JPH0634097B2 - Solidifying agent for radioactive waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is based on a solidifying agent for radioactive waste, specifically, a cementitious substance, ultrafine powder, a high-performance water reducing agent and water, and has a large treatment capacity. The present invention relates to a safe solidifying agent for radioactive waste, which can be stored permanently and has low elution of radioactive substances.

[Prior art]

As radioactive waste generated from nuclear facilities such as nuclear power plants and nuclear fuel reprocessing plants, concentrated waste liquid, used ion exchange resin, filter sludge, incineration ash, miscellaneous solids, various sludges and dismantling of nuclear power plants Examples include so-called low- and medium-level radioactive waste, such as concrete waste that is discharged, and high-level radioactive waste.

As a method for solidifying these radioactive wastes, particularly low- and medium-level radioactive wastes, a cement solidification method, a bitumen solidification method, and a plastic solidification method are in practical use.

[Problems to be solved by the invention]

However, although the cement solidification method has excellent durability, it has drawbacks such as low processing capacity and relatively high leachability. Further, although the bio-solidification method and the plastic solidification method have a large processing capacity, they have drawbacks such as a complicated processing method and a safety problem in terms of weather resistance.

From the above, there is a strong demand for a method of treating radioactive waste that has a large treatment capacity, a low leachability, and an excellent weather resistance.

As a result of various studies to eliminate the above-mentioned drawbacks, the inventors have found that the above-mentioned drawbacks are improved by using a solidifying agent containing a specific component as a main component, and the present invention is completed. Arrived.

[Means for solving problems]

That is, the present invention is based on a cementitious substance, an ultrafine powder having an average particle size smaller than that of the cementitious substance by at least one order of magnitude, a high-performance water reducing agent, and water as a main component, based on a total of 100 parts by weight of the cementitious substance and the ultrafine powder. The solidifying agent for radioactive waste is characterized in that ultrafine powder is 5 to 40 parts by weight, high-performance water reducing agent is 10 parts by weight or less, and water is 12.5 to 30 parts by weight.

Hereinafter, the present invention will be described in detail.

The cementitious material referred to in the present invention, normal, early strength, ultra early strength, various portland cement such as white or sulfate resistant, further mixed cement mixed admixtures such as blast furnace slag, fuyuatsushiyu, and mixed material and / or A mixed cement obtained by crushing mixed cement is generally used.

In addition, expansion cement is used to compensate for shrinkage, and rapid hardening cement is used to develop the required strength in a short time.
It is also possible to use a gypsum-based high-strength admixture together.

As the expansive component of the expansive cement, ettringite-based ones such as "CSA # 20" manufactured by Denki Kagaku Kogyo Co., Ltd. and calcined CaO
Is preferable, even in calcined CaO is calcined at 1100 to 1300 ° C,
Those having an average crystal diameter of 10 μm or less are particularly preferable.

The quick-hardening cement contains various calcium-aluminate-based quick-hardening components, such as various kinds of calcium sulphate aluminate alone or a mixture of calcium sulfate and calcium sulfate, manufactured by Denki Kagaku Kogyo Co., Ltd. Product name "Denka E
Examples include cement mixed with "S" and the product name "Jet Cement" manufactured by Onoda Cement Co., Ltd.

The high-strength admixture is a gypsum-based admixture, which is manufactured by Denki Kagaku Kogyo Co., Ltd. “Denka Σ-1000”, Nippon Cement Co., Ltd. “Asano Super Mix”, Osaka Cement Co., Ltd. “Nonclave”. , Etc.

The ultrafine powder used in the present invention has an average particle size lower than that of the above-mentioned cementitious substance by at least one digit, and in particular, an average particle size lower by two digits is preferable from the viewpoint of the flow characteristics of the kneaded product. Specifically, silicon, a silicon-containing alloy and silica dust by-produced in the production of zirconia (silica fume), and siliceous dust are particularly suitable, in addition, calcium carbonate, silk gel, opalaceous silica, fly ashes, Ultrafine powder such as slag, titanium oxide, and aluminum oxide can also be used. In particular, the use of ultrafine powder obtained by crushing opalaceous silica, fly ash, and slag with a jet mill equipped with a classifier is effective in improving curing shrinkage.

The total amount of ultrafine powder used is 100 for cementitious substances and ultrafine powder.
It is 5 to 40 parts by weight, preferably 10 to 35 parts by weight, based on parts by weight. If it is less than 5 parts by weight, it is difficult to obtain high strength (fastness), and if it exceeds 40 parts by weight, the fluidity of the kneaded product is remarkably reduced, making it difficult to mold it, and the strength is not sufficiently expressed. Will be enough.

The high-performance water-reducing agent (hereinafter referred to as water-reducing agent) used in the present invention is a surfactant having a large dispersibility that does not cause excessive delay of setting or excessive air entrainment even when added in a large amount to cement. Sulfonic acid formaldehyde condensate salt, melamine sulfonic acid formaldehyde condensate salt,
Examples thereof include those having a high molecular weight lignin sulfonate, a polycarboxylic acid salt, etc. as a main component. The water reducing agent is necessary for obtaining a kneaded product at a low water ratio, and the conventional amount used is 0.3 to 1% by weight as solid content with respect to the cementitious substance.
However, in the present invention, it is preferable to add a larger amount than that. Specifically, the solid content is 1% with respect to 100 parts by weight of the mixture of the cementitious substance and the ultrafine powder.
It is used up to about 0 parts by weight, and if it is added in a larger amount, it adversely affects the curing reaction. A particularly preferred amount of addition is 1 to 5 parts by weight. When the water reducing agent is used in such an amount, it is possible to obtain a flowable kneaded product that can be molded by an ordinary method even when the ratio of the water cementitious substance to the ultrafine powder is 25% or less.

The water used in adjusting the mixture in the present invention is necessary for molding, but it is better to make it as small as possible in order to obtain a high-strength cured body, 100 weight of the mixture of cementitious substance and ultrafine powder. 12.5 to 30 parts by weight is used per part, and 15 to 28 parts by weight is preferable. If the amount of water is more than 30 parts by weight, it is difficult to obtain a high-strength cured product, and if it is less than 12.5 parts by weight, ordinary molding such as casting becomes difficult. In the case of compaction molding and the like, molding is possible even when the amount is less than 12.5 parts by weight, which is not described above.

To treat radioactive waste (hereinafter referred to as waste) using the solidifying agent according to the present invention, a conventional cement solidification method can be applied. That is, the method of kneading the waste in a disposal container such as a drum or a concrete container, the method of filling the kneaded mixture in the disposal container in advance, the waste being packed in the disposal container in advance, and then solidifying in the void A method of filling the agent, or conversely, a method of filling the solidifying agent in the disposal container in advance and depressurizing it or pressurizing the waste material and injecting it into the disposal container is applied. At this time, the amount of the solidifying agent to be added largely varies depending on whether the waste is solid or contains water, but is generally about 10 to 500 parts by weight with respect to 100 parts by weight of the waste. From the viewpoint of increasing the processing capacity, the less the solidifying agent is, the more preferable. However, if it is 10 parts by weight or less, it is difficult to solidify, and the effect of suppressing the elution of radioactive substances is poor.

[Examples] The present invention will be described in more detail below with reference to Examples.

Example 1 A radioisotope was kneaded into the formulation shown in Table 1 No. 2 to give 0.2 μCi ³⁶ C ⁻ / cm ³ to prepare a specimen of φ5 × 5 cm, which was then cured in a closed container. After 3 days, a leaching test was conducted in a 0.1 Mol NaC solution, and the effective diffusion coefficient De was determined from the relationship between the number of immersion days and the amount of elution. Furthermore, a thin film having a thickness of 1 cm was prepared according to the composition shown in Table-1 NO.4, and 10 ^-4 Mol of CsC containing ¹³⁴ Cs ⁺ was included on one side of the thin film.
Was added to obtain a diffusion coefficient D of ¹³⁴ Cs ⁺ . The results are shown in Table-2.
Shown in.

<Materials used> Cement: Denki Kagaku Kogyo Co., Ltd., ordinary Portland cement Ultrafine powder: Nippon Heavy Chemical Co., Ltd., Silica Hyme Water reducing agent: Daiichi Kogyo Seiyaku Co., Ltd., “Cellflow 110P” Comparative Example 1 The same procedure as in Example 1 was carried out except that No. 1 and compound No. 3 were used. The results are shown in Table-2.

Example 2 Waste consisting of ion-exchange resin regeneration waste liquid, filter sludge, used ion-exchange resin, etc. discharged from a boiling water reactor was evaporated and concentrated, dehydrated and sampled. Was treated with the following solidifying agent. The water content of the waste is 80%.
The solidifying agent was 200 parts by weight with respect to parts by weight. The compressive strength and leaching rate in water at 3 days of age were measured and shown in Table-3.

Comparative Example 2 The procedure of Example 2 was repeated, except that the composition of Experiment No. 5 was used. The results are shown in Table-3.

Example 3 Concrete waste materials generated by the dismantling of a building in a nuclear power plant were packed in a drum pipe in advance, and the experimental NO.
A solidifying agent using the composition of 6 was injected to prepare a test piece of φ15 × 30 cm, and the compressive strength on the 28th day was calculated to be 1,077k.
It was gf / cm ² . For comparison, a compressive strength was obtained when the same test was performed using a solidifying agent using the composition of Experiment No. 5.
Not only 586 kgf / cm ^2, but also voids due to breathing water appeared remarkably on the lower surface of the concrete waste material.

〔The invention's effect〕

As described above, the solidification method using the solidifying agent of the present invention has a larger processing capacity than the conventional cement solidification method, and has a chemical resistance higher than those of the vitamin solidification method and the plastic solidification method.
It has excellent durability, simple treatment method, excellent heat resistance, large compressive strength and is safe during transportation. It is a treatment method that enables not only storage of waste but also permanent storage. is there.

Claims (1)

[Claims] 1. A cementitious substance, an ultrafine powder having an average particle size at least one digit smaller than that of the cementitious substance, a high-performance water reducing agent, and water as main components, and the total amount of the cementitious substance and the ultrafine powder is 100.
A solidifying agent for radioactive waste, characterized in that 5 to 40 parts by weight of ultrafine powder, 10 parts by weight or less of a high-performance water reducing agent, and 12.5 to 30 parts by weight of water are used with respect to parts by weight.