JPH08105988A - Nuclear fuel assembly - Google Patents

Abstract

PURPOSE: To arrest a foreign filament type material such as a wire with a lower nozzle by inclining the axial angles of flow holes relative to the flow passage direction of a support lattice, and forming the flow holes of adjacent flow passages in directions opposite to each other. CONSTITUTION: A fuel assembly has the lowest lattice 3' in contact with the upper surface of the adapter plate 8 of a lower nozzle 6 having flow holes 7, and the outlets of the holes 7 are subdivided with a lattice plate 9. Also, the holes 7 are formed, so that the axial angles 7a thereof are inclined approximately at 30 degrees relative to the direction 10a of flow passages 10 formed out of the plate 9. In addition, the inclination of the holes 7 of adjacent rows is aligned in directions opposite to each other. According to this construction, when a long-sized rod type foreign substance T tries to pass the holes 7, a route formed out of the holes 7 and the lattice 3' is bent like a U-shape. Thus, the foreign substance T is hindered and arrested with the bent route.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a pressurized water reactor (PW).
The present invention relates to a fuel assembly used in R), and more specifically, to a nuclear fuel assembly that captures foreign matter in cooling water flowing out through a water flow hole of a lower nozzle.

[0002]

2. Description of the Related Art A fuel assembly used in a pressurized water reactor includes a fuel rod bundle portion in which a large number of fuel rods are arranged in parallel, and thimble tubes and the like are mixed and supported by a plurality of support grids. It is composed of an upper nozzle and a lower nozzle for fixing. The lower nozzle 6'is, as shown in FIG.
A rectangular adapter plate 8'having a plurality of thimble screw holes S for fixing the thimble tube serving as the skeleton of the fuel assembly and a large number of water flow holes 7 ', and hanging from a corner portion of the adapter plate 8', It is composed of four legs 12 'for supporting the adapter plate 8', with a predetermined space provided between the core plate B and the core plate B.

On the other hand, in the above pressurized water reactor, the cooling water reaches the lower nozzle 6'of the fuel assembly through the core plate water flow hole H provided in the lower core plate B as shown in FIG. The cooling water which has reached the ′ ′ flows into the fuel assembly through the large number of water flow holes 7 ′ formed in the lower nozzle 6 ′ as shown in FIG. Reach Then, the cooling water that has passed through the water flow holes of the upper nozzle reaches the lower core plate B through the steam generator or the like and is circulated.

By the way, foreign matter such as metal pieces mixed in the cooling water system is often caught between the fuel rods of the fuel assembly after passing through the water flow hole of the lower nozzle.
The foreign matter thus caught may violently vibrate by the flow of the cooling water and damage the fuel rod.

[0005] As a countermeasure against the foreign matter, improvement of the foreign matter trapping ability of the lower nozzle or foreign matter trapping ability of the lowermost support grid has been carried out from the viewpoint of preventing foreign matter from entering the fuel assembly. Have been done.

To improve the foreign matter trapping ability of the lower nozzle, there is a reduction in the diameter of the water hole in the adapter plate, and a foreign matter filter is attached. However, since these designs increase the pressure loss of the assembly, there is a limit to reducing the size of the water flow pores and the mesh size of the filter. Therefore, it is difficult to prevent foreign matter having a small cross section from entering.

On the other hand, the improvement of the foreign substance trapping ability of the lowermost support grid includes the lowering of the position and the addition of a foreign substance trapping dimple. The lowering of the lowermost support grid is to divide the lower nozzle water flow holes by the straps of the support grid to prevent foreign substances having a smaller cross section from entering the aggregate.

[0008]

However, as a result of observing the lower nozzle portion of the fuel assembly by conducting a running water test in which a foreign matter is mixed, all of the measures against the foreign matter described above can be applied to a foreign matter having a minimum cross section diameter of 4 mm or more. Although effective against this, it has been found that it is almost useless for linear foreign matter having a diameter of 2 mm or less such as a wire having a small cross section.

Observations using high-speed video show that these linear debris tend to align their longitudinal direction with the coolant flow direction after impacting the lower nozzle. Therefore, as shown in FIG. 7, the linear foreign matter T whose tip is inserted in the water flow hole of the lower nozzle adapter plate changes its posture so that its longitudinal direction coincides with the axial direction of the fuel assembly and enters the assembly. To go. It must be said that the probability that the foreign matter T having such a posture can be trapped by the lower nozzle 6'or the combination of the lower nozzle 6'and the lowermost support grid 3'is extremely low.

In view of the above situation, it is an object of the present invention to catch a linear foreign matter such as the wire at the lower nozzle by finding a new structure in the water flow hole of the lower nozzle. .

[0011]

That is, the feature of the nuclear fuel assembly of the present invention which meets the above-mentioned object is that a support grid is brought close to the upper surface of the adapter plate of the lower nozzle, and the above-mentioned adapter is provided by the grid plate of the support grid. In a fuel assembly formed by subdividing the outlets of the water holes of the plate, the axial angle of the water holes is inclined with respect to the flow path direction of the support grid, and the inclinations of the water holes of adjacent rows are opposite to each other. It's where I did it.

Further, in the above fuel assembly of the present invention,
It is also possible to dispose a front plate having a large number of water flow holes below the adapter plate and make the axial angles of these water flow holes in the opposite direction to the water flow holes of the adapter plate located above.

Regarding the axial angles of the water flow holes of the adapter plate and the front plate, the longer the foreign matter to be captured, the smaller the inclination, but in reality, the axial angle is about 20 to 20 with respect to the flow path formed substantially vertically. It is preferable to incline in the range of 40 degrees.

[0014]

In the above fuel assembly of the present invention, since the path formed by the water flow holes and the support grid is bent in a dogleg shape, the bent path clogs the linear foreign matter as described above, Can be captured.

By reversing the inclination of the water flow holes in the adjacent rows, the coolant flow rising from the lower nozzle does not generate a lateral flow component that is biased in one direction, and a uniform cooling action of the core is maintained. It is possible to

Further, by disposing the front plate as described above, the dogleg-shaped path has two steps,
It is possible to further improve the probability of capturing foreign matter.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a partially enlarged sectional view showing a lower nozzle / adapter plate and a supporting grid of a fuel assembly of an embodiment of the present invention, FIG. 2 is a partially enlarged perspective view of an adapter plate of the same embodiment, and FIG. 3 is the same embodiment. FIG. 4 is a schematic diagram of the fuel assembly, and FIG. 4 is an explanatory view showing the lower nozzle and the lowermost support grid of the fuel assembly.

As shown in FIG. 3, the fuel assembly of the above-described embodiment of the present invention has a large number of fuel rods 1 arranged in parallel and has thimble tubes 2 and the like mixed therein, and is supported by a plurality of support grids 3. The fuel rod bundle section 4 is provided with an upper nozzle 5 and a lower nozzle 6 for fixing the fuel rod bundle section 4. Then, as also shown in FIG. 4, in the above fuel assembly, the lowermost support grid 3 ′ is brought into contact with the upper surface of the adapter plate 8 of the lower nozzle 6 having a large number of water flow holes 7.
The outlet of the water flow hole 7 is subdivided into a cross shape by the lattice plate 9 of the support lattice 3 '.

As the support grid to be brought into contact with the upper surface of the adapter plate 8, instead of lowering the lowermost support grid 3 ', a support grid (not shown) dedicated to foreign matter countermeasures in which plate materials are combined in a grid shape. The above adapter plate 8
It is also possible to add so as to contact the upper surface.

On the other hand, in the embodiment of the present invention, in the fuel assembly as described above, as shown in FIG. 1, all the axial angles 7a of the water flow holes 7 are in the direction 10a of the flow passage 10 formed by the lattice plate 9. The water flow holes 7 are formed so as to be inclined at an angle of about 30 degrees, and as shown in FIG. 2, the water flow holes 7 in adjacent rows are inclined in opposite directions.

The axial angle of the water flow holes 7 varies depending on the length of the foreign matter to be captured and the thickness of the adapter plate 8, but the flow path 10 is formed substantially vertically.
It is preferable to incline within a range of approximately 20 to 40 degrees with respect to the flow path direction 10a in order to capture linear foreign matter such as a wire.

On the other hand, what is shown in FIGS. 5 and 6 is a fuel assembly according to the second embodiment of the present invention.
In addition to the configuration of the embodiment, a front plate 11 is arranged below the adapter plate 8 so as to be fixed to the leg portion 12 of the lower nozzle 6, and the axial angle of a large number of water flow holes 13 formed in the entire front plate 11 can be adjusted. , The rows of the water holes 7 of the adapter plate 8 located above are inclined in the opposite direction. That is, also in the front plate 11, the inclinations of the water flow holes 13 in the adjacent rows are opposite to each other. The water flow hole 13 of the front plate 11
The inclination angle is preferably in the same range as the inclination angle of the water flow hole 7 of the adapter plate 8 described above.

In this embodiment, as shown in FIG. 5, the water flow hole 13 of the front plate 11 is arranged at a predetermined position so as not to overlap directly under the upper adapter plate water flow hole 7. There is.

Therefore, in the fuel assembly of the embodiment of the present invention having the above structure, even if the long rod-shaped foreign matter T tries to pass through the water flow hole 7 of the lower nozzle 6 as shown in FIG. Since the path formed by the hole 7 and the support grid 3 is bent in a dogleg shape, it is possible to catch the foreign material T by clogging the bent path as shown in the figure.

Since the water flow holes 7 and 13 in the adjacent rows are made to have opposite inclinations, the coolant flow rising from the lower nozzle 6 does not generate a lateral flow component which is biased in one direction, and the core is uniformly cooled. It is possible to maintain the action.

Further, in the second embodiment of the present invention, by disposing the front plate 11 as described above, the above-mentioned dogleg-shaped path becomes two steps, and the probability of capturing foreign matter can be further improved. It is possible.

[0028]

As described above, in the nuclear fuel assembly of the present invention, the axial angles of the water flow holes of the lower nozzle / adapter plate are inclined with respect to the flow direction of the support grid, and the adjacent rows are arranged in a row. The inclination of the water flow holes are opposite to each other, even when a linear foreign matter such as a wire is going to pass through the water flow hole, the foreign matter can be clogged and captured in this path, Moreover, by reversing the inclination of the water flow holes in the adjacent rows, it is possible to maintain a uniform cooling action of the core without generating a unidirectional lateral flow component in the coolant flow rising from the lower nozzle. It has a great effect.

[Brief description of drawings]

FIG. 1 is a partially enlarged sectional view showing a lower nozzle / adapter plate and a support grid of a fuel assembly according to an embodiment of the present invention.

FIG. 2 is a partially enlarged perspective view of an adapter plate of the same embodiment.

FIG. 3 is a schematic view of the fuel assembly of the embodiment.

FIG. 4 is an explanatory view showing a lower nozzle and a lowermost support grid of the fuel assembly.

FIG. 5 is a partially enlarged cross-sectional view showing an adapter plate, a front plate, and a support grid according to a second embodiment of the present invention.

FIG. 6 is a perspective view showing a support grid and a front plate of the same.

FIG. 7 is a partially enlarged sectional view showing a lower nozzle / adapter plate and a support grid of a conventional fuel assembly.

FIG. 8 is an explanatory diagram showing a positional relationship between a lower core plate water flow hole and a lower nozzle.

FIG. 9 is a perspective view showing a lower nozzle of a conventional example.

[Explanation of symbols]

 1 Fuel Rod 2 Thimble Tube 3 Support Lattice 4 Fuel Rod Bundle 5 Upper Nozzle 6 Lower Nozzle 7 Flow Hole 7a Flow Angle Axial Angle 8 Adapter Plate 9 Lattice Plate 10 Support Grid Flow Path 10a Flow Direction 11 Front Plate 12 Lower nozzle leg 13 Front plate water hole

Claims (3)

[Claims] 1. A nuclear fuel assembly in which a support grid is brought close to an upper surface of an adapter plate of a lower nozzle having a large number of water flow holes, and the flow water hole outlet is subdivided by a grid plate of the support grid. The nuclear fuel assembly is characterized in that the axis angle of the above is tilted with respect to the flow path direction of the support grid, and the tilts of the water flow holes in adjacent rows are opposite to each other. 2. A front plate having a large number of water flow holes is arranged below the adapter plate, and the axial angles of the water flow holes are inclined in the opposite direction to the water flow holes of the adapter plate located above. The nuclear fuel assembly according to claim 1. 3. The axial angle of the water flow holes of the adapter plate and the front plate is inclined within a range of about 20 to 40 degrees with respect to the flow path of the support grid formed substantially vertically. Nuclear fuel assembly.