JPH10227883A - Core support structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve economy in producing and wasting, mechanical strength and operability of a boiling water reactor employing large fuel assemblies by arranging fluid inertia pipes in the upper part of control rod guide tubes. SOLUTION: In the upper part of cross shape control rod guide tubes 17 combined with fuel support metals 16, fluid inertia pipes 18 are arranged, whose upper part is supported with a fluid inertia pipe support grid 26 consisting of a ring 24 and a plate 25 so that horizontal vibration is prevented. Coolant elevates outside the cross shape control rod guide tubes 17 from the bottom of a pressure vessel, goes in the fluid inertia pipes 18 limited by the fuel support metals 16 and is guided by fuel assemblies. The fluid inertia pipes 18 give inertia to the coolant and improves flow stability in the channels. Especially, the improvement of the flow stability in the channels during natural circulation is remarkable. By this, a core support structure superior in economy in producing and wasting, mechanical strength and operability, etc., is obtained for a boiling water reactor employing large fuel assemblies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a core support structure.

[0002]

2. Description of the Related Art FIG. 3 shows a cross section of a current boiling water reactor. The boiling water reactor includes a pressure vessel for accommodating a nuclear reactor, a core in which a large number of fuel assemblies 2 are installed, a shroud surrounding the reactor core 3 to form a coolant flow path, and a pressure vessel 1.
A plurality of internal pumps 5 (coolant coolant circulation pumps) provided at the bottom of an annular flow path formed by the lower plenum 7 and the core 3 by a control rod driving mechanism 6 penetrating the bottom of the pressure vessel 1. A control rod 8, which moves the control rod 8 up and down, a control rod guide tube 9 for storing and guiding the control rod 8 of the lower plenum 7, a steam-water separator 10 for separating steam and water generated in the reactor core 3, and a steam dryer. 11 and so on.

FIG. 4 shows a support structure (part A in FIG. 3) of the core 3 according to the present invention. The outermost housing 6 ′ of the control rod drive mechanism 6 penetrating the bottom of the pressure vessel 1
Welded to. The control rod guide tube 9 is cylindrical and has an upper surface that is entirely open, but has a bottom plate at the lower portion, and a nozzle 9 ′ through which the drive shaft 12 of the control rod drive mechanism 6 passes is provided on the bottom plate.

The control rod guide tube 9 is inserted into a hole provided in the core plate 13, and a nozzle 9 'is inserted into the housing 6'. The fuel support 14 is inserted into the opening above the control rod guide tube 9, and the fuel assembly 2 is mounted thereon. Therefore, the weight of the fuel assembly 2 (core 3) is supported by the pressure vessel 1 via the fuel support fitting 14, the control rod guide tube 9 and the housing 6 '.

[0005] The coolant discharged from the internal pump 5 rises between the control rod guide pipes 9, and a coolant passage in which a hole provided in the control rod guide pipe 9 and a hole provided in the fuel support fitting 14 coincide. 15 enters the fuel support fitting 14, and the fuel assembly 2
It is led to.

With respect to such existing boiling water reactors, a boiling water reactor employing a large fuel assembly has been proposed for the purpose of improving fuel efficiency. FIG. 5 shows a cross section of a part of the core of the existing boiling water reactor. The cross wing 8 ′ of the control rod 8 is in contact with only two sides of the fuel assembly 2. On the other hand, as shown in FIG. 6, the cross section of the core employing the large fuel assembly has the cross wings 8 ′ of the control rod 8 in contact with four sides of the fuel assembly 2. Therefore, similarly to the existing boiling water reactor, when the cylindrical control rod guide tubes 9 are employed, the adjacent control rod guide tubes 9 interfere with each other, and the structure is not established.

In order to avoid interference between the control rod guide tubes 9, Japanese Patent Application Laid-Open No. 63-83691 discloses a cross-shaped control rod guide tube 17 integral with the fuel support bracket 16 as shown in FIG.
Has been proposed. When the direction of the cross control rod guide tube 17 is changed by 90 degrees, the fuel support bracket 16 covers the lower part of the core 3, restricts the coolant flow path like the core plate 13, and sets the upper end of the cross control rod guide tube 17. Of vibration. Therefore, the core plate 13 becomes unnecessary. FIG. 8 is a view taken in the direction of arrows BB in FIG.
, The weight of the fuel assembly 2 (core 3) is controlled by the pressure through the fuel support bracket 16, the control rod guide tube 17 and the housing 6 ′, as in the current boiling water reactor. Container 1 supports.

The cruciform control rod guide tube 17 has a lower mechanical strength than the cylindrical control rod guide tube 9 and therefore requires a correspondingly thicker wall.
Expenditure on disposal after the service life is expected to increase. In addition, the cross-shaped control rod guide tube 17 having a large thickness allowed in the core arrangement.
Although the buckling strength is sufficient, the torsional strength is insufficient and there is a concern about torsional vibration due to the flow of the coolant.

As another method for avoiding interference between the control rod guide tubes 9, there is Japanese Patent Application Laid-Open No. 5-249275. In the present invention, although an example is shown in FIG. 9, a fluid inertia tube (coolant guide tube) 18 is employed without using a control rod guide tube. Drive shaft 12
And a hole 20 communicating with the fluid inertial tube 18
Is placed on the housing 6 '.

The fluid inertia tube 18 is set upright in accordance with the hole 20 of the partition plate 21, and the fuel assembly 2 is mounted thereon. The upper portion of the fluid inertial tube 18 is supported by a support grid 22. The support grid 22 prevents the fluid inertial tube 18 from swinging, but does not restrict the vertical movement of the fluid inertial tube 18.

Accordingly, the weight of the fuel assembly 2 (core 3) is supported by the pressure vessel 1 via the fluid inertia tube 18, the partition plate 21, and the housing 6 '.

The coolant discharged from the internal pump 5 flows between the bottom of the pressure vessel 1 and the partition plate 21 and enters the fuel assemblies 2 from the respective fluid inertia tubes 18. The control rods 8 do not come into contact with the main coolant flow as in the current boiling water reactor (even when the control rod guide tube 17 is used).
In the present invention, since the space between the bottom of the pressure vessel 1 and the partition plate 21 is narrow, the pressure loss increases, and there is a direction that the coolant may not be distributed to the fuel assembly 2 in a well-balanced manner.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a boiling water reactor employing a large fuel assembly, in which the economics, mechanical strength, and operating performance during production and disposal are comprehensively considered. It is another object of the present invention to provide an excellent core support structure.

[0014]

SUMMARY OF THE INVENTION In Japanese Unexamined Patent Publication No. 5-249275, a pressure vessel 1 is used to eliminate the concern of coolant distribution.
It is necessary to make the space between the bottom of the partition and the partition plate 21 wider. To widen the space between the pressure vessel 1 and the partition plate 21 without increasing the size of the pressure vessel 1, the partition plate 21 may be moved upward. When the partition 21 below the control rod 8 is moved upward, the cross-shaped control rod 8 penetrates the partition 21 as shown in FIG. The through hole of the control rod 8 of the partition plate 21 is of course cross-shaped, and the control rod 8 and the coupling 23 of the drive shaft 12 are provided at the center.
There is a round hole for passing through. When the lower end of the control rod 8 gets out of the partition 21, only the drive shaft 12 penetrates the partition 21, and the flow rate of the coolant bypassing the fuel assembly 2 increases. That is, it is inconvenient that the size of the gap between the partition plate 21 and the control rod 8 (drive shaft 12) changes depending on the position of the control rod 8, and that the bypass flow rate of the coolant changes. Further, since the control rods 8 below the partition plate 21 are in contact with the main flow of the coolant, there is a concern that the control rods 8 generate flow vibration.

The change in the bypass flow rate of the coolant depending on the position of the control rod 8 and the generation of the flow vibration of the control rod 8 cover the control rod 8 below the partition plate 21 with a cross-shaped control rod guide tube 17 or the like. Can be solved. Further, since the cross-shaped control rod guide tube 17 is short, the torsional strength is increased, and the torsion due to the flow vibration can be prevented.

As described above, by combining the structures disclosed in JP-A-5-249275 and JP-A-63-83691, an excellent core supporting structure which solves individual disadvantages can be provided.

[0017]

1 and 2 show an embodiment of the present invention.
It was shown to. FIG. 1 is a perspective view showing an assembled state of a cruciform control rod guide tube 17 and a fluid inertia tube 18 integrated with a fuel support bracket 16. The half of the conventional length is made the same as the conventional length by combining the cross-shaped control rod guide tube 17 and the fluid inertia tube 18.
The top of the fluid inertial tube 18 is prevented from swaying by a fluid inertial tube support grid 26 consisting of a ring 24 and a plate 25.

FIG. 2 is a cross-sectional view showing a state in which the core is supported. In the short cross-shaped control rod guide tube 17, the nozzle at the lower end is inserted into the housing 6 'and the housing 6'
Be independent on top. The fluid inertia tube 18 is inserted into the fuel support bracket 16 integrated with the control rod guide tube 17, and the fuel assembly 2 is mounted on the fluid inertia tube support lattice 26 and the fluid inertia tube 18 supporting the upper part. The weight of the fuel assembly 2 (core 3) is
8, the fuel container 16 is supported by the pressure vessel 1 via the cross-shaped control rod guide tube 17 and the housing 6 '.
The coolant is supplied from the bottom of the pressure vessel 1 to the cross-shaped control rod guide tube 17.
, And is restricted by the fuel support fitting 16, enters the fluid inertia tube 18, and is guided to the fuel assembly 2.

FIG. 11 shows the details of the fuel support bracket 16, and there is a nozzle below the fuel support bracket 16 shown in Japanese Patent Application Laid-Open No. 63-83691 as shown by a chain line. Since this nozzle increases the pressure loss at the inlet, the present invention provides a curved chamfer at the inlet as shown. The upper part of the hole of the fuel support bracket 16 is counterbored, and the fluid inertia tube 18 is provided.
The lower part of the fluid inertia tube 18 is inserted by welding a ring-shaped holding member 27 to the fuel support member 16 or by integrally forming the same with the fuel support member 16 in order to compensate for a shortage of the insertion depth. Helps you become independent.

FIG. 12 shows the cross-sectional dimensions of the fluid inertia tube 18 and the cruciform control rod guide tube 17 which are currently planned. The cross-sectional area of the fluid inertia tube 18 is approximately 1,500 mm ² and The cross-sectional area of the rod guide tube 17 becomes about 10,000 mm ² . As shown in FIG. 9, one fluid inertia tube 18 supports one fuel assembly 2 while one cross-shaped control rod guide tube 17 supports two fuel assemblies 2. Therefore, comparing the cross-sectional areas of the two fluid inertia tubes 18 and the one cross-shaped control rod guide tube 17, the cross-shaped control rod guide tube 17 is 3.3 times larger. That is, the cross-shaped control rod guide tube 17
When the fluid inertia tube 18 and the cross-shaped control rod guide tube 17 are each used for half the length, the raw material is 1.
Only one sixth is required, and costs for processing and disposal are lower. Further, when the cross-shaped control rod guide tube 17 has a half length, the torsional strength increases, so that there is no need to worry about torsional vibration.

It has not been ascertained how long the distance from the bottom of the pressure vessel 1 to the inlet of the fluid inertial tube 18 will make the flow distribution to the fluid inertial tube 18 uniform. However, since the internal pump 5 discharges the coolant toward the bottom of the pressure vessel 1, if the inlet of the fluid inertia pipe 18 is located at an intermediate position of the lower plenum 7 as in the present invention, the flow distribution is considered to be uniform. Can be

The fluid inertia tube 18 provides inertia to the coolant and serves to improve the flow stability in the channel. In particular, the flow stability in the channel during natural circulation is significantly improved. The relative length (the ratio of the length of the fluid inertia tube 18 to the length of the fuel assembly 2) and the relative width reduction ratio (the ratio of the width reduction ratio with and without the fluid inertia tube 18 and the width reduction ratio in FIG. 13 are stable) An example of the relationship is shown below. Increase the length of the fluid inertia tube 18 to the height of the lower plenum 7 (substantially equal to the length of the fuel assembly 2)
Even if it is 1/2 (relative length 0.5), the relative width reduction ratio is 0.5.
9 That is, even if the length of the fluid inertia tube 18 is reduced to half, there is an effect that the flow stability in the channel is improved by 10% as compared with the case where the fluid inertia tube 18 is not provided, and the operation margin during natural circulation is increased.

As described above, as an embodiment of the present invention, an example is shown in which the fluid inertia tube 18 having a length of 1/2 and the cross-shaped control rod guide tube 17 are combined. As shown in FIG. If it is 0.2 or more, the relative width reduction ratio becomes small, and there is an effect of improving the flow stability in the channel. However, if the fluid inertia tube 18 is too short, the cross-shaped control rod guide tube 1
7, the problem of torsional vibration resurfaces, and conversely, the fluid inertia tube 18
If the length is too long, the effect of improving the flow stability in the channel will increase, but the problem of non-uniform distribution of coolant flow will resurface.

Fluid inertia tube 18 and cruciform control rod guide tube 17
The optimal ratio of both lengths when combining
It is considered that the combination of the 慣 length fluid inertia tube 18 and the cruciform control rod guide tube 17 may not be optimal, but eliminates the disadvantages when used individually. You.

The control rod guide tube is not limited to a cross shape, but may be a control rod guide tube such as a square control rod guide tube having a square side curved inward as shown in Japanese Patent Application Laid-Open No. 5-249275. If the pipes do not interfere with each other and a coolant flow path can be secured in the lower plenum portion where the fluid inertia pipe opens, the same effect as that of the cross-shaped control rod guide pipe can be obtained.

[0026]

According to the present invention, it is possible to provide a boiling water reactor employing a large fuel assembly, which can provide a core support structure which is excellent in economy, mechanical strength, operation performance, and the like at the time of production and disposal. .

[Brief description of the drawings]

FIG. 1 is a perspective view showing a part of a core support structure according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a part of a core support structure showing an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a current boiling water reactor.

FIG. 4 is a sectional view of a core support structure of a current boiling water reactor.

FIG. 5 is a cross-sectional view of a part of a core of a current boiling water reactor.

FIG. 6 is a cross-sectional view of a part of a core employing a large fuel assembly.

FIG. 7 is a perspective view of a cross-shaped control rod guide tube with a fuel support fitting.

FIG. 8 is a cross-sectional view showing a core-supported state of a cruciform control rod guide tube with a fuel support fitting.

FIG. 9 is a cross-sectional view showing a core support state by a fluid inertial tube.

FIG. 10 is a cross-sectional view showing a state in which a core is supported by a fluid inertial tube when a partition plate is set at a high position.

FIG. 11 is a partial sectional view showing an assembled state of the fluid inertial tube of the present invention.

FIG. 12 is a cross-sectional view of a fluid inertia tube and a cross-shaped control rod guide tube.

FIG. 13 is a characteristic diagram showing an effect of improving channel stability of a fluid inertial tube.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pressure vessel, 2 ... Fuel assembly, 6 '... Control rod drive mechanism housing, 8 ... Control rod, 16 ... Fuel support bracket, 17 ...
Cross-shaped control rod guide tube, 18 ... fluid inertia tube, 24 ... ring, 25 ... plate, 26 ... fluid inertia tube support lattice.

Claims (4)

[Claims] 1. A core support structure for supporting a core in which a large number of fuel assemblies in which a large number of fuel rods are bundled are arranged, wherein the upper part is a tube for imparting inertia to the fluid, and the lower part is shaped so as to avoid interference with an adjacent one. A core support structure comprising a rod guide tube. 2. The core supporting structure according to claim 1, wherein the pipe for imparting inertia to the fluid is a right circular pipe, the length of which is at least 0.2 times the length of the fuel assembly. 3. The core support structure according to claim 1, wherein the control rod guide tube has a cross shape. 4. The core support structure according to claim 1, wherein the control rod guide tube has a square shape.