KR810000918B1 - Volume reduction of spent radioactive ion-exchange material - Google Patents

Abstract

A method of volume reduction of spent radioactive ion-exchange material is characterized: Ion-exchange material is dried to get moisture proportion of weight 50% and less. A mixture of the air and carrier gas (20) is mixed with preheating air in preheater (34), and put in the reactor (16). after heated and its part is pyrolyzed. The originating noriadioactive drain gas is removed from the carrier gas and gas mixture after analysis of ion-exchange material. The oxygen-coutaining gas is supplied with the behind-combustion chamber (24) after reheated and analyzing ion-exchange material which is pyrolyzed and transferred. The oxygen which remains unburnt behind-combustion chamber is kept up at>7000oC.

Description

Volume reduction method of waste radioactive ion exchange material

1 is a schematic of a volume reduction method.

2 is a typical temperature curve in a fluidized bed reactor.

The present invention relates to a method for volume reduction of fecal radioactive ion exchange materials.

Ion exchange resins are used to remove minerals, metals, and other impurities from water circulating reactors and other parts in reactor coolants, make-up water, and other equipment. Radioactive resins used in nuclear reactors are not normally regenerated, and once used, they must be disposed of as radioactive waste, different from industrial ion exchange resins and commercial ion exchange resins for domestic use.

Various methods of treating radioactive resin and water have been developed. The resins presently used are separated from the resin-water mixture using a centrifuge to separate the resins, eventually forming a radioactive waste or cake which is processed in a suitable container. Where there is no removal of water, it is recycled to the waste disposal system again.

In another method, the resin-water mixture is mixed with the fixing agent and released into a suitable waste package. In the third method, the resin-water mixture is filled with a dry mixture of cement and mica and discharged into a blank drum with a screen box inserted. The mixture fills the box, the water oozes through the screen and enters the cement mica mixture in the box, where the solidified concrete dining forms a sealed resin.

The above-described methods and other treatment methods are expensive because the bulk of the radioactive resin is large and should be contained in a suitable container so as not to contaminate the surrounding area where the container is buried or stored. Moreover, in order to comply with the laws and regulations on the disposal of radioactive waste, such as time, labor and material costs for radioactive waste disposal and packaging,

In order to minimize the economic costs for radioactive waste disposal, many attempts have been made to reduce the volume of radioactive ion exchangers. One of these methods is incineration carbonization of ion exchange materials. Incineration carbonization shows a reduction in solid residues. Incineration carbonization, however, occurs at high temperatures above 1000 ° C. and in oxidizing atmospheres. These operating conditions can add fine dust and form radioactive volatiles such as ruthenium tetraoxide (RuO ₄ ) and cesium sulfate (CS ₂ SO ₄ ). Removing contaminated solids and volatile radioactive gases from hot waste gases is the most important and difficult process.

Another volume reduction method is acid immersion. Acid soaking is a wet oxidation form of solid waste. The radioactive ion exchange material is immersed in concentrated sulfuric acid and nitric acid. The gases generated are passed through an absorber to remove sulfur dioxide and nitrogen oxides. Acid soaking shows a high volume reduction with respect to solid residues. However, acid immersion produces a large amount of contaminated liquid waste that must be treated in glass containers, which requires radioactive treatment of the gas as incinerated carbonization.

The mechanical volume reduction of the radioactive ion-exchange material is undesirable since only a very small volume is reduced.

It is therefore a primary object of the present invention to provide a method of significantly reducing the volume of radioactive organic ion-exchange material while minimizing the amount of radioactivity emitted from the offgas system.

It is an object of the present invention that the pion-exchange material is dried to have a moisture content of 50% by weight or less, the dried ion-exchange material is supplied to a fluidized bed reactor and sufficient carrier gas in the reactor is ion exchanged in the liquid state. In a method of reducing the volume of a pion exchanger introduced to support a material, the carrier gas lacks oxygen and the ion-exchange material is heated to thermally decompose, where the effluent gas is regenerated and the fluidized bed reactor Is removed by the carrier gas as a gas mixture and introduced into the reactor to combust the ion exchange material in which oxygen-containing gas remains after the decomposition of the ion exchange material, the amount of oxygen to maintain the temperature of the fluidized bed below 700 ° C. Controlled, and that the remaining unburned portion in the reactor includes a volume that is greatly reduced. A method of reducing the volume of radioactive Fe ion exchange material according to.

According to the above method, a final volume reduction of about 20: 1 is obtained from the original ion-exchange material. Preferably, the effluent gas is fed to the reburner, where the effluent gas is combusted with air or oxygen, passes through a filter to remove entrained solids, removes acidic or radioactive gases, absorbs and remains To remove fine ash, it passes through a high-efficiency particle filter and is released into the atmosphere. The final gaseous composition consists of carbon dioxide, water nitrogen and oxygen.

A better example will be described with reference to the accompanying drawings.

1 is a schematic of the volume reduction process wherein ion exchange material 10 is placed in the exchanger. Ion exchangers are part of a reactor system (not shown). Once the ion exchanger 10 is discarded, the ion exchanger 10 is removed from the ion exchanger and dried in the dryer 14. The drying process is carried out in various forms of methods such as drum drying, fluid bed-drying, air drying or vacuum drying. The ion exchange material 10 is dried until the moisture content of the ion exchange material 10 is 50% by weight or less.

After drying, the ion exchange material is fed into the fluidized bed reactor 16. After the ion exchange material is charged into fluidized bed reactor 16, carrier gas 20 is introduced into fluidized bed reactor 16. The carrier gas 20 serves to fluidize the ion exchange material 10. Carrier gas 20 is an inert gas such as nitrogen, helium, argon or a non-oxidizing gas such as hydrogen or a gas of limited free oxygen such as carbon dioxide. Carrier gas 20 is heated to a temperature of about 400 ° C. in preheater 34. After the ion exchanger 10 is fluidized, the ion exchanger 10 and the fluidized bed reactor 16 are preferentially heated by the heater 18 and some heat is supplied by the heated carrier gas. Heaters 18 are conventional heaters such as electric heaters or gas heaters. The ion exchange material 10 is heated to 500 ° C. or less, preferably about 400 ° C. The heating of the ion exchanger 10 is for pyrolyzing the structure of the ion exchanger 10. The pyrolysis function to decompose the interconnected polymer structure is manifested in ion exchange material 10 to form volatile products and angled ash residues.

Emission gases are produced in pyrolysis and non-volatile processes. The effluent gas is carried continuously from the fluidized bed reactor by carrier gas 20.

Pyrolysis is an endothermic reaction. That is, the heat absorbed is greater than the heat released (see Figure 2). Just as heat is added to ion exchange material 10, it also occurs in pyrolysis and non-volatile processes. Maximum pyrolysis occurs at about 400 ° C. When this occurs, heater 18 must supply more heat to reactor 16. Increased heating occurs until pyrolysis is complete.

It can be seen that pyrolysis is complete when the temperature of ion exchanger 10 no longer decreases and the amount of heat supplied remains constant. Pyrolysis is generally complete at about 500 ° C.

Once pyrolysis is complete, all volatiles are removed from ion-exchange 10 and the inlet of carrier gas 20 into reactor 16 is stopped. Oxygen containing gas 22, such as pure oxygen or air, is introduced into the fluidized bed reactor 16. After the pyrolysis process, the remaining ion exchange material 10 is burned together with the oxygen containing gas 22.

Residual ion exchanger 10 after pyrolysis burns naturally with oxygen of gas 22 when at a temperature of about 500 ° C.

For this reason, heater 18 does not need to work anymore.

In order to prevent the formation of radioactive volatiles such as ruthenium tetraoxide (RuO ₄ ), they must be maintained in reactor 16 during combustion in a reducing atmosphere. Retention of the reducing atmosphere is achieved by controlling the inflow of oxygen-containing gas 22 into reactor 16 as the gases produced in the combustion process are rich in carbon monoxide and hydrogen, but carbon dioxide is very poor (less than stoichiometric air). In addition, the amount of oxygen-containing gas 22 introduced into reactor 16 is limited not to exceed 700 ° C in temperature in reactor 16. Maintaining the reactor temperature below 700 ° C. minimizes the production of radioactive volatiles ruthenium and cesium. The volume of ion exchange material 10 remaining in reactor 16 after the combustion process is about 1/20 of the volume of precipitated phase removed from the ion exchanger depending on the level of inorganic material initially present in the resin. The reduced volume of ion exchanger 10 can be removed for storage or processing.

Carrier gas 20 introduced into reactor 16 to flow the ion exchange material 10 in order to maintain the residual ion exchange material 10 in the cage-flow state so that it is easily discharged from the reactor 16 is introduced at a rate of more than twice the minimum flow rate Lose. The minimum flow rate is the minimum outflow rate for the ion exchange material 10 to flow. If the carrier gas inlet rate is maintained, ion exchange material 10 is generally in spherical form and does not accumulate in agglomerates.

The gas mixture of the carrier gas and the effluent gas obtained in the nonvolatile process is supplied to the afterburning chamber 24. The afterburner chamber 24 is externally heated by a heater 26 such as an electric or gas heater. Oxygen 28 enters the afterburning chamber 24. In the post-combustion chamber 24, the gas mixture and oxygen 28 are combusted at temperatures between 760 ° C and 1093 ° C. To achieve complete oxidation, excess oxygen 28 is introduced into the afterburner 24. Oxygen reacts with the effluent gas, especially with hydrocarbons in CNHx form to obtain carbon dioxide and water.

After combustion in the post-combustion chamber 24, the residual gas is cooled and filtered by filter 36 and cooler-cleaner 31 to remove entrained solids or unburned hydrocarbons in the gas. The process of removing the entrained solids and residual hydrocarbons is usually by a fine filter.

The cooler-cleaner 31 cools the inlet gas stream and removes most of the incoming particles and unburned hydrocarbons. The above is caused by condensation of an alkaline solution of water vapor in a cooling gas stream by evaporation spray using a cleaning solution or dust removal. Maintaining the temperature of the cleaned gas above 100 ° C. is useful before the processing of the gas takes place.

The cleaning solution can be recycled or treated appropriately by conventional methods.

After removing the entrained solids, the gas passes through absorber 30. During the absorption process, some gases are not removed in the cooler-cleaner 31 such that sulfur dioxide, nitrogen oxides or radioactive volatile gases can be absorbed by the absorbent material in the absorber 30.

After the absorption process, the remaining gas is filtered through a high stabilization particle complete filter 32. The high efficiency particle complete filter 32 is well known in the art as a complete filter and removes all solid particles that may be present in the gas. The gas passes through the filter 32 to remove fine dust that may be present therein. After filtration, the remaining gas is released to the atmosphere, such as carbon dioxide, water, nitrogen, and oxygen.

Therefore, the method provides a method of easily and economically reducing the volume of the radioactive ion exchanger, while providing a method of minimizing the production of any radioactive volatiles. In addition, all removed volatiles and generated gases are released to the atmosphere as non-toxic gases.

Claims (1)

The radioactive ion-exchange material is dried to have a water content of 50% by weight or less and the dried ion-exchange material is supplied to a fluidized bed reactor so that sufficient carrier gas in the reactor supports the ion exchange material in the fluid state. In the method of reducing the volume of the radioactive ion exchange material introduced for the purpose, the carrier gas is deficient in oxygen, and the ion-exchange material is heated to thermally decompose a portion thereof, where a non-radioactive effluent gas is generated to generate a carrier gas and a gas. The mixture is removed from the fluidized bed reactor as a mixture, and after decomposition of the ion exchange material, oxygen-containing gas is introduced into the reactor to combust the remaining ion exchange material, the amount of oxygen being controlled to maintain the fluidized bed temperature below 700 ° C. And the unburned portion remaining in the reactor is significantly reduced. A method for reducing the volume of the ion exchange material.

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