JPS6360357B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a radiation shielding plug inserted into a pressure tube extension in a pressure tube nuclear reactor that requires fuel exchange during power operation. .

In a pressure tube reactor, in order to support the pressure associated with high temperature and high pressure coolant, the reactor core is constructed by arranging a large number of fuel assemblies and coolant contained in pressure tubes of appropriate diameter. be done. The end of the pressure pipe is equipped with a plug called a seal plug to prevent high-temperature, high-pressure water from leaking outside. In this case, in order to enable fuel exchange during output operation, a small hole for injecting coolant should be provided in the center of the radiation shielding plug, which is in contact with the inside of the seal plug, and run vertically through it. Coolant is injected through this small hole to prevent high-temperature water from flowing back into the recirculation system. However, this small hole for injecting coolant extends above the recirculating water inlet pipe, so during normal operation, recirculating water, which is the primary coolant, flows through this small hole to the top of the seal plug. This has the drawback of increasing the temperature of the sealing part and shortening the life of the sealing material.

If fuel exchange is not planned during reactor power operation, there is no need to provide such a small hole for injecting coolant, so it is possible to keep the temperature of the sealing material of the seal plug low. When exchanging fuel during operation, it is necessary to provide a small hole for injecting cooling water. Therefore, in preparation for the future when fuel must be exchanged during power operation in a commercial reactor, etc., there is a strong desire to develop a mechanism that can provide a small hole for injecting cooling water and maintain the temperature of the seal part low. .

SUMMARY OF THE INVENTION In view of the drawbacks of the prior art as described above, an object of the present invention is to provide an effective mechanism for solving the technical problems. This prevents hot recirculating water from flowing to the top of the seal plug, thereby keeping the seal temperature low, significantly improving safety, maintainability, and economy. An object of the present invention is to provide an improved shielding plug for a pressure tube type nuclear reactor.

The present invention, devised to achieve such an object, is provided with a ball valve mechanism in the middle of the coolant injection flow path that runs vertically through the shielding plug body, and the ball valve mechanism prevents recirculation during normal operation. It is configured to operate in the direction of closing the flow path by the dynamic pressure of water.

Hereinafter, the present invention will be explained in more detail based on the drawings. FIG. 1 is an explanatory diagram showing a pressure tube extension on the fuel exchange port side of a pressure tube nuclear reactor. Although not shown, the upper part of the pressure pipe 3 extends further upward, and the fuel assembly is housed inside the upper part of the pressure pipe 3. As is well known, the high-temperature, high-pressure cooling water flows into the pressure pipe 3 through the inlet pipe 1 formed at the lower side of the pressure pipe 3, and rises inside the pressure pipe 3 to form the fuel assembly. The steam and water are boiled in the furnace, forming a two-phase flow of steam and water, which flows from the outlet pipe at the top of the pressure pipe through the riser pipe of the primary cooling system to the steam drum.

As shown in the figure, a shield plug body 7 and a seal plug 9 are incorporated in the pressure pipe extension on the fuel exchange port side. The shielding plug body 7 is for shielding radiation (neutron beams and gamma rays) from the core, and its structure is generally in the shape of a block made of stainless steel. Also, the seal plug 9
is a stopper for preventing high-temperature, high-pressure water from leaking outside from the recirculation system, and has a structure that includes a sealing part to which a sealing material 8 is attached.

When replacing the fuel assembly without stopping the output operation of the reactor, the shielding plug body 7 must be installed to prevent hot recirculated water from entering the fuel exchanger.
A coolant injection channel is formed so as to extend vertically through the tube.
The upper end of this coolant injection channel 6 opens in the vicinity of the recirculation water inlet pipe 1 . The present invention is significantly different from the prior art in that a ball valve mechanism 5 is incorporated in the middle of the coolant injection channel 6. This ball valve mechanism 5 is designed to operate in the direction of closing the flow path 6 by the dynamic pressure of the recirculated water during normal operation. Also, the ball is made of a material that will not rust on the shielding plug.

Next, the operation of this device and the effects brought about by it will be explained. First, when performing fuel exchange during reactor power operation, coolant is injected from the fuel exchanger side using the coolant injection channel 6.
By injecting high-pressure cooling water, the ball 5a of the ball valve mechanism 5 floats, and the cooling water is injected into the pressure pipe 3 from the main flow path 6a through a plurality of branch flow paths 6b arranged in the radial direction. be done. In other words, since the ball 5a floats in response to the injection of cooling water at this time, the flow is not obstructed at all, and the injection of cooling water can be carried out in the same manner as in the conventional case. On the other hand, after the fuel exchange operation is completed, that is, during normal operation, dynamic pressure due to high temperature and high pressure recirculated water is applied to the ball valve mechanism 5 from the branch flow path 6b arranged in the radial direction. In order to press the ball 5a downward, the flow path 6 is closed, and as a result, high temperature and high pressure recirculated water can be prevented from flowing into the seal plug 9. As a result, the temperature of the sealing material 8 is significantly lowered, resulting in a dramatic increase in the life of the sealing material. FIG. 2 is a graph showing a comparison between the prior art and the present invention regarding the inner surface temperature of the pressure tube. The conventional case without a ball valve mechanism is shown by a broken line, and the case of the present invention with a ball valve mechanism is shown by a solid line. Looking at the pressure tube inner surface temperature at the sealing position, it was about 230°C in the prior art, but it was reduced to about 110°C according to the present invention. Since the sealing material 8 is usually a titanium alloy, this provides great advantages in terms of economy and operational maintainability.

Since the present invention is a shielding plug for a pressure tube type nuclear reactor configured as described above, it is possible to inject cooling water, making it possible to exchange fuel during reactor operation, which is extremely advantageous in practical reactors, etc. During normal operation, high temperature recirculated water, which is the primary coolant, is prevented from flowing into the upper part of the seal plug, making it possible to significantly lower the seal temperature, significantly extending the life of the seal material. It is possible to achieve excellent effects in all aspects of nuclear reactor safety, maintainability, and economic efficiency.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG.
The figure is a graph showing a comparison of pressure tube inner surface temperatures between the prior art and the present invention. DESCRIPTION OF SYMBOLS 1... Inlet pipe, 3... Pressure pipe, 5... Ball valve mechanism, 6... Channel for coolant injection, 7... Shielding plug body, 8... Seal material, 9... Seal plug.

Claims (1)

[Claims] 1. In a shielding plug inserted into a pressure pipe extension of a pressure tube reactor, there is a main flow passage that extends vertically through the lower part of the main body of the shield plug and extends upward, and a recirculation flow branching from the main flow passage in the pressure pipe extension. The dynamic pressure of the recirculated water that flows from the branch flow path during normal reactor operation is applied to the branch part of the coolant injection flow path, which consists of a branch flow path that opens near the water inlet pipe. A shielding plug for a pressure tube type nuclear reactor, characterized in that it is provided with a ball valve mechanism that operates in a direction to close the main flow path.