JPH0226758B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for decontaminating radioactive metal waste such as piping of nuclear power generation equipment. Generally, radioactive metal waste generated at nuclear power plants is permanently stored within the plant to prevent it from affecting the environment. However, if this is done, the amount of radioactive metal waste stored will continue to increase, making it difficult to secure storage space. In particular, piping and the like created during renovation of nuclear power generation facilities are large in size and cannot be easily reduced in use, making it difficult to store them. For this reason, consideration is being given to decontaminating radioactive metal waste to reduce its radioactivity level to the radioactivity level found in nature, that is, to the background level, so that it can be handled in the same way as general waste.
However, since the material on the inner surface of piping, valves, etc. is itself radioactive, complete decontamination cannot be achieved simply by removing the radioactive crud that has accumulated on the inner surface, and it is not possible to completely decontaminate the material by grinding the inner surface. It is necessary to remove the hardened surface layer. However, piping etc. are long and have vents, and although conventional honing using a grindstone can easily remove the crud, the grinding speed of the material itself is slow;
There is also a limit to the depth of grinding. Furthermore, it was necessary to replace the grindstone depending on the material of the pipes, making it difficult to reliably grind and decontaminate the inner surfaces of these pipes. The present invention was developed based on the above circumstances, and its purpose is to reliably grind the inner surfaces of pipes, valves, etc., completely decontaminate them, and reduce the radioactivity level to background level. An object of the present invention is to provide a decontamination device for radioactive metal waste that can decontaminate radioactive metal waste until it can be handled in the same way as general waste. That is, the present invention provides a flexible shaft;
A grinding body that is attached to the tip of the flexible shaft and comes into elastic contact with the inner surface of the radioactive metal waste, and a power supply device and an electrolyte supply device that apply voltage between the grinding body and the radioactive metal waste to be ground. This decontamination apparatus for radioactive metal waste is characterized by comprising: and a drive mechanism that rotates and moves the flexible shaft in the axial direction. The present invention will be described below with reference to an embodiment shown in the drawings. Reference numeral 1 in FIG. 1 is a base, and a support 2 is erected on this base 1. A fixing mechanism 3 is attached to this column 2 so as to be able to move up and down, and the fixing mechanism 3 is configured to fix radioactive metal waste to be decontaminated, such as a bent pipe 4, in a predetermined position. . Further, a receiver 5 is placed on the base 1, and the bent pipe 4 is accommodated in the receiver 5. Further, a drive mechanism 6 is provided at the upper end of the pillar 2. This drive mechanism 6 has a drive shaft 7 projecting downward, and this drive shaft 7 is rotationally driven by a motor (not shown) or the like, and is configured to move in the vertical direction, that is, in the axial direction. . A conductive and flexible flexible shaft 9 is detachably attached to the lower end of the drive shaft 7 via a connector 8.
is inserted into the bent pipe 4. A grinding body 11 is detachably attached to the tip of the flexible shaft 9 via a conductive connector 10. As shown in FIGS. 2 and 3, this grinding body 11 has a large number of flexible wires 13 that protrude radially from a conductive central shaft 12, and these flexible wires 13... It has great elasticity and is made of non-conductive fiber-reinforced plastic material. And these flexible wire materials 13
A spherical grinding ball 14 made of abrasive grains hardened with a binder is attached to the tip of each. In addition, the cathode of the DC power supply 15 is connected to the flexible shaft 9.
through a contactor 16. On the other hand, the anode of the DC power source 15 is connected to the bent tube 4.
Furthermore, a supply mechanism 17 for supplying a grinding aid and an electrolyte is attached to the pillar 2. The supply mechanism 17 is configured to spray the grinding aid and electrolyte from a nozzle 18 and supply it to the inner surface of the bent pipe 4. The drive mechanism 6 is configured to be remotely operated by a control panel 19. One embodiment of the present invention configured as described above firstly deals with solid radioactive waste to be decontaminated, such as a bent pipe 4.
is fixed in a predetermined position by the fixing mechanism 3. Next, the grinding body 11 attached to the tip of the flexible shaft 9 is inserted into the upper end of the bent tube 4, and the drive shaft 7 of the drive mechanism 6 is rotated to rotate the grinding body 11 via the flexible shaft 9. The grinding balls 14 of this grinding body 11 are the flexible wire rods 1
3 are brought into contact with the inner surface of the bent tube 4 by elastic bending, so that the rotation of the grinding body 11 causes the inner surface of the bent tube 4 to be ground by the grinding balls 14 . Also, along with this, the drive shaft 7 of the drive mechanism 6
is moved in the axial direction, the grinding body 11 is inserted into the bent tube 4, and grinds the inner surface of the bent tube 4 over its entire length. As described above, the grinding balls 14 of this grinding body 11 are in contact with the inner surface of the bent tube 4 due to the elastic bending of the flexible wires 13, and since the flexible shaft 9 is flexible, these By doing this, this grinding body 11 becomes a bent pipe 4.
It is possible to freely pass through bends in the road. Further, as the grinding body 11 rotates and moves forward, the nozzle 1 of the grinding aid and electrolyte supply mechanism 17
Grinding aid and electrolyte are ejected from 8 and supplied to the inner surface of the bent pipe 4. At the same time, a voltage is applied to the bent tube 4 and the central shaft 12 by the DC power source 15, and a current flows through the electrolytic solution, thereby electrolytically polishing the inner surface of the bent tube 4. First, the radioactive crud adhering to the inner surface of the bent pipe 4 is removed by the grinding body 11 . Subsequently, the contaminant layer on the inner surface is removed by electrolytic polishing of the grinding body 11 . The removed radioactive cladding and the grinding dust of the contaminated layer are washed away by the grinding aid and the nuclear power plant, and accumulate in the receptor 5. Therefore, the radioactive cladding and the contaminated layer on the inner surface of the bent pipe 4 have been removed, and the radioactivity level has been lowered to the so-called background level, which is the radioactivity level found in nature, and can be handled in the same manner as general waste. Incidentally, the results of an experiment conducted to confirm this effect are shown in FIG. In FIG. 4, curve a shows only the grinding body, curve b shows the combination of grinding and electrolytic polishing, and horizontal line c shows the background. Note that the vertical axis represents the amount of surface contamination, and the horizontal axis represents the grinding time in arbitrary units. As is clear from FIG. 4, by combining grinding and electrolytic polishing, the grinding speed and amount can be increased, and the amount of surface contamination can be reduced to below the background level. The rotation speed of the grinding body 11 is 100 r.pm to 4000 r.pm, and the axial movement speed of the grinding body 11 is in the range of 1 cm/min to 100 cm/min, depending on the material of the solid radioactive waste such as the bent pipe 4, Settings are made according to the shape, degree of contamination, etc., and the grinding ball 14...
For example, when the material of the solid radioactive waste is stainless steel, carbon steel, etc., aluminum oxide is used as the material of the abrasive grains. Further, in this embodiment, the grinding body 11 is detachable from the flexible shaft 9, so that the grinding body 11 can be easily adjusted according to the shape, size, material, etc. of the radioactive metal waste to be decontaminated. Can be exchanged. Further, the grinding time is appropriately selected depending on the depth of penetration of the radioactive substance into the metal crystal structure and the degree of surface contamination determined by its concentration. Furthermore, the drive mechanism 6 can be remotely controlled by a control panel 19, thereby reducing the radiation exposure of the workers. Note that the present invention is not limited to the above embodiment. For example, the grinding body is not necessarily limited to the structure as in the above embodiment, but may be of any type as long as it can elastically abut against the inner surface of the radioactive metal waste to be decontaminated. Moreover, this grinding body does not necessarily have to be detachably attached to the flexible shaft. Further, the flexible shaft does not necessarily have to be inserted into the radioactive metal waste from above, but may be inserted horizontally or from below. Furthermore, the radioactive metal waste to be decontaminated is not limited to bent pipes, but also radioactive metal waste such as straight pipes and valves. Although the case where the grinding aid and electrolyte are disposable has been described above, they may be recovered from the receiver 5 by the pump 20 and used for circulation. Furthermore, the entire radioactive metal waste may be ground while being immersed in the receiver 5 containing a grinding aid and an electrolyte. Usually, grinding is carried out using the tube 4 to be ground as an anode and the central shaft 12 as a cathode, but sometimes the tube 4 to be ground is cleaned with the central shaft as an anode. In some cases, grinding and cleaning are repeated alternately as an anode and a cathode. Furthermore, the inner surface of the tube 4 may be finished using only the grinding body 11 at the end. As described above, in the present invention, a grinding body that elastically contacts the inner surface of solid radioactive waste to be decontaminated is attached to the tip of a flexible shaft, and this flexible shaft is rotated and moved in the axial direction by a drive mechanism. While grinding the inner surface of radioactive metal waste, the central axis is used as an anode and the metal waste is used as a cathode.
It is electrolytically polished. Therefore, this grinding body always comes into contact with the inner surface of the radioactive metal waste in accordance with the shape of the inner surface of the radioactive metal waste, and the flexible shaft is bent in accordance with the shape of the inner surface of the radioactive metal waste. Even if the inner surface has a complex shape, the entire inner surface can be reliably ground. Therefore, the attached radioactive metal waste and contaminated layer can be removed quickly and reliably, and the radioactivity level of radioactive metal waste can be lowered to the background level, and this solid radioactive waste can be disposed of as general waste. The effect is great, such as being able to handle it in the same way. In particular, compared to the case where only the grinding body 11 is used, the grinding speed is increased by more than 10 times, there is no limit to the grinding depth, and it is easy to control. The amount of wear on the grinding body is also less than half. Further, even if the electrolytic solution is a neutral inorganic salt, the effect of electrolytic polishing is sufficiently exhibited, and the polishing is safe and easy to handle.

[Brief explanation of drawings]

1 to 4 show an embodiment of the present invention, in which FIG. 1 is a side view partially showing the device, and FIG.
The figure is a front view of the grinding body, Figure 3 is a side view of the grinding body,
FIG. 4 is a diagram showing the relationship between grinding time and reduction in the amount of surface contamination. 1... Base, 2... Support, 3... Fixing mechanism, 4
...Bent pipe (radioactive metal waste), 5...Receptor,
6... Drive mechanism, 7... Drive shaft, 8... Connector,
9...Flexible shaft, 10...Connector,
11... Grinding body, 13... Flexible wire, 14... Grinding ball, 15... DC power supply, 16... Contactor.

Claims (1)

[Claims] 1. A flexible shaft, a grinding body attached to the tip of the flexible shaft and elastically abutting against the inner surface of the radioactive metal waste, and between the grinding body and the radioactive metal waste to be ground. 1. A decontamination device for radioactive metal waste, comprising: a power supply device and an electrolyte supply device that apply a voltage; and a drive mechanism that rotates and moves the flexible shaft in the axial direction. 2. The radioactive metal waste decontamination apparatus according to claim 1, wherein the grinding body has a central axis of the conductor and an insulating grinding ball attached around the central axis.