JP6114055B2 - Radioactive substance immobilization material and radioactive contaminant treatment method - Google Patents

Description

The present invention relates to a material capable of immobilizing a radioactive substance such as radioactive cesium and a method of treating radioactive contaminants, particularly low-level radioactive contaminants, using the material.
Here, the low-level radioactive contaminants are those excluding the radioactive waste liquid separated by the reprocessing operation of the spent nuclear fuel and high-level radioactive wastes such as vitrified materials thereof. And radioactive contaminants such as soil (hereinafter referred to as “contaminated ash”), ash (hereinafter referred to as “contaminated ash”), and dust (hereinafter referred to as “contaminated dust”).

  Due to the accident at the Fukushima Daiichi Nuclear Power Station, a huge amount of radioactive material spread over a wide area, mainly in Fukushima Prefecture. Among these radioactive substances, radioactive cesium (cesium 137) has a long half-life of 30 years and a large residual amount. Therefore, in order to cope with such a situation, quick and wide-ranging decontamination work is necessary. However, it is difficult to secure a storage place and a delivery destination for contaminated soil that accumulates in large quantities along with decontamination, and to prevent scattering when transporting the contaminated soil, and there are many problems in processing contaminated soil by decontamination.

  In addition, even in incineration sites in the Tokyo metropolitan area far away from the power plant, a large amount of contaminated ash is generated every day due to the incineration of sludge and the like containing radioactive materials. However, radioactive contaminants with a radiation dose exceeding 8,000 Bq / kg are difficult to secure a recipient, and soluble cesium from incinerated fly ash is concentrated in the environment even if the radiation dose is 8,000 Bq / kg or less. There is a possibility of generating hot spots, and certain considerations are required even in managed disposal sites. As a result, there are still a lot of fly ash still stored in the incineration plant and waste before incineration.

  In addition, as a method for treating radioactive contaminants, it is conceivable that the radioactive contaminants are separated from the radioactive contaminants, and non-contaminated contaminants that have reached a level of no problem are refilled in the original position or reclaimed at a disposal site. As the separation means, for example, application of a chlorination volatilization method useful for separation and recovery of heavy metals can be considered for radioactive contaminants. However, with this measure, further processing of contaminants (dust) highly concentrated in radioactive material remains as a final challenge.

Conventionally, expansive bentonite and porous zeolite containing natural clay minerals have been used for the treatment of underground radioactive waste, filtration and adsorption of radioactive substances in water, and the like.
By the way, recently, when the contaminated soil caused by the accident was examined, radioactive cesium was fixed by specific natural clay minerals in the contaminated soil, such as weathered mica, so that the deep layer of cesium The move to is expected to be slow. Such a cesium immobilization mechanism is based on a site where a cesium ion having a stronger binding force is immobilized by ion exchange with a cation such as potassium existing in an anion site between layers in a clay mineral having a layered structure. It is thought to have. Therefore, it is conceivable to fix radioactive cesium using natural clay minerals.
However, since these natural clay minerals are scarce resources, there is concern over depletion when used in large quantities, and because they are relatively expensive, they are suitable for uses that consume large quantities as a treatment for contaminated soil for economic reasons. Absent.

Therefore, Patent Document 1 proposes a cementitious substance, ultrafine powder such as fly ash and opal silica, a high-performance water reducing agent, and a solidifying agent for radioactive waste mainly composed of water. However, as described in lines 3 to 6 in the lower left column on page 546, these ultrafine powders are only effective in terms of improving the curing shrinkage of the solidified body, and the elution suppression effect of radioactive substances is unknown. It is.
Moreover, in patent document 2, the cement solidification method of a radioactive waste is proposed. The feature of the method is that the calcium content in the cement mainly composed of calcium, silicon and aluminum is limited to a cement satisfying a specific formula having the silicon and aluminum contents as parameters. is there. Then, as described in the lower left column on pages 824 and lines 1 to 1 and the upper right column on lines 1 and 2, the cement generates an insoluble gel and generates voids that enhance radioactivity leaching from the solidified body. To prevent. However, as described above, this method requires the use of a special cement having a limited calcium content, which increases costs.

JP 61-215999 A JP-A-2-49197

  Then, an object of this invention is to provide the fixing material with the high elution suppression effect of a radioactive substance, and the processing method of the radioactive contaminant which can solidify a radioactive contaminant in large quantities and cheaply.

  The inventor has studied an immobilizing material that meets the above-mentioned object, and as a result, found that an immobilizing material containing siliceous shale and cement has an excellent effect on immobilizing radioactive substances, and has completed the present invention.

That is, the present invention is a radioactive material immobilization material and a processing method having the following configuration.
[1] A radioactive material immobilization material containing siliceous shale and cement.
[2] The radioactive substance immobilization material according to [1], wherein the radioactive substance is radioactive cesium.
[3] The radioactive material immobilization material according to [1] or [2], including 1 to 50 parts by mass of the siliceous shale with respect to 100 parts by mass of cement.
[4] The siliceous shale is determined by powder X-ray diffraction using Cu—Kα rays (the strongest diffraction intensity of cristobalite and tridymite 2 θ = 21.5 to 21.9 deg in the siliceous shale) / (the siliceous The intensity ratio of 2θ = 26.6 deg peak peak of quartz in the shale is in the range of 0.2 to 2.0, according to any one of the above [1] to [3]. Radioactive material immobilization material.
Here, “the strongest diffraction intensity of cristobalite and tridymite 2 θ = 21.5 to 21.9 deg” refers to the diffraction intensity of cristobalite and tridymite existing in the range of 2 θ = 21.5 to 21.9 deg. The strongest strength.
[5] The radioactive material immobilization material according to any one of [1] to [4], wherein the siliceous shale has a BET specific surface area of 10 to 1000 m ² / g.
[6] The immobilization of the radioactive substance according to any one of [1] to [5] , so that the content of the radioactive substance is 100 ppm or less with respect to the total mass of the radioactive substance immobilization material and radioactive contaminants. A method for treating radioactive contaminants by mixing materials and radioactive contaminants.
[7] The radioactive contaminants according to [6], contaminated dust, polluted soil, and is at least one selected from the contaminated ash treatment method of radioactive contaminants according to [6].

  The radioactive substance immobilization material of the present invention is highly effective in suppressing elution of radioactive substances. Moreover, the processing method of the radioactive contaminant of this invention can fix and process a radioactive contaminant in large quantities and cheaply.

It is a figure which shows the powder X-ray-diffraction peak of the siliceous shale used in the Example.

  As described above, the present invention is a radioactive material immobilization material containing siliceous shale and cement, and a method for treating radioactive contaminants using the immobilization material. Hereinafter, the present invention will be described separately for the components of the immobilizing material and the processing method. Hereinafter, “%” means “% by mass” unless otherwise specified.

1. Radioactive material immobilization material
(1) Siliceous shale The siliceous shale used in the present invention is altered by the diagenesis caused by temperature and pressure fluctuations caused by sedimentation of plankton dead bodies such as diatoms with siliceous shells on the seabed. Hardened shale, containing minerals such as opal CT, mica, clay minerals, quartz, cristobalite and tridymite.
The siliceous shale is preferably (in the X-ray powder diffraction by Cu-Kα rays) (the strongest diffraction intensity of cristobalite and tridymite in the siliceous shale is 2θ = 21.5 to 21.9 deg) / (the siliceous The shale has an intensity ratio of 2θ = 26.6 deg peak intensity of quartz in the shale in the range of 0.2 to 2.0. FIG. 1 shows an example of the powder X-ray diffraction peak of the siliceous shale. The opal CT described in the figure refers to cristobalite, tridymite, or a mixture thereof having a low crystallinity.
Further, the siliceous shale is more preferably in powder X-ray diffraction by Cu-Kα ray (diffraction intensity of 2θ = 19.6 to 20.0 deg of mica or clay mineral in the siliceous shale) / ( In the siliceous shale, the shale has an intensity ratio of 2θ = 26.6 deg peak intensity of quartz in the range of 0.1 to 0.5.
The immobilization material containing siliceous shale having the intensity ratio in the above range has a higher elution suppression effect of radioactive substances.

The BET specific surface area of the siliceous shale used in the present invention is preferably 10 to 1000 m ² / g, more preferably 30 to 500 m ² / g, and still more preferably 50 to 300 m ² / g. When the value is 10 to 1000 m ² / g, the radioactive substance elution suppression effect is high, and the pulverization cost is low. For crushing siliceous shale, a jaw crusher, a top grinder mill, a cross beater mill, a ball mill or the like is used. However, the BET specific surface area is strongly dependent on the internal structure of the siliceous shale, and the brane specific surface area and the particle diameter due to laser diffraction / scattering are more suitable as indicators for the change in particle diameter due to grinding. The brane specific surface area of the siliceous shale is preferably 0.2 to ⁵ m ² / kg, more preferably 0.25 to ¹ m ² / kg. Moreover, although the average particle diameter of the siliceous shale measured using laser diffraction / scattering depends on the particle size distribution, it is preferably 0.1 to 100 μm, more preferably 1 to 20 μm.
In addition, the Wakkanai siliceous shale produced in northern Hokkaido is preferable in terms of the pulverization property and the elution suppression effect of radioactive substances.

(2) Cement Any cement can be used as the cement, for example, ordinary Portland cement, early-strength Portland cement, ultra-early strong Portland cement, moderately hot Portland cement, low heat Portland cement, sulfate-resistant Portland cement, blast furnace Examples thereof include one or more selected from cement, fly ash cement, silica cement, and ordinary eco cement. It may be a mixed cement in which various other minerals are mixed, for example, limestone filler cement, or a composite cement in which a plurality of admixtures are mixed. Further, a functional admixture such as an expansion material can be mixed.
Moreover, the fixing material of the present invention contains 1 to 50 parts by mass of the siliceous shale with respect to 100 parts by mass of the cement. When the value is less than 1 part by mass, the elution suppression effect of the radioactive substance is low, and when it exceeds 50 parts by mass, the strength expression of the immobilizing material may be reduced.

(3) Other optional components The radioactive material immobilization material of the present invention includes, as optional components, blast furnace slag, magnesium carbonate, gypsum, magnesium sulfate, ferrous sulfate, calcium chloride, heavy burned phosphorus, molten phosphorus, and the like. One or more selected solidification accelerators, one or more cesium adsorbents selected from soils and clays that have the property of adsorbing cesium, insoluble ferrocyanides, montmorillonite-containing materials, zeolites and beidellite-containing materials, etc. You may include in the range which does not affect the intensity | strength expression property of a fixing material.

2. Treatment method of radioactive contaminants The treatment method comprises a radioactive material content of 100 ppm or less, preferably 50 ppm or less, more preferably 10 ppm or less, even more preferably 2 ppm or less with respect to the total mass of the immobilizing material and radioactive contaminants. In this method, the immobilizing material and radioactive contaminants are mixed so that the concentration is preferably 1 ppm or less. When this content rate exceeds 100 ppm, the elution suppression effect of a radioactive substance may not be enough.
Moreover, the immobilizing material of the present invention can be used by any method of powder mixing or slurry mixing for radioactive contaminants. Moreover, the water used for preparation of a slurry is not specifically limited, A tap water, reclaimed water, rain water, etc. are mentioned.

  The object to be treated in the present invention is a low-level radioactive contaminant excluding a high-level radioactive waste such as a radioactive waste liquid or a vitrified product thereof separated by a reprocessing operation of spent fuel. , Contaminated soil, and contaminated ash.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
1. Preparation of test body and leaching test of cesium A solidified body containing cesium was prepared according to the following procedures (i) to (vii).
(I) Silica shale (chemical composition; SiO ₂ : 77%, Al ₂ O ₃ : 10%, Fe ₂ O ₃ : 3%, K ₂ O: 2%) from the Wakkanai Formation from the northern Hokkaido region with a ball mill By grinding, a powder having a BET specific surface area of 110 m ² / g (maximum particle size: 0.5 mm) was obtained.
(Ii) 11 parts by mass of the powder was mixed with 100 parts by mass of ordinary Portland cement to prepare an immobilizing material (M).
(Iii) A mixture was prepared by mixing incineration ash with a mass ratio of 1: 1 to the immobilizing material (M), and further mixing 2 ppm (mass ratio) of cesium chloride with the mixture to prepare a powder mixture. .
(Iv) Distilled water was added to the powder mixture at a water / powder ratio (mass ratio) of 0.76 and kneaded to prepare a kneaded product.
(V) After molding the kneaded material to prepare a cured body having a diameter of 5 cm and a length of 10 cm, the cured body was cured at room temperature for 10 days and further at 40 ° C. for 50 days to prepare a test body.
(Vi) For the sake of comparison, ordinary Portland cement (C) and mixed cement (F) having a mass ratio of ordinary Portland cement / pozzolanic admixture of 6/4 are the same as the above (iii) to (v) A test body (two types) was prepared and used for the test as a comparative example.
(Vii) Using the test specimens (three types), the leaching test of cesium was stirred with a propeller, the tank leaching test with a liquid-solid ratio of 10 (JIS K 0058-1), and Environmental Agency Notification No. 13 According to the same procedure.
The results of the tank leaching test are shown in Table 1. Table 2 shows a comparison (an immobilization material ratio) of elution suppression effects of the immobilization material (M) of the present invention and the immobilization materials (C, F) of the comparative example.
Moreover, the elution rate calculated | required by the test according to Ministry of the Environment notification No. 13 is 0.37 for the immobilizing material (M), 0.90 for the immobilizing material (C), and 0.00 for the immobilizing material (F). 51.
FIG. 1 shows a powder X-ray diffraction peak of the siliceous shale described in (i) above.

2. About the cesium elution inhibitory effect As shown in Tables 1 and 2, the immobilization material (M) of the present invention suppresses the cesium leaching rate to 29 to 40% as compared with ordinary Portland cement (C).
Further, even when compared with the mixed cement (F) corresponding to the fixing material described in Patent Document 1, the fixing material of the present invention suppresses the cesium leaching rate to 40 to 57%.
The dissolution rate can be reduced by reducing the water / cement ratio to make a dense cement hardened body. However, in the test according to the Environmental Agency Notification No. 13 which evaluates the dissolution of pulverized fine particles, the fact that M showed a remarkably low dissolution rate was not only that siliceous shale decreased the dissolution rate, but also cesium. It shows that sorption and suppression to the liquid phase itself are suppressed.
Therefore, it is understood that the radioactive substance immobilization material of the present invention has a high elution suppression effect of the radioactive substance.

Claims (7)

  Immobilization material for radioactive materials including siliceous shale and cement.   The radioactive substance immobilization material according to claim 1, wherein the radioactive substance is radioactive cesium.   The radioactive material immobilization material according to claim 1 or 2, comprising 1 to 50 parts by mass of the siliceous shale with respect to 100 parts by mass of cement.   The siliceous shale is, in powder X-ray diffraction by Cu-Kα ray, (the strongest diffraction intensity of 2θ = 21.5 to 21.9 deg of cristobalite and tridymite in the siliceous shale) / (in the siliceous shale) The radioactive material immobilization material according to any one of claims 1 to 3, wherein the intensity ratio of quartz (2θ = 26.6 deg peak top) of quartz is in the range of 0.2 to 2.0. . The radioactive material immobilization material according to any one of claims 1 to 4, wherein the siliceous shale has a BET specific surface area of 10 to 1000 m ² / g. The immobilization material and the radioactive contaminant are added so that the content of the radioactive material is 100 ppm or less with respect to the total mass of the radioactive material immobilization material and the radioactive contamination according to any one of claims 1 to 5. A method for treating radioactive contaminants to be mixed. The method for treating radioactive contaminants according to claim 6, wherein the radioactive contaminant according to claim 6 is at least one selected from contaminated dust, contaminated soil, and contaminated ash.

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