JPS6317198B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to solidified radioactive waste. More specifically, the present invention relates to a radioactive waste solidified body comprising a chlorinated polyolefin resin, a polyethylene resin, and a used granular and/or powdered ion exchange resin that is radioactive waste. In recent years, as the peaceful uses of nuclear energy have progressed, the amount and types of radioactive waste generated have been increasing year by year. In particular, among the waste generated from nuclear power plants, granular ion exchange resins present in demineralizers installed in water supply systems are removed from the debasing system when their performance deteriorates and reach the end of their service life. It becomes waste. Conventionally, used granular ion exchange resin, which is radioactive waste, is filled into drums, mixed with water, cement, etc. in the drum, solidified using the solidification of cement, and sealed at the top of the drum. Treatment methods include forming a solidified substance and dumping it in the ocean. To dump the solidified radioactive waste into the ocean,
It is required that the solidified material has an unconfined compressive strength of 150 Kg/cm ² or more and a density of 1.2 g/cm ³ or more. However, cement solidification generates gas and bubbles inside during hydration and solidification, making it difficult to satisfy the required strength. Furthermore, in recent years, melting of asphalt,
An asphalt solidification method that takes advantage of its solidifying properties, and a polyethylene solidification method that utilizes the melting and crystallization of polyethylene resin are being studied. However, in either method, in order to make the unconfined compressive strength of the solidified product 150 Kg/cm ² or more, the amount of granular or powdered ion exchange resin to be filled per 100 parts by weight of any of these is required. must be less than 100 parts by weight. In this way, the filling amount of used ion exchange resin, which is radioactive waste, is 100
The fact that it is less than 1 part by weight means that the amount of waste increases by more than twice due to solidification of the waste. Also, when cement solidifies,
The compressive strength may change significantly due to the water-cement ratio, or radioactive cement may adhere to the stirrer used to stir and solidify the water, cement, and granular ion exchange resin in the drum, and cleaning Therefore, there are drawbacks such as the generation of a large amount of radioactive cleaning water, which causes various problems when put into practical use. On the other hand, asphalt solidification has the advantages of good affinity and adhesion with ion exchange resins and extremely low elution of radioactive substances in water or salt solutions over a long period of time. However, it has not been put to practical use because it contains about 1% free water and has a significantly low compressive strength. In addition, in the polyethylene resin solidification method, it is possible to uniformly fill and solidify up to 100 parts by weight of ion exchange resin per 100 parts by weight of polyethylene resin, but the molten polyethylene resin with the ion exchange resin evenly mixed is crystallized. During solidification, shrinkage occurs inside the drum, and distortion due to crystallization occurs within the solidified body, causing cracks, etc.
Drums and polyethylene resin shrink as they shrink.
At present, this method has not been put into practical use because it has drawbacks such as gaps occurring between the solidified materials, making it impossible to seal the drum. Based on the above, the present inventors have conducted various searches to eliminate these drawbacks and carry out ocean dumping, and have found that (A) polyolefin resin, (B) chlorinated polyethylene resin, and (C) radioactive waste. Consisting of a used granular and/or powdered ion exchange resin, the total amount of the polyolefin resin and chlorinated material is 100%.
The blending ratio of ion exchange resin to parts by weight is 100
~500 parts by weight, and 50 parts by weight of polyolefin resin
The blending ratio of chloride to ~90 parts by weight is 10 to 50
We have discovered that by filling and solidifying a certain amount of radioactive waste, it is possible to obtain a solidified material that has sufficient strength to be dumped into the ocean and can also hold a large amount of radioactive waste, and has arrived at the present invention. The polyolefin resins used in the present invention are generally referred to as high pressure polyethylene, medium pressure polyethylene, low pressure polyethylene and polypropylene. High-pressure polyethylene is a homopolymer of ethylene or a copolymer of ethylene and another vinyl compound (copolymerization ratio is generally 50% by weight or less). The density of this polyethylene is 0.900 to 0.930g/cc
The molecular weight is 50,000 to 300,000. In addition, medium-pressure and low-pressure polyolefins are generally made by homopolymerizing ethylene using a Phillips catalyst or Ziegler catalyst, or by copolymerizing ethylene with an α-olefin having at most 8 carbon atoms (copolymerization ratio is at most 20% by weight). It is obtained by polymerization (including block copolymers).
The density of this polyethylene is 0.900 to 0.970g/
cc, and the molecular weight is generally 50,000 to 500,000. Furthermore, polypropylene can be produced by homopolymerizing propylene using a Ziegler-Natsuta catalyst, or by polymerizing propylene and ethylene or α-
It is obtained by copolymerizing olefin (copolymerization ratio generally 10% by weight or less) (including block copolymers). The molecular weight of this polypropylene is usually 30,000 to 500,000. During melt-kneading to produce the composition described below, some ion exchange resins may undergo thermal decomposition if the melt-kneading temperature is high. Therefore, depending on the ion exchange resin used, it goes without saying that a polyolefin resin must be used that has a melting point lower than the temperature at which the ion exchange resin decomposes. In addition, the chlorinated polyethylene resin used in the present invention can be obtained by chlorinating polyethylene resin powder or particles in an aqueous suspension, or by chlorinating the polyethylene resin powder or particles in an organic solvent (for example, carbon tetrachloride) that can dissolve the polyethylene resin. It is obtained by chlorinating dissolved polyethylene resin.
This chlorinated polyethylene resin is widely produced industrially and is commonly used. In general, it is a chlorinated product of amorphous or crystalline polyethylene resin with a chlorine content of 20 to 50% by weight, and in particular, an amorphous one with a chlorine content of 24 to 45% by weight is preferred. be. Polyethylene resin, which is the starting material for this chlorinated polyethylene resin, generally has a density of
0.910~0.970g/cc, especially 0.93~0.960g/cc
Preferably. In addition, the molecular weight is generally 5
The value ranges from 10,000 to 500,000, with 100,000 to 400,000 being particularly desirable. Regarding the method of producing a radioactive ion exchange resin solidified body using the above-mentioned polyolefin resin and chlorinated polyethylene resin, a nuclear power plant,
In particular, a commonly used boiling water nuclear power plant will be explained as an example. Various drains generated from boiling water nuclear power generation are purified by a filter and a demineralizer. The ion exchange resin filled in the condensate demineralizer and demineralizer is adjusted to a moisture content of 36 to 42% by a centrifugal dehydrator while its performance deteriorates and it becomes radioactive.
Further, the used radioactive ion exchange resin in a dry state is passed through the steam pipe and temporarily stored in the hopper. The ion exchange resin thus obtained is uniformly melt-kneaded with the chlorinated polyethylene resin of the present invention, and the sufficiently kneaded state is supplied into a drum. The ion exchange resin and chlorinated polyethylene resin filled in the drum are cooled and solidified within the drum. It goes without saying that in the present invention, similar effects can be achieved by using various drains generated from nuclear power generation, iron sulfate oxide, inorganic fillers, etc. in place of the used ion exchange resin. The blending ratio of chlorinated polyethylene resin to polyolefin resin is 50~
The amount is preferably 10 to 50 parts by weight relative to 90 parts by weight, and particularly preferably 20 to 40 parts by weight relative to 60 to 80 parts by weight of the polyolefin resin. In addition, the blending ratio of used ion exchange resin to chlorinated polyolefin resin and polyethylene resin (including these when blending rubber-like materials described later) is 100 to 500 parts by weight, especially 200 to 400 parts by weight. Parts by weight are preferred. Incorporating as much ion exchange resin as possible increases the proportion of ion exchange resin in the solidified body, thereby increasing treatment efficiency. When 500 parts by weight or more of ion exchange resin is blended with 100 parts by weight of polyethylene resin, it is difficult to obtain a uniform solidified material, and the unconfined compressive strength of the obtained solidified material is 150% by weight.
Since it is less than Kg/cm ² , it is not suitable for the present invention. Furthermore, when the ion exchange resin contains water, it is preferable to use a commonly used inorganic water-containing powder because it can further promote uniformity of kneading and further increase the blending ratio. . In producing the solidified radioactive waste of the present invention, it can be produced by uniformly mixing an ion exchange resin with a chlorinated polyolefin resin, but it is also possible to produce the radioactive waste solidified material by uniformly mixing an ion exchange resin with a chlorinated polyolefin resin. A rubber-like material with excellent properties may be blended. Examples of the rubber-like material include ethylene-propylene-diene ternary copolymer rubber (EPDM), natural rubber, chloroprene-based rubber, chlorosulfonated polyethylene-based rubber, styrene-butadiene copolymer rubber, and acrylonitrile. - Rubbers such as butadiene copolymer rubbers and butadiene rubbers and silicone rubbers. The Mooney viscosity ML ₁₊₄ ) 100° C. of these rubbery materials is generally 10-150. When compounding these rubber-like materials, it is of course necessary to highly fill the used ion exchange resin of the present invention and to do so in a manner that does not essentially impair its characteristics of excellent mechanical strength. It is. Therefore, the blending ratio of these is generally at most 40 parts by weight per 100 parts by weight of the chlorinated polyethylene resin. Although the composition of the present invention can be obtained by uniformly blending the above-mentioned materials, it is possible to obtain the composition of the present invention by uniformly blending the above substances, but in addition, stabilizers, other fillers, flame retardants and colorants commonly used in the rubber and resin industries may be added. Additives such as the following may be added depending on the intended use of the composition. In producing the composition of the present invention containing only the polyolefin resin, chlorinated polyethylene resin, and used ion exchange resin, after dry blending the polyolefin resin, the chlorinated polyethylene resin, and a part of the ion exchange resin in advance, Melt-kneading may be carried out uniformly, and then melt-kneading may be carried out while sequentially adding the remaining ion-exchange resin to a uniform state. Alternatively, melt-kneading may be carried out while sequentially adding the remaining ion-exchange resin directly as described above without performing dry blending. You may do so. Alternatively, all of these may be melted and kneaded at the same time. The temperature during melt-kneading by these methods is generally 150 to 220°C. The composition obtained as described above can be molded using a molding method such as compression molding using a mold, injection molding, or press-fit molding to produce a solidified product of the present invention in a predetermined drum. The solidified material obtained as described above not only had sufficient unconfined compressive strength for ocean dumping, but also was filled with an ion exchange resin with excellent water resistance. Hereinafter, the present invention will be explained in more detail with reference to Examples. In the Examples and Comparative Examples, the unconfined compressive strength was measured according to JIS K-6911 when a vertical load was applied and the compressive strain reached 60%. Moreover, the density was measured according to JIS K-6911. Examples 1 to 6, Comparative Example 1 Polyethylene resin (average molecular weight approximately 100,000, hereinafter referred to as "PE") with a density of 0.920 g/ ^cm3 ,
0.950g/ ^cm3 polyethylene resin (average molecular weight approx. 30
Chlorinated polyethylene resin (amorphous, chlorine content 30.0% by weight, hereinafter referred to as "CPE") obtained by pre-chlorinating (10,000 yen) by an aqueous suspension method, dried powder Ion exchange resin (anion resin/cation resin = 1/2, average particle size 0.2 mm) and tribasic lead sulfate as a stabilizer were mixed in advance for 1 minute using a Henschel mixer at the mixing ratios shown in Table 1. . In Example 6, dioctyl phthalate (DOP) was further added as a plasticizer to the obtained mixture gradually through the observation port of the upper lid of the Henschel mixer, and the mixture was thoroughly mixed (for about 3 minutes). Each of the obtained mixtures was processed using a twin screw extruder (diameter 30
mm, set temperature _C1 : 130℃, _C2 : 160℃, _C3 : 160
_C4 : 160°C, adapter: 160°C, die: 160°C, rotation speed: 60 revolutions/min), and melt-kneaded. The mixture obtained in the molten state from the die of the extruder has a diameter of 20 cm and a height of 30 cm.
accepted into the can. The molten mixture flowed and solidified in the can. After sufficiently cooling, a solidified material approximately the same size as the can was taken out. The cylindrical solidified body was vertically divided into two equal parts in order to observe the cross section of the obtained solidified body, and the observation results are shown in Table 1. In addition, the density and unconfined compressive strength of each solidified body were measured. The results are shown in Table 1. It is clear from the density and unconfined compressive strength results that the solidified bodies obtained in Examples 1 to 6 can sufficiently withstand ocean dumping. On the other hand, the solidified body obtained in Comparative Example 1 not only has a density of 1.2 g/cm ³ or less and a significantly lower compressive strength, but also has a cross-section of
There were many cracks that appeared to have occurred when the polyethylene resin was cooled and crystallized, and it was clear that it could not withstand being dumped into the ocean.

[Table] ×: There are countless cracks and voids.
Example 7 Instead of the ion exchange resin used in Example 6, a mixture of mirabilite (Na ₂ SO ₄ ) and red iron (Fe ₂ O ₃ ) [Mixing ratio of Na ₂ SO ₄ and red iron (weight)
Mixing was carried out using a Henschel mixer in the same manner as in Example 6, except that 300 parts by weight of 5:1 was used.
The resulting mixture was melt-kneaded using a twin-screw extruder under the same conditions as in Example 6, and then received in a can. The density of the obtained solidified body was 2.03 g/cm ³ ,
The unconfined compressive strength was 361 g/cm ³ . Further, when the cross section of this solidified material was observed, no cracks or voids were observed. Comparative Example 2 Mixing was carried out in the same manner as in Comparative Example 1 using a Henschel mixer, except that the mixture of mirabilite and red iron sulfate used in Example 7 was used instead of the ion exchange resin used in Comparative Example 1. The resulting mixture was melt-kneaded using a twin-screw extruder under the same conditions as in Comparative Example 1, and then received in a can. The density of the obtained solidified product was 1.78 g/cm ³ and the unconfined compressive strength was 109 g/cm ³ . Further, when the cross section of this solidified body was observed, numerous cracks and voids were observed as in Comparative Example 1. From these results, the solidified body obtained in Comparative Example 2 had a high density, but a low compressive strength. From these facts, it is clear that even if a solidified body of waste such as mirabilite is made using only polyethylene resin, it will not be able to withstand being dumped into the ocean.

Claims (1)

[Scope of Claims] 1 Consisting of (A) a polyolefin resin, (B) a chlorinated polyethylene resin, and (C) a used granular and/or powdered ion exchange resin that is radioactive waste, the polyolefin resin and chlorine Total with monsters: 100
The blending ratio of ion exchange resin to parts by weight is 100
~500 parts by weight, and 50 parts by weight of polyolefin resin
The blending ratio of chloride to ~90 parts by weight is 10 to 50
Solidified radioactive waste in parts by weight.