JPS6383697A - Solidifying processing method of radioactive molten water-cooled slag - Google Patents

Abstract

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

Description

[Detailed description of the invention]

OBJECTS OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a method for assimilating radioactive molten water-cooled slag into a form suitable for final storage or land disposal. [Prior Art] For example, during periodic inspections of nuclear power plants, various solid wastes with low levels of radioactivity are generated. These must be stored for final storage until their radioactivity is reduced to a stable level, and then put into a form suitable for land disposal. Among solid wastes, miscellaneous solid wastes such as ion exchange resins, HEPA filters, heat insulating materials, and plastic pipes used in the treatment of radioactive waste liquids are bulky and require vast storage space if they are solidified as they are. Become. Therefore, a method of incinerating the organic matter of these miscellaneous solid wastes to reduce their volume and make them inorganic, and then melting and stabilizing them together with other inorganic wastes, is attracting attention. Methods for processing the melt include a method in which it is directly filled into a container and allowed to cool and assimilate, and a method in which it is granulated by air cooling or water cooling. In the former case, the molten material is directly packed into a container, so in order to improve its fluidity, consideration must be given to raising the temperature or adding a flux component, and handling is also difficult. The latter does not require such consideration, but
Since the product is in particulate form, there are transportation problems such as scattering when the filled container is broken, and it must be solidified using a suitable binder. Binders include plastic, asphalt, water glass, and cement, but cement is considered the best in terms of cost and long-term stability. As a solidification method using cement, there is an ``out-drum method'' in which waste and cement mortar are mixed outside and transferred to a container such as a drum. This method can obtain high-quality assimilate through thorough mixing, but it requires mixers and other equipment, and it also requires treatment of secondary waste such as wash water (which is also radioactive). A new problem arises that must be done. Possible methods to avoid this problem include the ``in-drum mixer type,'' which involves kneading in a drum, and the ``impregnation method,'' which allows cement mortar to penetrate between particles. Among these, the one-type in-drum mixer requires strong agitation because the target material is particulate solid, which has the disadvantage of poor filling efficiency, as well as the disposal of secondary waste using mixer wash water. The same problem as above remains. In the impregnation method, since the object is water-cooled slag with a small particle size, it is not easy to impregnate cement mortar, unlike when the object is a large object such as a piece of iron pipe. Therefore, the miscibility of the water-cooled slag with the binder is low, leaving a large number of cavities in the assimilate. The presence of cavities can become a starting point for cracks, leading to problems such as corrosion of the container and leakage of contents, so cavities must be kept as solid as possible.

[Problems to be solved by the invention]

As a result of extensive research to solve the above problems, the inventors of the present invention have discovered that, in an impregnation method in which cement mortar is injected over water-cooled slag filled into a container and penetrates between the slag particles, It was found that cement mortar penetrates into the slag to a certain depth and forms a void-free assimilated body with uniform strength. The present invention was made by taking advantage of this knowledge, and its purpose is to convert molten water-cooled slag with low levels of radioactivity into
The object of the present invention is to provide a treatment method that can be easily and reliably assimilated into a state in which no harmful cavities remain without the problem of secondary waste treatment. Structure of the Invention [Means for Solving the Problems] The method for solidifying radioactive molten water-cooled slag of the present invention is to melt radioactive waste and cool it with water, and then granular slag is placed in a drum or square container. Fill the container to a height of 300M or less, and place 45 to 55 of the slag filling capacity on top of the filled slag.
% of the cement mortar or cement paste, vibrate the container to infiltrate the cement mortar or cement paste between the slag particles, and repeat the above filling and injection process until the container is filled. It consists of repeating one action after another. As mentioned above, molten water-cooled slag is produced by melting combustible miscellaneous solids with low levels of radioactivity together with iron scraps, concrete, insulation materials, and other wastes at a temperature of 1,200 to 1,500 degrees Celsius, and solidifying this by water-cooling. The average particle size is several meters. To be treated with the present invention, the particle size is 2-3 #
A slag in which the latter accounts for 50% or more is preferable. Powdered particles with a particle size smaller than 1 m prevent impregnation with cement mortar or paste, and are therefore preferably reprocessed in a melt water cooling process. In addition, even lumps having a particle size of more than 58 mm can be solidified by the method of the present invention if the amount is small. Cement mortar or paste (hereinafter referred to as “
For the preparation of the "paste", any cement including ordinary Portland cement can be used. In order to prevent cracks caused by heat generation and corrosion of drums caused by water evaporation and condensation,
It is preferable to use a low heat generation type cement such as blast furnace cement or fly ash cement. In order for the paste to penetrate well into the slag, it is important to have as high fluidity as possible. According to experiments, it has been found that in order to achieve reliable penetration of the paste, the flow value of the paste should be set to 40 seconds or less, preferably 35 seconds or less using the JIO funnel method. Of course, in order to increase fluidity, it is possible to increase the water/cement ratio, but from the viewpoint of reducing paste strength and preventing corrosion of the container due to breathing,
The water/cement ratio is 40% or less, preferably 35% or less, and is selected to satisfy the above flow value. In order to improve fluidity, water reducing agents are useful when added to concrete or mortar in civil engineering or construction work, especially when grouting. By using this water reducing agent, the amount of mixed water is reduced, and by suppressing the generation of free water, a double effect is obtained: a decrease in the strength of the paste and prevention of corrosion occur. It goes without saying that other hydraulic substances and aggregates such as sand can be added as long as they do not impair the fluidity of the paste and the strength of the solidified product. The filling height and depth of slag filling into the container is 300 seconds.
I have to stop below. If it gets deeper than this,
It is difficult to impregnate the paste and the degree of filling and mixing with the slag varies, making it impossible to obtain an assimilate with uniform strength. In addition, the amount of paste to be injected is such that the porosity of the granular slag is 4.
Since the amount is 0 to 48%, it is selected from the range of 45 to 55% by volume of the slag filling amount. The vibration that is performed during or following the injection of paste is a process in which the paste penetrates between the granular slag particles, filling the voids and expelling the air bubbles that form the cavities, so that the paste is spread as evenly over the slag as possible. It is best to choose injection conditions that minimize the generation of bubbles from the beginning, such as gradually injecting the liquid so that it spreads evenly. To add photography, an appropriate vibration generating means such as a photography motor or an air vibrator is used. To process a large amount of slag, a special vibration table should be prepared to vibrate the entire container. If the target is a small amount, it is also possible to apply vibration to the bottom or side wall of the container. The frequency and amplitude of vibration should be determined during implementation.
It may be determined to suit individual conditions. In general,
Frequency: 1,000-10. Ooovpm, amplitude 0.5~
3 familiarity is appropriate. When processing a large amount of slag, the filling amount of slag and paste is determined by the container (for example, a drum), so by using a constant volume (or constant weight) hopper, the solidification process can be automated. can do. All operations can be performed automatically using known sequence control. [Function] The paste injected onto the slag gradually permeates and fills the gaps between the slag particles due to vibrations applied to the container and contents. As a result, there are virtually no cavities and a constant degree of mixing.
In other words, a cement assimilated body with uniform compressive strength is formed. The flow resistance of the paste gradually increases as it penetrates, and once a certain depth is reached, further penetration becomes difficult. The limit is that the initial filling depth into the slag is 350
It is around ~400m, and beyond this, the compressive strength, which is a measure of penetration, decreases rapidly. Stable compressive strength is
Obtained with an impregnation depth of 3001M1 or less. [Example 1] A water-cooled slag with an average particle size of 2.8 m was obtained by melting a mixture of combustible materials, concrete, iron scrap, heat insulating material, and HEPA filter at about 1300° C. and cooling it with water. This slag was filled into an open drum of 200 ρ, and cement mortar was poured into the drum while being vibrated on a vibration table. The composition of the cement mortar was ordinary Portland cement/water = 3.0/1.0, and a water reducer (1.5% by weight based on the cement) was added so that the JIO funnel value was 25 seconds. The work was continued until this cement mortar no longer penetrated into the slag, and after 4 weeks, the depth of cement impregnation was examined by core polling. As a result, it was found that the cement was impregnated to about 40 C)s. The results of measuring the compressive strength at each point are shown in the drawing. Additionally, a large number of water droplets, which were thought to be condensation of water that evaporated due to heat generation during cement solidification, were attached to the top lid of the drum. [Example 2] The water-cooled slag used in Example 1 was heated to 200. The Q open drum was filled to a height of approximately 250 m. The vibrator was run for approximately 5 minutes to bring the slag level to approximately level. On top of this slag, 32 g of cement paste prepared at Type 0 blast furnace cement: water: water reducing agent = 75.0:23° 9:1.1 (heavy ffi ratio) was gradually poured, and after all was poured, approx. Vibration was applied for 10 minutes. Then, a new 63.1! The drum was filled with water-cooled slag, and cement paste was injected in the same manner.Finally, the slag was filled to 95% of the drum level, and the paste was injected on top of it to reach about 100%. After 4 weeks of curing, the compressive strength of each part was measured by core polling, and all of them were within the range of 351±20 to 9/cri, and no air bubbles (voids) were observed on the cut surfaces. Effects of the Invention The method for solidifying molten water-cooled slag of the present invention requires the following steps in carrying out the method:
Simple equipment such as a cement mortar or paste mixer, a metering hopper, and a vibrator are all that is needed, so equipment costs are low, and since mixing and punching does not involve handling radioactive slag, maintenance is easy, and cleaning water treatment is easy. There are no secondary waste problems, and overall processing costs can be kept low. The molten water-cooled slag can be safely stored, since the impregnation with cement mortar or paste ensures solidification with virtually no harmful cavities.

[Brief explanation of the drawing]

The drawing shows implementation data of the solidification treatment method of the present invention, and is a graph showing the relationship between the filling depth of water-cooled slag and the compressive strength of the solidified body.

Claims (4)

[Claims] (1) Fill a container with granular slag obtained by melting radioactive waste and cooling it with water to a height of 300 mm or less, and place an amount equivalent to 45 to 55% of the slag filling capacity on top of the filled slag. Radioactive melting consists of injecting cement mortar or cement paste, shaking the container to infiltrate the cement mortar or cement paste between the slag particles, and repeating the above filling and injection steps until the container is filled. Solidification treatment method for water-cooled slag. (2) The solidification treatment method according to claim 1, which is carried out using water-cooled slag in which particles with a particle size of 2 to 3 mm account for 50% or more of the total. (3) J_ of cement mortar or cement paste
The solidification treatment method according to claim 1, which is carried out using a material having a 1_0 funnel value of 35 seconds or less. (4) The solidification treatment method according to claim 1, which is carried out using a low heat generation type cement such as blast furnace cement or fly ash cement as the cement.