JP2017116468A - Decontamination method for iron containing radioactive cesium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination method for iron containing radioactive cesium, allowing the radioactive cesium to be separated from the iron.SOLUTION: [1] The decontamination method for iron containing radioactive cesium is provided in which an iron material containing the radioactive cesium is mixed with coke and heated in a furnace, the radioactive cesium is vaporized from steel slag melted in the furnace under a reduction atmosphere, and the radioactive cesium exhausted to the outside of the furnace is cooled and collected. [2] The decontamination method for iron containing radioactive cesium is provided which is identical to the method described in the [1] except that coal is charged into the furnace and heated. [3] The decontamination method for iron containing radioactive cesium is provided which is identical to the method described in the [1] or [2] except that a temperature in the furnace is 1500°C or higher. [4] The decontamination method for iron containing radioactive cesium is provided which is identical to the method described in any of [1] to [3] except that 20-30 pts.mass of the coke is mixed with 100 pts.mass of the iron material.SELECTED DRAWING: None

Description

  The present invention relates to a method for purifying iron containing radioactive cesium.

  The contaminated water generated at nuclear power plants contains radioactive cesium. As a current response to the contaminated water, the contaminated water is temporarily stored in an iron tank. After treating the contaminated water, an iron tank with radioactive cesium attached to the inner wall surface remains. Since iron tanks where very high doses are observed cannot be used for other purposes, they are being considered for disposal. However, since iron is not activated, if it is possible to separate a small amount of radioactive cesium from iron, it is not necessary to treat iron as radioactive waste, and it can be treated as general waste.

  As a method of decontaminating the surface of the iron plate, a method of suspending the surface of the iron plate constituting the inner wall surface of the tank (scraping the surface) has been studied. However, since dust generated by fishing contains radioactive cesium, dust scattering can be a problem.

  For radioactive cesium adhering to concrete, soil, etc., a chlorination volatilization method is disclosed in which it is volatilized as cesium chloride and recovered in fly ash by melting at high temperature in the presence of chlorine and separated from molten slag. (Patent Documents 1 and 2). However, since iron becomes a chloride and volatilizes in the same manner as cesium and moves to the gas side, it is difficult to separate radioactive cesium from iron even if a conventional chlorination volatilization method is applied.

JP 2013-120136 A JP2013-134085A

  This invention is made | formed in view of the said situation, and provides the purification method of the iron containing radioactive cesium which can isolate | separate radioactive cesium from iron.

In order to achieve the above object, the present invention provides the following means.
[1] Iron material containing radioactive cesium and coke are mixed and heated in a furnace, the radioactive cesium is vaporized from steel slag melted in a reducing atmosphere furnace, and the radioactive cesium exhausted outside the furnace is cooled. A method for purifying iron containing radioactive cesium, wherein
[2] The method for purifying iron containing radioactive cesium according to [1], wherein lime is charged into the furnace and heated.
[3] The method for purifying iron containing radioactive cesium according to [1] or [2], wherein the temperature in the furnace is 1500 ° C. or higher.
[4] The method for purifying iron containing radioactive cesium according to any one of [1] to [3], wherein 20 to 30 parts by mass of coke is mixed with 100 parts by mass of the iron material. .
[5] The method for purifying iron containing radioactive cesium according to any one of [1] to [4], wherein chlorine is not introduced into the furnace.

  According to the method for purifying iron containing radioactive cesium according to the present invention, radioactive cesium can be separated from iron. Molten slag containing iron from which radioactive cesium has been removed can be treated as general waste. Since the removed radioactive cesium is recovered as a relatively small amount of fly ash, the volume of radioactive waste can be reduced.

It is a schematic diagram which shows an example of the purification method of iron containing the radioactive cesium concerning this invention.

  1st embodiment of the purification method of iron containing the radioactive cesium concerning this invention has the following heating processes, a collection process, and a solidification process. Details of each step will be described below, but steps or processes other than these steps may be included.

<Heating process>
The heating process of this embodiment is a process of mixing the iron material containing radioactive cesium and coke and heating in a furnace. The inside of the furnace can be made a reducing atmosphere by heating the iron material together with the coke.

The temperature at which the mixture of iron material and coke is heated is not particularly limited as long as it is equal to or higher than the temperature at which the iron material melts, and usually 1500 ° C. or higher, which is close to the melting point of iron 1538 ° C., is preferable. Even if the iron material contains iron oxide, it becomes iron in a reducing atmosphere and can be melted at about 1500 ° C. In order to lower the melting point of iron, it is preferable to add lime and heat.
The melting point of triiron tetroxide that forms an oxide film on the surface of iron is 1597 ° C.

The boiling point of cesium alone is 670 ° C, the boiling point of cesium hydroxide is 990 ° C, and the boiling point of cesium chloride is 1295 ° C. Can do.
The upper limit of the heating temperature is preferably not more than the boiling point of iron of 2862 ° C., and more preferably, for example, about 1700 ° C. to 2000 ° C. in consideration of the durability of the heating furnace.

  The time for heating at the above temperature is not particularly limited and is appropriately set according to the amount of the iron material. For example, from the viewpoint of sufficiently vaporizing the radioactive cesium, the molten state is continued for about 0.5 hours to 3 hours. It is preferable to heat it.

  In the heating process of the present embodiment, unlike the conventional chlorination volatilization method, it is preferable not to introduce chlorine into the furnace. When chlorine is introduced, a large amount of iron chloride is formed together with cesium chloride. Since the boiling point of iron (II) chloride is 677 ° C. and the boiling point of iron (III) chloride is 351 ° C., iron chloride volatilizes together with cesium chloride (boiling point 1295 ° C.), and iron and cesium are separated. It becomes difficult.

As a mixing ratio of the iron material and coke heated in the furnace, for example, 5 to 80 parts by mass of coke is preferable with respect to 100 parts by mass of the iron material, and 10 to 50 parts by mass of coke is more preferable. More preferred are parts by mass of coke.
Within the above range, the inside of the furnace can be sufficiently reduced and iron oxide can be reduced to iron and sufficiently melted.

As a mixing ratio in the case of mixing lime with the iron material and coke heated in the furnace, for example, 5 to 80 parts by mass of lime is preferable with respect to 100 parts by mass of the iron material, and 10 to 50 parts by mass of lime. More preferably, 20-30 mass parts lime is further more preferable.
Within the above range, the melting point of the iron material can be lowered and the heating temperature required for melting can be set low.

  The iron material to be put into the furnace is preferably in a state of being roughly (roughly) cut in advance before heating. Since melting by heating becomes easy and mixing with coke and lime becomes easy, vaporization of radioactive cesium can be promoted.

  The furnace that heats and melts the iron material is more preferably a closed type furnace that melts the iron material in a reducing atmosphere and collects vaporized radioactive cesium and exhaust ash. An example of such a furnace is a coke bed type melting furnace.

<Collection process>
The collection step of the present embodiment is a step of vaporizing radioactive cesium from a molten iron material and cooling and collecting the radioactive cesium exhausted outside the furnace.

  Volatilized radioactive cesium is discharged outside the furnace by the combustion gas in the furnace. The exhaust gas containing the discharged radioactive cesium is cooled on the exhaust path. It is preferable to collect the condensed or solidified radioactive cesium with a predetermined collector installed on the exhaust path. Examples of the collector include known dust collectors such as a bag filter and a ceramic filter. A pre-stage of a known dust collector is often provided with a cooling mechanism for cooling high-temperature exhaust gas to about 200 ° C., for example. Such a cooling mechanism is also useful in this embodiment. The collected radioactive cesium is disposed of by a publicly known method in accordance with laws and regulations.

<Solidification process>
The solidification process of this embodiment is a process of cooling the molten iron material to obtain a solidified molten slag. By sufficiently heating and melting, the molten slag can be processed to such an extent that radioactive cesium is not substantially contained. The obtained molten slag is disposed of by a known method in accordance with laws and regulations. This disposal method includes reuse.

  An outline of the purification method of the present embodiment is shown in FIG. An iron material (for example, an iron plate) contaminated with radioactive cesium is roughly cut, mixed with an appropriate amount of coke and lime, and charged into the heating furnace 10. Air is supplied into the furnace and heated to about 1500 ° C. to melt the iron material. The radioactive cesium vaporizes during heating for several hours. The radioactive cesium gas is exhausted to the outside of the furnace and collected by the bag filter 12. Exhaust gas from which radioactive cesium has been removed is released into the atmosphere. Thereafter, the molten slag is discharged out of the furnace.

10 g of waste incineration ash containing cesium and iron was heated in a reducing atmosphere at 1500 ° C. for 30 minutes, and then slowly cooled to obtain treated incineration ash (slag).
When the amount of each element of cesium and iron contained in incineration ash and treated incineration ash was measured by ICP-MS made by Agilent, about 85% of the cesium contained in the incineration ash before heating was about 85%. It was removed from the incineration ash, and about 15% of cesium remained in the treated incineration ash. On the other hand, it was found that most of the iron remained in the treated incineration ash. This result shows that cesium was volatilized from incineration ash and separated from iron. It was confirmed separately that volatile cesium could be recovered by cooling. In this experiment, incineration ash containing cesium and iron was treated in order to carry out the experiment with a simple apparatus, but similar results are also obtained when treating iron materials containing cesium.
Therefore, it is clear that when the iron material containing radioactive cesium is treated by the method of the present invention, the volatilized radioactive cesium is cooled and collected, and a molten slag having a sufficiently reduced radioactivity can be obtained.

  The configurations and combinations thereof in the embodiments described above are examples, and additions, omissions, substitutions, and other modifications of known configurations are possible without departing from the spirit of the present invention.

  The present invention can be widely applied in the field of handling radioactive cesium.

10 ... heating furnace, 12 ... bag filter

Claims (5)

  Iron material containing radioactive cesium and coke are mixed and heated in a furnace, the radioactive cesium is vaporized from the iron material melted in a reducing atmosphere furnace, and the radioactive cesium exhausted outside the furnace is cooled and collected A method for purifying iron containing radioactive cesium, comprising:   The method for purifying iron containing radioactive cesium according to claim 1, wherein lime is charged into the furnace and heated.   The method for purifying iron containing radioactive cesium according to claim 1 or 2, wherein the temperature in the furnace is 1500 ° C or higher.   The method for purifying iron containing radioactive cesium according to any one of claims 1 to 3, wherein 20 to 30 parts by mass of coke is mixed with 100 parts by mass of the iron material.   The method for purifying iron containing radioactive cesium according to any one of claims 1 to 4, wherein chlorine is not introduced into the furnace.

Images