JPS6319591A - Fuel aggregate - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement of a fuel assembly for a boiling water nuclear reactor (hereinafter referred to as BWR).

(Prior Art) FIG. 7 is a perspective view of the fuel assembly 1, and reference numeral 2 in the figure indicates a channel box. The channel box 2 has a substantially square cross section and is hollow. Inside this channel box 2, a plurality of fuel rods 3 (for example, 64 in 8 rows x 8 columns) are arranged in a grid pattern.

These plurality of fuel rods 3 are supported at their upper and lower ends by an upper tie plate 4 and a lower tie plate 5. Further, spacers 6 are installed at multiple locations in the axial direction, and these spacers 6 prevent the fuel rods 2 from being photographed.

The channel box 2 forms a coolant flow path, and is made of Zircaloy-4, for example, and has a plate thickness of 80 mm.
Mil (2,03 rewards), 100 Mil (2,54,),
It is made of 120 mil (3.05s).

Also, the differential pressure between the inside and outside of channel box 2 is approximately 1 (K9/
ci) and used at high temperatures, creep deformation or bending occurs due to differences in neutron flux. Therefore, it reaches the end of its lifespan in about 4 to 10 years. The channel box 2 that has reached the end of its life is replaced with a new one in the fuel storage pool.

By the way, recently, a new material superior in strength to Zircaloy-4 and superior in creep resistance has been used, and in this case, the thickness of the channel box 2 becomes thinner than before. Also, when considering plant standardization, plates with thinner thickness than conventional ones are used. Furthermore, it is expected that the thickness of the channel box 2 will be made thinner for purposes such as improving burnup. If the thickness of the channel box 2 is reduced due to various reasons, a gap will be created between the channel box 2 and the upper grid plate at its upper end (the internal dimensions of the channel box 2 are based on the fuel rods 3 and It is not preferable to change it due to the relationship with the upper and lower tie plates 4.5, etc., so if the plate thickness is to be made thinner, the outer dimensions should be made smaller).

Due to the occurrence of such a gap, the fuel assembly 1 is loaded in a state slightly inclined from the vertical. This was not desirable considering not only the nuclear characteristics but also the control rod insertion and withdrawal operations, and improvements were required.

(Problem to be solved by the invention) In response to this tendency for the thickness of the channel box to become thinner, in the conventional configuration, a gap occurs between the upper grid plate and the fuel assembly is tilted. There is a problem that fuel assemblies are loaded, and the present invention has been made based on this point, and its purpose is to provide a fuel assembly that can prevent the fuel assembly from being loaded in an inclined state. It's about doing.

[Configuration 3 of the Invention (Means for Solving the Problem) That is, the fuel assembly according to the present invention has a plurality of fuel rods loaded in a lattice shape in a channel box, and the upper end and the lower end are connected to the upper tie plate and the fuel assembly. In a fuel assembly supported by a lower tie plate, the channel box is characterized in that at least a part of its upper end, which faces the upper grid plate, protrudes toward the upper grid plate. .

(Function) In other words, by protruding at least a part of the surface of the upper end of the channel box relative to the upper lattice plate,
This effectively fills the gap that occurs between the channel box and the upper grid plate when the plate thickness of the channel box is made thin, thereby preventing the fuel assembly from being loaded in an inclined state.

(Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a perspective view of a channel box 102 according to this embodiment.
2 has a thinner plate than before due to the adoption of new materials. 2 at the upper end of the channel box 102 facing the upper grid plate 107 (shown in FIG. 2).
Two surfaces 102a and 102b are expanded. This is because the channel box 102 is thin as described above, and if left as is, a gap (indicated by the symbol δ in FIG. 3) will occur between it and the upper grid plate 107. This is because the fuel assembly is loaded at an angle. FIG. 2 shows one lattice part of the upper lattice plate 107, in which four fuel assemblies 101 are loaded, and the two surfaces 102a and 102b of each channel box 102 are expanded as described above. has been done.

Further, FIG. 3 is a sectional view taken along the line ■-■ in FIG. 2.

According to the above configuration, in the channel box 102 whose plate thickness is thinner than in the past, the upper lattice plate 1
Since the two surfaces 102a and 102b facing 07 are expanded by the gap δ between the channel box 102 and the upper grid plate 107, when the fuel assembly 101 is loaded, it can be loaded vertically without tilting. It will be done. Therefore, it is possible to effectively eliminate the conventional problems of deterioration of nuclear properties or problems with control rod insertion and withdrawal operations, which had been a concern.

Next, a second embodiment will be described with reference to FIGS. 4 and 5. Note that FIG. 5 is a sectional view taken along line v--■ in FIG. 4. This second
In this embodiment, two surfaces 102a and 102 are located at the upper end of the channel box 102 and face the upper grid plate 107.
protrusions 108 are formed on b, and these protrusions connect the channel box 102 and the upper lattice plate 107.
This is to fill the gap δ between. Furthermore, the above-mentioned protrusion 10
8 is molded by extrusion. Therefore, the same effects as in the first embodiment can be achieved, and processing is easier than in the case where the entire surface is expanded as in the first embodiment.

Next, regarding a third embodiment, as shown in FIG. 6, a protrusion 109 is formed in a smaller area than the protrusion 108 in the second embodiment. This is to fill the gap δ. Therefore, in this case as well, the same effects as in the first and second embodiments can be achieved.

[Effects of the Invention] As detailed above, according to the fuel assembly according to the present invention, a gap is generated between the channel box and the upper grid plate, and the fuel The problem of the set pair being loaded in an inclined state can be effectively solved. Therefore, it is possible to reliably prevent deterioration of nuclear characteristics and deterioration of control rod insertion/extraction characteristics.

[Brief explanation of the drawing]

1 to 3 are diagrams showing a first embodiment of the present invention,
Fig. 1 is a perspective view of the channel box, Fig. 2 is a plan view showing one lattice part of the upper lattice plate, Fig. 3 is a sectional view taken along the line ■-■ of Fig. 2, and Figs. FIG. 4 is a perspective view of the upper end of the channel box;
5 is a cross-sectional view taken along the line v--2 in FIG. 4, FIG. 6 is a perspective view of the upper end of the channel box according to the third embodiment, and FIG. 7 is a perspective view of the fuel assembly. 3...Fuel rod, 4...Upper tie plate, 4...
Lower tie plate, 101... fuel assembly, 102 curved channel box, 102a, 102b... surface of the channel box relative to the upper grid plate. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 3 Figure 6

Claims (3)

[Claims] (1) In a fuel assembly in which a plurality of fuel rods are loaded in a channel box in a lattice pattern and the upper and lower ends are supported by an upper tie plate and a lower tie plate, the channel box is 1. A fuel assembly characterized in that at least a part of a surface facing an upper lattice plate projects toward the upper lattice plate. (2) The fuel assembly according to claim 1, wherein the channel box has an enlarged upper end portion and a surface facing the upper lattice plate. (3) The fuel assembly according to claim 1, wherein the channel box has a plurality of protrusions formed on an upper end thereof and a surface facing the upper grid plate.