JP2975654B2 - Core monitoring device - Google Patents

Description

Description: Object of the Invention (Industrial Application Field) The present invention relates to a monitoring apparatus for a thermal margin state of a boiling water reactor, and more particularly, to a fuel assembly in which a fuel assembly has a proper position in design. The present invention relates to a core monitoring device capable of evaluating a thermal margin in consideration of an influence of deviation from a core.

(Prior Art) Generally, in a boiling water reactor, it is important to accurately evaluate the power distribution and thermal margin of the operating reactor in order to operate the reactor safely and efficiently. . For this reason, conventionally, a large number of neutron detectors are arranged in the reactor, and based on the detection signals from the neutron detectors, a tertiary reactor in the reactor is used using a fitting model or a physical model such as a three-dimensional nuclear thermal hydraulic model. Calculate the original power distribution and furthermore, the critical power ratio (CPR)
A core monitoring device for obtaining a thermal margin such as a power density and a linear power density is provided.

By the way, in the conventional core monitoring device, the fitting formula for calculating the power distribution and the thermal margin and the constants of the three-dimensional nuclear thermal hydraulic model are determined assuming that the fuel assembly is at a regular position in design. Have been.

This is shown in FIG. FIG. 2 (A) schematically shows the arrangement of the fuel assemblies 101, control rods 102 and in-core neutron instrumentation 103 in the core, and FIG. 2 (B) shows the arrangement in the core. This shows a unit cell system of a set of four fuel assemblies 101 around an arbitrary control rod 102. Each fuel assembly 101 includes a plurality of bundled fuel rods 104 and a channel box 105 surrounding the fuel rods 104. It is composed of FIG. 2 (C)
In the same unit cell system as in FIG. 2 (B), as an example of a case where one fuel assembly 101B deviates from a regular lattice position, two diagonally located fuel assemblies are deviated. In this case, the fuel assembly at a normal position is denoted by reference numeral 101A, and the fuel assembly having a misalignment is denoted by reference numeral 101B.

Conventionally, the evaluation of the thermal margin is performed assuming that the arrangement of the fuel assemblies 101 is at a regular design position as shown in FIG. 2B at all positions in the furnace.

(Problems to be Solved by the Invention) In the conventional core monitoring apparatus, since all the fuel assemblies 101 are evaluated as having a thermal margin assuming that they are at a regular position in design, the fuel assemblies 101 However, due to the intersection of the manufacturing position, the deformation of the channel box 105, or the offset placement of the fuel assembly 101 from the original design position, when the design position is shifted from the designed It is not possible to consider the effect on the margin, and it is necessary to operate the vehicle separately considering the effect of deviation from the normal position.

That is, as shown in FIG.
As the city in one grid changes, the moderator area outside the channel changes. For this reason, for example, in the case shown in FIG. 2 (C), the output of the fuel rod 104 close to the side where the moderator region has expanded is compared with the case where the fuel rod 104 is at the regular position as shown in FIG. 2 (B). As a result, the output of the fuel rod 104 near the side where the moderator region is narrowed decreases substantially in direct proportion to the displacement amount, and similarly decreases. FIG. 3 shows a change in the output of the fuel rod 104 at the corner closest to the control rod 102 as an example of the change.

Conventionally, the effect on the thermal margin due to the change in the output of the fuel rod 104 was evaluated offline, and in actual operation, the operator judged the effect on the thermal margin calculated by the core monitoring device and corrected it. There is a problem that the work is not easy and the reliability is not always high.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a core monitoring device which is easy to operate and has high reliability.

[Configuration of the invention]

(Means for Solving the Problems) The present invention provides, as means for achieving the above object, a power distribution calculating means for calculating a power distribution in a core based on current data of a core, a control rod in the core or a nuclear meter in the core. The four fuel assemblies surrounding the mounting system are defined as one unit cell, and for each unit cell,
A fuel rod output evaluation means for evaluating a change in fuel rod output caused by the deviation based on a deviation amount of the fuel assembly from a designed normal position; and output signals from the power distribution calculation means and the fuel rod output evaluation means. And a thermal margin evaluating means for evaluating a thermal margin such as a critical output ratio and a linear output density.

(Operation) In the core monitoring apparatus according to the present invention, the fuel rod output evaluation means evaluates a change in the fuel rod output caused by a deviation of the fuel assembly from a designed normal position, and furthermore, a thermal margin The evaluation means evaluates a thermal margin such as a critical power ratio and a linear power density. For this reason, the operator does not need to perform a correction operation, and high reliability can be obtained.

In addition, the fuel rod output evaluation means evaluates the change in the fuel rod output for each unit cell, so that it can handle the change in the fuel rod output irrespective of the other fuel assemblies in the core. Easy.

(Embodiment) An embodiment of a core monitoring apparatus according to the present invention will be described below with reference to FIG.

FIG. 1 shows an example of a reactor core monitoring apparatus according to the present invention. In the figure, reference numeral 1 denotes a reactor vessel, in which a cooling water (moderator) 2 and a reactor core 3 are provided. The reactor core 3 includes a plurality of fuel assemblies (not shown), control rods, and the like.

As shown in FIG. 1, a plurality of neutron detectors 4 are installed in the core 3. Each of the neutron detectors 4 detects a neutron flux at each preset measurement point in the core 3. It can be measured. Each neutron detector 4 is usually a mobile type, and moves in a vertical direction along a conduit (not shown) so that a neutron flux can be measured at a required point in the vertical direction. Note that each of the neutron detectors 4 may be of a fixed type instead of the mobile type.

As shown in FIG. 1, a reactor core status data measuring device 5 is installed in the reactor pressure vessel 1, and the reactor core status data measuring device 5 allows the reactor core status data (hereinafter referred to as CSD data), for example, Data such as the total flow rate of the coolant, the furnace pressure, the inlet / outlet temperature, and the position of the control rod are measured. Then, the signal S5 from the core current state data measuring instrument 5
Is input to a data sampler (referred to as DS) 6 together with a signal S4 from each of the neutron detectors 4, and the core current state data measuring device S5 further outputs power distribution calculation means (hereinafter CS) from DS6.
7).

The CS7 performs a three-dimensional nuclear thermal-hydraulic coupling calculation using the CSD data and the built-in physical model, or a method using a fitting formula, and further corrects the three-dimensional model by reading of the neutron detector 4. A three-dimensional output distribution is obtained by a method or the like, and a fuel degree distribution or the like of the fuel assembly is calculated. The signal from the CS 7 is supplied to a fuel rod output evaluation device 8 and a thermal margin evaluation device 9 as shown in FIG.

The fuel rod output evaluation device 8 focuses on a set of four fuel assemblies around the control rod or a set of four fuel assemblies surrounding the neutron detector 4 as one unit cell. Then, based on the loading position in the core of the channel box and the history of the fuel level, etc., the amount of deviation from the normal position in the grid of the fuel assembly is evaluated, and the output change of the fuel rod due to this deviation is considered. Fuel rod output is required. The neutron detector 4 is used for all the fuel assemblies 4 in the core.
Although it is not always present at one ratio in the body, in the present embodiment, it is referred to as a neutron detector position including a symmetric position utilizing the symmetry of the core.

In this way, the fuel rod output obtained by the fuel rod output evaluation device 8 is input to the thermal margin evaluation device 9 together with the three-dimensional output distribution from the CS 7 as shown in FIG. The thermal margin evaluating device 9 evaluates thermal margins such as the linear power density and the critical power ratio of the fuel rods based on these inputs. Then, the calculated output distribution and thermal margin are displayed on the display unit of the input / output device 10.

 Next, the operation of the present embodiment will be described.

The signal S5 of the CSD data measured by the core status data measuring device 5 is combined with the signal S4 from each neutron detector 4 in DS.
6, and the signal S5 is further input to CS7.

In CS7, based on the CSD data, a three-dimensional power distribution in the core is obtained using a fitting formula or a physical model, and further, a fuel degree distribution of the fuel assembly is calculated. Then, the output signal from CS7 is given to fuel rod output evaluation device 8 and thermal margin evaluation device 9, respectively.

In the fuel rod output evaluation device 8, a set of four fuel assemblies surrounding the control rod or the neutron detector 4 is worn as one unit cell, and each unit cell has a normal position in the grid of the fuel assembly. The deviation amount is evaluated, and the fuel rod output is determined in consideration of the change in the fuel rod output due to the deviation. Then, the obtained fuel rod output is supplied to the thermal margin evaluation device 9 together with the three-dimensional output distribution from the CS 7, where the thermal margin such as the linear power density and the critical power ratio of the fuel rod is evaluated. Then, the calculated output distribution and thermal margin are displayed on the display unit of the input / output device 10.

By the way, in the fuel rod output evaluation device 8, the change in the fuel rod output is evaluated by being worn on a unit cell of a set of four fuel assemblies. It has been found that the change in the fuel rod output due to the displacement of the fuel assembly is also affected by the state of the displacement of the fuel assemblies around the fuel assembly of a set of four unit cells. However, since the influence was found to be extremely small, focusing on the unit cells of a set of four fuel assemblies, it is possible to deal with changes in fuel rod power regardless of other fuel assemblies in the core. And the evaluation method becomes very simple.

The relationship between the displacement of the fuel assembly and the change in the fuel rod output can be evaluated by performing two-dimensional neutron diffusion calculation. I can't say. On the other hand, as described above with reference to FIG. 3, since the change in the fuel rod output is proportional to the displacement of the fuel assembly, the relationship between the displacement and the variation is determined in advance for each fuel rod. By having an expression, evaluation can be made more easily, and this embodiment employs this method.

Therefore, even when the fuel assembly deviates from the normal position in the core lattice, the thermal margin of the fuel assembly is evaluated in consideration of the effect on the fuel rod output. The reliability of the surveillance monitoring can be greatly improved, and the effective use of fuel and the reliability of the plant can be improved.

In the embodiment, for each unit cell of a set of four fuel assemblies, a change in the output of each fuel rod of the fuel assembly belonging to that cell is evaluated. As a result, all the fuel assemblies in the core are evaluated. Although the case where the change of the fuel rod output is evaluated for each is described, the problem when the fuel rod output changes is that
This is a change in the direction in which the fuel rod output increases, and it is considered that attention should be paid to the most severe fuel rod. Therefore, only the change in the fuel rod having the largest output peaking may be evaluated. As a result, the amount of data and the amount of calculation can be reduced.

First, the average displacement of the fuel assemblies of all the cores was evaluated, and the average fuel rod output change due to the average displacement was calculated. , The thermal margin may be evaluated. Thereby, evaluation can be performed more easily.

Further, although not specifically described in the above embodiment, the displacement amount of the fuel assembly is determined by the loading position and the burnup of the fuel assembly,
Parameters related to positional deviation, such as the history of irradiation dose, may be evaluated by tracking and managing online, and the values evaluated online are given to the fuel rod output evaluation device 8 as data, You may make it use for evaluation of a fuel rod output change.

〔The invention's effect〕

As described above, according to the present invention, the fuel rod output is determined in consideration of the displacement of the fuel assembly in the core lattice, and the thermal margin of the fuel assembly is evaluated based on this. Therefore, the reliability of the thermal margin monitoring can be greatly improved, and the burden on the operator can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a core monitoring apparatus according to one embodiment of the present invention, FIG. 2 (A) is a plan view showing an arrangement of fuel assemblies and the like in a reactor core, and FIG. FIG. 2 (C) is an explanatory view showing a unit cell system of a set of four fuel assemblies surrounding a rod, FIG. 2 (C) is an explanatory view showing an example of misalignment of a fuel assembly in a similar unit cell system, and FIG. 6 is a graph illustrating an example of a relationship between a displacement amount of a fuel assembly and a fuel rod output. 3 ... core 4 neutron detector 5 core current data measuring device 7 CS (power distribution calculating means) 8 fuel rod power evaluation device 9 thermal margin evaluation device

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Claims (1)

(57) [Claims] 1. A power distribution calculating means for calculating a power distribution in a core based on current data of a core, and four fuel assemblies surrounding a control rod or a core instrumentation system in the core as one unit cell, A fuel rod output evaluation means for evaluating a change in fuel rod output caused by the deviation based on a deviation amount of the fuel assembly from a designed normal position for each unit cell; the power distribution calculating means and the fuel rod output evaluation; A core margin monitoring unit for evaluating a thermal margin such as a critical power ratio or a linear power density based on each output signal from the core unit.