JPS6122278B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for predicting power distribution that changes due to changes in coolant flow rate in a nuclear reactor, temporal changes in xenon spatial distribution, and the like.

An object of the present invention is to provide a method for predicting the power distribution of a nuclear reactor that can easily and accurately determine the future power distribution.

The present invention is characterized by a means for determining the neutron reflectance corresponding to the detected current power distribution of the reactor based on a power distribution calculation model, and a power distribution calculation adjusted by the obtained neutron reflectance. The present invention also includes means for predicting future power distribution by inputting a predetermined core state signal into the model. As a result,
The calculation model only needs to be modified using the neutron reflectance that corresponds to the reactor's current power distribution, and the future power distribution can be predicted easily and with high accuracy.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 shows a block diagram of an example of an apparatus for carrying out the method of the invention. 1 is a reactor core, 2 is a current power distribution detection means, 3 is a parameter setting means for adjusting parameters included in a predictive calculation model so that the calculation model best represents the core state according to the power distribution, and 4 is an adjusted calculation A power distribution prediction calculation means that predicts the power distribution using a model; 5 is the core state to be predicted (core flow rate, xenon concentration);
6 is a prediction condition specifying means for specifying the predicted output distribution. Typically, the prediction conditions are specified by the reactor operator, and the prediction results are displayed to the reactor operator.

Next, the principle of the prediction method will be explained.

FIG. 2 is a cross-sectional view of the core. 7 indicates a fuel assembly. We now turn our attention to localized regions containing one or more assemblies (examples shown at 8a, 8b), which are illustrated in FIG. 8 is the local region of interest.

Generally, within a reactor core, neutrons are exchanged between fuel assemblies. The amount of interaction is
Focusing on a certain assembly, as shown in FIG. 3, it is expressed by the neutron reflectance α(Z). Here, Z indicates a position in the height direction, and the reflectance changes in the height direction. It was found that this reflectance hardly changes when the reactor core flow rate or xenon concentration changes, which is the object of the present invention. This is because although the axial power distribution of each fuel assembly changes due to changes in the core flow rate and xenon concentration, the change is almost uniform at any position in the radial direction, and as a result, the above-mentioned fuel assemblies differ from each other. This is based on a newly discovered physical phenomenon that causes almost no change in the balance of neutron exchange. Therefore, before making a prediction, calculate the reflectance from the current output distribution, that is, the reflectance that corresponds to the current output distribution (parameter setting of the prediction model), and use the prediction model that uses this reflectance to predict and calculate the output distribution. For example (output distribution prediction calculation), highly accurate prediction is possible.

The present invention has been made based on the above study results, and a preferred embodiment of the present invention will be described below.

One way to express the equation satisfied by the output distribution is
There is the following expression.

P _k =K _∞k {W ^v _k-1 P _k-1 +W ^v _k+1 P _k+1 +[1-2W ^v _k -(4-α _k )W ^H _k ]P _k } (1) P _k : Output of node k in height direction k _∞k : Infinite multiplication coefficient of neutron of node k W ^v _k : Probability (kernel) that neutron of node k is absorbed by the node adjacent above or below W ^H _k : of node k Probability ( _kernel ) that a neutron is absorbed by a horizontally adjacent node 9a, 9b,
It is...

FIG. 4 shows an embodiment of the predictive model parameter setting means 3 based on equation (1). 10 is a k∞ distribution calculation means, 11 is a kernel distribution calculation means, 12 is a burnup and control rod position detection means, 13 is a void distribution calculation means, and 14 is a reflectance calculation means. k∞
is determined by the current power distribution, burnup, control rod position, and void distribution. Also, the kernel is calculated from the void distribution. Given the output distribution, k∞, and the kernel, the reflectance α _k corresponding to the current output distribution can be found from equation (1).

α _k =1/W〓{1/P _k (P _k /k _∞k −W ^v _k−
1 P _k-1 −W ^v _k+1 P _{k +1} )−1+2W ^v _k +4W ^H _k } (2) Through the above series of calculations, the reflectance α _k , which is a parameter of the model, is determined, and in the next prediction calculation,
This α _k is used.

FIG. 5 shows an embodiment of the output distribution prediction calculating means 4 and the prediction condition specifying means 5. 15 is a power distribution calculation means, 16 is a xenon concentration setting means, and 17 is a core flow rate setting means. The output distribution calculation means 15 calculates the output distribution P _k for the given k∞, kernel, and reflectance. The core xenon concentration and core flow rate to be predicted are given by the reactor operator from 16 and 17, and serve as input information for k∞ and void distribution calculations. Note that since the void distribution and the output distribution influence each other, calculations of the output distribution and the void distribution are repeated alternately until the predicted output distribution converges. The results are shown to the operator using the predicted output distribution display means 6.

Examples of predictions made by the above prediction device are shown in FIGS. 6 and 7. Figure 6 shows the results of predicting the power distribution 36 hours after the scram when the reactor is restarted 24 hours after the reactor program and the power distribution at that time is known. In both the current and predicted state, the reactor core coolant flow rate is 40% of the rated value, and the change in power distribution is as follows.
Due to differences in xenon concentration. Also, Figure 7 shows
This is a prediction of the power distribution when the core coolant flow rate is 100% when operating at 40% of the rated flow rate. Together, the predicted distribution and the actual distribution are
Shows very good agreement.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic configuration of an apparatus for carrying out the method of the present invention, Fig. 2 is a cross-sectional view of the reactor core, Fig. 3 is a sketch of the local area, and Fig. 4
5 and 5 are block diagrams showing the specific configuration of the main parts of the apparatus for carrying out the method of the present invention, and FIG.
FIG. 7 and FIG. 7 are diagrams showing an example of prediction results obtained by the apparatus of the present invention.

Claims (1)

[Claims] 1 Find the current power distribution of the reactor, find the neutron reflectance corresponding to the obtained current power distribution based on the power distribution calculation model, and apply it to the power distribution calculation model using the obtained neutron reflectance. A method for predicting the power distribution of a nuclear reactor, which comprises inputting a predetermined core state signal to predict the future power distribution.