JPH0224358B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a pressure vessel filled with sodium as a coolant and an inert gas as a cover gas, such as the reactor vessel of a sodium-cooled fast breeder reactor or an ex-core spent fuel storage tank. This relates to guide passage pipes that are installed in the nuclear reactor and used to take in and take out nuclear fuel.

First, an outline of the guide passage pipe described above, which is installed in a reactor pressure vessel and serves as a fuel guide when loading and unloading fuel bodies into the reactor core using a fuel exchanger or the like, will be explained with reference to FIGS. 1 and 2. In the figure, 1 is a flexible rotary plug as an upper shield of the reactor pressure vessel, 2 is a reactor fuel assembly that constitutes the reactor core inside the vessel, 3 is sodium as a primary coolant that fills the inside of the vessel, and 4 is a A cover gas sealed in the pressure vessel interior space above the sodium liquid level H, 5
Reference numeral 6 indicates a guide passage pipe for taking in and taking out fuel, which is the object of the present invention; 6 a support and elevating drive device for the guide passage pipe; and 7 a fuel exchanger connected to the guide passage pipe through a door valve. The guide passage pipe 5 is suspended and supported by the drive device 6 installed above the rotary plug 1, and is drawn into the pressure vessel through the rotary plug 1 and placed therein. The tip thereof is immersed below the liquid level of the sodium 3 and extends to near the top of the fuel body 2. On the other hand, the drive device 6 includes a main body casing 62 containing a shingle member 61, a hanging support part 63 for the guide passage pipe 5, a rotary operating shaft 64 connected to the support part 63 at a position eccentric to the guide passage pipe 5, and a drive unit 65 that rotates the operating shaft 64 in the direction of the arrow.
By rotating the operation shaft 64, the guide passage cylinder 5 is moved up and down by a small distance in a linked manner via the support portion 63 as shown by the arrow. As a result, when replacing fuel, it is suspended to the top of the core and held down to prevent the surrounding fuel bodies adjacent to the replacement fuel from floating up, and when other rotating plug operations are performed and after fuel replacement, it is lifted upward and on standby. can be done. The diameter of the guide passage cylinder 5 is determined so that the fuel body 2 and a gripper such as a fuel exchanger can smoothly pass through the inside thereof.

Conventionally, the guide passage pipe 5 has been made as a simple cylinder. For this reason, considering that the tip is immersed below the sodium liquid level and installed in a pressure vessel, the inner space of the tube and the cover gas atmosphere inside the vessel are separated by the sodium liquid level and communicate with each other. Do not fit. Under these circumstances, when the fuel exchanger is connected and the gripper (for the structure of the gripper, see, for example, Japanese Patent Application Laid-Open No. 1983-6209) is lowered into the furnace from outside the furnace through the guide passage pipe 5, A small amount of impurities adhering to the surface of the gripper will be eluted into the sodium inside the guide passage tube 5 to generate sodium impurities, which will be trapped in that area. Furthermore, when connecting the fuel exchanger 7 to the guide passage pipe 5, gas replacement is performed at the door valve each time, but during this operation, a small amount of inert gas mixed in the newly supplied inert gas is removed. Oxygen reacts with sodium in the guide passage tube to generate sodium compounds such as NaOH and Na ₂ O in the presence of trace amounts of moisture, and phenomena such as these compounds floating near the boundary of the sodium liquid level in the tube occur. .
For this purpose, the fuel is withdrawn through the guide passage pipe 5,
When loading, the above impurities may become obstacles and obstruct the smooth movement of the fuel body and gripper within the pipe, or floating impurities may enter the internal mechanism of the gripper and obstruct the movement of the mechanism. Furthermore, it may get into the gaps between the fuel pins in the fuel body, causing problems such as blocking the gaps. Floating impurities may enter the claw 3 and actuator 5 portion of the gripper device as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 53-62095, and for example, after gripping a fuel body, the claw 3
If the movement of the fuel body is obstructed, recovery of the fuel body becomes impossible. In this case, the reactor will have to be shut down, resulting in fatal damage to the reactor. Additionally, during reactor operation, the inert gas sealed in the guide passage pipes becomes radioactive due to radiation from the core, so this prevents this radioactively contaminated gas from leaking outside during refueling. For this purpose, clean gas is pumped into the guide passage pipe from the outside for gas replacement each time, but in this case as well, the internal space of the guide passage pipe 5 is a dead end, so the gas replacement work is difficult. Moreover, it requires a separate clean gas supply line and a polluted gas discharge treatment line, making the equipment complicated and inconvenient.

This invention was made in consideration of the above points, and its purpose is to prevent impurities from being trapped in the pipes that serve as fuel passages, and to facilitate the injection of clean gas from outside the furnace, thereby improving the soundness of fuel handling. It is an object of the present invention to provide a guide passage tube that is advantageous in maintaining the

According to the present invention, this purpose is achieved by opening a long opening in the direction of the guide passage pipe in the middle of the guide passage pipe, with the position near the sodium liquid level in the pressure vessel, and opening the inside of the pipe in the vicinity of the sodium liquid level on the pressure vessel side and the upper cover gas. This is achieved by opening internal and external communication holes that communicate with the atmosphere.

Next, the present invention will be explained in detail based on illustrated embodiments.

In FIG. 1, in the middle of the guide passage pipe 5, an internal/external communication hole 51 is formed in the peripheral wall of the guide passage pipe 5 to match the sodium liquid level H in the pressure vessel and extend above and below the liquid level H. It is opened.
In the illustrated example, the holes 51 are formed as elongated holes in the vertical direction, and a plurality of holes are opened in the peripheral wall of the tube. Therefore, even if the sodium liquid level fluctuates up and down, the inside of the guide passage pipe 5 communicates with the cover gas atmosphere and the sodium liquid level in the pressure vessel through the internal and external communication holes 51.

According to the above configuration, various impurities generated during the handling operation of moving the fuel body 2 up and down through the guide passage pipe 5 do not remain in the pipe, but are transferred to the communication hole 5.
1, it quickly overflows out of the tube on the sodium circulating flow on the pressure vessel side, and is treated in the sodium purification line on the pressure vessel side. Therefore, the accumulation of sodium impurities in the guide passage pipe is eliminated, and various troubles caused during handling of the fuel assembly can be prevented. In addition, the inert gas inside the guide passage pipe 5 communicates with the cover gas atmosphere on the pressure vessel side, so even when clean gas is sent into the pipe from outside the furnace during fuel exchange, etc., until now the inside of the pipe has been The radioactive contaminated gas that had been trapped in the
Since the clean gas is discharged to the pressure vessel side through the gas, the work of feeding this clean gas can be carried out easily and smoothly. Note that the gas released to the pressure vessel side is appropriately treated together with the cover gas in the gas breathing discharge line on the pressure vessel side. In this way, it is possible to greatly contribute to maintaining the soundness of fuel handling performed through the fuel inlet/outlet guide passage pipe.

Although the illustrated embodiment illustrates a guide passage pipe installed in a reactor pressure vessel and connected to a fuel exchanger,
In addition, a guide passage pipe connected to the fuel inlet/outlet machine,
Alternatively, similar effects can be achieved by applying the present invention to a guide passage pipe installed in an extra-core fuel storage tank.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the structure of an embodiment of the invention, and FIG.
The figure is a sectional view taken in the direction of the arrows in FIG. 1: Rotating plug as upper part, 2:
Fuel body, 3: Sodium, 4: Cover gas, 5:
Guide passage pipe, 51: Inner/outer communication hole, H: Sodium liquid level.

Claims (1)

[Claims] 1 In a guide passage pipe for reactor fuel in and out, which penetrates the upper shield body and is installed in the pressure vessel with the lower tip immersed below the sodium liquid level, it is located near the sodium liquid level in the pressure vessel. A sodium cooling type characterized by having an internal/external communication hole that opens vertically in the middle of the guide passage pipe and communicates the inside of the pipe with the sodium liquid level on the pressure vessel side and the upper cover gas atmosphere. A guide passage pipe for fuel in and out of a nuclear reactor.