JPH0433000B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The present invention relates to a method of obtaining data for control protection device adjustment by an analytical method, and more particularly to a method of obtaining data for nuclear instrumentation calibration. [General Description] To monitor the axial neutron flux distribution within a nuclear reactor, the axial power distribution deviation (△) is usually used. Here, △ is defined as follows. △=AO・P AO=P _T −P _B /P _T +P _BWhere , P: Relative power, P _T : Reactor upper half power, P _B : Reactor lower half power, AO: Axial offset , is. Signals corresponding to P _T and P _B are obtained by processing currents from a long neutron detector installed outside the target nuclear reactor. Although such a detector system has four channels, the current from each detector varies depending on variations in the characteristics of the detector itself and the power distribution characteristics within the reactor. be.
Therefore, by adjusting these,
Both channels are required to accurately represent the axial neutron flux deviation within the reactor. By the way, the axial power distribution inside the nuclear reactor is determined by the Movable Detector (M/M).
Insert the means called D) into the simple instrumentation tube of the nuclear fuel assembly loaded in the reactor,
Obtained by scanning in the axial direction. Assuming that the axial power distribution within the reactor obtained in this manner is the true value, adjustments are made so that the reactor AO can be accurately grasped by nuclear instrumentation other than the reactor. In order to make such adjustments, it is necessary to moderately oscillate the axial power distribution inside the reactor and obtain data on the power distribution inside the reactor and the neutron detector current outside the reactor at several points. be. [Prior art] In order to obtain this kind of data, conventional methods have been used to intentionally create disturbances in the axial power distribution by operating control rods, etc., to cause sequinon oscillations in the power distribution of the reactor. It has been taken. In this case, since xenon oscillations as described above are used, the output level of the entire reactor is reduced by about 25% to prevent local high output from being generated in the nuclear fuel. Ta. However, it can be pointed out that this conventional method has the following drawbacks. (1) During normal operation, it is necessary to reduce the reactor power in order to obtain this data. (2) It is necessary to intentionally generate xenon vibrations that do not occur during normal operation. It is desirable to avoid these drawbacks as much as possible from the viewpoint of economic efficiency and safety of nuclear power plant operation. [Summary of the Invention] This invention has been made to eliminate the above-mentioned drawbacks, and uses a response matrix of the external core instrumentation calculated in advance by analysis and a plurality of axial outputs of the target core determined by separate analysis. The required data is obtained by calculating the product of each of the distributions, calculating the response of the upper and lower half detectors from this result, and calculating the correlation with each axial offset of the axial output distribution. Its purpose is to provide a method for obtaining. [Embodiment of the invention] Figure 1 shows a nuclear reactor 1 and an extra-reactor neutron detector.
FIG. 2 is a model diagram in which the relationship between Di is discretized, focusing in particular on the axial component. In this Figure 1, Pi: discretized axial power distribution (i=1, 2,
...2n) Di: Discretized detector sensitive part, a: Distance from the outermost periphery of the core 2 to the outermost periphery of the pressure vessel 3, b: Distance from the outermost periphery of the pressure vessel 3 to the center of the detector Di, . In the discretized model of FIG. 1, if the detection current of each detector Di is i, then the upper half detection current _T and the lower half detection current _B can be respectively expressed as follows. I _B = _o 〓 ⁱ⁼¹ I _T = _2o 〓 ⁱ⁼ⁿ⁺¹ _i . From this, it is recognized that in order to find the relationship between the reactor power distribution and the external detector current, it is sufficient to find the relationship between the in-reactor power distribution and the detector current _i of the detector Di. I ₁ is calculated using the following calculation. _{| I} | ₌ ^| D| P ₁ , P ₂ , ..., P _2o | ^Tr I _B = _o 〓 ⁱ⁼¹ I _i , I _T = _2o 〓 ⁱ⁼ⁿ⁺¹ _i . However, T _r indicates an inverted matrix. In this way, it becomes possible to analytically evaluate the |D| matrix. Rewriting the above formula, it becomes as follows. I ₁ I ₂ 〓 I _2o = d ₁₁ , d ₁₂ , d _1,2o d ₂₁ , d ₂₂ , d _2,2o d _2o1 , d _2o2 , d _2o2o P ₁ P ₂ P ₂ n I _i = _2o 〓 ^{j= 1} d _ij・P _j From this, the current I _i of the detector D _i is the output P ₁ ~ P _2o
It is recognized that is the sum of the contributions each makes to the detector D _i . The above d _ij represents the conversion coefficient of P _j to the response of the detector D _i . This can be evaluated as follows by assuming a simple model. First, move the surface of the pressure vessel 3 in the axial direction (↑ direction)
Divide into 2n equal parts. In each of these parts, the following neutron flux from the neutron source from the unit output at the axial position Z _i is calculated.
Let S _k be obtained as follows.

〔Effect of the invention〕

It has been confirmed through follow-up tests based on a large amount of data including the initial core and replacement core that the evaluation results obtained using the method of this invention are sufficiently valid.
There is no problem with its reproducibility. Therefore, according to the method of the present invention, the product of the response matrix of the external core instrumentation calculated in advance by analysis and each of the plurality of axial power distributions of the target reactor core obtained by separate analysis is calculated, and this result is calculated. from,
By calculating the responses of the upper and lower half detectors and finding the correlation with each axial offset of the axial power distribution, data can be accurately acquired for nuclear instrumentation calibration in the reactor. be.

[Brief explanation of drawings]

Figure 1 is a discretized model diagram showing the relationship between the nuclear reactor and the ex-core neutron detector, Figure 2 is an explanatory diagram for obtaining the angle ω _j looking into the detector D _j from the neutron flux S _K ,
FIG. 3 is a block diagram illustrating the configuration of an apparatus for carrying out the method of the present invention. 1, 11... Nuclear reactor, 2... Core, 3... Pressure vessel, D _i , 12, 13... Ex-core neutron detector, 1
4...AO calculation device, 15...Calibration data calculation device.

Claims (1)

[Claims] 1 Find the product of the response matrix of the external core instrumentation calculated in advance by analysis and each of the multiple axial power distributions of the target reactor core obtained by separate analysis, and from this result, calculate the response of the upper and lower half detectors. 1. A data acquisition method for nuclear instrumentation calibration, characterized by calculating the correlation between the axial power distribution and each axial offset of the axial power distribution.