x=x _p +a
This corresponds to the coefficient _a 1 when (x) is approximated by a quadratic function q(x)=a ₁ x ² +a ₂ x+a ₃ .

x _a = {x _i | d(x _i )=g(x _p )} ...(4), then x _a = x _p + a, and conversely, a=x _a −x _p ...(5) a is required.

In order to improve the accuracy of this detection, calculate the deviation a _j for each spacer position x = x _pj j = 1, 2, 3,...m (m: total number of spacers) and calculate the average value. Define and use a in .

〔Effect of the invention〕

Measuring neutron flux with high precision improves the accuracy of core performance calculations, which enables efficient operation. Furthermore, this Dip detection method does not rely on the absolute value of the neutron flux value, and can be applied even when the neutron flux intensity is weak, and can also accurately reflect the shape of the output distribution.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the present invention, Fig. 2 is an explanatory diagram of DIP occurring in the neutron flux measurement value due to the spacer, and Fig. 3
The figure is a diagram of the principle of correcting neutron flux measurement values. 1... Reactor core, 2... Neutron flux measuring device guide tube,
3...Movable neutron measurement device, 4...Neutron measurement device drive device, 5...Process input/output device, 6...
...Process computer, 7...Output device, 8...Operator, 9...Spacer.

Claims (1)

[Claims] 1. A movable neutron flux measurement device that moves vertically within the core of a nuclear reactor to measure neutron flux intensity;
It consists of a drive device that drives this, and a process computer that inputs the measured values detected by the movable neutron flux measurement device, calculates the power distribution in the core, and outputs the calculation results via the output device. In the neutron flux measuring device, the process computer determines the position of the neutron absorber from the singular point of the second-order difference value of the measured value near the neutron absorber and the singular point of the quadratic approximation curve, and calculates the position of the neutron absorber from the singular point of the second-order difference value of the measured value near the neutron absorber, and calculates the position of the neutron absorber from the singular point of the second-order difference value of the measured value near the neutron absorber A neutron flux measurement characterized by comprising a measurement value correction means for determining the deviation from the position of the neutron absorber for each neutron absorber and correcting the vertical deviation of the entire measured value using the average value of this deviation. Device.