JP2522576B2 - Volume-cutting device for radioactive waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to a long radioactive waste object such as a channel box and a control rod blade of a spent fuel assembly generated in a light water reactor. The present invention relates to a volume reduction cutting device that finely cuts a waste object to reduce its volume.

[Conventional technology]

At present, the channel boxes and control rods of spent fuel assemblies with high radiation dose irradiated in reactors such as light water reactors are stored in the spent fuel pool inside the reactor building after being taken out of the reactor core. After transfer from the site to the site bunker in another building, the volume of the channel box is reduced by an appropriate method. This is because appropriate technology and measures for volume reduction of large radioactive waste such as channel box in the spent fuel storage pool have not been established yet.

About 100 channel boxes will be generated annually from a 1 million kW class nuclear power plant. Moreover, the channel box is a long item with a length of 4 m or more,
Conventionally, a used channel box is taken out from the spent fuel storage pool and stored in a heavy caster for radiation protection, which is then mounted on a trailer and transported from the reactor building to a site bunker in another building. .

On the other hand, as a method for reducing the volume of radioactive waste that is carried out after moving from the reactor building to the site bunker of another building as described above, conventionally, the hot water jet cutting method (JP-A-59)
-162495), plasma cutting method, gas cutting method, or other existing underwater cutting technology, or punching method, wire cutting method, or other mechanical cutting technology, used fuel assembly channel box, control rod blade The current situation is to cut the volume and reduce the volume.

[Problems to be Solved by the Invention]

By the way, as described above, the conventional treatment method of transferring the radioactive waste generated from the nuclear reactor from the spent fuel storage pool to the site bunker of another building to reduce the volume has the following problems.

In other words, it takes a huge amount of labor and time to transport a long waste object, and also a heavy cask for transportation, a large-capacity side bunker facility for temporary storage and treatment of waste, and expenses associated with storage. However, for this reason, the expenses spent for transportation work throughout the year are extremely high.

In addition, the above-mentioned conventional cutting techniques have low work efficiency and take a long time to cut the channel box, etc. In addition, especially in the electrode watershed cutting method and the plasma cutting method, electrolysis of water accompanying cutting is performed. By-products such as hydrogen gas generated in the process may cause an explosion, and the fusing width or the amount of fusing material associated with cutting will be relatively large, so water contamination by high levels of radioactive materials will occur. Occurs. Furthermore, in the mechanical cutting method, the cutting machine itself comes into direct contact with the radioactive waste material, which increases the exposure during maintenance. In addition, since the cutting machine itself becomes large, there is a problem in installing it in the existing spent fuel pool, where the installation space and load bearing strength are limited.

The present invention has been made in view of the above points, and eliminates the problems caused by the conventional volume reduction processing method, improves the efficiency of volume reduction processing, reduces the processing cost, and saves radioactive waste. An object is to provide a volume cutting device for an object.

[Means for solving the problem]

In order to solve the above problems, the volume reduction cutting device of the present invention is a housing constructed in water of a spent fuel storage pool, and a waste object taken out from a storage rack in the pool and carried into the housing for cutting processing. An optical fiber interconnects between a means for transferring a waste object that is sequentially sent to a predetermined cutting processing position in accordance with the progress, and a laser oscillator that is installed at the cutting processing position facing the waste object and is placed outside the pool. Further, an underwater laser processing means including a laser processing head connected to an assist gas supply source by a pipe and a scanning drive unit that moves the laser processing head along a cutting line relative to the waste object is housed in the bottom of the housing. And a recovery cask for receiving the cut pieces of the waste object and the drop dross generated by the cutting process below the cutting process position, and attached to the housing. The laser processing head is configured so that the laser light introduced into the processing head case by an optical fiber is converged by a condenser lens. A nozzle provided for ejecting and ejecting the assist gas from a common hole is provided at the tip of the case.

[Action]

With the above configuration, the radioactive waste object taken out from the storage rack in the spent fuel pool is isolated from the surrounding environment and carried into the housing constructed in the pool water, and the lower end of the waste object faces the laser processing head. It is hung down and positioned so as to come to a predetermined cutting processing position. Here, the laser beam emitted from the laser oscillator installed on the floor surface of the pool side is guided to the laser processing head through the optical fiber, and the assist gas (eg, air, inert gas) is pressurized from the gas supply source. While supplying, 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 remove surrounding water, and the laser beam emitted from the laser processing head irradiates the surface of the waste object through this portion. To cut the waste object along the cutting line. The laser beam is not absorbed by water in the middle of the light guide path due to the interposition of the assist gas, but is irradiated onto the waste object under the same conditions as the laser irradiation in the atmosphere. By this method, it is possible to cut a waste object such as a channel box (made of Zircaloy) at a high cutting speed in water.

On the other hand, the cut pieces that have been cut and separated from the waste object fall in the water in the housing and are received in the recovery cask arranged in the lower position. In addition, dropped dross such as cutting powder generated by cutting is also collected in the cask like the cut pieces. Note that the exhaust gas of the assist gas blown into the housing is recovered through a pipe into an exhaust gas recovery container, from which it is sent to an exhaust gas processing system for appropriate processing. Further, minute floating clads in water generated by the cutting process are removed by a filter of water purifying means attached to the housing. This can prevent water pollution in the spent fuel storage pool and environmental pollution due to exhaust gas.

Then, by performing the cutting process by alternately repeating the lateral movement scanning of the laser processing head and the vertical feeding of the waste object suspended in the housing, the entire waste object is finely cut and all the cut pieces are turned into casks. Will be collected. When the collected cask is full of cut pieces, the cask is pulled out from the housing and then stored in a shipping container, carried out from the spent fuel storage pool and carried to a predetermined waste storage place. In addition, the cutting process can be performed by simultaneously performing the horizontal movement scanning and the vertical feeding.

Moreover, in the above configuration, since the laser processing head mounted in the housing and the laser oscillator installed on the pool side are connected by the flexible optical fiber, the distance of the light guide path of the laser beam is increased. The laser beam can be efficiently guided to the laser processing head with almost no restriction on location. For this reason, only the processing head is required as a cutting device that needs to approach the waste object, and it is possible to apply the cutting device to a spent fuel pool or the like having a limited installation space and load bearing strength. Further, since the laser processing head is driven to scan relative to the waste object, the waste object can be sliced or shredded into pieces by combining the feeding of the waste object itself and the moving scanning of the laser processing head. . Also, since the processing head is small and lightweight, the direction of the processing head can be changed flexibly. Furthermore, the waste object is cut in the spent fuel storage pool of the reactor building for volume reduction processing. Therefore, it is not necessary to store a long waste object in its original shape in a heavy-weight cask and transport it to a site bunker in another building, which can significantly reduce the cost.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. First
The figure is a schematic diagram of the entire structure of the volume cutting apparatus according to the present invention. In the figure, 1 is a spent fuel storage pool installed in the reactor building, and 2 is a spent fuel assembly 3 installed in the pool. It is a storage rack, and the volume reduction cutting device according to the present invention is installed in one corner of this spent fuel storage pool.

Further, the volume cutting device is roughly classified into a housing 4 constructed in the water of the spent fuel storage pool 1, and the storage rack 2
A transporter 5 that carries the channel box 8 taken out into the housing 4 and sends it to a predetermined cutting position,
It is composed of an underwater laser processing system including a laser processing head 6 incorporated in the housing 4 and a cutting piece collecting cask 7 installed at the bottom of the housing 4.

Here, the housing 4 accommodates a vertically elongated channel-shaped container 4a for accommodating a channel box 8 as a radioactive waste object to be cut, an intermediate container 4b incorporating the laser processing head 6, and a recovery cask 7. The lower container 4c is composed of a lower container 4c, and the channel-shaped container 4a has a holding guide 4d for the channel box 8 and the lower container 4c has a shutter 4e for closing the space between the lower container 4c and the intermediate container 4b. It has 4f.

Further, the transfer device 5 has a gripper 5b and a gripper 5b at the tip of the support wire 5a which is extended downward from the transfer device main body.
It is equipped with a rotary drive unit 5c and runs along a rail 5d laid above the pool 1.

On the other hand, two or four laser processing heads 6 are arranged side by side in the peripheral region of the housing 4 and are connected to, for example, a pendulum type scanning drive unit 9, and a laser oscillator 10 and an assist gas supply source 11 installed on the pool side. Are interconnected via an optical fiber 12 and a gas pipe 13, respectively. The detailed structure of the laser processing head 6 is as shown in FIG. 2. The probe case 6a has a collimator lens 6b, a condenser lens 6c and a protective glass 6d built therein, and the assist gas pipe 13 has a protective glass. Connected to the front of 6d,
Further, a small-diameter hole is formed at the tip of the case 6a, and a nozzle tip 6e is provided therein. As the laser beam, a YAG laser having good optical transmission efficiency in the optical fiber is suitable.

Returning to FIG. 1, a gas pipe 15 connects between the top of the housing 4 and an exhaust gas recovery container for assist gas installed on the pool side, and a circulation pump is installed in the lower container 4c of the housing 4. Water purification device consisting of a filter
16 are attached. In addition, 17 is a drive cylinder for carrying out and carrying in the recovery cask 6 to and from the housing 4,
Reference numeral 18 is an operation control unit.

Next, the operation of the above configuration will be described. First, the spent fuel assembly 3 stored in the rack 2 of the spent fuel storage pool 1 in FIG. 1 is separated into the fuel body and the channel box 8 as shown in FIG. 8 is hoisted by the transfer device 5 and carried into the housing 4, and further hoisted so that its lower end portion comes to a predetermined cutting processing position and held by the holding guide 4d. Next, an operation command is given to the laser oscillator 10 and the assist gas supply source 11 installed on the pool side, the laser beam and the assist gas emitted from the laser oscillator are guided to the laser processing head 6 through the optical fiber 12 and the gas pipe 13, and scanning is performed. The laser processing head 6 is swung in the left-right direction along the surface of the channel box 8 by the operation of the drive unit 9.

Here, as shown in FIG. 2, the assist gas (air or an inert gas such as nitrogen gas) blown into the case 6a is jetted forward from the nozzle tip 6e to form an air curtain, and Eliminate water. Meanwhile, the optical fiber 12
The laser beam guided through the collimator lens 6
b, After passing through the condensing laser 6c, the channel box 8 passes through the assist gas atmosphere and is not attenuated.
Is irradiated on the surface of. In this case, the diameter of the hole opened in the nozzle tip 6e is slightly larger than the core diameter of the optical fiber 12, and for example, if the core diameter of the optical fiber is 0.6 mm, the hole diameter is 0.8 to 1.
It is preferable to select about 3 mm, and the gas pressure of the assist gas is at least 3 to 4 kg / cm ² or more in order to remove surrounding water. Furthermore, the distance between the nozzle tip 6e and the surface of the channel box 8 is as narrow as possible, and it is preferable to set it to about 0.5 to 1.5 mm. In order to keep the distance between the laser processing head 6 and the channel box 8 constant at all times, for example, a contact sensor is provided on the laser processing head side.

In this way, while irradiating the laser beam from the laser processing head 6 onto the surface of the channel box 8, at the same time, the laser processing head 6 is moved and scanned in the left-right direction relative to the channel box 8, so that the channel box 8 is moved to the position shown in FIG. It is sliced along the cutting line P shown in FIG. Then, the cut pieces 8a that have been cut fall into the water in the housing 4 and are received by the recovery cask 7 that is in the standby position below the pieces. At the same time, the falling dross such as cutting powder generated by the cutting process is also collected in the collecting cask 7. The recovery cask consists of a storage container for storing fine fragments of waste and a removable shield, and the shield can be reused by taking out the storage container after storing the waste in the storage. Also, the cost for the container is reduced. On the other hand, the exhaust gas of the assist gas rises inside the housing 4 shown in FIG. 1, and is collected in the exhaust gas collection container 14 from the top through the gas pipe 15. Further, minute floating clads generated in the water in the housing are removed by the filter of the water purification device 16. As a result, the above-mentioned exhaust gas, floating clad, etc. will not diffuse from the housing 4 to the surroundings.

Then, the channel box 8 is formed by the above cutting process.
When the lower end of is cut, the channel box 8 is lowered by the operation of the transfer device 5 and the lower end is fed again to the cutting position, where laser cutting is performed again.
By alternately repeating the feeding of the channel box 8 by the transfer device 5 and the laser cutting in this manner, the channel box 8 is finely shredded over the entire length, and the cut pieces are cut.
All 8a are collected in the cask 7. When the recovery cask 7 is filled with the cutting pieces 8a, the side door 4f is opened after the shutter 4e of the lower container 4c in the housing 4 is closed, and the recovery cask 7 is pulled out to the outside. After being stored in a container, it is carried out to a designated waste storage location.

Next, a specific cutting method for shredding the channel box 8 will be described with reference to FIGS. First,
FIG. 3A shows a method of cutting the channel box 8 in a circular manner by using two laser processing heads 6 arranged diagonally. The laser processing head 6 is laterally moved and scanned at the illustrated position. After cutting the two sides of 8, the channel box 8 is rotated 90 degrees by the operation of the gripper rotation driving unit 5c shown in FIG. Cut the sides and cut into rings. On the other hand, in FIG. 6B, four laser processing heads 6 are arranged around the channel box 8, and the four laser processing heads 6 are interlocked and moved laterally at the illustrated position. Due to this, a piece of cutting 8a can be made in one scan.
Is sliced. With this method, the cutting processing time is half that of the method shown in FIG. On the other hand, (c) figure is (b)
As shown in the figure, four laser processing heads 6 are provided, and the left and right movement scanning of each laser processing head 6 and the downward feed of the channel box 8 are combined to follow a zigzag trajectory shown by the dotted line in the figure. The channel box 8 is continuously cut. According to this cutting method, the cutting pieces 8a are cut as four plate pieces, and the volume reduction rate can be significantly increased as compared with the above-described ring cutting method.

In addition, the channel box of the fuel assembly (length 4200m
m, width 140 mm, thickness 2-3 mm, made of zircaloy), the inventors conducted laser cutting in water according to the above-mentioned method. According to the experimental results, the conventional hot-water jet cutting method, plasma cutting method, etc. Compared to the above, there is no generation of explosive gas due to electrolysis, and the kerf width of the cutting process is extremely narrow, so the amount of dross generated during processing is small, and when using a YAG laser with an output of 80 W, 2.5m (plate thickness
It has been confirmed that it can cut at a high cutting speed of 3 mm) to 3.5 m (plate thickness 2 mm).

Although the volume reduction cutting of the channel box is described in the illustrated example, it goes without saying that various waste objects such as control rods can be shredded using the same device.

〔The invention's effect〕

Since the device for cutting the volume of a radioactive waste object according to the present invention is configured as described above, the following effects can be obtained.

(1) Since radioactive waste materials such as channel boxes and control rods of spent fuel assemblies generated in the nuclear reactor were shredded in the spent fuel storage pool in the reactor building to reduce the volume. Compared with the conventional method that transfers the volume from the reactor building to the site bunker in another building and then reduces the volume, the equipment, labor, and time required to transport the waste object in its original form are omitted, and the cost is reduced. Significant savings and labor savings can be achieved.

(2) By adopting a laser cutting method in water, which is performed by supplying an assist gas to the method of cutting a waste object, the cutting speed is faster and the work efficiency can be improved as compared with various conventional cutting methods. Since the amount of dross such as cutting powder generated during cutting is extremely reduced, water contamination is extremely small, and by-products due to cutting can be easily treated, and filters etc. need to be replaced. And so on.

(3) Unlike the mechanical cutting method, since there is no wear of the cutting edge, it is possible to eliminate the time required for its replacement and the exposure to radiation.
The time required for maintenance can be reduced.

(4) Moreover, since the laser processing head and the laser oscillator installed on the poolside floor are interconnected via an optical fiber, the installation location of the laser oscillator can be improved.
Almost without restrictions such as distance and water depth of the pool,
The laser beam can be guided to the laser processing head, and the cutting device can be installed even in a narrow space.

(5) Since the laser processing head is moved relative to the waste object by the scanning drive unit, the waste object is reduced by cutting it into pieces or cutting it into plate pieces in combination with the feeding of the waste object itself. It is possible to significantly increase the efficiency.

(6) In the laser processing head, the laser light introduced into the processing head case by the optical fiber is converged by the condenser lens to be emitted, and the emission of the laser beam and the ejection of the assist gas are common. Since the process is performed from the small diameter nozzle, the laser beam can be efficiently processed without being absorbed by water in the air curtain created by the assist gas. In addition, since the area where water is removed by the assist gas is spot-like, it is possible to perform processing well even if the squareness between the surface to be processed and the laser beam axis is deviated or even if the flatness of the surface to be processed is poor. Further, since the machining head is not in contact with the object to be machined, problems such as wear of the head portion and catching during machining with the object to be machined do not occur. Furthermore, since the assist gas is jetted onto the laser processing surface,
It is possible to prevent damage to the condenser lens due to bounce of spatter caused by laser processing. As a result, processing efficiency, processing flexibility, stability, and safety are generally improved.

(7) Since the recovery cask is provided at the bottom of the housing to directly receive the cut pieces of the waste object that have dropped from above, it is easy to collect and carry out the cut pieces.

[Brief description of drawings]

FIG. 1 is a schematic view of the entire structure of a volume cutting apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view showing a detailed structure of a laser processing head in FIG. 1, and FIG. 3 is a channel box of a fuel assembly. FIG. 4A, FIG. 4B, and FIG. 4C are principle diagrams of the cutting process of the target waste object, respectively, and are operation explanatory diagrams of a specific method of cutting the waste object. In the figure, 1: spent fuel storage pool, 2: storage rack, 3: fuel assembly, 4: housing, 5: transfer machine, 6: laser processing head, 7
...... Recovery cask, 8: Channel box (radioactive waste object), 9: Scan drive part of laser processing head, 10: Laser oscillator, 11: Assist gas supply source, 12: Optical fiber, 13:
Assist gas pipe, 14: exhaust gas collection container, 16: water purification device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Katsumi Hirono 1-1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Takanori Toyoyoshi 1-Tanabe, Shinagawa, Kawasaki-ku, Kanagawa Prefecture No. 1 within Fuji Electric Co., Ltd. (56) Reference JP-A-59-162495 (JP, A) JP-A-63-242483 (JP, A)

Claims (2)

(57) [Claims] 1. A volume reduction cutting device for shredding and recovering radioactive waste objects of a nuclear reactor, the housing being constructed in the water of a spent fuel storage pool, and taken out from a storage rack in the pool. A transfer means for the waste object that sequentially feeds the waste object carried into the housing to a predetermined cutting processing position according to the progress of the cutting processing, and a laser oscillator that is installed at the cutting processing position facing the waste object and arranged outside the pool Underwater laser including a laser processing head interconnected with an optical fiber by an optical fiber, and further connected to an assist gas supply source by piping, and a scanning drive unit that moves the laser processing head along a cutting line relative to a waste object. A processing means and a recovery carrier that is housed in the bottom of the housing and that receives cut pieces of waste objects and drop dross generated by cutting processing below the cutting processing position. And an exhaust gas collecting means for assist gas attached to the housing and a water purifying means. The laser processing head converges the laser light introduced by an optical fiber into the processing head case with a condenser lens. And a volume reduction cutting of a radioactive waste object, characterized in that it has a nozzle provided at the tip of the case for emitting the laser beam and ejecting the assist gas from a common small hole. apparatus. 2. The apparatus according to claim 1, wherein the housing has a lower container for accommodating the recovery cask, the upper part of the lower container is provided with a shutter, and the lower side surface is provided with a carry-out door. Volume reduction cutting equipment for radioactive waste.