JP2005315617A - Radioactive material monitoring material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the operability in the case of measuring by taking out the sampler monitoring material to transfer the same to the general-purpose test tube glass column monitoring, and to make it possible to monitoring the integrated radiation doses by repeatedly using the monitoring material, at the time of monitoring the iodine in the atomic facility etc. <P>SOLUTION: The monitoring material is characteristically formed by laminating the sheet-like material containing an active carbon fiber into a sheet whose thickness is ≤4 mm, and bending resistance is ≤0.2 Ncm, and is put into a glass column for easy measuring. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is used for an exhaust system of a radioisotope or an establishment using a radiation generator, for example, a nuclear facility or a RI use room of a medical institution, and presents a radioactive substance present in the exhaust, particularly a radioactive substance. The present invention relates to a monitoring material for monitoring iodine and methyl iodide.

  In recent years, energy consumption has increased, and many nuclear power plants have been built accordingly. It is necessary to completely remove the radioactive gas in the exhaust gas discharged from these nuclear facilities. In addition, with the increase in nuclear facilities, it is important to collect and monitor radioactive gases in the environment in order to effectively cope with accidental nuclear disasters. In addition, radioisotopes are used in many places such as universities, various research institutions, medical facilities, etc., and exhaust treatment and monitoring are important. Activated carbon is mainly used as a collector for radioactive iodine contained in the discharged exhaust gas.

Narutomi, Fukuda "Air Cleaner" Vol. 10, No. 2, p. 79-94 (1972)

  Radioactive iodine is continuously collected by a sampler, and the concentration and released amount of radioactive iodine during that period are evaluated by measuring collected samples periodically. The sampler has an activated carbon-impregnated filter paper and a particle collecting filter paper on a supporting wire net, and an activated carbon cartridge under it. The sampled air is first freed from particulate radioactive material through a filter paper for collecting particles, adsorbs gaseous inorganic iodine with a filter paper containing activated carbon, and further removes organic iodine with an activated carbon cartridge. The removed amount is performed online through a radiation detector attached directly to the sampler. If the amount is small, a general-purpose detector prepared separately is used. In this case, in the case of a facility such as a hospital or research institution where the radiation dose is very small and is monitored offline, the activated carbon impregnated filter paper inside the sampler is once taken out and placed in a general-purpose detector. In a well-type gamma counter, which is generally used, measurement is performed in a glass column such as a test tube for measurement. However, in the currently used activated carbon-impregnated filter paper, the filter itself is a hard disk shape, and thus dedicated detection is performed. A part is destroyed because it is inserted into the glass column by being bent or inserted into the glass column. Furthermore, when measuring a long-term integrated radiation dose, it is necessary to repeatedly replace the glass column and the sampler. However, if the radiation dose is broken, it is impossible to return to the original column.

  The object of the present invention is to solve the above-mentioned problems, and to handle well-used gamma counter detectors for commonly used wells when taking in and out of a test tube glass column, and to measure the accumulated radiation dose by repeated use. It is a technical problem to provide a radioactive material monitoring material that enables this.

The present invention has been obtained as a result of intensive studies in view of such problems. That is, the present invention
1. A radioactive material monitoring material characterized in that a plurality of sheets containing activated carbon fibers are laminated.
2. The radioactive material monitoring material is characterized in that the thickness of the sheet is 4 mm or less and the bending resistance is 0.2 N · cm or less.
3. It is a radioactive substance monitoring material characterized in that the loop repulsion rate of the sheet is 25% or more.
4). The radioactive activated carbon having a pore volume of 3 to 30 nm in pore diameter of 0.15 cc / g or less and a pore volume of 3 nm or less in pore diameter of 0.50 cc / g or more Material monitoring material.
5). The radioactive activated carbon monitoring material is characterized in that the mean pore diameter of the fibrous activated carbon is 2 nm or less.
6). The radioactive carbon monitoring material is characterized in that an amine is attached to the sheet composed of the activated carbon fiber, and the amount of the amine attached is 3 to 40% by weight of the fibrous activated carbon.
7). It is a radioactive substance monitoring material characterized in that the desorption rate of methyl iodide is 50% or less and the thermal desorption rate of methyl iodide is 50% or less.
8). It is a radioactive substance monitoring material characterized by measuring the radiation dose by rolling the monitoring material into a test tube having an inner diameter of 6 mm to 30 mm.
It is found that the basic iodine adsorption performance is maintained and can be bent freely, the work efficiency when putting in and out of the glass column is good, and the accumulated radiation dose by repeated use can be measured. It led to the invention.

  With the present invention, at business establishments that use radioisotopes or radiation generators, when monitoring materials are taken out from a collection sampler and transferred to a glass column of a general-purpose radiation detector, they are easily rounded and have excellent handleability. The accumulated radiation dose can be monitored by taking out the rounded material and reusing it.

  In the present invention, sheets including at least activated carbon fibers are joined and laminated using an adhesive or the like, and another reinforcing sheet can be laminated. By providing sheets to each other for joining, sheets having various bending resistances and loop repulsion rates are joined to obtain predetermined properties, and it is possible to provide an option that is difficult to handle with a single sheet.

  The bending resistance in the present invention is measured by a sliding method defined in JISL1096. In this case, the required bending resistance is 0.1 N · cm or less, more preferably 0.19 N · cm, and even more preferably 0.18 N · cm. When the bending resistance is higher than 0.2 N · cm, it is not preferable because the sheet is stiff and the sheet cannot be rolled and handled. Further, the thickness is preferably 4.0 mm or less, desirably 3.9 mm, and more desirably 3.8 mm or less. When the thickness is larger than 3.0 mm, the sheet becomes bulky and it becomes difficult to roll and insert it into a glass column such as a test tube. In this case, the test tube column used has an inner diameter of 8 to 30 mm, and the lower the bending resistance, the smaller the inner diameter of the test tube.

  Further, when the monitoring material is taken out from the test tube and returned to the original position, the rounded sheet is preferably returned to the original flat sheet. In this case, it is preferable that the bending resilience rate in the loop compression method is 25% or more in the bending resilience defined in JIS L1096. Preferably it is 26% or more, and 27% is more preferable. When the bending repulsion rate is less than 25%, the sheet used for the evaluation is not preferable because the sheet is rounded and cannot be returned to the original flat sheet while being rounded, and the handleability when returning to the original sampler is deteriorated.

  The present invention is a material suitable for monitoring of inorganic iodine by reusing which the activated carbon filter paper is impossible conventionally. However, the activated carbon fiber having a pore diameter of 3 to 30 nm of 0.15 cc / g or less, a pore volume of 3 nm or less of pore volume of 0.50 cc / g or more, and an average pore diameter of 2 nm or less is amine. It is possible to make it difficult for desorption of organic iodine compounds and desorption by heating to occur, so that the desorption rate of methyl iodide is 50% or less, and the desorption rate of methyl iodide is 50%. It is possible to provide a high-performance radioactive substance monitoring material characterized in that the activated carbon is fibrous as follows.

The desorption rate of methyl iodide in the present invention is the ratio of the desorbed methyl iodide weight after the dry nitrogen gas is passed through the sample that has reached equilibrium adsorption to the methyl iodide equilibrium adsorption weight, and this value is small. This means that desorption is suppressed to a certain extent. That is, using the apparatus specified in 5.7 of JIS K 1477, dry nitrogen gas is passed through the sample that has reached equilibrium adsorption for 30 minutes, and the weight is calculated by the following formula from the weight before and after the aeration.
Desorption rate = (A−B) / A × 100
A: Methyl iodide equilibrium adsorption weight of sample B: Methyl iodide retention weight after aeration of sample

When the desorption rate of methyl iodide exceeds 50%, a large amount of methyl iodide is desorbed and the amount of methyl iodide retained in the sample decreases, which is not preferable as a radioactive substance monitoring material. The thermal desorption rate of methyl iodide is the ratio of the desorbed methyl iodide weight after heating of the sample that has reached equilibrium adsorption to the methyl iodide equilibrium adsorption weight. The smaller this value, the more heat desorption is suppressed. Means that That is, the heat desorption rate is obtained by heating the sample that has reached equilibrium adsorption at 100 ° C. for 3 hours in a 160 L incubator and calculating the weight of the sample before and after heating by the following formula.
Heat desorption rate = (A−C) / A × 100
A: Equilibrium methyl iodide adsorption weight of sample B: Retention weight of methyl iodide after heating of sample

  If the thermal desorption rate of methyl iodide exceeds 50%, methyl iodide is desorbed in a large amount due to the temperature rise, and the amount of methyl iodide retained in the sample decreases, which is not preferable as a radioactive substance removal filter.

  In the present invention, the activated carbon impregnated with amine preferably has an average pore diameter of 2 nm or less because the smaller the average pore diameter, the higher the adsorption rate of radioactive gas. Those having an average pore diameter of 2 nm or more are not preferable because a large amount of adsorbed gas is desorbed. The average pore diameter here is measured using, for example, a high-speed specific surface area / pore distribution measuring apparatus (ASAP 2010 manufactured by Shimadzu Corporation), and is determined by the BET method assuming that the pore shape of the activated carbon fiber is cylindrical. It is calculated from the specific surface area and pore volume.

  Furthermore, since the pore volume of pore diameters of 3 to 30 nm is 0.15 cc / g or less and the pore diameter is 3 nm or less and the pore volume is 0.50 cc / g or more, desorption due to desorption and heating is less likely to occur. . If the pore volume with a pore diameter of 3 to 30 nm is 0.15 cc / g or more, or the pore volume is 3 nm or less and the pore volume is 0.50 cc / g or less, the effect is almost constant. The pore volume here is measured using, for example, a high-speed specific surface area / pore distribution measuring apparatus (ASAP2010 manufactured by Shimadzu Corporation). It calculates from the pore distribution calculated | required by HK (Horvath-Kawazoe) method.

  In the present invention, it is important to use activated carbon fibers. Activated carbon fiber has a higher gas adsorption rate than conventional granular activated carbon, can exhibit an excellent collection and removal effect, and is flexible and flexible in terms of shape molding. Active carbon fibers include natural cellulose fibers such as cotton and hemp, regenerated cellulose fibers such as rayon, polynosic, and melt spinning, and polyvinyl alcohol fibers and acrylic fibers, aromatic polyamide fibers, crosslinked formaldehyde fibers, and lignin fibers. Synthetic fibers such as phenolic fibers and petroleum pitch fibers are preferable. Recycled cellulose fibers and phenolic fibers are preferred because the obtained activated carbon fibers have high physical properties (strength, etc.) and excellent adsorption performance. It is good to manufacture using acrylic fiber. Specifically, after weaving, knitting, or nonwoven fabric using these short fibers or long fibers of the raw material fiber, an appropriate flameproofing agent is added as necessary, and flameproofing is performed at a temperature of 450 ° C. or lower. Activated carbon fibers can be produced by a known method in which carbonization is activated at a temperature of 500 ° C. or higher and 1000 ° C. or lower after treatment.

The activated carbon fiber may be formed into a sheet form such as a woven fabric, a knitted fabric, a nonwoven fabric, or a felt shape, and a paper-like material obtained by mixing activated carbon fibers with other fiber materials is also used. Is possible. However, a woven fabric or a knitted fabric is preferably used as the activated carbon fiber which is suitable for obtaining a suitable bending resistance and thickness and producing a high-performance sheet. As a woven fabric, a plain plain weave, a twill weave, and a satin weave are suitable, and as a knitted fabric, a smooth knitting, a milling knitting, and a mari freeze are preferably used. The basis weight of the sheet, preferably ^{30~1000g / m 2, 50~700g / m} 2 is particularly preferred. If it is less than 30 g / m ² , not only the ability to collect radioactive substances is lowered, but also the sheet strength is extremely lowered, which is not preferable in handling. On the other hand, if it exceeds 1000 g / m ² , the air permeability is impaired and the sheet becomes too thick and the handleability is lowered.

  The fiber diameter of the activated carbon fiber is desirably 3 to 20 μm, and more desirably 5 to 15 μm. When the fiber diameter is less than 3 μm, it is difficult to obtain sufficient strength, and when the fiber diameter exceeds 20 μm, it may be difficult to round the sheet.

The amine used in the present invention is represented by the following general formula.

  In which R1, R2 and R3 are hydrogen and substituted or unsubstituted alkyl, aryl, alkaryl, aralkyl, alicyclic, heterocyclic and the formula -NR'R "is the same group as R1, R2, R3 R1, R2 and R3 cannot all be selected from hydrogen and methyl, but can be taken together with any of R1 and R2 together with nitrogen to represent a heterocyclic group, or R1, Together with any two of R2 and R3, it comprises a group of the formula = CR '' 'R' '' '(R' '' and R '' '' are selected from R1, R2 and R3) Selected from the group. Included in R1, R2 and R3 are also unsaturated, polymeric substituted or unsubstituted aliphatic or aromatic groups.

  Specifically, 1,4-diaza-2,2,2-picyclooctane (triethylenediamine), N, N′-bis- (3-aminopropyl) -piperazine, N, N-dimethyl-aminoethyl methacrylate N, N-dimethylaminopropylamine, 3-aminopropyltrimethoxysilane, 1,5-diazabicycloundecene, poly-tert-butylaminoethyl methacrylate, polyethyleneimine, 1,5-diazapicyclo [4,3 , 0] non-5-ene, 1,5-diazapicyclo [5,4,0] unde-7-5-ene, 2-methyl-1,4-diazapicyclo [2,2,2] octane, phenylhydrazine, 2 -Cyanopyridine, diisopropylamine, trimethylaminoethylpiperazine, hexamethylenetetramine, methylpolyethyleneimine And polyalkyl polyamines. In particular, 1,4-diaza-2,2,2-picyclooctane (triethylenediamine) is excellent in the amount of attachment and handling.

  The amount of amine added is preferably 3 to 40% by weight, particularly 5 to 30% by weight. If it is less than 3% by weight, the effect that desorption and desorption due to heating are difficult to occur is small, and if it exceeds 40% by weight, the adsorbent fills pores more than necessary and the adsorption performance is lowered, which is not preferable. Examples of the method for attaching the amine include a method in which a sheet made of the activated carbon fiber is dipped in an amine solution and dried, or a method in which an amine solution is sprayed to attach the solution and then dried.

  In the present invention, as a method of laminating sheets made of activated carbon fibers or sheets made of activated carbon fibers and a sheet made of another material, a thermoplastic adhesive sheet is sandwiched between the laminated sheets and heated rolls. Inserting and pressurizing into a powder, spraying a powdery adhesive made of thermoplastic resin between the heated rolls and applying pressure, or spraying with a spray nozzle in a molten state of the thermoplastic resin A known technique such as a method of inserting and pressing between rolls or a needle punching method can be arbitrarily used.

Furthermore, in the present invention, the sheet made of activated carbon fibers can be laminated for the purpose of protecting a sheet made of another material on at least one side if necessary. As the form of the sheet, an appropriate one such as woven, knitted, non-woven, or paper can be used. Although there is no particular limitation, the basis weight of the sheet is preferably ²⁰ to 150 g / m ² . If it is less than 20 g / m ² , the effect of protecting the sheet made of activated carbon fibers is small, and if it exceeds 150 g / m ² , the air permeability becomes poor, and it is difficult to efficiently vent gas to the sheet made of activated carbon fibers. Therefore, it is not preferable.

  Various materials can be used for the protective sheet in accordance with the bending resistance after lamination and the air permeability shown above, but polypropylene (PP) having a fiber diameter of 0.5 to 100 μm (preferably 1 to 50 μm). Spunbond such as polyester (PET) can be suitably used.

  The present invention will be described in further detail with reference to the following examples. However, the following examples are not intended to limit the present invention, and all modifications that do not depart from the spirit of the present invention are included in the technical scope of the present invention. .

The measurement method was based on the following method.
Bending softness: Method B (sliding method) was adopted among the bending resistance tests defined in 6.19 of JIS L 1096-1990.
Thickness: The method defined in 6.5 of JIS L1096-1990 was followed.
Loop rebound rate: The loop rebound rate described in the C method (loop compression method) in the bending rebound characteristic test defined in 6.20 of JIS L1096-1990 was adopted.
Average pore diameter: ASAP2010 manufactured by Shimadzu Corporation was used, and the pore shape was calculated from the specific surface area and pore volume by the BET method, assuming a cylindrical shape.
Pore volume: ASAP2010 manufactured by Shimadzu Corporation was used, and the mesopores were calculated from the pore distribution determined by the BJH (Barrett-Joyner-Halenda) method and the micropores by the HK (Horvath-Kawazoe) method.
Amine addition amount: It was calculated from the difference between the weight of the activated carbon before being attached to the aqueous amine solution and the weight of the activated carbon after being dried at 100 ° C. for 1 hour after the addition.
Desorption rate: Using an apparatus defined in 5.7 of JIS K 1477, a 25 ° C. nitrogen stream containing methyl iodide vapor was aerated at a rate of 2 L / min for 1 hour, and then dry nitrogen gas at 25 ° C. was added. It was determined from the weight loss of the monitoring material sample after aeration for 30 minutes at 1.8 L / min.
Heat desorption rate: Using a device defined in 5.7 of JIS K 1477, a nitrogen stream containing methyl iodide vapor at 25 ° C. was aerated at a rate of 2 L / min for 1 hour, and then 100 ° C. in a 160 L thermostat. It was determined from the weight loss of the monitoring material sample after heating at 0 ° C. for 3 hours.

Example 1
The basis weight is 55 g / m ² , the thickness is 0.50 mm, the pore volume with a pore diameter of 3 to 30 nm is 0.01 cc / g, the pore volume with a pore diameter of 3 nm or less is 0.73 cc / g, and the average pore diameter is A knitted sheet made of fibrous activated carbon having a fiber diameter of 1.80 nm and a fiber diameter of 10 μm is immersed in a 1.0% aqueous solution of 1,4-diaza-2,2,2-picyclooctane (triethylenediamine) for 1 hour, A sheet made of impregnated fibrous activated carbon having a dried and amine adhering amount of 14.7% by weight was obtained. Two sheets of this sheet were laminated and bonded at 82 ° C. with a heat-melt adhesive sheet (sheath PVA / core PP) having a basis weight of 15 g / m ^{2, and} a polyester spunbond nonwoven fabric having a basis weight of 80 g / m ² (fiber diameter) 7 μm) was laminated and bonded at 82 ° C. with a heat-melt adhesive sheet (sheath PVA / core PP) having a basis weight of 15 g / m ² to obtain Example 1.

(Example 2)
The basis weight is 120 g / m ² , the thickness is 1.1 mm, the pore volume with a pore diameter of 3 to 30 nm is 0.01 cc / g, the pore volume with a pore diameter of 3 nm or less is 0.73 cc / g, and the average pore diameter is 1. A knitted sheet composed of activated carbon fibers having a fiber diameter of 1.80 nm and a fiber diameter of 10 μm is immersed in a 1.0% aqueous solution of 1,4-diaza-2,2,2-picyclooctane (triethylenediamine) for 1 hour, A sheet made of impregnated activated carbon fibers with an amount of amine adhering of 14.7% by weight was obtained. Laminating adhesive at 82 ° C. to afford Example 2 This sheet 2 sheets of basis weight 15 g / m ² hot melt adhesive sheet (sheath PVA / core PP).

Example 3
The basis weight is 120 g / m ² , the thickness is 1.1 mm, the pore volume with a pore diameter of 3 to 30 nm is 0.01 cc / g, the pore volume with a pore diameter of 3 nm or less is 0.73 cc / g, and the average pore diameter is A knitted sheet composed of 1.80 nm activated carbon fibers is immersed in a 1.0% aqueous solution of 1,4-diaza-2,2,2-picyclooctane (triethylenediamine) for 1 hour, dried, and attached with amine. A sheet made of impregnated activated carbon fibers in an amount of 14.7% by weight was obtained. Three of these sheets were adhered and laminated with a basis weight of 15 g / m ² hot-melt adhesive sheet (sheath PVA / core PP) to obtain Example 3.

(Comparative example)
The basis weight is 120 g / m ² , the thickness is 1.1 mm, the pore volume with a pore diameter of 3 to 30 nm is 0.01 cc / g, the pore volume with a pore diameter of 3 nm or less is 0.73 cc / g, and the average pore diameter is A knitted sheet made of 1.80 nm fibrous activated carbon is immersed in a 1.0% aqueous solution of 1,4-diaza-2,2,2-picyclooctane (triethylenediamine) for 1 hour, dried, and attached with amine. A single layer sheet made of impregnated fibrous activated carbon having an amount of 14.7% by weight was obtained.

In each of Examples 1, 2, 3 and Comparative Examples, nitrogen containing 1/10 saturated methyl iodide vapor at 25 ° C. was aerated at a rate of 2 L / min for 1 hour, and then dry nitrogen gas at 25 ° C. After degassing at a rate of 8 L / min for 30 minutes and nitrogen containing 1/10 saturated methyl iodide vapor at 25 ° C. for 1 hour at a rate of 2 L / min, the inside of a 160 L thermostat Table 1 shows the heat desorption rate obtained by heating at 100 ° C. for 3 hours. Table 1 shows the bending resistance, thickness, loop repulsion rate, and handling property when inserted into a glass column on a test tube.

As is apparent from Table 1, Examples 1, 2, and 3 are easier to handle than a comparative example 1 in terms of handling when measured with a general-purpose detector as a monitoring material for collecting radioactive substances, and methyl iodide. It can be said that it is an excellent radioactive substance monitoring material that has a low desorption rate and thermal desorption rate, and is less susceptible to desorption of methyl iodide and desorption due to heating.
On the other hand, the comparative example is weak and easy to become fine wrinkles, suitable to be put into a glass column, difficult to round into a shape, and when bent forcibly, it was broken into powder or the activated carbon fiber dropped out, After taking out from the glass column, it was difficult to return to the original flat sheet, and remeasurement for monitoring the integrated radiation dose was difficult.

  According to the present invention, in an establishment that uses a radioisotope or a radiation generator, the handling material is excellent when the monitoring material is taken out from the collection sampler and transferred to a glass column of a general-purpose radiation detector, and reused. The integrated radiation dose can be monitored by In addition, it has excellent ability to collect and monitor organic iodine compounds contained in radioactive gas exhausted from the office, especially to collect radioactive iodine and methyl iodide by suppressing desorption and heat desorption. A suitable radioactive substance monitoring material can be obtained.

Claims (8)

A radioactive material monitoring material, wherein a plurality of sheets containing activated carbon fibers are laminated. The radioactive substance monitoring material according to claim 1, wherein the thickness is 4 mm or less and the bending resistance is 0.2 N · cm or less. 3. The radioactive substance monitoring material according to claim 1, wherein the repulsion rate is 25% or more. The fibrous activated carbon has a pore volume at a pore diameter of 3 to 30 nm of 0.15 cc / g or less, and a pore volume of a pore diameter of 3 nm or less is 0.50 cc / g or more, Item 4. The radioactive substance monitoring material according to any one of Items 1 to 3. The radioactive substance monitoring material according to any one of claims 1 to 4, wherein an average pore diameter of the fibrous activated carbon is 2 nm or less. The radioactive material according to any one of claims 1 to 5, wherein an amine is attached to the laminated sheet containing activated carbon fibers, and the amount of the amine attached is 3 to 40% by weight of the fibrous activated carbon. Substance monitoring material. The radioactive substance monitoring material according to any one of claims 1 to 6, wherein the desorption rate of methyl iodide is 50% or less and the thermal desorption rate of methyl iodide is 50% or less. The radioactive substance monitoring material according to any one of claims 1 to 7, wherein the radiation dose is measured by being rolled into a test tube having an inner diameter of 6 mm to 30 mm.