JPH08327777A - Critical point prediction device - Google Patents

Abstract

PURPOSE: To provide a critical point prediction device for fully automatically and accurately predicting a critical point and aiding an operator by automatically taking in the detector count for using in critical point prediction, and monitoring reverse multiplication factor against the effective multiplication factor using a table of a core state given in advance and the effective multiplication factor. CONSTITUTION: A critical point prediction device 5 comprises a detector count memory part 6 for taking in the count output by an power detector for monitoring the reactor power and storing it and a reverse multiplication factor operation part 7 for calculating the reverse multiplication factor from the initial count and the count at every moment of the power detector. Also it includes a critical point prediction part 8 for predicting the criticality of the reactor by the reverse multiplication method by monitoring reverse multiplication factor calculated in a reverse multiplication factor operation part 7 against the effective multiplication factor in accordance with the core state at every moment prepared in advance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a critical point prediction device for predicting and monitoring the arrival of criticality during critical operation of a nuclear reactor.

[0002]

2. Description of the Related Art Conventionally, when a nuclear reactor is made critical, the prediction of its critical point is calculated using the inverse multiplication method. In this inverse multiplication method, when neutrons generated from a neutron source having an intensity S reach the neutron detector through the core having an effective multiplication factor k, the intensity S _{0 of} the neutrons that have arrived is expressed by the following equation (1 ).

S ₀ = S + kS + k ² S + k ³ S + ... = S / (1-k) (1)

In this equation (1), the fact that the reactor reaches the critical point corresponds to the fact that the effective multiplication factor k reaches 1. Therefore, when the reactor becomes critical, the intensity of neutrons that reach the neutron detector, that is, the detection The instrument count S ₀ is infinite. This corresponds to the fact that the reactor physically becomes critical and the output increases. In fact, considering the detection efficiency of the neutron detector, the intensity of neutrons reaching the neutron detector is not equal to the detector count, but here it is assumed to be equal for convenience.

Here, the inverse multiplication factor R is defined as the ratio of the initial detector count S ₀ 0 (= S / (1-k0), k0: initial effective multiplication factor) by the neutron detector and the detector count S _0. Then, it becomes like the following formula (2). The "initial" refers to the state immediately before the start of critical operation.

R = S ₀ 0 / S ₀ = S (1-k) / S (1-k0) = (1-k) / (1-k0) (2)

As the reactor reaches the critical point, that is, the effective multiplication factor k approaches 1, the reverse multiplication factor R linearly approaches 0 with respect to the effective multiplication factor k as shown in the above equation (2). The reverse multiplication factor R becomes 0 at the critical point. An example of the transition of the reverse multiplication factor R at this time is shown in the characteristic curve diagram of FIG.

In the inverse multiplication method, the fact that the inverse multiplication factor R approaches 0 in a linear manner is utilized to constantly plot the inverse multiplication factor R in the process of making the reactor critical and extrapolate it. By doing so, the critical point is predicted. In the critical point prediction by this inverse multiplication method, the operator directly reads the neutron count from the output detector of the neutrons from the count display instrument and uses this to divide the initial detector count recorded in advance. Then, the reverse multiplication factor is obtained.

Next, this is pulled out, such as the number of control rods,
The operator predicted the critical point by drawing a graph for what is representative of the effective multiplication factor. The reason why the effective multiplication factor itself is not plotted is that the effective multiplication factor must be obtained by performing a separate analysis.

[0010]

The critical point prediction work by the conventional inverse multiplication method is all done by the operator, and this work is extremely complicated and directly plotted against the effective multiplication factor. The prediction accuracy was poor because it was not possible. As shown in FIG. 4, the reverse multiplication factor shows linearity with respect to the effective multiplication factor, but regarding the number of pull-out control rods for performing critical operation, the reactivity value is different, and the number of pull-out control rods is different. With respect to the change with respect to, due to poor linearity, a highly accurate critical point could not be predicted even by extrapolation.

An example of a graph in which the relationship between the reverse multiplication factor and the number of pull-out control rods is plotted in the characteristic curve diagram of FIG. 5 in the case of the critical operation of pulling out the control rods in the boiling water reactor in the order of pulling out the control rods Indicates. In addition, since the conventional critical point prediction cannot quantitatively grasp the margin to the critical point, there is a problem that the operator cannot know how much the critical point will be exceeded by the next operation in the process of critical operation. There were obstacles such as possible mistakes.

The object of the present invention is to automatically take in the detector counts used for predicting the critical point and use the table of the core state and the effective multiplication factor given in advance to reverse the effective multiplication factor of the core. It is an object of the present invention to provide a critical point prediction device that monitors a multiplication factor and predicts a critical point with high accuracy by full automation and assists an operator.

[0013]

In order to achieve the above object, a critical point predicting apparatus according to the invention of claim 1 is a detector for capturing and storing a count output by an output detector for monitoring the output of a nuclear reactor. A counter storage unit, a reverse multiplication factor calculation unit that calculates a reverse multiplication factor from the initial count from the output detector and the counts at each time, and a reverse multiplication factor calculated by the reverse multiplication factor calculation unit in advance. It is characterized by comprising a critical point prediction unit that predicts the criticality of the reactor by the inverse multiplication method with respect to the effective multiplication factor depending on the core state at any time.

A critical point predicting apparatus according to a second aspect of the present invention is a detector count storage unit for capturing and storing a count output from an output detector for monitoring the output of a nuclear reactor, and an initial stage from the output detector. A counter multiplication factor calculation unit that calculates a reverse multiplication factor from the count and the count at each time, a core performance calculation unit that analyzes the effective multiplication factor according to the core state, and a reverse multiplication factor calculated by the reverse multiplication factor calculation unit. Is analyzed by the core performance calculation unit, and a critical point prediction unit that predicts the criticality of the reactor by an inverse multiplication method with an effective multiplication factor according to the core state at that time is characterized.

In the critical point predicting apparatus according to the third aspect of the present invention, the critical point predicting unit issues an alarm when the margin to the critical limit becomes less than the set value during the critical operation of the reactor, and a predetermined critical operation is performed by the next critical operation. It is characterized by preventing critical operation when it is predicted that a period equal to or more than a value will occur.

[0016]

According to the first aspect of the invention, the detector count storage section automatically captures and stores the initial count output from the output detector and the count at each time. This detector count is input to the reverse multiplication factor calculation section, and the reverse multiplication factor is calculated by dividing the initial detector count by the detector count at that time. The inverse multiplication factor at each time is sent to the critical point prediction unit, and the critical point prediction is performed from the effective multiplication factor table for the core state separately input in the critical point prediction unit.

According to the second aspect of the present invention, the detector count storage section automatically captures and stores the initial count output from the output detector and the count at each time. This detector count is input to the reverse multiplication factor calculation section, and the reverse multiplication factor is calculated by dividing the initial detector count by the detector count at that time. The inverse multiplication factor at each time is sent to the critical point prediction unit, and the effective multiplication factor according to the core state at that time is calculated from the control rod operation sequence separately input in the core performance calculation unit to calculate the critical point prediction unit. Then, the critical point prediction unit predicts the criticality.

According to the third aspect of the present invention, as a result of the prediction by the critical point predicting unit, if the margin to the critical value is smaller than the set value, an alarm is issued to notify the operator, and the critical value is exceeded by the next critical operation. When it is determined that the period of 1 occurs, the critical operation is blocked and the operation can be performed by the confirmation of the operator.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. In the first embodiment, as shown in the block diagram of FIG. 1, a reactor pressure vessel 1 which is a nuclear reactor contains a reactor core 2. However, the control rod 3 is not fully inserted into the reactor core 2. The control rod 3 is in a critical state, and the control rod driving device 4 controls pulling and inserting.

The critical operation for a subcritical nuclear reactor is to pull out the control rod 3 from the core 2 by the control rod driving device 4. By gradually pulling out the control rod 3 from the core 2, the reactivity is injected into the reactor and approaches the critical level. Note that, as an output detector for monitoring the output in the core at this time, there are, for example, a neutron source region neutron monitor and a startup region neutron monitor, and the output detector (not shown) for monitoring the output of the core 2 detects the output. The count is output.

The critical point predicting device 5 includes a detector count storage unit 6 for automatically capturing and storing the count output from the output detector, and an initial detector count input from the detector count storage unit 6. A reverse multiplication factor calculation unit 7 for calculating a reverse multiplication factor from the detector count at each time is provided.

Further, the critical point predicting unit 8 for predicting the critical point of the nuclear reactor according to the effective multiplication factor corresponding to the core state at that time, which is provided with the reverse multiplication factor calculated by the reverse multiplication factor calculation unit, is provided. It is configured. A control rod pattern-to-effective multiplication factor table 9 is input to the critical point predicting unit 8.

Next, the operation of the above configuration will be described. In general, a nuclear power plant is provided with a process computer (not shown) relating to the operation of a nuclear reactor, and monitors process signals from various parts. Therefore, the detector count storage unit 6 in the critical point prediction device 5 is
In addition to directly taking in the detector count from the output detector provided in the reactor, it also automatically detects the detector count of the output in the reactor from the output detector in real time through a process computer. It can be imported accurately and easily.

First, in the detector count storage unit 6, the detector count before the critical operation, that is, the detector count in the state before the pulling-out operation of the control rod 3 is started is fetched as the initial detector count. Next, when the critical operation is started and the control rod 3 is gradually pulled out according to a predetermined pattern, the reactivity is injected into the reactor and the count from the output detector increases, but the detection is detected. The counter is automatically fetched periodically and sent to the inverse multiplication calculator 7 together with the initially stored initial detector count.

The inverse multiplication factor calculation unit 7 calculates the inverse multiplication factor according to the following equation (3) and sequentially sends it to the critical point prediction unit 8. Reverse multiplication factor = initial detector count / detector count at that time (3)

The control point pattern vs. effective multiplication factor table 9 created in advance is inputted to the critical point predicting section 8. By reading out the effective multiplication factor corresponding to the control rod pattern at that time, the inverse multiplication factor pair is read. Create a graph of effective multiplication factor. This graph is displayed on a display device such as a CRT (not shown) connected to the critical point prediction unit 8 and provided to the operator.

Incidentally, the control rod pattern in the control rod pattern vs. effective multiplication factor table 9 changes every moment during the critical operation, but this is always monitored by the process computer like the count of the output detector. It is stored in the process computer as an input of, for example, the Rodworth Minimizer, and it is easy to import this.

However, in the past, since the effective multiplication factor (predicted analysis value) of the core corresponding to the control rod pattern at that time was not known, the effective multiplication factor was estimated on the basis of the number of control rods and the like. .

In the present embodiment, the effective multiplication factor and the control rod pattern are obtained in advance by analysis, and this is input as a control rod pattern vs. effective multiplication factor table 9 to, for example, a process computer, so that the control rod at that time is controlled. An effective multiplication factor corresponding to the pattern can be obtained. As described above, the point at which the reverse multiplication factor becomes 0 is the critical point, so the graph is extrapolated and the effective multiplication factor at which the reverse multiplication factor becomes 0 is calculated and obtained.

If the control rod pattern vs. effective multiplication factor table 9 input in advance is correct, it becomes critical when the effective multiplication factor is 1, but normally the reaction site in the core 2 and the output detector are The point where the effective multiplication factor is 1 on the table is not necessarily the critical point because it includes various analytical errors such as the positional relationship and the relationship with the control rod pattern at that time.

As shown in the characteristic curve diagram of FIG. 3, for example, the actual reverse multiplication factor varies depending on the positional relationship between the output detector and the core, and various routes until the effective multiplication factor reaches the critical point of 1. Although it passes, it is known that near the critical point, it behaves uniformly regardless of the positional relationship between the power detector and the core.

Further, the effective multiplication factor (critical prediction value) corresponding to the critical point prediction control rod pattern obtained by the critical point prediction device 5 and the effective multiplication factor (prediction analysis value) previously obtained by analysis.
Since the error due to the above-mentioned analysis can be estimated by comparing with, the accuracy can be further improved by correcting this error value when calculating the critical point prediction.

In the critical point predictor 8, the reverse multiplication factor is 0.
Since the control rod pattern corresponding to the effective multiplication factor predicted to become the critical prediction control rod pattern itself, the control rod pattern is obtained from the first control rod pattern vs. effective multiplication factor table 9, and this is used as the critical prediction control rod pattern. It is displayed on a display device (not shown).

As shown in FIG. 3, regardless of various analytical errors in the vicinity of the critical point, even if various routes are traced along the way, they are finally aggregated into the effective multiplication factor of 1. It is highly accurate to display the criticality prediction control rod pattern when the reverse multiplication factor becomes small, and it is suitable for predicting the critical point.

Here, for example, when the reverse multiplication factor follows the curve of the downward slack in FIG. 3, the point B on the extension indicated by the linear dotted line at the point A is the critical prediction point, and the control rod pattern is effective. By reading the multiplication factor table 9 in the opposite manner, it is possible to know the control rod pattern corresponding to the critical prediction point at point B, and this is the critical prediction control rod pattern.

Further, the difference D between the points B and C of the effective multiplication factor at this time is the margin to the critical level, and the margin to the critical level can be quantitatively known from this difference D. That is, by displaying this criticality prediction control rod pattern, the operator can visually and sensuously grasp how much more the critical operation is performed by pulling out the control rod to reach the criticality.

As described above, according to the critical point prediction device 5, the control rod pattern for the criticality prediction can be displayed without the operator's hand intervening, but at the same time, the effective increase corresponding to the criticality prediction control rod pattern can be displayed. The difference between the magnification and the effective multiplication factor corresponding to the control rod pattern at that time is the margin to the critical level.

Therefore, this value is calculated in the critical point predicting section 8 by using the control rod pattern vs. effective multiplication factor table 9, and the value is also displayed at the same time, so that the operator can quantitatively grasp the margin to the critical point. Therefore, it is possible to effectively support the critical operation.

In the second embodiment, as shown in the block diagram of FIG. 2, the critical point prediction device 10 includes a detector count storage unit 6, a reverse multiplication factor calculation unit 7 and a critical value calculation unit similar to those of the first embodiment. The point prediction unit 8 and a core performance calculation unit 11 that calculates an effective multiplication factor according to the control rod pattern at each time are provided. In addition, a control rod operation sequence 12 is input to the core performance calculation unit 11.

Next, the operation of the above configuration will be described. In the above-mentioned first embodiment, it was necessary to prepare the control rod pattern vs. effective multiplication factor table 9 corresponding to many conditions before the critical operation. Further, in reality, the control rod pattern vs. effective multiplication factor table 9 cannot be assumed to be a control rod pattern that covers all the conditions, and it has been unavoidable to make it discrete. Therefore, this control rod pattern vs. effective multiplication factor table 9
It was not possible to deal with control rod operations that were not taken into consideration when creating.

However, in the second embodiment, for example, by combining the core performance calculation unit provided in the process computer as the core performance calculation unit 11 or by providing the same function, it is possible to normally use the nuclear power plant. The control rod pattern monitored by the process computer and the effective multiplication factor at each time can be obtained in real time, and it is possible to easily deal with an unexpected control rod operation.

Therefore, the core performance calculation unit 11 automatically calculates the effective multiplication factor according to the control rod pattern at each time of the critical operation, so that the operator's work during the critical operation is as follows. It is only necessary to input the withdrawal order of the control rod 3. As a result, in the critical point predicting apparatus 10, the core performance calculation unit 11 automatically calculates the effective multiplication factor in accordance with the pull-out order of the control rods 3 input by the operator, and creates necessary data.

In the second embodiment, the analysis and prediction function by the core performance calculation unit 11 is added to change the initially planned control rod withdrawal order for some reason, or the operator desires it. When it is desired to obtain the effective multiplication factor of the control rod pattern, it is possible to flexibly respond by flexibly drawing an inverse multiplication curve, and it becomes possible to make a more precise prediction of the critical point.

Further, since the work of preparing the complicated control rod pattern vs. effective multiplication factor table 9 in advance is eliminated, the human burden is reduced and the trouble caused by mistake is eliminated, so that the reliability in the critical operation is also improved.

The third embodiment is the same as the first embodiment and the second embodiment.
The critical point predicting unit 8 in the embodiment has a function of issuing an alarm signal when the margin of the effective multiplication factor due to the critical operation to the critical value becomes smaller than the preset value input in advance. Further, when it is predicted that the criticality will be reached by performing the next critical operation or that a period of a certain value or more will be emitted, a function for preventing the critical operation is added.

The function of this structure is to notify the operator by the alarm that the critical point is nearing the critical point in the critical point predicting section 8, and to alert the operator about the next critical operation and to confirm the critical operation by the operator. By performing this, for example, it is possible to prevent the criticality due to the reactivity input due to an erroneous operation, so that the safety in the critical operation of the nuclear reactor is further improved.

[0047]

As described above, according to the present invention, the critical point can be easily predicted during the critical operation of the nuclear reactor, the burden on the operator can be significantly reduced, and the operation accuracy can be improved.
Further, since the margin to the criticality can be grasped quantitatively, the operator can visually and sensibly operate by displaying the core state predicted to be critical. Also,
Since it is possible to flexibly respond to changes in critical operation, it is possible to flexibly and finely predict the critical point and prevent inadvertent injection of reactivity by the next critical operation, thus improving the reliability and safety of reactor operation. There is.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a critical point prediction device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a critical point prediction device according to a second embodiment of the present invention.

FIG. 3 is a characteristic curve diagram of an inverse multiplication factor showing a criticality reaching and a margin to the criticality.

FIG. 4 is a characteristic curve diagram of reverse multiplication factor until reaching criticality.

FIG. 5 is a characteristic curve diagram of the reverse multiplication factor with respect to the number of pull-out control rods.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Reactor core, 3 ... Control rod, 4 ... Control rod drive device, 5, 10 ... Critical point prediction device, 6 ... Detector count storage unit, 7 ... Inverse multiplication factor calculation unit, 8 ... Critical point prediction unit, 9 ...
Control rod pattern vs. effective multiplication factor table, 11 ... Core performance calculation section, 12 ... Control rod operation sequence, A ... Point of reverse multiplication factor, B ... Critical prediction point at point A, C ... Point of effective multiplication factor at point A , D ... Difference in effective multiplication factor (margin until criticality).

Claims (3)

[Claims] 1. A detector count storage unit that captures and stores counts output by an output detector that monitors the output of a nuclear reactor,
A reverse multiplication factor calculation unit for calculating a reverse multiplication factor from the initial count from the output detector and the count at each time, and a core state at each time provided with the reverse multiplication factor calculated by the reverse multiplication factor calculation unit in advance. A critical point prediction apparatus comprising: a critical point prediction unit that predicts the criticality of a reactor by an inverse multiplication method with respect to the effective multiplication factor. 2. A detector count storage unit that captures and stores the counts output by an output detector that monitors the output of the nuclear reactor,
A reverse multiplication factor calculation unit that calculates a reverse multiplication factor from the initial count from the output detector and the counts at each time, a core performance calculation unit that analyzes an effective multiplication factor according to a core state, and the reverse multiplication factor calculation unit It is characterized by comprising a critical point prediction unit that predicts the criticality of the reactor by the reverse multiplication method with the effective multiplication factor according to the core state at that time analyzed by the core performance calculation unit Critical point prediction device. 3. The critical point prediction device issues an alarm when the margin to criticality becomes less than a set value during critical operation of a nuclear reactor, and it is predicted that a period of a predetermined value or more will be generated by the next critical operation. The critical point predicting device according to claim 1 or 2, wherein the critical operation is prevented in such a case.