JPS61200494A - Flow control simple tube - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an improvement of a simple control rod guide tube (hereinafter simply referred to as a simple tube) in a fuel assembly for a pressurized water reactor, and particularly relates to the improvement of a control rod guide simple tube (hereinafter simply referred to as a simple tube) in a fuel assembly for a pressurized water reactor. Concerning improvements to stoppers.

(Prior Art) In a fuel assembly for a pressurized water reactor, simple control rod guide tubes (3) for guiding control rods are mixed with the fuel rods, and the upper and lower ends are connected to upper nozzles (1) as shown in FIG. ), are fixedly attached to the lower nozzle (2), which has a lower end plug (4) inserted at the lower end, and a hole (5) for water to flow when the control rod falls. There are four locations at the bottom.

Therefore, the simple tubes in the assembly where no control rods are inserted are covered with simple plugs from the upper nozzle side to prevent too much coolant from flowing.

Also, when inserting a control rod in a scram, it is necessary to control the speed at which the control rod falls, and for this reason, the diameter of the lower part of the simple pipe is made slightly smaller < L (61, to reduce water flow resistance in the final process of falling. By increasing the speed, the speed is naturally slowed down and the impact with the fuel assembly is reduced.

(Problem to be solved by the invention) However, in the case of a fuel assembly in which no control rods are inserted in a simple pipe as described above, it is essential to install a plug, and furthermore, the water flowing out from the water hole can leak into the surrounding fuel rods. This results in a direction perpendicular to the axis, which poses a problem of placing a burden on the fuel rods.

Furthermore, as mentioned above, making a part of the simple tube smaller in diameter is complicated in manufacturing.

In view of this situation, the present invention eliminates the need for the above-mentioned plug by improving the lower end plug of the simple pipe.
The purpose of this invention is to maintain a constant flow rate and to easily control the speed at which the control rod falls when the control rod is inserted.

(Means for Solving the Problems) That is, the feature of the present invention is that, as shown in FIG. The end plug (4) is formed of a hollow cylinder having a valve chamber (4a) inside, and a drain port (7) is provided at the lower part of the side wall, and a valve chamber (4a) is provided at the upper part of the drain port (7). ) A floating valve (8) having a flow rate adjustment hole (9) in the axial direction is biased upwardly in the closing direction by a spring αψ to support the inner case.

(Function) Next, the function of the simple pipe using the lower end plug of the above configuration will be explained.

During normal reactor operation, water flows from the flow rate adjustment hole to the simple pipe. At this time, the floating valve (8) is connected to the floating valve spring α.
O) is in the energized position and the valve is in the closed state.

When the control rod falls from the top and descends during scram, the water in the simple pipe becomes downward water, and the floating valve (
8) is acted upon by a force that pushes it downward, the valve becomes open, and the water flows out through the drain port (7).

In this way, a constant water flow rate is ensured without using a simple plug, there is no need to provide a water flow hole (5), and even when the control rod is inserted, the speed at which the control rod falls can be controlled and impact with the fuel assembly can be controlled. can be alleviated.

(Example) Hereinafter, an example of the simple pipe of the present invention will be described further based on FIG.

FIG. 1 shows the lower end plug (4) of the fuel assembly which constitutes the main part of the present invention, and the lower end plug (4) has a valve chamber (4) inside.
4a) is formed by a hollow cylinder. An appropriate number of drain ports (7) are bored in the lower part of the side wall in the radial direction.

The internal valve chamber (4a) has a slightly enlarged space in the center, and a gradually narrowing part in the upper part, which connects to a narrower diameter part, and also in the lower part, it becomes a narrower diameter part at the bottom of the drain port (7). A floating valve (8) having a bulge in the middle is housed inside the valve chamber.

The floating valve (8) has a shape that matches the shape of the valve chamber (4a), and has a flow rate adjustment hole (9) bored through it along its central axis, and has a large lower surface of the floating valve. A spring 0 is interposed between the step surface between the enlarged diameter part and the narrow diameter part in the inner lower part of the valve chamber (4a), and normally biases and supports the floating valve (8) in the upward closing direction. It's forcing me.

In the above configuration, the diameter of the flow rate adjustment hole and the shape of the floating valve can be freely designed, and thereby the flow rate of the flowing water can be adjusted.

Therefore, the lower end plug configured as described above is inserted into the lower end of the simple pipe by fixing its upper part to the simple pipe by welding or the like and fixing its lower part to the lower nozzle, but normally the valve is closed. In the closed state, water flows only through the flow-1 adjustment hole. Therefore, the flow rate is adjusted by designing the pore size.

Then, when the control rod falls and descends inside the simple pipe, the water inside the simple pipe is pressed by the control rod and flows downward, pushing the floating valve (8) downward, and the valve is opened. Water flows out from the drain (7).

At this time, the resistance of the flowing water to the control rod increases, the falling speed is naturally reduced, and the impact with the fuel assembly is alleviated.

(Effects of the Invention) As described above, the present invention improves the lower end plug of a simple pipe, and includes a floating valve having a flow rate adjustment hole therein so that it is in a closed state during normal operation, that is, when no control rod is inserted. In addition, a drainage port is provided at the bottom of the side wall, and by allowing water to flow into the simple pipe through the flow rate adjustment hole under normal conditions, the flow rate of water will not become excessive even when the control rod is not inserted. Therefore, it is possible to omit the simple plug that was considered indispensable in conventional fuel assemblies that do not use control rods, and the flow rate in the simple pipe can be easily achieved by free design of the flow rate adjustment hole, making it possible to use it as a simple flow control pipe. It has extremely significant effects.

In addition, the present invention not only adjusts the flow rate as described above, but also opens the valve when the control rod falls and discharges water through the drain port, so there is no need for a small diameter part or a water hole in a simple pipe as in the past. Since there is no flow perpendicular to the axis from the hole, it is possible to reduce the burden on adjacent fuel rods, and it is also expected to have an excellent effect of making the fabrication of a simple tube easier than before.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of the lower end plug of a simple flow rate control tube which is a main part of the present invention, and FIG. 2 is a schematic partial cross-sectional view showing a state in which a conventional control rod guide simple tube is attached. (4)...lower end plug, (4a)...valve chamber. (7)...Drain port, (8)...Floating valve 5 (9).
...Flow rate adjustment hole, αψ...Spring. etc. 1 etc. Z harden

Claims (1)

[Claims] 1. In a control rod guide simple tube used in a fuel assembly for a pressurized water reactor, the lower end plug is formed of a hollow cylinder with a valve chamber inside, and a drain port is provided at the bottom of the side wall, and the upper position of the drain port is A simple flow control pipe characterized in that a floating valve having a flow rate adjustment hole passing through the valve chamber in the axial direction is supported and biased in an upward closing direction by a spring.