JPS61100697A - Method of fixing radioactive iodine - 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 [Industrial Application Field] The present invention relates to a method for immobilizing radioactive iodine, and particularly to a method for immobilizing radioactive iodine using a silicate-based adsorbent carrying silver.

[Conventional technique $1 Volatile radioactive iodine generated from spent nuclear fuel reprocessing plants, nuclear power plants, etc. is generally captured in the form of a solution or adsorbed by an adsorbent such as activated carbon or silver-supported zeolite. has been done. However, it remains adsorbed to the solution or adsorbent! is extremely unstable in both physical properties (e.g. mechanical strength, heat resistance, etc.) and chemical properties (e.g. water resistance, acid resistance, alkali resistance, etc.) and is unsuitable for long-term storage. Therefore, the immobilization method has been extensively researched in recent years, and IR-compatible adsorption method that adsorbs radioactive iodine has been studied extensively in recent years. A method of solidifying the F agent with cement has been proposed. (For example, the University of Tokyo Faculty of Engineering Research Facility Report IJ)
TNL-RO134 (1982), Burger
, 5chee le, PNL-4689 (1983)
).

[Problems to be Solved by the Invention] As mentioned above, since iodine adsorbed by the adsorbent is an unstable chamber, it is necessary to perform some kind of solidification treatment. The solidification method using cement is simple and is expected to be highly practical, but it is difficult to obtain a dense cement solidified product, and there is a risk of iodine elution. (In particular, the half-life of iodine-129 is extremely long (16 million years), so it needs to be sealed in a dense and high-strength solidified material.) Also, the amount of cement required to harden the adsorbent is large. mold, the volume of the resulting solidified body becomes larger. Therefore, it is necessary to take up a large storage space, which is also a practical bottleneck.

In addition, DOE/ET/41900-9 (ESC-DO
E-13354) NUCLEAR WASTE MAN
AGEMENT UC-70 describes a method of mixing a silicic acid compound with an alkaline waste liquid containing radioactive iodine to form sodalite, and sintering this at 1000℃, but it is sufficient to use high temperature while preventing the volatilization of captured iodine. Since the method must be sintered, there are various technical problems in putting it into practical use, such as complicating the equipment.

As described above, conventional immobilization methods have problems such as insufficient iodine containment and difficulty in practical application. In the invention, radioactive iodine is adsorbed onto a silicate-based adsorbent carrying silver, and an alkali or alkaline earth metal hydroxide such as sodium hydroxide is mixed with the adsorbent and a hydrothermal reaction is performed to form a solidified material. It was designed to do so.

The present invention will be explained in more detail below.

FIG. 1 is a system diagram illustrating the method of the present invention.

As shown in FIG. 1, the present invention first introduces radioactive iodine into
to adsorb radioactive iodine.

Although radioactive iodine is generated in nuclear fuel reprocessing plants, nuclear power plants, etc., the method of the present invention can be generally applied regardless of the source of radioactive iodine.

The adsorbent used in the present invention is a silicate-based adsorbent supporting silver, such as silver-supported zeolite, *m-supported mordenite, etc. The amount of silver supported is not particularly limited, but is 20 to 50% by weight, especially 30 to 50% by weight.
About 40% by weight is preferably used.

In order to bring such silver into contact with the adsorbent and radioactive iodine, a general R absorption device may be used. For example, the adsorbent is filled in a metal casing, and the casing contains the radioactive iodine. All you have to do is introduce the fluid and let it pass.
When radioactive iodine is brought into contact with a silicate-based adsorbent containing IR, the radioactive iodine is adsorbed by this adsorbent, and some of it becomes Agl, while the other part is in a simple state or in an unstable bond with Ag. To exist.

In the present invention, next, this adsorbent contains 1 M! of sodium hydroxide, potassium hydroxide, and barium hydroxide! Or add two or more types. By adding such an alkali or alkaline earth metal hydroxide, the iodine physically adsorbed on the adsorbent can be converted into stable A g I JtfAg I O according to the following reaction formula. 6
゜3I* +f30H-+6Ag":' A t I 03 + 5 A gI +
3 Hp O In the present invention, a mixture of an adsorbent adsorbing iodine and an alkali or alkaline earth metal hydroxide is subjected to a hydrothermal reaction as described below.
It is preferable to add the water necessary for the reaction, since barium hydroxide usually contains a large amount of water of crystallization.
It is not necessary to add water; that is, the hydrothermal reaction can proceed due to the water of crystallization contained in barium hydroxide.

When adding water, water may be added alone, but sodium hydroxide, potassium hydroxide, or barium hydroxide may be dissolved in water and added as an aqueous solution.

In this way, a mixture (hereinafter sometimes simply referred to as a mixture) of a silicate-based adsorbent adsorbing radioactive iodine containing water (or water of crystallization) and an alkali or alkaline earth metal hydroxide is heated under pressure. The cuff is maintained under heating and pressure at a temperature of 0 kg/crn' or more and a temperature of 150° C. or more to cause a hydrothermal reaction and solidify the mixture.

This hydrothermal synthesis reaction forms a three-dimensional skeletal structure (network) of at least partially hydrated flucarial aluminosilicate, which makes the silicate-based adsorbent mixture a dense, high-strength solid. The iodine adsorbed on the adsorbent becomes trapped within this network.

During the hydrothermal reaction, sodium hydroxide, potassium hydroxide, or barium hydroxide absorbs 5tO2 and AJ, which constitute the adsorbent.
It reacts with l 20 s and promotes the network formation reaction and hydration reaction of aluminosilicate. If the amount of the alkali or alkaline earth metal hydroxide added is less than 1%, the parallel progress of this reaction will be insufficient;
If the amount exceeds , the aluminosilicate network is broken, the strength J of the solidified body is reduced, and the iodine sequestration function of the network is reduced.

The amount of water to be included in the mixture is 10
The water content is preferably in the range of 2 to 20 parts by weight relative to 0 parts by weight. If the water content is less than 2 parts by weight, the hydrothermal reaction will not proceed sufficiently, and on the contrary, if it exceeds 20 parts by weight. for,
The number of pores in the solidified body increases and its diameter increases, and the strength thereof decreases, and there is a possibility that more iodine will be leached from the solidified body.

In the present invention, the pressure of the hydrothermal reaction is 70Kg/crn'
That's all. The upper limit of pressure is practically 500 Kg
The pressure is, however, higher than the vapor pressure of water at the reaction temperature, so that it is in a hydrothermal state.

If the temperature of the hydrothermal reaction is lower than 150°C, the solidification reaction will not proceed and only a solidified product with extremely low strength will be obtained.
A particularly preferable temperature is 200 to 350°C or higher.1 The hydrothermal reaction time is approximately 5 minutes to 1 hour. If the pressure and temperature of the hydrothermal reaction are low, the reaction time will be long; on the other hand, if the pressure and temperature are high, the reaction time will be short. According to research by the present inventors, within the above pressure and temperature ranges.

It has been found that the strength of the solidified product obtained is higher when it is held for a longer time under the lowest possible pressure and temperature conditions.

In the method of the present invention, in order to carry out the hydrothermal reaction, it is convenient to use an apparatus in which a compression piston is fitted to one or both ends of a cylindrical body and a reaction filling chamber is formed in the center of the cylindrical body.

That is, a mixture obtained by adding water and kneading is filled into this reaction filling chamber, and the filling is heated while being compressed by a compression piston to cause a hydrothermal reaction to occur.

After a predetermined period of time has elapsed, the temperature of the first reactor is lowered and the solidified material is taken out.

Therefore, in the method of the present invention, it is sufficient that the mixture to be treated is in a heated and pressurized state during the solidification reaction, and the mixture is heated to a predetermined reaction pressure and heated to a predetermined reaction temperature. Either of these may be performed first, or they may be performed simultaneously.

Note that, since the process shown in FIG. 1 shows an example of the method of the present invention, the *invention method is not limited to the process shown in FIG. 1.

[Function] After radioactive iodine is adsorbed on an adsorbent, an alkali or alkaline earth metal hydroxide is added to the adsorbent,
Further, after adding water as necessary, this is reacted with water to obtain a solidified body having a three-dimensional net of at least partially hydrated flucarium aluminosilicate. The radioactive iodine adsorbed by the adsorbent is Ag
It is retained in this solidified body as a very stable compound such as I or A g I O*. Since this solidified material has extremely high strength and is extremely dense, the elution of iodine is extremely small and the size of the solidified material is also extremely small.

[Example] Examples of the present invention will be described below.

Example 1 A cylindrical container was filled with silver-supported zeolite (manufactured by Rasa Kogyo Co., Ltd., trade name: Silver Zeolite) (Type 1) OKg, and a gas containing 0.13% iodine was heated at a rate of 100 fi/min for 12 minutes. Then, the adsorbent was taken out from the cylindrical container, and 200 cc of 6N sodium hydroxide solution was added to 1 kg of the adsorbent to achieve a rate of 300 kg/crn.
(7) Apply pressure and hold at a temperature of 200°C for 30 minutes,
A hydrothermal reaction was performed to form a solidified product. The strength of this solidified product was measured and the results are shown in Table 2. The leaching rate was also measured when the obtained solidified product was immersed in distilled water at 70°C for 24 hours.

The results are also shown in Table 2. Examples 2 to 4 The concentration and addition time of the sodium hydroxide aqueous solution, the reaction pressure, and the temperature for 1 hour were as shown in Table 1, and in the same manner as in the flow side 1. A solidified product was obtained. The strength and leaching rate of this solidified body were measured in the same manner as in Example 1. The results are shown in Table 2.

Example 5.6 Potassium hydroxide instead of sodium hydroxide (Example 5
) and barium hydroxide (Example 6), a solidified body was obtained in the same manner as in Example 1 under the reaction conditions shown in Table w41. The measurement results of the strength and leaching rate of the solidified body are also shown in Table 2.

Table 1 Reaction conditions Table 2 Measurement results From Table 2 1 According to the method of the present invention, it is possible to obtain a solidified material with extremely high strength and an extremely low leaching rate.

Effect C] As detailed above, 1. The method of immobilizing radioactive iodine of the present invention involves adsorbing radioactive iodine onto a silver-supported silicate adsorbent, and then applying hydroxylation of alkali or alkaline earth metal to this adsorbent. It is made by adding substances and causing a hydrothermal reaction, and it is possible to obtain a dense solidified product with extremely high strength. The elution of iodine from this solidified material is extremely small.
It can be stored stably for a long period of time. In addition, the volume of the solidified material is extremely small, and the method of the present invention is easy to carry out, and is practical because it can be carried out using an ordinary hydrothermal reaction apparatus91. Excellent.

[Brief explanation of drawings]

FIG. 1 is a system diagram illustrating the method of the present invention. Agent: Patent attorney Tsuyoshi Tunno Figure 1

Claims (2)

[Claims] (1) Radioactive iodine is adsorbed onto a silicate-based adsorbent carrying silver, and then at least one of sodium hydroxide, potassium hydroxide, and barium hydroxide is added to this adsorbent in amounts of 1 to 3
0% by weight mixed, in the presence of water, pressure 70Kg/cm^
A method for immobilizing radioactive iodine, characterized in that the adsorbent is solidified by holding the adsorbent in a heated and pressurized state at a temperature of 150° C. or higher to carry out a hydrothermal reaction. (2) The immobilization method according to claim 1, wherein the silicate-based adsorbent is zeolite and/or mordenite.