JP2017227633A - Radioactive iodine adsorbent and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radioactive iodine adsorbent having durability under a high temperature and a high humidity, having the adsorption capacity of radioactive iodine in a gas to be treated including both of radioactive iodine and a radioactive iodine compound, and capable of reducing the used amount of a material acting on adsorption, and provide a method for manufacturing the same.SOLUTION: The radioactive iodine adsorbent comprises a base material activated carbon, tri-ethylene diamine attached to the base material activated carbon, and an alkali metal iodide attached to the base material activated carbon. The attached amount of the tri-ethylene diamine is 0.5 to 2.5 wt.% of the weight of the radioactive iodine adsorbent, and the attached amount of the alkali metal iodide is 1 to 3 wt.% of the weight of the radioactive iodine adsorbent. The method for manufacturing the radioactive iodine adsorbent comprises: the cleaning step of cleaning the activated carbon by acid to dry them so as to obtain the base material activated carbon; the first attaching step of mixing and drying an alkali metal iodide aqueous solution; and the second attaching step of mixing and drying a tri-ethylene diamine aqueous solution.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radioactive iodine adsorbing material and a method for producing the same, and more particularly to an iodine adsorbing material having improved adsorption efficiency of a gaseous iodine compound and a producing method therefor.

In nuclear fuels used in general uranium reactors such as light water reactors, uranium ( ²³⁵ U) is the main element of the fission reaction. As nuclides of radioactive substances generated by the fission reaction of uranium ( ²³⁵ U), for example, strontium ( ⁹⁰ Sr), iodine ( ¹³¹ I), cesium ( ¹³⁴ Cs, ¹³⁷ Cs) and the like exist.

  Normally, uranium, which is a nuclear fuel, is housed inside the fuel rod, and the uranium fission material inside does not diffuse outside. Here, after the nuclear fission of uranium has progressed to some extent, the fuel rods are opened for processing into MOX fuel or the like, disposal of nuclear fuel, or the like. There is also a risk of damage to the fuel rods themselves. In such a case, although the work is performed in a shielded environment in principle, there is a possibility that the radioisotope is scattered outside in the unlikely event.

In radioisotope nuclides produced by uranium fission, iodine is known to exist as an organic iodine compound such as gaseous I ₂ or methyl iodide (CH ₃ I). Although the half life of iodine ( ¹³¹ I) is about 8 days, it disintegrates to xenon (Xe) while emitting high-energy β rays. Therefore, the problem of suppressing the diffusion of radioactive iodine into the atmosphere is also important compared to other nuclides. In particular, it is necessary to pay attention to human consumption, and it is clear from the fact that iodine is recommended.

  In nuclear power plants, nuclear facilities (reprocessing facilities, storage facilities), etc., air conditioning equipment is provided in the work area of facility workers and is equipped with an adsorbent for adsorbing radioactive iodine contained in air in the atmosphere. Yes. In addition to installation in such facilities, installation of air-conditioning equipment in evacuation facilities for residents in the vicinity has begun to be considered. Therefore, the demand for radioactive iodine adsorbents is expected to increase in the future.

  As conventional radioactive iodine adsorbents, for example, activated carbon impregnated with potassium iodide, zeolite impregnated with silver, and the like are known. However, the adsorption performance of iodine and iodine compounds of these adsorbents is not always sufficient. Therefore, an adsorbent in which triethylenediamine and potassium iodide are impregnated on activated carbon has been proposed (see Patent Documents 1 and 2).

  The radioactive iodine adsorbents represented by Patent Documents 1 and 2 are extremely suitable adsorbents because they have durability even under high temperature and high humidity, and have adsorption performance of both iodine and iodine compounds. However, the adhering component for exhibiting the adsorption performance of radioactive iodine is expensive, and reduction of the amount used has been studied.

JP 2012-2606 A JP2015-45588A

  After that, the inventor conducted extensive studies on the material and manufacturing process of the radioactive iodine adsorbent, and confirmed that sufficient adsorption efficiency was exhibited even if the amount of the adhering substance was reduced as compared with the previous conditions.

  The present invention has been proposed in view of the above situation, has durability even under high temperature and high humidity, and adsorption performance of radioactive iodine from the gas to be treated containing both radioactive iodine and radioactive iodine compound And a radioactive iodine adsorbent capable of reducing the amount of a substance that acts on adsorption and a method for producing the same.

  That is, the first invention is a radioactive iodine adsorbent that adsorbs radioactive iodine from a gas to be treated containing radioactive iodine, and the radioactive iodine adsorbent is attached to the base activated carbon and the base activated carbon. Triethylenediamine and an alkali metal iodide attached to the base activated carbon, the amount of the triethylenediamine added is 0.5 to 2.5% by weight of the radioactive iodine adsorbent, and the alkali metal The radioactive iodine adsorbent is characterized in that the amount of iodide added is 1 to 3% by weight of the weight of the radioactive iodine adsorbent.

  A second invention relates to the radioactive iodine adsorbent according to the first invention, wherein the alkali metal iodide is potassium iodide.

  A third invention relates to the radioactive iodine adsorbing material according to the first invention, wherein the amount of the triethylenediamine added is 1.7 to 2.5% by weight of the weight of the radioactive iodine adsorbing material.

4th invention concerns the radioactive iodine adsorption material as described in 1st invention whose BET specific surface area of the said base material activated carbon is 1900 m < ² > / g or less.

  5th invention is the manufacturing method of the radioactive iodine adsorption material which adsorb | sucks a radioactive iodine from the to-be-processed gas containing a radioactive iodine, Comprising: The washing | cleaning process of obtaining activated carbon by acid cleaning and drying, and an alkali metal, The aqueous solution of iodide and the base activated carbon are mixed and dried to obtain the first impregnated activated carbon; the aqueous solution of triethylenediamine and the first impregnated activated carbon are mixed and dried to obtain the second impregnated activated carbon. A second attaching step, wherein the amount of alkali metal iodide added in the first attaching step is 1 to 3% by weight of the radioactive iodine adsorbent, and the triethylenediamine in the second attaching step The method according to the present invention relates to a method for producing a radioactive iodine adsorbent, characterized in that the amount of attachment is 0.5 to 2.5 wt% of the weight of the radioactive iodine adsorbent.

  6th invention concerns the manufacturing method of the radioactive iodine adsorption material as described in 5th invention whose said alkali metal iodide is potassium iodide.

  7th invention concerns the manufacturing method of the radioactive iodine adsorption material as described in 5th invention whose addition amount of the said triethylenediamine is 1.7 to 2.5 weight% of the weight of the said radioactive iodine adsorption material.

8th invention concerns on the manufacturing method of the radioactive iodine adsorption material as described in 5th invention whose BET specific surface area of the said base material activated carbon is 1900 m < ² > / g or less.

  According to the radioactive iodine adsorbing material according to the first aspect of the present invention, the radioactive iodine adsorbing material adsorbs radioactive iodine from the gas to be treated containing radioactive iodine, and the radioactive iodine adsorbing material includes base activated carbon and the base A triethylenediamine adhering to the activated carbon and an alkali metal iodide adhering to the base activated carbon, the amount of the triethylenediamine adhering is 0.5 to 2.5% by weight of the radioactive iodine adsorbent. Yes, since the amount of the alkali metal iodide is 1 to 3% by weight of the radioactive iodine adsorbent, the adsorption performance of radioactive iodine from the gas to be treated containing both the radioactive iodine and the radioactive iodine compound In addition, it is possible to obtain a radioactive iodine adsorbent that can reduce the amount of a substance that acts on adsorption.

  According to the radioactive iodine adsorbent according to the second invention, in the first invention, since the alkali metal iodide is potassium iodide, the properties are stable and the procurement is relatively easy.

  According to the radioactive iodine adsorbing material according to the third invention, in the first invention, the amount of triethylenediamine added is 1.7 to 2.5% by weight of the weight of the radioactive iodine adsorbing material. With adsorption capacity.

According to the radioactive iodine adsorbent according to the fourth invention, in the first invention, since the BET specific surface area of the base activated carbon is 1900 m ² / g or less, the amount of chemical adhering per volume and the fine amount affecting the adsorption capacity are reduced. It is possible to avoid performance degradation due to a decrease in breakthrough time due to a decrease in pore volume.

According to the method for producing a radioactive iodine adsorbent according to the fifth aspect of the present invention, there is provided a method for producing a radioactive iodine adsorbent that adsorbs radioactive iodine from a gas to be treated containing radioactive iodine. Cleaning step to obtain activated carbon, mixing first aqueous solution of alkali metal iodide and base activated carbon, drying to obtain first impregnated activated carbon, mixing aqueous solution of triethylenediamine and first impregnated activated carbon And a second attaching step for drying to obtain a second impregnated activated carbon, wherein the amount of alkali metal iodide attached in the first attaching step is 1 to 3% by weight of the radioactive iodine adsorbent, Since the amount of triethylenediamine added in the second attaching step is 0.5 to 2.5% by weight of the radioactive iodine adsorbent,
A simple method for producing a radioactive iodine adsorbent that is capable of adsorbing radioactive iodine from a gas to be treated containing both radioactive iodine and a radioactive iodine compound, and that can reduce the amount of substances that act on the adsorption. Can be obtained.

  According to the method for producing a radioactive iodine adsorbent according to the sixth invention, in the fifth invention, since the alkali metal iodide is potassium iodide, the properties are stable and the procurement is relatively easy.

  According to the method for producing a radioactive iodine adsorbent according to the seventh invention, in the fifth invention, the amount of triethylenediamine attached is 1.7 to 2.5% by weight of the weight of the radioactive iodine adsorbent. Further, the adsorption capacity can be increased.

According to the method for producing a radioactive iodine adsorbent according to the eighth invention, in the fifth invention, since the BET specific surface area of the base activated carbon is 1900 m ² / g or less, the chemical adhering per volume affecting the adsorption capacity It is possible to produce a radioactive iodine adsorbent that avoids performance degradation due to reduction in breakthrough time due to reduction in the amount and pore volume.

It is a schematic process drawing explaining the manufacturing method of the radioactive iodine adsorption material of this invention.

The radioactive iodine adsorbent of the present invention is an adsorbent for suppressing the diffusion of radioactive iodine into the atmosphere by adsorbing radioactive iodine from the gas to be treated containing radioactive iodine (mainly ¹³¹ I or the like). . Iodine ( ¹³¹ I, etc.) generated by uranium fission is a kind of halogen, and therefore has high reactivity. Depending on temperature conditions, iodine (I ₂ ) exists as a gas. It is also known that an organic iodine compound such as methyl iodide (CH ₃ I) is produced by reacting with an organic substance-derived methyl group by a reaction between ionized I ⁻ and another organic substance. The radioactive iodine adsorbent of the present invention is proposed as an efficient adsorbent for the gas to be treated containing radioactive iodine and iodine compounds in such a gas.

  Therefore, the radioactive iodine adsorbing material will be described together with its manufacturing method together with the schematic process diagram of FIG. Substrate activated carbon is prepared as the main material of the radioactive iodine adsorbent. The base activated carbon is a granular material of a known activated carbon. Activated carbon is carbonized, fired, and appropriately pulverized pulverized products of woody plant materials rich in cellulose, such as wood saws, sawdust (wood sawdust) and sawdust generated during processing, waste wood, thinned wood, waste bamboo, felled bamboo, palm shell It is the carbide obtained through the activation of. In addition to plant materials, carbides of various resin products such as old tires and phenol resins can be added to the activated carbon. Therefore, the base activated carbon can be procured relatively inexpensively and quantitatively.

  Activated carbon is used as an adsorbing and filtering material, and is highly safe and can cover a wide range of substances due to the pores developed on the activated carbon surface. Therefore, the surface of the activated carbon and its pores adhere to the following substances, and the permeation performance of the gas to be treated containing radioactive iodine and iodine compound into the pores of the activated carbon is also high. The size of the activated carbon is a granular body of about 1 to 5 mm, and the size is irregular. The size and shape of the activated carbon can be arbitrarily controlled by crushing, crushing, sieving, or the like. However, the radioactive iodine adsorbing material targets the gas to be treated containing radioactive iodine for adsorption. When the particle size is extremely fine, pressure loss such as clogging becomes large, and there is a possibility that gas ventilation may be affected. However, powdered activated carbon can be selected as long as the gas to be processed can be ventilated while being pressurized.

A specific surface area (m ² / g) by the BET method is used as an evaluation index of the adsorption performance of activated carbon. As a general tendency, as the specific surface area increases, the pores inside the activated carbon develop and the adsorption performance increases. However, in relation to the object to be adsorbed, it is important which pore size should be developed, and simply increasing the specific surface area does not lead to improvement in adsorption performance. In particular, the radioactive iodine adsorbent of the present invention mainly uses organic iodine compounds and the like as adsorption targets. In this case, the activated carbon having a relatively large number of mesopores (pores in the range of approximately 2 to 50 nm) is considered to be preferable in consideration of the size of the molecule to be adsorbed.

Therefore, based on the verification of Examples described later, the specific surface area of activated carbon when adsorbing organic iodine compounds such as methyl iodide by the BET method is derived to be 1900 m ² / g or less. When the specific surface area by the BET method exceeds 1900 m ² / g, performance deterioration due to reduction in breakthrough time of methyl iodide appears. Further, the upper limit of the specific surface area of 1750m ² / g or less, more 1550 m ² / g or less, more preferably defined below 1400 m ² / g. The lower limit of the specific surface area is preferably 1100 m ² / g. An increase in the specific surface area leads to a decrease in the amount of chemical adhering per volume and the pore volume, which affect the adsorption capacity, leading to a decrease in breakthrough time as an adsorbent.

  First, the activated carbon is immersed in a weak acid solution such as dilute hydrochloric acid and boiled in the weak acid solution. Then, the base activated carbon used for the following process is obtained through water washing and drying ("washing process"). In order to finish cheaply, as described above, many raw materials derived from natural products are used for activated carbon. Therefore, the quality variation is not completely wiped out. Further, if organic substances and salts are present on the surface and pores of the activated carbon, it is considered that the addition of alkali metal iodide and triethylenediamine described below may be inhibited. Thus, when activated carbon is boiled in a weakly acidic solution such as dilute hydrochloric acid, the organic matter is decomposed and salts can also be dissolved. As a result, it becomes possible to stabilize the quality in advance. In particular, triethylenediamine exhibits basicity. Therefore, it is considered preferable that the basic group on the activated carbon surface is reduced by acid cleaning.

  Next, an aqueous solution of alkali metal iodide is prepared, the aqueous solution and the base activated carbon are mixed, and then dried to obtain a first impregnated activated carbon (“first impregnation step”). The alkali metal iodide is specifically potassium iodide (KI) or sodium iodide (NaI). In the case of other alkali metals, the amount used is increased in relation to the equivalent amount (grams per mole), and the price is higher than that of potassium iodide. Potassium iodide is preferably used because it is stable and relatively easy to procure.

The action of radioiodine adsorption by alkali metal iodide (potassium iodide or sodium iodide) is considered as follows. When radioactive iodine (such as ¹³¹ I ₂ ) in the gas to be treated comes into contact with iodine ( ¹²⁷ I ₂ ), which is a stable isotope on the adsorbent side, exchange of iodine nuclides occurs. For this, reference is made, for example, to the reaction of formula (i). Formula (i) is an example of potassium iodide “KI”, where “I ^* ” represents the radioactive isotope of iodine. As a result, radioactive iodine in the gas to be treated is reduced more than before contact. Accordingly, the alkali metal iodide acts to remove radioactive organic iodine compounds such as radioactive iodine ( ¹³¹ I ₂ etc.) and radioactive methyl iodide (CH ₃ ¹³¹ I etc.) present alone in the gas to be treated.

  After potassium iodide or sodium iodide is dissolved in water, it is sufficiently mixed with the aqueous solution by spray coating, dipping, etc. on the base activated carbon. The concentration of the aqueous alkali metal iodide solution is adjusted in consideration of the final amount of adhesion. Then, it is dried over a temperature and time sufficient for evaporation of moisture. Since alkali metal iodide is a salt, it is possible to increase the temperature during drying. However, since it is necessary to avoid thermal decomposition of the substrate, the heating and drying conditions are approximately 100 to 200 ° C.

  The amount of alkali metal iodide applied in the first attaching step is controlled to 1 to 3% by weight, more preferably 1.5 to 3% by weight, based on the weight of the final radioactive iodine adsorbent. When the weight ratio per unit radioactive iodine adsorbent is less than 1% by weight, the amount of alkali metal iodide (potassium iodide, etc.) decreases and the adsorption effect decreases. And if it exceeds 1.5 weight%, an effect will increase more. Regarding the upper limit, even if the weight ratio exceeds 3% by weight, the improvement of the adsorption effect reaches its peak, and it is considered excessive from the viewpoint of the effect. Therefore, the upper limit is defined as 3% by weight for the purpose of reducing the amount used.

Subsequently, an aqueous solution of triethylenediamine is prepared. The triethylenediamine aqueous solution and the first impregnated activated carbon are mixed and then dried to obtain a second impregnated activated carbon (“second impregnation step”). Triethylenediamine has a structure represented by the formula (f) and is also referred to as 1,4-diazabicyclo [2.2.2] octane. Triethylenediamine has two tertiary amines in its molecule. In addition, the bond around the nitrogen atom is a structure tied back. For this reason, the lone pair of electrons is a region that is less susceptible to steric hindrance and rich in nucleophilicity. Therefore, it is considered that a nucleophilic reaction is likely to occur with methyl iodide (CH ₃ ¹³¹ I) containing radioactive iodine in the gas to be treated, and a quaternary ammonium salt is generated. The reaction is described as, for example, the mechanism of formula (ii).

  After triethylenediamine is dissolved in water, it is sufficiently mixed with the aqueous solution by spray coating, dipping, etc. on the base activated carbon. The concentration of the aqueous solution of triethylenediamine is also adjusted in consideration of the final amount of adhesion. Then, it is dried over a temperature and time sufficient for evaporation of moisture. However, triethylenediamine is thermally decomposed at a high temperature exceeding 100 ° C., and the amount of adhesion decreases. Therefore, in order to avoid thermal decomposition, the drying is performed under a temperature condition of approximately 80 ° C. or less, preferably 70 ° C. or less. Therefore, the drying depending on the high temperature described in the first attaching step cannot be performed. Therefore, for the convenience of drying, when triethylenediamine is dissolved in water, the amount of water used is such that the first impregnated activated carbon gets wet in consideration of low temperature drying.

  The amount of triethylenediamine added in the second attaching step is controlled to 0.5 to 2.5% by weight of the weight of the final radioactive iodine adsorbent. The upper limit of the amount of attachment is based on the verification of examples described later. Even if the amount of attachment exceeds 3% by weight, the performance improvement effect corresponding to the excess is small. This is because the adsorption results were improved even in the case of further reduction. As for the lower limit, it is considered that the effect is poor unless an attachment amount of about 0.5% by weight is accompanied. Therefore, in order to enhance the effect, an amount of attachment of 1.7% by weight or more is desired. Therefore, the amount of triethylenediamine applied is defined as a range of 0.5 to 2.5% by weight, and further a range of 1.7 to 2.5% by weight. The process up to the second attaching step is completed, and the “radioactive iodine adsorbent” is completed.

  In addition to such extremely simple properties, the adhering components were suppressed as compared with the conventional adsorbent. Therefore, the radioactive iodine adsorbent is filled, for example, in a dust collector, an air purifier, an intake of appropriate air or the like of an air conditioner, a storage unit, and the like (not shown) as a gas filter medium. These devices are installed in nuclear power plants, nuclear fuel reprocessing facilities, nuclear fuel disposal and storage facilities, and evacuation facilities outside these facilities. In particular, since the same effect is expected even if the component adhering to the activated carbon is suppressed, there are advantages such as a reduction in the amount used and an extension in the period of use.

[Raw materials]
The inventor used the following raw materials in order to create a radioactive iodine adsorbent.
Activated charcoal Co., Ltd. made by Tsurumi Coal Co., Ltd., coconut shell activated carbon “HC-20” (particle size: 1.18-2.36 mm) was used (activated carbon 1).
-Alkali metal iodide Potassium iodide (made by Wako Pure Chemical Industries, Ltd.) was used as an alkali metal iodide.
-Triethylenediamine Triethylenediamine was manufactured by Kanto Chemical Company.

[Production of radioactive iodine adsorbent (I)]
The inventor produced four types of radioactive iodine adsorbents while changing the amount of triethylenediamine (Prototype Examples 1 to 4). First, 120 mL of 1N hydrochloric acid was added to 3 L of water to prepare a diluted hydrochloric acid solution, and 1500 g of activated carbon was added thereto. Here, the activated carbon was boiled for about 30 minutes. After boiling, the activated carbon was washed with running water. Washing with running water was continued until the pH of the wash water was in the range of 6-8. After washing with water, it was dried at 115 ° C. for 16 hours to obtain a base activated carbon.

  A potassium iodide aqueous solution was prepared by dissolving 8 g of potassium iodide in 300 mL of water. A potassium iodide aqueous solution was added to 400 g of the above-mentioned base activated carbon, and mixed well so that both became familiar. Then, it was set as potassium iodide impregnated activated carbon (first impregnated activated carbon) at 115 ° C. for 16 hours.

  12 g of Triethylenediamine (Prototype Example 1), 20 g (Prototype Example 2), 28 g (Prototype Example 3) and 10.8 g (Prototype Example 4) were dissolved in 67 mL of water to prepare triethylenediamine aqueous solutions of the respective examples. did. A triethylenediamine aqueous solution was sprayed on the above-mentioned potassium iodide-impregnated activated carbon, and mixed well so that both would become familiar. Subsequently, the film was dried while maintaining a temperature of 80 ° C. or lower, mainly around 70 ° C. Drying was continued until a weight change of approximately 2% was confirmed before and after drying. In this way, the radioactive iodine adsorbents of prototype examples 1 to 4 were produced.

[Physical property measurement]
<Physical properties of activated carbon pores>
The physical properties of both the base activated carbon and the radioactive iodine adsorbent adhering both substances were measured. The results are as shown in Table 1. Among the measurement items, packing density (g / mL), loss on drying (%), benzene adsorption power (%), ignition residue (%), particle size distribution (%), hardness (%), and ignition point (° C. ) Was measured according to JIS K 1474 (2014).

The specific surface area (m ² / g) is obtained by measuring the nitrogen adsorption isotherm at 77K using an automatic specific surface area / pore distribution measuring device “BELSORP-miniII” manufactured by Microtrack Bell Co., Ltd., and obtained by the BET method. (BET specific surface area). The pore volume described later was also measured with the same apparatus.

<Amount of potassium iodide added>
For the radioactive iodine adsorbent of each prototype, the amount of potassium iodide actually attached was measured. In the extraction of potassium iodide from the radioactive iodine adsorbent, 200 mL of ion-exchanged water was used as a solvent for 10 g of the radioactive iodine adsorbent, and extracted using a Soxhlet extractor over 24 hours. The extract was collected, and ion-exchanged water was added to the extract and diluted to prepare an extract solution having a total amount of 250 mL.

  The extraction solution and ion-exchanged water were added to a 100 mL separatory funnel to make a total volume of 10 mL. To this, 5 mL of 2N sulfuric acid and 2 mL of 30% hydrogen peroxide were added and allowed to stand for 5 minutes. Subsequently, 20 mL of chloroform was added and shaken for 1 minute, and then the chloroform layer separated into the lower layer was collected. Again, 20 mL of chloroform was added to the separatory funnel and shaken for 1 minute, and then the chloroform layer separated into the lower layer was separated. Separate chloroform was added to the collected chloroform layer to prepare a sample solution having a total volume of 50 mL.

  The sample solution was transferred to a quartz cell (optical path length 1 cm), and the absorbance at a wavelength of 510 nm was measured using an absorptiometer (manufactured by Hitachi High-Tech Science Co., Ltd., U-2001, double beam spectrophotometer). A calibration curve was prepared in advance with a solution of potassium iodide having a known concentration, and the concentration was determined. And the amount of attachment (weight%) per unit weight activated carbon was computed from the amount of potassium iodide (attachment amount) of base material activated carbon.

<Amount of triethylenediamine attached>
For the radioactive iodine adsorbent of each prototype, the amount of triethylenediamine actually attached was measured. At the time of triethylenediamine extraction of the radioactive iodine adsorbent, 200 mL of methanol was used as a solvent for 10 g of the radioactive iodine adsorbent, and extraction was performed using a Soxhlet extractor over 24 hours. The extract was collected, and methanol was added thereto and diluted to prepare an extract solution having a total amount of 250 mL.

  The amount of triethylenediamine in the extraction solution with methanol described above was measured using gas chromatography (manufactured by Hitachi High-Tech Science Co., Ltd., G-3900). Nitrogen was used as the carrier gas, and a column (Unisole 10T + KOH, manufactured by GL Science Inc.) and a detector (FID) were used. Prepare a calibration curve by filling a gas chromatography with a triethylenediamine solution of a known concentration in advance, measure the amount by comparing the peak areas in the detection chart, and calculate the unit weight activated carbon from the amount of triethylenediamine (attachment amount) of the base activated carbon The amount of adhesion per weight (% by weight) was calculated.

<Measurement of adsorption amount of radioactive iodine>
When measuring the amount of radioactive iodine adsorbed, the performance of the radioactive iodine adsorbent of each prototype was evaluated based on the amount of radioactive methyl iodide adsorbed. Therefore, a radioactivity methyl iodide containing a radioactive isotope of iodine was used, and the accuracy of its removal efficiency was tested (unit:%). The content of the test conformed to ASTM D3803-91.

Moist air (pressure: about 1 atm, temperature: 30.0 ° C., relative humidity: about 95%) was passed through the radioactive iodine adsorbent of each prototype for 16 hours to saturate the moisture. Subsequently, humid air (pressure: about 1 atm, temperature: 30.0 ° C., relative humidity: about 95%) was aerated for 120 minutes. Thereafter, moist air (pressure: about 1 atm, temperature: 30.0 ° C., relative humidity: about 95%) containing methyl iodide (mass concentration 1.75 mg / m ³ ) was aerated for 60 minutes, and ¹³¹ I gamma rays The radioactivity intensity was measured to determine the transmittance, and the radioiodine removal efficiency was determined.

[Results and discussion of preparation of radioactive iodine adsorbent (I)]
According to Prototype Examples 1, 2, and 3, the amount of potassium iodide (alkali metal iodide) added was almost the same, and the amount of triethylenediamine added increased in order. However, when looking at the final removal efficiency of radioactive iodine, the difference in numerical values is smaller as the amount of triethylenediamine added is different. For this reason, there is room for reduction in the amount of triethylenediamine attached. In particular, it can be derived that the preferable amount of triethylenediamine added is in the range of 0.5 to 2.5% by weight, considering that even if the amount is less than 3.0% by weight, it contributes to the adsorption of radioactive iodine. it can. Regarding the amount of potassium iodide attached, it can be considered that the range of 1 to 3% by weight is appropriate based on the actual measurement values in each prototype.

  Prototype Example 4 is an example using activated carbon different from Prototype Examples 1 to 3 as a base material. Therefore, it is thought that the difference in the physical properties of the activated carbon used as the base material has an influence. According to a comparison between prototype examples 1 and 4, the amount of potassium iodide added is the same or slightly higher. Moreover, the amount of triethylenediamine added is also increasing. However, the removal efficiency of radioactive iodine slightly decreased. Although this effect has not been fully elucidated, it is considered that the relationship with the abundance of surface acidic groups, hydrophilic groups, etc. on the activated carbon surface is likely to be strong.

[Production of radioactive iodine adsorbent (II)]
From the above-mentioned “Preparation of Radioactive Iodine Adsorbent (I)”, it was possible to grasp the basic physical properties and the amount of attachment when preparing the radioactive iodine adsorbent. Therefore, a more detailed range of addition amounts of potassium iodide and triethylenediamine was verified, and at the same time, a range of specific surface area suitable for the base activated carbon was also verified. Examples in which the amount of triethylenediamine added was changed to Prototype Examples 11 to 14, Samples in which the amount of potassium iodide was changed were changed to Samples 15 to 17, and examples in which the specific surface area was changed were prepared as Prototype Examples 18 to 22.

In the evaluation of different BET specific surface areas, the following activated carbons 2 to 8 were further used. The measurement of the BET specific surface area of each activated carbon was the same as described above.
When producing activated carbons 2 to 8, common coconut shell activated carbon was prepared, and activated carbons having different specific surface areas were obtained while changing activation conditions (time). All the activated carbons were adjusted to have the same particle size distribution in the range of 1.18 to 2.36 mm.
(Activated carbon 2): Specific surface area: 1173 m ² / g
(Activated carbon 3): Specific surface area: 1223 m ² / g
(Activated carbon 4): Specific surface area: 1394 m ² / g
(Activated carbon 5): Specific surface area: 1519 m ² / g
(Activated carbon 6): Specific surface area: 1725 m ² / g
(Activated carbon 7): Specific surface area: 1552 m ² / g
(Activated carbon 8): Specific surface area: 1723 m ² / g

<Production of Prototype Examples 11 to 14>
In the production of prototype examples 11 to 14 in which the amount of triethylenediamine was changed, 4.0 g (prototype example 11), 6.0 g (prototype example 12), and 8.8 g (prototype example 13) of triethylenediamine dissolved in 67 mL of water were prepared. ), 9.6 g (Prototype Example 14), and the triethylenediamine aqueous solution was prepared by increasing the amount in order. The amount of potassium iodide used in Prototype Examples 11 to 14 was the same as that in Prototype Examples 1 to 4 described above. In Prototype Examples 11 to 14, the same activated carbon 1 as in Prototype Examples 1 to 4 was used as the base activated carbon, and the same preparation was performed.

<Production of prototype examples 15 to 17>
In the production of prototype examples 15 to 17 in which the amount of potassium iodide added was changed, 12.0 g (prototype example 15), 20.0 g (prototype example 16), and 28.0 g (prototype) of potassium iodide dissolved in 300 mL of water. As Example 17), an aqueous potassium iodide solution was prepared by increasing the amount in order. All the addition amounts of triethylenediamine were the same, and a solution was prepared by dissolving 10.8 g of triethylenediamine in 67 mL of water. In Prototype Examples 15 to 17, the same activated carbon 1 as in Prototype Examples 1 to 4 was used as the base activated carbon, and the same preparation was performed.

<Production of Prototype Examples 18 to 22>
In Prototype Examples 18 to 22, activated carbons having different specific surface areas were used as the base activated carbon. Prototype 18 was “activated carbon 2”, prototype 19 was “activated carbon 3”, prototype 20 was “activated carbon 4”, prototype 21 was “activated carbon 5”, and prototype 22 was “activated carbon 6”. In the production of Prototype Examples 18 to 22, the amount of triethylenediamine added was the same, and a solution was prepared by dissolving 10.8 g of triethylenediamine in 67 mL of water. The amount of potassium iodide used in the prototypes 18 to 22 was the same as that of the prototypes 1 to 4 described above. The activated carbon was prepared in the same manner as described above.

The production methods and analysis methods of the prototype examples 11 to 22 are the same as those of the prototype examples 1 to 4 described above. The results of prototype examples 11 to 22 are shown in Tables 2 to 5. However, in the preparation (II), for the sake of simplification, the “measurement of radioactive iodine removal efficiency” was omitted, and the breakthrough time of methyl iodide was measured. In addition, in order to grasp the properties of the activated carbon substrate, the total pore volume (cm ³ / g) and the pore diameter intervals (“less than 2 nm”, “2 to 4 nm”, “4 to 10 nm”, “10 to The pore volume of “50 nm” and “50 nm or more”) was also measured.

<Measurement of breakthrough time>
Methyl iodide was diluted with air to adjust the concentration of aeration gas to 20 ppm, and sent to a column packed with each prototype. The column had an inner diameter of 2.0 cm, a layer height of 5.0 cm, and a packing amount of 15.7 mL. As ventilation conditions, the air volume is 3770 mL / min, the LV is 0.20 m / sec, the SV is 14408 h ⁻¹ , the direction is downflow, the temperature is 29.6 to 30.0 ° C., and the relative humidity is 86.0 to 96. The condition was 0%. And the density | concentration at the time of breakthrough was 2 ppm, and it measured with the detector tube. The time from the start of aeration (20 ppm) to exceeding the concentration (2 ppm) at the time of breakthrough was defined as breakthrough time.

[Results and discussion of preparation of radioactive iodine adsorbent (II)]
<1. Addition amount of triethylenediamine>
From prototype examples 11 to 14, the breakthrough time becomes longer in proportion to the amount of triethylenediamine, and the performance as an adsorbent is improved. Here, considering the performance required for the radioactive iodine adsorbent, the range exceeding the breakthrough time of 240 min is very good, and already exhibits sufficient performance. Note that the breakthrough time 240 min is a standard value for existing adsorbents, and thus was adopted as a standard. Therefore, the upper limit for the amount of triethylenediamine is 2.5% by weight. The lower limit is 0.5% by weight, preferably 1.2% by weight, more preferably 1.5% by weight from the viewpoint of performance. Further, when the lower limit is specified from the amount of adhesion exceeding the breakthrough time 240 min, it is 1.7% by weight.

<2. Amount of potassium iodide added>
From prototype examples 15 to 17, the breakthrough time of potassium iodide decreased in inverse proportion to the increase in the amount of adhering. When the amount of potassium iodide applied in Prototype Example 17 was 6.1% by weight, the breakthrough time was less than 240 min. Probably, the adsorption to the adsorbent of the prototype was hindered by the physical obstacle of potassium iodide. The role of potassium iodide, which is an additive component of the base activated carbon, is considered not as adsorption of methyl iodide itself, but rather as substitution of iodine atoms (see the above formula (i)). Therefore, the amount of potassium iodide added and the evaluation of methyl iodide adsorption should be considered separately. Therefore, as a range in which both interference suppression during adsorption and substitution promotion are compatible, the upper limit of the amount of potassium iodide added exceeding the breakthrough time of 240 min is 5% by weight, and a more preferable upper limit is 3% by weight.

<3. BET specific surface area of base activated carbon>
From the relationship between the BET specific surface area and breakthrough time in the prototypes 18 to 22, when the BET specific surface area of the prototype 22 exceeded 1700 m ² / g, the breakthrough time decreased to 240 minutes. Moreover, when the BET specific surface area increased to the trial example 21, it gradually decreased from the other trial examples. Further, when focusing on the pore volume for each section in Table 4, the range of mesopores decreased and the range of micropores increased in Experimental Example 22 having the largest BET specific surface area. From this point, it can be expected that the difference in size between methyl iodide molecules and pores affects the adsorption efficiency. Therefore, considering the BET specific surface area in addition to the pore distribution, the upper limit is defined as 1900 m ² / g or less, further 1850 m ² / g or less, more preferably 1750 m ² / g or less. The lower limit of the specific surface area, 1100 m ² / g in light of Prototype Example 18 preferably derives a prototype example 19 1200 no more than 20 to 1300 m ² / g, more preferably a prototype example 20 to 1400 no more 21 and 1500 m ² / g be able to.

[Production of radioactive iodine adsorbent (III)]
Considering the results of preparation of the radioactive iodine adsorbent (I and II), a more optimal amount of adhesion and range of specific surface area were determined. Therefore, the radioactive iodine adsorption effect of the radioactive iodine adsorbent with specifications satisfying the range (prototype examples 31 to 35) was verified.

<Production of prototype examples 31 and 32>
When producing Prototype Examples 31 and 32, triethylenediamine aqueous solutions were prepared with 4.0 g (Trial Example 31) and 10.8 g (Trial Example 32) of triethylenediamine dissolved in 67 mL of water. The amount of potassium iodide applied in the prototype examples 31 and 32 was the same as that in the prototype examples 1 to 4 described above. Trial manufacture examples 31 and 32 used the same activated carbon 1 as trial manufacture examples 1 thru / or 4 for substrate activated carbon, and performed the same preparation.

<Production of Prototype Example 33>
In the production of prototype 33, an aqueous potassium iodide solution was prepared with 12.0 g (prototype 15) of potassium iodide dissolved in 300 mL of water. The amount of triethylenediamine added was prepared by dissolving 10.8 g of triethylenediamine in 67 mL of water. Trial Example 33 uses the same activated carbon 1 as Trial Examples 1 to 4 as the base activated carbon, and the same preparation was performed.

<Production of prototype examples 34 and 35>
In the production of prototype examples 34 and 35, “activated carbon 7” was used for prototype example 34, and “activated carbon 8” was used for prototype example 35. In the production of prototype examples 34 and 35, the amount of triethylenediamine added was the same, and a solution was prepared by dissolving 10.8 g of triethylenediamine in 67 mL of water. The amount of potassium iodide applied in the prototype examples 34 and 35 was the same as that in the prototype examples 1 to 4 described above. The activated carbon was prepared in the same manner as described above.

  The production methods and analysis methods of the prototype examples 31 to 35 are the same as those of the prototype examples 1 to 4 described above. The results of prototype examples 31 to 35 are shown in Tables 6 and 7. Measurement of the amount of radioactive iodine adsorbed in Prototype Examples 31 to 35 was performed under common conditions in accordance with ASTM D3803-91 described in the above-mentioned preparation (I) of the radioactive iodine adsorbent.

[Results and discussion of preparation of radioactive iodine adsorbent (III)]
From the result of the removal efficiency of radioactive iodine when using the radioactive iodine adsorbents of the prototype examples 31 to 35, the actual removal performance of radioactive iodine almost coincided with the production of the radioactive iodine adsorbent (I and II). Therefore, the amounts of potassium iodide (alkali metal iodide) and triethylenediamine added to the above-mentioned base activated carbon are appropriate. Moreover, the suitability of the specific surface area of the base activated carbon was confirmed.

  The radioactive iodine adsorbent of the present invention exhibits good adsorption performance while reducing the amount of the adhering substance supported on the activated carbon compared to the existing product, and can be manufactured at a lower cost, replacing the existing product. It works advantageously. In addition, according to the method for producing a radioactive iodine adsorbent, the performance of the adhering substance is made easier to extract, and therefore the effect can be maintained even if the amount of the adhering substance is reduced.

Claims (8)

A radioactive iodine adsorbent that adsorbs radioactive iodine from a gas to be treated containing radioactive iodine,
The radioactive iodine adsorbent comprises a base activated carbon, triethylenediamine attached to the base activated carbon, and an alkali metal iodide attached to the base activated carbon.
The amount of triethylenediamine added is 0.5 to 2.5% by weight of the radioactive iodine adsorbent,
The radioactive iodine adsorbent characterized in that the amount of the alkali metal iodide is 1 to 3% by weight of the weight of the radioactive iodine adsorbent.   The radioactive iodine adsorbent according to claim 1, wherein the alkali metal iodide is potassium iodide.   2. The radioactive iodine adsorbent according to claim 1, wherein the amount of triethylenediamine added is 1.7 to 2.5 wt% of the weight of the radioactive iodine adsorbent. The radioactive iodine adsorbent according to claim 1, wherein the base activated carbon has a BET specific surface area of 1900 m ² / g or less. A method for producing a radioactive iodine adsorbent that adsorbs radioactive iodine from a gas to be treated containing radioactive iodine,
A cleaning step of acid cleaning the activated carbon and drying to obtain a base activated carbon;
A first impregnation step of mixing an aqueous solution of alkali metal iodide and the base activated carbon and drying to obtain a first impregnated activated carbon;
A second adhering step of mixing an aqueous solution of triethylenediamine and the first impregnated activated carbon and drying to obtain a second impregnated activated carbon;
The amount of the alkali metal iodide applied in the first attaching step is 1 to 3% by weight of the weight of the radioactive iodine adsorbent;
The method for producing a radioactive iodine adsorbent, characterized in that the amount of triethylenediamine added in the second attaching step is 0.5 to 2.5% by weight of the weight of the radioactive iodine adsorbent.   The method for producing a radioactive iodine adsorbent according to claim 5, wherein the alkali metal iodide is potassium iodide.   The method for producing a radioactive iodine adsorbent according to claim 5, wherein the amount of the triethylenediamine added is 1.7 to 2.5% by weight of the weight of the radioactive iodine adsorbent. The method for producing a radioactive iodine adsorbent according to claim 5, wherein the base activated carbon has a BET specific surface area of 1900 m ² / g or less.

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