JPH03257399A - Volume reduction and cutting device for radioactive waste body - Google Patents

Abstract

PURPOSE:To improve working efficiency of volume reduction treatment work and to decrease required cost by providing a waste body transfering mean by which the waste body brought into a housing is transfered to a specified cutting process position, a processing mean utilizing a submerged laser, a collection cask and the like. CONSTITUTION:A spent fuel assembly 3 is severed into a fuel body and a channel box 8 and thereafter the channel box 8 is lifted by a transfer machine 5 to be housed in a housing 4 and then is lifted down until its lower end reaches a specified cutting process position, in order to be held by a holding guide 4d. After that, a laser oscillator 10 and an assisting gas supplying source 11 are given by an operation order and a laser processing head 6 is made to swing and move along a surface of the channel box 8. Severed segments 8a fall into water within the housing 4 and are received by the collecting cask 7. The assisting gas is also collected by an exhaust gas collector device 14 via a gas piping 15, and suspended fine cruds generated in the water and the like are removed by a filter of water purification device 16.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention targets long radioactive waste objects such as channel boxes and control rod blades of spent fuel assemblies generated in light water nuclear reactors. The present invention relates to a volume reduction cutting device that cuts the waste object into small pieces to reduce its volume.

[Conventional technology]

Currently, channel boxes, control rods, etc. of spent fuel assemblies that are irradiated with high radiation dose in reactors such as light water reactors are stored in the spent fuel pool inside the reactor building after being removed from the reactor core. After being transferred to the site bunker in a separate building, the volume of the channel box is reduced using an appropriate method. This is because appropriate technology and measures for reducing the volume of large highly radioactive waste objects such as channel boxes within spent fuel storage pools have not yet been established.

Approximately 100 channel boxes are generated per year from one 1 million kW class nuclear power plant. Moreover, channel boxes are long objects, measuring more than 4 meters in length. Conventionally, spent channel boxes were taken out of the spent fuel storage pool, stored in a heavy cask for radiation protection, and then loaded onto a trailer. It is then transported from the reactor building to the site bunker in a separate building.

On the other hand, as mentioned above, conventional methods for reducing the volume of radioactive waste after it has been transferred from the reactor building to the site bunker in a separate building include existing methods such as the electrolyte water jet cutting method, plasma cutting method, and gas cutting method. Spent fuel assembly channel box using underwater cutting technology or mechanical cutting technology such as punching method or wire force cutting method.
Currently, control rod blades and other parts are cut to reduce the volume.

[Problem to be solved by the invention]

By the way, as mentioned above, the conventional treatment method in which radioactive waste generated from a nuclear reactor is transferred from a spent fuel storage pool to a site bunker in a separate building to reduce its volume has the following problems.

In other words, it takes a huge amount of labor and time to transport long waste objects, and it also requires heavy casks for transportation, large-capacity side bunker facilities for temporary storage and processing of waste, and expenses associated with storage. However, this makes transportation costs extremely high throughout the year.

In addition, the various conventional cutting techniques mentioned above have low work efficiency and take a long time to cut channel boxes, etc., and in particular, with the electrode water jet cutting method and plasma cutting method, the electrolysis of water that accompanies cutting Hydrogen gas and other by-products produced by nuclear reactors can cause explosions, and high levels of radioactive materials can contaminate water.

Furthermore, in the mechanical cutting method, the cutting machine itself comes into direct contact with radioactive waste objects, which increases radiation exposure during maintenance. Furthermore, since the cutting machine itself is large, there are problems in installing it in an existing spent fuel pool, which has restrictions on installation space and load-bearing strength.

The present invention has been made in consideration of the above points, and is a radioactive waste that solves the problems caused by conventional volume reduction processing methods, improves the efficiency of volume reduction processing work, reduces processing costs, and saves labor. The object of the present invention is to provide a cutting device for reducing the volume of objects.

[Means to solve the problem]

In order to solve the above problems, the volume reduction cutting device of the present invention has the following features:
A housing built underwater in a spent fuel storage pool,
a waste object transfer means for sequentially feeding the waste object taken out from a storage rack in the pool and carried into the housing to a predetermined cutting position as the cutting process progresses; and installed at the cutting position opposite to the waste object. A laser oscillator placed outside the pool is interconnected with an optical fiber, and a laser processing head is connected to an assist gas supply source and piping, and the laser processing head is connected relative to the waste object along the cutting line. an underwater laser processing means consisting of a moving scanning drive unit; a collection cask housed at the bottom of the housing and receiving cut pieces of the waste object and falling dross generated by the cutting process below the cutting process position; It shall consist of an assist gas exhaust gas recovery means and a water purification means attached to the housing.

[Effect]

With the above configuration, the radioactive waste object taken out from the storage rack in the spent fuel pool is isolated from the surroundings and carried into a housing constructed under water in the pool, and the lower end of the waste object faces the laser processing head. It is lowered and positioned so that it comes to a predetermined cutting position. here,
A laser beam emitted from a laser oscillator installed on the poolside floor is guided to the laser processing head through an optical fiber, and an assist gas (e.g. air, inert gas) is supplied under pressure from a gas supply source. , the laser processing head is moved relatively along the cutting line of the waste object.

As a result, the assist gas ejected from the tip nozzle of the laser processing head forms an air curtain to locally eliminate surrounding water, and the laser beam emitted from the laser processing head irradiates the surface of the waste object through this part. Cut the waste object along the cutting line. Note that due to the presence of assist gas, the laser beam is not absorbed by water during the light guide path, and the waste object is irradiated under the same conditions as laser irradiation in the atmosphere. This method makes it possible to cut waste objects, such as channel boxes (made of Zircaloy), at high cutting speeds underwater.

On the other hand, the cut pieces separated from the waste object fall through the water in the housing and are received in the collection cask disposed below the housing. In addition, falling dross such as cutting powder generated during cutting is also collected in the cask in the same way as the cut pieces. Note that the exhaust gas of the assist gas blown into the housing is collected through piping into an exhaust gas recovery container, and sent from there to an exhaust gas treatment system where it is appropriately treated. In addition, minute floating crud in the water that is generated during the cutting process is
It is removed by the filter of the water purification means attached to the housing. This can prevent water pollution in the spent fuel storage pool and environmental pollution due to exhaust gas.

Then, the cutting process is performed by alternately repeating the horizontal movement scanning of the laser processing head and the vertical feeding of the waste object suspended in the housing, so that the entire waste object is cut into small pieces and all the cut pieces are made into casks. It will be collected. Once the recovery cask is full of cut pieces, the cask is pulled out of the housing, placed in a shipping container, and removed from the spent fuel storage pool and transported to a designated waste storage location. Note that the cutting process can also be performed by performing horizontal movement scanning and vertical feeding at the same time.

Moreover, in the above configuration, since the laser processing head installed inside the housing and the laser oscillator installed on the poolside are connected by a flexible optical fiber, the distance of the light guide path of the laser beam is , there are almost no restrictions on location, and the laser beam can be efficiently guided to the laser processing head. Therefore, the only cutting device that needs to get close to the waste object is the processing head, making it possible to apply it to spent fuel pools, etc., where installation space and load-bearing strength are limited. In addition, since the laser processing head is scanned and driven relative to the waste object, the waste object can be shredded into rings or plates by combining the feed of the waste object itself and the movement and scanning of the laser processing head. . In addition, the processing head is small and lightweight, so the direction of the processing head can be changed flexibly.
Since waste objects are cut and reduced in volume in the spent fuel storage pool of the reactor building, long waste objects are stored in heavy casks in their original form and transported to the site bunker in a separate building. There is no need for this, and significant cost savings can be achieved in this aspect.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic diagram of the overall configuration of the volume reduction cutting device according to the present invention. 3, and a volume reduction cutting device according to the present invention is installed in one corner of this spent fuel storage pool.

In addition, the volume reduction cutting device can be roughly divided into spent fuel storage pool 1
A housing 4 constructed in water, a transfer machine 5 that transports the channel box 8 taken out from the storage rack 2 into the housing 4 and sends it to a predetermined cutting position, and a laser processing head 6 built into the housing 4. It consists of an underwater laser processing system including an underwater laser processing system, and a cut piece collection cask 7 installed at the bottom of the housing 4.

Here, the housing 4 houses an upper vertically elongated channel-shaped container 4a for storing a channel box 8 as a radioactive waste object to be cut, an intermediate container 4b incorporating a laser processing head 6, and a recovery cask 7. The channel-shaped container 4a has a holding guide 4d for the channel box 8, and the lower container 4 has a holding guide 4d for the channel box 8.
c is provided with a shutter 4e that closes the gap with the intermediate container 4b, and a field 4f for loading and unloading the recovery cask 7.

The transfer machine 5 is equipped with a gripper 5b at the tip of a support wire 5a extending downward from the main body of the transfer machine, and a rotation drive section 5c of the gripper 5b, and runs along a rail 5d laid above the pool 1. do.

On the other hand, the laser processing head 6 has two
One to four units are connected to a pendulum-type scanning drive unit 9, for example, and a laser oscillator 10 installed at the poolside. An optical fiber 12. is connected to the assist gas supply source 11, respectively. They are interconnected via gas piping 13. Further, the detailed structure of the laser processing head 6 is as shown in FIG. 2. A collimator lens 6b, a condensing lens 6c, and a protective glass 6d are built into the inside of the probe case 6a, and the assist gas pipe 13 is connected to the protective glass 6d. Further, a small diameter hole is bored at the tip of the case 6a, and a nozzle tip 6e is provided therein. In addition,
As the laser beam, a YAG laser having good optical transmission efficiency within an optical fiber is suitable.

Returning to FIG. 1, the top of the housing 4 and an exhaust gas collection container for assist gas installed on the pool side are connected by a gas pipe I5, and the lower container 4c of the housing 4 is connected to a circulation pump, A water purification device 16 consisting of a filter is attached.

Note that 7 is a drive cylinder for carrying the collection cask 6 into and out of the housing 4, and 18 is an operation control section.

Next, the operation of the above configuration will be explained. First, the spent fuel assembly 3 stored in rank 2 of the spent fuel storage pool 1 in FIG. 1 is separated into a fuel assembly and a channel box 8 as shown in FIG. 8 is lifted up by the transfer device 5 and carried into the housing 4, and then lowered and held by the holding guide 4d so that the lower end thereof is at a predetermined cutting position. Next, a laser oscillator 10 installed on the pool side. Assist gas supply source 1
1, and the laser beam and assist gas emitted from the laser oscillator are transferred to the optical fiber 12. Gas piping 13
At the same time, the laser processing head 6 is guided to the laser processing head 6 through the channel box 8, and the laser processing head 6 is swing-moved in the left-right direction along the surface of the channel box 8 by the operation of the scanning drive section 9.

Here, as shown in Fig. 2, the assist gas (air 3 or inert gas such as nitrogen gas) blown into the case 6a is blown out forward from the nozzle tip 6e and forms an air curtain here. Eliminate water. On the other hand, the laser beam guided through the optical fiber 12 passes through the collimator lens 6b and the condensing laser 6c, and then passes through the assist gas atmosphere and is irradiated onto the surface of the channel box 8 without attenuating much. In this case, the diameter of the hole opened in the nozzle tip e is one size larger than the core diameter of the optical fiber 12, for example, if the core diameter of the optical fiber is 0.61 nm.
In this case, the hole diameter should be selected to be about 0.8 to 1.3 mm, and the gas pressure of the assist gas should be at least 3 to 4 kg/crA to exclude surrounding water. Furthermore, the distance between the nozzle tip 6e and the surface of the channel box 8 is preferably set to be as narrow as possible, at about 0.5 to 1.5 an. Note that, in order to always maintain a constant distance between the laser processing head 6 and the channel box 8, a contact type sensor is provided on the laser processing head side, for example.

In this way, by irradiating the laser beam from the laser processing head 6 onto the surface of the channel box 8 and simultaneously moving and scanning the laser processing head 6 in the left and right direction relative to the channel box 8, the channel box 8 is formed as shown in FIG. It is cut into rounds along the cutting line P shown in . Then, the cut pieces 8a fall through the water within the housing 4, and are received by the collection cask 7 that is waiting there below. At the same time, falling dross such as cutting powder generated during the cutting process is also collected in the collection cask 7.

The collection cask consists of a storage container that stores small pieces of waste and a removable shield. After the waste is delivered to the storage facility, only the storage container can be taken out and stored, and the shield can be reused. , the costs associated with containers are also reduced. On the other hand, the exhaust gas of the assist gas rises inside the housing 4 shown in FIG. 1, and is collected from the top of the housing 4 through the gas pipe 15 in the exhaust gas recovery container 14. Further, minute floating crud generated in the water inside the housing is removed by a filter of the water purification device 16. This prevents the above-mentioned exhaust gas, floating crud, etc. from diffusing from the housing 4 to the surroundings.

When the lower end of the channel box 8 is cut by the above-mentioned cutting process, the channel box 8 is lowered by operating the transfer device 5 and the lower end is sent to the cutting position again, where the laser cutting process is performed again. I do. In this way, by alternately repeating the feeding of the channel box 8 by the transfer device 5 and the laser cutting, the channel box 8 is finely chopped over its entire length, and the cut pieces 8
a is all collected into cask 7. Note that when the collection cask 7 is full of cut pieces 8a, after closing the shutter 4e of the lower container 4c in the housing 4, the side door 4f is closed.
The cask 7 is opened, the collection cask 7 is pulled out, and the cask 7 is placed in a shipping container (not shown) and then transported to a predetermined waste storage location.

Next, a specific cutting method for cutting the channel box 8 into pieces will be explained with reference to FIGS. 4(a) to 4(C). First, (a
) The figure shows a method of cutting the channel box 8 into rounds using two diagonally arranged laser processing heads 6.
After cutting the two sides of the channel box 8 by moving and scanning the laser processing head 6 in the horizontal direction at the illustrated position, the channel box 8 is rotated 90 degrees by operating the gripper rotation drive unit 5c shown in FIG. At this position, the laser processing head 6 is again scanned in the horizontal direction to cut the remaining two sides and cut into rings.

On the other hand, the figure shows 4 channels around channel box 8.
By moving and scanning the four laser processing heads 6 in the horizontal direction in conjunction with each other at the positions shown, the cut piece 8a is sliced into rounds in one scan. With this method, the cutting processing time can be cut in half compared to the method shown in FIG.

On the other hand, Figure (C) is equipped with four laser processing heads 6 as in Figure (B), and combines the movement scanning of each laser processing head 6 in the left and right direction with the downward feeding of the channel box 8. The channel box 8 is continuously cut along a zigzag trajectory shown by dotted lines in the figure. According to this cutting method, the cut piece 8a is cut into four plate pieces, making it possible to significantly increase the volume reduction rate compared to the above-described round cutting method.

In addition, the channel box of the fuel assembly (length 4200 mm)
According to the experimental results of the inventors' underwater laser cutting of Zircaloy with a diameter of 140 mm, a width of 140 mm, and a thickness of 2 to 3 nII11, it was found that the conventional methods such as molten electrode water jet cutting, plasma cutting, etc. Compared to this, there is no generation of explosive gas due to electrolysis, and the cut width of the cutting process is extremely narrow, so the amount of dross generated during processing is small, and moreover, when using a YAG laser with an output of 80W, It has been confirmed that cutting can be performed at a high cutting speed of 2.5 m (3 mm thick) to 3.5 m (2 mm thick).

In the illustrated example, the volume reduction cutting of a channel box has been described, but it goes without saying that various waste objects such as control rods can also be shredded using the same apparatus.

〔Effect of the invention〕

Since the volume reduction cutting device for radioactive waste objects according to the present invention is constructed as described above, it achieves the following effects.

(1) Radioactive waste objects such as channel boxes and control rods of spent fuel assemblies generated in nuclear reactors are reduced in volume by being shredded in the spent fuel storage pool inside the reactor building. Therefore, compared to the conventional method, which transfers the waste from the reactor building to the site bunker in a separate building and then processes it for volume reduction, this method saves money by eliminating two hours of equipment and labor required to transport the waste in its original form. It is possible to achieve a significant reduction in costs and labor savings.

(2) By adopting an underwater laser cutting method that supplies assist gas to waste objects, the cutting speed is faster and work efficiency is improved compared to various conventional cutting methods. Also, the amount of cutting powder and dross generated during the cutting process is extremely reduced, so water pollution is extremely small, by-products from the cutting process can be easily disposed of, and filters, etc. Replacement can be reduced.

(3) Unlike mechanical cutting methods, there is no wear and tear on the cutting edge, so the time required to replace it and exposure to radiation can be eliminated, and the time involved in maintenance can also be reduced.

(4) In addition, by interconnecting the laser processing head and the laser oscillator installed on the poolside floor surface via optical fiber, the installation location of the laser oscillator
With almost no restrictions such as distance or pool depth,
The laser beam can be guided to the laser processing head, making it possible to install the cutting device even in narrow spaces.

(5) Since the laser processing head is moved relative to the waste object by the scanning drive unit, the waste object can be cut into rounds by combining this with the feeding of the waste object itself.

The volume reduction rate of the waste object can be greatly increased by cutting it into pieces.

(6) Since the collection cask is disposed at the bottom of the housing to directly receive the cut pieces of waste objects falling from above, it is easy to collect the cut pieces.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the overall configuration of the volume reduction cutting device according to the embodiment of the present invention, Fig. 2 is a sectional view showing the detailed structure of the laser processing head in Fig. 1, and Fig. 3 is a diagram showing the channel box of the fuel assembly. 4(a), (b), and (C) are diagrams illustrating the principle of cutting the target waste object, and are explanatory diagrams of the specific cutting method of the waste object, respectively. In the figure,

Claims (1)

[Claims] 1) A volume reduction cutting device for shredding and recovering radioactive waste from a nuclear reactor, which comprises a housing built underwater in a spent fuel storage pool and a storage rack in the pool. a waste object transfer means for sequentially sending the waste object taken out and carried into the housing to a predetermined cutting position as the cutting process progresses; and a waste object transfer means installed at the cutting position facing the waste object and placed outside the pool. A laser processing head interconnected with a laser oscillator by an optical fiber and further connected by piping to an assist gas supply source, and a scanning drive unit that moves the laser processing head along a cutting line relative to the waste object. a collection cask that is housed at the bottom of the housing and receives cut pieces of waste objects and falling dross generated by the cutting process below the cutting position; and an assist gas attached to the housing. 1. A volume reduction cutting device for radioactive waste objects, comprising: an exhaust gas recovery means; and a water purification means. 2) The apparatus according to claim 1, wherein the housing has a lower container for accommodating the collection cask, and the lower container is equipped with a shutter at the upper part and an ejection door at the lower side surface. Volume reduction cutting device for waste objects.