JP3456780B2 - How to fix radioactive iodine - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a nuclear power plant, <br/> about solid of how radioactive iodine generated from nuclear facilities such as nuclear fuel reprocessing plant.

[0002]

2. Description of the Related Art Radioactive iodine, which is a problem at spent nuclear fuel reprocessing plants and nuclear power plants, is mainly ¹³¹ I, ¹²⁹
I etc. Especially ¹²⁹ I generated frequently from reprocessing plants
Has a very long half-life of 1.6 × 10 ⁷ years and is known to be an important nuclide in evaluating the dose equivalent of exposure.

This radioactive iodine is a silver adsorbent from a reprocessing plant (iodine gas adsorbed on an iodine adsorbent (silver silica gel, silver zeolite, silver alumina, etc.)).
Generated as waste (waste silver adsorbent). Iodine in this waste silver adsorbent is mainly present in the form of AgI and AgIO ₃ .

As a method for fixing the waste silver adsorbent, there are hydrothermal solidification, low melting point glass solidification, and cement solidification. Hydrothermal solidification is to prepare a solidified body by mixing waste silver adsorbent with glass powder or silicate powder and hot pressing at a temperature of about 300 ° C and a pressure of about 20 MPa in a state of containing water. This solidified body suppresses radioactive iodine leaching by covering the waste silver adsorbent with a dense solidified matrix.

Low melting point vitrification is at low temperature (about 500 ° C)
The waste silver adsorbent is covered with a glass matrix to form a solidified body using a glass that melts at. Leaching of radioactive iodine is controlled by the compactness of the glass matrix.

Cement solidification is to produce a solidified product by a hydration reaction between a hydraulic inorganic compound and water. Since the cement hydrate has adsorptivity for iodine, it suppresses the leaching of radioactive iodine by the delaying effect.

[0007] Further, as the structural material of the disposal site for storing these solidified bodies for a long time, mortar and concrete in which sand, gravel and the like are mixed with cement-based solidified material are mainly used.

[0008]

As described above, radioactive iodine, particularly ¹²⁹ I, has a very long half-life and is an important nuclide in terms of the exposure to the human body. Such important nuclides are disposed in the deep strata. This stratum environment is a reducing atmosphere, and AgI and AgIO ₃ in the waste silver adsorbent are expected to decompose into Ag and I. Therefore, in order to process and dispose of this waste silver adsorbent, an immobilizing material and an immobilizing method capable of immobilizing radioactive iodine in a long-term stable compound are required.

Therefore, there are the following problems when the conventional solidification method is used.

Since the hydrothermally solidified body is treated at high temperature and high pressure, iodine may be separated when the solidified body is produced. In addition, since the solidified matrix formed does not have a bond between the solidified matrix and AgI or AgIO ₃ , it is expected that iodine will be instantly released if the solidified matrix loses its soundness during geological disposal. It

Since the low-melting-point vitrified body is treated at a high temperature of about 500 ° C., iodine may be separated during preparation of the solidified body. In addition, as with the hydrothermal solidified product, the solidified product that is formed does not have a bond between the solidified product matrix and AgI or AgIO ₃ , so if the soundness of the solidified product matrix is lost during geological disposal, iodine will be released instantly. Expected to be done.

Cement solidification is the most effective solidification method because there is no risk of radioactive iodine being separated during the solidification reaction because it solidifies at room temperature. However, since the solidified body is water-permeable and reducing, the iodine compound in the solidified body may hydrolyze to release radioactive iodine. In addition, the cement-based solidifying material has a high radioactive iodine content in the solution (iodine concentration 1 x
It has been considered that the adsorbability decreases at 10 ^-3 mol / l or more).

Further, since the structural material of the disposal site for disposing of these solidified bodies is also a cement-based solidified material, it has been considered that the radioactive iodine-confining property is low like cement solidification.

[0014] Problem to decrease adsorptivity as iodine concentration increases there Ru in the conventional cement materials.

[0015]

[0016] I I, object of the invention is to provide an immobilized how radioactive iodine can be immobilized to a long-term stable compound in the radioactive iodine to address the above aspect of the present invention.

[0017]

According to the present invention, a cement-based solidifying material characterized by comprising 15 to 70% by weight of alumina cement and the balance being a calcium compound, or a hardened and ground product of alumina cement is 20% by weight. 90% immobilizing material balance of calcium compounds and calcium aluminate 20% and 80%, Ru using an immobilized material balance of calcium compounds.

The method of immobilizing radioactive iodine according to the present invention is a monosorbate type compound (3CaO.Al ₂ O ₃ .CaI ₂ .mH) formed by a reaction between a calcium compound of each immobilizing material and an aluminate phase mineral. ₂ O (or 3CaO ・ Al ₂ O ₃・ Ca (IO ₃ ) ₂・ mH
₂ O)) is a method of immobilizing radioactive iodine.

[0019]

[Function] Radioactive iodine is converted to monosulfate type compound (3CaO.Al ₂ O ₃ .CaI ₂₎ by converting calcium compound from alumina cement into a cement-based solidifying material.
・ MH ₂ O or 3CaO ・ Al ₂ O ₃・ Ca (IO
₃ ) Can be immobilized as ₂ · mH ₂ O).

[0020]

[Equation 1]

Since the main component of the cement-based solidifying material is calcium aluminate, it has little dependence on iodine concentration. The reason for limiting the amount of alumina cement to 15% to 70% in weight% is that if the concentration of alumina cement is 15% to 70%, a higher distribution coefficient is obtained compared to conventional cement-based solidifying materials. If it is out of%, it is not possible because the partition coefficient is lowered and the adsorptivity of iodine is lowered.

Further, the reason why the amount of the alumina cement pre-cured and crushed by weight% is limited to 20% to 90% is that if the concentration of the cured alumina cement is 20% to 90%, the conventional cement-based solidifying material is used. A high value is obtained in comparison with the adsorptivity, but if it deviates from 20% to 90%, the adsorptivity will decrease, which is not possible.

Furthermore, the reason why the calcium aluminate is limited to 15% to 60% by weight is that the calcium aluminate concentration is 15% to 60%, which is higher than that of the conventional cement-based solidifying material. Is obtained, but from 15% to 60%
If it is out of the range, the distribution coefficient will decrease, which is not possible.

[0024]

EXAMPLES Examples of the material for immobilizing radioactive iodine and the immobilization method according to the present invention will be described. (Example 1) Two kinds of JIS standard alumina cement were used, and calcium hydroxide was added thereto to prepare a raw material so as to be 100% by weight.

After mixing these uniformly, water was added in an amount of water / adjusted raw material ratio of 0.5 and kneaded with a mixer for about 5 minutes. Aged at room temperature and 90% relative humidity for 28 days. After curing, the hydrate was crushed to 42 mesh or less. Then, 3 g of the ground product was collected. The ground product was added to 30 ml of a 0.1 M NaI solution and kept in a thermostat at 25 ° C. for 7 days. This solution was filtered through a membrane filter having a pore size of 0.45 μm, and iodine in the filtrate was measured by ICP emission spectrometry. From these measurement results, the distribution coefficient was calculated by the following formula.

[0026]

[Equation 2]

That is, the larger the partition coefficient is, the larger the amount of iodine contained in the solid phase, and the better the sorption of radioactive iodine. The test results are shown in FIG. FIG. 1 shows the relationship between the partition coefficient and the alumina cement concentration weight%. From FIG. 1, it is recognized that when the concentration of alumina cement is 15% to 70%, a distribution coefficient higher than that of conventional cement-based solidified materials by one digit or more can be obtained.

(Example 2) Two kinds of JIS-standard alumina cement were preliminarily cured at a water / cement ratio of 0.5 and crushed to 42 mesh or less, and the crushed product and calcium hydroxide were combined to obtain 100 wt%. The raw materials were prepared as follows.

Next, 3 g of the raw material was collected. The sampled raw material was added to 30 ml of 0.1 M NaI solution, and the mixture was kept in a thermostat at 25 ° C. for 7 days. This solution was filtered through a membrane filter having a pore size of 0.45 μm, and iodine in the filtrate was measured by ICP emission spectrometry. From these measurement results, the distribution coefficient was calculated by the following formula.

The test results are shown in FIG. FIG. 2 shows the relationship between the partition coefficient and the concentration weight of the hardened alumina cement. From FIG. 2, it is recognized that when the concentration of the hardened alumina cement is 20% to 90%, a value higher by one digit or more than that of the conventional cement-based solidifying material can be obtained.

(Example 3) Calcium aluminate (Ca
Al ₂ O ₃ ) was used, and calcium hydroxide was added thereto, and the raw material was mixed so as to be 100% by weight.

Next, 3 g of the prepared raw material was collected. 0.
The separated raw material was added to 30 ml of a 1M-NaI solution, and the mixture was kept in a thermostat at 25 ° C for 7 days. This solution was filtered through a membrane filter having a pore size of 0.45 μm, and iodine in the filtrate was measured by ICP emission spectrometry. The partition coefficient was calculated from these measurement results.

The test results are shown in FIG. FIG. 3 shows the relationship of the distribution coefficient to the calcium aluminate concentration weight. From Fig. 3, the concentration of calcium aluminate is 15%
If it is 60%, it is 1 compared to the conventional cement-based solidifying material.
It is recognized that a partition coefficient higher than an order of magnitude can be obtained.

Example 4 JIS standard alumina cements 1, 2, 3, 4, and 5 were used as cement, and calcium hydroxide was mixed and adjusted to a weight ratio of 1: 2.

After mixing these uniformly, water was added in an amount of water / adjusted raw material ratio of 0.5 and kneaded with a mixer for about 5 minutes. Aged at room temperature and 90% relative humidity for 28 days. After curing, the hydrate was crushed to 42 mesh or less. Then, 3 g of the ground product was collected. The ground product was added to 30 ml of a 0.1 M NaI solution and kept in a thermostat at 25 ° C. for 7 days. This solution was filtered through a membrane filter having a pore size of 0.45 μm, and iodine in the filtrate was measured by ICP emission spectrometry. The partition coefficient was determined from these measurement results.

The test results are shown in Table 1. From Table 1, JIS
It is recognized that the use of any of the standard alumina cements 1, 2, 3, 4, and 5 makes it possible to obtain a partition coefficient higher than that of conventional cement-based solidified materials by one digit or more.

[0037]

[Table 1]

(Example 5) 3C in calcium aluminate
aO ・ Al ₂ O ₃ , CaO ・ Al ₂ O ₃ , CaO ・ 2A
l ₂ O ₃ and CaO · 6Al ₂ O ₃ were used, and calcium hydroxide was mixed and adjusted to a weight ratio of 2: 3.

Next, 3 g of the prepared raw material was collected. 0.1M
-The separated raw material was added to 30 ml of NaI solution and kept in a thermostat at 25 ° C for 7 days. This solution was filtered through a membrane filter with a pore size of 0.45 μm to remove iodine in the filtrate.
It was measured by CP emission spectrometry. The partition coefficient was calculated from these measurement results.

The test results are shown in Table 2. From Table 2, calcium aluminate with 3CaO ・ Al ₂ O ₃ and CaO ・ Al
₂ O ₃ , CaO · 2Al ₂ O ₃ , CaO · 6Al ₂ O ₃
It is recognized that any of the above can provide a partition coefficient higher than that of conventional cement-based solidified materials by one digit or more.

[0041]

[Table 2]

(Example 6) JIS standard alumina cement was used as cement, and calcium hydroxide and calcium oxide were mixed and adjusted to a weight ratio of 1: 2.
After mixing them uniformly, water was added in an amount of water / adjusted raw material ratio of 0.5 and kneaded with a mixer for about 5 minutes. Aged at room temperature and 90% relative humidity for 28 days. After curing, the hydrate
It was crushed to 42 mesh or less. Then, 3 g of the ground product was collected. Add the crushed material to 30 ml of 0.1 M NaI solution, and add 25
It was kept in a constant temperature bath at ℃ for 7 days. This solution was filtered through a membrane filter having a pore size of 0.45 μm, and iodine in the filtrate was measured by ICP emission spectrometry. The partition coefficient was determined from these measurement results.

The test results are shown in Table 1. It is recognized from Table 1 that a distribution coefficient higher than that of conventional cement-based solidified materials by one digit or more can be obtained by using either calcium hydroxide or calcium oxide.

Example 7 Calcium aluminate (Ca
Al ₂ O ₃ ) was used, and calcium hydroxide was added to the mixture to prepare an adsorbent having a concentration of 100 wt%. Next, the prepared adsorbent and Portland cement were uniformly mixed to obtain a cement-based solidifying material, and water was added to the solidifying material in an amount of water / adjusting material ratio of 0.5 and kneaded with a mixer for about 5 minutes. Aged at room temperature and 90% relative humidity for 28 days. After curing, the compressive strength of the cement solidified product and the partition coefficient test of iodine used in Example 1 were performed.

The test results are shown in FIG. From FIG. 4, it can be seen that the cement-based solidified material containing 5 to 70% of the adsorbent does not affect the compressive strength and the partition coefficient is higher than that of conventional cement by one digit or more.

(Embodiment 8) Alumina cement and calcium hydroxide were mixed in advance at a weight ratio of 1: 2 and hardened, and the crushed product was admixed with Portland cement at a weight ratio of 1: 1 to prepare water. The cement solidification material kneaded at a ratio of / adjusted raw material of 0.5 was used for filling solidification or kneading solidification of the waste silver adsorbent.

Here, the waste silver adsorbent is a waste of silver silica gel or silver zeolite silver alumina adsorbing radioactive iodine. In addition, filling and solidification is a method of filling cement-based solidifying material in a disposal container containing waste to solidify it, kneading and solidifying and kneading the waste and cement-based solidifying material, and pouring them into the disposal container to form a solidified body. Is the way to do it.

The density, compressive strength and partition coefficient of iodine of the solidified product were measured. The results are shown in Table 3. It is recognized that the density and compressive strength are comparable to conventional cement, and the distribution coefficient is higher than that of conventional cement.

[0049]

[Table 3]

[0050]

According to the present invention, it is possible to easily form a hardened product of radioactive waste that is particularly highly adsorbable to radioactive iodine by mixing and solidifying alumina cement and a calcium compound. , Radioactive iodine can be immobilized in long-term stable compounds. Moreover, radioactive iodine can be fixed by using this cured product as an adsorbent.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a partition coefficient of iodine with respect to an alumina cement concentration according to Example 1 of the present invention.

FIG. 2 is a characteristic diagram showing the partition coefficient of iodine with respect to the concentration of the hardened alumina cement according to Example 2 of the present invention.

FIG. 3 is a characteristic diagram showing the partition coefficient of iodine with respect to the calcium aluminate concentration according to Example 3 of the present invention.

FIG. 4 is a characteristic diagram showing the partition coefficient of iodine and the compressive strength of a solidified body with respect to the amount of adsorbent added according to Example 7 of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikio Wada 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Corporation Yokohama Works (56) Reference JP-A-5-34649 (JP, A) JP-A-63 -255695 (JP, A) JP-A-60-171498 (JP, A) JP-A-7-256091 (JP, A) JP-A-8-146194 (JP, A) G. W. Bird and V.J. Lopata, Solutio n interaction of n clear waste anion s with selected geological material s, In Scientific Bas sis pu ran wa, 980. 2, pp. 419-426 Peter Taylor and Vincent J. Lopata, Stability of bismuth oxydiodes in a queous solutions at 25 ° C, Can. J. Chem. 1986, Vol. 64, pp. 290- 294 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G21F 9/30 515 G21F 9/16 521 G21F 9/02 511

Claims (6)

(57) [Claims] 1. Alumina cement of 15 to 70% by weight.
% And the balance is a calcium compound, or 20 to 90% that is obtained by previously curing and grinding alumina cement, and the balance is a calcium compound, or calcium aluminate is 15 to 60% and the balance is a material consisting of a calcium compound. Type compound 3CaO
Al ₂ O ₃ · Ca I ₂ · mH ₂ O or 3CaO · A
l ₂ O ₃ · Ca (IO ₃ ) ₂ · mH ₂ O (where m is
Any one of 10 to 12) , which is a method for immobilizing radioactive iodine. 2. Alumina cement of 15 to 70% by weight.
%, The immobilization method of radioactive iodine according to claim 2, characterized by using the balance was crushed by curing a cement solidifying material consisting of calcium compound to the adsorbent iodine. 3. A method for immobilizing radioactive iodine according to claim 1, which comprises using a cement solidifying material using the adsorbent filling solidification of Haigin adsorbent. 4. A method for immobilizing radioactive iodine according to claim 1, which comprises using a cement solidifying material using the adsorbent kneading solidification of Haigin adsorbent. Wherein said cement solidifying material Portland cement or Portland cement and method for immobilizing radioactive iodine claim 1, wherein the blast furnace slag is a mixture of,. 6. A pulverized one obtained by preliminarily hardening the cement solidifying material, method for immobilizing radioactive iodine according to claim 1, which comprises using the aggregate aligned particle size.