JPS6229759B2 - - 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 drag becomes significantly large, sometimes causing a galling phenomenon, which may make it difficult to pull out the fuel. There is. To date, various methods have been proposed as countermeasures against this problem, and technological development is progressing. The main methods are: (a) The gap between fuel assemblies is set to a slightly larger value after estimating these phenomena. (b) During reactor operation, the gap between the fuel assemblies is kept small to form a tight core, while at the time of fuel exchange, the gap between the fuel 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 a state in which the present fuel extraction device is installed in a reactor vessel, and FIG. 2 is an explanatory view of the gripper portion of FIG. 1. 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 set at its top.

By the way, in the design of fast breeder reactors, an ``under-the-plug refueling system'' is usually adopted, which allows refueling to be performed 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 connected to the 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 present fuel extraction device 6 is roughly composed of an upper support structure 6a, a guide tube 7, a connection structure 8, a gripper 9, a large gear 10, a small gear 11, a swing drive shaft 12, a drive mechanism 13, and the like.

The guide pipe 7 normally also serves to prevent the fuel assembly 4 from being lifted up when the fuel assembly 4 that cannot be pulled out is taken in by a fuel exchanger.

As shown in FIG. 2, a protrusion 16 is provided on the side of the gripper 9 and can be moved in and out by fluid supplied from a flow path 17, and a step portion provided above the fuel assembly 4 is provided. It is designed so that it can be engaged with.

A large gear 10 is fitted into this gripper 9,
Further, a connecting structure 8 is rotatably connected to the upper side, and by driving the connecting structure 8 upward, the gripper 9 can be pulled out upward. A guide pin 10a is fixed to the lower surface of the large gear 10 in a protruding manner, and engages with a hole 15 provided on the upper surface of the fuel assembly 4 to transmit the rotational force of the large gear to the fuel assembly. It is configured. Teeth are formed on the outer peripheral surface of the large gear 10, and a swing drive shaft 1 is attached to the small gear 11 that meshes with the teeth.
By applying the rotational force from the drive mechanism 13 via 2, the rotational force can be applied to the large gear.

Therefore, the rotational force generated by the drive mechanism 13 is finally applied to the fuel assembly, and a pulling force is applied upward via the gripper, so that a strong pulling ability can be exhibited.

The drive mechanism 13 is driven to provide rocking rotation under necessary and effective operating conditions while observing the condition of the material to be handled with the help of a separately installed furnace observation device such as a sodium fluoroscopy device. You can drive as you like. By vertically pulling up the fuel assembly 4 with the gripper 9 while applying this oscillating rotational motion, the pulling effect is significantly increased.

In addition, each part of the drive mechanism 13, such as the drive mechanism 13, small gear 11, and large gear 10, is also provided near the fuel assembly 4, which is the driven body, so rotational torque is transmitted more effectively and the oscillating rotational force is generated. It can be made powerful.

In this way, this extraction device swings and rotates the fuel assembly 4 using the small gear 11 and the drive mechanism 13, while
It has a mechanism that allows the gripper 9 to powerfully pull it up in small strokes.

In the embodiment, the swing rotation motion is transmitted by gears, but it can be easily inferred that a swing rotation transmission mechanism such as a cam or a link mechanism may be used as the transmission mechanism. Also, the small gear 1 on the drive shaft 12 side
1 may be set to one or more as required, and a plurality of drive systems may be used.

By pulling up while rocking and rotating in this way, it is possible to reduce the stiffness coefficient of the contact surface, it is also possible to alleviate the situation where excessive pressing force is locally generated, and it is possible to reduce the sliding Since the slight adhesion of the stick surface that occurs on the surface can be released, the pulling force of the fuel assembly 4 can be significantly reduced. Furthermore, by using the gripper 9 with the strong jacking force of the gripper 9, which has a slight stroke, the fuel assembly that could not be pulled out can be pulled out little by little. 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-described operations, the fuel assembly 4 is eventually released from the strong pressing relationship with the adjacent fuel assembly, and thereafter the pulling operation, which can be smoothly lifted, is completed. As described 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 swing rotation drive mechanism 1
The rotational torque of No. 3 is applied to the fuel assembly 4 through a guide pin 10a that is mechanically integrally connected to the large gear 10.
Since the fuel assembly 4 can be effectively oscillated and rotated, the above-mentioned drawing effect is increased.

Further, the upper handling head of the fuel assembly 4 is engaged with the gripper 9 by installing a plurality of protrusions 16 projecting in the radial direction of the gripper 9. This protrusion 16 has a piston structure and moves forward and backward by hydraulic pressure from a flow path 17 communicating within the gripper 9.

As explained above, the fuel extraction device of the present invention uses the gripper 9 to jack up the fuel assembly, which is stuck in the furnace and cannot be extracted by a normal fuel exchanger, little by little while driving the fuel assembly in a powerful oscillating rotation. Therefore, it has the following effects.

(a) By rocking and rotating, the contact state with adjacent fuel assemblies changes dynamically, and the fuel assembly can be pulled out with a smaller pulling force than static pulling force, which can reduce frictional drag, so the fuel assembly is not damaged. No more debris remains in the furnace.

(b) By arranging the oscillating rotation drive mechanism at a position different from the axis of the fuel assembly, one set of the oscillation rotation drive mechanism is installed near the fuel assembly, so the rotational torque is effectively transferred to the fuel assembly. Since the vibration is transmitted to the body, the fuel assembly can be easily oscillated and rotated without causing cracks or deformation of surrounding reactor equipment such as the shield, the shield plug, and the reactor vessel due to the oscillating motion.

(c) The drive stroke of the clipper is small and the fuel assemblies are pulled out little by little, so by using a furnace observation device such as a sodium fluoroscope, it is possible to observe the pressing situation with the fuel assemblies on the side. Since the work can be carried out while the fuel assembly is being damaged, the work conditions etc. can be adjusted to prevent damage to the fuel assembly and the fuel assembly.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an installed state of a fuel extraction device according to an embodiment of the present invention, and FIG. 2 is a partially cutaway front view of the gripper portion of FIG. 1. 9...Gritzpa, 10...Big gear, 10a...
Guide pin, 13... Drive mechanism, 16... Projection.

Claims (1)

[Claims] 1. A gripper that has a protrusion that engages with the upper part of the fuel assembly from the inside and applies a pulling force to the fuel assembly, a large gear that is fitted into and connected to the gripper, and a large gear that is connected to the large gear and the fuel assembly. A fuel extraction device comprising a guide pin that engages with the body, and a drive mechanism that applies rotational force to the large gear.