JPH02263199A - Radioactive iodine removing material - Google Patents

Abstract

PURPOSE:To increase the amt. of carbon to be attached to a radioactive iodine removing agent and to reduce the cost of the above material by attaching the radioactive iodine removing agent to the microbodies of optically anisotropic porous carbon. CONSTITUTION:An active carbon layer filter 2 is constituted by superposing filters formed by attaching the radioactive iodine removing agent, such as potassium iodide KI and triethylene diamine TEDA, to the radioactive iodine removing material in multiple stages. The dust contained in the raw gas discharged from an atomic reactor, etc., is removed by a dust removing filter 1 in such constitution and thereafter, the raw gas after the dust removal is passed through the active carbon layer filter 2 to remove radioactive methyl iodide 127-CH3<127>I, 131-CH3<131>I from the raw gas after the dust removal; thereafter, the gas is released from a discharge cylinder (not shown) into the atm.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention uses radioactive iodine, particularly radioactive methyl iodide-12"1CH3, in air conditioning systems of facilities that handle radioactive materials, such as nuclear power plants. This invention relates to a radioactive iodine removal material used in an activated carbon layer filter that adsorbs and removes "7I" and radioactive methyl iodide-131CH31"l I.

<Prior Art> As this type of radioactive iodine removal material, the following are generally known.

(A) First conventional example Iodizing power IJ reacts with radioactive iodine on ordinary activated carbon
A radioactive iodine removing agent such as K I is impregnated to constitute a radioactive iodine removing material.

(B) Second prior art example As shown in Japanese Patent Application Laid-Open No. 58-96299,
A radioactive iodine removing material is constructed by impregnating a radioactive iodine removing agent such as an amine that reacts with radioactive iodine to fibrous activated carbon having a specific pore distribution.

<Problems to be Solved by the Invention> However, the first and second conventional examples described above each have the following drawbacks.

(a) Disadvantages of the first conventional example In ordinary activated carbon, the maximum specific surface area measured by the BET method is about 1500n (/g), and the amount of radioactive iodine removing agent attached to it is small, and the use of radioactive iodine adsorbed. When disposing of used radioactive iodine removal material, the amount of radioactive iodine removal material that must be disposed of increases in proportion to the amount of radioactive iodine adsorbed, which increases the bulk of the waste and increases the cost required for processing. was there.

(b) Disadvantages of the second conventional example Although the breakthrough time of radioactive iodine can be lengthened and the amount of radioactive iodine removal agent impregnated can be increased, purified cellulose fibers such as regenerated cellulose fibers, purified cotton fibers and wood pulp fibers, Fibrous activated carbon must be manufactured using purified raw materials with low ash content, such as hardened phenolic resin fibers and polyacrylonitrile fibers, and the yield during activation is low, making it expensive to manufacture. There was a drawback.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radioactive iodine removing material that can increase the amount of impregnated radioactive iodine removing agent, has a high yield, and is inexpensive.

<Means for Solving the Problems> In order to achieve the object -F, the radioactive iodine removal material of the present invention contains 90% or more of particles with a particle size of 80 μm or less and has a specific surface area of 1000 to 5000 n(/g). So, and
The total volume of pores with a pore diameter of 300 Å or less is 0.8 to 3. O
ml/g and a pore diameter of 20 for the total volume.
A radioactive iodine removing agent is attached to optically anisotropic porous carbon microspheres in which the volume of ~300 pores accounts for 10% or more.

As the porous carbon microspheres, activated mesocarbon microbeads are used, for example.

In recent years, during the development of needle coke carbon fiber using pitch as a raw material, during the process of heating petroleum-based and coal-based pitch, spherulites with six-membered carbon ring network planes stacked parallel to each other appeared in the pitch. has been found. This spherulite forms a phase different from that of the matrix pinch, and is isolated by an antisorgent method, a centrifugation method, or the like. The isolated spherulites are called mesocarbon microbeads, which are microspheres with a diameter of 1 to 80 μm and have an optically anisotropic porous structure.

As a result of extensive research, we found that when the above mesocarbon microbeads are activated, as detailed below,
It has been found that activated carbon, ie, optically anisotropic porous carbon microspheres, can be obtained that has completely new shapes and properties compared to ordinary activated carbon and activated carbon fibers.

In the above activation treatment, the mesocarbon microbeads may be activated as they are, or the mesocarbon microbeads may be activated after applying an appropriate activation aid to the surface.

As activation aids, KOH, NaOH, CsOH, Zn
C1,,H3P0. ,Ni,So,,K.

Examples include S, and at least one of these may be used. The amount of the activation aid applied is preferably 1 to 10 times the weight of the mesocarbon microbeads.

It is presumed that such an activation aid promotes the oxidation of carbon in mesocarbon microbeads. That is,
It is presumed that the activation aid reacts with the carbon atoms on the six-membered carbon ring network constituting the mesocarbon microbeads, converting this into carbon oxide or carbon dioxide, and discharging it out of the system.

Since the degree of activation is approximately proportional to the amount of the activation aid applied, it is possible to adjust the specific surface area of the optically anisotropic porous carbon microspheres by adjusting the amount applied.

Note that when using an activation aid that is solid at room temperature, such as KOH, it is used in the form of an aqueous solution, but when using an activation aid that is liquid at room temperature, such as H3PO4, it is not necessary to make it into an aqueous solution. Not particularly.

Furthermore, in order to improve the wettability of the activation aid to the surface of the mesocarbon microbeads, acetone, methyl alcohol, 5-ethyl alcohol, or the like may be used in combination as a surfactant. The amount of the surfactant used is usually preferably about 5 to 10% by weight of the total weight of the mesocarbon microbeads and the activation aid or the solution containing the activation aid.

The activation treatment is performed by heating mesocarbon microbeads with or without an activation aid added to 400 to 1200°C.

Although there are no particular limitations on the temperature increase rate and heating holding time, usually, after reaching the above temperature range, it is immediately cooled or held in the above temperature range for a maximum of about 3 hours.

The atmosphere during activation may be an inert atmosphere such as nitrogen or argon, or an oxidizing atmosphere containing water vapor, carbon oxide, oxygen, etc.; It is preferable to activate by.

When activation is performed in an inert atmosphere, an activation aid is used and the temperature is usually raised to a temperature of about 400 to 1200°C for 30°C.
It is preferable to heat at a rate of temperature increase of about 0 to 600°C/hour and maintain the temperature at the same temperature for about 30 to 60 minutes.

When activation is performed in an oxidizing atmosphere, an activation aid is usually not required, but it may be used in combination. When an activation aid is not used, the temperature is usually about 600 to 900°C, and when an activation aid is used, the temperature is usually
Up to a temperature of about 400 to 900°C, each from 300 to
It is preferable to heat at a temperature increase rate of about 600° C./hour and hold the temperature at the same temperature for about 2 to 3 hours. Note that when using an activation aid, care must be taken as bumping may occur.

In addition, there is an optimum activation temperature for each activation aid, for example, K
80 for OH, 2SO4 and S, respectively.
0-1000°C, approximately 600°C for each of NaOH and CsOH, 4 for ZnC1z
The temperature is about 50°C.

After the activation treatment, the mesocarbon microbeads are cooled to room temperature, and the unreacted activation aid and activation aid reactant are removed by water washing, and then dried to form an optically anisotropic porous structure. It becomes carbon microspheres.

Note that the reaction between the activation aid and carbon proceeds very violently, so if you use ordinary carbon fibers instead of mesocarbon microbeads and perform the same activation as above, the shape will be so strong that it will not retain its original shape. and the strength is significantly reduced. On the other hand, in the case of mesocarbon microbeads, their spherical shape is maintained even after activation, and no significant decrease in strength is observed.

The optically anisotropic porous carbon microspheres have almost the same dimensions and spherical shape as the raw material mesocarbon microbeads, and more than 90% of them have a diameter of 8.
It is 0 μm or less.

In addition, porous carbon microspheres are optically anisotropic, and the value of their specific surface area measured by the BET method is not critical, but is usually 1000 to 5000n? /g is used. When the specific surface area is less than 1000rrf/g, the pore volume decreases, while when the specific surface area is 500゜n? /
This is because if it exceeds g, the strength will decrease. Preferably,
3000 to 5 GOOn(/g).

In addition, in the porous carbon microspheres, the pore diameter is 30
The total volume of pores of 0 Å or less is 0.8 to 3.0 mQ/g, and the pore diameter is 20 to 30 mQ/g relative to the total volume.
The ratio of the volume of pores of 0 people is 10% or more.

By press-molding the optically anisotropic porous carbon microspheres obtained as described above using an appropriate binder, a layer of activated carbon with high density and high specific surface area in the form of granules, paper, fibers, etc. A radioactive iodine removing agent such as potassium iodide or an amine (tetraethylenediamine TEDA) is attached to the molded product to produce a radioactive iodine removing material.

<Function> The optically anisotropic porous carbon microspheres, for example,
By the T method, the specific surface area is up to 5000 rff/g and the pore volume is up to 3. Omρ/g, and has a much larger specific surface area and pore volume than ordinary activated carbon or activated carbon fibers, so molded products made from optically anisotropic porous carbon microspheres A radioactive iodine removal material impregnated with a radioactive iodine removing agent has an extremely large amount of radioactive iodine removing agent impregnated per unit weight, and a large amount of radioactive iodine is adsorbed to the point where it becomes necessary to dispose of it.

Furthermore, mesocarbon microbeads, which are the raw material for optically anisotropic porous carbon microspheres, have a diameter of 1 to 80 μm.
It is a microsphere with a diameter of m, and it maintains its shape even after activation and becomes spherical, so when using this molded product to construct a radioactive iodine removal material, the filling efficiency is very high and there are almost no voids. In addition, the radioactive iodine removing material has an extremely large amount of impregnation per unit volume of the radioactive iodine removing agent.

In the second conventional example described above, the total volume of pores of 300 Å or less is 0.68 mff1/g or more, and the pore diameter is 30 to 3
00 people's pore volume is 0.16~Q, 95mff1/g
In comparison, for example, optically anisotropic porous carbon microspheres obtained by activating mesocarbon microbeads with a diameter of 3 to 30 μm have a high specific surface area of 1000 to 4500 nf/g. , and the total volume of pores of 300 Å or less is 0.13 to 3.0 mfl/g, and the pore diameter is 20
The volume of ~300 pores is 0.2 to 1.5 ml/g, and the amount of radioactive iodine remover impregnated can be greatly increased.

<Example> Next, an example of the present invention will be described in detail based on the drawings.

FIG. 1 shows a schematic diagram of a radioactive methyl iodide-containing gas treatment equipment, in which radioactive methyl iodide 127CH31271,
A dust removal filter 1, an activated carbon layer filter 2, and an exhaust fan 3 are connected in series in this order to an exhaust line for raw gas containing 131-CH31311, thereby configuring a radioactive methyl iodide-containing gas treatment apparatus.

The activated carbon layer filter 2 is constructed by layering filters in which a radioactive iodine removing agent such as potassium iodide KT or triethylenediamine TEDA is attached to a radioactive iodine removing material.

With this configuration, after the dust contained in the raw gas discharged from a nuclear reactor is removed by the dust removal filter l,
The raw gas after dust removal is passed through the activated carbon bed filter 2, and radioactive methyl iodide 127-C) (31
After removing ``7I, 131-CH, +31■, it is configured to be discharged into the atmosphere from an exhaust stack (not shown).

As the radioactive iodine removing material constituting the activated carbon layer filter 2, one produced as follows is used.

The mesocarbon microbeads used as raw materials had a weight distribution shown in the graph of FIG. 2 and a number distribution shown in the graph of FIG. 3.

Mix 10 g of the above-mentioned Metsucapone microbeads with 30 g of potassium hydroxide as an activation aid, add 60 ml of water and acetone 15 as a surfactant to the mixture, and mix evenly. The mixture was stirred and mixed to form a slurry. The slurry was granulated into 10 to 14 meshes, then heated from room temperature to 850'C at a heating rate of 10'C/min in a nitrogen gas atmosphere, and after reaching 850°C, the temperature was increased by 1 Activation treatment is carried out by holding for a certain period of time, and then the reaction product is
The mixture was cooled to 00°C or less, washed with water, and then dried to obtain optically anisotropic porous carbon microspheres having a specific surface area of 1715 nf/g as measured by the BET method. A radioactive iodine removal material was prepared by spraying an aqueous solution of tetraethylenediamine onto the porous carbon microspheres and then drying them to impregnate 15 weight of tetraethylenediamine.

11 Mix 10 g of the above mesocarbon microbeads with 50 g of potassium hydroxide as an activation aid, add 100 m of water [and 20 m of acetone as a surfactant] to the mixture.
and stirred and mixed uniformly to form a slurry. The slurry was activated in the same manner as in Example No. 001, and the specific surface area measured by the BET method was 3006 rrT.
Optically anisotropic porous carbon microspheres with a weight of /g were obtained. A radioactive iodine removal material was prepared by impregnating tetraethylenediamine with the porous carbon microspheres in the same manner as in Example No. 11 described above.

Mix 10 g of the above mesocarbon microbeads with 70 g of potassium hydroxide as an activation aid, and add 140 mft of water and 30 mft of acetone as a surfactant to the mixture.
and stirred and mixed uniformly to form a slurry. The slurry was activated in the same manner as in the above-mentioned Example No. 011, and the specific surface area measured by the BET method was 415 Onf/g.
Optically anisotropic porous carbon microspheres were obtained. A radioactive iodine removal material was prepared by impregnating tetraethylenediamine with the porous carbon microspheres in the same manner as in the above-mentioned Example No. 091.

Mix 10 g of the above mesocarbon microbeads with 100 g of potassium hydroxide as an activation aid, and add 200 m of water and 40 m of acetone as a surfactant to the mixture.
1 was added and stirred and mixed uniformly to form a slurry. The slurry was activated in the same manner as in the above-mentioned Example No. 011, and the specific surface area measured by the BET method was 4578n? /g
Optically anisotropic porous carbon microspheres were obtained. A radioactive iodine removal material was prepared by impregnating tetraethylenediamine with the porous carbon microspheres in the same manner as in Example No. 11 described above.

In each of the radioactive iodine removal materials of Examples No. 001 to 4 above, the total volume of pores with a pore diameter of 300 Å or less (
mffi/g) and the ratio (%) of the volume of pores with a pore diameter of 20 to 300 people to the total volume is as shown in Table 1.

Table 1 Activated carbon from palm granulated into 10 to 14 meshes and having a specific surface area of 1000r4/g as measured by the BET method was impregnated with 5% by weight of tetraethylenediamine in the same manner as in the previous example. We created a radioactive iodine removal material. In addition,
In this comparative example, it was not possible to impregnate more than 5% by weight of tetraethylenediamine.

The radioactive iodine removal materials of Examples and Comparative Examples of Nos. 1 to 4 above were prepared with an inner diameter of 50 mm and a thickness of 10 mm.
The cartridges are filled with 8 g, and the cartridges are stacked in 5 stages to form a filter, and each filter is filled with 8 g.
Nitrogen gas adjusted to 80% humidity at 50°C at a linear velocity of 2
While flowing at a rate of 0 cm/sec, +27130 mg of radioactive methyl iodide-127CH was mixed into the nitrogen gas so as to evaporate in 1 hour, and the breakthrough time was determined.

As a result, the breakthrough times of Examples No. 001 to 4 were as shown in Table 2, whereas the breakthrough times of Comparative Examples were 0 minutes.
It was clear that the radioactive iodine removal material of the example of the present invention could adsorb an extremely large amount of radioactive iodine.

Table 2 <Effects of the Invention> As explained above, the radioactive iodine removal material of the present invention can remove mesocarbon microbeads, which are spherulites that are developed during the process of heating petroleum-based and coal-based pitches. Since it can be obtained by simply activating it, even if an activation aid is used, it can be produced with high yield using an inexpensive activation aid, and when produced from special fibrous activated carbon. Comparatively, it can be manufactured at a very low cost.

Moreover, the pore diameter is 20, which is suitable for attaching the radioactive iodine removal material.
The volume of the pores can be increased by up to 300 pores, and the amount of impregnated radioactive iodine removal agent can be increased as a whole, while providing a high-yield and inexpensive radioactive iodine removal material.

In addition, since the amount of radioactive iodine removing agent impregnated can be increased, when the filter is constructed from the radioactive iodine removing material and used in a radioactive methyl iodide-containing gas treatment device,
If the size is the same as the conventional example, the filter will not need to be replaced frequently, making management easier, and the amount of waste generated per unit adsorption amount of radioactive iodine will be smaller, reducing the cost of waste treatment. Economical.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a radioactive methyl iodide-containing gas treatment equipment to which the radioactive iodine removal material according to the present invention is applied, and Figure 2 is the weight distribution of metsucarbon microbeads used in Examples of the present invention. FIG. 3 is a graph showing the number distribution of mesocarbon microbeads used in Examples of the present invention.

Claims (2)

[Claims] (1) Contains 90% or more of particles with a particle size of 80 μm or less, has a specific surface area of 1000 to 5000 m^2/g, and has a total volume of pores with a pore diameter of 300 Å or less of 0.8 to 3.
0ml/g, and the pore diameter is 20~20% for the total volume.
A radioactive iodine removal material characterized in that a radioactive iodine removal agent is attached to optically anisotropic porous carbon microspheres in which the volume of 300 Å pores accounts for 10% or more. (2) A radioactive iodine removal material, wherein the porous carbon microspheres according to claim (1) are activated mesocarbon microbeads.