JPS63228099A - Solidifying processing method of radioactive waste - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for solidifying radioactive waste.

(Prior Art) Conventionally, in the treatment of so-called radioactive waste derived from nuclear power plants, spent nuclear fuel reprocessing plants derived therefrom, factories that handle radionuclides, and research institutions, WJK as much as possible
+, Cement, asphalt, plastic as a solidifying material for the purpose of passivating radioactive substances after volume reduction by compression, cutting, extraction, etc., JP-A-56-14196, JP-A-56-14196; Publication No. 60-104299, etc.) (Problems to be Solved by the Invention) In the conventional solidification treatment using cement, the following problems can be cited.

The primary purpose of cement solidification treatment is to passivate radioactive materials. That is, when processing and disposing of a solidified body, the lower the rate of radioactive material leaching from the inside of the solidified body when it comes into contact with external water such as groundwater or rainwater, the more suitable it is for the purpose. The leaching rate of radionuclides from solidified cement is 10-1 to 1O-
4VC! ``2 days and relatively large.-10,000.
The leaching rate from asphalt or solidified plastic is 10-3 to 10-6 2 days. Because cement is solidified using more water than is required for hydration due to its workability, it has many internal pores. It is thought that these various capillary amphibious land, voids, and water channels have a significant effect on water permeability, and radionuclides are also thought to leach out with the movement of water.Cement. In order to further reduce the leaching of radionuclides from the solidified material, one of the measures is to minimize the presence of these voids.According to the present invention, although the solidified material is the same cement type, An unexpected effect was obtained in that a solidified material with improved radioactive nuclear leaching amount was obtained compared to conventional cement solidified material.The reason for this is not clear at present, but the present invention Accordingly, it cannot be considered that this is due to the effective reduction of voids in the solidified material as described above.

Next, according to the conventional cement solidification method Dream ζ, whether cement solidification material and radioactive waste are kneaded or one is poured into the other without kneading, the amount of waste that can be mixed is small and the solidified material is Either the total capacity becomes large, or the processing container is poorly filled, and there is a tendency to leave pores due to air present in the gaps between the waste materials or accompanying air during filling.

One of the most important factors in solidifying radioactive waste is to reduce the processing volume as much as possible. Until now, it has not always been possible to adequately meet this demand for volume reduction. In order to solve this problem, it is necessary to improve the fluidity of the cement solidifying agent by increasing the water/cement ratio, or by increasing the water/cement ratio by mixing as much waste as possible per unit volume of cement composition. Another option is to take time during the filling operation to extract the pores. However, increasing the amount of water more than necessary increases the number of water channels as described above, which increases the leaching of radionuclides. Further, the time-consuming filling operation reduces work productivity. According to the present invention, the filling performance of the solidifying material is significantly improved more than expected, and when kneading, the fluidity filling property is sufficiently high even when a large amount of waste is mixed, and the material can be added naturally without adding any cross-contamination. With this method, radioactive wastes having various shapes derived from coral can be smoothly solidified without leaving almost any pores in the assimilate.

In addition, with conventional cement solidification methods, cracks occur in the solidified material, and these cracks may lead to the collapse of the solidified material, which is particularly detrimental to the long-term shape stability required for the disposal of radioactive waste. It may lead to losses. Furthermore, cracks in the solidified material increase the contact area when the solidified material comes into contact with water, leading to increased leaching of radionuclides, and the impact of their occurrence is significant. As described above, there are various factors that cause cracks to occur in conventional cement solidification methods, but the presence of water, which causes shrinkage of the solidified product, such as hydrolysis of the cement composition with water, hydration reactions, and the release of so-called free water. is greatly involved.

According to the present invention, the occurrence of cracks in the solidified body can be effectively prevented. This is due to the water/fluid cement composition of the present invention.
It is thought that being able to reduce the cement ratio is particularly effective. Furthermore, regarding the solidification method according to the present invention, the feature of good fluid filling properties as described above contributes to preventing the occurrence of cracks in the solidified product. That is, due to good fluid filling properties, assimilative adhesion to the surface of the object to be treated is good, and it is possible to prevent cracks that may occur when the solidified composition is peeled off from the surface. This leads to the prevention of phenomena such as cracks caused by expansion caused by rusting from the surface of iron materials, for example.

When filling the causes of cracks in these conventional cement solidified bodies,
It is necessary to fill the mouth of the container as full as possible. If there is a gap, cover the container, and when containers are stacked in multiple tiers for long-term disposal management, the load may be reduced and the container may deform.
There are concerns that the stability of the solidified material may be impaired, such as damage caused by the solidified material, and the voids becoming a source of water such as underground water. As a countermeasure to this, in conventional solidification methods, a method has been considered in which the gap at the mouth of the container is refilled with an appropriate solidification material (referred to as post-filling) after the solidification process. The reason why post-filling is required in conventional methods of solidifying cement or other materials is related not only to the absorption phenomenon of the solidified materials but also to their poor fluidity. That is, it is difficult to align the liquid level with the container mouth surface during filling. This is based on the following reasons. First, because the solidifying material has a high flow viscosity, the liquid level does not easily become flat in order to maintain effective filling productivity, and therefore the filling amount becomes heaped during filling, so the filling amount must be adjusted slightly. Next, due to poor filling properties, some of the voids such as pores or voids caused by entrained air are replaced by the solidifying material over time, and the liquid level therefore decreases by that amount. According to the present invention, since the filling properties of the fluid cement composition are extremely good, this problem can be effectively solved. The fluid cement composition used in the present invention can also be applied to post-filling of solidified bodies with other solidifying agents, and is highly effective. That is, it is easy to adjust the liquid level due to good fluidity.

(Means for Solving the Problem) The present invention provides a method of solidifying radioactive waste in a container using a fluid cement composition containing at least cement, a water-reducing material, and water. Concerning a solidification treatment method. The radioactive waste treated in the present invention is radioactive waste generated from various institutions that handle radioactive nuclear materials, as described above.

Radioactive waste comes in various forms depending on the location, facility, process, or treatment equipment where it is generated. For example, in nuclear power plants, ion exchange resins, plastic moldings, synthetic resins such as films and sheets, metal compositions called cladding which are dispersed in process water, and sodium sulfate derived from the regeneration of ion exchange resins are used. Examples include salts such as salts or their solutions, work clothes, laundry waste, ash from incineration of combustible materials, metal structural materials such as piping derived from plant maintenance, insulation materials, and concrete materials. To solidify these radioactive wastes using a passivation material containing cement, there are three methods: in-drum mixing, out-drum mixing, and a method that does not involve mixing.

The in-drum mixing method is a method of kneading assimilated material and radioactive waste in a container such as a drum.The waste, solidifying material, and water if necessary are mixed in advance in a mixer and then filled into a disposal container. The out-drum mixing method is used to solidify. In the eighth method, the disposal container is filled with a solidifying material, an admixture if necessary, or water, and the radioactive waste is injected or thrown into the void, or the radioactive waste is disposed of as the reverse process. Pour solidifying material etc. into the container.

The present invention can exhibit its characteristics in any of these filling and solidifying methods. In particular, the eighth solidification method that does not involve mixing can exhibit unique and excellent characteristics.

As the cement in the present invention, a mixture of Portland cement, early-strength Portland cement, super-early-strength Portland cement, super-rapid-hardening Portland cement, white cement, colored cement, and pozzolane cement is used.

There are no restrictions on the water-reducing material as long as it is used for the purpose of reducing mixing water while improving the fluidity of cement, cement mortar, or concrete. Generally, sulfonic acid or its salt, droxy acid or its salt, hydroxylated product, etc. are mentioned. Specifically, sodium or calcium genin sulfonate, β-naphthalene sulfonic acid sodium salt-formaldehyde condensate, β-creonate sulfonic acid, cresol sulfonic acid sulfonate, melamine formaldehyde condensate sulfonate or sulfite, phosphoric acid ester surfactant,
Examples include polyacrylic dispersants and alkylaryl sulfonates. Auxiliary additives may also be used to more smoothly exhibit the effects of these water-reducing materials. Examples include copolymers of olefins and ethylenically unsaturated dicarboxylic acids, as well as carboxylic acid imides, or their neutralized products,
Alternatively, an oxyethylene group-containing water-soluble polymer compound or the like may be used. The amount of these water-reducing agents added varies depending on the type of water-reducing agent used or whether or not it is used in combination with a commonly used surfactant, but is usually 0.05 to 15 parts by weight, preferably 0.05 to 15 parts by weight per 100 parts by weight of cement. .1
5 to 6 parts by weight are used alone or in combination. If it is used outside these ranges, fluidity may decrease, setting hardenability, various void contents, etc. may be adversely affected.

The flowable cement composition used in the present invention includes:
In addition, one or more of water retaining materials, -1 hardening modifiers, admixtures, aggregates, antifoaming materials, waterproofing materials, etc. can be added to improve the properties.

The water retaining material serves to prevent solid-liquid separation, floating water, and bleeding before the cement composition begins to solidify and gel in the container. When such floating water or breathing occurs in the solidification process of radioactive waste, when the water evaporates, a gap is created between the solidified material and the container lid as described above. Water retaining materials generally include cellulose, vinyl, and acrylic materials, and cellulose materials are widely used, particularly methyl cellulose, hydroxypropyl methyl cellulose, and glyoxal-added hydroxy-propyl methyl cellulose. The water retaining material serves as a viscosity regulator for the cement composition, and care must be taken not to reduce fluidity. The amount added is 2.
0.31 parts by weight or less, preferably 0.01 to 0.6 parts by weight, alone or in combination.

The expanding agent has the role of alleviating and adjusting the hydration and drying shrinkage of the cement composition depending on the purpose of use. Those commonly used for cement solidification can be used. Specific examples include those based on ettringite and lime.

Ettringite-based expanding material (a material that expands by producing ettringite through a hydration reaction when cement is mixed with water)
Specific examples include those containing calcium sulfoaluminate as a main component, and those containing calcium oxide, aluminum oxide, and sulfur trioxide as main components. Examples of lime-based expansive materials include Onoda Expan (trade name manufactured by Onoda Cement Co., Ltd.), 8AC! 8 (product name manufactured by Sumitomo Cement Co., Ltd.). The amount of these expanding agents added is 0.8 to 80 parts by weight or 1 to 15 parts by weight per 100 parts by weight of cement.

As the hardening adjustment agent, a cement quick setting agent or a slow setting agent, which is generally used for cement-based hardening materials, is used. For example, as a quick setting agent (aQ2, water glass, NazC
! Examples of setting-reducing agents include Ca salts such as gypsum, field salts, whip hydroxides, Ba salts, B&hydroxides, NazPO4, Na2B4O7, tannins, and polysaccharides.

Admixtures and aggregates are used to compensate for and improve the shortcomings of cement. Specific examples include blast furnace slag, pozzolan, fly ash, silica, fine aggregate, and coarse aggregate. Sand is commonly used as fine aggregate. Artificial sand such as silica sand, crushed sand, and crushed blast furnace slag sand, and natural sand such as river sand, sea sand, and mountain sand are used. Coarse aggregates are aggregates with large dimensions, and also include artificial aggregates and natural aggregates. In the present invention, coarse aggregate is rarely used for purposes other than special purposes. It is preferable to use admixtures and aggregates other than coarse aggregate as necessary. Although it is not used when it is not absolutely necessary, it is important to consider which factors are important, such as fluidity, hydration and drying shrinkage, strength, watertightness, or cracking, or depending on the type of radioactive waste. You need to choose. Sand has various sizes, but a diameter of approximately 6 seconds or less is preferred, and a diameter of 2.5 meters or less is particularly preferred. The amount of silica sand is preferably 1.21 ml or less. The amount added is 20 to 200 parts by weight per 100M parts of cement, especially 7
0 to 140 parts by weight is preferred. Depending on the type of cement,
If the amount is too small, the heat of hydration of the cement will be large and cracks may occur in the solidified product, while if it is too large, too much water will be needed to maintain fluidity, leading to increased breathing and reduced strength. Blast furnace slag can generally be added in an amount of 70 parts by weight or less per 100 parts by weight of cement. Fly ache is cement 10
2 to 80 parts by weight, preferably 6 to 16 parts by weight, is added to 0 parts by weight. Other admixtures and aggregates can be used according to the standards for adding them during cement solidification.

When adding the water-reducing material and the water-retaining material in the present invention, some foaming may occur depending on the conditions of use. In that case, it is effective to add a commercially available silicone antifoaming agent or the like if necessary. Substances commonly used in cement can be added as waterproofing materials.

The amount of water used in the present invention varies depending on the operational goals of solidifying radioactive waste according to the present invention. That is, it depends on the type, shape, and water content of the radioactive waste, the content of the fluid cement composition used, and the method of processing and disposing of the solidified material, such as whether it is aboveground or underground disposal. In some cases, it also depends on the type of solidification container. According to the purpose of the present invention, the amount of water added may be the same as that of general cement, but the amount of water can be reduced while maintaining fluidity. Specifically, 80 to 100 M parts of water can be added to 100 parts by weight of cement, preferably 85 to 80 parts by weight, particularly 85 to 60 parts by weight.

The solidification container used in the present invention is not particularly limited as long as it is used for processing and disposing of radioactive waste. In other words, drums with a cylindrical or prismatic shape, containers made of cement or epoxy materials with a hexagonal shape, or containers lined with cement, asphalt, plastics, or a mixture thereof. Examples include containers. The capacity may be within a range that is easy to use.

(Effects of the Invention) The present invention is directed to radioactive waste generated from various institutions that handle radioactive nuclear materials, particularly nuclear power plants, spent nuclear fuel reprocessing plants, and plants that handle pharmaceuticals, agricultural chemicals, or chemical products containing radioactive isotopes. Alternatively, by solidifying and passivating radioactive waste generated from research institutions involved in these areas in a container with a fluid cement composition, it is possible to prevent radioactive materials from leaching and eliminate voids, pores, and entrained air in the solidified material. Effectively removes pores to prepare airtight and volume-reduced passivates, prevents cracking, and improves workability by making it easy to adjust the liquid level during filling. It has a significant improvement effect.

(Examples) The present invention will be illustrated below by examples, but the gist of the present invention is not limited thereby.

Example 1 80mm metal cylindrical can with a diameter of 8/8 to 8 inches and a length of 100mm
~800 m5 of carbon steel straight and curved pipes were placed in a mixture of horizontal, upright and diagonal configurations. The cavity volume was previously measured with water and adjusted to 21°.

On the other hand, cement compositions of type 2'a were prepared as follows.

1) 100 parts by weight of Portland cement to 10 parts by weight of sea sand
0 parts by weight, 40 parts by weight of water, 1 part by weight of a sulfonated modified resin of melamine formaldehyde condensate, 0.11 parts by weight of methylcellulose, and 1 part by weight of α-gypsum.

2) 100 parts by weight of Portland cement to 10 parts by weight of sea sand
A cement composition prepared by adding 0 parts by weight and 65 parts by weight of water.

These two types of cement compositions were poured into the above-prepared containers using a gravity drop method, and the liquid level was adjusted to fill the containers. The amount of liquid that could be added at that time was 1) 20
．． 8, 2) It was 15.8. After solidification for two weeks, the container was cut and observed, and as a result, sample 1) had the cavity filled smoothly, whereas sample 2) had many unfilled areas of various sizes.

When the compressive strength of the separately Mjg test piece after 2 weeks of solidification was measured using an Amsler tester, both the image sample and the sample were 2 Q O! 47C-2, and had sufficient strength as a cement assimilate.

Example 2 Cesium carbonate was added to the same cement composition as in Example 1 at a concentration of 8 f-/l. The composition was solidified, and after curing for 30 days at room temperature, samples were taken and subjected to the following leaching test. is.

Sample shape: Diameter: 4.51 m, height: 4.4 cm Cylindrical The sample was immersed in an amount of ion-exchanged water equivalent to t of ion-exchanged water/sample surface area -7, and the water was exchanged once a day for 10 days at 20°C. The cesium ions dissolved and leached into the water were concentrated and analyzed. As a result, the leaching amount was 8.8 x 10''P/2days for sample 1) and 1.4 x 10''V2days for sample 2).

Example 8 Co was added to a strongly acidic ion exchange resin with an average particle size of 210 mμ
Ions adsorbed on a 6w9/- ion exchange resin were mixed as the following cement composition and filled into an 80 metal can and solidified.

1) 100 parts by weight of Portland cement, 1.4 parts by weight of sulfonated modified resin of melamine formaldehyde condensate, 88 parts by weight of water, 42 parts by weight of ion exchange resin 2) 100 parts by weight of Portland cement
65℃ Kabebe ion exchange resin
6x parts The compressive strength of the solidified bodies of these compositions (cured for 7 days) was evaluated using an Amsler tester, and the result was 185 for each.
Kf/m" and 152 Kp/m".

In the former case, a considerable amount of ion-exchange resin is mixed and the compressive strength of the solidified material is 1, which is the standard value for dumping into the ocean.
A sufficient strength of 50 Vcm2 was ensured.

In the latter case, if the amount of ion exchange resin mixed in is increased further, the strength will decrease and the above criteria will not be satisfied.

Procedural amendment (voluntary) May q, 1986

Claims (1)

[Claims] 1. A method for solidifying radioactive waste, comprising solidifying radioactive waste in a container using a fluid cement composition containing at least cement, a water-reducing material, and water.