JPH0640159B2 - Method for solidifying radioactive waste - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for solidifying radioactive waste, and more specifically, it stabilizes radioactive used ion exchange resin and solid waste generated in a nuclear power plant or the like. Immobilized as a solid material,
The present invention relates to a method for solidifying radioactive waste, which can be converted into a form convenient for temporary storage or final disposal and can prevent leaching due to radioactivity.

[Problems to be Solved by Conventional Techniques and Inventions] Today, ion exchange resins are used in nuclear facilities such as nuclear power plants for the purpose of condensate purification or wastewater treatment.
When this ion-exchange resin is disposed of, since it is contaminated with radioactivity, the method of disposal is a problem.

For example, some of the used ion exchange resins have
High as 10 ¹ -10 ^-2 μCi / cc and Cs of long half-life nuclide
Since it contains Sr and Sr, long-term storage in a safer form is necessary, and therefore the treatment is carried out by decomposition or volume reduction such as incineration or wet decomposition, or by direct solidification treatment such as cement solidification, asphalt solidification or plastic solidification. Has been developed and researched, and part of it has been put to practical use. However, in the former method of decomposition and volume reduction by incineration, the exchange group of the cation resin of the ion exchange resin decomposes because it is processed at high temperature,
There is a problem in that SOx gas is generated, the material of the treatment equipment for the generated exhaust gas is a problem, and the SOx gas is recovered. Also,
In wet decomposition, SO ₄ ^2- remains in the decomposition liquid, so post-treatment such as neutralization with caustic soda and evaporative concentration is necessary, and the decomposition agent is expensive, which is a problem in economic efficiency. There is. The latter direct solidification treatment method has problems such as poor volume reduction and expensive treatment equipment.

On the other hand, even an ion-exchange resin, which has an extremely low level of radioactivity and is almost harmless, must be disposed of in a highly sound container (HIC) because it is a radioactive substance in the United States. However, since this HIC is expensive, there is a problem in that it is difficult to apply costly to the ion exchange resin treatment with a medium or lower level of radioactivity, so that it is generally stored in a tank and actually treated. There are few places.

Further, in the treatment of radioactive solid waste generated from a nuclear facility, it is difficult to directly apply the treatment using general solid waste such as incineration treatment, so that there are various problems.

An object of the present invention is to solidify radioactive used ion-exchange resin and solid waste generated in a nuclear power plant etc. without generating new secondary waste, which is highly economical.
Another object of the present invention is to provide a method for solidifying radioactive solid waste, which can obtain a stable solidified product.

[Means for Solving the Problems] The present invention has been completed as a result of an examination in response to the above problems, and shreds or crushes a mixture of a used radioactive ion exchange resin and a radioactive solid waste, After crushing and processing to a set size, it is compressed in an extruder having a compression screw at a temperature condition of 100 to 190 ° C generated by frictional heat to solidify the thermoplastic resin contained in the radioactive solid waste. A method for solidifying radioactive waste, which comprises solidifying a part or all of the material.

That is, the problem of the above-mentioned prior art was solved by the following processing policy. First, the SOx gas was treated at a low temperature to prevent the SOx gas from being generated. Next, with respect to the problem that the volume cannot be reduced in the direct solidification treatment, the thermoplastic resin contained in the radioactive solid waste (hereinafter simply referred to as solid waste) and the thermoplastic resin partially introduced from the outside as necessary are solidified. It was solved by mixing and compressing as a chemical agent and reducing the volume as a whole. Regarding the problem of containing radioactivity, by confining it with solidified material,
The exudation can be prevented. Furthermore, the free water in the used radioactive ion exchange resin (hereinafter simply referred to as the used ion exchange resin) is almost completely evaporated in the treatment process in the solidified product obtained by the present invention. Therefore, it is possible to prevent radioactivity from leaching out without using an expensive HIC, and it is possible to store it in an ordinary drum.

Specifically, the solidifying material is solid waste generated as waste, and polyethylene (P
E) or a thermoplastic resin such as polyvinyl chloride (PVC) is solidified. Further, by stirring and compressing the mixture of the used ion exchange resin and the solid waste at 100 to 190 ° C., which is the temperature range in which the thermoplastic resin such as PE or PVC is melted, SOx gas is not generated (SOx gas). The temperature at which the gas is generated is 200 to 350 ° C.), and since the water in the ion exchange resin evaporates and the free water of the molded product also disappears, there is no need to use HIC.

In the present invention, the solid waste containing the thermoplastic resin is preferably finely chopped or crushed. this is,
Since the solidification treatment is carried out by extrusion molding, it is necessary to subdivide into a size that can correspond to the die diameter of the extruder, and after shredding or crushing,
Further crushing is desirable.

Further, the used ion exchange resin is preferably dehydrated to the extent of draining.

Needless to say, the solid waste can be solidified by the present invention even if the solid waste contains the used ion exchange resin.

In the present invention, the thermoplastic resin is used as the solidifying material as described above, but the kind and property thereof are not limited, and it is sufficient that the resin has moldability to the extent required for solidification. As the thermoplastic resin, PE, PVC or the like contained in solid waste is usually used, but a part thereof may be introduced from the outside and used. Since it is solidified even when it is introduced from the outside, it does not need to be a new product, and a recycled product or a generally discharged thermoplastic waste may be used.

As described above, any resin can be used as long as it is a thermoplastic resin, but a resin that softens or melts at a temperature of about 100 to 190 ° C. is most easily used. Further, when solidified, the content of the thermoplastic resin needs to be in the range of 10% by weight or more, and it is better that the water content is less than 30%.
Up to wt% can be solidified. The content of the thermoplastic resin within this range includes the amount introduced from the outside.

In the present invention, the solidification of the used ion-exchange resin or the like is performed by an extruder, but friction heat is generated due to sliding of solid waste in the gap between the inner wall of the machine and the compression screw. No heating is required, or solidification is performed by auxiliary heating of the die part.

[Operation] The present invention will be described further individually. FIG. 1 is a block diagram showing steps of a method for solidifying radioactive waste according to the present invention.

For example, used ion-exchange resin and solid waste of low-level radiation discharged from a nuclear power plant, etc. are introduced into a shredder or crusher from a hopper, coarsely crushed, and optionally further crushed by a crusher, and then mixed. It is stored in a storage tank which communicates with a constant quantity supply device, and then solidified by an extruder. When a part of the thermoplastic resin is supplied from the outside, it is supplied to the hopper. In this extruder, the used ion-exchange resin and solid waste are kneaded and then molded into a certain shape, for example, rod-shaped, strand-shaped or cut pellet-shaped, and stored in a storage container such as a drum can. To be done. Further, even when performing incineration and melting treatment with a higher volume reduction property, there is an advantage that handling is easy because of these shapes. Further, since the used ion exchange resin is granular or powdery, it may be directly supplied to the mixing / quantitative supply device.

In this solidification treatment, the thermoplastic resin is softened or melted by friction heat generation by appropriately selecting the compression ratio of the extruder, etc. It is not necessary to supply heat to the vicinity of the part from the outside, or only auxiliary heating is sufficient, which is preferable from the viewpoint of energy saving. The solidification in this extruder is carried out at a temperature of about 100 to 190 ° C.

By carrying out such a treatment, the used ion-exchange resin and the solid waste are, so to speak, a solidified product embedded in the plastic, so that it is extremely compact, and the outer surface of the solidified product is closely packed in the molten plastic. Since it is covered, it becomes a stable object even when immersed in water, and the volume reduction effect can be greatly improved. Moreover, since it is usually possible to use only the resin contained in the solid waste without introducing the thermoplastic resin from the outside, the volume-reducing effect is additionally exerted.

[Examples] Hereinafter, the present invention will be specifically described based on Examples and Reference Examples.

Examples 1 to 4 and Reference Example Table 1 shows the case where the used ion-exchange resin (water content 42 wt%) that had been drained and dehydrated was mixed by changing the mixing ratio of the simulated waste and solidified. As can be seen from Examples 1 to 4, the volume of pellets after the solidification treatment is about 10 liters, which is about 1/5 of the volume of the input wastes of about 50 liters.

The solidification treatment of the input waste shown in Table 1 was carried out by crushing the mixture into 4 mm square or less with a cutter mill and then supplying the mixture to an extruder as shown in FIG. In FIG. 2, 1 is a hopper, 2 is a constant quantity feeder, 3 is a compression screw, and 4 is a die. The blade of the compression screw 3 at the tip (closer to the die 4) has a cutter shape, and the crushed and crushed mixture is sufficiently mixed therein.

The simulated waste supplied from the hopper 1 to the compression screw 3 having a rotation speed of 150 rpm through the constant quantity feeder 2 is compressed and kneaded, and heat generated on the barrel surface of the extruder causes
The thermoplastic resin is in a softened or melted state and faces the open end of the compression screw 3, where it is subjected to the shearing force of the rotating cutter-like part, and then continuously passes through the die 4 to the outside to obtain 20 pieces with a diameter of 12 mm. Since it was sent out in the form of rod or strand, when it reached an appropriate length, it was bundled and torn off. When these were allowed to cool, in Examples 1 to 4, good solidified products were obtained without mutual fusion, as in Reference Example.

The water content of the solid thus obtained is 2 wt%
It was below. Moreover, the surface of the solidified product became better as the resin mixing ratio increased. The solidified product in room temperature water,
After soaking for 3 months, it was found that the shape and weight were the same and the water resistance was good.

The apparatus shown in FIG. 3 is another example of the apparatus suitable for carrying out the solidification of the present invention. After the mixture to be solidified is crushed into 4 kg square or less by a cutter mill, the rotation speed is 16 rpm and the diameter is 150 mmφ.
It is supplied to the extrusion molding machine by the twin-screw paddle screw type constant-quantity feeder, and the die with 8mmφ × 62 holes (130mmφ
It is a device that extrudes into a 35 mm section.

[Effects of the Invention] As described above, according to the present invention, radioactive used ion-exchange resin and solid waste, which are difficult to process, can be processed together without substantially heating. The physical properties of the obtained solidified product are good, and the leaching of radioactivity and the like is small as in the case of solidified with plastic and solidified with cement.

In addition, the treatment and disposal cost of this radioactive waste is 2 to 10 times more than that of HIC, post-decomposition treatment, and direct solidification. It is possible to reduce the volume. This is because the initial equipment cost, operating cost, decomposing agent, solidifying material cost, etc. are extremely low in the method of the present invention. Especially, most of the solidifying material is a thermoplastic resin contained in radioactive solid waste. Since it is covered, it will significantly contribute to the improvement of economic efficiency.

[Brief description of drawings]

FIG. 1 is a flow sheet showing the steps of the present invention, FIG. 2 is a side view of an extrusion molding apparatus used as one specific example, and FIG. 3 is a side view of an extrusion molding apparatus which is another specific example. 1 ... Hopper, 2 ... Constant quantity feeder, 3 ... Compression screw, 4 ... Die, 5 ... Twin screw paddle screw type mixed constant quantity feeder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Saburo Jota 4-2-20 Sendagi, Bunkyo-ku, Tokyo (72) Inventor Ihiko Uchida 1-20-1 Awata, Yokosuka City, Kanagawa Prefecture (56) References JP-A-58-82200 (JP, A) JP-A-52-13100 (JP, A) JP-A-50-90900 (JP, A) JP-A-57-48700 (JP, A) JP-A-53-40200 (JP , A)

Claims (1)

[Claims] 1. A mixture of a used radioactive ion exchange resin and a radioactive solid waste is shredded or crushed, crushed and processed to a set size, and then 100 to 100 to be generated by friction heat in an extruder having a compression screw. A method for solidifying radioactive waste, comprising compressing under a temperature condition of 190 ° C. to solidify the thermoplastic resin contained in the radioactive solid waste as a part or all of a solidifying material.