JP2005049160A - Fuel supporting metal fixture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent foreign articles from coming in a foreign article filter structure of fuel supporting metal fixture without degrading gas-liquid counter-current flow limit characteristics. <P>SOLUTION: The fuel supporting metal fixture 7 supports the lower part of a nuclear fuel assembly and has inside a coolant flow path room for guiding coolant from a coolant flow inlet 16 directing to the nuclear fuel assembly. A filter 50 is arranged at the coolant flow inlet, and the filter has a plurality of flow paths nearly parallel to each other. Each flow path inclines upward at the inlet, changes the direction in the path, and inclines downward at the part going out the coolant flow path room. The wall of the flow path in the filter remains roughened. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel support fitting for a light water reactor, and in particular, captures foreign matter (debris) contained in a coolant to prevent or suppress foreign matter inflow into a nuclear fuel assembly (hereinafter also simply referred to as “fuel assembly”). The present invention relates to a fuel support metal fitting provided with a filter.
[0002]
[Prior art]
A fuel support fitting and a fuel assembly in a boiling water nuclear reactor (hereinafter referred to as BWR) will be described with reference to FIG. FIG. 10 is an elevational view partially showing a main part of the internal structure of the BWR in a longitudinal section. In a normal BWR, as shown in FIG. 10, a core support plate 3 is provided on a shroud 2 that is integral with the reactor pressure vessel 1. A control rod drive mechanism housing 4 is provided at the bottom of the reactor pressure vessel 1 positioned below the core support plate 3, and a control rod drive mechanism 5 is installed in the housing 4.
[0003]
A control rod guide tube 6 is provided at the upper part of the housing 4, and this control rod guide tube 6 protrudes and is supported on the core support plate 3. A fuel fitting 7 is inserted into the upper end opening of the control rod guide tube 6. It is provided detachable.
[0004]
The control rod guide tube 6 and the fuel support fitting 7 are fixed by positioning pins 8 provided on the core support plate 3. A control rod 9 having a cross-shaped horizontal cross section is provided in the control rod guide tube 6 so as to be movable up and down, and the lower end of the control rod 9 is connected to the upper end of the control rod activation mechanism 5. The control rod 9 can be inserted into the space between the fuel assemblies 10 and 10 from the upper end of the control rod guide tube 6.
[0005]
The upper part of the fuel support bracket 7 places and supports the lower tie plates 11 of the four fuel assemblies 10. The upper tie plate 12 of the fuel assembly 10 is supported in the lateral direction by an upper lattice plate 13 provided in the shroud 2.
[0006]
A through hole having a cross-shaped cross section into which the control rod 9 is inserted along the axial direction is formed at the center of the fuel support bracket 7, and the lower end of one fuel assembly 10 is provided at each of the upper four corners. Four fuel assembly support holes for supporting the four fuel assemblies 10 are formed in two rows and two columns.
[0007]
In addition, a coolant inlet 16 is formed in the lower side surface of the fuel support bracket 7, and a coolant channel for guiding the coolant from the coolant inlet 16 into the lower tie plate 11 of the fuel assembly 10 therein. A chamber 17 is formed. An inlet orifice 18 for adjusting the coolant flow rate is provided in front of the coolant inlet port 16.
[0008]
In the BWR fuel assembly 10, elongated fuel rods are arranged in a lattice pattern. The fuel rods arranged in a grid are supported between the lower tie plate 11 and the upper tie plate 12. A water rod is provided at the center of the fuel rod array. These fuel bundles are covered with a rectangular tubular channel box 22 to constitute a fuel assembly 10.
[0009]
An inlet nozzle for injecting a coolant is formed at the lower end of the lower tie plate 11, and the inlet nozzle has a coolant inlet opening surrounded by a fuel guide insertion guide having a multiple guide arm shape. . The outer surface of the lower end portion of the lower tie plate 11 of each fuel assembly 10 is placed in close contact with the seat surface 25 of the fuel support bracket 7, and the fuel support bracket 7 is supported laterally by the core support plate 3 to control rod guides. It is supported vertically by a tube 6.
[0010]
Reactor coolant flows from the inlet orifice 18 and the coolant inlet 16, passes through the coolant channel chamber 17, enters the inlet nozzle of the fuel assembly 10, and flows out of the fuel support fitting 7. The fuel assembly 10 is in close contact with the seat surface 25, thereby preventing the generation of a flow that bypasses the coolant inlet opening of the fuel assembly 10.
[0011]
By the way, when a cooling water loss accident assumed in BWR occurs, cooling water is rapidly lost from the exothermic core, the fuel rods are exposed from the cooling water and run out of heat. As a result, the fuel rods may rupture and radioactive materials may leak into the core.
[0012]
Therefore, when a cooling water loss accident occurs, a control rod that suppresses the progress of the nuclear reaction is immediately inserted into the core, and the emergency core cooling system is activated so that the cooling water is sprayed from the upper part of the core toward the fuel assembly. Is forcibly injected. The spray-like cooling water falls in the heat exchange channel of the fuel assembly and directly falls on the fuel rod to remove heat, and falls and accumulates in the channel box 22. The cooling water further falls in the lower tie plate, but the vapor-liquid counterflow restriction occurs at the inlet orifice 18 as the steam generated by the boiling under reduced pressure rises through the inlet orifice 18 from below the inlet orifice 18. As a result, the water level in the channel box 22 is gradually increased, and the fuel rods exposed from the cooling water are submerged.
[0013]
[Patent Document 1]
JP-A-64-38691
[Problems to be solved by the invention]
In order to reduce fuel cycle costs, fuel assemblies have been promoted to have a higher burnup.In recent years, fuel assemblies have been used for a longer period of time compared to conventional fuel assemblies. There may be an increase in body damage events. When the fuel assembly is damaged, it is considered that the plant is stopped, and the operation efficiency is deteriorated due to replacement of the damaged fuel assembly.
[0015]
One of the problems related to the operation of the nuclear reactor is the possibility that foreign substances of various sizes may enter the reactor water. Foreign objects are generated during construction, operation, and periodic inspection, and include, for example, small bolts, nuts, split pins, metal clicks, weld slugs, and small wire pieces. During the operation of the nuclear reactor, foreign substances existing in the reactor and in the primary system are carried by the cooling water and mixed into the fuel assembly, which may damage the fuel rods and fuel spacers that constitute the fuel assembly. .
[0016]
In particular, the wire-like foreign matter may vibrate due to the flow of the coolant, wear the cladding tube, and possibly damage the fuel assembly. Since the wire-like foreign matter is light and has a large surface area, there is a particular problem because it easily flows into the fuel assembly by the cooling water.
[0017]
In order to prevent such a bad influence of the foreign matter on the fuel assembly, for example, as shown in Patent Document 1, instead of the four core orifices provided in front of the coolant inlet of the fuel support fitting, A fuel support fitting provided with a filter having a pressure loss equivalent to that of the core orifice has been proposed.
[0018]
However, the structure of the filter function part of this fuel support metal fitting has a large influence on the gas-liquid countercurrent restriction characteristic during the operation of the above-mentioned emergency core cooling system. There is a risk of deterioration. That is, the cooling water easily flows down in the filter, the water level in the channel box cannot be raised, and it may be difficult to reflood the fuel rod.
[0019]
The present invention has been made in view of such circumstances, and an object of the present invention is to prevent or suppress the inflow of foreign substances without deteriorating the gas-liquid countercurrent restriction characteristic as compared with the core inlet orifice of the conventional fuel support fitting. It is to provide a fuel support fitting.
[0020]
[Means for Solving the Problems]
The present invention achieves the above-mentioned object, and the invention according to claim 1 supports a lower part of the nuclear fuel assembly and introduces a coolant flow from the coolant inlet to the nuclear fuel assembly. In the fuel support fitting having a passage chamber inside, a filter is disposed at the coolant inlet, and the filter has a plurality of channels substantially parallel to each other, and these channels are formed at the inlet. It is inclined upward, changes its direction in the flow path, and inclines downward in the part that goes out to the coolant flow path chamber.
[0021]
The invention according to claim 2 is a fuel support bracket that supports a lower portion of the nuclear fuel assembly and has a coolant passage chamber that guides the coolant from the coolant inlet toward the nuclear fuel assembly. The coolant inlet is arranged so that the coolant flows into the coolant channel chamber in a substantially horizontal direction, and a filter is arranged at the coolant inlet, and the filters are substantially parallel to each other. It has a plurality of flow paths, these flow paths change directions in the flow paths, and unevenness is provided on the wall surface of each flow path.
[0022]
According to a third aspect of the present invention, there is provided a fuel support fitting that supports a lower portion of a nuclear fuel assembly and has a coolant passage chamber that guides the coolant from a coolant inlet toward the nuclear fuel assembly. The coolant inlet is arranged so that the coolant flows into the coolant channel chamber in a substantially horizontal direction, and a filter is arranged at the coolant inlet, and the coolant passes through the filter. A filter function part and a filter frame that surrounds the filter function part and holds the filter function part, and the filter function part is disposed at a position shifted from the center of the filter frame. Features.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a fuel support fitting with a foreign matter filter according to the present invention will be described with reference to FIGS. Here, parts common or similar to those in the prior art, or parts common or similar to each other are denoted by common reference numerals, and redundant description is omitted.
[0024]
[First Embodiment]
A first embodiment of a fuel support fitting according to the present invention will be described with reference to FIGS. FIG. 1 is a perspective view of a state in which a filter 50 is attached in place of a core orifice to the coolant inlet 16 on the side surface 38 of the fuel support fitting 7 installed in the upper end opening of the control rod guide tube 6 (see FIG. 10). Indicates. FIG. 2 shows a longitudinal section in a state where the filter 50 in front of the coolant inlet of the fuel support fitting 7 is attached.
[0025]
The filter 50 includes a filter function unit 32 having a filter function and a filter frame 30 that holds the filter function unit 32 and forms an outer frame. The filter function part 32 and the filter frame 30 may be manufactured separately and then joined, or may be manufactured integrally from the beginning. Filter mounting recesses 31 are formed on the front surface of the four coolant inlets 16 formed on the side surface 38 of the fuel support fitting 7 so as to fit with the filter frame 30, and the filter 50 is placed in the filter mounting recess 31. It is fixed by tightening.
[0026]
FIG. 3 shows a first embodiment of a fuel support fitting with a filter according to the present invention. FIG. 3 (a) is a front view of a filter attached to the front surface of the coolant inlet of the fuel support fitting, and FIG. These are the BB arrow directional cross sections of the filter in (a). Filter attachment holes 33 are provided at the four corners of the filter frame 30.
[0027]
As shown in FIG. 3A, in this embodiment, the outer shape of the filter function unit 32 is substantially circular. As a modification, the outer shape of the filter function unit 32 may be a horizontally long ellipse (not shown). If the filter function part 32 has a vertically long shape, there is no inflow of steam from the filter function part side part 56, and the disturbance to the falling water in the coolant inlet 16 and the coolant channel chamber 17 is reduced. There is a risk that the steam having a low specific gravity will flow upward and the cooling water having a high specific gravity will separate and flow smoothly without mixing the steam. In this case, it is considered that the resistance of the flow of both the gas and the liquid decreases, and water easily falls down the filter function unit. Therefore, the filter function part 32 is made into a substantially circular or horizontally long ellipse, and the separation of water and steam can be prevented by allowing steam to flow from the side of the filter function part, and the water drop in the filter function part 32 is suppressed, The gas-liquid countercurrent limiting characteristic can be improved.
[0028]
As shown in FIG. 3B, the fluid flow path of the filter function unit 32 of the present embodiment is composed of a plurality of substantially parallel flow paths, and each flow path has an inverted V-shape. That is, each flow path of the filter function part 32 has a turning point at the center, the turning point is at the highest position, and the inlet and outlet parts are at the lower position. Considering the flow of coolant during normal operation of the reactor, it flows upwardly from the inlet to the center, and flows downward from the center to the coolant channel chamber 17 (see FIG. 2). Flowing.
[0029]
During the operation of the emergency core cooling system, spray water flows from the lower tie plate 11 through the coolant passage chamber 17 of the fuel support fitting 7 to the coolant inlet 16, and the filter function section 32 is moved as shown by an arrow 60 in FIG. Try to fall through. At this time, the flow 60 passing through the filter function part 32 of the spray water is suppressed by the influence of the flow of the steam indicated by the arrow 62 trying to rise up through the filter function part 32. In this embodiment, since the flow path of the filter function part 32 is an inverted V-shaped flow path, the effect of suppressing the flow 60 through the filter function part 32 of the spray water is particularly large, and the gas-liquid countercurrent restriction characteristic Is good. Therefore, the coolant is easily accumulated in the channel box 22 and the safety of the nuclear reactor is improved.
[0030]
[Second Embodiment]
FIG. 5 shows a filter according to a second embodiment of the fuel support fitting according to the present invention. In this embodiment, the filter function unit 32 is substantially square. As a modification, the filter function unit 32 may be a horizontally long rectangle (not shown). By adopting such a shape, it is possible to prevent separation of water and steam by allowing steam to flow in from the side portion 56 of the filter function unit 32, and to suppress the fall of water in the filter function unit 32. Can be improved.
[0031]
[Third Embodiment]
FIG. 6 shows a filter according to a third embodiment of the fuel support fitting according to the present invention. 6A is a vertical cross-sectional view of the filter 50, and FIG. 6B is an enlarged cross-sectional view of a portion B of FIG. 6A. In this embodiment, each flow path of the filter function unit 32 is composed of a plurality of flow paths substantially parallel to each other as in the embodiment shown in FIG. 3B. Unlike the form, each flow path has a V-shaped flow path shape. That is, the direction change point of the center part of each flow path of the filter function part 32 is at the lowest position, and the inlet and outlet parts are at higher positions. In this embodiment, irregularities 64 are provided on the surface of each flow path of the filter function unit 32.
[0032]
The unevenness 64 makes it difficult for the spray water flowing out from the lower tie plate through the filter 50 to flow, and makes it easier for the liquid to accumulate in the lower tie plate, thereby improving the gas-liquid countercurrent limiting characteristic. The unevenness 64 is preferably a wedge-shaped protrusion as shown in FIG.
[0033]
Also, providing such irregularities 64 in each flow path of the filter function unit 32 can be applied to the inverted V-shaped flow path shown in FIG. Further, the outer shape of the filter function unit 32 may be any of a rectangle, a circle, an ellipse, and the like.
[0034]
[Fourth Embodiment]
7 and 8 show a fourth embodiment of the fuel support fitting according to the present invention. FIG. 7 is a front view of the filter, and FIG. 8 is a longitudinal section of the filter attached to the fuel support fitting. In this embodiment, as shown in FIG. 7, the outer shape of the filter function unit 32 is circular, and is arranged at a position that is biased upward from the center of the filter frame 30. Thereby, the part which obstruct | occluded the flow path in the lower part of the filter 50 is made. For this reason, when the emergency core cooling system is in operation, the cooling water is likely to be accumulated inside the lower portion of the filter 50, whereby the way in which the cooling water is accumulated in the channel box 22 can be accelerated.
In FIG. 7, the outer shape of the filter function unit 32 is circular. However, it may be a horizontally long oval, a horizontally long rectangle, or a square.
[0035]
[Fifth Embodiment]
FIG. 9 shows a fifth embodiment of the fuel support fitting according to the present invention. This embodiment is a modification of the fourth embodiment, and the filter function unit 32 is arranged at a position offset upward from the center of the filter frame 30. In this embodiment, a protruding plate 66 that protrudes in the horizontal direction toward the inside of the coolant channel chamber 17 is further provided below the filter function part 32 of the filter 50. During the operation of the emergency core cooling system, the protruding plate 66 allows cooling water to flow into the lower portion of the protruding plate 66, making it easier to collect water in the lower tie plate 11 than in the case of the fourth embodiment. is there.
[0036]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the gas-liquid countercurrent flow restriction | limiting characteristic of the filter with which the coolant inlet_port | entrance front surface of a fuel support metal fitting is improved can improve the safety | security of a nuclear reactor.
[Brief description of the drawings]
FIG. 1 is a perspective view of a first embodiment of a fuel support fitting according to the present invention, showing a state in which one filter is removed.
FIG. 2 is a partial longitudinal sectional view of the fuel support fitting of FIG.
FIGS. 3A and 3B are enlarged views of the filter portion of FIGS. 1 and 2, wherein FIG. 3A is a front view of the filter portion, and FIG. 3B is a sectional view taken along line BB in FIG. FIG.
4 is a schematic longitudinal sectional view showing the flow of fluid in the vicinity of the filter portion of FIG. 3B when the emergency core cooling system is operated.
FIG. 5 is a front view of a filter portion of a second embodiment of a fuel support fitting according to the present invention.
6A and 6B are views showing a filter of a third embodiment of a fuel support fitting according to the present invention, in which FIG. 6A is a schematic longitudinal sectional view of the filter, and FIG. 6B is an enlarged view of a portion B in FIG. FIG.
FIG. 7 is a front view of a filter portion of a fourth embodiment of a fuel support fitting according to the present invention.
FIG. 8 is a partial longitudinal sectional view of a fourth embodiment of a fuel support fitting according to the present invention.
FIG. 9 is a partial longitudinal sectional view of a fifth embodiment of a fuel support fitting according to the present invention.
FIG. 10 is a partially cutaway sectional view showing a core structure and the like centering on a fuel support fitting of a conventional typical boiling water nuclear reactor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Shroud, 3 ... Core support plate, 4 ... Control rod drive mechanism housing, 5 ... Control rod drive mechanism, 6 ... Control rod guide tube, 7 ... Fuel support metal fitting, 8 ... Positioning pin, DESCRIPTION OF SYMBOLS 10 ... Fuel assembly, 11 ... Lower tie plate, 12 ... Upper tie plate, 13 ... Upper support plate, 14 ... Cross-shaped through-hole, 15 ... Fuel assembly support hole, 16 ... Coolant inlet, 17 ... Cooling Material flow path chamber, 18 ... inlet orifice, 22 ... channel box, 25 ... sheet surface, 30 ... filter frame, 31 ... filter mounting recess, 32 ... filter function part, 33 ... filter mounting hole, 34 ... filter plate mounting screw Hole, 38 ... side surface of fuel support fitting, 50 ... filter, 54 ... filter function part flow path, 56 ... filter function part side part, 60 ... flow of spray water, 62 ... flow of steam, 64 ... unevenness, 6 ... projections plate.

Claims (4)

In a fuel support fitting that supports a lower part of the nuclear fuel assembly and has a coolant channel chamber inside for guiding the coolant from the coolant inlet toward the nuclear fuel assembly.
A filter is disposed at the coolant inlet,
The filter has a plurality of flow paths that are substantially parallel to each other, and these flow paths are inclined upward at the inlet, and change the direction in the flow path and exit to the coolant flow path chamber. Now, tilt down,
A fuel support bracket characterized by In a fuel support fitting that supports a lower part of the nuclear fuel assembly and has a coolant channel chamber inside for guiding the coolant from the coolant inlet toward the nuclear fuel assembly.
The coolant inlet is disposed so that the coolant flows into the coolant flow path chamber in a substantially horizontal direction, and a filter is disposed at the coolant inlet.
The filter has a plurality of flow paths that are substantially parallel to each other, the flow paths change direction within the flow paths, and the wall surface of each flow path is provided with irregularities,
A fuel support bracket characterized by In a fuel support fitting that supports a lower part of the nuclear fuel assembly and has a coolant channel chamber inside for guiding the coolant from the coolant inlet toward the nuclear fuel assembly.
The coolant inlet is disposed so that the coolant flows into the coolant flow path chamber in a substantially horizontal direction, and a filter is disposed at the coolant inlet.
The filter has a filter function part through which a coolant passes, and a filter frame that surrounds the filter function part and holds the filter function part, and the filter function part is displaced above the center of the filter frame. Being placed in the
A fuel support bracket characterized by 4. The fuel support fitting according to claim 3, wherein a protruding plate is provided in the coolant channel chamber below the filter function portion.

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