JPH01123192A - Fuel assembly - Google Patents

Abstract

PURPOSE:To intend cost saving for a fuel cycle, by increasing a radius of curvature of a channel box corner section to the extent through which a corner fuel rod can not be inserted. CONSTITUTION:A large diameter water rod 21 is located at the center of a channel box inside 20, and a coarse and dense typed bundle are inserted at a space portion in the channel box 20. This coarse and dense typed bundle has a constitution which sub-bundles having fuel rods 22 being arranged in a 3 by 3 matrix are further arranged in a 3 by 3 matrix with intervals 24 one another and corner rods of the channel box from the matrix are removed to be moved to the location close to the side surface of the large diameter water rod 21. Therewith, a radius of curvature of the channel corner can be increased, thus the channel can be thinned more than 0.5mm. Thereby, the parasitic absorption of neutrons with the channel is diminished and a fuel cycle cost can be saved.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to a fuel assembly, in particular a fuel assembly with a square channel box.

(Prior Art) In recent years, with the increase in the amount of power generated by power reactors, there has been a severe demand for improvement in the economical efficiency of power generation.

Therefore, power reactors have been researched and developed to meet these demands, but the present invention is particularly useful in boiling water reactors (8WR>) that use square channel boxes. The type nuclear reactor will be explained with reference to the drawings.

FIGS. 9(A) and 9(B) are a perspective view of a conventional fuel assembly and a schematic vertical sectional view of fuel rods constituting the fuel assembly, respectively.

In Figure 9 (A), the fuel assembly is a water rod (not shown).
After regularly arranging the fuel rods 2 and 4, the upper tie plate 4. Spacer 5. It is fixed by a lower tie plate 6 and surrounded by a rectangular channel box 1 on the outside. As shown in the figure (B), the fuel rod 2 has fuel pellets 8 disposed in a cladding tube 7, a spring 9 provided in the gas plenum above the cladding tube 7, and an upper end plug 10 at the upper end.
A lower end plug 11 is provided at the lower end.

FIG. 10 is a cross-sectional view of the conventional fuel assembly shown in FIG. 9. Sixty-two fuel rods 2 and two water rods 3 are arranged in the channel box 1 to form a fuel assembly.

The water rods 3 suppress the shortage of water, which is a moderator, inside the reactor assembly, but since these water rods 3 are uniform in the axial direction, there is a problem that there is an excess of water below the core and a lack of water above the core. There is a point.

The fuel assembly shown in FIG. 11 was developed to improve the characteristics of the fuel assembly described above, and has one large diameter water rod 12 in the center of the channel box 1.

60 fuel rods 2 inside the remaining channel box 1
are placed. Although non-boiling water is introduced into the large-diameter water rod 12, this example also has the problem of excess water below the core and insufficient water above the core.

The fuel assembly shown in FIG. 12 is also an improvement of the fuel assembly shown in FIG. By making the cross-shaped gap 14 a non-boiling moderator region, the horizontal power distribution is flattened, but it is said that this type of fuel assembly also suffers from excess water below the core and insufficient water above the core. There is a problem.

The fuel assembly shown in FIG. 13 was developed as an improved version of the fuel assembly shown in FIG. This fuel assembly has nine subassemblies 15 in a rectangular channel box 1. Each subassembly 15 has 9
It is composed of two fuel rods. A rather wide gap 16 is provided between the subassemblies 15. Since this fuel assembly has 9 x 97 lays, it is more advantageous in terms of fuel cycle cost (FCC) and fuel health than an 8 x 8 array, but since it is a coarse-pitch method, the effective multiplication factor keff increases during high-temperature output operation. However, there is a problem in that the cooling capacity of the corner portions is reduced.

The fuel assembly shown in FIG. 14 was developed as an improved version of the fuel assembly shown in FIG. A large-diameter water rod 17 corresponding to nine fuel rods 2 is placed in the center of the channel box 1, which has a similar external shape, and fuel rods 2 are arranged in nine rows and nine columns in other spaces inside the channel box 1. The structure is arranged in such a way that Conventional BWR fuel was rarely used with 8 x 87 lays, but it was found that making the fuel rods slightly smaller in diameter and using 9 x 97 lays was superior in terms of lower fuel cycle costs and increased fuel integrity. Currently, a 9x97 ray type bundle is being developed. In the 9×9 array type bundle, water rods 17 equivalent to about nine fuel rods are provided in the center of the bundle, and the inside of the water rods 17 is set as a non-boiling region. This example also has a problem in that the cooling capacity at the corner portions is reduced.

The fuel assembly shown in FIG. 15 has a large diameter water rod 17 arranged in the center of the fuel assembly shown in FIG. 13. In this way, even in a 9x9 array, if the fuel rods are grouped into small groups, the effective multiplication factor k during high-temperature output operation. ff can be increased, and is more advantageous than the uniform lattice type fuel rod arrangement as shown in FIG. 14 in terms of fuel cycle cost. This is due to the increased probability of escaping resonance due to small grouping.

(Problems to be Solved by the Invention) However, in a fuel assembly with a 9x9 array of fuel rods as described above, there is a problem in that cooling water concentrates in the wide gap portions, reducing the cooling ability in the bundle corner portions. occurs.

Therefore, as a way to avoid such a decrease in the cooling capacity of the bundle corners, there are two methods: removing the fuel rods at the bundle corners (1, 1) or (2, 2), or reducing the flow of cooling water into wide gaps. A possible solution would be to install a flow control to control the flow.

This light was created to solve the above problems.
The purpose is to provide a fuel assembly that improves fuel cycle cost and prevents a decrease in the cooling capacity of bundle corner portions.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention comprises a bundle in which a large number of fuel rods are regularly arranged, and a metal rectangular channel box is arranged around the outer periphery of the bundle. In this case, all the fuel rods located at the bundle corners are removed, and the curvature of the channel box corners is correspondingly relaxed to such an extent that the corner fuel rods cannot be inserted, thereby reducing the channel internal pressure. The feature is that the wall thickness of the channel box material is reduced to compensate for the correspondingly generated stress.

(Function) According to the fuel assembly of the present invention, since the fuel rods at the corner portions are removed, the curvature of the channel box corner can be increased, and thereby the stress generated due to the channel internal pressure can be alleviated. . Therefore, 1. Since the channel box material can be made thinner and the inside of the channel can be expanded accordingly, the cooling capacity for all fuel rods is restored and the health of the fuel is increased. Additionally, since the channel material becomes thinner, unnecessary neutron absorption is reduced, and the area of the coolant is increased, improving neutron moderation characteristics and reducing fuel cycle costs.

Next, the concept of the present invention will be explained.

FIG. 2 is a stress distribution diagram based on the internal pressure of cooling water in the channel box. That is, in the same figure, the solid line A is the conventional channel box, the dotted line opening is the channel box of the present invention (one with a large corner radius), and the dashed line C is the channel box of the present invention (one with a corner surface).
FIG. 2 is an internal pressure stress distribution diagram. As can be seen from the figures, the channel boxes according to the present invention all have much smaller internal pressure stress at their corner parts than the conventional ones.

FIG. 3(A) is a plan view of a corner portion of a conventional fuel assembly, and as shown in the figure, fuel rods 2 are uniformly arranged within a rectangular channel box 1. Now, in this conventional fuel assembly, if the fuel rods 2a at the corners are removed, the radius of curvature of the channel inner corner will change from Romm in the same figure (B
), the radius of curvature can be increased to R1 mm (R1>R17).

As a result, as can be seen from FIG. 2 described above, the internal pressure stress in the i-space portion is reduced, so that the thickness of the channel plate can be reduced. Therefore, if this is used to expand the inside of the channel, the cooling characteristics of the outer periphery of the dense and dense lattice will be improved. Also,
When used to expand out-channels, the non-boiling region increases, the reactivity during high-temperature power operation increases, and control rod insertion becomes easier.

Roughly speaking, as shown in the same figure (C), if the corners are chamfered, the same effect as described above will be obtained, but both ends of the chamfer should be bent as gently as possible to avoid stress concentration. . Note that FIGS. 3(B) and 3(C) both show the channel box of the present invention.

(Example) Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic plan view of an embodiment of the present invention.

As shown in FIG. 1, the fuel assembly of this example has an external shape of
A large diameter water rod 21 is placed in the center of the channel box 20.
, and loose and dense bundles are inserted into other spaces within the channel box 20. This sparsely dense bundle has fuel rods 22 arranged in 3 rows and 3 columns, sub-bundles 23 arranged in 3 rows and 3 columns with rough gaps 24, and corner rods (1, 1) removed. The structure has been moved to the side of 21. As a result, this embodiment has the following effects. That is, since the radius of curvature of the channel corner can be increased, the channel can be made thinner by 0.5# or more. This reduces the parasitic absorption of neutrons by the channel and reduces the fuel cycle (FCC). In addition, the channel material surface is enlarged and the cooling ability of the fuel in the outer circumference of the bundle is improved, so that fuel health can be ensured. Roughly speaking, as the radius of curvature of the channel corner increases, the non-boiling water at the corner comes a little closer to the inside of the bundle than before, so the reactivity improves. Therefore, since the diameter of the central large-diameter water rod 21 can be reduced to some extent, the fuel rod 22 located at the corner (1, 1)
A can be inserted into the side of this large-diameter water rod 21, and a decrease in fuel inventory can be prevented. Furthermore, since the wide water gap portion on the side of the large-diameter water rod is occupied by the fuel rod 22a, concentration of cooling water near the large-diameter water rod 21 is suppressed, and the cooling effect of the fuel in the bundle can be made uniform. , fuel health is improved.

Although not shown, it is naturally possible to roughly reduce the wall thickness of the channel side surface in accordance with the stress distribution curve (however, the effect is not large).

FIG. 4 is a schematic plan view of the second embodiment of the present invention, and the only difference from the first embodiment is that the corner portions of the channel box are chamfered. Identical parts will be given the same reference numerals and detailed explanations thereof will be omitted. Note that the same applies to the following examples.

In the first embodiment and the conventional channel box, outward stress occurs at the corners, and the side surfaces (excluding the areas near the corners at the top, bottom, left and right of the figure) respond to internal pressure. Inward stress is generated, but in this embodiment, an inward stress component is generated even at the corner chamfered portions, so the outward stress at the corner portion is significantly alleviated. Therefore, the channel thickness can be reduced and made thinner than in the first embodiment.

FIG. 5 is a schematic plan view of a third downstream example of the present invention. In this embodiment, a rectangular water rod 2 is installed in the center of the channel box 26.
7, fuel rods 22 are uniformly arranged in other parts,
It is a fuel assembly in which the corners of the channel box 26 are roughly chamfered.

In this embodiment, the fuel pitch is uniform and the corner fuel rods 22a are moved to the sides of the square water rods 27 to prevent inventory reduction, so the square water rods 27 tend to be slightly smaller.

FIG. 6 is a schematic plan view of a fourth embodiment of the present invention. In this embodiment, the corners of the channel box 28 are chamfered, and the fuel pitch is arranged in a 4-1-4 configuration. Therefore, it is possible to arrange a large rectangular water rod 29 in the center of the channel box 28.

According to this embodiment, the following effects are achieved.

(1) Since the channel corners are chamfered, the channel material can be made thinner, and the fuel rods can be made larger by using the coarse and fine pitch method.

In other words, since the non-boiling water near the corners is guided into the bundle, the effective multiplication factor keff is improved.

(2) Since the corner rods are not included, the cooling capacity in the vicinity thereof is improved, and since the large diameter water rods are used, concentration of the coolant near the water rods is suppressed.

Therefore, the uniformity of cooling is improved, which improves fuel integrity.

(3) Since fuel is removed from the fuel rod P within the wide gap extending in the diagonal direction of the rectangular water rod at a portion where the reactor shutdown margin becomes severe, the reactor shutdown margin is greatly improved. If the upper part of the fuel rod P is cut off to shorten it and form a so-called burnishing rod, the pressure loss can be significantly reduced.

FIG. 7 is a schematic plan view of a fifth embodiment of the present invention. In this embodiment, a large rectangular water rod 31 is placed in the center of the channel box 30.
2-4 type), with chamfered corners.

As in this embodiment, when the number of fuels increases, the corner chamfering method is advantageous because the rate at which the inventory is reduced even if fuel is removed from the channel corner portions decreases.

FIG. 8 is a schematic plan view of a sixth embodiment of the present invention. This example is applied to an IOX 10 array. That is, the large diameter water rod 3 is installed in the center of the channel box 32.
3 is adopted, a cross-shaped channel 34 is roughly provided inside this channel box 32, and this cross-shaped channel 34
Fuel rods 22 are uniformly arranged in a space partitioned by a channel box 32 and a sub-bundle 35. The structure is such that non-boiling moderator water flows in the cross-shaped channel 34 and large-diameter water rod 33, and boiling water cooling water flows in the sub-bundle 35.

[Advantageous Effects] As described above, according to the present invention, the radius of curvature of the corner portion of the channel box is set so sharply as to make it impossible to insert the corner fuel rod, so that the channel internal pressure stress can be alleviated. Therefore, the channel box material can be made thinner,
Since the inside of the channel can be enlarged accordingly, the cooling effect is improved, the health of the fuel is increased, and the fuel cycle cost is reduced.

[Brief explanation of the drawing]

Figure 1 is a schematic plan view of an embodiment of the present invention, Figure 2 (A)
FIG. 3(8) is a diagram for explaining the internal pressure stress in the conventional channel box and the channel box of the present invention, and FIGS. 3(A) to (C) are the conventional channel box and the channel of the present invention at the corner part Figures 4 to 8 are schematic plan views of different embodiments of the present invention, and Figures 9 (A) and 9 (B) are diagrams for comparing the characteristics of the box, respectively. 10 is a schematic plan view of the conventional fuel assembly shown in FIG. 9, and FIGS. 11 to 15 are different conventional fuel rods. FIG. 3 is a schematic plan view of a fuel assembly. 20, 25.26.28.30.32... Channel box 21.33... Large diameter water rod 22.22a... Fuel rod 23, 35... Subbundle 24... Gaps 27, 29 .31...Square water bar 34...Cross-shaped gap (8733) Agent Patent attorney Yoshiaki Inomata (Idiot)
1 person) Figure 1 Figure 2 (A) Figure 3 Figure 4 Figure 5 Figure 6 Summer O Figure 1T Figure 12 Figure 13 Figure 14 51 Figure 15

Claims (3)

[Claims] (1) In a fuel assembly in which a large number of fuel rods are arranged regularly to form a bundle and a metal rectangular channel box is arranged around the outer periphery of the bundle, all the fuel rods located at the bundle corners are removed and the corresponding The curvature of the channel box corner is relaxed to such an extent that the corner fuel rod cannot be inserted, and the wall thickness of the channel box material is increased to compensate for the stress generated in response to the reduced channel internal pressure. A fuel assembly characterized by reduced fuel consumption. (2) The fuel assembly according to claim 1, wherein the channel box corner portion has a radius of curvature so large that a corner fuel rod cannot be inserted therein. (3) The fuel assembly according to claim 1, wherein the channel box corner portion is chamfered to such an extent that a corner fuel rod cannot be inserted therein.