JPH0894783A - Lower nozzle of PWR fuel assembly - Google Patents

Abstract

(57) [Abstract] [Purpose] In a lower nozzle of a PWR fuel assembly, foreign matter flowing into the upper portion of the fuel from between the nozzles is captured. [Structure] In the vicinity of each side portion 3a of the lower surface of the adapter plate 3, a concave groove 6 having a water flow hole 2 is formed at least between each leg portion 5 of the nozzle and in parallel with the side portion 3a. It is characterized by the fact that it is made.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a pressurized water reactor (PW).
R) relating to the lower nozzle of the fuel assembly, and more specifically, by trapping foreign matter in the cooling water flowing out through the nozzle leg portions to the outside, It relates to a lower nozzle that prevents intrusion.

[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 N'is, as shown in FIG.
A rectangular adapter plate 3 having a plurality of thimble screw holes 1 for fixing the thimble tube serving as the skeleton of the fuel assembly and a large number of water flow holes 2, and the adapter plate 3
4 to suspend the adapter plate 3 from the corner of the lower core core plate 4 by providing a predetermined gap with the lower core plate 4.
It is constituted by the leg portion 5 of the book.

On the other hand, in the pressurized water reactor, the cooling water reaches the lower nozzle N of the fuel assembly through the water flow holes H provided in the lower core plate 4 as shown in FIG. The cooling water is the lower nozzle N as shown in FIG.
It flows into the fuel assembly through the large and small water flow holes 2 formed in the fuel cell, passes through between the support grid and the fuel rod, and reaches the upper nozzle. Then, the cooling water that has passed through the water flow holes of the upper nozzle reaches the lower core plate 4 and circulates through the steam generator and the like.

By the way, foreign matter such as metal pieces mixed in the cooling water system is often caught by the support grid after passing through the lower nozzle. The trapped foreign matter violently vibrates due to the flow of the cooling water and may damage the fuel rods in the vicinity. Therefore, conventionally, in order to prevent the foreign matter from flowing into the fuel body, improvements such as reducing the diameter of the water flow hole of the adapter plate and stacking a foreign matter capturing filter on the adapter plate have been taken. By trapping with the lower nozzle adapter plate, damage to the fuel assembly due to the foreign matter was prevented.

[0005]

However, all of the above-mentioned conventional countermeasures against foreign matter are effective against foreign matter that attempts to enter through the lower nozzle water flow hole, but adjacent fuel assemblies as shown in FIG. 6 are used. It is helpless against the foreign matter Y that enters through the gap between them.

[0006] The gap of the fuel assembly is about 1 to 2 mm, and if the maximum cross section is a foreign matter having a size smaller than this, the gap can serve as an invasion route of the foreign matter. Further, it is not preferable to provide a protrusion or the like on the outer periphery of the lower nozzle to prevent this, because it becomes an obstacle when the fuel is taken in and out of the core.

Therefore, in order to examine in detail the state of the foreign matter entering through the gap, as shown in FIG. 7, a test sample T simulating the aggregate gap is loaded into a transparent test tank, and running water mixed with the foreign matter is loaded. The test was conducted. In this test, as a result of observing the fuel assembly lower nozzle part using a high-speed video, a few percent of the foreign matter that arrived at the lower nozzle part could enter the effective fuel part through the gap with the adjacent fuel assembly. Do you get it. In particular, many linear foreign matters with a diameter of about 1 mm entered.

According to the observation using the high speed video, it was found that the linear foreign matter having a posture parallel to the assembly gap, particularly on the lower surface of the adapter plate, easily flows into the gap after the collision with the lower nozzle. did.

In order to deal with the above situation, the present invention proposes a measure for trapping the foreign matter, which is trying to enter through the gap between the fuel assemblies, on the upstream side of the lower nozzle adapter plate.

[0010]

That is, the feature of the lower nozzle of the present invention is that the fuel is provided with a rectangular adapter plate having a large number of water flow holes and a plurality of legs hanging from the corners of the adapter plate. In the lower nozzle of the assembly, in the vicinity of each side portion of the lower surface of the adapter plate, a concave groove having a water flow hole is formed at least between the respective leg portions substantially parallel to the side portion. It is in.

In the lower nozzle of the present invention,
It is also preferable that the groove of each of the side portions is continuously formed in an annular shape inside the leg portion.

[0012]

According to the running water test, it is known that the linear foreign matter, which has become parallel to the assembly gap on the lower surface of the adapter plate after the collision with the lower nozzle, easily flows into the assembly gap. The groove can semi-permanently trap the foreign matter in such a posture on the lower surface of the adapter plate and prevent the foreign matter from entering the effective fuel portion through the fuel assembly gap. Is possible.

[0013]

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

FIG. 1 is a perspective view showing the lower nozzle of the first embodiment of the present invention from below, and the lower nozzle N of this embodiment is shown.
Is a square stainless steel adapter plate 3 having a plurality of thimble screw holes 1 for fixing the thimble tube and a large number of water flow holes 2, as shown in FIG.
It has a basic structure including four legs 5 that hang down from the corners of the adapter plate 3 and support the adapter plate 3 with a predetermined gap from the lower core plate.

Further, in the lower nozzle of the embodiment of the present invention, as shown in the drawing, there are four water holes 2 each having a width and a depth of about several mm, which are provided in the lower surface of the adapter plate 3 near each side portion 3a. The concave grooves 6 are formed independently between the respective leg portions and in parallel with the respective side portions 3a in the vicinity thereof.

2 is a perspective view showing the lower nozzle of the second embodiment of the present invention from below, the groove 6 is formed in an annular shape so as to be continuous inside the leg portion 5 as shown. You can also do it.

In each of these embodiments, the concave groove 6 is
By cutting the lower surface of the adapter plate 3 of a normal lower nozzle at the position where the water flow hole 2 is present, the water flow hole 2
It is possible to extremely easily manufacture the concave groove 6 provided with.

Further, the width, depth, and cross-sectional shape of the concave groove 6 can be selected optimally depending on the flowing water conditions to which the lower nozzle is exposed. For example, as the cross-sectional shape, FIGS. As shown in, a square, a rhombus, or a right-angled triangle in which a right-angled portion is arranged on the outer peripheral side of the lower surface of the adapter plate is given as an example.

There is a possibility that the lower nozzle strength will not meet the design requirements by forming the groove 6 large, but in this case, the material of the lower nozzle is high strength such as Inconel. Change to steel.

In the lower nozzle of each of the above-described embodiments of the present invention, however, the concave groove 6 absorbs the linear foreign matter which is parallel to the gap of the fuel assembly on the lower surface of the adapter plate 3 and is about to flow into this gap. Before the inflow, by the action of the water flow hole 2 of the concave groove 6, it can be sucked as it is and semi-permanently captured on the lower surface of the adapter plate 3,
It is possible to prevent the foreign matter from entering the effective fuel portion through the gap and prevent the fuel from being damaged.

[0021]

As described above, in the lower nozzle of the fuel assembly of the present invention, a concave groove having a water flow hole is provided near each side of the lower surface of the adapter plate, at least between the legs of the nozzle. Are formed substantially parallel to the above-mentioned side portions, and linear foreign matter that is about to flow in parallel with the gap of the fuel assembly on the lower surface of the adapter plate is acted on by the action of the above-mentioned water flow holes. The concave groove can be sucked as it is and can be semi-permanently captured on the lower surface of the adapter plate, which prevents the foreign matter from entering the effective fuel portion through the gap and prevents the fuel from being damaged. Is played.

[Brief description of drawings]

FIG. 1 is a perspective view showing a lower nozzle of a first embodiment of the present invention from below.

FIG. 2 is a perspective view showing a lower nozzle of a second embodiment of the present invention from below.

FIG. 3 is an end view showing an example of a groove.

FIG. 4 is an end view showing another example of a groove.

FIG. 5 is an end view showing still another example of the groove.

FIG. 6 is a front view showing a path of entry of foreign matter into the fuel assembly gap.

FIG. 7 is a front view showing a test piece simulating a fuel assembly gap.

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 conventional lower nozzle.

[Explanation of symbols]

 1 thimble screw hole 2 water flow hole 3 adapter plate 3a side 4 lower core plate 5 leg 6 concave groove

Claims (2)

[Claims] 1. A lower nozzle of a fuel assembly comprising a rectangular adapter plate having a large number of water holes and a plurality of legs hanging from a corner portion of the adapter plate, wherein each side of the lower surface of the adapter plate. A lower nozzle of a PWR fuel assembly, characterized in that a concave groove having a water flow hole is formed in the vicinity of the portion, at least between the respective leg portions and formed substantially parallel to the side portions. 2. The lower nozzle of the PWR fuel assembly according to claim 1, wherein the concave groove of each side portion is continuously formed inside the leg to form an annular shape.