JPS60171494A - Method of charging fuel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a pressure tube nuclear reactor when a 1/4 core rotationally symmetric fuel exchange pattern is adopted, and to a fuel loading method therefor.

[Background of the invention]

When a 1/4 core rotationally symmetrical refueling pattern is adopted, new fuel collects in the core periodically, so if the fuel assembly at the center of the reactor is the same as other fuels, it will be collected periodically as shown in Figure 5. A large power peaking occurs at the center of the furnace, and the maximum linear power density exceeds the limit value.

(1) In order to suppress the above-mentioned output peaking, it is possible to use control rods for output flattening. When the control rods are inserted and the control rods are inserted, heat generation from the fuel, which has not yet been combusted, is rapidly added, so power peaking is not improved.

On the other hand, if the control rods are used until the end of the cycle without being withdrawn in the middle of the cycle in order to suppress this power peaking, a loss in burnup will result.

Based on the above results, in the conventional example, as shown in FIGS. 1 and 2, the entire core uniformly distributed fuel exchange pattern is adopted as the fuel exchange pattern.

This eliminates the periodic concentration of new fuel.
Output beaking has been improved. However, by adopting a uniform distributed refueling pattern for the whole core, each region (quadrant by quadrant)
The area outputs of the two areas differ, causing an output imbalance between the areas.

[Purpose of the invention]

(2) An object of the present invention is to provide a fuel loading method for a pressure tube nuclear reactor that eliminates the above-mentioned drawbacks and allows a 1/4 core rotationally symmetric fuel exchange system to be realized without using control rods.

[Summary of the invention]

If a 1/4 core rotationally symmetric fuel exchange pattern is adopted,
In order to prevent the four bodies in the core of the reactor from periodically receiving new fuel at the same time and increasing the output peaking, a
Load fuel with lower enrichment than other fuel assemblies. At this time, since newly using fuel with a low enrichment level will increase the cost of the fuel, a special fuel assembly is loaded at this position. The enrichment of the special fuel assembly will be reduced to an enrichment level that can suppress output peaking within the limit value, but even with this, the cumulative amount of fast neutron irradiation of the irradiated test piece of the pressure pipe member in the special fuel assembly will be limited. satisfy the value.

[Embodiments of the invention] Examples of the present invention are shown in FIGS. 3 and 4.

As the fuel exchange pattern, the 1/4 reactor (3) rotationally symmetrical fuel exchange pattern shown in Figure 4 will be adopted. In addition, for standard fuel assembly 1, fuel exchange is performed for the entire 1 in each cycle.
74 will be replaced in 4 batches. That is, in FIG. 4, the number of each fuel assembly indicates the fuel assembly l to be replaced at the same time, and the fuel assemblies 1 are replaced in order from the smallest number.

On the other hand, the special fuel assembly 2 is loaded in the center of the core, and the fuel exchange is performed in two batches due to the maximum burnup limit for the special fuel assembly.

By loading the special fuel assembly 2 at the center of the 1/4 core rotationally symmetrical refueling pattern, periodic large power peaking occurs, and when the special fuel assembly 2 is loaded with the same enrichment as the conventional example, the maximum Although the linear power density exceeds the limit value, conversely, by adopting the special fuel assembly 2 with a lower enrichment level, the power peaking of the special fuel assembly 2 can be obtained at the same level as the conventional one, and the irradiation test specimen The integrated amount of fast neutron irradiation can be secured.

The results of this example are shown in FIG. By adopting the low concentration special fuel assembly, the power peaking, that is, (4), the maximum linear power density is within the limit value.

Further, in this case, there is no difference in the area output between the areas as shown in FIG.

〔Effect of the invention〕

According to the present invention, it is possible to reduce the power peaking at the center of the reactor when adopting a /4 core rotationally symmetrical refueling pattern without newly using other fuel assemblies, and it is possible to suppress the maximum linear power density within the limit value. . Furthermore, the enrichment level of the special fuel assembly can be reduced.

[Brief explanation of drawings]

Fig. 1 is a fuel arrangement diagram in the conventional example, Fig. 2 is a fuel production pattern diagram in the conventional example, Fig. 3 is a fuel arrangement diagram in the embodiment of the present invention, Fig. 4 is also a fuel exchange pattern diagram, and Fig. 5 The figure shows an example of the present invention and a diagram of the output peaking change when adopting the conventional 1/4 fuel exchange pattern, Figure 6 is a diagram of the area output change in the conventional example, and Figure 7 shows the example of the present invention. FIG. 3 is a diagram of area output changes in an example; 1...Standard fuel assembly, 2...Special fuel assembly. Agent Patent attorney Akio Takahashi (5) Figure 1

Claims (1)

[Claims] 1. In a pressure-controlled nuclear reactor in which a special fuel assembly containing a member for monitoring pressure pipe material is loaded, the special fuel assembly is loaded in the center of the reactor when a 1/4 core rotationally symmetric fuel exchange pattern is adopted. How to load fuel.