JPS605920B2 - Spherical vitrification method for radioactive waste - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for disposing of radioactive waste.

More specifically, the present invention relates to improvements in the method of solidifying radioactive waste into vitrified material. High-level radioactive waste (aqueous solutions containing fission products) generated by the reprocessing of spent fuel is usually evaporated and concentrated, then glass powder, etc. is added, and the radioactive materials (fission products) are heated and melted into a glass structure. It is conceivable that the radioactive waste be buried in a radioactive waste processing plant where the radioactive waste is fixed in a canister and sealed in a cylindrical container (canister) such as a stainless steel mesh and stored until the heat generation due to decay becomes low.

In order to make this safer, it is thought to be effective to form a composite solidified body by forming glass into small spheres and filling the gaps with lead. It is desirable that the shape be as close to a perfect sphere as possible for handling, etc. Radioactive waste that has been vitrified for the above purpose has a The present invention relates to the prilling of radioactive waste that has already been vitrified into pellets with the diameter of one mosquito. Many methods are known for making spheres (including microspheres) of glass or similar amorphous materials.

'1' A method of mechanically shearing a molten glass-like substance and rolling it in a gutter-like groove, [2] A method of mechanically shearing a molten glass substance and making it spheroidize by retaining it in the air due to surface tension, '3' A method of using centrifugal force 4) A method of dividing the particles into spheres using surface tension; 4) A method of applying vibration or vibration in a liquid medium that does not mix with each other to form spheres; discharging the particles from a wind nozzle and forming them into spheres using surface tension in an electric field. Method, ■Method of vibrating the divided molten material in non-adhesive powder to make it into spheres, '7) Method of mechanically shearing and rolling it on a flat plate, [8-Casting, ■Korokiri, plate Mechanical molding (wear), etc. are known. All of the above methods require some kind of mechanical manipulation, and none of them are suitable for the purposes of the present invention, which must be manufactured by remote control in a shielded room for handling highly radioactive materials. is also inconvenient.
It is well known that when a droplet falls from a nozzle, the size of the falling droplet becomes constant due to the surface tension of the liquid, and conversely, the surface tension of the liquid can be measured by measuring the weight of the droplet.

Although it should be possible to manufacture spheres of glass-like material by applying this principle, such a manufacturing method has never been carried out in an industrial sense. The reason for this is probably that there were limitations on the manufacturing speed and the size of the balls that could be manufactured, so no consideration was given to this. However, in situations where remote control is required within a shield, such as the purpose of the present invention, it is of great significance to consider the possibility of this method.
The present inventors (and others) took this up and completed the present invention.

According to the present invention, a glass-like material containing radioactive waste is dropped from a nozzle having a cap that forms droplets of a desired size, is subjected to an inclined vertical vibration by a gutter-like body, and then the top of the glass-like material is dropped. A method of forming into spherules by rolling is provided.

The material and size of the container for melting the glass-like substance can be selected appropriately, but heat-resistant stainless steel is one of the preferred materials, and the container is preferably heated by external heat radiation.

The diameter of the spheres produced by this method is limited by the properties of the glass-like material, but usually 2 to 20 spheres are possible.

However, for purposes of the present invention, the diameter of the sphere is determined by the properties of the glass-like material itself, such as its surface tension, and the outer diameter of the nozzle through which it is discharged. the substance appears in a molten state at the tip of the nozzle, forming droplets and growing to a constant weight as allowed by the surface tension of the substance;
When it reaches that point, it separates from the nozzle and falls.

A falling droplet tries to assume a spherical shape due to surface tension, but
For this purpose, as mentioned in a part of the explanation of the prior art, a gas L liquid having an appropriate temperature and viscosity is required for a considerable period of time (until it is cooled until it becomes a sphere and does not lose its shape). or need to be kept in powder.

In the method of the present invention, the fallen sphere is received by a vibrating, slightly inclined gutter-like body (shaping rail), and is cooled and solidified while being rolled thereon.

The cross section of the trough-like body is V-shaped, and the corner of the V-shape is, in extreme terms, 1
It is possible if it is less than 80℃, but preferably 60~120℃
, most preferably around 90o. The apex portion of the V-shape may have a curvature or may be open in an inverted eight-shape. If it has a curvature, the radius of curvature is preferably equal to the radius of the desired sphere. If the small sphere is solidified, it is desirable that the gap is smaller than the radius of the desired sphere. length of the shape,
It is determined by the correlation with the conditions for excitation of the gutter-like portion, which will be described later.

This trough-like body is given vibration with appropriate frequency, acceleration, and amplitude by appropriate means.

As a result, the droplets that have fallen onto the trough-like body are thrown up into the air at a frequency determined by the vibrations, during which time they try to form into a sphere due to their own surface tension, while being acted upon by the sides of the trough-like body to form a sphere. is cooled while being shaped into a spherical shape. Without vibration, liquid bottles may stick to the walls of the gutter, become spheroidal, or solidify in the form of drops when they fall. In the case of glass, the frequency is preferably around 10 plates Z, and the acceleration is preferably on the order of 1 to 1. The amplitude varies depending on the repulsive force of the droplet, but is most preferably 0.1 to 5 ribs. The length of the trough-like body is long enough to hold the liquid bottle until it has cooled sufficiently and is no longer deformed or fused with other spheres. It is determined by the correlation with time and the slope of the gutter-like body (forming rail), etc., but it is not a single long gutter, but it may be a spiral shape, or it may be a combination of multiple relatively short gutter in a zigzag pattern. .

By doing so, space can be saved, and in the latter case there is an advantage that vibrations corresponding to the solidification state of the droplets can be applied to each unit gutter. Vibration may be applied by any method, but the most preferred is a vibration generating mechanism that combines a magnet and a spring, and since this can be easily designed and manufactured by those skilled in the art, it will not be described in detail here.

Note that it is preferable that the dripping nozzle and the gutter-shaped body correspond to each other one to one.

However, a combination of a plurality of nozzles and one gutter-like body is also possible if the plurality of dripping nozzles are provided at a sufficient distance (at least a distance beyond which there is no possibility of contact between droplets). However, it is generally advantageous to provide one melting vessel with a plurality of drip nozzles and associated troughs. The material of the gutter-like body may be any material as long as it does not adhere to the glass-like substance, but ``actually, it is stainless steel aluminum, etc.
・As mentioned above, the size of the droplet formed at the tip of the nozzle is determined by the surface tension (density), so once the conditions (i.e., the outer diameter of the nozzle and its material, the temperature of the kudzu liquid and the physical properties determined by it) Once the value (weight and pressure applied to the liquid, etc.) is determined, it can be realized reproducibly.

Next, the present invention will be specifically explained with examples.
It is a container made of heat-resistant and corrosion-resistant steel with a depth of 100 arcs and a wall thickness of 5 mm.It has a reshaped nozzle at the bottom with an outer diameter of 6.5 ribs and an inner diameter of 4 ribs, and is heated externally by an electric resistance heating furnace. A molten glass-like material having the following composition was held in the heated one.

Si02 43%, Eagle0314% Li20, K20, Ca○, Zn○ Total 11% N20
3, Na20 and others Total of 34% Below the nozzle, the V-shaped angle is 90o, the length is 2, so the combination of a spring and an electromagnet is tilted to 70, the frequency is 100 days, the acceleration is 4G, the amplitude is A trough-like body made of stainless steel and subjected to vibrations of 0.1 to 1 rib was provided.

When the nozzle was opened at a temperature of 1150 qo of the molten shark glass-like substance, the droplets fell onto the gutter at intervals of about 2 seconds, recoiled and rolled in the form of almost perfect spheres due to the vibrations.

The results obtained by replacing the nozzles with various outer diameters are shown in Table 1 below, and in all cases in Table 1, the weights show extremely close constant values.

However, as the diameter of the sphere increases, the variation in the weight of the sphere increases. One of the reasons for this is that at the moment the molten glass separates from the nozzle, droplets are generated and fall as microspheres. In some cases, these microspheres adhere to a larger sphere on the trough-like body, and in this case, if this occurs on the upstream side where the temperature of both is sufficiently high, it will be completely shaped into one slightly larger particle, and the temperature will increase. It was observed that when the temperature was low, it had a protruding shape, and in extreme cases, it became a sphere with a cup. However, this degree of variation is acceptable for the purposes of the present invention. In any case, the method of the present invention is extremely superior as a method for treating radioactive waste in that it does not require complicated mechanical operations, can be operated in a relatively narrow space, and can produce small spheres with uniform particle size. The present invention provides a method for producing spherical bodies of glass-like material.

Claims (1)

[Claims] 1 A glass-like material containing radioactive waste is dropped from a nozzle with an outer diameter that forms droplets of a desired size, is subjected to an inclined vertical vibration by a gutter-like body, and is rolled on top of the nozzle to form small droplets. How to form into spheres.