JPS6155079B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment method for reducing the volume of radioactive waste generated from nuclear power plants and the like.

Conventionally, the operation of nuclear power plants generates wastewater containing various radionuclides, and this wastewater is treated with ion exchange resins, filtered, or evaporated. Waste ion exchange resins, filter aids, or evaporation residues generated in these processes, as well as radioactive wastes generated from other facilities, are extremely dangerous.
These are mixed with cement or asphalt, solidified in drums, and then stored in a designated location. However, the amount of these radioactive wastes continues to increase, and securing storage space and ensuring safety have become serious problems. Therefore, when solidifying radioactive waste, great attention has been paid to minimizing the volume of solidified waste as much as possible. For example, there is a method of reducing the volume of waste ion exchange resin using a mixed acid of sulfuric acid and nitric acid. but,
In this case, since sulfuric acid and nitric acid are used, the following CmHn+n/2H ₂ SO ₄ → nH ₂ O+n/2SO ₂ +mC C +2H ₂ SO ₄ →2H ₂ O+2SO ₄ +CO ₂ 3C +4HNO ₃ →4NO+2H ₂ O+3CO ₂ As a result, undesirable SOx
and NOx are generated. Therefore, these SOx and NOx
An oxidation tower and an absorption tower are required to recover the sulfuric acid and nitric acid, which makes the recovery process complicated and requires the use of concentrated sulfuric acid, concentrated nitric acid, etc. as the liquid for regeneration and recovery, which increases safety and equipment costs. requires considerable investment. Additionally, since nitric acid is used, measures must be taken to prevent explosions due to by-products of nitro compounds.

The purpose of the present invention is to reduce the volume of radioactive waste organic matter that requires strict treatment and storage, without any fear of generating SOx due to conventional incineration methods or NOx due to nitric acid methods, and to recover these materials. It is an object of the present invention to provide a volume reduction treatment method for radioactive waste organic matter that does not require any steps, is easy to control the reaction, and is advantageous in terms of process, equipment, and economy.

That is, the method of the present invention is characterized by charging concentrated sulfuric acid with radioactive waste organic matter, and decomposing the radioactive waste organic matter by adding hydrogen peroxide while maintaining the temperature at 150 to 300°C.

In this invention, the radioactive waste organic materials that are subject to volume reduction treatment include ion exchange resins, filter aids, etc. discharged during the process of treating wastewater containing various radionuclides generated from nuclear facilities, etc., as well as radioactive organic materials. Contaminated clothing, materials, etc. These radioactive organic substances may contain moisture or may contain heavy metals.

Next, the present invention will be explained in more detail based on the accompanying drawings.

The drawing shows an example of the device implementing the present invention.
In the figure, 1 is a radioactive waste organic matter tank, and 4 is a stirred reactor. Radioactive waste organic matter is stored in tank 1.
From there, it is fed to a stirred reactor 4 via a hopper 2 having a double damper and a feeder 3 attached at the bottom of the hopper 2. The stirred reactor 4 is made of glass or acid-resistant metal material, and contains concentrated sulfuric acid previously maintained at 150 to 300°C. A portion of the radioactive waste organic matter supplied to the stirring reactor 4 is decomposed by heated concentrated sulfuric acid;
By adding a hydrogen peroxide aqueous solution dropwise from tank 5 to this, decomposition proceeds rapidly. That is, the decomposition is promoted by the oxygen produced by the decomposition of hydrogen peroxide, and therefore the radioactive waste organic matter is decomposed into carbon dioxide gas and water vapor. In this case, since the decomposition occurs at a temperature of 150° C. or higher, there is no generation of unstable peroxides and safe operation is possible, and the decomposition temperature is preferably 300° C. or lower to suppress evaporation of concentrated sulfuric acid. In addition, the amount of hydrogen peroxide added should be adjusted until all the radioactive waste organic matter in the heated concentrated sulfuric acid is decomposed.
That is, it is preferable to heat the concentrated sulfuric acid until it becomes transparent.

The carbon dioxide gas and water vapor produced by the above chemical decomposition and the oxygen gas produced by the decomposition of hydrogen peroxide enter the cooling absorption tower 6 from the stirred reactor 4, where the water vapor is cooled by cooling water and becomes recovered water. . While the cooled absorption water is circulated by the pump 7, a part of it is removed from the distillation column 8, and most of the remaining water is distilled in the distillation column 8, passes through the cooler 9, passes through the separator 10, and is stored in the circulating water tank 11. and pump 12
is recycled to the cooling absorption tower 6. Distillation column 8
The residue may contain radioactive substances, so safety measures must be taken such as solidification. The gas leaving the cooling absorption tower 6 enters the activated carbon absorption tower 13, where trace amounts of radioactive iodine and the like are removed, and the gas is discharged by the blower 14 as clean waste gas with a concentration below the allowable concentration.

On the other hand, when radioactive organic waste contains inorganic substances such as heavy metals, some of the inorganic substances turn into sulfates, and most of the remaining remains in concentrated sulfuric acid without being decomposed. Therefore, if these inorganic substances accumulate in the reactor, stop stirring the reactor and let the reaction liquid stand still to remove the precipitated substances, or cool the reactor to remove the precipitated substances. Alternatively, the concentrated sulfuric acid in the reactor can be extracted and subjected to similar treatment to remove precipitated substances. Note that the removed precipitate is subjected to solidification treatment.

By performing the above-mentioned treatment, the radioactive waste organic matter is completely oxidized and becomes carbon dioxide gas and water vapor. According to this method, concentrated sulfuric acid and hydrogen peroxide are used as oxidizing agents, so NOx is not produced as is the case when nitric acid is used, and SO ₂ also reacts with excess hydrogen peroxide to form sulfuric acid. will be played. Furthermore, unlike in the case of nitric acid oxidation, there is no generation of explosive nitro compounds, so safety measures are easy, and the decomposition reaction is not rapid, making it easy to control the reaction. Furthermore, since the reaction system uses sulfuric acid and hydrogen peroxide, corrosion of the equipment is reduced and inexpensive materials can be selected.

Example 1 1.0055g of ion exchange resin was charged into a glass reactor containing 60ml of 97wt% H ₂ SO ₄ and the temperature was raised, and 30wt% hydrogen peroxide was added dropwise from the sulfuric acid solution temperature of 200°C to a reaction temperature of 200 to 240°C. Chemical decomposition was carried out. When the amount of hydrogen peroxide dropped was 16.3 ml and the dropping time was 60 minutes, the color of the liquid changed from black to pale yellow and transparent. The amount of gas generated during this period is
At 1481 c.c., the initial produced gas is
O ₂ 54.82, N ₂ 20.60, CO2.78, CO ₂ 21.80, the gas produced in the middle of the reaction is O ₂ 34.00, N ₂ 16.68, CO 8.78,
CO ₂ 40.54, the final product gas is O ₂ 59.99,
N ² 16.26, CO 3.00, CO ₂ 20.75. The treatment rate was 1.01 gr/hr per 100 ml of reaction volume.

Example 2 1.0035g of benzoic acid was charged into a glass reactor containing 70ml of 97wt% H ₂ SO ₄ and heated to raise the temperature of the sulfuric acid solution.
30wt% hydrogen peroxide was added dropwise from 210℃, and the reaction temperature
Chemical decomposition was carried out at 230-240°C. After 70 minutes of dropping 15ml of hydrogen peroxide, the color of the liquid changed from black to pale yellow and transparent. The amount of gas generated during this period was 1594c.c.
and the average gas composition is O ₂ 32.90 in volume percent,
N ₂ 7.06, CO 7.73, CO ₂ 52.31. The processing rate was 0.86 gr/hr per 100 ml of reaction volume.

Example 3 Filter aid - floc 1.0013gr 97wt%H ₂ SO ₄ 60
Pour 20 ml of concentrated sulfuric acid into a reactor with a reaction volume of 100 ml, heat and raise the temperature of the black liquid, and add 30 wt% hydrogen peroxide dropwise from the sulfuric acid solution temperature of 220°C. I did the disassembly. The amount of hydrogen peroxide dropped was 19.3 ml.The liquid color became black and transparent after dropping time of 41 minutes. The amount of gas generated during this period was 1995 c.c., and the average gas composition was O ₂ 76.32, N ₂ 0.85,
CO6.55, _CO2 16.28. The processing rate was 1.58 gr/hr per 100 ml of reaction volume.

Reference example 1 Filter aid - floc 1.5300gr 97wt%H ₂ SO ₄ 80
ml of the solution was placed in a glass reactor, the temperature was raised, and 70 wt% nitric acid was added dropwise from the sulfuric acid solution temperature of 220°C to carry out chemical decomposition at a reaction temperature of 220 to 230°C. Nitric acid dripping amount
After 41 minutes of dropping 8.2ml, the color of the liquid changed from black to colorless and transparent. The amount of gas generated during this period was 2658c.c., and the average gas composition was 65.82 _% by volume, 17.50% _N2 ,
SO ₂ 7.00, NO 3.70, CO 3.00, N ₂ O 1.98.
The processing rate was 2.24 gr/hr per 100 ml of reaction volume.

[Brief explanation of the drawing]

The drawing is a schematic diagram of an apparatus for implementing the present invention. 1... Radioactive waste organic matter tank, 4... Stirring type reactor, 5... Hydrogen peroxide tank.

Claims (1)

[Claims] 1. Add radioactive waste organic matter to concentrated sulfuric acid, 150 to 300
A method for reducing the volume of radioactive waste organic matter, characterized by decomposing the radioactive waste organic matter by adding hydrogen peroxide while maintaining the temperature at ℃.