JPH077109B2 - How to dispose of radioactive waste - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for treating radioactive waste,
More specifically, it relates to the treatment of used resin.

(Prior Art) In radioactive material handling facilities, spent resin containing sulfur such as powder resin and granular resin is discarded as radioactive waste from a demineralizer in a condensate purification system and a waste treatment system. Conventionally, these used resins have been stored in a tank as they are or mixed with cement, plastic, etc., and solidified and stored in a drum can.

(Problems to be Solved by the Invention) However, in the conventional storage method, the volume reduction property was poor, and the used resin remained an organic substance and was chemically unstable. Therefore, it is possible to incinerate the used resin in the same manner as the combustible miscellaneous solid that has already been incinerated, but even in that case, there were the following problems.

(1) Since sulfur is contained in the cation resin that is a component of the used resin, sulfur oxides are generated in the combustion exhaust gas and the incinerator is easily corroded, and sulfur oxidation is included in the gas released to the atmosphere. Things are included.

(2) Since the specific activity (Ci / g) of the used resin is generally higher than that of the coarse solids, the specific activity of the dust generated from the dust remover is also higher than that of the incinerator of the coarse solids. The surface dose rate of the ash extraction part, ash drum, etc. becomes high and the exposure dose increases. Depending on the dose rate (200 mR / Hr or more), some drums cannot be transported to storage as they are.

The object of the present invention is to eliminate the above-mentioned problems and to remove the sulfur oxides in the combustion exhaust gas by providing a coating layer of a specific component on the surface of the ceramic filter, and to increase the specific activity of the dust generated by the dust remover. An object of the present invention is to provide a method for treating radioactive waste that can reduce the amount of used resin and safely incinerate it.

(Means for Solving Problems) The present invention is directed to a method for treating radioactive waste, in which exhaust gas generated by incineration of used resin generated in a radioactive substance handling facility is a porous, bottomed cylindrical ceramic filter. When the element is processed by passing through a high temperature dust remover disposed inside the element, on the exhaust gas introduction side surface of the ceramic filter element, calcium oxide, ferric oxide,
A coating layer made of any one or more of zinc oxide and cuprous oxide, which is a powder and has a filter aid having an average particle diameter of 100 μm or less is provided, and the sulfur oxide in the exhaust gas is coated with the coating layer. The concentration of sulfur oxides in the exhaust gas after filtration, which is collected by the bed and discharged from the high-temperature dust remover, is reduced, and the filter aid of the coating layer reacts with the stoichiometrically equal sulfur, resulting in desulfurization efficiency. Backwash before it drops sharply, the collected radioactive particles and the filter aid are dropped together and discharged from the high temperature dust remover to obtain dust ash with low specific activity. To do.

(Operation) Desulfurization of exhaust gas using inorganic substances such as calcium carbonate generally yields only about 50% efficiency. The reason is that, in general, sulfur dioxide (SO ₂ ) accounts for 90% or more of sulfur oxides generated by combustion of heavy oil, coal, etc., and sulfur trioxide (SO ₃ )
Is less than 10%, while SO ₃ is highly reactive and easily desulfurized, but SO ₂ is less reactive than SO ₃ and is less desulfurized. Therefore, the desulfurization efficiency cannot be obtained so much, so that it has not been put to practical use.

On the other hand, since sulfur in the used resin exists in the form of -SO ₃ H (sulfone group), the main component of the generated sulfur oxide is SO ₃ , and it exists in an oxide form that is easily desulfurized. To do.
Therefore, a desulfurization effect of 50% or more can be obtained.

Most of the ash (clad) generated by the used resin moves to the dust remover and is collected, but the generation rate is 1 to 5% of the resin.

On the other hand, since the sulfur content in the resin is 10 to 15%, about 15 to 20% of the resin is stoichiometrically required for desulfurizing the sulfur. Therefore, the specific activity when these collected dusts are discharged together with the filter aid can be reduced to 1 to 5/15 to 20 = 1/20 to 1/3 as compared with the case where the filter aid is not used. .

FIG. 1 is a perspective sectional view showing an embodiment of a high temperature dust remover used in the present invention. In the present embodiment, the dust remover 1 is provided with a flue gas inlet 3 and a combustion burner 4 in the lower portion, an exhaust gas outlet 5 in the upper portion, and an air inlet 6 for backwashing in the upper portion. It has a structure in which 100 cylindrical ceramic filter elements 8 having a bottom are suspended. Combustion exhaust gas from an incinerator that incinerates radioactive waste is supplied into the dust remover 1 through the exhaust gas inlet 3, passes through the ceramic filter element 8 from the outer surface, and is filtered to remove dust and the like contaminated with radioactivity. Exhaust gas is discharged from the exhaust gas outlet 5 to the outside of the machine, and has the functions of dust removal of combustion exhaust gas, recombustion of unburned dust, and complete combustion of unburned gas.

FIG. 2 is a diagram showing an embodiment of the filter element 8 used in the present invention. The filter element 8 of this embodiment is preferably made of porous ceramics in which fine particles such as SiC are bound by an inorganic binder and has a length of 10
It has a bottomed cylindrical shape with a diameter of 00 mm or 1500 mm, a diameter of 60 mm, and a wall pressure of about 10 mm, and has a structure in which exhaust gas passes from the outer periphery of the tubular body to the inside.

FIG. 3 shows an embodiment of the filter element 8 used in the present invention. In this example, calcium oxide (CaO) and ferric oxide (Fe) are formed on the entire outer surface of the filter element 8.
₂ O ₃ ), zinc oxide (ZnO), cuprous oxide (CuO), or a coating layer 11 made of a powdery or granular filter aid made of a plurality thereof. At this time, the average particle diameter of the powdery particulate filter aid made of CaO, Fe ₂ O ₃ , ZnO, and CuO must be 100 μm or less, and preferably 10 μm to 50 μm. The reason is that if the average particle size of the coating layer 11 is 100 μm or more, the effect is small, and if it is 10 μm or less, the initial pressure loss becomes too large. In the filter element 8 shown in FIG. 3, since the radioactive waste containing sulfur is coated with a filter aid that is stoichiometrically excessive with respect to the amount of sulfur, the exhaust gas is exhausted. The sulfur oxide in
It becomes CaSO ₄ , Fe ₂ (SO ₄ ) ₃ , ZnSO ₄ , CuSO _{4 and} can be favorably collected on the coating layer.

The filter aid in the coating reacts with the stoichiometrically equal sulfur,
It is possible to reduce the specific activity of dust by performing backwashing before the desulfurization efficiency sharply decreases and discharging the collected radioactive particles and the filter aid together from the dust remover.

To perform backwashing, in the high temperature dust remover shown in FIG.
First, for example, in a state where the exhaust gas outlet port 5 is closed and the air inlet port 6 is connected to an air tank (not shown) via a shutoff valve,
A vacuum pump or the like is connected to the exhaust gas inlet 3 to make the inside of the dust remover 1 a negative pressure of about -1000 mmAq. In this state, the shut-off valve is opened, and compressed air is instantaneously flown from the inner peripheral side to the outer peripheral side of the cylindrical body of the filter element 8, whereby the coating layer 11 on the surface of the filter element is peeled off and dropped, and the regeneration treatment can be performed.

Example 1 A used resin (cationic resin / anionic resin = 1/1) containing 7.5% of sulfur was incinerated in a solid-state incinerator, and the ceramic filter elements shown in Table 1 are attached to each and shown in FIG. The desulfurization efficiency was measured using a dust remover, the desulfurization efficiency was measured, and backwash was performed before the desulfurization efficiency decreased, and the ash drum surface dose rate when the backwash ash was filled in 200 drums was measured. The results are shown in Table 1.

As is clear from Table 1, desulfurization is hardly performed and the ash drum surface dose rate greatly exceeds the transport standard value of 200 mR / Hr in the conventional example in which no coating layer is provided on the filter element. In comparison, when a coating layer consisting of one or more of CaO, Fe ₂ O ₃ , CuO, ZnO, etc. was provided, a desulfurization effect was obtained at 90% or more, and the surface dose rate of the ash drum filled with backwash ash was obtained. Could be less than 200mR / Hr.

(Effect of the Invention) As is clear from the above description, according to the method for treating radioactive waste of the present invention, the ceramic filter element having the coating layer made of the desulfurizing agent on the surface of the exhaust gas introduction side is used. By filtering the radioactive exhaust gas, the sulfur oxides generated during the incineration of the used resin can be removed, so that the air pollution can be reduced.
Further, it is possible to reduce the corrosion of the incineration equipment due to the sulfur oxides and to reduce the specific activity of the ash taken out by the backwash, so that the radiation exposure dose from the dust remover and the ash drum can be reduced.

[Brief description of drawings]

FIG. 1 is a perspective sectional view showing an embodiment of a high temperature dust remover used in the present invention, FIG. 2 is a diagram showing an embodiment of a filter element used in the present invention, and FIG. It is sectional drawing which expands and shows one Example of the filter element used. 1 ... Dust remover, 2 ... Ash removal port 3 ... Exhaust gas inlet port, 4 ... Secondary combustion burner 5 ... Exhaust gas outlet port, 6 ... Backwash air inlet port, 7 ... Refractory material, 8 ... … Filter element 11… Coating layer

Claims (2)

[Claims] 1. Exhaust gas generated by incineration of used resin generated in a radioactive material handling facility is passed through a high temperature dust remover having a porous, bottomed cylindrical ceramic filter element disposed therein. During processing, on the exhaust gas introduction side surface of the ceramic filter element,
The exhaust gas is provided with a coating layer made of any one or more of calcium oxide, ferric oxide, zinc oxide, and cuprous oxide, which is in the form of powder and has an average particle diameter of 100 μm or less. Sulfur oxides in the collected by the coating layer, reducing the concentration of sulfur oxides in the exhaust gas after filtration discharged from the high temperature dust remover, the filter aid of the coating layer stoichiometrically Reacts with equal sulfur, backwashes before the desulfurization efficiency drops sharply, removes the collected radioactive particles and filter aid together, and discharges them from the high temperature dust remover, resulting in low specific activity A method for treating radioactive waste, characterized by obtaining dust ash. 2. The method for treating radioactive waste according to claim 1, wherein the temperature of the high-temperature dust remover is 500 ° C. or higher.