JPS589400B2 - How to dispose of radioactive organic liquid waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating radioactive organic liquid waste.

Recently, radioisotopes have been used in medical and various research facilities, and in particular, 3H and 14C radioisotopes have been used in large numbers.

Liquid scintillation is used for the measurement.
As a result, the waste liquid discharged from the measurement always contains a large amount of aromatic hydrocarbons such as toluene.

Therefore, these radioactive liquid wastes fall under category 4 of hazardous materials stipulated in the Fire Service Act, and it is difficult to store more than a certain amount.
Furthermore, the ceramic containers used for this also have problems such as breakage.

Currently, the following methods are being tried to dispose of these radioactive liquid wastes, but there are still many problems and there is no definitive method.

■ Method of fractionating waste liquid and solidifying the residue After fractionating aromatic hydrocarbons with a low boiling point, radioactive waste such as 3H14C in the remaining residue is solidified with cement etc. However, the amount of solids increases from the amount originally disposed of, and disposal costs are considerable.

Further, since additional fuel is required to stop the solidification of the residue and incinerate the residue, the same problem as the next incineration method occurs.

■How to incinerate waste liquid Waste liquid from liquid scintillation always contains a large amount of aromatic hydrocarbons such as toluene and is flammable.

Therefore, when these waste liquids are completely burned, carbon dioxide gas (CO
2) and water (H20).

Since the radioactive isotopes 3H and 14C exist in CO2 and H20, respectively, it is sufficient to collect CO2 and H20.

Generally, when organic matter is burned in air, it becomes carbon dioxide and water.
This carbon dioxide gas is the other component of the air that did not contribute to combustion.
2 and water (in the form of water vapor) are released from the chimney.

At this time, when the exhaust gas is cooled to below atmospheric temperature, the water vapor liquefies and becomes water, which can be recovered.

In addition, carbon dioxide gas can be neutralized by washing with alkaline water and can be recovered as a salt and precipitate.

Now, assuming that the waste liquid is entirely composed of toluene, the amount of CO2 generated in the combustion generated exhaust gas is 3.35 kg per 1 kg of toluene, based on the chemical formula C7H8 + 902 → 7CO2 + 4H20, and when this is neutralized with sodium chloride, the chemical formula becomes 2NaOH + C02- + NaC03 + H20, C
2.4 times more NaCO3 is generated from 1 kg of O2.

Therefore, the weight ratio for 1 kg of toluene is 3.35 x 2.4≒
Since 8 times as much Na2CO3 will be generated, the amount of waste will be extremely large and difficult to dispose of.

The present invention was made in order to eliminate the drawbacks of the above-mentioned methods, and is a method for safely incinerating radioactive organic waste liquid by reducing the amount of secondary waste.The main feature of this invention is that it contains radioactive materials. Organic waste liquid can be separated into soot and water without burning and producing CO or CO2 by supplying an amount of air commensurate with the oxygen content required to burn the hydrogen content in the organic waste liquid. (the oxidation of H is C
This method goes further and treats radioactive substances by incorporating them into soot and water (C remains in the form of soot because there is no O necessary for oxidizing C).

The present invention will be explained in detail below with reference to illustrative drawings, but the present invention is not limited thereto.

FIG. 1 is a longitudinal sectional view of an apparatus that is an embodiment of the present invention.

In the present invention, as shown in Fig. 1, the combustion furnace 1 is a vertical cylindrical type, and a radioactive organic waste liquid spray burner 2 is attached downward to the upper part of the furnace, and an auxiliary combustion is installed on the side of the furnace in a tangential direction to the cylindrical cross section of the furnace. Burner 3 is installed.

The shape of the furnace may be rectangular, but in our experience, a cylindrical vertical furnace has better combustion efficiency.

The lower part of the furnace has an inverted conical shape and is provided with a residual ash discharge port 4 that can be opened and closed for convenient removal of combustion residues, soot, etc.

The auxiliary combustion burner mentioned above may be omitted and electric heating may be used instead.

(See FIG. 2) The dust collector 5 is provided with a sand filter 7 for filtering out the high temperature exhaust gas (700 to 800 DEG C.) containing soot discharged from the furnace 1.

The grain size of the sand is around 1 mmφ, and the passage area is wide to reduce ventilation resistance as much as possible, and the soot adhering to the surface is taken out from the bottom of the dust collector through the residual ash discharge port 6, which has the same shape as the combustion furnace.

The soot adsorbed in the sand may be discharged together with the sand and only the soot may be sieved and reused, but since sand is inexpensive, it may be disposed of together with the sand.

The exhaust gas leaving the dust collector enters the cooler 8.

The cooler 8 contains a coil 9 through which cold water passes, and the cold water is cooled by a separate cooling device.

The water vapor in the exhaust gas is cooled by a cooling coil, becomes a drain, and is discharged from an openable/closeable outlet 10 at the bottom of the cooler.

The exhaust gas leaving the cooler passes through a quicklime filter 11 and is discharged from a chimney 13 by an induction fan 12.

An oxygen meter 14 for measuring the amount of oxygen in the exhaust gas is provided at the location where the exhaust gas exits the cooler.

In addition, instead of the above-mentioned quicklime filter 11, solid CO, C
It may also be an O2 absorber.

The method for treating radioactive organic liquid waste using this device is to first burn an auxiliary burner in a combustion furnace to bring the temperature of the furnace to about 70℃.
Keep at around 0℃.

The combustion air at this time should be as close to the theoretical combustion air amount as possible, with a slight excess of air.

The amount of excess air can be measured by an oxygen meter within the system.

This amount of excess air is an amount of air corresponding to the amount of oxygen required to combust the hydrogen content in the radioactive organic waste liquid.

When the furnace temperature reaches a constant level of about 700°C, adjust the amount of air in the auxiliary burner without checking the oxygen meter.

Next, radioactive organic waste liquid is sprayed into the furnace from a waste liquid burner to generate soot.

Air is not used for atomization of this waste burner.

If the waste liquid burner is an air spray type burner, it can be used by drawing exhaust gas (because it does not contain O2).

The furnace may be an electric furnace and the temperature may be raised electrically.

At that time, an amount of air corresponding to the oxygen content required to burn the hydrogen content in the radioactive organic waste liquid is separately introduced together with the waste liquid.

Now, if we use only toluene as the radioactive organic waste liquid, its chemical change will show the following reaction.

C7H8+2O2→7C+4H2O The mass of C, ie, soot, generated from this is less than the mass of the original toluene.

At this time, the C isotope becomes soot, and the H isotope is contained in water vapor.

Also, inorganic substances can be removed together with soot.

Ash containing soot and inorganic substances generated in the furnace is discharged from the residual ash outlet at the bottom of the furnace.

The remaining soot and water vapor laden exhaust gas enters the precipitator where most of the soot is removed while passing through a sand filter and some of it is trapped in the sand.

Sand filters are suitable for high temperature exhaust gases and are good for collecting soot.

Since the water vapor is at a high temperature, it passes through the sand filter and enters the cooler.

While passing between the cooling coils of the cooler, the water vapor in the exhaust gas is cooled to below the dew point, becomes drain, falls to the bottom of the cooler, and is discharged from the drain outlet.

If the exhaust gas that has passed through the cooler is removed and the water vapor is completely collected, the exhaust gas contains only excess nitrogen gas in the combustion air.

However, for example, if toluene is not completely decomposed into C and H2O, CO2 will be generated.If CO2 is generated, when it is passed through a filter made of quicklime, for example, the next chemical reaction will occur. can capture a small amount of CO2.

CaO+C02→CaCOs The exhaust gas that has passed through the quicklime filter is sucked in by an induction fan and discharged from the chimney without containing radioactive substances.

The soot and residual ash discharged from the lower part of the combustion furnace and dust collector can be collected and solidified to be safely disposed of as radioactive solid waste.

Also, sand containing soot and quicklime that has absorbed CO2 gas can be removed when their absorption limit is reached, and since they are inexpensive materials, they can be considered consumables and disposed of as radioactive solid waste.

Since the recovered water contains 3H, it is only necessary to measure the radioactivity concentration and dispose of it according to the method prescribed by law.

The present invention is as described above, and eliminates the disadvantages of the conventional methods (1) and (3) described above, that is, the amount of waste to be treated can be reduced and the treatment cost can be reduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory front view of an apparatus for carrying out the treatment method of the present invention, and FIG. 2 is an explanatory front view of a combustion furnace using electric heating means in place of the combustion furnace using an auxiliary burner in the apparatus of FIG. 1. Examples are given for each. 1, 1'... Combustion furnace, 2, 2'... Waste liquid spray burner; 3... Assist burner, 3'... Electric heating means, 4
, 4'... Ash discharge port, 5... Dust collector, 6... Residual ash discharge port, 7... Sand filter, 8... Cooler,
9... Coil, 10... Outlet, 11... Quicklime filter, 12... Induction fan, 13... Chimney, 14... Oxygen meter.

Claims (1)

[Claims] 1 Organic waste liquid containing 3H and 14C radioactive substances is combusted to produce soot (Q and 1. A method for treating radioactive organic liquid waste, which comprises decomposing radioactive materials into soot (H2O) and incorporating radioactive materials into the soot and water.