JPH0656438B2 - Solidification method for radioactive molten water cooled slag - Google Patents

Description

Detailed Description of the Invention

 Purpose of the invention

[Industrial applications]

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.

[Prior art]

For example, periodic inspections of nuclear power plants generate various solid wastes with low levels of radioactivity. These must be finally stored and made suitable for land disposal until their radioactivity falls to a stable level. Among solid wastes, miscellaneous solid wastes such as ion exchange resins, HEPA filters, heat insulating materials, and plastic pipes used for treatment of radioactive waste liquids are bulky and require a vast storage space if they are solidified as they are. Become. Therefore, a method of incineration of organic matter of these miscellaneous solid wastes to reduce the volume and mineralize it and to melt-stabilize it together with other inorganic wastes has attracted attention. As a method for treating the melt, there are a method of directly filling a container and solidifying by cooling, and a method of granulating by air cooling or water cooling. The former directly packs the melt in a container, so that 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 the form of particles, it has a transportation problem such as scattering when the filling container is broken, and must be solidified by using an appropriate binder. Binders include plastics, asphalt, water glass, cement, etc., but cement is considered to be the most suitable in terms of its cost and long-term stability. As a solidification method using cement, there is an "out-drum system" in which waste and cement mortar are mixed externally and transferred to a container such as a drum can. This method can obtain a good quality solidified body by sufficient kneading, but it requires a mixer and other equipment and treats secondary waste such as washing water (which is also radioactive). There is a new problem that you have to do. As a method for avoiding this problem, an "in-drum mixer method" in which kneading is performed in a drum and an "impregnation method" in which cement mortar is allowed to permeate between particles can be considered. Among them, the in-drum mixer method requires strong stirring because the object is a particulate solid and has a problem in filling efficiency, and in addition, it is called a secondary waste treatment by the washing water of the mixer. The same problems as above remain. In the impregnation method, since the target is water-cooled slag having a small particle size, it is not easy to impregnate cement mortar unlike the case where a large object such as a piece of iron pipe is targeted. Therefore, the degree of filling and mixing of the water-cooled slag and the binder becomes low, and many cavities remain in the solidified body. The existence of the cavities may be a starting point of crack generation, which may cause problems such as corrosion of the container and eventually leaching of the contents. Therefore, the cavities should be prevented as much as possible.

[Problems to be Solved by the Invention]

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention, when a container filled with cement mortar or paste was charged with granular slag and the container was vibrated, the slag was in the mortar or paste. It was found that they fell into the ground and were buried, forming a solidified body with uniform strength without voids. The present invention has been made by utilizing this knowledge, and its purpose is to keep molten water-cooled slag having a low level of radioactivity without causing a problem of treatment of secondary waste without leaving harmful cavities. It is to provide a treatment method that can be easily and surely solidified into a state. Structure of the invention

[Means for Solving the Problems] A method for solidifying radioactive molten water-cooled slag according to the present invention is obtained by melting radioactive water in a container such as a drum or a rectangular container filled with cement mortar or paste and cooling it with water. Granular slag is added, and the container is vibrated to drop the slag into mortar or paste and then solidify. The molten water-cooled slag is obtained by melting flammable miscellaneous solids having a low level of radioactivity together with iron scraps, concrete, heat insulating materials and other wastes at a temperature of 1200 to 1500 ° C. and solidifying them by water cooling. The average particle size is about several mm. For processing in the present invention, slag having a particle size of 2 to 3 mm occupying 50% or more is preferable. For the preparation of cement mortar or paste (hereinafter sometimes represented by "paste"), ordinary cement such as Portland cement can be arbitrarily selected and used. In order to prevent cracking due to heat generation and corrosion of the drum can due to 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 to allow the slag to settle smoothly in the paste, it is important to have as high fluidity as possible. Experiments have shown that the flow value of the paste should be 40 seconds or less, preferably 35 seconds or less by the J ₁₀ funnel method in order to quickly drop the slag into the paste and densely fill it. . Of course, in order to increase the fluidity, the water / cement ratio may be increased, but the water / cement ratio is 40% or less, preferably 35% or less, from the viewpoint of preventing deterioration of paste strength and corrosion of the container due to breathing. %
The following values are selected so that the flow value is satisfied. In order to improve the fluidity, a water-reducing agent which is added and used in the construction of concrete or mortar in civil engineering or construction work, especially when pouring grout material is useful. The use of this water reducing agent reduces the amount of mixed water, and suppresses the generation of free water, so that the dual effect of preventing the strength of the paste from decreasing and the occurrence of corrosion can be obtained. Needless to say, other hydraulic substances and aggregates such as sand can be added as long as the fluidity of the paste and the strength of the solidified product are not impaired. The amount of slag added to and filled in the paste is 10
50 to 80 parts by volume, preferably 60 to 0 parts by volume
70 parts by volume. If it is less than 50 parts by volume, the amount of paste with respect to the slag is large, which is economically disadvantageous. Also, 80
When the content exceeds the capacity part, the slag does not substantially drop into the paste, so that a solidified body having uniform strength cannot be obtained. The vibration applied at the time of adding the slag, or subsequent to the addition, causes the slag to drop into the paste as quickly as possible (settling).
In addition, since it is a work to expel air bubbles that form harmful cavities in the gap of the slag, consider the conditions such as pouring so that the slag spreads evenly over the paste, and select conditions that are easy to fill from the beginning. Good. To apply the vibration, an appropriate vibration generating means such as a vibration motor or an air vibrator is used. In order to process a large amount of slag, a dedicated vibrating 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 in practice to suit individual conditions. Generally, the frequency is 1,000 to 10,
000 vpm and an amplitude of 0.5 to 3 mm are suitable. When a large amount of slag is processed, the filling amount of slag and paste is specified by the container (for example, drum can) that is fixed, so the solidification process is automated by using a constant volume (or constant weight) hopper. can do. The drawing shows an example of such a solidification treatment apparatus, in which 1 is a kneader for cement and water, 2 is a scale, and 3 is a constant volume hopper for water-cooled slag. A supply conveyor 5 is horizontally provided below the hopper 3 via a rotary valve 4, and a cone-type distributor 6 for uniformly distributing and supplying the slag is arranged at the tip of the supply conveyor 5. 7 is a filling container V
Is a belt conveyor for transporting and moving 8). To use this device, predetermined amounts of cement and water are weighed, and a 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, the capacity can be confirmed by measurement with the weight scale 2. Then, the container V filled with the paste is transported by the conveyor 7 and placed at the slag charging position. Here, a certain amount of slag is extracted from the rotary valve 4, and the supply conveyor 5
The slag is evenly put on the paste by the distributor 6. All the operations can be performed automatically by known sequence control.

[Work]

The granular slag put on the paste settles in the fluid paste due to the vibration applied to the container and the contents, and becomes a densely packed state. The periphery of each slag is covered with the paste, and voids are substantially absent, so that a cement-solidified body having a constant degree of mixing, that is, having a uniform compressive strength is obtained.

Example 1 A mixture of a combustible material, concrete, iron scraps, a heat insulating material and a HEPA filter was melted at about 1300 ° C. and water-cooled to obtain a water-cooled slag having an average particle diameter of 2.8 mm. On the other hand, as cement paste, type C blast furnace cement: water: water reducing agent =
The mixture was kneaded at a weight ratio of 75.0: 23.9: 1.1 to prepare a J ₁₀ funnel value of 27 seconds. 200 of the above cement paste 55 (140 kg)
420kg of granular slag (200)
Was charged for 20 minutes while vibrating the drum, and after the charging, vibration was continued for another 10 minutes. The granular slag was completely embedded in the cement paste, and a paste layer of about 1 cm was formed on the slag. After curing for 4 weeks, core boring was carried out at 5 locations on the same circumference from the center of the drum, and a total of 25 samples, 5 in the lengthwise direction of each core, were collected. As a result of measuring the specific gravity and the compressive strength, they were in agreement with each other within an error range of ± 5%, and the mixing degree of slag filling was uniform. Also,
No void was observed even by visual observation.

Comparative Example 1 Contrary to Example 1, 420 kg (200) of granular slag was first charged into a 200-drum can, and the cement paste was gradually poured from above while applying vibration. Do this work 3
It was run for 0 minutes, but the paste contained only about 12 (about 31 kg). That is, the paste penetrated only about 30 cm from the surface of the slag, and below it remained granular slag.

[Comparative Example 2] Inner diameter 100 mm, outer diameter 120 at the center of 200 drums
A pipe with a height of 50 mm and a width of 50 mm cutouts in four directions was placed at the lower end of the pipe, and 400 kg of granular slag was placed around it, and the cement paste was gradually poured through the pipe while applying vibration. . When this work was carried out for 3 minutes, almost no more paste entered and the work was stopped.
The paste only contained about 17 (about 43 g). Since the volume in the pipe is about 9, only 8 was filled in the voids of the granular slag.
In fact, it was found that the paste was only in the area around the pipe, with a diameter of 250 mm and a height of about 200 mm. Effects of the Invention The molten water-cooled slag solidification treatment method of the present invention, in its implementation,
Simple equipment such as a cement mortar or paste kneader, a constant quantity hopper, and a vibration machine is sufficient, and the equipment cost is low, and since the kneader does not handle radioactive slag, maintenance is easy and cleaning of the kneader is possible. The treatment of water is non-radioactive, there are no so-called secondary waste problems and the treatment costs can be kept low overall. The molten water-cooled slag can be safely stored by dropping and filling it in cement mortar or paste to ensure solidification in the substantial absence of harmful cavities.

[Brief description of drawings]

The drawings are explanatory views showing an example of an apparatus for carrying out the solidification treatment method of the present invention. 1 ... Kneading machine, 5 ... Supply conveyor, 2 ... Weighing machine, 6 ... Distributor, 3 ... Constant capacity hopper, 7 ... Belt conveyor, 4 ... Rotary valve, 8 ... Shaking table

Claims (3)

[Claims] 1. A container filled with cement mortar or paste is charged with granular slag obtained by melting radioactive waste and cooling with water, and the container is vibrated to drop the slag into the mortar or paste. A method for solidifying radioactive molten water cooled slag, which comprises solidifying afterwards. 2. The solidification treatment method according to claim 1, which is carried out using a cement mortar or paste having a J ₁₀ funnel value of 30 seconds or less. 3. The solidification treatment method according to claim 1, wherein the cement is a low heat-generating type cement such as blast furnace cement or fly ash cement.