JPS61204586A - Nuclear reactor core - 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 Industrial Application] The present invention relates to the core of a nuclear reactor, and more specifically, to an arrangement method of control rod clusters in a reactor core simultaneously loaded with two or more types of fuel having significantly different reaction effects against neutrons. Regarding.

[Conventional technology]

Uranium oxide fuel, gadolinia-containing uranium oxide fuel, or uranium-plutonium mixed oxide fuel (MOX: Mi
In a reactor core loaded with two or more types of fuel that have significantly different reaction effects against neutrons (e.g. In order to ensure
Conventionally, various restrictions have been placed on the core fuel loading system, including the fuel type configuration, resulting in a lack of design flexibility.

- As an example, the case where uranium oxide fuel and MOX fuel are simultaneously loaded into a pressurized water reactor (PWR) is as follows.

In other words, when deciding on the fuel loading method for the reactor core, it is important to ensure that even if one of the control rod clusters becomes stuck and cannot be inserted into the reactor core, the reactor can be shut down with sufficient margin using the remaining control rods, and that It is necessary to satisfy the condition that the reactor will not be damaged even if one of the control rod clusters ejects from the reactor during insertion, but in order to do so, the neutron absorption effect of each control rod cluster must be It is desirable that there be no difference compared to the neutron absorption effect of .

Traditionally, only one type of control rod cluster has been used in the reactor core, but uranium oxide fuel and MOX
When loading fuel at the same time, the neutron absorption effect of MOX fuel is greater than that of uranium oxide fuel, so
There is a problem that control rod clusters of the same type have different neutron absorption effects, and depending on the fuel loading method, the above-mentioned reactor shutdown margin and safety conditions may not be satisfied.

[Problems to be solved]

The present invention solves the problems of the prior art described above and changes the type and arrangement of control rod clusters depending on the fuel loading method, thereby ensuring the safety of the reactor and limiting the fuel loading method. The aim is to provide a nuclear reactor core with flexibility in fuel loading methods.

[Means for solving problems and their effects]

According to the present invention, two or more types of control rod clusters having different neutron absorption effects are placed in a predetermined control rod cluster position in a nuclear reactor core, which is made up of a nuclear reactor core that is simultaneously loaded with multiple types of fuels having greatly different reaction effects to neutrons. , and are arranged to provide optimal reactor safety depending on the fuel loading method. In this case, the arrangement pattern is selected so that the neutron absorption effect of each control rod cluster differs as little as possible from the neutron absorption effect of the fuel into which it is inserted. A control rod cluster with a large neutron absorption effect is placed at the insertion position of the region,
A control rod cluster with a small neutron absorption effect is placed at an insertion position in a fuel region with a small neutron absorption effect.

In the present invention, differences in neutron absorption effects within the reactor core due to simultaneous loading of different types of fuel are equalized by the complementary arrangement of different types of control rod clusters, thus ensuring sufficient reactor shutdown margin and flattening the power peaking. It is possible to provide flexibility in the fuel loading method while maintaining a higher level of safety.

Examples of the present invention will be shown below for a better understanding of the present invention.

〔Example〕

Figures 1 to 3 show MO in the core of a pressurized water reactor (PWR).
This shows an embodiment of the present invention in which 60 bodies of X fuel and 61 bodies of uranium oxide fuel are loaded. 2
The figure is a schematic cross-sectional view showing the loading method of MOX fuel (x mark) and uranium oxide fuel (no mark), and Figure 3 shows the insertion positions of different control rod clusters (marked 0 and O) arranged according to the present invention. FIG.

As shown in FIG. 1, fuel loading is performed in the pattern shown in FIG. 2 with respect to the control rod cluster insertion position determined in advance. Here, even if the same type of control rod cluster is inserted at each insertion position, the neutron absorption effect of the control rod cluster inserted into the uranium oxide fuel region at the periphery of the core will be absorbed by the MOX fuel region at the center of the core. Because the control rod cluster is relatively large compared to that of the control rod cluster, in the event of an accident such as the ejection of a control rod cluster in the vicinity, the neutron absorption effect will be lost to a large extent, leading to a rapid increase in reactivity and severe power output. The safety of the reactor cannot be ensured due to the occurrence of beaking, etc. In contrast, in the present invention, as shown in FIG. 3, a plurality of types of control rod clusters having different neutron absorption effects are arranged and inserted in accordance with the loading method of different types of fuel. That is, in the embodiment shown in FIG. 3, five control rod clusters 21 having a large neutron absorption effect are arranged in the area of the MOX fuel 11 having a large neutron absorption effect in the center, and four control rod clusters 21 near the periphery of the center are arranged. A similar control rod cluster 21 is arranged for each of the MOX fuels 11a to lid, and the control rod cluster 21 is arranged around the core formed by the uranium oxide fuel 12, which has a relatively small neutron absorption effect. A total of 20 control rod clusters 22 of a different type having a smaller neutron absorption effect than the rod clusters 21 are arranged in a shape of tread force.

In a PWR loaded with uranium oxide fuel and MOX fuel distributed approximately half and half, as shown in Fig. 2, there is a case in which all control rod clusters are of the same type, and a case in which two types of control rods with different neutron absorption effects are used according to the present invention. An example of a comparison of the reactor shutdown margin with a cluster and the output peaking in the event of a cluster ejection accident is shown in the table below. It can be seen that according to the present invention, reactor safety can be ensured with dissimilar fuel loading systems, which cannot be achieved with the use of homogeneous control rod clusters. .

〔Effect of the invention〕

As described above, according to the present invention, in a reactor core where multiple types of fuel with different reaction effects to neutrons are simultaneously loaded, multiple types of control rod clusters with different neutron absorption effects are arranged according to the fuel loading method. Therefore, it is possible to ease the restrictions on the different fuel loading method and achieve flexibility in the reactor with sufficient safety.

[Brief explanation of the drawing]

The drawings relate to one embodiment of the present invention, and Fig. 1 is a schematic cross-sectional view of the reactor core in which the predetermined insertion position of the control rod cluster in the reactor core is indicated by an O mark, and Fig. 2 is a schematic cross-sectional view of the reactor core showing the predetermined insertion position of the control rod cluster in the reactor core. Uranium oxide combustion! 4 (unmarked) is a schematic cross-sectional view of the core showing the loading method, and FIG. 3 is a schematic cross-sectional view of the core showing the insertion positions of different control rod clusters arranged according to the present invention. 11, 11a-d: MOXfi family, 12: Uranium oxide fuel, 21: Control rod cluster with relatively large neutron absorption effect, 22: Control rod cluster with relatively small neutron absorption effect. Agent Patent Attorney Sanro Kimura Figure 1

Claims (1)

[Scope of Claims] 1) In a nuclear reactor core that is simultaneously loaded with multiple types of fuel that have greatly different reaction effects on neutrons, two or more types of fuel that have different neutron absorption effects are inserted into a predetermined control rod cluster insertion position. A nuclear reactor core characterized in that control rod clusters are arranged so as to provide optimal reactor safety according to a fuel loading method. 2) A control rod cluster with a large neutron absorption effect is arranged at the insertion position of a fuel region with a large neutron absorption effect, and a control rod cluster with a small neutron absorption effect is arranged at an insertion position of a fuel region with a small neutron absorption effect. A nuclear reactor core according to scope 1.