JPH0684999B2 - Method for solidifying radioactive waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing an intermediate storage body for waste generated from a radioactive material handling facility.

(Prior Art) Concentrated liquid wastes and sludges generated from nuclear facilities and nuclear fuel reprocessing facilities have an undetermined disposal standard. Therefore, at present, an intermediate storage policy is adopted in which they are stored until it becomes clear. Conventionally, as a technique relating to such a storage method, a method of pelletizing with a suitable pelletizer has been developed. This is an extrusion molding granulator or a compression molding granulator, which converts powder of waste into several hundred kg per unit area.
This is a method of applying pressure of several tons to coagulate and mold the powder.

The advantage of this method is that it is more volume-reducing than the conventional cement and asphalt solidification methods, and that it is less corrosive than waste liquid storage and powder storage, which are considered as other intermediate storage methods. There is little concern about pollution due to scattering.

(Problems to be Solved by the Invention) The above method has an advantage that the waste can be pelletized by a simple process, but since the binder is not included in the waste, in order to give the produced pellets a certain physical property. Is
Very high pressure had to be applied. For example, the main component of the waste liquid generated from the nuclear fuel reprocessing facility is sodium nitrate, but about 50% is required to form this into pellets.
A pressure of 0 kgf / cm ² or higher is required. Furthermore, if the waste contains impurities such as silica that deteriorate the moldability, it is about 10
A pressure of around 00 kgf / cm ² was required, which made it difficult to take out the pellets, and in the worst case, there were problems such as cracking or cracking of the pellets.

In order to solve this problem, a method of adding an organic lubricant such as stearic acid has been proposed, but in this case, there is a problem that the strength of the pellet is deteriorated. In particular, as for nitrate-containing waste generated from the reprocessing plant, there is a problem that there is a risk of fire explosion as described in Dangerous Goods Category 1 of the Fire Service Act.

[Structure of the Invention] (Means for Solving Problems) As a result of focusing attention on the above problems and examining the solution, the inventors have found that good pellets can be obtained by the method described below. That is, in the present invention, after the radioactive waste liquid is dried to give a dry powder, it is dried in the method for solidifying the radioactive waste by pressure molding using a compression granulator into pellets for intermediate storage. 0.5 to 5% for powder
Water is added and the mixture is pressure-molded.

Furthermore, as an improved method, the radioactive waste liquid is dried to form a dry powder, which is then pressure-molded using a compression granulator to form intermediate storage pellets. 0.5 to 5% by weight of water and 0.5 to 5% by weight of water absorbing agent for absorbing this water are added to the treated powder,
It is characterized in that this mixture is pressure-molded.

A more effective waste in these inventions is BW.
R Dry powder of concentrated waste liquid containing sodium nitrate as the main component generated from the power plant, dry powder of waste liquid containing sodium borate as the main component generated from the PWR power plant, and sodium nitrate generated from the nuclear fuel reprocessing plant. Examples thereof include dry powder of waste liquid containing nitrate as a main component.

Examples of the water absorbing agent include hydraulic cement mainly containing calcium silicate or calcium aluminate, silica gel, magnesium aluminometasilicate, and the like.

(Function) The radioactive waste liquid becomes a fine powder having a particle size of about 100μ by a drying process. Since these powders have a large surface area and are very active and easily aggregated, they can be formed into pellets by a granulator. However, to be molded into pellets having stable mechanical properties, about 700 kgf / cm ² or more with sodium sulfate powder, 500 kgf / cm ² sodium borate powder
More compression is required. Therefore, the compressed powder adheres to the inner surface of the cylinder of the molding machine, and it is necessary to apply a considerable pressure to push it out. However, if the powder contains water, a thin water film forms at the interface between the cylinder and the molding powder, so that it can be easily taken out at 1/5 to 1/6 of the pellet extrusion pressure that was conventionally required. It will be possible.

Also, by introducing water into the dry powder, the surface of the powder particles gets wet with water, so that the individual powder particles adhere to each other, and when this water is removed, it is dissolved in the water on the contact surface. This has the effect of precipitating the material components and finally integrating the powder. As a result, the strength of the pellets increases, and in the present invention, the reinforced pellets are extruded at the above-mentioned low take-out pressure, which makes it easier to extrude.

Further, in the present invention, the water absorbing agent is added in order to further improve the effect by further stabilizing the added water. As water-absorbing agents, hydraulic cement mainly composed of calcium silicate or calcium aluminate, silica gel, and magnesium aluminometasilicate are effective. In particular, it has been found that hydraulic cement, while absorbing water, undergoes a hydration reaction to harden itself and contributes to hardening of pellets.

The amount of water added should be 0.5 to 5% by weight. If it is less than this range, the lubricating effect is small, and the same extrusion as in powder pressure molding is required. On the other hand, if it is larger than this, water drops will adhere to the surface of the pellet or the surface of the piston / cylinder during molding, which is unsatisfactory.

The amount of water absorbing agent added must also be 0.5 to 5% by weight. If it is less than this, the amount of water absorption of the waste powder itself becomes large.
On the other hand, if it is larger than this, there is a disadvantage in terms of volume reduction.

In the present invention, the substance added as a lubricant is water, and these do not react with waste materials and ignite or explode.

(Example) Example 1 Sodium nitrate powder was pelletized by applying various pressures with a compression molding machine, and the pressure when the pellets were taken out was examined. Further, pellets were molded when the powder was mixed with 3% by weight of water, and when 3% by weight of water and 3% by weight of water-absorbing agent were mixed, and the pressure when the pellets were taken out was measured.

Blast furnace cement was used as the water absorbing agent. The results are shown in the figure. From this figure, when adding water and water + water absorbent,
It can be seen that the pushing pressure is very small. It is also found that it is almost the same as when stearic acid is added.

Example 2 0.3 to 10% by weight of water was added to sodium sulfate, sodium borate and sodium nitrate, and 1 was added in order with a compression molding machine.
^{000kgf / cm 2, 1000kgf / cm} 2, was pressure molded at 500 kgf / cm ^2.
The extrusion pressure of the pellet and the appearance of the pellet (water vapor and water droplet adhesion state) were examined. The results are shown in Table 1. As is clear from this table, it is found that the addition amount of water is preferably within 0.5 to 5% by weight.

Example 3 Sodium sulphate and sodium nitrate 3-6 respectively
Water and a water-absorbing agent of weight% were added, and the mixture was pelletized with a compression molding machine and the extrusion pressure and appearance of the pellets were examined. The results are shown in Table 2. As is clear from this table,
It can be seen that the effect is obtained when 0.5% by weight or more is added.

[Effects of the Invention] As described above, according to the present invention, it is easy to take out pellets from the granulator by adding a predetermined amount of water or water and a water-absorbing agent to the dry powder of waste. In addition, since the strength of the pellet itself is increased, there is an excellent effect that the pellet is not damaged and the cost of the solidification processing apparatus itself is reduced.

[Brief description of drawings]

The figure is a view showing the relationship between pellet extrusion pressure and pellet molding by the method for solidifying radioactive waste according to the present invention.

Claims (3)

[Claims] 1. A method for solidifying radioactive waste, which comprises press-molding a dry powder of a radioactive waste liquid generated from a radioactive handling facility using a compression granulator.
A method for solidifying radioactive waste, comprising adding 5% by weight and a water absorbing agent in an amount of 0.5 to 5% by weight. 2. A dry powder is obtained by drying a concentrated waste liquid containing sodium sulfate as a main component, a concentrated waste liquid containing sodium borate as a main component, or a concentrated waste liquid containing sodium nitrate as a main component. The method for solidifying radioactive waste according to claim 1. 3. The water absorbing agent is a hydraulic cement containing calcium silicate or calcium aluminate as a main component,
The method for solidifying radioactive waste according to claim 1, which is silica gel or magnesium aluminometasilicate.