JP2021028615A - Manufacturing method of clumpy metal substance - Google Patents

Abstract

To provide a manufacturing method of a clumpy metal substance allowing easy and accurate determination of effectiveness of use of the clumpy metal substance and efficiently providing the effectively usable clumpy metal substance, by suppressing a difference between a radioactive concentration of a sample obtained from a molten metal and the radioactive concentration of the clumpy metal substance obtained from the molten metal.SOLUTION: One embodiment of the present invention relates to a manufacturing method of a clumpy metal substance by melting metal in a nuclear power facility, and comprises the steps of: melting the metal; sampling one or more samples of the molten metal; solidifying the molten metal obtained in the melting step; measuring external radiation of the one or more samples obtained in the sampling step; and suppressing contamination and adhesion of radioactive materials in the atmosphere into the molten metal.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a bulk metal article.

Metals used in nuclear facilities with high radioactivity concentration are disposed of as waste, but some of the metals with low radioactivity concentration can be effectively used. Even if the metal is used in a nuclear facility, it can be melted to produce usable lumpy articles, and if it has a high radioactivity concentration, it becomes lumpy waste. As a method of producing a usable massive article, the metal in the crucible is melted by a high-frequency melting furnace that can be divided into an upper furnace body and a lower furnace body, and after the upper furnace body is removed and the melt is cooled and solidified. , A method for facilitating the processing work by taking out the solidified material together with the crucible with a hanging tool from the lower furnace body and moving it to a predetermined position has been proposed (Japanese Patent Laid-Open No. 60-172300).

Among the massive metal articles obtained by the above method, those having a low radioactivity concentration may be effectively used, and if the effective utilization amount can be increased, the amount of waste can be relatively reduced. Therefore, it is important to measure the radioactivity concentration of the massive metal article and determine whether or not it can be effectively used. Therefore, it is conceivable to adopt a method of measuring the radiation emitted from the metal before melting to the outside using a radiation measuring instrument and evaluating the radioactivity concentration of the above-mentioned massive metal article from the measurement result.

Japanese Unexamined Patent Publication No. 60-172300

However, for example, when a nuclear power plant is decommissioned, a large amount of metal to be processed is generated. Therefore, the above method for measuring the radiation of individual metals makes the radioactivity concentration of the massive metal article efficient. It may not be evaluated well. As a more efficient method, the metal is melted, and the radiation emitted to the outside of the sample collected from the melt is measured by using a radiation measuring instrument to radiate the metal article in which the melt is agglomerated. It is also conceivable to adopt a method for evaluating the ability concentration. According to this method, the number of objects to be measured can be reduced, but when the radioactive substance suspended in the space is mixed in the melt after the sample is collected, the radioactivity evaluated by measuring the external radiation from the sample. There is a problem that the difference between the concentration and the radioactivity concentration of the metal article in which the melt is agglomerated becomes large.

In view of the above circumstances, the present invention eliminates or suppresses the difference between the radioactivity concentration of the sample obtained from the molten metal and the radioactivity concentration of the massive metal article obtained from the molten metal. An object of the present invention is to provide a method for producing a lump metal article, which makes it easy and reliable to determine whether or not the lump metal article can be effectively used, and can efficiently obtain a lump metal article that can be effectively used.

One aspect of the present invention made to solve the above problems is a method of melting a metal in a nuclear facility to produce a massive metal article, which comprises a step of melting the metal and one of the molten metal or one of the molten metal. It includes a step of collecting a plurality of samples and a step of solidifying the molten metal obtained in the above-mentioned melting step, and a step of measuring external radiation of one or a plurality of samples obtained in the above-mentioned collecting step, and the above-mentioned molten metal. Further provided with a step of suppressing the mixing and adhesion of radioactive substances in the space to the space.

The method for producing the bulk metal article can eliminate or suppress the difference between the radioactivity concentration of the sample obtained from the molten metal and the radioactivity concentration of the bulk metal article obtained by solidifying the molten metal. Therefore, it is possible to easily and surely determine whether or not the lump metal article can be effectively used, and it is possible to efficiently obtain the lump metal article that can be effectively used. The magnitude of radioactivity contained in the object is indicated by becquerel (Bq). The radioactivity concentration referred to here is the amount of radioactivity of a radioisotope in a metal waste having a unit mass, and the unit is [Bq / g] as an example.

It is a flowchart which shows the manufacturing method of the lump metal which is one aspect of this invention. It is a conceptual side view which shows the state of the melting process of FIG. It is a conceptual side view which shows the state of the melting process different from FIG. It is a conceptual side view which shows the state of the melting process different from FIGS. 2 and 3. It is a conceptual side view which shows the state of the melting process different from FIGS. 2, 3 and 4. It is a conceptual side view which shows the state of the solidification process of FIG. It is a conceptual side view which shows the state of the solidification process different from FIG. It is a conceptual side view which shows the state of the solidification process different from FIGS. 6 and 7.

Hereinafter, a method for producing a massive metal article, which is one aspect of the present invention, will be described in detail.

[Manufacturing method of massive metal articles]
As shown in FIG. 1, the method for producing a lump metal article, which is one aspect of the present invention, is a method for producing a lump metal article by melting a metal in a nuclear facility, and is a step of melting the metal. A step of collecting one or more samples of the molten metal and a step of solidifying the molten metal obtained in the melting step are provided, and external radiation of the one or a plurality of samples obtained in the collecting step is emitted. The step of measuring and the step of suppressing the mixing and adhesion of radioactive substances in the space to the molten metal are further provided. The lumpy metal article is manufactured in the nuclear facility and effectively used outside the nuclear facility.

(metal)
The metal used in the method for producing the lump metal article is a metal used in a nuclear facility and may be contaminated by adhesion of radioactive substances or the like. Examples include equipment, piping, valves, wiring, support structures, reinforcing bars, steel frames, and the like. Examples of the radioactive substance to be attached include radionuclides such as radioactive cobalt, radioactive cesium, and radioactive strontium.

<Melting process>
The melting step melts the metal in a furnace. As shown in FIG. 2, the melting step includes a step of separating and cutting the metal in the nuclear facility accumulated in a predetermined place and storing it in the storage area P in preparation for melting the metal 1, and as shown in FIG. Includes a step of melting the stored metal 1 and transporting the stored metal 1 to a processing area R for producing a massive metal article and charging the stored metal 1 into the furnace 3.

(Storage process)
In the storage process, the metals accumulated in a predetermined place are sorted and cut for each type of metal and stored in a storage area. The separated metal 1 is cut into a size that can be put into the furnace 3 and stored in the container 2. The container 2 is transported to the storage area P by a forklift L or the like.

(Input process)
In the charging step, the stored metal is transported to the processing area R and charged into the furnace 3. Specifically, the container 2 stored in the storage area P is transported to the processing area R in which the furnace 3 is installed, the container 2 is opened, and the metal 1 is lifted by the overhead crane 4 to lift the metal 1 in the furnace 3. Put it in.

The metal 1 is melted while being charged into the furnace 3. When the charge of the metal 1 reaches a predetermined amount, the charge is stopped, and the molten metal H is sampled in the sampling step described later while continuing the melting. As shown in FIG. 4, the melting is preferably performed while appropriately checking the state. Specifically, it is preferable to melt while checking the melting temperature, the melting state of the input material, and the like.

(Fire pot)
The furnace used in the melting step may be an electric furnace or the like, but a high frequency induction furnace is preferable. Since the high-frequency induction furnace has an excellent ability to agitate the molten metal H in the furnace 3 as compared with an electric furnace or the like, the molten metal H can be homogenized. If the molten metal H can be homogenized, the representativeness of the sample measured in the measurement step described later can be increased.

The furnace 3 has a lid 5 that covers the opening. By having the lid 5, it is possible to prevent radioactive substances in the space from entering the furnace 3. In order to effectively suppress the ingress of radioactive substances, the lid 5 is opened only when necessary, such as when the metal 1 is put in and the above-mentioned molten state is confirmed, and otherwise it is closed as shown in FIG. preferable.

Further, it is preferable that the furnace 3 further includes a ring hood 7. When the metal 1 is charged into the furnace 3, the metal 1 being charged is brought into contact with the molten metal H and is rapidly heated, so that the radioactive material adhering to the metal 1 is easily transferred to the space. At this time, since the lid 5 is in the open state, the radioactive material that has migrated to the space may further migrate to the surrounding equipment, the floor, the ceiling, and the surface of the wall and adhere to it. If these deposits are later peeled off and mixed into the molten metal H again via the space, the radioactivity concentration of the molten metal H may increase. Further, if the invasion of the deposits is after collecting the sample of the molten metal H, the radioactivity concentration evaluated by measuring the external radiation from the sample and the radioactivity concentration of the massive metal article obtained from the molten metal H The difference may be large. Therefore, by arranging the ring hood 7 at the mouth of the furnace 3, the radioactive material migrating from the furnace 3 to the space is recovered to prevent the radioactive material from migrating and adhering to the surroundings, and as a result, the surrounding radioactive material is prevented. It is possible to prevent the substance from being mixed into the molten metal H in the furnace 3.

<Collection process>
In the sampling step, one or more samples of the molten metal H are sampled. Specifically, a part of the molten metal H in which all of the metal 1 charged into the furnace 3 is melted and the molten state is substantially uniform is collected as a sample.

<Coagulation process>
In the solidification step, the molten metal H is solidified. In this embodiment, as shown in FIGS. 6 to 8, the solidification step includes a step of temporarily discharging the molten metal H of the furnace 3 into the ladle 8 and a step of pouring the molten metal H from the ladle 8 into the mold 10. It will be described as a process.

(Hot water discharge process)
In the hot water discharge process, the molten metal H is discharged from the furnace 3 to the ladle 8. Specifically, it is as follows. Preheat the inside of the prepared ladle 8 with a gas burner or the like. The opening of the preheated ladle 8 is closed with the ladle lid 9 and moved to the furnace 3 (FIG. 6). The lid 5 of the furnace 3 and the ladle lid 9 of the ladle 8 are opened, and the furnace 3 is tilted to discharge the molten metal H into the ladle 8 (FIG. 7). The lid 5 of the furnace 3 and the ladle lid 9 of the ladle 8 are closed, and the ladle 8 is moved to the mold pouring place. The furnace 3 initiates the next melting step or prepares to start the next melting step.

(Pouring process)
In the hot water pouring step, the molten metal H discharged from the ladle 8 is poured into the mold 10 (FIG. 8). Specifically, it is as follows. The ladle 8 moved to the mold pouring place is tilted, and the molten metal H is poured into the prepared mold 10. It is preferable that at least the opening of the prepared mold 10 is covered with a sheet 11 or the like until just before pouring. By covering at least the opening of the mold 10 with the sheet 11 or the like, it is possible to prevent radioactive substances in the space from entering the mold 10 before pouring.

The ladle 8 is preferably capable of pouring hot water with the ladle lid 9 closed. By pouring hot water with the ladle lid 9 closed, it is possible to prevent radioactive substances in the space from being mixed into the ladle 8.

It is preferable to place a dust collector (not shown) to pour hot water into the mold 10. It is more preferable that the dust collector has a local hood 12, and the local hood 12 is placed close to the pan 8 and the mold 10 to pour hot water into the mold 10. By doing so, it is possible to prevent radioactive substances in the space from being mixed into the mold 10.

After the completion of pouring into the mold 10, it is preferable to immediately close the opening of the mold 10 with the mold lid 13 and keep the opening closed until the solidification of the molten metal H is completed. By doing so, it is possible to prevent radioactive substances in the space from being mixed into the molten metal H that solidifies. Further, it is preferable that the dust collector or the local hood 12 thereof is placed close to the mold 10 to solidify it. By doing so, it is possible to further suppress the mixing and adhesion of radioactive substances in the space into the solidified molten metal H.

By cooling the poured mold 10 for a predetermined time, the molten metal H in the mold 10 solidifies. After the lapse of the predetermined time, the solidified molten metal H is taken out from the mold 10 as an ingot to obtain a lump metal article. Since the radioactivity concentration of the lump metal article is substantially the same as the radioactivity concentration obtained from the measurement of the external radiation of the sample in the measurement step described later, it is not necessary to measure the radioactivity concentration of the lump metal article metal.

<Sample measurement process>
In the sample measurement step, the external radiation of one or more samples obtained in the above sampling step is measured. The sample measurement can be performed at any time after the sample is collected. For example, the sample may be measured immediately after the sample is collected and after the molten metal H has solidified. Specifically, in the sample measurement step, the external radiation of the sample collected from the molten metal H in the above collection step is measured, and the radioactivity concentration of the sample is estimated from the result. This estimated value can be substantially the same as the radioactivity concentration of the massive metal article obtained from the molten metal H, unless a radioactive substance is mixed in the molten metal H after obtaining the sample. That is, the representative system of the sample can be ensured by controlling the radioactive substance in the space from the sampling to the acquisition of the massive metal article and suppressing the radioactive substance from being mixed into the molten metal H or the like.

Whether or not the massive metal article can be effectively used is determined based on the measured value of the sample measured by a radiation measuring device or the radioactivity concentration of the sample estimated from the measured value.

<Suppression process>
The suppressing step suppresses the mixing and adhesion of radioactive substances in the space to the molten metal. That is, the suppressing steps include melting in the furnace 3, discharging the molten metal H from the furnace 3 to the ladle 8, injecting the molten metal H from the ladle 8 into the mold 10, solidifying the molten metal H in the mold 10, and solidifying from the mold 10. Until the molten metal H is taken out, the mixing and adhesion of radioactive substances in the space in the treatment area R are suppressed.

Specifically, as means for suppressing the mixing and adhesion of radioactive substances in the space, each of the furnace 3, the ladle 8 and the mold 10 is provided with a lid, the furnace 3 is provided with a ring hood 7, and before pouring. The mold 10 of the above is covered with a sheet 11, and a dust collector or a local hood 12 thereof is appropriately arranged.

In addition to the above-mentioned suppressing means, it is preferable that the suppressing step includes a step of constantly ventilating the room where the melting step and the solidifying step are performed, and a step of measuring the radioactivity concentration in the space of the room. That is, regardless of each step in progress, the inside of the treatment area R is constantly ventilated, the retention of radioactivity in the air in the space inside the treatment area R is suppressed, and the radioactivity concentration in the air is measured. , It is preferable to keep the radioactivity concentration in the air low.

(Ventilation process)
In the ventilation step, the room where the melting step and the solidifying step are performed is constantly ventilated. That is, in order to prevent radioactive substances existing in the air in the treatment area R from migrating to the molten metal H or adhering to the inside of the furnace 3, the inside of the ladle 8, the inside of the mold 10, the massive metal article, or the like. It is preferable to constantly ventilate the inside of the treatment area R.

As a method of ventilating the inside of the treatment area R, for example, an intake port and an exhaust port are provided in the treatment area R, clean air is taken into the treatment area R from the suction port, and the air passing through the treatment area R is taken in. A method of taking out from the discharge port can be adopted. By such a method, the air in the treatment area R can be replaced with clean air to reduce the concentration of radioactive substances in the air.

(Indoor measurement process)
The indoor measurement step measures the radioactivity concentration in the indoor space. That is, the radioactivity concentration in the air in the space in the treatment area R is measured. The method for controlling the radioactivity concentration in the air is not particularly limited, but a method for constantly monitoring the radioactivity measuring device or the like installed in the treatment area R can be adopted.

[advantage]
In the method for producing the lump metal article, management is performed so as to prevent radioactive substances from being mixed and adhered to the molten metal or the like in the space of the room where the lump metal article is produced. Therefore, the radioactivity concentration obtained from the measurement of the external radiation of the sample collected from the molten metal can be made substantially the same as the radioactivity concentration of the massive metal article, and the massive metal article that can be effectively used can be efficiently obtained. Can be done.

That is, the furnace 3 has a lid 5 and a ring hood 7, the ladle 8 has a ladle lid 9, and the mold 10 has a mold lid 13, and the mold 10 before pouring is covered with a sheet 11. 3. It is managed so that radioactive substances in the space can be suppressed from being mixed and adhered to the ladle 8, the mold 10, the mold 10 before pouring, and the molten metal H contained therein. In addition, the dust collector or its local hood 12 moves from the molten metal H into the space, or collects radioactive substances mixed in the molten metal H or the like from the space, so that the amount of radioactive substances in the room increases and the radioactive substances increase. Manage so that contamination and adhesion can be suppressed. Further, in the method for manufacturing the massive metal article, the room is constantly ventilated to reduce the radioactive substances in the space in the room, the concentration of the radioactive substances in the room is measured, and the state of the radioactive substances in the space in the room is determined. to manage. Therefore, it is possible to effectively suppress the mixing and adhesion of radioactive substances in the space to the molten metal H and the like, and the radioactivity concentration obtained from the measurement of the external radiation of the sample collected from the molten metal H is the radiation of the massive metal article. It can be a high concentration and the representativeness of the sample is guaranteed.

Further, since the homogeneity of the molten metal H in the furnace 3 can be achieved by using the high frequency guide path having excellent stirring power of the molten metal, the radioactivity obtained from the measurement of the external radiation of the sample collected from the molten metal H. The identity between the concentration and the radioactivity concentration of the metal article can be further improved, and the representativeness of the sample can be further ensured.

[Other Embodiments]
It should be considered that the disclosed embodiments are exemplary in all respects and not restrictive. The scope of the present invention is not limited to the configuration of the above embodiment, but is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. To.

1 Metal 2 Container 3 Furnace 4 Overhead Crane 5 Lid 7 Ring Hood 8 Ladle 9 Ladle Lid 10 Mold 11 Sheet 12 Local Hood 13 Mold Lid H Molten L L Forklift P Storage Area R Processing Area

Claims (3)

A method of melting metal in a nuclear facility to produce massive metal articles.
The process of melting the metal and
The step of collecting one or more samples of the molten metal and
It is equipped with a step of solidifying the molten metal obtained in the above melting step.
The step of measuring the external radiation of one or more samples obtained in the above sampling step, and
A method for producing a massive metal article further comprising a step of suppressing mixing and adhesion of radioactive substances in the space to the molten metal. The above suppression step
A step of constantly ventilating the room where the melting step and the solidifying step are performed, and
The method for producing a massive metal article according to claim 1, further comprising a step of measuring the radioactivity concentration in the indoor space. The method for producing a massive metal article according to claim 1 or 2, wherein the furnace used in the melting step is a high-frequency induction furnace.

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