JP2948754B2 - Radioactive waste gas treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a radioactive waste gas containing RuO ₄ generated by incineration or melting of radioactive waste.

[0002]

2. Description of the Related Art Conventionally, radioactive waste such as vinyl chloride resin and rubber contaminated with Ru (ruthenium) generated from a nuclear power plant or the like has been stored in a drum or the like as it is. However, since there is a limit in securing a storage space, it has recently been required to reduce the volume by incineration or melting.

[0003] When such vinyl chloride resin or rubber contaminated with Ru is incinerated or melted, gases such as RuO ₄ , HCl, and SO _X are generated, and these gases are generated due to emission regulations or corrosion prevention of equipment. Above, it is necessary to remove. For this purpose, conventionally, a processing method as shown in a flow sheet of FIG. 5 has been proposed.

In this conventional method, first, radioactive waste gas containing RuO ₄ discharged from an incinerator is filtered at a high temperature in a temperature range of 700 to 800 ° C. to remove dust. Next, the temperature of the gas is reduced to about 200 to 250 ° C. by spraying with water, and then washed with alkaline or neutral washing water to remove HCl, SO _X
Etc. are removed. Next, the water in the gas is condensed and removed, heated to about 80 ° C. and further dried, and then RuO ₄ is adsorbed and removed by silica gel.

However, the method shown in FIG. 5 has a problem that a large amount of waste liquid containing radioactive components is generated from the washing and condensation steps, and this waste liquid treatment requires a large amount of equipment and operation work. Further, since the high-temperature waste gas is once cooled in the washing and condensation steps, it is heated again for the purpose of drying it so that it can be brought into contact with the silica gel, and there is also a problem that a large amount of energy is lost.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned conventional problems and reduces the radioactive waste gas containing RuO ₄ without generating a waste liquid and energy loss such as reheating of the waste gas. The purpose of the present invention is to provide a method for treating radioactive waste gas that can be treated without the need for wastewater.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The present invention mainly uses silica and iron oxide to convert radioactive waste gas containing RuO ₄ generated by incineration or melting of radioactive waste. after having adsorbed remove RuO ₄ in contact with the adsorbent as a component, and is characterized in that calcium absorption remove HCl and SO _X in contact with the absorbent mainly composed of. The absorption of RuO _{4 and} the absorption of HCl and SO _X were
It is preferable to carry out in a temperature range of -350 ° C.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIG. As shown in the flow sheet of FIG. 1, in the present invention, radioactive waste gas containing RuO ₄ generated from an incinerator or melting furnace for radioactive waste is also used.
First, dust is removed by primary filtration and secondary filtration in the temperature range of 700 to 800 ° C, and water is sprayed to reduce the gas temperature to 150 ° C.
Lower to the temperature range of ~ 350 ° C. As will be described later, this temperature range is more preferably set to about 200 to 250 ° C. Although the temperature of the waste gas is lowered by this water spray, the water maintains a dry state of 7 to 8%.

Next, this waste gas is brought into contact with an adsorbent mainly composed of silica and iron oxide to adsorb and remove RuO ₄ . The adsorbent is "iron-supported silica gel" in which iron oxide is supported on the surface of silica gel. For example, a silica particle having a particle size of 75 to 3000 μm and an iron oxide content of 1.6% by weight can be used.

FIG. 2 is a graph in which the effect of adsorption and removal of RuO ₄ by this adsorbent is represented by DF (inlet concentration / outlet concentration of RuO _{4 in} waste gas) on the vertical axis and the reaction temperature on the horizontal axis. is there. For comparison, the case of silica gel alone is also shown. As shown in the graph of FIG. 2, the iron-supported silica gel (denoted as iron silica in the graph) has a DF above 150 ° C.
There show excellent results exceeding 10 ^3. However, if the temperature is raised beyond that, the DF does not improve much. Therefore, considering the heat resistance of the equipment, the temperature range is 150 to 350 ° C, more preferably
A temperature range of 200-250 ° C is preferred.

FIG. 3 shows that the moisture (volume%) in the waste gas is D
6 is a graph showing the effect on F. When iron-supported silica gel at a temperature of 200 ° C. is used, the moisture content is 5 to 10
It can be seen that DF shows an excellent value within the range of%.

FIG. 4 is a graph showing the effect of the HCl concentration in the waste gas on the RuO ₄ adsorption / removal effect. As shown in this graph, when the HCl concentration is 0% and 1%
Compared with the case of the above, when iron-supported silica gel is used, the DF is higher when the waste gas contains HCl. Therefore, in the present invention, RuO ₄
Is adopted, and HCl and SO _X are removed later. This makes it possible to reduce the RuO ₄ concentration in the waste gas to 1/1000 or less.

[0013] Waste gas is removed RuO ₄ in the manner described above while being maintained at a temperature of 0.99 to 350 ° C., are calcium absorption of HCl and SO _X in absorbent mainly composed of removal. Examples of such an absorbent include granules or pellets obtained by mixing Ca (OH) ₂ with clay and steam-curing. HCl and SO _X in the waste gas are almost completely removed by the contact with the absorbent, and filtration may be performed by a HEPA filter or the like.

[0014] Note that the SV to mean gas flow rate / adsorbent volume and gas flow rate / absorbent volume and 1000h ^-1 ~2000h ^-1,
The superficial velocity is preferably 0.5 m / s or less.

According to the method for treating radioactive waste gas of the present invention, RuO ₄ , HCl, SO _{X and the} like can be removed from radioactive waste gas containing RuO ₄ without generating any waste liquid. Moreover, since the processing can be performed while maintaining the waste gas at a temperature of 150 to 350 ° C., there is no need to reheat the once-cooled waste gas as in the prior art, and there is no energy loss. Next, examples of the present invention will be described.

[0016]

[Example] RuO ₄ and HCl generated from radioactive waste incinerator
The 700 to 800 ° C. of the waste gases containing SO _X or the like, 120 Nm ³ / h
The dust was removed by flowing the mixture through a ceramic filter at a flow rate of, and the temperature was lowered to 200 ° C by spraying with water. Next, this waste gas was brought into contact with iron-carrying silica gel to adsorb and remove RuO ₄ . Iron-supported silica gel with a particle size of 500 to 2000 μm
14 m ³ was packed in a tower 0.5 m in diameter and 0.7 m in height, SV = 1500 h ⁻¹ .

The waste gas leaving the packed column of iron-supported silica gel was led to a packed column of an absorbent containing calcium as a main component while maintaining the temperature at 200 ° C. The packed column is provided in two groups, absorbent, respectively (diameter 2.3 ～3.4Mm particle, the chemical composition CaO is 51 wt%, SiO ₂ of 20 wt%, Al ₂ O ₃ is 4
% By weight, 2% by weight of CaSO _{4 and} 0.5% by weight of Fe ₂ O ₃ )
each m ³ is filled and used alternately. The packed tower has a diameter of 0.5 m, a height of 0.7 m and an SV = 1500 h ^-1 . here
The waste gas from which HCl and SO _X had been removed was directly filtered through a HEPA filter and released to the atmosphere. Table 1 shows the effect of removing RuO ₄ , HCl and SO _X in the waste gas in this embodiment.

[0018]

[Table 1]

[0019]

As described above, according to the present invention, RuO ₄ , HCl, SO _{X and the} like can be removed from a radioactive waste gas containing RuO ₄ without generating any waste liquid. There is an advantage that a large amount of equipment and operation work are not required for waste liquid treatment as in the related art. Further, since the processing can be performed while maintaining the waste gas at a temperature of 150 to 350 ° C., there is an advantage that there is no need to reheat the once cooled waste gas as in the conventional case, and there is no energy loss. Ru further containing HCl
Since O ₄ is adsorbed, a more excellent RuO ₄ removal effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a flow sheet of the present invention.

FIG. 2 is a graph showing the effect of temperature on the DF of an adsorbent.

FIG. 3 is a graph showing the effect of moisture on the DF of an adsorbent.

FIG. 4 is a graph showing the effect of HCl on the DF of the adsorbent.

FIG. 5 is a flow sheet of a conventional method.

Claims (2)

(57) [Claims] 1. A radioactive waste gas containing RuO ₄ generated by incineration or melting of radioactive waste is brought into contact with an adsorbent mainly composed of silica and iron oxide to adsorb and remove RuO ₄ , HCl by contact with an absorbent containing
Method for treating a radioactive waste gases, characterized by absorbing and removing or SO _X. 2. The absorption of RuO _{4 and} the absorption of HCl and SO _X are reduced by 15%.
The method for treating radioactive waste gas according to claim 1, wherein the method is performed in a temperature range of 0 to 350 ° C.