JP3187255B2 - Method and apparatus for decontamination of radioactive metal waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for decontaminating radioactive metal waste whose surface is contaminated with radioactive substances.

[0002]

2. Description of the Related Art A method of decontaminating radioactive metal waste by injecting abrasives with compressed air into the radioactive metal waste whose surface is contaminated with radioactive material and shaving off the surface layer has been known. Have been. However, conventionally, as shown in FIG. 5, for example, the radioactive metal waste W is placed on the conveyor 21 and the abrasive is sprayed from the nozzles 22 and 23 onto the surface thereof. It is necessary to invert W on the conveyor 21, and even if the abrasive is injected while moving the nozzles 22 and 23, it is not easy to uniformly decontaminate the entire surface of the radioactive metal waste W.

In the conventional decontamination method shown in FIG. 5, since radioactive substances also adhere to the conveyor 21, if the low-contamination waste is put into the decontamination chamber 24 after the high-contamination waste is treated, the conveyor is contaminated. There was also a problem that low-contamination waste was contaminated by radioactive substances adhering to 21.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned conventional problems, is capable of uniformly decontaminating the entire surface of radioactive metal waste, and is capable of reducing the contamination after treating highly contaminated waste. The present invention has been made in order to provide a method for decontaminating radioactive metal waste in which low-contamination waste is not reversely contaminated even when treating waste.

[0005]

Means for Solving the Problems A method for decontaminating radioactive metal waste according to the present invention, which has been made to solve the above problems, comprises:
The radioactive metal waste is stored inside the barrel, the abrasive is projected on the surface while the radioactive metal waste is stirred by rotating the barrel, and the projected abrasive is taken out.
Classify and dry while circulating abrasives of a specified particle size or more.
This is a method for decontamination of radioactive metal waste for blast decontamination.
Te, 循of high pollution abrasive projected against high pollution waste
Low-pollutant abrasives projected on ring paths and low-pollutant waste
Separate from the circulation path of
Projected on high-contamination abrasive and low-contamination waste
It is characterized by preventing mixing with the low-contamination abrasive. Further, the radioactive metal waste of the present invention
Decontamination method stores radioactive metal waste inside the barrel
And rotate the barrel to remove radioactive metal waste.
Abrasive material is projected onto the surface while stirring, and the entire surface is
Live-last decontamination and at the same time dry the inside of the barrel
Blast decontamination and the abrasive used for this decontamination
Classify the abrasive fines and the radioactive metal waste surface layer
Separated part is separated, and abrasive material with a predetermined particle size or more is circulated.
It is characterized by being used for The present invention
Radioactivity concentration detector monitors the radioactivity concentration of abrasives.
While circulating the abrasive, the drive-last decontamination
The radioactivity concentration of the abrasive used at the start of decontamination.
Concrete form characterized by lowering from low to low concentration
Can be In addition, the radioactive metal waste decontamination device of the present invention is a barrel that stores and rotates radioactive metal waste,
And abrasive projector, and classified the recovered abrasive, abrasive
Provided with a <br/> classifier for separating the peeling amount of fines and the radioactive metal waste surface layer, between the hopper of the classifier and abrasive projector, provided circulation path of Ken work material It is characterized by the following.

[0006]

According to the present invention, while the radioactive metal waste is agitated inside the barrel, the abrasive is projected from the abrasive projectile onto the surface to perform drive-last decontamination, so that the entire surface of the radioactive metal waste is decontaminated. The abrasive is uniformly projected on the surface, and the entire surface can be uniformly decontaminated. Moreover, since the inner surface of the barrel is also always decontaminated by the abrasive,
The inner surface of the barrel is always kept clean and there is no risk of contaminating the radioactive metal waste.

Further, in the present invention, since the dry-last decontamination is performed while circulating the high-contamination abrasive and the low-contamination abrasive through different routes, the low-contamination waste may be reversely contaminated by the high-contamination abrasive. Absent. Further, in the present invention, contrary to the conventional wisdom, a method of circulating and using a highly contaminated abrasive at the start of decontamination until a low-contaminated abrasive can be adopted. According to this method, highly contaminated waste can be sufficiently decontaminated without replacing the abrasive. In this case, it is preferable to perform decontamination while monitoring the radioactivity concentration of the abrasive using a radioactivity concentration detector provided in the circulation path of the abrasive.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the illustrated embodiments. FIG. 1 shows a first embodiment of the present invention, wherein 1 is a metal barrel that rotates as shown by an arrow.
The radioactive metal waste W is supplied from the metal waste supply container 2 to the inside of the barrel 1, and is stirred by the rotation of the barrel 1. Reference numeral 3 denotes a grinding material projector connected to the barrel 1, which rotates the impeller 4 at a high speed and projects the grinding material toward the bottom of the barrel 1 by the centrifugal force to peel off the surface layer of the radioactive metal waste W. Decontamination. It is preferable that the barrel 1 has a structure in which the contents can be discharged downward by inclining the rotation shaft downward.

A classifier 5 is provided below the barrel 1 and classifies the projected abrasive according to the particle size. Then, the finely ground abrasive is stored in the dust box 6.
The surface layer of the radioactive metal waste W that has been peeled off is also stored in the dust box 6. On the other hand, the abrasive having a predetermined particle diameter or more is returned to the hopper 9 of the abrasive projector 3 by the high-contamination abrasive conveyor 7 or the low-contamination abrasive conveyor 8, and is circulated. Thus the circulation path of the high pollution abrasive projected for high contaminated waste, projecting with respect to low-contaminated waste
Having separated from the circulation path of Isa the low contamination abrasive, both mix with it are prevented. The outer circumferences of the barrel 1, the abrasive material projector 3, and the circulation path of the abrasive material are hermetically sealed, and the blower 10 sucks air containing dust therein, and the dust is removed by the bag filter 11 and the HEPA filter 12. Filtered. Part of the air is used as air for classification in the classifier 5.

Next, a method for decontaminating radioactive metal waste of the present invention using the above apparatus will be described. First, radioactive metal waste W is supplied from the metal waste supply container 2 into the barrel 1. It is assumed that the surface contamination density is, for example, 80 Bq / cm ² and is classified as highly contaminated waste. By agitating the radioactive metal waste W by rotating the barrel 1 slowly, the abrasive is projected from the abrasive projector 3 to perform drive-last decontamination. Since the abrasive is contaminated by contact with the highly contaminated waste, it is returned to the hopper 9 of the abrasive projector 3 via the highly contaminated abrasive conveyor 7 and is circulated.

[0011] When such dry blast decontamination is continued for a predetermined time, the surface layer of the radioactive metal waste W is gradually peeled off together with the attached radioactive material, and its surface contamination density is, for example, about 4 Bq / cm ² (DF = 20). In addition, since the inner surface of the barrel 1 is also decontaminated by the projection of the abrasive, the surface contamination density of the barrel 1 is reduced by the radioactive metal waste W.
Similarly to the above, it is, for example, about 4 Bq / cm ² .

Next, a new abrasive is supplied to the hopper 9,
Similarly, drive-last decontamination is performed while rotating the barrel 1 slowly. At this time, the abrasive is circulated through the low-contamination abrasive conveyor 8 and reused. As a result, the surface contamination density of the radioactive metal waste W is reduced to, for example, about 0.2 Bq / cm ² (DF = 20), so that the processed radioactive metal waste W is taken out of the barrel 1 into the collection container 13.

In the first embodiment described above, a high-contamination abrasive and a low-contamination abrasive are selectively used. This is because abrasives projected on highly contaminated waste are contaminated into highly contaminated abrasives, and the radioactive concentration of the abrasives reaches a certain level and does not decrease below that level. It is a method according to the conventional common sense that it must be exchanged with.

However, in the second embodiment shown in FIG. 2, the highly contaminated abrasive is circulated several tens of times by a single abrasive conveyor 7a. As described above, when the highly contaminated abrasive at the start of decontamination is repeatedly projected on the radioactive metal waste W in the barrel 1, the radioactivity concentration of the abrasive gradually decreases as shown in FIG. .

When the highly contaminated abrasive is circulated, for example, about 45 times by the apparatus shown in FIG. 2, the radioactivity concentration of the abrasive is reduced to 1 Bq / g or less as shown in FIG. . As a result, as shown in the graph of FIG. 4, the attained surface contamination density of the radioactive metal waste W by this low-contamination abrasive decreases to about 1 Bq / cm ² . As shown in FIG. 2, if the radioactivity concentration detector 14 for the abrasive is provided in the circulation path of the abrasive and the decontamination is performed while monitoring the radioactivity concentration of the circulating abrasive, more accurate control can be achieved. It can be performed. Further, as shown in FIG.
It is more preferable if a detector 15 for detecting the concentration of radioactivity in dust is provided in an exhaust system connecting the apparatus 11 with the apparatus so that completion of decontamination can be confirmed. Needless to say, the radioactivity concentration detector 14 of these abrasives and the radioactivity concentration detector 15 in dust can be similarly incorporated into the apparatus shown in FIG. 1 and used.

[0016]

As described above, according to the method for decontaminating radioactive metal waste according to the present invention, the abrasive is projected onto the surface of the radioactive metal waste while stirring the radioactive metal waste inside the barrel, and the drylasting is performed. Since decontamination is performed, the entire surface of the radioactive metal waste can be uniformly decontaminated. Also, since the inner surface of the barrel is always decontaminated by the abrasive, the low-contamination waste is reverse-contaminated by the barrel even when processing low-contamination waste after processing high-contamination waste. However, it is also possible to adopt a method in which a highly-contaminated abrasive is recycled until it becomes a low-contaminated abrasive. Therefore, the present invention is extremely valuable as a decontamination method suitable for treating relatively small radioactive metal waste such as a piece of piping discarded from a nuclear power plant or the like.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing a first embodiment of the present invention.

FIG. 2 is a flow sheet showing a second embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the number of circulations of an abrasive and its radioactivity concentration.

FIG. 4 is a graph showing the relationship between the radioactivity concentration of an abrasive and the surface contamination density of radioactive metal waste.

FIG. 5 is a flow sheet showing a conventional example.

[Explanation of symbols]

1 barrel, 2 metal waste supply container, 3 abrasive projectile, 4 impeller, 5 classifier, 6 dust box, 7 high-contamination abrasive conveyor, 7a abrasive conveyor,
8 Low-contamination abrasive conveyor, 9 Hopper, 10 blower, 11 Bag filter, 12 HEPA filter, 13 Collection container, 14 Radioactivity concentration detector, 15 Radioactivity concentration detector

Claims (6)

(57) [Claims] 1. A housing a radioactive metal waste in the interior of the barrel, the abrasive is projected onto the surface while stirring the radioactive metal wastes by rotating the barrel to the projection grinding
Take out the material, classify it, and circulate abrasive material of a specified particle size or more.
Of radioactive metal waste for dry blast decontamination
A high-contamination project
Dyeing Abrasive Circulation Pathway and Projected on Low Pollution Waste
Separate the circulation path for low-contamination abrasives and dispose of high-contamination abrasives
For high-contamination abrasives and low-contamination waste projected on
To prevent mixing with low-contamination abrasives projected
Decontamination method of radioactive metal wastes, characterized by. 2. The storage of radioactive metal waste inside a barrel.
And rotate the barrel to remove radioactive metal waste.
Abrasive material is projected onto the surface while stirring, and the entire surface is
Live-last decontamination and at the same time dry the inside of the barrel
Blast decontamination and the abrasive used for this decontamination
Classify the abrasive fines and the radioactive metal waste surface layer
Separation amount is separated, and abrasive material having a predetermined particle size or more is circulated.
A method for decontamination of radioactive metal waste, characterized in that it is used for 3. A method for radiating abrasives using a radioactivity concentration detector.
While monitoring the active concentration, circulate the abrasive to
Perform blast decontamination to remove the radioactivity concentration of the abrasive used.
It is characterized by decreasing from high concentration at the start of dyeing to low concentration
The method for decontaminating radioactive metal waste according to claim 2. 4. A grinding material projector and a collected grinding material are classified into a rotating barrel containing radioactive metal waste.
The amount of separation between the abrasive powder and the surface layer of the radioactive metal waste
Provided with a classifier to separate, between the hopper of the classifier and abrasive projector, the decontamination apparatus of radioactive metal wastes, characterized in that a circulation path of the research work material. 5. The apparatus for decontaminating radioactive metal waste according to claim 4, wherein a radioactivity concentration detector for the abrasive is provided in a circulation path of the abrasive. 6. The apparatus for decontaminating radioactive metal waste according to claim 4, wherein a detector for detecting a radioactivity concentration in dust is provided in an exhaust system from the barrel.