JPS61274299A - Solidification of radioactive waste - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for stably immobilizing (solidifying) radioactive waste generated from nuclear power plants and the like.

(Prior Art) Conventionally, these radioactive wastes are stored after being solidified with cement, asphalt, or the like.

Among these, solidified cement is porous, so it has the disadvantage that a large amount of radionuclides leach out when it is submerged in water.

Furthermore, it does not have a high volume reduction ratio, and since it contains crystallization water, it has the disadvantage of cracking when heated.

Solidified asphalt has disadvantages in that it tends to swell and cannot be expected to have heat resistance or fire resistance.

In recent years, solidification methods using plastic polymers such as urea resin have been proposed, but because they are coal/petrochemical synthetic materials, they are expensive and are said to be unreliable in terms of stability over tens to hundreds of years. ing. Furthermore, since these are polymeric substances, they have drawbacks such as radiation deterioration.

On the other hand, there is a method that targets particularly high-level radioactive waste and involves heating and melting it with silicic acid, alkali metal salts, etc. and solidifying it as a glassy substance, but this method has disadvantages such as high energy costs and complicated operations. .

Recently, it has been reported and proposed that if silicate powder is compressed together with an alkaline aqueous solution under hydrothermal conditions, radioactive waste can be easily turned into artificial rock through a hydrothermal reaction (Japanese Patent Application No. 57-231250 Specification of No. 59-10868, JP-A-58-165100, JP-A-Sho 58
-204395 publication).

However, in this method, silicates containing silicon dioxide as a main component, such as crushed stone or acid clay, are used.

This increases the volume of waste other than those to be solidified.

(Problems to be Solved by the Invention) The present invention provides a method for converting radioactive waste into a stable solidified material that can withstand final disposal, and proposes the above-mentioned method that is easy to operate and inexpensive. It is something.

(Means for Solving the Problems) The present invention provides a method for solidifying and stabilizing radioactive waste using a hydrothermal solidification method, in which combustible material generated from the radioactive waste is used as a source of silicon dioxide, which is the base of the solidification reaction. The present invention relates to a radioactive waste O solidification method characterized by using incineration ash or fly ash generated from a coal-fired power plant.

The present invention is characterized in that incineration ash generated from the facility or fly ash generated from a coal-fired/co-fired thermal power plant is used as the silicic acid source for causing a hydrothermal reaction with radioactive waste. be.

Examples of the radioactive waste to be solidified in the present invention include the following: A common waste from pressurized water nuclear power plants is boric acid (HsBOs), which is
If it is incinerated or calcined after conditioning, it becomes Nag B407 (so-called borax). Additionally, a common waste from boiling water nuclear power plants is borax (NalSO4). usually,
These are the main components, and the remaining number 2 is Fe, Mn, S
ing, organic matter, etc.

The essential components for causing an alkaline hydrothermal reaction with radioactive waste to be solidified (hereinafter simply referred to as waste) are a solidification substrate mainly composed of silicon, and KOH, NaOH, Ca(O
H)z t Ba(OH), and other alkalis. Note that, as the alkali, a hydroxide obtained by reacting an oxide with water can also be used.

In the present invention, 10 to 50% by weight of waste is added to 50 to 90% by weight of incineration ash or fly ash generated from power plants as the solidification substrate, and an alkali (KsOtNI!LxO, etc.) is added to this. Add α4~4% by weight and an equivalent amount of water. The reason for setting the waste content to 10 to 50% by weight is that as shown in Figure 1, if it is less than 10% by weight, there is little practical significance in solidifying the waste, and if it is more than 50% by weight, the strength will drop significantly. It's because I do it. Depending on this amount,
The amount of solidified substrate is determined and the amount of alkali is determined correspondingly.

After kneading this, as shown in Fig. 2, it is filled into a cylinder 2 surrounded by a heater 1, and then, using a piston push rod 3 and a piston/4, for example, a hydraulic cylinder (not shown) is used to mix 100 to 500 kg, preferably 7 ci. is 250-50
After pressurizing to 0 to 9/ad, the temperature is raised. 150-40
A desired solidified product can be obtained by holding at 0°C, preferably 250 to 550°C, for 20 to 30 minutes.

In the present invention, setting the temperature as described above is advantageous because the higher the temperature, the higher the reaction rate, but the pressure must be increased accordingly (to prevent boiling), and heat-resistant materials are used to manufacture the device. This is because it is necessary to use Further, the reason why the pressure is set as above is that a vapor pressure of at least the relevant temperature is required, and if it is too high, it will be disadvantageous in terms of container manufacturing.

In addition, in FIG. 2, 5 is the above-mentioned interfering object, and 6 is a ground packing.

The present invention focuses on the fact that incineration ash or fly ash mainly contains 8101, KIO, A140@y F820s, etc. in terms of chemical components. The composition ratio varies depending on the object to be incinerated, but in general, the 5in2 content in incinerated ash or fly ash is 50 to 80%, which satisfies the requirements for hydrothermal solidification.

(Effect of the invention) According to the present invention, the following effects can be obtained.

(1) The total amount of waste will decrease.

Traditionally, incineration ash or fly ash and other wastes are
were processed independently. Therefore, when solidifying waste, it was necessary to newly transport cement, asphalt, or a silicic acid source in the case of hydrothermal solidification to the processing area. In the case of the present invention, K! O.

Since Na20 or the like is used as an alkali, the total amount of waste is reduced to about 100% compared to the conventional method. That is, conventional method: Incineration ash approximately 1 + solidifying agent approximately 1 = solidified material approximately 2 (weight ratio)
Other waste approximately 1-)-1i! I1 converting agent: Approximately 1 = Solidified material approximately 2 (weight ratio) Total approximately 4 (weight ratio) Method of the present invention: The volume reduction rate varies depending on the absolute amount of incinerated ash and the IT ratio of other waste, but if this is equivalent This ratio varies depending on the plant and operating conditions, but it generally decreases to about %.

Of course, the amount of incinerated ash or fly ash and the amount of other waste are not necessarily generated in the quantitative ratio required for the hydrothermal reaction described above, and in that case there will be excess or deficiency, but even in that case, the amount of waste The purpose of the present invention, which is to reduce the total amount of , is not impaired.

(2) Solidification costs are lower.

The solidification substrate required for the hydrothermal reaction is preferably as fine as possible in order to accelerate the solidification reaction rate. Incineration ash or fly ash is suitable for this purpose because it is ground into fine powder on the order of microns due to its nature, and energy costs such as pulverization can be saved. Of course, costs such as quarrying and transporting raw materials are also unnecessary.

(3) Effective use of fly ash can be achieved.

The so-called EP ash (fly ash) that is collected in the dust collectors of thermal power plants, especially coal-fired power plants, is currently used in part for purposes such as freshly dumping, but the majority is left in the field. This has caused problems such as dust scattering.

Its main components are 5i0147~80% (same below weight ratio), Az, o, 10=30%, Fe1O1 (1,
5-1591;, Cao (lL2-10%, other T1
01 s r1# Contains small amounts of O, KsO, V, O, etc. - Examples are shown in Table 1.

Table 1 Example of composition of coal ash (fly ash) As is clear from Table 1, 810. The amount is comparable to that in incineration ash and can be fully used as a source of 8102 in the present invention.

Therefore, fly ash, which conventionally had no way of being effectively used, can be effectively used in the present invention. In particular, when the ratio of generated amount of incinerated ash to waste is unbalanced, fly ash can be used as a substitute for incinerated ash.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the preferred content of radioactive waste in the present invention, and FIG. 2 is a diagram showing an example of an embodiment when solidifying radioactive waste in the present invention. Sub-agents 1) Meifuku agent Ryo Hagiwara - Sub-agent Atsuo Anzai Figure 1 Amount of radioactive waste (wt%)

Claims (1)

[Claims] In the method of solidifying and stabilizing radioactive waste by hydrothermal solidification, as a source of silicon dioxide, which is the base of the solidification reaction,
A method for solidifying radioactive waste, characterized by using combustible incineration ash generated from the radioactive waste or fly ash generated from a coal-fired power plant.