JP2001033575A - Low pressure loss type upper nozzle of pwr fuel assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fulfill design requirement strength of upper nozzle and realize lowering pressure loss by reducing water flow resistance of water flow hole inlet. SOLUTION: The shape of a water flow hole 5 in the upper nozzle of a PWR fuel assembly is made basically a square, R-shape of four corners is made small, the opening ratio of the water flow hole 5 is made large within the strength requirement range, and the resistance at the inlet of the water flow hole 5 of an upper nozzle plate 3 is made small by forming the beam 4 cross section shape of the water flow hole 5 of the upper nozzle plate 3 in a stream line or a resembling tapered shape. Besides, this upper nozzle is useful for the upper nozzle of 17×17 PWR fuel assembly upper nozzle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly member for adjusting a pressure loss of a fuel assembly from the viewpoint of a mixed fuel system in a PWR reactor core, and in particular, a low pressure loss type upper nozzle of a PWR fuel assembly. It is about.

[0002]

2. Description of the Related Art A fuel assembly is constituted by arranging a number of fuel rods in parallel, mixing a thimble tube or the like, and supporting a fuel bundle supported by a plurality of support grids with an upper nozzle and a lower nozzle. However, the main design requirements of the upper nozzle attached to the PWR fuel assembly are not only strength as a structure, but also compatibility with the reactor core structure, compatibility with the fuel assembly handling tool, and control. It is mentioned that the rod and the thimble plug are fitted together, and that the upper nozzle can prevent the fuel rod from projecting upward in the axial direction when the fuel assembly is damaged.

The upper nozzles of fuel assemblies of different designs are designed in accordance with the above-mentioned design requirements, and therefore have substantially the same major dimensions. The main differences are the shape and shape of the water flow holes in the upper nozzle. There are chamfers in consideration of patterns and fitting.

[0004] Naturally, similar design requirements are required for the lower nozzle, but unlike the lower nozzle, the upper nozzle is located at the most downstream of the flowing water flowing through the fuel assembly. No blocking resistance is required. In addition, there is no particular requirement for pressure drop adjustment for preventing lateral flow DNB characteristic failure, which is a concern from the viewpoint of fuel coexistence as seen in support grid design requirements. Therefore, except for the upper nozzle having a special function, the upper nozzle of each fuel assembly follows the design of the conventional upper nozzle, and it can be said that the upper nozzle is a member that is hardly subject to design change.

[0005]

However, recently, adjustment of pressure loss has been pursued not only for the lower nozzle but also for the upper nozzle, and a low pressure loss type upper nozzle has been studied.

The present invention responds to the trend of the era by improving the shape of the inlet portion of the upper nozzle plate and the flow hole pattern in the upper nozzle of the conventional design, thereby satisfying the design required strength of the upper nozzle and improving the flow of the upper nozzle. It is an object of the present invention to reduce the pressure loss by reducing the flow resistance at the hole entrance.

[0007]

That is, the configuration of the upper nozzle of the PWR fuel assembly according to the present invention that meets the above-mentioned object is based on the fact that the shape of the water holes of the upper nozzle is based on a square shape and the R shape at the four corners is reduced. To increase the opening ratio of the flowing water holes within the required strength range, and make the beam cross-sectional shape between the flowing water holes a streamlined shape or a tapered shape similar to it to reduce the resistance to flowing water at the inlet hole of the upper nozzle plate. It is in the point where it tightened. The upper nozzle of the present invention is 17 × 17.
It is very useful as an upper nozzle of a type PWR fuel assembly.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the upper nozzle of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an example of an upper nozzle of a fuel assembly according to the present invention. In the figure, 1 denotes an upper nozzle body, 2 denotes a leaf spring, 3 denotes an adapter plate, and a beam 4 is attached to the adapter plate 3. And water flow holes 5 and the like are provided.

FIG. 2 shows a flow hole pattern conventionally designed on the adapter plate 3 in the upper nozzle as described above. Conventionally, as shown in the same pattern, a flowing water hole 5 partitioned by a beam 4 is formed in a large and small elliptical shape on the entire surface, and a fixing hole 6 for a control rod thimble tube is provided in a mixed manner. Have been. The upper nozzle designed with this flow hole pattern is designed to prevent the axial movement of the fuel rod in a fuel assembly accident or the like, and also satisfies the design requirements in terms of strength and pressure loss. However, in this conventional flow hole pattern, as described above, since it has not been the subject of design change, reduction of pressure loss is hardly considered.

On the other hand, FIG. 3 shows a flow hole pattern of the upper nozzle to which the present invention is applied to achieve a low pressure loss. As shown in FIG. The shape of each water hole 5 is changed without changing the width of the beam 4 between the five, and the pressure loss is reduced as a large and small water hole shape in which the R shape at the four corners is reduced based on a square. That is, the opening ratio of the flowing water hole is increased by about 5% within the range in which the strength requirement is satisfied as in the related art. Further, in addition to the above-mentioned shape of the water hole, the present invention also changes the shape of the cross section of the beam 4 between the water holes 5 as shown in FIG.

FIG. 4A shows the cross-sectional shape of the beam of the conventional upper nozzle, while FIG. 4B shows the cross-sectional shape of the beam according to the present invention. Drilling and chamfering 7 of the flowing water hole are carried out, but it is preferable that the upper nozzle of the present invention is manufactured mainly by a precision casting method. This is because, as can be seen from the same cross-sectional shape, it is easy to manufacture a streamline shape within a range satisfying the strength requirement and a cross-section having a taper similar thereto. Of course, the upper nozzle of the present invention may be manufactured by machining. What is necessary is just to select what suits it according to the shape of the beam between flowing water holes.

The thus-obtained flowing water hole 5 of FIG.
And a low pressure loss type upper nozzle having a beam 4 having a cross-sectional shape as shown in FIG. 4 (b), the strength of which was analyzed by the finite element method as a strength evaluation. Although the maximum stress is slightly larger than that of, it has been confirmed that the required strength of the upper nozzle is satisfied.

Next, when a flow test was carried out using the low pressure loss type upper nozzle according to the present invention, the pressure loss at the upper part of the fuel assembly was reduced by about 20% as compared with the prior art.
From this, it can be seen that the upper nozzle according to the present invention can realize a reduction in pressure loss for flowing water flowing through the fuel assembly.

[0015]

As described above, according to the present invention, in the upper nozzle of the PWR fuel assembly, the shape of the water flow hole is based on a square, and the R shape of the four corners is reduced so that the opening ratio of the water flow hole is within the required strength range. At the same time, the cross section of the beam between the flow holes is made to have a streamline shape or a tapered shape similar thereto, thereby reducing the resistance of the upper nozzle plate to the flow hole inlet portion against flowing water. The pressure loss can be reduced even in the upper nozzle which was not provided, and therefore the flow resistance of the entire fuel assembly can be reduced not only in the lower nozzle but also in the upper nozzle, and the PW in the future can be reduced.
From the viewpoint of the fuel mixture system in the R reactor core, it is expected to be extremely effective in adjusting the pressure loss of the fuel assembly.

[Brief description of the drawings]

FIG. 1 is a partially cutaway schematic view of an upper nozzle of a fuel assembly.

FIG. 2 is a view showing a flow hole pattern of a conventional upper nozzle.

FIG. 3 is a view showing a flowing water hole pattern of a low pressure loss type upper nozzle according to the present invention.

FIG. 4 shows a beam cross-sectional shape of an adapter plate of an upper nozzle. FIG. 4A shows a case of a conventional type, and FIG.

[Explanation of symbols]

 1 Upper nozzle body 4 Beam between upper nozzle running water holes 5 Running water holes

Claims (1)

[Claims] 1. An upper nozzle of a PWR fuel assembly,
The shape of the flowing water hole is based on a square shape, the R shape of the four corners is reduced, the opening ratio of the flowing water hole is increased within the required strength range, and the beam cross-sectional shape between the flowing water holes is tapered or similar. A low pressure loss type upper nozzle of a PWR fuel assembly, characterized in that the resistance to flowing water at an inlet of a water hole of an upper nozzle plate is reduced.