JP6283203B2 - Method for producing granulated recycled crushed stone with reduced radioactivity from radioactive waste - Google Patents

Description

  The present invention relates to a method for producing granulated reclaimed crushed stone with reduced radioactivity from radioactive waste.

  Conventionally, radioactive waste has been stored or disposed of depending on the strength of its radioactivity (Bq / Kg). However, the reuse of radioactive waste has not been sufficiently performed since the radioactivity needs to be at least a predetermined value (for example, 3000 Bq / kg) or less.

  On the other hand, there is a problem that radioactive cesium released in the external environment due to the accident at the nuclear power plant accompanying the 2011 earthquake is contained in a large amount in waste or soil. As a result, although the amount of radioactive waste containing cesium to be processed (decontaminated) has increased, the processing including the reuse is delayed.

  Published Patent Publication No. 2013-104824 discloses a granulation process for obtaining a granulated product by granulating a raw material containing waste contaminated with radioactive cesium so that the actual rate is 60% or more, and the granulation thereof. A method for removing radioactive cesium is disclosed that includes a heating step of heating an object to 900 ° C. or more to volatilize radioactive cesium in waste.

  However, the method described in this publication requires a heating step for heating the granulated product to 900 ° C. or more to volatilize radioactive cesium in the waste, and therefore requires a large heating furnace and its consumption. Due to the high power, it is not always a suitable method for treating large quantities of radioactive waste quickly and relatively inexpensively.

JP 2013-104824

  It is an object of the present invention to provide a method for producing granulated reclaimed crushed stone with reduced radioactivity from radioactive waste, which can process a large amount of radioactive waste quickly and relatively inexpensively. And

  The present invention provides a method for producing a granulated recycled crushed stone with reduced radioactivity from radioactive waste. The method includes a step of crushing radioactive waste to obtain a crushed material, a step of mixing 10 to 15% by weight of cement and water with the crushed material to obtain a mixture, and granulating the mixture. A granulated regenerated crushed stone by mixing a granulated product having a particle size of 5 mm or more and 70 to 90% by weight of recycled concrete (RC) 40 with 10 to 30% by weight of the granulated product. The granulated reclaimed crushed stone is characterized in that its radioactivity is reduced by a self-shielding effect by the granulated material and a shielding effect by mixing the granulated material and the RC-40.

In one embodiment of the present invention, the radioactive waste includes cesium 134 ( ¹³⁴ Cs) and cesium 137 ( ¹³⁷ Cs).

  In one embodiment of the present invention, the radioactivity of the granulated reclaimed crushed stone is reduced to 3000 Bq / kg or less that can be reused.

It is a figure which shows the process of the method of manufacturing the granulated reproduction crushed stone of one Embodiment of this invention. It is a figure which shows the radioactivity reduction effect of the granulated material obtained with the manufacturing method of this invention. It is a figure which shows the radioactivity reduction effect of the granulated regenerated crushed stone obtained with the manufacturing method of this invention. It is a schematic diagram in the case of utilizing the granulated recycled crushed stone obtained by the production method of the present invention as a roadbed material for asphalt pavement.

  Embodiments of the present invention will be described with reference to the drawings. Drawing 1 is a figure showing a process of a method of manufacturing a granulation regenerated crushed stone object of one embodiment of the present invention. The manufacturing process of FIG. 1 can be performed using, for example, equipment of an intermediate processing facility (for example, “Zero Emi Plant” owned by the applicant) that recycles construction waste.

  In step S1 of FIG. 1, the recovered radioactive waste is crushed by a crusher (pulverizer) to obtain a crushed material. The crushed material is crushed so as to have a predetermined size according to the intended use. The predetermined size is, for example, a size of 10 mm or less. In the crushing step S1, the radioactive waste crushing material previously crushed in another facility or the like is collected and crushed again to a predetermined size and adjusted, or the collected radioactive waste crushing material is collected. You may make it utilize as it is, after performing inspections, such as confirmation of the magnitude | size.

  In the mixing step of step S2, 10-15% by weight of cement and water are mixed with the radioactive waste crushing material obtained in step S1 to produce a mixture. For example, the blast furnace cement type B corresponds to the cement. In addition, this mixing process can also be performed as a part of granulation process of the following process S3.

  In step S3, the mixture obtained in mixing step S2 is granulated in a granulator to produce a granulated product. The particle size of the granulated product varies depending on the rotation speed and rotation time of the agitation blade of the granulator, and the proportion of the granulated product having a large particle size is increased by increasing the rotation time (ie granulation time). Can do. By this step, it is desirable to produce a granulated product having a particle size of 5 mm or more.

  In step S4, the granulation obtained in the mixing step S3 is cured. Curing is important in improving the strength of the granulated product, and is also important in terms of reducing the radioactivity of the granulated product. The curing period is not an essential requirement in the production method of the present invention, and can be arbitrarily selected according to the use of the granulated product and the granulated regenerated crushed stone.

  In step S5, the granulated product after mixing step S3 or the granulated product after curing in step S4 is mixed with recycled concrete (RC) 40 to generate a granulated recycled crushed stone product. At that time, it is desirable to produce a granulated reclaimed crushed stone by mixing 70 to 90 wt% RC40 with 10 to 30 wt% granulated product.

  In step S6, quality control of the granulated recycled crushed stone is performed. In quality control, the radioactivity of granulated recycled crushed stones is inspected / confirmed that it meets the specifications (below a predetermined standard value) that suit the application.

  The radioactivity reduction effect of the granulated product obtained by the production method of the present invention and the granulated regenerated crushed stone will be described with reference to FIGS. FIG. 2 shows the data of the granulated product, and FIG. 3 shows the data of the granulated regenerated crushed stone product.

In FIG. 2, first three raw materials (mixture obtained in step 2 of FIG. 1) were prepared. The raw material 1 is obtained by adding 15% of cement, and has a high measured value of radioactivity of cesium ( ¹³⁴ Cs and ¹³⁷ Cs) as 10850 Bq / kg. The raw material 2 is obtained by adding 15% of cement. The measured value of the radioactivity of cesium ( ¹³⁴ Cs and ¹³⁷ Cs) is 5630 q / kg, which is about half of that of the raw material 1. The raw material 3 is obtained by adding 10% of cement, and the measured value of the radioactivity of cesium ( ¹³⁴ Cs and ¹³⁷ Cs) is as high as 12520 Bq / kg.

Granules (granulated products) 1 to 3 obtained in Step 3 of FIG. Furthermore, the granulated products 1 to 3 were cured for 14 days. As a result of measuring the radioactivity of cesium ( ¹³⁴ Cs and ¹³⁷ Cs) for granulated products (granulated products) 1 to 3 and comparing with the radioactivity of cesium ( ¹³⁴ Cs and ¹³⁷ Cs) of raw materials 1 to 3, FIG. As shown in the column of the actual reduction rate, it was found that the radioactivity was reduced by about 35 to 39% after granulation and about 39 to 42% after curing. In this case, the dilution effect by mixing cement is included.

In order to eliminate the dilution effect due to cement mixing, the radioactivity of cesium ( ¹³⁴ Cs and ³⁷ Cs) for raw materials 1 to 3 estimated from the added amount of cement (10%, 15%) was calculated. Estimated as “estimated value from the amount of cement added”. As a result of comparing the estimated radioactivity with the activity after granulation / post-curing, there is an effect of reducing radioactivity by about 28-30% after granulation, and about 30-33% after curing. It was found that there is a reduction effect.

These data, in granules obtained by the process of the present invention, be reduced by about 28-30% by only granulating effect radioactivity cesium original radioactive waste ^{(134 Cs} and ^{137 Cs)} In addition, it became clear that the original radioactivity could be reduced by about 35-42%, including the effects of curing and the dilution effect of cement.

FIG. 3 compares the radioactivity of the granulated product (granulated product) 4 obtained in step 3 with the radioactivity of the granulated reclaimed stone product obtained in step 5, It is the result of measuring the radioactivity reduction effect. As is clear from the data of FIG. 3, when the granulated product 4 is changed at 10 to 30% by weight with respect to RC40, the radioactivity of the granulated product (granulated product) 4 is reduced by about 18% to 36%. I found out that As in the case of FIG. 2, the radioactivity of the cesium ( ¹³⁴ Cs and ¹³⁷ Cs) of the granulated product 4 estimated from the mixing ratio of RC40 is calculated as an estimated value, and the estimated radioactivity and granulation regeneration are calculated. The radioactivity of the crushed stone was compared.

From the results shown in FIG. 2 and FIG. 3, in the granulated recycled crushed stone obtained by the method of the present invention, the activity of the original radioactive waste cesium ( ¹³⁴ Cs and ³⁷ Cs) is granulated and mixed with RC40. It has become clear that it can be reduced by about 50 to 60% due to a synergistic effect. Therefore, according to the production method of the present invention, it is possible to obtain a granulated reclaimed crushed stone with reduced radioactivity to 3000 Bq / kg or less that can be reused under predetermined restrictions.

  The radioactivity reducing effect of FIGS. 2 and 3 is considered to be obtained for the following reason. That is, the radioactivity reduction effect after granulation in FIG. 2 is due to the self-shielding effect of the radiation (gamma rays, etc.) by the granulated material, and the radioactivity reduction effect of the granulated regenerated crushed stone is mixed with RC40. This is thought to be due to the shielding effect of radiation (gamma rays, etc.) due to. In addition, in granulation, as described above, there is a dilution effect by cement, and in mixing with RC40, it is considered that there is also a so-called dilution effect by RC40.

  Here, the self-shielding effect can be explained as follows. That is, when the primary particles are made into a granulated product having a diameter of 5 mm or more by granulation, the primary particles are fixed in the granulated product, resulting in a high-density massive substance. By becoming this high-density massive substance, the self-absorption rate of γ-rays is improved, and the apparent radioactivity concentration (radiation dose released to the outside) when measured from the outside due to the effect is a numerical value that decreases. Conceivable. Similarly, when the granulated product and RC40 are mixed, the effect of high density RC40 surrounding the granulated product becomes apparent as compared with the granulated product, and the apparent radioactivity concentration (radiation dose released to the outside) is reduced. I think that.

  FIG. 4 is a schematic diagram when the granulated regenerated crushed stone obtained by the production method of the present invention is used as a roadbed material for asphalt pavement. The roadbed material for asphalt pavement means the roadbed material 20 disposed under the surface layer / base layer 10 containing asphalt in the asphalt pavement, and particularly means a material for the lower layer roadbed of the roadbed material. As shown in FIG. 4, the granulated reclaimed crushed stone includes a granulated material 24 mixed as a roadbed material 20 so as to fill a space between RC 40 (22). As illustrated in the data of FIG. 3, the granulated material 24 is mixed at a ratio of 10 to 30 wt% with respect to 70 to 90 wt% of RC40 (22), for example.

  Embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to these embodiments. The present invention can be implemented in variously modified, modified, and modified embodiments based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

10 Surface layer / base layer containing asphalt 20 Roadbed material (lower roadbed material)
22 RC40
24 Granulated material

Claims (3)

A method for producing granulated reclaimed crushed stone with reduced radioactivity from radioactive waste,
Crushing radioactive waste to obtain crushed material;
A step of mixing the crushed material with 10 to 15% by weight of cement and water to obtain a mixture;
A step of granulating the mixture to produce a granulated product having a particle size of 5 mm or more;
Including mixing 70 to 90% by weight of recycled concrete (RC) 40 with 10 to 30% by weight of the granulated product to obtain a granulated recycled crushed stone,
The granulated recycled crushed stone has a reduced radioactivity due to a self-shielding effect by the granulated material and a shielding effect by mixing the granulated material and the RC40. The method of claim 1, wherein the radioactive waste comprises cesium 134 ( ¹³⁴ Cs) and cesium 137 ( ¹³⁷ Cs).   The method of claim 2, wherein the radioactivity of the granulated reclaimed crushed stone is reduced to reusable 3000 Bq / kg or less.

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