JPS6116037B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a device for extracting reactor core components such as fuel assemblies (hereinafter referred to as fuel assemblies) from a reactor core, and in particular, the reaction force of the fuel spacer pad portion exceeds the predicted value due to some factor. The present invention relates to a fuel extraction device that implements an effective extraction method when the fuel cannot be extracted from the core by the normal method using a normal fuel exchanger due to the size of the fuel turning around or the occurrence of stuck fuel.

For example, in a liquid metal cooled fast breeder reactor, the structural material of the fuel assembly expands in volume due to irradiation swelling when irradiated with high-density fast neutrons, and as the operation progresses, the fuel assembly curves into a complicated shape. Dimensions change. As a result, the pressing load on the contact areas between the fuel assemblies increases, and when the fuel is pulled out for fuel exchange, the frictional resistance force increases significantly, sometimes causing galling, making it difficult to pull out the fuel. There is a risk. To date, various methods have been proposed as countermeasures against this problem, and technological development is progressing. The main methods are: (a) The spacing between fuel assemblies is set to a slightly larger value after estimating these phenomena. (b) During reactor operation, while keeping the spacing between fuel assemblies small to form a tight core,
At the time of fuel exchange, the distance between the assemblies is increased by loosening the core support frame, etc. (The device for this purpose is called a core restraint mechanism.) (c) Improving the load capacity of the refueling machine (d) Changing the direction of the fuel assembly in the middle of combustion and installing it in the core. However, each method has its own limitations and cannot be considered a definitive countermeasure, and further improvements are required for practical use.

For example, regarding (c), it is desirable that the extraction load capacity of the refueling machine be as large as possible, but due to the dimensional constraints of the reactor structure, the refueling machine is a long machine with a small diameter and a significantly long length. Increasing capacity may result in an increase in diameter dimensions, which in turn may result in an increase in reactor size. In addition, since fuel exchange is usually carried out once or twice a year, and it is necessary to handle a large number of fuel assemblies during one fuel exchange period, the method must be easy to operate and short in operation time. is essential. In order to meet the conflicting demands mentioned above, ordinary fuel exchangers have a simple structure, are easy to operate, and have a short operation time, and have a load capacity that is resistant to factors with many uncertainties such as irradiation swelling. The capacity should be calculated using a predicted value based on a certain degree of probability to avoid excessive capacity. It is also necessary to prepare a special fuel extraction device with a large extraction load capacity in case the refueling machine becomes inoperable.

The present invention has been made to address the above-mentioned problems, and an object of the present invention is to provide a fuel extraction device that can pull out fuel assemblies that cannot be pulled out using a normal fuel exchanger in a relatively simple manner. shall be.

The present invention will be described in detail below with reference to the drawings of one embodiment.

FIG. 1 shows how this fuel extraction device is installed in the reactor vessel. A reactor core support structure 2 for holding a reactor core 5 is provided within a reactor vessel 1, and supports a large number of fuel assemblies 4 in an array. On the other hand, a shield plug 3 forming the lid of the reactor vessel 1 is installed at its top.

By the way, in the design of fast breeder reactors, an "under-the-plug fuel exchange system" is usually adopted, which allows fuel exchange without opening the lid of the thin plug 3. Among these methods, a design using a "direct-acting fuel exchanger" is adopted in which rotating plugs are installed in double or triple layers so that the center of the fuel exchange shaft can reach directly above the fuel assembly 4 to be replaced. There are many. A small-rotation plug 3a is installed inside the low-speed plug 3, and the small-rotation plug 3a is further equipped with a direct-acting fuel exchanger.
Normal fuel exchange is performed using a direct-acting fuel exchange machine installed on the small rotating plug 3a. If it becomes impossible to extract fuel using this method,
The fuel extraction device 6 according to the present invention is a small rotation plug 3a.
The fuel assembly 4 that has been installed in the upper fuel exchanger mounting hole and cannot be pulled out is pulled out. The fuel extraction device 6 is broadly divided into an upper support structure 6a, a guide pipe 7, a connection structure 8, a gripper 10 containing a second piston 9 and a first piston 22, a liquid pressure supply and control device 11, and the like.

The guide pipe 7 also serves to prevent an adjacent fuel assembly surrounding the fuel assembly 4 that cannot be pulled out in a normal fuel exchanger from being lifted up.

The upper support structure 6a is mounted on the small rotation plug 3a, and its lower end is connected to a guide tube 7 passing through the small rotation plug 3a. A connecting structure 8 is built inside the guide tube 7 , and this connecting structure 8 is further connected to a gripper 10 via a second piston 9 .

The fluid pressure supply/control device 11 is installed on the small rotation plug 3a, and the fluid passage 26 extending to the tip of the gripper 10 is connected to the upper support structure 6a,
It is configured inside the connection structure 8. The connecting portion between the upper end of the connecting structure 8 and the fluid pressure supply/control device 11 is designed to absorb axial movement using a flexible tube, bellows, or the like. The other end of the fluid passage 26 communicates with a side wall of a cylinder 21 installed at the lower end of the gripper 10, as shown in FIG. A first piston 22 having a shaft seal 23 is housed inside the horizontal hole 27 in the side wall. Further, a locking member 28 is formed at the outlet of the horizontal hole 27 to prevent the first piston 22 from jumping out. A metal bellows 25 is installed between the locking member 28 and the shaft seal 23 to form a boundary between the inside of the furnace vessel 1 and the inside of the fluid passage 26. Further, a spring 24 is installed between the locking member 28 and the shaft seal 23 to supply pressure for housing the first piston 22 in the horizontal hole 27. The first pistons 22 are installed at a plurality of locations on the same circumference of the cylinder 21. The second piston 9, which is provided independently of the first piston 22, can slide within the guide tube 7 integrally with the gripper 10 over a desired stroke. The sliding movement of this second piston is caused by the small rotation plug 3.
This can be achieved by a liquid supply source 30 installed on a. In other words, the connection structure 8 and the liquid filled in the guide tube 7 enable vertical movement.

Next, the handling procedure will be explained. With the first piston 22 housed in the cylinder 21, the second piston 9 is lowered together with the gripper 10. The gripper 10 is then inserted into the handling head of the fuel assembly 4.

The first piston 22 is then actuated by fluid pressure from the fluid pressure supply control device 11 to push the handling head outward from the inside surface as shown in FIG. Then, a high cycle fluctuating pressure is supplied from the fluid pressure supply control device 11 to the first piston 22,
High cycle vibration is applied to the first piston 22. This vibration is transmitted to the handling head without significant attenuation because the first piston 22 strongly presses against the handling head. Moreover, since the vibrating part is close to the vibrated part, the vibrating part is more effectively vibrated.

On the other hand, the second piston 9 uses fluid pressure to jerk the entire gripper 10 upward by a small distance with great force.

In this way, the fuel assembly 4 is
As is well known, the friction coefficient can be reduced by applying high cycle vibrations to the contacting sliding surfaces. Since delicate adhesion of the stick surface occurring on the sliding surface can be released, the pulling force of the fuel assembly 4 can be significantly reduced. Furthermore, by using the liquid supply source 30, the fuel assembly 4, which could not be pulled out, can be pulled out little by little by using the small stroke but in combination with the strong jacking force of the second piston 9. By pulling it out little by little in this way, the whole including the fuel assembly 4 is moved upward little by little by the connection structure 8 and the upper support structure 6a. By repeating the above operations, the fuel assembly 4 is eventually released from the strong pressing relationship with the adjacent fuel assembly. Thereafter, a separate fuel exchanger may be used, or the fuel exchanger may be incorporated into this device by adjusting the length of the bellows, etc. of the fluid pressure supply system of the fluid pressure supply/control device 11, and the fuel assembly Just pull out body 4. As a result of the above, it is possible to pull out a fuel assembly 4 that cannot be pulled out by a normal method using a normal fuel exchanger due to a pulling force that is higher than expected or stuck with an adjacent fuel assembly.

In addition, as illustrated in FIG. 2, the shaft sealing portion 23 of the piston
By adopting a structure in which the shaft seal part 23 is surrounded by a metal bellows 25 to prevent the shaft seal part 23 from coming into contact with the reactor coolant, the reactor coolant does not deteriorate the performance and life of the shaft seal part 23, and the piston is further improved. reliability,
Durability has been improved.

As explained above, the fuel extraction device of the present invention uses a hydraulic piston to jack up the fuel assembly, which is stuck in the reactor and cannot be extracted by a normal fuel exchanger, little by little while vibrating it powerfully and at high cycles. As a result, it has the following effects.

By applying vibration, the frictional drag force can be reduced, so the fuel assembly can be pulled out with a smaller pulling force than static pulling force, which prevents damage to the fuel assembly and leaving behind debris in the reactor.

Since the first piston, which is a vibrator, is placed near the vibrating body, the vibrations are transmitted only to the necessary local areas, so that surrounding reactor equipment such as the plug and reactor vessel are not affected by the vibrations. No cracks will occur.

The stroke of the second piston is small and the fuel assembly is pulled out little by little, so by using a furnace observation device such as a sodium fluoroscopy device, you can work while observing the pressing situation with the surrounding fuel assemblies. It is possible to do so, and the working conditions etc. can be adjusted so as to prevent damage to this and surrounding fuel assemblies.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view showing an installed state of a fuel extraction device according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing an enlarged gripper portion of FIG. 1. 7...Guide tube, 8...Connection structure, 9...Second piston, 10...Gripper, 11...Liquid pressure supply/control device, 25...Bellows, 26...Fluid passage.

Claims (1)

[Claims] 1. A connecting structure hanging down through a shield plug covering the upper part of the reactor vessel, a gripper attached to the lower part of a second piston that is attached to the lower part of this connecting structure and making an expanding and contracting action, and this gripper. at least two piston-cylinder mechanisms each having a piston portion that is provided at the bottom and can freely protrude in the horizontal direction; and a fluid pressure supply control that supplies fluid to these piston-cylinder mechanisms and fluctuates the pressure of the supplied fluid at high cycles. A fuel extraction device comprising: a device; and a liquid supply source that supplies liquid to the second piston to lift and drive the gripper.