JP2003121579A - Fuel support metal fittings - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain fuel support metal fittings which can prevent foreign matter from flowing into fuel assemblies for new fuel assemblies and spent fuel assemblies, without the need for altering or changing the fuel assemblies or their design. SOLUTION: In fuel support metal fittings, which are located in a reactor pressure vessel of a boiling water reactor and hold four fuel assemblies and where flow channels for leading coolant to the fuel assemblies and holes for guiding control rods are formed, an orifice 45 for regulating the flow rate of the coolant, which has the function of filtering the foreign matter is placed in a section of a coolant inflow hole 44 formed near the lower part of the fuel support metal fittings 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel support fitting for supporting a fuel assembly in a boiling water reactor.

[0002]

2. Description of the Related Art FIG. 8 is a sectional view of a fuel assembly 10 mounted on a fuel support fitting in a boiling water nuclear reactor.
Plural fuel rods 11 are arranged in a square lattice shape in rows of 8 × 8, 9 × 9, or 10 × 10 (9 × 9 in the figure), and are arranged at intervals in the axial direction. The plurality of spacers 12 appropriately maintain the gap between them, and two large-diameter water rods 13 are provided in place of the seven fuel rods in the center of the fuel rods 11 arranged in this way. Has been. The upper and lower ends of the fuel rod 11 and the water rod 13 are held by an upper tie plate 14 and a lower tie plate 15, respectively. The channel box 16 is coated on these fuel bundles. The lower tie plate 15 has an inlet nozzle 1
7 is provided, the inlet nozzle 17 of which has a coolant inlet opening 19 which is surrounded by a fuel assembly insertion guide 18 in the form of a multi-guide arm. Such a fuel assembly 10 is mounted on a fuel support fitting 22 vertically supported by a core support plate 20 by a control rod guide tube 21.

FIG. 9 is an enlarged cross-sectional view of a fuel assembly mounting portion of the fuel support fitting 22, in which a coolant passage 25 is formed by an outer wall 23 and an inner wall 24. The outer wall 2
A coolant inflow hole 26 is formed in the lower portion of 3, and a coolant inlet orifice 27 is provided in the coolant inflow hole 26. A seat surface 28 is provided at the upper edge of the coolant flow path 25, and the seat surface 28 is in close contact with the outer peripheral surface of the lower tie plate 15. Then, the coolant of the nuclear reactor flows into the coolant passage 25 through the coolant inlet orifice 27 provided in the coolant inlet hole 26, passes through the coolant passage 25, and passes through the lower tie plate 1
4 enters the fuel assembly 10 through the coolant inlet opening 19.

FIG. 10 is a view showing the details of the fuel support fitting 22, FIG. 10 (a) is a top view of the fuel support fitting 22, and FIG. 10 (b) is a line AA of FIG. 10 (a). FIG. 10C is a sectional view taken along the line BB of FIG. 10A. As shown in the top view, the fuel support fitting 22 is provided with four openings 30.
The lower part of the fuel assembly is inserted into and engaged with each. A cross-shaped opening 31 into which a cross-shaped control rod is inserted is provided at the center of the four openings 30, and the control rod is vertically penetrated through this opening 31.

By the way, in recent years, in the fuel assemblies as described above, higher burnup has been promoted for the purpose of reducing the fuel cycle cost, and the fuel assemblies are 1.2 to 1.5 in comparison with the conventional ones. The long-term use is being doubled, and the damage event of the fuel body tends to increase with the extension of the use period. It has been pointed out that if such fuel damage occurs, the plant may be stopped and the damaged fuel may be replaced, resulting in deterioration of operating efficiency.

One of the problems associated with operating a nuclear reactor is the accumulation of foreign particles of various sizes within the fuel assembly. Foreign matter is generated during construction, operation and regular inspection, and is, for example, small bolts, nuts, split pins, metal clips, welding slugs, and small wire pieces. During the operation of the nuclear reactor, foreign substances existing in the nuclear reactor and in the primary system are carried by the cooling water and mixed into the fuel assembly to be mixed into the fuel assembly 1.
There is a possibility of damaging the fuel rods 11 and the fuel spacers 12, which are components of No. 0. In particular, foreign matter in the form of wire pieces may vibrate due to the flow of the coolant and cause abrasion of the fuel cladding tube, resulting in fuel damage.

[0007] In particular, since wire-like foreign matter is light and has a large surface area, it is a particular problem because it easily flows into the fuel assembly by cooling water. The inflowing wire-like foreign matter is caught by the fuel spacer 12, excited by the Karman vortex generated by the flow of the coolant, vibrates, and comes into contact with the surface of the fuel rod 11, causing the cladding of the fuel rod 11 to be worn and damaged. This type of wear, called fretting wear, damages the fuel rods along with accelerated corrosion under high temperature and pressure conditions within the reactor. When fuel rod damage occurs, the uranium and / or fission products loaded in the fuel rod leak into the coolant.

Therefore, when the fission products leak into the cooling water, it is necessary to stop the reactor and perform shipping to find a damaged fuel assembly and replace it with a new fuel assembly.

In order to prevent such adverse effects of foreign matter on the fuel assembly, attempts have recently been made to incorporate a filter mechanism into the lower tie plate of a new fuel assembly. Since the incorporation causes an increase in pressure loss and the like in the design of the fuel assembly, it cannot be incorporated with a certain 9 × 9 type fuel. Furthermore, when incorporating a filter function into a new fuel assembly, it takes about 5 to 7 years until all the conventional fuel assemblies loaded in the reactor are replaced with fuel having the filter function. In view of this situation, it is desired to provide a filter function regardless of the type of the fuel assembly and whether the fuel assembly is old or new. However, if the fuel assembly in use is provided with a filter function, the fuel assembly has to be disassembled / reassembled by remote control in the nuclear power plant, and it is inevitably expensive.

Further, in recent years, a proposal has been proposed to prevent foreign matter from entering the fuel assembly by inserting a foreign matter filter into the fuel support fitting from above the fuel support fitting. Interfering with the seat surface of the lower tie plate 15 of the assembly, stable performance cannot be obtained (positional deviation), and further, it is pressed against the lower tie plate seat surface, and the foreign matter filter is stuck to the fuel assembly during fuel extraction. It has been pointed out that there is a possibility that it will be taken out. Further, in the case of the same type, the landing position of the fuel assembly is changed to a high position, and the loading position of the fuel body varies depending on the presence or absence of the foreign matter filter, which affects the core performance.

[0011]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention provides a new fuel assembly and a spent fuel assembly without the need to modify or change the fuel assembly or its design. An object of the present invention is to provide a fuel support fitting that prevents foreign matter from flowing into the fuel assembly.

[0012]

SUMMARY OF THE INVENTION The present invention provides a flow path and a control rod installed in a reactor pressure vessel of a boiling water reactor for holding four fuel assemblies and guiding coolant to the fuel assemblies. In a fuel support fitting having a hole for guiding, a coolant flow rate adjusting orifice having a foreign matter filter function is provided in a coolant inflow hole provided near a lower portion of the fuel support fitting. .

That is, in the present invention, the foreign matter carried by the coolant is captured before it enters the fuel assembly and damages the fuel rod cladding tube, and further before the foreign matter flows into the fuel support fitting. By providing the orifice with the filter function in the fuel support fitting, it is possible not only to prevent foreign matter from flowing into the fuel support fitting itself, but also to provide a conventional coolant support inlet for the fuel support fitting. By eliminating the flow rate adjusting orifice and adopting an orifice with a filter function, the pressure loss can be designed to be exactly the same as the conventional type, and it can be applied to all boiling water reactors.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a view showing a fuel support fitting 40 according to the present invention. FIG. 1A is a sectional view of the fuel support fitting 40 of the present invention showing the same portion as FIG. 8B, and FIG. 1B is an orifice. It is a front view of a part.

The fuel support fitting 40 has an outer wall 4
A coolant passage 43 is formed by the inner wall 42 and the inner wall 42. In addition, a coolant inflow hole 44 is formed in the lower portion of the outer wall 41.
Is formed, and the coolant inflow hole 44 is provided with an orifice 45 with a filter function.

FIG. 2 shows an enlarged detailed view of the orifice 45 with the filter function. FIG. 2 (a) is a front view showing a vertical plate 45a having a simple flat plate shape and 90 ° to 1 at the center.
An orifice 45 with a filter function is configured by assembling a horizontal plate 45b bent in a V shape at an angle of 50 degrees, preferably about 120 degrees into a substantially lattice shape. The vertical plate 45a and the horizontal plate 45b are formed. The coolant channel 46 is formed by. The vertical plate 45a and the horizontal plate 45b are assembled and fixed in a substantially circular frame 47, and the circular frame 47 is mounted in the coolant inflow hole 44. Orifice with filter function 4
5 is a wire-like foreign substance having a length of 10 mm, and a plate-like foreign substance having a length of about 10 mm on one side, which does not pass through, by assembling the vertical plate 45a and the horizontal plate 45b into a substantially lattice shape as described above. It is configured to have filtration performance.

During operation of the reactor, however, the coolant passes through the orifice 45 with a filter function provided in the coolant inflow hole 44 of the fuel support fitting 40, and passes through the coolant passage 43 into the fuel assembly 10. Inflow. Then, during this time, the foreign matter contained in the coolant is captured by the orifice 45 with the filter function, and the foreign matter is prevented from flowing into the fuel support fitting 40 and the fuel assembly 10.

FIG. 2 (b) is a sectional view taken along the line D--D in FIG. 2 (a), in which the horizontal plate 45b is approximately 120 at the center.
It shows a state of being bent in a V shape at an angle of degrees.
Further, in the above embodiment, the horizontal plate 45b is bent in a V shape, but the flow direction of the coolant may be bent up and down at a plurality of positions. In addition, horizontal plate 4
A plurality of grids 5b are inclined obliquely downward or obliquely upward with respect to the flow direction of the coolant at an angle of 15 to 45 degrees so that the flow direction of the coolant is increased by stacking a plurality of grids so that the inclination directions are different. It may be bendable.

FIG. 3 shows an example in which the orifice 50 with a filter function is formed in a substantially rectangular shape. FIG.
3B shows a cross section taken along the line EE in FIG. The orifice 50 with a filter function is also formed by constructing the vertical plate 50a and the V-shaped horizontal plate 50b in a grid shape like the orifice 45 with a filter function. Then, the orifice 50 with the filter function
The same effect as that shown in FIG. 2 can be obtained by using.

Further, FIG. 4 is devised in consideration of the manufacturability of the substantially quadrangular orifice 51 with a filter function shown in FIG. 3, and is constituted by a vertical plate 51a and a horizontal plate 51b in a substantially lattice shape. . 4A shows a front view, and FIG. 4B shows a cross section taken along line FF in FIG. 4A. The horizontal plate 51b is tilted at an angle of about 30 degrees from the horizontal, and a plurality of orifices 51 with a filter function, which are thus configured in a substantially lattice pattern, are stacked to form a plate similar to that shown in FIG. It can be configured.

FIG. 5 is a view showing another form of the orifice with a filter function, which is an orifice 52 with a filter function.
Is a large number of thin-walled circular tubes 52 having an outer diameter of about 2 mm to 5 mm.
It is configured by collecting a in a bundle shape, and the flow path constituted by the thin-walled circular tube 52a is bent at 90 to 150 degrees at at least one place.

As the orifice with a filter function, a circular hole 5 having a diameter of 2 mm to 5 mm as shown in FIG.
It is also possible to construct the orifice 53 with a filter function by stacking a plurality of plates each having a large number of 3a and having a thickness of 5 to 10 mm, and as shown in FIG. Thickness 5 with many square holes 54a
By stacking multiple 10 mm to 10 mm plates,
The orifice 54 with a filter function can also be configured.

FIG. 7 is a view showing another embodiment of the fuel support fitting of the present invention, in which the coolant inlet hole 26 of the inner wall 24 is shown.
A rectifying portion 6 for diverting the coolant, which has flowed into the fuel support fitting from the coolant inflow hole 26, upward on the surface facing the
0 is formed below the straightening portion 60, and a foreign matter reservoir 61 that communicates with the coolant passage 25 via the lower end edge of the straightening portion 60 is formed. Then, the coolant flows into the coolant flow path 25 through the coolant inflow hole 26 and enters the rectifying section 6
Foreign matter that has collided with 0 and has become an upward flow, while flowing into the coolant passage 25 from the upper portion of the fuel support fitting, enters the foreign matter reservoir 61 provided below the rectifying section 60 and cools even after the operation is started. It does not roll up due to the flow of material. It goes without saying that the filter function can be further improved by combining the fuel support fitting with foreign matter reservoir with the orifice with filter.

Although the embodiment of the present invention has been shown and described above, various modifications can be made to the orifice with a filter function without departing from the technical idea of the present invention.

[0026]

As described above, according to the present invention, the coolant inflow hole portion provided near the lower portion of the fuel support fitting is provided with
Since the coolant flow rate adjusting orifice having the foreign matter filter function is provided, the foreign matter filter function reliably prevents foreign matter from flowing into the fuel assembly, and can prevent damage to the fuel rods, spacers, etc. Moreover, since it is only necessary to replace the conventional coolant inlet orifice with the coolant flow rate adjusting orifice having the foreign matter filter function of the present invention, the pressure loss can be designed to be exactly the same as the conventional one, and the fuel assembly itself can be designed. The effect that there is no need to modify or change

[Brief description of drawings]

FIG. 1A is a partially broken cross-sectional view of a fuel support fitting of the present invention, and FIG. 1B is a front view of an orifice with a filter function.

FIG. 2A is a detailed front view of an orifice with a filter function, and FIG. 2B is a sectional view taken along the line D-D of FIG.

3A is a front view of an embodiment of an orifice with a filter function, and FIG. 3B is a sectional view taken along line EE of FIG.

4 (a) and 4 (b) are a front view and a cross-sectional view taken along line FF thereof showing an example of components of the orifice with a filter function shown in FIG.

FIG. 5 is a diagram showing another embodiment of the orifice with a filter function of the present invention.

6A and 6B are views showing still another embodiment of the orifice with a filter function of the present invention.

FIG. 7 is a partial sectional view of a fuel support fitting having a foreign matter reservoir of the present invention.

FIG. 8 is a cross-sectional view of a boiling water reactor fuel assembly disposed on a conventional fuel support fitting.

9 is an enlarged cross-sectional view of a lower portion of the fuel assembly, a fuel support fitting, and a core support plate in FIG.

FIG. 10 (a) is a top view of a conventional fuel support fitting,
(B) is sectional drawing which follows the AA line, (c) is sectional drawing which follows the BB line.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Fuel assembly 11 Fuel rod 12 Spacer 15 Lower tie plate 22 Fuel support fitting 25 Coolant flow path 26 Coolant inflow hole 27 Coolant inlet orifice 40 Fuel support fitting 43 Coolant flow path 45, 50, 51, 52, 53 Orifice with filter function 45a Vertical plate 45b Horizontal plate 46 Coolant flow passage 60 Rectifying part 61 Foreign material reservoir

Claims (8)

[Claims] Claims: 1. A reactor installed in a reactor pressure vessel of a boiling water reactor, which holds four fuel assemblies and is provided with a passage for guiding a coolant to the fuel assembly and a hole for guiding a control rod. In the fuel support fitting, a coolant flow rate adjusting orifice having a foreign matter filter function is provided in a coolant inflow hole portion provided near a lower portion of the fuel support fitting. 2. An orifice having a foreign matter filter function,
2. The fuel support fitting according to claim 1, wherein the fuel support fitting is formed in a substantially lattice shape, and the coolant passage is formed by the lattice. 3. An orifice having a foreign matter filter function,
2. The fuel support fitting according to claim 1, wherein the thin-walled circular pipes are formed into a bundle, and the coolant passages are formed by the circular pipes. 4. The fuel support fitting according to claim 2, wherein the coolant passage of the orifice having a foreign matter filter function is bent at one or more locations in the direction of the flow of the coolant. . 5. The fuel according to claim 2, wherein the coolant flow channel is inclined with respect to the flow direction, and a plurality of bundles of lattices or thin-walled circular tubes are superposed on each other. Support metal fittings. 6. An orifice having a foreign matter filter function,
The fuel support fitting according to claim 1, wherein the fuel support fitting is constructed by stacking a plurality of plates having a large number of substantially circular holes. 7. An orifice having a foreign matter filter function,
The fuel support fitting according to claim 1, wherein the fuel support fitting is constructed by stacking a plurality of plates having a large number of substantially square holes. 8. A flow path for guiding the coolant to the fuel assembly and a hole for guiding the control rod are provided in a reactor pressure vessel of a boiling water reactor for holding four fuel assemblies. In the fuel support fitting, a rectifying section having an inclined surface that allows the flow of the coolant to flow upward is provided in the coolant passage formed in the fuel supporting fitting, and below the rectifying section from above. A fuel support fitting characterized in that a foreign matter reservoir for catching inflowing foreign matter is provided.