Treatment equipment and method for radioactive substance

Abstract

To reduce radioactivity by easily incurring disintegration in a radioactive substance such as tritium or cesium 137 by simple equipment by utilizing ceramic material.SOLUTION: Treatment equipment comprises: a ceramic material containing SiO2 in 45 to 75 wt.%, Al2O3 in 7.5 to 20 wt.% and Fe in 3 to 25 wt.% and containing Ca, Na, Mg and K in a total amount in 3 to 10 wt. / %; a processing tank filled with the ceramic material; and a circulation pump which circulates water containing a radioactive substance in the processing tank. In the processing tank, water containing the radioactive substance is brought into contact with the ceramic material. A strong electric field is generated on a pole surface of the ceramic material, electric energy is accumulated in the radioactive substance by such an electric field top promote beta decay. Thus, disintegration is easily made occur in the radioactive substance by the simple equipment, and radioactivity can be reduced.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for treating radioactive materials, which induces decay of radioactive materials such as tritium and cesium-137, thereby reducing their radioactivity. [Background technology]

[0002] It is an urgent task to render radioactive materials such as tritium-containing water harmless and dispose of them. The applicant is aware of the following Patent Document 1 as a prior art document related to the decomposition and removal of such tritium-containing water. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-41988 A

[0004] The above-mentioned Patent Document 1 relates to a method and an apparatus for decomposing and removing tritium-containing water, and includes the following description: [summary] [Challenge] Decompose and remove tritium, a radioactive substance contained in tritium-containing water, which is radioactively contaminated water. [Solution] A closed tritium decomposition and removal furnace 140 is prepared, which includes a tritium-containing water storage container 110 and a ceramic body 120 for decomposing and removing tritium containing a first natural radioactive element consisting of an element that emits alpha rays, and promotes tritium removal while utilizing the alpha decay of the first natural radioactive element, and superheated steam of tritium-containing water is generated using superheated air generated by burning fuel while introducing air, and the superheated steam of tritium-containing water is mixed and filled with the superheated air, and a first chemical reaction is caused by the alpha rays to change the nitrogen of the superheated air into oxygen with a mass number of 17 and a proton number of 8 by the protons, and a second chemical reaction is caused to react with tritium and protons to change it into helium, thereby decomposing and removing tritium. DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0005] In the technology of Patent Document 1, a first chemical reaction occurs in which oxygen with eight protons is obtained by superheating combustion and alpha rays, and a second chemical reaction occurs in which protons and tritium are converted into helium. In this way, superheating by combustion is necessary to cause a complex two-stage reaction. Therefore, there is a problem in that large-scale facilities such as a combustion furnace and a superheated steam gas generator, as well as a large amount of combustion energy are required.

[0006] The present invention has been made in order to solve the above problems and with the following objectives. The present invention provides an apparatus and method for treating radioactive materials that can easily cause radioactive materials such as tritium and cesium-137 to decay and reduce radioactivity using a simple apparatus by utilizing a ceramic material. [Means for solving the problem]

[0007] The present inventors have conducted extensive research into a technology that can easily cause radioactive materials to decay using a simple device to solve the above problems. In the process, they have focused on the generation of a strong electric field on the extreme surface of the ceramic material. The generation of an electric field on the surface of the ceramic material is based on information obtained from the paper "Scale Prevention by Ceramic Balls" (Hideo Kawarada and Olivier Pironneau, doi:10.4208 / eajam 310718.02020119 East Asian on Applied Mathematics Vol.9 No.3, pp424-446 August 2019).

[0008] The inventors conceived the idea that the above-mentioned electric field would generate electric energy in the molecules of radioactive substances such as HTO, which would accelerate beta decay, and conducted further research. As a result, they discovered that the above-mentioned phenomenon occurs when using a ceramic material containing 45-75% by weight of SiO2, 7.5-20% by weight of Al2O3, and 3-25% by weight of Fe, as well as 3-10% by weight of Ca, Na, Mg, and K in total, and completed the present invention.

[0009] In order to achieve the above object, the radioactive material treatment device according to claim 1 employs the following configuration. a ceramic material containing 45 to 75 weight percent SiO2, 7.5 to 20 weight percent Al2O3, and 3 to 25 weight percent Fe, and containing 3 to 10 weight percent Ca, Na, Mg, and K in total; a treatment tank filled with the ceramic material; a circulation pump for circulating water containing radioactive materials through the treatment tank; In the treatment tank, the ceramic material is brought into contact with water containing the radioactive material.

[0010] In order to achieve the above object, the method for treating radioactive materials according to claim 2 employs the following configuration. a ceramic material containing 45 to 75 weight percent SiO2, 7.5 to 20 weight percent Al2O3, and 3 to 25 weight percent Fe, and containing 3 to 10 weight percent Ca, Na, Mg, and K in total; a treatment tank filled with the ceramic material; a circulation pump for circulating water containing radioactive materials through the treatment tank; In the treatment tank, the ceramic material is brought into contact with water containing the radioactive material. Effect of the Invention

[0011] That is, the radioactive material treatment device according to claim 1 includes a ceramic material, a treatment tank filled with the ceramic material, and a circulation pump that circulates water containing radioactive materials through the treatment tank. The water containing radioactive materials is contacted with the ceramic material in the treatment tank. The ceramic material contains 45-75% by weight of SiO2, 7.5-20% by weight of Al2O3, and 3-25% by weight of Fe, and also contains 3-10% by weight of Ca, Na, Mg, and K in total. This generates a strong electric field at the extreme surface of the ceramic material, and this electric field accumulates electrical energy in the radioactive material, accelerating beta decay, making it possible to easily cause the radioactive material to decay and reduce its radioactivity using the simple device.

[0012] The method for treating radioactive materials according to claim 2 includes preparing a ceramic material, a treatment tank filled with the ceramic material, and a circulation pump for circulating water containing radioactive materials through the treatment tank. In the treatment tank, the water containing radioactive materials is brought into contact with the ceramic material. The ceramic material used contains 45-75% by weight of SiO2, 7.5-20% by weight of Al2O3, and 3-25% by weight of Fe, and also contains 3-10% by weight of Ca, Na, Mg, and K in total. This generates a strong electric field at the extreme surface of the ceramic material, and this electric field accumulates electrical energy in the radioactive material, accelerating beta decay, making it possible to easily cause the radioactive material to decay and reduce its radioactivity using the simple device. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing an example of a model device for implementing the radioactive material treatment device and method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention relates to an apparatus and method for treating radioactive materials, which uses a ceramic material, a treatment tank filled with the ceramic material, and a circulation pump that circulates water containing radioactive materials through the treatment tank. In the treatment tank, the water containing radioactive materials is brought into contact with the ceramic material.

[0015] [Ceramic materials] The ceramic material contains 45 to 75% by weight of SiO2, 7.5 to 20% by weight of Al2O3, and 3 to 25% by weight of Fe, as well as 3 to 10% by weight of Ca, Na, Mg, and K in total.

[0016] As an example of such a ceramic composition, specifically, one containing granite as a main component can be used. The composition of granite is, for example, 1.0-2.5% by weight of Na2O, 1.0-2.5% by weight of MgO, 13-20% by weight of Al2O3, 55-70% by weight of SiO2, 1.0-2.0% by weight of SO3, 3-4% by weight of K2O, 2-4% by weight of CaO, 0.5-1.2% by weight of TiO2, and 7-15% by weight of iron oxide.

[0017] The above ceramic material may be homogeneously molded as one piece, but it is sufficient that at least the surface is formed from such a ceramic material. Therefore, a glaze (glaze) can be applied to the surface of various base materials that can withstand high temperatures, and then fired to form at least the surface from the specified ceramic material.

[0018] For example, a glaze made with a specific composition is applied to the surface of a bisque-fired material made from molded clay, dried, and then loaded into a firing furnace for firing. The firing process involves increasing the temperature at a rate of about 150°C / hour up to about 900°C, then carrying out an oxidation firing solid solution process (holding the specified temperature for a specific time) up to the specified temperature, and then holding the material at 1280°C (±10°C) for a specific time in the "reducing furnace atmosphere process" where the temperature is increased and the oxygen concentration is adjusted, and then the material is cooled slowly to 950°C in an oxidizing atmosphere, and then released into the oxidizing atmosphere in the furnace for rapid cooling. In particular, the reduction function can be strengthened by adjusting the Fe content ratio, the oxidation / reduction firing process, the required holding time, and the cooling rate, and the reaction force can be strengthened by modifying the glaze composition and firing method.

[0019] In addition, the above ceramic material can employ, as a glaze, a ceramic composition having a surface layer formed thereon, which contains 100 parts by weight of mineral fine powder containing Na, Mg, Al, Si, S, K, Ca, Ti and Fe as main components in an amount of 95% or more by weight calculated as oxide, 1 to 4 parts by weight of titanium phosphide (TiP), 3 to 5 parts by weight of manganese oxide and 1 to 2 parts by weight of magnetite.

[0020] The ceramic material is preferably formed into particles such as spheres. For forming the ceramic material into a spherical shape, for example, spherical particles having a diameter of about 3 to 12 mm can be used. In addition, when an inorganic foam or sintered body is used as the base material, it is preferable that the ceramic material is a porous material having interconnecting pores with a pore size of about 20 μm to 1 mm.

[0021] In the present invention, water containing radioactive substances is passed through and circulated in a treatment tank filled with the ceramic material, and the water containing radioactive substances is brought into contact with the ceramic material in the treatment tank.

[0022] [Processing principle] Hydrogen atoms (H) are the most abundant atom in the world around us, and when they combine with oxygen atoms (O) they become water (H2O). Tritium does not exist alone, but in many cases combines with oxygen to form tritiated water (HTO). Both H2O and HTO have similar chemical properties. Radioactive materials other than tritium that are dissolved and mixed in the water can be removed by filtration or adsorption (multi-nuclide removal equipment, etc.). However, tritium exists as tritiated water, so it cannot be removed by these methods. This is where the difficulty of removing tritium lies.

[0023] In this embodiment, "When tritiated water passes near the surface of a ceramic material placed in the treated water, electrical energy is generated in the contacting tritiated water (dielectric) based on an electric moment. That energy is distributed to the electrons emitted during tritium beta decay, increasing the maximum kinetic energy of the emitted electrons. Referring to the formula for the half-life of beta decay, this results in a decrease in the half-life. Here, the half-life means the time it takes for half of a radioactive substance to be converted into a converted substance. The shorter the half-life, the less radioactive material there is.

[0024] A ceramic material (for example, a sphere with a radius of about 1 cm) placed in natural water generates a huge electric field in an extremely thin membrane-like region (about a few nm thick) on its surface. The generation of this electric field is described in the aforementioned paper "Scale Prevention by Ceramic Balls" (Hideo Kawarada and Olivier Pironneau, doi:10.4208 / eajam 310718.02020119 East Asian on Applied Mathematics Vol.9 No.3, pp424-446 August 2019).

[0025] If the electric field above is E (V / m), its magnitude is 10 7 <E<10 13 This is described on page 429 of the above paper.

[0026] Describe the electrical energy generated in tritium water (HTO). When tritium water (a dielectric) passes near the surface of a ceramic material and is irradiated with an electric field, electrical energy W is generated in the contacting tritium water according to the following formula. W = 1 / 2 × ελ × ε0 × E 2 (J / m 3 (Refer to page 114 (4.7.4) of "Electromagnetics of Substances" by Masatoshi Nakayama, Iwanami Shoten)

[0027] E = p × 10 12 (V / m), and when the relative permittivity of tritium water ελ = 80 (almost the same as the relative permittivity of H2O), W = p 2 × 3.54 × 10 -14 (J / m 3 ) is obtained. Here, ε0 is the permittivity of vacuum = 8.8542 × 10 -12 . Let p be any positive number satisfying 0 < p < 10.

[0028] On the other hand, the molecular weight of tritium water (HTO) is 20.0275. Therefore, the mass q of one HTO molecule is q = molecular weight / NA (g) = 20.0275 × 10 -3 (kg) / 6.02 × 10 23 = 3.327 × 10 -26 (kg / molecule). Here, NA is Avogadro's number.

[0029] The specific gravity of HTO is 1.214 × 10 3 (kg / m 3 ). Therefore, when calculating the volume v per one HTO molecule, v = q / specific gravity (kg / m 3 ) = 2.74 × 10 -29 (m 3 / molecule).

[0030] The electrical energy w per one tritium water molecule in tritium water obtained by irradiation with an electric field is w = W × v = p 2x3.54x10 14 x2.74x10 -29 = p 2 x9.7x10 -15 =p 2 x6x10 4 (eV)= 0.06×p 2 × (MeV / molecule). However, 1 eV = 1.6 × 10 -19 (J).

[0031] Next, we will explain the energy obtained by the electric polarization of the tritium water molecule. The charge distribution of the tritium water molecule is H 2 It can be thought of as one H in an O molecule being replaced with a T. When tritium water molecules are exposed to an electric field, the atoms shift their relative positions, acquiring potential energy (a kind of spring energy). This energy can be thought of as the w mentioned above.

[0032] When the tritium water molecule returns to its original positional relationship after a certain time, w is released and added to the energy based on the mass difference between tritium and helium (0.02 MeV, which is also the maximum energy of the electron emitted in beta decay). As a result, the maximum energy of the electron emitted in the beta decay of the tritium atom mentioned above increases. This increase in maximum energy results in a decrease in the half-life of tritium beta decay. For example, if equation (22), which expresses the total transition probability of beta decay on page 5 of the literature (Matsumoto Kenichi, Tritium Beta Decay and Neutrino Mass, Toyama University Tritium Chemical Center Research Report 2:1-9, 1982), is differentiated by the maximum energy Emax of the emitted electron, a simple calculation can show that the derivative is always positive. Note that pmax can be expressed by equation (23). Therefore, the half-life is the inverse of the total transition probability, and therefore a decreasing function of the maximum energy Emax of the emitted electron. In this way, the decrease in the half-life of tritium beta decay can be demonstrated, and the mechanism behind this will be specifically illustrated in paragraph

[0034] below. Thus, the effect of the ceramic material is to reduce the half-life of beta decay, i.e. to accelerate the conversion of tritium to helium.

[0033] In general, when an atomic nucleus undergoes beta decay, an electron and a neutrino are emitted. The transition probability or half-life of beta decay depends on the transition probability of the nucleus and the maximum kinetic energy of the emitted electron (for example, reference: Kenichi Matsumoto, Beta Decay of Tritium and Neutrino Mass, Toyama University Tritium Chemistry Center Research Report 2:1-9, 1982). Incidentally, the maximum kinetic energy of the emitted electrons in the beta decay of tritium is At approximately 0.02 MeV (additional energy = 0), The half-life is approximately 12 years.

[0034] According to the above-mentioned document (by Kenichi Matsumoto), Table 1, equation (25) on page 5 and equation (26) on page 6, the energy added to the emitted electron in standard tritium beta decay (in paragraph

[0033] ) by electric field irradiation is, (1) At 0.04 MeV (corresponding to p = 0.817), the maximum energy of the emitted electrons is 0.06 MeV in total. As a result, Half-life = 106 days It becomes. (2) At 0.18 MeV (corresponding to p = 1.73), the maximum energy of the emitted electrons is 0.2 MeV in total, which is the maximum energy of tritium beta decay. Half-life = 32 hours A rapid decrease in the half-life is observed. The half-life of standard beta decay (additive energy = 0) in paragraph

[0033] (approximately 12 years) and the results of (1) and (2) illustrate the decrease in the half-life of beta decay due to an increase in the maximum energy of the emitted electron.

[0035] As explained above, by placing ceramic materials in the contaminated water channel and increasing the contact area between them and the contaminated water, it is possible to shorten the half-life of the tritium water.

[0036] [Device Description] FIG. 1 is a diagram showing an example of a model device for implementing the radioactive material treatment device and method of the present invention.

[0037] This apparatus comprises a treatment tank 10, a water tank 11, a circulation pump 12, a flow meter 13, and a control valve 14.

[0038] The treatment tank 10 is filled with the above-mentioned ceramic material (not shown). In this example, four 1 m long carbon steel piping pipes (50A: inner diameter 52.9 mm) are used as the treatment tanks 10. The treatment tanks 10 are filled with 4 kg of the above-mentioned ceramic material (approximately spherical with a diameter of 10φ). In other words, 1 kg is filled in each treatment tank 10, for a total of 4 kg. The four treatment tanks 10 are piped in series, and the treated water flows and circulates in order.

[0039] The circulation pump circulates the treated water, which is water containing radioactive materials, through the treatment tank 10, and has a flow rate of 200 L / hour or more. The treated water is RO water to which radioactive materials have been added. The system is also equipped with an electrolytic level meter, a pH meter, and a radiation meter (not shown).

[0040] The above-mentioned device was configured so that treated water was caused to flow and circulate through the treatment tank 10, and the water containing the radioactive material was brought into contact with the ceramic material within the treatment tank 10. EXAMPLES

[0041] Tritium was used as the radioactive material and treated with the above-mentioned device, and the radioactivity concentration was measured before and after the treatment.

[0042] The treated water was prepared by diluting tritium stock solution (50 mL x 5 bottles) with 10 L of RO water. The radioactivity concentration at the start of treatment was 25 kBq / L. The treated water was circulated while being in contact with the ceramic material using the above-mentioned device. The water temperature is preferably 10 to 60°C. If the temperature is less than 10°C, the viscosity of the treated water is low, and the impact effect of water molecules on the surface of the ceramic material is reduced, which is not effective. In this Example 1, the water temperature was 50°C. The pH of the treated water is preferably 5 to 9. In this Example 1, the pH was 7.

[0043] After 24 hours, the radioactivity concentration had decreased to 14.9 kBq / L, and it was confirmed that the radioactivity concentration had decreased. A germanium semiconductor detector (Seiko EG&G, GEM20P4 type) was used as the measuring device. The measurement method was in accordance with the Ministry of Education, Culture, Sports, Science and Technology and the Nuclear Regulation Authority's Radioactivity Measurement Method Series (γ-ray spectrometry using No. 7 germanium semiconductor detector). The amount of sample was 2000 cm 3 , the measurement time is 3600 seconds. EXAMPLES

[0044] Cesium-137 was used as the radioactive substance, and it was treated using the above-mentioned device, and the radioactivity concentration was measured before and after treatment.

[0045] The treated water was prepared by diluting cesium-137 stock solution (50 mL x 1 bottle) with 8 L of RO water. The radioactivity concentration at the start of treatment was 1 kBq / L. The treated water was circulated while being in contact with the ceramic material using the above-mentioned device. The water temperature is preferably 10 to 60°C. If the temperature is less than 10°C, the viscosity of the treated water is low, and the impact effect of water molecules on the surface of the ceramic material is reduced, which is not effective. In this Example 2, the water temperature was 50°C. The pH of the treated water is preferably 5 to 9. In this Example 2, the pH was 7.

[0046] After 24 hours, the radioactivity concentration had decreased to 0.71 kBq / L, and it was confirmed that the radioactivity concentration had decreased. The measurement device used was a liquid scintillation system (Hitachi AccuFLEX LSC-8000). The measurement method was in accordance with the Ministry of Education, Culture, Sports, Science and Technology and the Nuclear Regulation Authority's Radioactivity Measurement Method Series (No. 9 Tritium Analysis Method). The sample volume was 3 cm 3 , the measurement time is 600 seconds.

[0047] The experimental results performed in Example 1 will be verified based on the above-mentioned "principle of processing."

[0048] Let T be the half-life and t be the contact stirring time. If No is the initial amount of radioactive material and N(t) is the amount remaining after time t, the following "decay formula for radioactive material" holds true. N(t) / No=(1 / 2) t / T

[0049] From Example 1, the following results have become clear. No=25B / cc, t=24 hours, N(24)=14.9B / cc

[0050] The half-life T is calculated from the experimental results using the "decay formula for radioactive materials" above. T = [ln(1 / 2) / ln((N(t) / No)] × t = [ln(1 / 2) / ln(14.9 / 25)]×24= (0.693 / 0.517)×24=32.2(hour)

[0051] This result is in fairly good agreement with the half-life of 32 hours obtained in paragraph (2) of

[0034] . The above results suggest that the experimental results can be explained by the logical system developed in the "Principles of Processing." In other words, when tritiated water molecules are irradiated with a strong electric field near the surface of the ceramic material, electrical energy is generated inside them. This energy is added to the maximum energy of the electrons emitted in beta decay. As a result, the half-life of the beta decay decreases. The above discussion proves that it is possible to reduce tritium radioactivity using ceramic spheres.

[0052] As described above, this means that the conversion of tritium to helium is accelerated by the tritiated water passing near the ceramic material. In other words, it can be seen that there is a change in the tritium content before and after the passage, with the content decreasing. This is understood to result in a "decrease in the becquerel number." This "decrease in the becquerel number" can be expressed using the concept of a "decrease in half-life," and it can be seen that radioactivity is decreasing.

[0053] [Industrialization Plan] In the case of tritium, for example, the amount of ceramic material required to treat 50 tons of treated water per day is 10 tons, and the pump capacity is 500 t / h. The amount of ceramic material is approximately 20% of the amount of treated water. In the case of cesium-137, the amount of ceramic material required to treat 10 tons of treated water per day is 2 tons, and the pump capacity is 100 t / h.

[0054] [Effects of the embodiment] As described above, this embodiment includes a ceramic material, a treatment tank 10 filled with the ceramic material, and a circulation pump 12 that circulates water containing radioactive substances through the treatment tank 10. The water containing radioactive substances is brought into contact with the ceramic material in the treatment tank 10. The ceramic material used contains 45-75% by weight of SiO2, 7.5-20% by weight of Al2O3, and 3-25% by weight of Fe, and also contains 3-10% by weight of Ca, Na, Mg, and K in total. This generates a strong electric field at the extreme surface of the ceramic material, and this electric field accumulates electrical energy in the radioactive material, accelerating beta decay, making it possible to easily cause the radioactive material to decay and reduce its radioactivity using the simple device.

[0055] [Modifications] Although the above describes a particularly preferred embodiment of the present invention, the present invention is not intended to be limited to the embodiment shown, but can be modified and embodied in various forms, and the present invention is intended to encompass various modified examples.

[0056] For example, in the above embodiment, the radioactive material is tritium or cesium 137, but the present invention is not limited to this and can be applied to various types of radioactive material. [Explanation of symbols]

[0057] 10: Treatment tank 11: Aquarium 12: Circulation pump 13:Flowmeter 14: Control valve

Claims

1. SiO ２ :45-75% by weight, Al ２ O ３ A ceramic material containing 7.5 to 20% by weight of Mn, 3 to 25% by weight of Fe, and 3 to 10% by weight of Ca, Na, Mg, and K in total; a treatment tank filled with the ceramic material; a circulation pump for circulating water containing radioactive materials through the treatment tank; In the treatment tank, the ceramic material is brought into contact with water containing the radioactive material. A radioactive material treatment device comprising:

2. SiO ２ :45-75% by weight, Al ２ O ３ A ceramic material containing 7.5 to 20% by weight of Mn, 3 to 25% by weight of Fe, and 3 to 10% by weight of Ca, Na, Mg, and K in total; a treatment tank filled with the ceramic material; a circulation pump for circulating water containing radioactive materials through the treatment tank; In the treatment tank, the ceramic material is brought into contact with water containing the radioactive material. A method for treating radioactive materials.

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