JPH065314B2 - Nozzle of nuclear fuel assembly - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nozzle of a nuclear fuel assembly used in a nuclear reactor such as a pressurized water type light water reactor, and in particular, it can remove foreign matter in cooling water. Regarding

"Prior Art" FIG. 3 is a front view showing a general nuclear fuel assembly.

In the figure, reference numerals 1 and 2 are an upper nozzle and a lower nozzle which are vertically opposed to each other, and a plurality of control rod guide tubes 3 ... Are suspended and fixed between the upper nozzle 1 and the lower nozzle 2. ing. A plurality of support grids 4 are attached to the middle of the guide tubes 3 ..., and a large number of fuel rods 5 ... ing.

A large number of such nuclear fuel assemblies are vertically inserted into the core of a nuclear reactor vessel, and are supported by being sandwiched between the upper core plate and the lower core plate. And when the reactor is in operation,
Cooling water is circulated vigorously from the lower part to the upper part in the core, and this cooling water flows in from the nozzle hole formed in the lower nozzle 2 and passes between the fuel rods 5 ... It is adapted to be heated while flowing out from the nozzle hole formed in the upper nozzle 1.

By the way, in such a fuel assembly, it has been conventionally pointed out that the lower end portions of the fuel rods 5 may be damaged. That is, when foreign matter such as dust or metal scraps is mixed into the cooling water for some reason, these foreign matters pass through the nozzle holes of the lower nozzle 2 together with the cooling water, and the lower end of the fuel rods 5 where the flow of the cooling water is severely disturbed. It cannot be said that there is a possibility that the lower end of the cladding tube may be damaged by colliding with the cladding tube near the portion.

Therefore, the applicants of the present invention have proposed in Japanese Patent Application No. 61-220678 a lower nozzle 10 as shown in FIGS. 4 and 5, which can prevent such cladding tube damage.

This nozzle 10 is formed by integrally forming cross-shaped or one-letter-shaped grids 11A and 12A in the upper end openings of the nozzle holes 11 and 12 so as to close these openings. It is configured to capture foreign matter in the cooling water.

[Problems to be Solved by the Invention] By the way, in order to capture even a relatively small foreign substance in the nozzle 10 described above, it is necessary to make the grid fine and to reduce the area partitioned by the grid. However, in this case, there is a problem that the flow passage cross-sectional area is inevitably reduced, the flow resistance increases, and the circulation of the cooling water is hindered.

Further, in order to integrally form the lattice having such a shape with the nozzle, there is a drawback that a complicated processing work is required and the cost is high.

"Means for Solving Problems" The present invention has been made to solve the above problems,
A cavity is formed in the central portion in the thickness direction of the nozzle flat plate portion, and a plurality of nozzle upper surface holes communicating from the upper surface of the flat plate portion to the cavity are formed, and a plurality of nozzle bottoms communicating from the lower surface of the flat plate portion to the cavity are formed. It is characterized in that the face hole is formed at a position which does not coincide with the upper face hole of the nozzle in the vertical direction.

[Operation] In the nozzle of the present invention, the cooling water flowing from the nozzle lower surface hole can spread and flow in all directions in the cavity, so that the flow passage cross-sectional area in the cavity is large, and accordingly, the liquid flow in the cavity is large. The resistance is small. On the other hand, the foreign matter in the cooling water is caught by the upper and lower wall surfaces in the thin hollow portion and is captured.

[Examples] Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a lower nozzle of one embodiment, and FIG. 2 is a plan view.

The lower nozzle 20 is composed of a nozzle body 21 in which legs 21B are provided at four corners of a lower surface of a square plate portion 21A, and a square upper plate 22 welded and fixed to an upper surface of the nozzle body 21. The upper plate 22 and the plate portion 21A form a nozzle flat plate portion 23.

On the upper surface of the plate portion 21A of the nozzle main body 21, a concave portion 24 having a constant depth T is formed over the entire surface except the peripheral portion thereof, thereby forming a cavity 25 between the upper plate 22 and the concave portion 24. There is. The thickness T of the cavity 25 corresponds to the size of the foreign matter to be captured by the nozzle 20, and is preferably determined in consideration of the liquid flow resistance. Further, on the bottom surface of the recess 24 of the plate portion 21A, a large number of small protrusions 26 are formed over the entire surface thereof, and a large number of circular nozzle lower surface holes 27 (diameter D1) are formed at regular intervals. Has been done.

On the other hand, on the lower surface of the upper plate 22, a large number of projections 28 similar to the above are formed on the entire surface forming the upper wall surface of the cavity 25, and a large number of circular nozzle upper surface holes 29 ... (Diameter D
2) is formed at a position that does not vertically match the nozzle lower surface holes 27.

Here, the diameter D1 of the nozzle lower surface hole 27 is set to a value larger than the thickness T of the cavity 25 so that foreign matter can easily pass therethrough. Further, the direct connection D2 of the nozzle upper surface hole 29 is set larger than the diameter D1 in order to reduce the flow resistance. And these nozzle holes 27,
It is desirable that 29 be formed with a density and a diameter as high as possible within a range where sufficient strength can be obtained for the plate portion 21A and the upper plate 22.

According to the lower nozzle 20 having such a configuration, even when foreign matter is mixed in the cooling water in the core, when the cooling water flows to the nozzle lower surface holes 27, the cavities 25, and the nozzle upper surface holes 29. Since the foreign matter is caught and caught on the upper and lower wall surfaces of the cavity 25 having the projections 26, 29, the damage of the fuel rod due to the collision of the foreign matter can be prevented.

Further, the cooling water flowing from the individual nozzle lower surface holes 27 is
Since the flow spreads in all directions in the cavity 25, the flow passage cross-sectional area in the cavity 25 is determined by the nozzle holes 27, ..., 29.
It is much larger than the opening area of. Therefore, even when the thickness of the cavity 25 is reduced to capture even a small foreign matter, the influence on the flow resistance is small.

Further, when manufacturing the lower nozzle 20, there is no complicated process such as forming a lattice in the opening of the nozzle hole, the machining is easy, and the manufacturing cost is low. Further, unlike the above-mentioned grid, there is no portion that may be damaged by collision of foreign matter, and reliability in strength is high.

It should be noted that in the above-described embodiment, a large number of protrusions 26, ..., 28 are formed on the upper and lower wall surfaces of the cavity 25, but these are auxiliary and are not always necessary.

Further, the present invention can be applied not only to the lower nozzle of the nuclear fuel assembly but also to the upper nozzle.

"Effects of the Invention" As described above, according to the nozzle of the nuclear fuel assembly of the present invention, the following excellent effects are obtained.

Even if foreign matter is mixed in the cooling water in the core, when the cooling water flows into the nozzle lower surface hole, the cavity, and the nozzle upper surface hole, this foreign matter is caught by the upper and lower wall surfaces of the cavity and is captured. It is possible to prevent damage to the fuel rods due to a collision.

Since the cooling water that has flowed in from the individual nozzle lower surface holes can spread and flow in all directions in the cavity, the flow passage cross-sectional area in this cavity is significantly larger than the opening area of the nozzle. Therefore, even if the thickness of the cavity is reduced to capture even small foreign matter,
Has little effect on flow resistance.

Since it is only necessary to form holes and cavities in the flat plate portion of the nozzle, machining is easier and cost is lower than that of forming a lattice in the opening portion of the nozzle hole.

[Brief description of drawings]

FIG. 1 is a sectional view of a lower nozzle of a nuclear fuel assembly according to an embodiment of the present invention, and FIG. 2 is a plan view of the nozzle. FIG. 3 is a front view of a conventional nuclear fuel assembly, FIG. 4 is a partial plan view of a lower nozzle previously filed by the applicant, and FIG.
The figure is a cross-sectional view of the same nozzle taken along the line V-V. 20 ... Lower nozzle, 23 ... Nozzle flat plate portion, 25 ... Cavity,
26, 28 ... Protrusions, 27 ... Nozzle lower surface holes.

Claims (1)

[Claims] 1. A cavity is formed in a central portion of a flat plate portion of a nozzle in the thickness direction, a plurality of nozzle upper surface holes communicating from the upper surface of the flat plate portion to the cavity are formed, and a lower surface of the flat plate portion is connected to the cavity. The nozzle of the nuclear fuel assembly is characterized in that a plurality of nozzle lower surface holes are formed at positions which do not vertically match the nozzle upper surface holes.