JPS6383698A - 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]

OBJECT OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a method for solidifying radioactive molten water-cooled slag into a form suitable for final storage or land disposal.

[Conventional technology]

For example, periodic inspections of nuclear power plants generate various solid wastes with low levels of radioactivity. These must be stored for final storage until their radioactivity has decreased to a stable level, and in 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, attention is being focused on 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 solid wastes. 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. Assimilation methods using cement include the ``out-drum method,'' in which waste and cement mortar are mixed externally and transferred to a container such as a drum. This method can produce a high-quality solidified material with sufficient crosstalk, but it requires mixers and other equipment, and it also generates secondary waste such as wash water (which also becomes radioactive). A new problem arises that must be dealt with. 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 degree of filling and mixing of the water-cooled slag and the binder becomes low, and a large number of cavities remain in the solidified body. The presence of cavities serves as a starting point for crack generation,
Cavities should be avoided as much as possible, as this can lead to problems such as corrosion of the container and leakage of the contents. [Problems to be Solved by the Invention] As a result of extensive research in order to solve the above problems, the present inventors discovered that granular slag was poured into a container filled with cement mortar or paste. It was found that when photographed, the slag falls into the mortar or paste and is buried, forming an assimilated body with uniform strength and no voids. The present invention has been made by utilizing this knowledge, and its purpose is to process molten water-cooled slag with low levels of radioactivity without the problem of secondary waste disposal and without leaving any harmful cavities. The purpose is to provide a processing method that can easily and reliably solidify the product. Composition of the invention

[Means to solve the problem]

The method of solidifying radioactive molten water-cooled slag of the present invention involves melting radioactive waste in a container such as a drum or a square container filled with cement mortar or paste, cooling it with water, and storing 1 q.
The method consists of adding granular slag to the container, causing the slag to drop and fill into mortar or paste by applying vibration to the container, and then solidifying the slag. Molten water-cooled slag is made by melting combustible miscellaneous solids with low levels of radioactivity at a temperature of 1,200 to 1,500 degrees Celsius along with iron scraps, concrete, insulation materials, and other wastes, as described above, and solidifying this by water-cooling. , with an average particle diameter of several meters. To be treated in the present invention, slag in which 50% or more of the slag has a particle size of 2 to 3 m is preferred. 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 the drum due to evaporation and condensation of water, it is preferable to use a low heat generation type cement such as blast furnace cement or fly ash cement. In order to allow the slag to settle smoothly into the paste, it is essential to have as high fluidity as possible. According to experiments, it was found that in order to cause the slag to quickly fall into the paste and fill it densely, the flow value of the paste should be set to 40 seconds or less, preferably 35 seconds or less using the J10 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, water/cement ratio should be increased.
The cement ratio is 40% or less, preferably 35% or less,
The flow value is selected so as 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. The use of this water reducing agent reduces the amount of mixed water and suppresses the generation of free water, which has the dual effect of preventing a decrease in the strength of the paste and the occurrence of corrosion. It goes without saying that other hydraulic substances and aggregates such as sand can be added as long as they do not impair the strength of the paste.
50 to 80 parts by volume, preferably 60 to 0 parts by volume
It is 70 volume parts. If the amount is less than 50 parts by volume, the amount of paste relative to the slag is large, which is economically disadvantageous. Also,
If it exceeds 80 parts by volume, the slag will not substantially fall into the paste, making it impossible to obtain an assimilate with uniform strength. Vibration performed during or following the introduction of the slag causes the slag to fall (sedimentation) into the paste as quickly as possible.
Since the work involves expelling air bubbles that form harmful cavities in the gaps between the slag, it is best to choose conditions that will make it easier to fill from the beginning by making sure that the slag is evenly distributed over the paste. good. To apply vibration, an appropriate vibration generating means such as a vibration motor or an air-by-break 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, vibration may be applied to the bottom or side wall of the container. The frequency and amplitude may also be determined to suit individual conditions in practice. Generally, the frequency is 1,000 to 10゜ooovpm, and the amplitude is 0.
．． A suitable length is 5 to 3 m. When processing a large amount of slag, the amount of filling of slag and paste is determined by the container (for example, a drum), so by using a fixed volume (or fixed size @) hopper, the solidification process can be carried out. Can be automated. The drawing shows an example of such an assimilation treatment apparatus, in which 1 is a cement and water mixer, 2 is a weighing scale, and 3 is a water-cooled slag constant volume hopper. A supply conveyor 5 is installed horizontally at the bottom of the hopper 3 via a rotary valve 4, and a cone-shaped distributor 6 is disposed at the tip of the conveyor 5 for uniformly distributing and supplying slag. 7 is a belt conveyor for transporting and moving the filled container (2), and 8 is a vibration table. To use this device, predetermined amounts of cement and water are weighed, and the required amount of cement paste is poured into the filling container V. Since the specific gravity and packing density of the cement paste are known in advance, its capacity can be confirmed by measurement using the weighing scale 2. Next, the container (2) filled with paste is transported by the conveyor 7 and placed at the slag input position. Here, a certain amount of slag is scooped out from the rotary valve 4 and sent by a supply conveyor 5, and the slag is uniformly thrown onto the paste by a distributor 6. All operations can be performed automatically using known sequence control. [Function] The granular slag placed on the paste settles in the fluid paste due to the vibrations applied to the container and its contents, resulting in a densely packed state. The periphery of each slug is covered with paste, and there are virtually no cavities.
A cement solidified body having a constant mixing degree, that is, a uniform compressive strength, can be obtained.

[Example 1] A mixture of combustible materials, concrete, iron scrap, heat insulating material and HEPA filter was melted at about 1300°C and cooled with water to obtain water-cooled slag with an average particle size of 2.8 m. On the other hand, as a cement paste, type 0 blast furnace cement: water: water reducing agent =
Kneaded at a weight ratio of 75.0:23°9:1.1, JIO
A funnel value of 27 seconds was prepared. Cement paste 5 above! M (14(1) to 20
After charging into the 0f1 drum, granular slag 42089 (20
0,9) was added to the drum for 20 minutes while vibrating the drum, and after the addition, the drum was continued to be roughly vibrated for 10 minutes. The granular slag was completely buried in the cement paste, and a paste layer of about 1 cm was formed on top of the slag. After curing for 4 weeks, core boring was performed at 5 locations on the circumference from the center of the drum, and 25 samples in total, 5 samples were roughly taken from each core in the longitudinal direction. As a result of measuring the specific gravity and compressive strength, they each agreed within an error range of ±5%, and the degree of filling and mixing of the slag was uniform. Further, no voids were observed in visual observation. [Comparative Example 1] Contrary to Example 1, 420 Ky (200, Q 2 ) of granular slag was first put into a 20 ON drum, and cement paste was gradually poured from above while applying vibration. This operation was carried out for 30 minutes, but only about 129 (about 31 kg) of paste could be contained. That is, the paste penetrated only about 30 cm from the slag surface, and the area below that remained as granular slag. [Comparative Example 2] At the center of a 200 fl drum, an inner diameter of 100 m and an outer diameter of 12
Insert a Q# pipe with 50m high and 50# width notches in four directions at the bottom end, put granular slag 400 into the surrounding area, and pour cement paste through the pipe while applying vibration. It was poured in gradually. After this operation was carried out for 30 minutes, no more paste was coming in, so the operation was stopped. The paste contained only about 17p (about 43g). Since the volume inside the pipe is approximately 91, this means that only 8,11 L of granular slag was filled into the voids. In fact, the paste is placed around the pipe with a diameter of 2
It turned out that it was only within a range of 50m and about 200# in height. Effects of the Invention The molten water-cooled slag solidification treatment method of the present invention includes 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 not necessarily required, and since the mixer does not handle radioactive slag, maintenance is easy, and the mixer is easy to maintain. Processing of wash water is non-radioactive, there is no problem of so-called secondary waste, and overall processing costs can be kept low. The molten water-cooled slag can be safely stored by falling into and filling a cement mortar or paste, which ensures solidification with virtually no harmful cavities.

[Brief explanation of the drawing]

The drawing is an explanatory diagram showing an example of an apparatus for carrying out the assimilation treatment method of the present invention.

Claims (3)

[Claims] (1) Pour granular slag obtained by melting radioactive waste and cooling it with water into a container filled with cement mortar or paste, and apply vibration to the container to cause the slag to fall and fill into the mortar or paste. A method for solidifying radioactive molten water-cooled slag, which comprises solidifying it. (2) The solidification treatment method according to claim 1, which is carried out using cement mortar or paste having a J_1_0 funnel value of 30 seconds or less. (3) 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.