JP2000171589A - Recovery method for radioactive rare gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a method superior in safety and efficiently, surely and quickly recovering radioactive rare gas generated from a reactor or in reprocessing process of spent nuclear fuel. SOLUTION: Radioactive rare gas generated from a reactor and a reprocessing process or spent nuclear fuel is recovered by contacting rock adsorbing in adsorbents consisting or natural zeolite rock especially an adsorbent which natural zeolite rock is controlled in hydrogen type by ion exchanging method. For the natural zeolite rock, that including mordenite and clinoptilolite is desirable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering a radioactive rare gas generated in a nuclear reactor or a radioactive rare gas generated in a reprocessing step of spent nuclear fuel.

[0002]

2. Description of the Related Art In a nuclear reactor such as a light water reactor for nuclear power generation, radioactive rare gases such as argon, krypton, xenon, and radon are generated in the fuel due to the nuclear fission reaction of the fuel. Some of these radioactive rare gases leak into the cooling water of the nuclear reactor and are discharged outside from condensers and the like. The radioactive rare gas in the fuel is released from the spent fuel to the outside when the spent fuel is reprocessed.

[0003] As described above, it is desirable that the radioactive rare gas generated in the nuclear reactor and related facilities be recovered in the facility. The following two methods are known as radioactive rare gas recovery methods for that purpose. Among them, the first method is a method in which activated carbon, molecular sieve carbon, molecular sieve 5A or molecular sieve 13X is used as an adsorbent, and a radioactive rare gas is contact-adsorbed and recovered. The second method is
It liquefies the radioactive rare gas by low-temperature distillation and collects it.

[0004]

Among the above-mentioned conventional methods for recovering a radioactive rare gas, in the first method using an adsorbent, when the adsorbent is a molecular sieve of an inorganic adsorbent, the method uses only a rare gas. There is a fatal drawback that a sufficient adsorption capacity cannot be obtained. On the other hand, with organic adsorbents such as activated carbon and molecular sieve carbon, the adsorption capacity is large,
Radiation acts on nitrogen oxides and oxygen generated from nitric acid used in the reprocessing step to generate ozone and the like, and there is a risk of explosion due to the ozone and the like.

[0005] In the second method of liquefying and recovering a radioactive rare gas by cryogenic distillation, the cryogenic distillation involves a large amount of energy consumption, so that the operating cost is greatly increased and the risk of explosion due to accumulated ozone is high. There was a disadvantage that there is.

The present invention has been made in view of such a conventional situation,
An object of the present invention is to provide a method that is excellent in safety and efficiently, reliably and quickly recovers a radioactive rare gas generated in a nuclear reactor or a reprocessing step of spent nuclear fuel.

[0007]

To achieve the above object, the present invention provides a method for recovering a radioactive rare gas provided by a radioactive rare gas generated in a nuclear reactor or a radioactive rare gas generated in a reprocessing step of spent nuclear fuel. It is characterized in that the gas is contact-adsorbed with an adsorbent made of natural zeolite rock and is recovered.
In particular, it is preferable to use an adsorbent obtained by adjusting natural zeolite rock to a hydrogen type by an ion exchange method.

In the method for recovering a radioactive rare gas according to the present invention, the natural zeolite rock used as an adsorbent includes mordenite, clinoptilolite, shabasite, erionite, lomontite, filipsite,
Those containing at least one of ferrierite, wairakite, faujasite, and hyurandite are preferable, and those containing mordenite and / or clinoptilolite are more preferable.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have focused on the recovery of radioactive rare gases by the adsorption method and have conducted intensive research on the development of non-explosive adsorbents having a large adsorption capacity for radioactive rare gases. As a result, they have found that natural zeolite rock has a large adsorption capacity for rare gases, despite being an inorganic adsorbent, and have completed the present invention.

The natural zeolite rock is a zeolite (zeolites) -containing mineral which is not industrially synthesized but is produced naturally, and a typical one is a tuff containing zeolite. Such natural zeolite rocks are widely produced in Japan, and typical localities include, for example, Itado, Minase-mura, Ogatsu-gun, Akita Prefecture, Futatsui-machi, Yamamoto-gun, Akita Prefecture, and Itaya, Yonezawa-machi, Yamagata Prefecture.

It is not clear why the adsorption capacity of natural zeolite rock for rare gases is much higher than that of industrially synthesized zeolites, ie, molecular sieves.
It is considered that the electronic state of the surface of natural zeolite rock may affect the noble gas adsorption capacity.

Further, in the method of the present invention using natural zeolite rock as an adsorbent, the adsorbent itself is not composed of carbon, but is composed of a metal oxide such as silicon or aluminum. And safe recovery of radioactive rare gas can be realized.

The natural zeolite rock as an adsorbent is used by pulverizing the natural zeolite rock produced into powder.
In particular, those obtained by adjusting natural zeolite rock to a hydrogen type by an ion exchange method are preferable as the adsorbent.

The higher the content of zeolite in natural zeolite rock is, the more preferable it is. The adsorption capacity varies depending on the zeolite component contained. Generally, if the content of zeolite is 50 to 80% by weight or more, good quality ore is obtained. Therefore, the rare gas can be efficiently, reliably and quickly adsorbed.

The superficial velocity of the gas introduced into the adsorbent layer of the natural zeolite rock depends on the reaction temperature conditions and the required recovery rate of the radioactive rare gas. However, in general, 0.1
The range is preferably from 100 to 100 m / min, and from 1 to 30 m / m.
The range of in is more preferable. Further, the use temperature at the time of adsorption is preferably from -100 ° C to 40 ° C, more preferably from -70 ° C to 20 ° C.

[0016]

EXAMPLE 1 A natural zeolite rock mainly composed of mordenite (produced in Itado, Akita Prefecture) was pulverized, and 33 g of the zeolitic rock was packed as an adsorbent in an atmospheric pressure flow reactor. At the operating temperature of 0 ° C,
Helium gas containing 0.27 to 2% krypton (Kr) was flown at a superficial velocity of 0.85 to 1.1 m / min, and the adsorption capacity of krypton was examined. The results are shown in FIG. 1 by black triangle symbols (▲).

Example 2 The same natural zeolite rock as in Example 1 was crushed and subjected to ion exchange with a hydrochloric acid solution to adjust to a hydrogen form. That is, the ground natural zeolite rock was immersed in a 1N hydrochloric acid solution at room temperature, allowed to stand for 3 days, and then repeatedly washed with distilled water until the washing liquid became neutral. After drying in air overnight, it was fired at 400 ° C. in an inert gas and used as an adsorbent.

22 g of the adsorbent is charged into a normal-pressure flow reactor, and at an operating temperature of 0 ° C., a helium gas containing 0.02 to 1.4% of krypton is superposed at a superficial velocity of 1.2 to 1.9 m / h. mi
Then, the krypton adsorption capacity was examined. The result is
In FIG. 1, it is shown by a white square symbol (□).

Example 3 The same natural zeolite rock as in Example 1 was pulverized and subjected to ion exchange with a nitric acid solution to adjust to a hydrogen type. That is, the ground natural zeolite rock was immersed in a 1N nitric acid solution at room temperature, allowed to stand for 3 days, and then repeatedly washed with distilled water until the washing liquid became neutral. After drying in air overnight, it was fired at 400 ° C. in an inert gas and used as an adsorbent.

24 g of this adsorbent is charged into a normal-pressure flow reactor, and at an operating temperature of 0 ° C., a helium gas containing 0.15 to 1.4% krypton is superposed at a superficial velocity of 1.2 to 2.2 m / h. mi
Then, the krypton adsorption capacity was examined. The result is
FIG. 1 shows a white circle symbol (記号).

Example 4 The same natural zeolite rock as in Example 1 was crushed and subjected to ion exchange with an ammonium nitrate solution to adjust to a hydrogen form. That is, the ground natural zeolite rock was immersed in an ammonium nitrate solution having a concentration of 1 mol / l at room temperature, allowed to stand for 3 days, and then repeatedly washed with distilled water until the washing solution became neutral. After drying this in the air overnight, 40
It was calcined at 0 ° C. and used as an adsorbent.

22 g of this adsorbent is charged into a normal pressure flow reactor, and at a working temperature of 0 ° C., a helium gas containing 0.13 to 1.4% krypton is blasted at a superficial velocity of 0.93 to 2.0 m / h. m
In flow, the krypton adsorption capacity was examined. The results are shown in FIG. 1 by white triangle symbols (△).

[0023]Comparative Example 1  Using commercially available molecular sieve 5A as the adsorbent,
1 to 280 g is charged into a normal pressure flow reactor,
Helium containing 0.03-2.2% krypton at 0 ° C
Flow of superficial gas at a superficial velocity of 0.2 to 2.2 m / min.
The adsorption capacity of Puton was investigated. The result is shown in black in Fig. 1.
Are shown by circular symbols (●).

COMPARATIVE EXAMPLE 2 A commercial activated carbon was used as an adsorbent.
Helium gas containing krypton of 02 to 11% was flowed at a superficial velocity of 0.88 to 1.6 m / min, and the adsorption capacity of krypton was examined. The results are shown in FIG. 1 by black square symbols (■).

As can be seen from FIG. 1 which summarizes the above Examples and Comparative Examples, the molecular sieve 5A of Comparative Example 1
In the case of (●), the adsorption capacity of krypton is small and is not suitable as an adsorbent for rare gases. On the other hand, the activated carbon (■) of Comparative Example 2 has a large noble gas adsorption capacity, but is an organic adsorbent made of carbon, so there is a danger of explosion due to reaction with nitrogen oxides. is happening.

On the other hand, when the untreated natural zeolite rock (▲) in Example 1 of the present invention is used as the adsorbent, the adsorption capacity is lower than that of activated carbon, but the adsorption capacity is lower than that of molecular sieve 5A. There is no danger of explosion because it is large and is an inorganic adsorbent.

Further, natural zeolite rock ion-exchanged with hydrochloric acid of Example 2 (□), natural zeolite rock ion-exchanged with nitric acid of Example 3 (３), Example 4
Each of the natural zeolite rocks (△) subjected to the ion exchange treatment with the ammonium nitrate aqueous solution has a rare gas adsorption capacity comparable to that of the activated carbon of Comparative Example 2, and the difference in adsorption capacity with the molecular sieve 5A of Comparative Example 1 is obvious. .

[0028]

According to the present invention, since natural zeolite rock is used as an adsorbent, the safety is superior to organic adsorbents such as activated carbon having explosive properties, and the adsorption capacity of rare gas is large. In addition, the radioactive rare gas can be safely and efficiently adsorbed and recovered. In particular, natural zeolite rock that has been converted to hydrogen form by ion exchange treatment has a higher noble gas adsorption performance, and is efficient, reliable, and quick for radioactive noble gas generated in the reactor and reprocessing of spent nuclear fuel. It is extremely effective for efficient recovery.

[Brief description of the drawings]

FIG. 1 shows each adsorbent used in Examples and Comparative Examples.
4 is a graph showing the relationship between krypton concentration in gas and krypton adsorption capacity.

Claims (3)

[Claims] 1. A radioactive rare gas characterized in that a radioactive rare gas generated in a nuclear reactor or a radioactive rare gas generated in a reprocessing step of spent nuclear fuel is contact-adsorbed with an adsorbent made of natural zeolite rock and recovered. Gas recovery method. 2. The method for recovering a radioactive rare gas according to claim 1, wherein the adsorbent comprising the natural zeolite rock is obtained by adjusting the natural zeolite rock to a hydrogen type by an ion exchange method. 3. The natural zeolite rock contains at least one of mordenite, clinoptilolite, shabasite, erionite, rhomontite, filipsite, ferrierite, wairakite, faujasite, and hyurandite. The method for recovering a radioactive rare gas according to claim 1 or 2, characterized in that: