JPS63201593A - Fuel aggregate for nuclear reactor - 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 [Industrial Field of Application] The present invention relates to a fuel assembly for a nuclear reactor, and particularly to a fuel assembly suitable for a fast breeder reactor.

[Conventional technology]

The trumpet tube deletion type fuel assembly was used in the N.N. Engineering International Conference ONF B R Tsuyuru Performance Tobical Meeting Proceedings.

Monterrey, C.N. (1979), pp. 758-776 (ANS International
Conf, onFBRFuel Perform
ance Topical Mtg.

Proceedings, Monterey CA
(1979) PP 758-776).

This fuel assembly eliminates the trumpet tube in a normal fuel assembly, and connects six corners of a group of fuel pins arranged in an equilateral triangular grid between the handling head and the entrance nozzle. The six hexagonal tie rods whose facing sides are larger than the diameter of the fuel bottle are replaced with six hexagonal tie rods, and the gaps between the fuel pins are connected to the six tie rods at their corners and arranged at appropriate axial intervals. held by grid-type spacers. In the reactor, the gap between adjacent fuel assemblies is secured by tie rods, so interference between grid-type spacers is prevented, and fuel assemblies can be smoothly inserted and withdrawn. In addition, it is desirable that the flow path gap formed by the three tie rods of three adjacent fuel assemblies be narrow because the tie rods are non-heat generating elements, but since hexagonal rod-shaped tie rods are used, the flow path The gap is narrow and waste flow can be suppressed.

The trumpet tube deleted fuel assembly has the following advantages compared to a normal fuel assembly. Since there is no interaction between the fuel bottle bundle and the trumpet tubes, and no interaction between the trumpet tubes, this is advantageous in extending the life of the fuel. Since the trumpet tube can be eliminated, neutron economy is improved, and it is also expected to reduce fuel fabrication costs, reprocessing costs, and the amount of waste materials. Furthermore, since coolant mixing occurs between adjacent fuel assemblies, the assembly exit temperature difference is reduced, reducing thermal shock to the upper core structure, as well as providing potential safety against flow path blockage. There is expected.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional technology has a problem in that the radial coolant temperature distribution within the fuel assembly is not sufficiently even, and the thermal curvature that occurs in the tie rod and the outermost layer fuel pin adjacent thereto is particularly large. As a result, the mechanical load applied to the grid spacer and the thermal stress generated in the cladding tube of the fuel pin become large, and the conditions for using the fuel assembly in the reactor may become severe.

Note that it is also possible to widen the flow path gap facing the tie rods in the fuel assembly by moving the conventional hexagonal bar-shaped tie rods toward the outside of the assembly.
In this case, it is necessary to widen the gap between adjacent fuel assemblies at the same time, which further lowers the coolant temperature in the flow path gap between the fuel assemblies, which is originally low in temperature, so the uniformity of the coolant temperature in the radial direction cannot be raised.

Since conventional fuel assemblies use hexagonal rod-shaped tie rods, the flow path gap facing the tie rods in the fuel assembly becomes extremely narrow, and the temperature of the coolant flowing through this gap becomes particularly high. The degree of uniformity of the coolant temperature distribution was poor.

An object of the present invention is to improve the evenness of the radial coolant temperature distribution.

[Means for solving problems]

The purpose of the above is to use a tie rod with a cross-sectional outline in which a part of the center side of the tie rod is shaved off so that the gap facing the tie rod is widened among the coolant flow path gaps in the fuel assembly. This is achieved by

(Function) According to the present invention, the flow path gap facing the tie rod in the fuel assembly widens, the axial flow rate flowing through this gap increases, and the temperature of the coolant flowing through this gap decreases, so that the temperature distribution is evened out. The level of support will improve.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. Figure 1 shows only the corner portions of the cross section of the trumpet tube deleted fuel assembly.
Fuel pins 1 having an outer diameter of φ8 are arranged in a triangular lattice shape with a center-to-center ratio of Ions (arrangement pitch), and tie rods 2 are arranged at the corners in place of the fuel pins.

Figure 2 shows only the portions of the three trumpet-deleted type fuel assemblies in which one tie rod 2 in each assembly is close to each other, and alphabetical symbols from a to e are shown. is for distinguishing between types of channel gaps within and between aggregates. b and d within the aggregate, and a.

Q, e, and f indicate the channel gap between the aggregates, respectively.

FIG. 3 shows a side view of the trumpet tube deletion type fuel assembly,
A plurality of fuel pins 1 and six tie rods 2 are connected at their upper and lower ends to a handling head 3 and an entrance nozzle 4, respectively, and the gaps between the fuel pins and between the fuel pins and the tie rods are arranged in the axial direction It is held by grid type spacers 5.

Fig. 4 is a diagram for explaining the cross-sectional shape of the tie rod, and the two corners of the regular hexagonal cross section are
It shows that it is a shape cut into an arc shape within a range of 120 degrees with the center 0 of the arc as the center of the arc.

Next, a second embodiment of the present invention will be described using FIG. 5. As shown in FIG. 5, the tie rod has a regular hexagonal cross section with two corners cut into straight lines, and as in the first embodiment, the cut points are The second embodiment is a fuel assembly with a trumpet tube removed, which is oriented toward the center of the assembly.

The effects of the first and second embodiments will be explained below with reference to Table 1. Channel gaps a and b are three, C and d are two
Since each of the flow path gaps a, b, c, d, and e is adjacent to one fuel pin, in order to equalize the temperature of the coolant flowing in the axial direction through each gap, the flow path gaps a, b, c, d, and e must be When the flow path areas are respectively A a vAb, Ac, Ad, and Ae, Aa/3°A b /3, A c /2,
It is sufficient if A d /2 and Ae are made equal to each other. As shown in Table 1, it can be seen that in the case of the conventional example, the value of Ad/2 is small, and the temperature of the coolant flowing through the gap d is high. In the case of the first and second embodiments, the value of Ad/2 is larger than that of the conventional example, and in the case of the first embodiment, the temperature of the coolant flowing through the gap d is the temperature of the coolant flowing through the gap. , and in the case of the second embodiment, it is found to be slightly lower than the temperature of the coolant flowing through the gap.

As described above, in each of the embodiments, the degree of uniformity of the coolant temperature is improved, and the effect is greater in the second embodiment. It is considered that the first embodiment is superior in terms of the connectivity between the grid spacer and the tie rod.

〔Effect of the invention〕

According to the present invention, it is possible to reduce the variation in the area of each coolant flow path divided by the number of fuel pins adjacent to the flow path gap, so there is an effect of improving coolant temperature uniformity.

[Brief explanation of the drawing]

Fig. 1 is a partial cross-sectional view of a nuclear reactor fuel assembly according to an embodiment of the present invention, Fig. 2 is a cross-sectional view of a portion where three assemblies of the embodiment are adjacent, and Fig. 3 is an embodiment thereof. FIG. 4 is a cross-sectional view of a tie rod in this embodiment, and FIG. 5 is a cross-sectional view of a tie rod in another embodiment of the present invention. 1...Fuel pin, 2...Tie rod, 3...Handlin 2...Kiku mouth/end 20th 3rd 4th 5th mouth, large t wooden 10hi...tie rod,・I\So1゛Rishiγto・ノY. 1 Transnos ° Le Griff F'! I! X'<-sa

Claims (1)

[Claims] 1. In a fuel assembly for a nuclear reactor in which a plurality of fuel pins are assembled and a tie rod is provided near the outer periphery of the assembly area, the tie rod has a portion near the center of the assembly: A nuclear reactor fuel assembly characterized by a smaller external shape than the opposite part. 2. In a nuclear reactor fuel assembly in which a plurality of fuel pins are assembled and a tie rod is provided near the outer periphery of the assembly area, the cross-sectional outline of the tie rod is at least a portion of the tie rod near the center of the assembly. A fuel assembly for a nuclear reactor, characterized in that it has a shape lacking. 3. The fuel assembly for a nuclear reactor according to claim 2, wherein the cross-sectional shape of the tie rod is a hexagonal shape with corners near the center of the fuel assembly removed. body. 4. A fuel assembly is formed by arranging a plurality of fuel pins and tie rods in an equilateral triangular grid, and the tie rods are arranged at the corners of the fuel assembly, and the tie rods connect the upper handling head and the entrance. In a fuel assembly that eliminates the trumpet feeling and is connected to a nozzle,
The tie rod is a rod having a cross-sectional external shape obtained by cutting two adjacent corners of a regular hexagon with a curve or a straight line, and the two corners are on the center side of the fuel assembly. A fuel assembly for a nuclear reactor. 5. The fuel assembly for a nuclear reactor according to claim 4, wherein the rod is a solid rod.