JP6132521B2 - Subcriticality measuring method and apparatus - Google Patents

Description

  The present invention relates to a subcriticality measuring method and apparatus for evaluating the subcriticality of a nuclear reactor.

  When the reactor starts up, critical operations are performed while monitoring that the reactor is subcritical. A representative example of the conventional subcriticality evaluation technique is the neutron source multiplication method. In the process of bringing the core closer to the criticality, the inverse count rate ratio between the detector response of the neutron detector in the reference state of the core and the detector response of the neutron detector in a certain core state different from the reference state is calculated. This is a technique for monitoring the subcriticality of the core by measuring. Patent Document 1 discloses a technique for accurately evaluating the subcriticality of a nuclear reactor.

JP 2004-170427 A JP 2008-157669 A

  Since the conventional neutron source multiplication method is based on a single point reactor model, it is suitable for subcritical monitoring in an actual core, but is not suitable for accurate subcriticality measurement. The technique disclosed in Patent Document 1 is a technique for evaluating subcriticality over a wide range from deep subcriticality to criticality, but there is still room for improvement. Moreover, although the technique disclosed in Patent Document 2 is an improvement of the technique of Patent Document 1, the application method of the subcriticality difference due to the boron concentration difference is not specific.

  The present invention solves the above-described problems, and an object of the present invention is to provide a subcriticality measurement method and apparatus that can accurately evaluate the subcriticality over a wide range from deep subcriticality to criticality.

In order to achieve the above object, the subcriticality measurement method of the present invention includes a detector output φ ^ref of the neutron detector in the reference state of the core and a reference state in the process of reaching the criticality of the reactor core. A corrected inverse count rate ratio obtained by correcting an inverse count rate ratio φ ^ref / φ, which is a ratio with the detector output φ of the neutron detector in a core state before reaching the criticality different from the above, is obtained, and the corrected inverse count The procedure for calculating the predicted subcriticality in the core state when determining the rate ratio by core analysis using the core analysis model, the control rod position and the boron concentration are changed, and the boron concentration measurement value at the time of changing the boron concentration and A method of obtaining a relational expression between the corrected inverse count rate ratio and the predicted subcriticality obtained in the process of reaching the criticality of the core by taking into account the calculation error when changing the control rod position. When and is characterized in that it comprises, a step of evaluating the subcriticality using the relational expression.

  Therefore, the subcriticality of the core is measured using a relational expression between the corrected inverse count rate ratio obtained in the process of reaching the criticality of the nuclear reactor and the predicted subcriticality obtained by the analysis. In this case, the corrected inverse count rate ratio and the predicted subcriticality are calculated by changing the control rod position and the boron concentration, and taking into account the boron concentration measurement value when the boron concentration is changed and the calculation error when the control rod position is changed. It can be obtained with high accuracy. As a result, the relational expression can be calculated using a wide range of corrected inverse count rate ratios from the deep subcriticality to the criticality. As a result, the subcriticality can be measured over a wide range from the deep subcritical state to the criticality.

  The subcriticality measuring method of the present invention is characterized in that the calculation error includes a correction using a boron concentration measurement value and a calculation error of a control rod value.

  Therefore, the error due to the effect of the subcritical error is corrected by obtaining the relational expression between the corrected inverse count rate ratio and the predicted subcriticality in consideration of the correction using the boron concentration measurement value and the calculation error of the control rod value. be able to.

  Further, the subcriticality measuring method of the present invention corrects the calculated value of the predicted subcriticality based on a measured value using the measured value of the predicted subcriticality and the boron concentration, and the corrected inverse count rate ratio and The relational expression with the predicted subcriticality is obtained again.

  Accordingly, the calculated value of the predicted subcriticality is corrected based on the measured value using the measured value of the predicted subcriticality and the boron concentration, and a relational expression between the corrected inverse count rate ratio and the predicted subcriticality is obtained. By correcting, the relational expression between the corrected inverse count rate ratio and the predicted subcriticality can be obtained with high accuracy.

  In addition, the subcriticality measurement method of the present invention adjusts the control rod nuclear constant so that the slope of the linear relational expression when the control rod position is changed and the slope of the linear relational expression when the boron concentration is changed coincide. Further, a relational expression between the corrected inverse count rate ratio and the predicted subcriticality is obtained again.

  Therefore, the control rod nuclear constant is calculated so that the slope of the linear relational expression when the control rod position is changed and the slope of the linear relational expression when the boron concentration is changed, and the corrected inverse count rate ratio and the predicted subcriticality are By recalculating the relational expression, the relational expression between the corrected inverse count rate ratio and the predicted subcriticality can be obtained with high accuracy.

Further, the subcriticality measuring apparatus of the present invention provides a detector output φ ^ref of the neutron detector in the reference state of the core in the process of reaching the criticality of the reactor core, and before the criticality is different from the reference state. When calculating the corrected inverse count rate ratio obtained by correcting the inverse count rate ratio φ ^ref / φ, which is the ratio with the detector output φ of the neutron detector in the core state of the reactor, by the correction coefficient, The core evaluation unit that calculates the predicted subcriticality in the core state by core analysis using the core analysis model, the control rod position and boron concentration are changed, and the boron concentration measurement value and control rod position change when the boron concentration is changed A calculation unit for obtaining a relational expression between the corrected inverse count rate ratio and the predicted subcriticality obtained in the process of reaching the criticality of the core by taking into account the calculation error at the time, and the relationship A correction unit for evaluating the subcriticality with, is characterized in that comprises a.

  Therefore, the subcriticality of the core is evaluated using a relational expression between the corrected inverse count rate ratio obtained in the process of reaching the criticality of the nuclear reactor and the predicted subcriticality obtained by analysis. In this case, the corrected inverse count rate ratio and the predicted subcriticality are calculated by changing the control rod position and the boron concentration, and taking into account the boron concentration measurement value when the boron concentration is changed and the calculation error when the control rod position is changed. It can be obtained with high accuracy. As a result, the relational expression can be calculated using a wide range of corrected inverse count rate ratios from a deep subcritical state to a critical vicinity. As a result, the subcriticality can be evaluated over a wide range from subcritical to critical.

  According to the subcriticality measuring method and apparatus of the present invention, the subcriticality can be accurately evaluated over a wide range from subcritical to critical.

FIG. 1 is a schematic diagram showing a configuration of a nuclear reactor to which a subcriticality measuring apparatus according to an embodiment of the present invention is applied. FIG. 2 is an explanatory diagram regarding a method for determining a proportionality constant. FIG. 3 is a flowchart showing a procedure for evaluating the control rod value. FIG. 4 is an explanatory diagram relating to a method of correcting the corrected inverse count rate ratio with respect to the predicted subcriticality based on the detector response. FIG. 5 is a schematic diagram showing the configuration of the subcriticality measuring apparatus according to the present embodiment.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited to the best mode for carrying out the invention. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same. The present invention can be applied to a facility that handles a nuclear reactor or nuclear fuel of a type that adjusts the reactivity by using boric acid and a control rod.

  The subcriticality measurement of this example is performed by evaluating the subcriticality of the core using the relational expression between the corrected inverse count rate ratio and the predicted subcriticality obtained in the process of reaching the criticality of the core, and in the vicinity of the criticality. It is characterized in that the core analysis model used for calculating the correction coefficient and the subcriticality is corrected by measuring the reactivity in (1).

  In addition, the subcriticality measurement of the present embodiment is performed by changing the control rod position and the boron concentration when evaluating the subcriticality of the core using the relational expression between the corrected inverse count rate ratio and the predicted subcriticality. It is characterized in that the corrected inverse count rate ratio and the predicted subcriticality are obtained by taking into account the calculation error that occurs at the time of the change.

  FIG. 1 is a schematic diagram showing a configuration of a nuclear reactor to which a subcriticality measuring apparatus according to an embodiment of the present invention is applied. As shown in FIG. 1, the nuclear reactor 1 detects the neutrons radiated | emitted from the core 2 by the neutron detector 30 arrange | positioned around the core 2 and outside, and the operation is controlled based on this neutron. . In the operation of the nuclear reactor 1, a neutron detector 30 capable of detecting neutrons in a source region (SR), an intermediate region (IR), and an output region (PR: Power Range). And the measurement range of each neutron detector 30 is overlapped. Thereby, the wide measurement range required for the operation of the nuclear reactor 1 can be sufficiently covered.

  The neutron detector 30 is connected to the subcriticality measuring apparatus 10 of the present embodiment, and a detector output, that is, a detector response φ is acquired. The subcriticality measuring apparatus 10 calculates an effective multiplication factor k from the acquired detector response φ. Further, the subcriticality measuring apparatus 10 is transmitted with the moderator temperature, boron concentration, control rod state, and other core parameters. Based on these pieces of information, the subcriticality measuring apparatus 10 evaluates the subcriticality of the core 2.

  A fuel 5 is disposed in the core 2. The fuel 5 is a fission material such as uranium or plutonium. A moderator 3 is disposed around the fuel 5. In order to carry the heat of the core 2 to the outside, the coolant is supplied from the coolant inlet 9i and taken out from the coolant outlet 9o. In the light water reactor, water serves as both the coolant and the moderator 3. The nuclear reactor 1 includes a plurality of control rods 4 that can be inserted into and extracted from the core 2. The state of the core 2 can be controlled by taking the control rod 4 into and out of the core 2 and adjusting the boron concentration of the core cooling water.

In the subcritical core 2, the relationship shown in the formula (1) is established.
1-k∝SCF ′ × (∫SdV / φ) (1)
Where φ is the detector response (detector output), SCF is the correction factor, and S is the neutron source intensity. k is an effective multiplication factor to be obtained, and subcriticality can be evaluated by (1-k) on the left side of Expression (1). In the following example, (1-k) is used as a scale for evaluating subcriticality, and the subcriticality and (1-k) are treated as synonymous. In the equation (1), when the ratio between the reference state ref with the core 2 and the state with the core 2 (for example, the core state before reaching the criticality) is taken, the term of the neutron source strength S can be eliminated. ) Is obtained.
(1-k) / (1-k ^ref ) = (SCF ′ / SCF ′ ^ref ) × (φ ^ref / φ) (2)
In equation (2), φ ^ref / φ is referred to as an inverse count rate ratio. Further, in equation (2), if correction coefficient SCF = (SCF ′ / SCF ′ ^ref ), equation (2) becomes equation (3).
(1-k) = (1-k ^ref ) × SCF × (φ ^ref / φ) (3)
Further, when (1-k ^ref ) is a and SCF × (φ ^ref / φ) is ICRR, Equation (3) becomes Equation (4).
1-k = a × ICRR (4)
Here, a is a proportionality constant, and the corrected inverse count rate ratio ICRR is obtained by correcting the ratio of the detector response to the detector response reference value in the reference state ref by the correction coefficient SCF. In equation (4), the corrected inverse count rate ratio ICRR can be obtained from the actually measured detector response φ. Therefore, if the proportionality constant a can be determined, the detector response in each core state, that is, the output signal value of the detector. From this, the subcriticality (1-k) can be determined.

Next, a method for determining the proportionality constant a will be described. FIG. 2 is an explanatory diagram regarding a method for determining the proportionality constant a. In order to determine the proportionality constant a, the corrected inverse count rate ratio ICRR in each subcritical state is plotted against the predicted subcriticality (1-k) ^P obtained by analysis, and for example, an approximation method such as a least square method Thus, a relational expression between the corrected inverse count rate ratio ICRR and the predicted subcriticality (1-k) ^P is calculated. Thereby, Formula (5) is obtained.
1-k = a _fit × ICRR + b _fit (5)
As can be seen from the equation (5), in this embodiment, this relational expression is a linear expression (hereinafter referred to as a linear relational expression). Here, a _fit and b _fit are constants obtained in the approximation calculation to the linear expression by the least square method. Subcriticality can be evaluated using equation (5).

  At this time, if the subcriticality of the state where the control rod 4 is inserted into the core 2 is measured, and the subcriticality is measured when the control rod 4 is pulled out, the difference becomes the control rod value. . Also, if the subcriticality is measured in a state where the concentration of boron in the coolant is a predetermined value, and the subcriticality is measured when the boron concentration in the coolant is diluted, the difference is due to the change in boron concentration. The reactivity changes. In this embodiment, the value of the control rod is evaluated by using the change in detector response when the position of the control rod 4 and the concentration of boron are changed.

In the core 2, the neutron flux distribution changes according to the subcriticality. Therefore, the correction coefficient SCF of the corrected inverse count rate ratio ICRR is not only the core condition such as the position of the control rod 4 and the boron concentration, but also the subcriticality. It is also a function of degree, and there is a considerable influence due to subcriticality error. That is, theoretically, if the predicted subcriticality (1-k) ^P can be accurately predicted, the relationship between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR is as follows: It can be expressed by a single linear relational expression with the same inclination at the time of pulling out and at the time of boron dilution. However, when the calculation error of the predicted subcriticality (1-k) ^P is linear, the linearity relation between the linear relational expression at the time of pulling out the control rod 4 and the linear relational expression at the time of boron dilution is maintained. Affect the tilt. The linear relational expression at the time of pulling out the control rod 4 and the linear relational expression at the time of boron dilution may have different slopes depending on the calculation error of the control rod value. Therefore, in this embodiment, the linear relational expression at the time of pulling out the control rod 4 and the linear relational expression at the time of boron dilution are obtained separately and corrected to one linear relational expression by an approximation method such as a least square method. .

Hereinafter, a method of correcting the relational expression (5) between the corrected inverse count rate ratio ICRR and the predicted subcriticality (1-k) ^P will be described with reference to FIGS. FIG. 3 is a flowchart showing a procedure for evaluating the control rod value, and FIG. 4 is an explanatory diagram regarding a method of correcting the corrected inverse count rate ratio with respect to the predicted subcriticality based on the detector response.

First, the detector response φ when the control rod 4 is pulled out and the detector response φ when the boron concentration is diluted are acquired (step S01). Then, based on the detector response φ when the control rod 4 is pulled out and the detector response φ when the boron concentration is diluted, as shown in FIG. 4, the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio A graph representing the relationship with ICRR is created (step S02). Here, the relationship between the predicted subcriticality (1-k) ^P when the control rod 4 is pulled out and the corrected inverse count rate ratio ICRR is represented by “◯” in the graph of FIG. 4, and is predicted when the boron concentration is diluted. The relationship between the subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR is represented by “x” in the graph of FIG.

The reactivity change at the time of boron dilution is due to the boron concentration change, and the difference in the predicted subcriticality (1-k) ^P at different boron concentration time points is due to the boron concentration error. Therefore, the calculated value of the predicted subcriticality (1-k) ^P is corrected to the measurement value base using the boron concentration measurement value. In this case, since the neutron flux distribution is affected by the effective multiplication factor, the correction coefficient SCF of the corresponding corrected inverse count rate ratio ICRR also changes according to the predicted subcriticality (1-k) ^P. Therefore, this prediction subcriticality (1-k) ^P and the correction factor SCF, previously given as a table evaluates prediction subcriticality (1-k) ^P and the correction coefficient SCF for pre plurality of boron concentration, the boron When the measurement value of the concentration is obtained by sampling, the table of the predicted subcriticality (1-k) ^P and the correction coefficient SCF is interpolated with respect to the boron concentration. As a result, the predicted subcriticality (1-k) ^P and the correction coefficient SCF (SCF ⁰¹ ) corrected based on the measurement value with respect to the boron concentration are obtained again (step S03). Then, the corrected inverse count rate ratio ICRR (ICRR ⁰¹ ) taking into account the boron concentration error is recalculated by using the correction coefficient SCF ⁰¹ recalculated using this measured value (step S04).

Here, as shown in FIG. 4, the relationship “O” between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR when the control rod 4 is pulled out is corrected to “□”, and the boron concentration The relationship “x” between the predicted subcriticality (1-k) ^P at the time of dilution and the corrected inverse count rate ratio ICRR is corrected to “Δ”. Then, based on a plurality of plot points representing the relationship between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR, for example, an approximate method such as a least square method is used to correct the corrected inverse count rate ratio ICRR. And a predicted subcriticality (1-k) ^P is obtained as a linear relational expression (fitting line). In this case, the linear relational expression between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR at the time of pulling out the control rod 4 corrected using the measured boron concentration is a plurality of “□” in FIG. 4 is a one-dot chain line A fitted, and the linear relational expression between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR at the time of boron concentration dilution corrected using the boron concentration measurement value is shown in FIG. The two-dot chain line B fitted from a plurality of “□” in FIG.

Thus, the linear relationship between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR at the time of pulling out the control rod 4 corrected using the measured boron concentration (the dashed line A in FIG. 4). ), And a linear relational expression (two-dot chain line B in FIG. 4) between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR at the time of dilution of boron concentration corrected using the measured boron concentration value. When obtained, theoretically, these two linear relational expressions are located on the same straight line. However, the inclination of the control rod value is slightly shifted due to the calculation error of the control rod value, and the calculation error of the control rod value is corrected by correcting this and matching the inclination.

The reactivity change at the time of pulling out the control rod 4 is based on the movement of the control rod 4, and the error of the predicted subcriticality (1-k) ^P at different time points (positions) of the control rod 4 is It can be considered to be based on a calculation error of value. Therefore, the correction coefficient SCF is evaluated in advance for a plurality of control rod nucleus constants and given as a table, and the control rod nucleus constants are adjusted to obtain a linear relational expression at the time of pulling out the control rod 4 (the one-dot chain line A in FIG. 4). ) And the correction coefficient SCF (SCF ⁰² ) and the predicted subcriticality (1-k) ^P are obtained again so that the slope of the linear relational expression (two-dot chain line in FIG. 4) at the time of boron concentration dilution matches. That is, first, the inclination of the linear relational expression (one-dot chain line A in FIG. 4) when the control rod 4 is pulled out and the inclination of the linear relational expression (two-dot chain line in FIG. 4) at the time of boron concentration dilution are obtained (step S05). ). Next, when the control rod nuclear constant is adjusted, the slope of the linear relational expression (the one-dot chain line A in FIG. 4) when the control rod 4 is pulled out, and the linear relational expression (the two-dot chain line in FIG. 4) when the boron concentration is diluted. Since the inclination changes, a correction coefficient SCF ^{02 in} which both inclinations coincide is obtained (step S06). The predicted subcriticality (1-k) ^P here is tabulated according to the control rod position, boron concentration, and control rod nuclear constant.

Then, the corrected inverse count rate ratio ICRR (ICRR ⁰² ) taking into account the calculation error of the control rod value is recalculated using the recalculated correction coefficient SCF ⁰² (step S07).
ICRR ⁰² = SCF ⁰² × ICRR
With this correction, it is possible to obtain a corrected inverse count rate ratio ICRR taking into account the calculation error of the control rod value after correcting the boron concentration on the basis of the measurement value. Here, as shown in FIG. 4, the relationship “◯” between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR when the control rod 4 is pulled out is corrected to “■”, and the boron concentration The relationship “×” between the predicted subcriticality (1-k) ^P at the time of dilution and the corrected inverse count rate ratio ICRR is corrected to “▲”. Based on a plurality of plot points representing the relationship between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR at the time of pulling out the control rod, for example, the corrected inverse count is performed by an approximation method such as the least square method. A linear relational expression (fitting line) between the rate ratio ICRR and the predicted subcriticality (1-k) ^P is obtained (step S08). In this case, the linear relationship between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR taking into account the control rod value calculation error is a solid line C fitted from a plurality of “■” in FIG. It becomes.

In this way, a linear relationship between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR taking into account the measurement value-based correction using the boron concentration measurement value and the calculation error of the control rod value (FIG. 4 is obtained, the predicted subcriticality (1-k) ^P is corrected to a value that is consistent with the measured values of the core state (control rod position, boron concentration) and the corrected inverse count rate ratio ICRR. It will be done. Therefore, the control rod value is obtained from the predicted subcriticality (1-k) ^{P of} 1-k _ARI at the time of all control rod insertion and 1-k _ARO at the time of all control rod withdrawal, and this is calculated as the value of all control rods. Measurement can be performed (step S09).

  Next, the configuration of the subcriticality measuring apparatus of this embodiment will be described. FIG. 5 is a schematic diagram showing the configuration of the subcriticality measuring apparatus according to the present embodiment. The subcriticality measuring method of this embodiment can be realized by the subcriticality measuring apparatus 10 of this embodiment. As shown in FIG. 5, the subcriticality measuring apparatus 10 includes an input processing circuit 11, an input port 12, a processing unit 20, a storage unit 25, an output port 13, an output processing circuit 14, and a display unit 16. It is comprised including. The processing unit 20 can be configured by combining, for example, a CPU (Central Processing Unit) and a memory. The processing unit 20 includes a core evaluation unit 21, a calculation unit 22, and a correction unit 23, and these are portions that execute the subcriticality measurement method of the present embodiment.

The processing unit 20 and the storage unit 25 are connected via the buses 15 ₁ to 15 ₃ , the input port 12 and the output port 13. Thereby, the core evaluation unit 21, the calculation unit 22, and the correction unit 23 constituting the processing unit 20 of the subcriticality measuring apparatus 10 can be configured to exchange control data with each other or issue commands to one side. Is done.

  An input processing circuit 11 is connected to the input port 12. A signal output from the neutron detector 30 or the reactivity meter 31 is converted into a signal that can be used by the processing unit 20 by a noise filter, an A / D converter, or the like provided in the input processing circuit 11, and then the input port 12 is connected. To the processing unit 20. Thereby, the process part 20 can acquire information required in order to obtain | require a subcriticality.

  An output processing circuit 14 is connected to the output port 13. The output processing circuit 14 is connected to a display means 16 and an external output terminal. The output processing circuit 14 includes a display means control circuit, a signal amplification circuit, and the like, and displays the control rod value and subcriticality calculated by the processing unit 20 on the display means 16 or outputs them to an external device. Or As the display means 16, for example, a liquid crystal display panel, a CRT (Cathode Ray Tube) or the like can be used.

  The storage unit 25 stores a computer program including a processing procedure of the subcriticality measurement method of this embodiment, a computer program for estimating an initial value of the effective multiplication factor, and the like. Here, the storage unit 25 can be configured by a volatile memory such as a RAM (Random Access Memory), a nonvolatile memory such as a flash memory, or a combination thereof.

  This computer program may be capable of realizing the processing procedure of the subcriticality measurement method of the present embodiment in combination with a computer program already recorded in the processing unit 20. Moreover, this subcriticality measuring apparatus 10 may implement | achieve the function of the core evaluation part 21, the calculation part 22, and the correction | amendment part 23 using a dedicated hardware instead of the said computer program.

  The subcriticality measurement method of the present embodiment can also be realized by executing a prepared subcriticality measurement program on a computer system such as a personal computer, a workstation, or a plant control computer. . The program may be capable of realizing the subcriticality measurement function of this embodiment in combination with a program already recorded in the computer system.

  Next, the procedure of the subcriticality measuring method by the subcriticality measuring apparatus of the present embodiment will be specifically described.

  As shown in FIGS. 3 and 5, the subcriticality measuring apparatus 10 measures the detector response φ with the neutron detector 30 when executing the subcriticality measuring method of the present embodiment. In addition, the subcriticality measuring apparatus 10 acquires core parameters such as a moderator temperature, a boron concentration, and a control rod state. During these measurements, the measured core parameters are appropriately noise-removed by the input processing circuit 11 provided in the subcriticality measuring apparatus 10, and the calculation unit 22 evaluates the variation of the measurement signal, that is, the standard deviation. The measurement result is displayed on the display means 16.

  The core evaluation unit 21 included in the subcriticality measuring apparatus 10 acquires a detector output that has been appropriately noise-removed after measurement, that is, a detector response φ, a control rod state R, a boron concentration B, a moderator temperature. Core parameters such as T are acquired (step S01). Next, the core evaluation unit 21 obtains the correction coefficient SCF of Expression (3) from the acquired core parameters. For example, a table describing the relationship of the correction coefficient SCF to the core parameter that changes according to the operating state of the reactor 1 is created in advance and stored in the storage unit 25, and the acquired core parameter is interpolated from the table or The correction coefficient SCF can be obtained by extrapolation.

  Alternatively, a core analysis program may be stored in the storage unit 25, and the correction coefficient SCF corresponding to the core state determined from the acquired core parameters may be calculated as needed using this core analysis program. In this way, the correction coefficient SCF of a certain core state before reaching the criticality can be obtained in real time.

Moreover, the core evaluation part 21 calculates | requires prediction subcriticality (1-k) ^P from the acquired core parameter. For example, a table describing the relationship of the predicted subcriticality (1-k) ^P with respect to the core parameters is created in advance and stored in the storage unit 25, and the acquired core parameters are interpolated or extrapolated from the table. , The predicted subcriticality (1-k) ^P can be obtained.

The core evaluation unit 21 obtains the ICRR using the correction coefficient SCF obtained based on the analysis and the actually measured detector response φ. Next, the calculation unit 22 included in the subcriticality measurement apparatus 10 uses the calculated ICRR and predicted subcriticality (1-k) ^P to perform ICRR and predicted subcriticality (1-k) ^P by approximate calculation. A linear relational expression (formula (5)) representing the relation is obtained (step S02). This linear relational expression can be obtained by, for example, the least square method.

In this case, the subcriticality and the value of the control rod are evaluated using the change in the detector response when the position of the control rod 4 is changed and the change in the detector response when the boron concentration is changed. The relationship between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR can be expressed by one linear relational expression when the control rod 4 is pulled out and when boron is diluted. However, at this time, since there is a calculation error of the boron value and a calculation error of the control rod value, the linear relationship between the two is different in slope although the linearity is maintained.

Therefore, the predicted subcriticality (1-k) ^P is corrected based on the measured value of the boron concentration. That is, the correction coefficient SCF for a plurality of boron concentrations is evaluated and given as a table in advance, and when the measurement value of the boron concentration is obtained by sampling, the correction coefficient SCF table is interpolated with respect to the boron concentration, The correction coefficient SCF ⁰¹ for the predicted subcriticality (1-k) ^P corrected based on the measured value is obtained again, and the corrected inverse count rate ratio ICRR ⁰¹ is recalculated (steps S03, S04S, S05, S06).

Next, the correction coefficient SCF is evaluated in advance for a plurality of control rod nuclei constants and given as a table, and the control rod nuclei constant is adjusted so that the slope of the linear relational expression when the control rod 4 is pulled out and the boron concentration The correction coefficient SCF ⁰² and the predicted subcriticality (1-k) ^P are obtained again so that the slope of the linear relational expression at the time of dilution matches, and the corrected inverse count rate ratio ICRR ⁰² is recalculated (step S07). By this correction, it is possible to obtain a linear relational expression between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR in consideration of the calculation error of the control rod value.

The subcriticality measuring apparatus 10 acquires the detector response φ and the core parameters according to the change in the core state of the nuclear reactor 1, and obtains the predicted subcriticality (1-k) ^P and ICRR by the above procedure.

Based on a plurality of plot points representing the relationship between the predicted subcriticality (1-k) ^P and the corrected inverse count rate ratio ICRR at the time of pulling out the control rod, for example, the corrected inverse count rate ratio by an approximation method such as the least square method A linear relational expression (fitting line) between ICRR and predicted subcriticality (1-k) ^P is obtained (step S08). Then, the control rod value is obtained from the predicted subcriticality (1-k) ^{P of} 1-k _ARI at the time of all control rod insertion and 1-k _ARO at the time of all control rod withdrawal, and this is used as the measurement of all control rod values. (Step S09).

DESCRIPTION OF SYMBOLS 1 Reactor 2 Core 3 Moderator 4 Control rod 5 Fuel 9i Coolant inlet 9o Coolant outlet 10 Subcriticality measuring device 11 Input processing circuit 12 Input port 13 Output port 14 Output processing circuit 15 Bus 16 Display means 20 Processing unit 21 Core evaluation unit 22 Calculation unit 23 Correction unit 30 Neutron detector 31 Reactivity meter 32 Core parameter

Claims (4)

In the process of reaching the criticality of the core of the reactor, the detector output φ ^ref of the neutron detector in the reference state of the core and the detector output φ ^ref of the neutron detector in the core state before reaching the criticality different from the reference state A corrected inverse count rate ratio obtained by correcting the inverse count rate ratio φ ^ref / φ, which is a ratio with the correction coefficient, and a predicted subcriticality in the core state when the corrected inverse count rate ratio is obtained is determined as a core analysis model. The procedure to calculate by core analysis using
The corrected inverse count rate obtained in the process of reaching the criticality by changing the control rod position and the boron concentration and taking into account the boron concentration measurement value at the time of changing the boron concentration and the calculation error at the time of changing the control rod position From the ratio and the predicted subcriticality, a procedure for obtaining a relational expression between them,
A procedure for evaluating subcriticality using the relational expression;
Only including,
By adjusting the control rod nuclear constant, the corrected inverse count rate ratio and the predicted subcriticality are adjusted so that the slope of the linear relational expression when the control rod position is changed matches the slope of the linear relational expression when the boron concentration is changed. Recalculate the relationship with degrees,
A subcriticality measuring method characterized by the above.   The sub-criticality measurement method according to claim 1, wherein the calculation error includes a correction using a boron concentration measurement value and a calculation error of a control rod value.   Using the measured value of the predicted subcriticality and the boron concentration, the calculated value of the predicted subcriticality is corrected based on the measured value, and the relational expression between the corrected inverse count rate ratio and the predicted subcriticality is obtained again. The subcriticality measuring method according to claim 1 or 2, wherein In the process of reaching the criticality of the core of the reactor, the detector output φ ^ref of the neutron detector in the reference state of the core and the detector output φ ^ref of the neutron detector in the core state before reaching the criticality different from the reference state A corrected inverse count rate ratio obtained by correcting the inverse count rate ratio φ ^ref / φ, which is a ratio with the correction coefficient, and a predicted subcriticality in the core state when the corrected inverse count rate ratio is obtained is determined as a core analysis model. A core evaluation unit that is calculated by core analysis using
The corrected inverse count rate obtained in the process in which the core reaches the criticality by changing the control rod position and boron concentration and taking into account the measured boron concentration at the time of changing the boron concentration and the calculation error at the time of changing the control rod position From the ratio and the predicted subcriticality, a calculation unit for obtaining a relational expression between them,
A correction unit for evaluating subcriticality using the relational expression;
Including
The calculation unit adjusts the control rod nuclear constant so that the inclination of the linear relational expression when the control rod position is changed and the inclination of the linear relational expression when the boron concentration is changed coincide with each other. And recalculate the relational expression between the predicted subcriticality and
A subcriticality measuring apparatus characterized by the above.

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