JPS6118156B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactor core condition prediction device for predicting core conditions of a nuclear power plant, such as performance, xenone concentration, and axial and radial reactor power distribution.

In the operation of a nuclear power plant, in order to maintain the safety of the reactor and the integrity of the fuel, there are various operating restriction conditions, such as maximum linear power density, critical heat flux ratio, etc. There is. When changing the reactor output by changing the coolant flow rate, it is very important to predict whether or not the various conditions described above are satisfied in the state of the core after the output is changed.

In order to predict the state of the reactor core, it is desirable to use a three-dimensional model that includes Zenon's dynamic characteristics, but this requires a huge amount of calculation due to the complexity of the model and the long time required for prediction. In particular, when adopting an operating method in which the reactor power is changed at a slow rate of increase in power density in order to prevent damage to the cladding due to interaction between the fuel cladding and the pellets inside the tube, it can take several days. It is extremely difficult to predict the future.

The purpose of the present invention is to change the reactor power and reactor power distribution when the coolant flow rate is changed based on the current core data in the operation of a nuclear power plant, and to satisfy the various limiting conditions described above. An object of the present invention is to provide a prediction device for predicting whether or not the answer is yes.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. The nuclear reactor 1 is equipped with various detectors (not shown) for detecting process variables such as the position of control rods inserted into the reactor core, neutron flux in the reactor core, flow rate, pressure, and temperature in the reactor core. Plant data signals 2 from various detectors are input to a core performance calculation device 3 that calculates the performance of the reactor core, and the performance value of the reactor core is calculated. The core performance calculation device 3 is composed of an electronic computer and is conventionally used.

The axial reactor power distribution prediction device 4 is disclosed in detail in Japanese Patent Application No. 106262/1987 previously filed by the present applicant, but to summarize, the reactor core is approximated by an axial one-dimensional model, and changes in xenone concentration, This is a device that quickly predicts the furnace output as the flow rate changes with the necessary accuracy.
Further, the xeno concentration distribution calculation device 5 is a device that calculates the current value of the axial xenon concentration change required for the former based on the output signal 6 of the core performance calculation device.

When the axial reactor power distribution prediction device 4 sends a data request signal 7 to the core performance calculation device 3 and the Zenon concentration distribution calculation device 5, signals 8 and 8' indicating the data are transferred from these devices 3 and 5, and then transferred. Using the obtained data as initial values, the axial power distribution prediction device 4 predicts the furnace output and the axial furnace power distribution.

The radial reactor power distribution prediction device 9 calculates the current (T) based on the signal 10 obtained from the core performance calculation device 3.
= ₀ ) and the signal 11 obtained from the axial furnace power prediction device 4.
From the axial furnace power distribution _K (T) after time, the output change rate R _K at the axial node K is determined by the following equation.

R _K = _K (T) / _K (0) (1) Here, node K is an arbitrary number among the numbers equally dividing the height in the core axis direction, T is time, and 0 is T = 0. , _K is the symbol representing the average furnace power at node K.

Next, by multiplying the in-core power distribution P _I,J,K (0) obtained from the core performance calculation device 3 by R _K obtained by equation (1), the in-core power distribution P _{I,J after T time elapses, K} (T) is predicted. Here, IJ indicates the planar coordinates of the core.

The operator input device 12 predicts the power distribution in the axial and radial furnace power distribution prediction devices 4 and 9.
Accordingly, a signal 13 representing the flow rate as a function of time is input, and initial conditions are set using a core performance calculation device 3 and a Zenon concentration distribution calculation device 5 that process plant data. Conversely, specify the furnace output,
In order to predict the core flow rate at that time, the reactor power may be given to the operator input device 12 as a function of time. These results are input to the prediction result display device 15 via a signal 14 and displayed.

The limiting condition comparing device 16 inputs the furnace output signal 17 obtained by the axial furnace power distribution predicting device 4 and the furnace power distribution signal 18 from the radial furnace power distribution predicting device 9, and compares items that become limiting conditions, such as the maximum line. This device calculates the output density, critical heat flow velocity ratio, etc., compares the results with the limit conditions set on the limit condition setting board 19, and outputs the results to the prediction result display device 15 as necessary.

An example of prediction using the core state prediction device according to the present invention is shown in FIG. 2 and below.

Figure 2 shows a reactor that was operating at 100% core flow rate and 94% reactor core flow rate, which suddenly drops to 40% core flow rate (time T at that time is taken as 0), and then the core flow rate is reduced to 40%. FIG. 4 is a diagram showing the results of prediction of changes in furnace output when the furnace output is maintained using the axial furnace output distribution prediction device 4. The dotted line shows the core flow rate and the solid line shows the reactor power.

FIG. 3 is a diagram showing the core control rod pattern used in the prediction of FIG. 2. The fuel assemblies that make up the core are arranged in a square grid, so
These are represented by the abscissa I and the ordinate J, and the numbers in the figure represent the withdrawal positions of the control rods inserted into the centers of the four square fuel assemblies. The grids without numbers correspond to the control rod positions assuming 24 total withdrawals.

Figure 4 shows the time after 7 hours (T = 7) when the xenone concentration reaches its maximum and the reference time (T
FIG. 3 is a diagram showing the axial furnace power distribution of node K with respect to node K. From the figure, the output change rate R _K for each node K in the axial direction after 7 hours is obtained from the above-mentioned equation (1).

Figure 5 shows the core position predicted by the radial power distribution prediction device 9 after 7 hours 1<I<26.I=13, J=13
(See FIG. 3 and FIG. 4 for core coordinates) A diagram showing the radial reactor power distribution. The dotted line in the figure is the current radial power distribution curve obtained from the core performance calculation device.

FIG. 6 is a diagram comparing the results predicted in FIG. 5 with the results predicted by a three-dimensional model including Zenon's dynamic characteristics. In the figure, the solid line shows the results from the three-dimensional model, and the dots show the results from the radial reactor power distribution prediction device.The latter is on the former curve, and it can be seen that the two coincide very well. Changes in the power distribution due to flow rate control are mainly changes in the axial power distribution, and all initial values are obtained online, so the prediction results by the radial furnace power distribution prediction device are accurate and the prediction calculation time is almost one-dimensional calculation. It can be done in the time required.

According to the device of the present invention, it is possible to predict the state of the reactor core during or after the change in output, so that it is easy to operate a nuclear power plant that satisfies the restrictive conditions necessary for safety.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a device for predicting the state of the reactor core according to the present invention, and FIG. 2 is a graph showing the predicted results of the reactor output with respect to changes in the core flow rate. Figure 3 is a diagram showing the control rod pattern inserted into the reactor core when predicting the core state in Figure 2, and Figure 4 is the reference time (T = 0) and the axial direction after 7 hours when the xenone concentration is at its maximum. A graph showing the relationship between height K and axial furnace power, Figure 5 is a graph showing the predicted results of radial furnace power distribution, and Figure 6 shows the radial furnace power distribution obtained by the three-dimensional model and the radial furnace power distribution obtained by the device of the present invention. This is a graph comparing the predicted radial reactor power distribution. DESCRIPTION OF SYMBOLS 1... Nuclear reactor, 2... Plant data signal, 3... Core performance calculation device, 4... Axial reactor power distribution prediction device, 5... Zenon concentration distribution calculation device, 6... Output signal, 7... Data request signal, 8, 8 ′...transfer signal,
9... Radial furnace power distribution prediction device, 10, 11... Signal, 12... Operator input device, 13, 14... Signal,
15... Prediction result display device, 16... Limit condition comparison device, 17, 18... Signal, 19... Limit condition setting board.

Claims (1)

[Claims] 1. A core performance calculation device that calculates core performance from plant data obtained from various detectors that detect the position of control rods inserted into the reactor core, neutron flux in the core, process quantities inside and outside the core, etc.; a Zenon concentration distribution calculation device that calculates the Zenon concentration using data output by the core performance calculation device;
an axial reactor power distribution prediction device that predicts axial reactor power output based on an axial one-dimensional diffusion model from data output by the core performance calculation device; a radial furnace power distribution prediction device that predicts a directional furnace power distribution; and a limit condition comparison device that compares the prediction results of the axial furnace power distribution prediction device and the radial furnace power distribution prediction device with preset limit conditions. A nuclear power plant reactor core state prediction device characterized by comprising: