JPS61264290A - 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 [Technical Field of the Invention] The present invention relates to a light water reactor core, and particularly to a light water reactor core with a reduced water-to-fuel volume ratio.

[Technical background of the invention and its problems] In recent years, high conversion light water reactors have been designed with the aim of effectively utilizing and storing plutonium recovered from the spent fuel of light water reactors.

In the core of this high-conversion light water reactor, the arrangement of the fuel rod lattice is denser than that of the conventional one in order to increase the conversion ratio and improve the fuel utilization rate. Since it has the same plant configuration as a light water reactor, it has the advantage that conventional technology can be used as is.

By the way, in a high conversion light water reactor, a hexagonal lattice arrangement is adopted as the basic arrangement of the fuel rod lattice.

Such a hexagonal lattice arrangement is preferable because it increases the fuel utilization rate, but on the other hand, from the point of view of core design, it is inferior to the conventional square lattice arrangement in terms of fuel assembly shape, control rod shape, etc. There is a problem that conventional technology cannot be applied because there is a significant difference compared to the conventional technology, which requires a lot of technological development.Also, in high-conversion light water reactors, the fuel lattice spacing is 71%.
%, and the pressure loss due to the coolant flow (2) increases, so it becomes necessary to make the core height, that is, the core axial length, smaller than that of conventional light water reactors, and the axial buckling increases accordingly, and the axial length ( : There was a problem that output distortion was likely to occur.Furthermore, from the core design standpoint, it was necessary to minimize the pressure loss to the coolant flow C2.

[Purpose of the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to reduce the water-to-fuel volume ratio and increase the fuel utilization rate, and to utilize the technology of the ζY square lattice system arrangement. (C) to provide a light water reactor core that can be used.

[Summary of the Invention] In order to achieve the above object, the present invention provides nine nuclear reactor cores C in which fuel rods are regularly arranged in a channel box. The axial output of the core is flattened by making the effluent to fuel volume ratio larger than that in the center of the core.The fuel rods have at least two different diameters. The fuel rods have different lengths depending on their type.Furthermore, the fuel rods are arranged in a square grid within the channel box.

Next, the basic idea of the present invention (two basic concepts will be explained).

In the present invention, the arrangement of fuel rods in a light water reactor core is divided into a horizontal arrangement and an axial arrangement and considered from both perspectives.

First, if we look at the horizontal arrangement of fuel rods, we can see that the general (
The hexagonal lattice arrangement of two fuel rods is the square lattice arrangement of fuel rods (
: It is known that it is possible to arrange more dense sea fuel compared to However, it has been found that even in a square lattice system, if the fuel rods have two or more diameters, the fuel rods can be arranged as densely as in a hexagonal lattice system.

Now, as shown in Fig. 2, the water-to-fuel volume ratio VR of each of the C2, hexagonal lattice system, 1 square lattice system, and square lattice system using two types of fuel rods is numbered 1°2.3. When expressed, it becomes C- as shown in the following formulas (1) to (3).

■Hexagonal lattice system ■Square grid system Square lattice system using 02 types of fuel rods Here, measure the outer diameter of the large diameter fuel rod. , the pellet diameter is Di.

The pitch between fuels in the fuel grid is P, the outer diameter of the small fuel rod is dO + the diameter of the pellet, cti, and the clearance between the large and small fuel rods is c'.

Let C be the clearance between large diameter fuel rods.

By the way, the above α is set at about 0.8 to 0.9 (−) in the actual design, but here, as an example, α=0.88.
β = 1.0 to 0.5. ) value and P/D.

The relationship with the value is shown in Figure 2 (=).

In the design of a high conversion light water reactor, the VR value is set to a value smaller than 1.0, so in Figure 2 1U, this range (: Note that β = 1.0 (the clearance between all fuel rods is equal) Then, the value V of the square lattice system ■ using two types of fuel rods
It can be seen that R8 is quite close to the value VRI +- of the hexagonal lattice system (2). Also, if β = 0.8, the value VR of both
It can be seen that 1 and VR8 are equal.

This figure also shows that in order to increase the clearance between the fuel rods without changing the water-to-fuel volume ratio (U), the pitch between the fuels and the diameter of the fuel rods can be increased while keeping α and β constant. It shows.

The above will be further explained using two specific examples.

In other words, Table 1 below shows a hexagonal lattice (system l) with 9 square lattices (
System 2) 92 types of fuel rod grids (System 3)

In Table 1 Table 1 (:), the outer diameter of the fuel rods is 11.5" (bellet diameter 10.111), and the clearance between the fuel rods is 2.3" in case (A) and 2.3" in case (B). 1.2-
When given, hexagonal lattice (system 1), square lattice (system 2
).

This is a comparison of the water-to-fuel volume ratio in a square grid (system 3) using two types of fuel rods as VR1, VRll, and VR8. Here, in system 3, the outer diameter of the small fuel is 5.
7” (bellet diameter 5.01).

In case (a), the clearance between fuel rods in system 1 and system 2 is the same as the clearance between large diameter fuel rods in system 3.
311J-j, that is, when β=1.0, the water to fuel volume ratio in this case is VR2>VR1>VR8, and system 3
is the most dense.

In case (B), the clearance between fuel rods in system 1 and system 2 is the same as the clearance between large and small diameter fuel rods in system 3, that is, β = 0.5, and the water in this case is The water-to-fuel volume ratio is VR2) VR8) With VR and Te, the water-to-fuel volume ratio of system 3 is larger than that of system 1, but its value is 0.6, and a sufficiently dense value is obtained.

As is clear from the above examples, 1. The use of fuel rods with multiple diameters (2) shows that the water-to-fuel volume ratio can be made small even in a square lattice system.

Next C2, the axial arrangement of fuel rods (one example is the use of fuel rods of different lengths (as explained below) ;

That is, changing the water to fuel volume ratio at the upper and lower ends of the core C;
Therefore, the output at the upper and lower ends is increased and the output distribution in the axial direction is flattened. This utilizes the effect that the infinite multiplication factor increases as the water-to-fuel volume ratio increases. In other words, as shown in Figure 4 C, infinite multiplication factor and water versus fuel volume in a square lattice system when unburned and during power operation (using mixed oxide fuel with fissile plutonium enrichment of 6T). The ratio relationship shows that as the water-to-fuel volume ratio increases, the infinite multiplication factor also increases. From this, it can be seen that the output at the upper and lower ends of the core increases and the axial power distribution is flattened. Further, as a means of increasing the water-to-fuel volume ratio, for example, by reducing the number of fuel rods in the upper part of the core, the flow passage area is increased and the thermal-hydraulic characteristics are improved.

[Embodiments of the invention] Embodiments of the present invention will be described with reference to the drawings. .

1A to 1C are schematic cross-sectional views for explaining the horizontal arrangement of a fuel assembly for a boiling water reactor according to the present invention. That is, FIG. 1a is a schematic cross-sectional view of one embodiment of the present invention, and as shown in the figure, 7'c64 (8×8) large-diameter fuels are arranged in a square grid in the channel box 10. Furthermore, a square grid C49 (7x7
) small-diameter fuel rods 12 are arranged, which is more densely arranged than the conventional fuel rod arrangement.

FIG. 1 is a schematic cross-sectional view of another embodiment of the present invention, and as shown in FIG. The fuel rods are arranged in a lattice pattern with 9 rows and 9 columns, and the pitch between fuels in adjacent fuel lattices is smaller than in the conventional fuel rod arrangement so that the fuel rods are densely packed.

In this embodiment, there are 40 large-diameter fuel rods and 41 small-diameter fuel rods, but it is of course possible to use an inverted C shape.

FIG. 1C is a schematic cross-sectional view of another embodiment of the present invention, and as shown in FIG.
In the central part C2 of 0, the large diameter fuel rods 11 are arranged in a lattice shape with 25 (5
X5) are arranged in a lattice-like manner (56 small-diameter fuel rods 12 are arranged around them, resulting in a total of 9 rows and 9 columns). It has a smaller water to fuel volume ratio.

The embodiments described above are examples in which fuel rods having two different diameters are arranged, but the present invention is not limited to this arrangement. Furthermore, an example in which the size is reduced and there are three types in total is also conceivable.

3a to 3c are schematic vertical cross-sectional views for explaining the axial arrangement of the fuel assembly for a boiling water reactor according to the present invention. That is, FIG. 3a is a schematic vertical cross-sectional view taken along the line ■-■ of FIG. The large diameter fuel rod 11 is shorter than the diameter fuel rod 11, and a gas blennium 13 is provided at its lower part.The large diameter fuel rod 11 is provided with a gas blennium 14 at its upper part C.The fuel rod has such a configuration. Therefore, the water-to-fuel volume ratio increases at the upper and lower ends of the core. Also, since only the large-diameter fuel rods 11 are arranged at the upper part of the core, the flow path area increases (-). According to this example, since the water-to-fuel volume ratio increases in the upper and lower parts of the core, the output also increases and the axial power distribution becomes flat, and the number of fuel rods in the upper part of the core is reduced, so the flow path area Thermal-hydraulic properties are improved.

FIG. 3 is a schematic vertical cross-sectional view similar to FIG. 3a of another embodiment of the present invention, and in this embodiment, as in FIG. 3a, the C2 small diameter fuel rod 16 is replaced by a large diameter fuel rod. It is shorter than 15. The lower portions C2 of both fuel rods 15.16 are provided with gas plenums 17.18 having different lengths.

FIG. 3C is a schematic vertical cross-sectional view similar to FIG. 3a of the embodiment of the present invention (Yu et al.); It is shorter than the diameter fuel rod 19.The upper and lower portions of both fuel rods 19.20 are provided with gas plenums 21.22 and 23.24 having different lengths, respectively, in a 9° configuration.

Figure 3 above Figure 3 C Since the flow area is reduced, the flow path area increases and the thermal hydraulic properties are improved.

In the embodiment shown above, the preheating effect differs depending on the thickness C2 of the fuel pin, and a design in which the content of fissile material is changed for each fuel rod may be considered accordingly.

[Effects of the Invention] Let me explain the above (-1) The reactor core of the present invention (2) According to the reactor core of the present invention, the water-to-fuel volume ratio is decreased in the central part in the height direction of the core to increase the conversion ratio, At the ends, the water-to-fuel volume ratio is increased to flatten the axial power distribution (the cross-sectional area of the flow passages is increased in the upper part of the two cores, so the thermal-hydraulic characteristics can be improved).

[Brief explanation of the drawing]

Figures 1a, b, and c are all schematic cross-sectional views of different embodiments of the present invention, and Figure 2 is a hexagonal lattice system, a square east lattice system, and a square lattice-shaped water-to-fuel volume ratio and P /
Figures 3a, b, and c are schematic longitudinal cross-sectional views of different embodiments of the present invention, and Figure 4 is a diagram showing the relationship with D0. It is a diagram showing a relationship. 10...Channel box 11, 15.19...Large diameter fuel rod 12.16.20...Small diameter fuel rod cylinder 1 Figure 1 Figure b Figure l Figure C Figure 3 α z2

Claims (3)

[Claims] (1) In a nuclear reactor core in which fuel rods are regularly arranged in a channel box, the water-to-fuel volume ratio at the upper and lower ends of the core is made larger than that at the center of the core, and A nuclear reactor core characterized by flattened directional output. (2) The nuclear reactor core according to claim 1, which is a fuel rod having at least two types of diameters and having different lengths for each type. (3) The nuclear reactor core according to claim 1, wherein the fuel rods are arranged in a square grid pattern.