GB2158986A

GB2158986A - Method and apparatus for burning radioactive organic waste

Info

Publication number: GB2158986A
Application number: GB08506624A
Authority: GB
Inventors: Taneaki Yahata
Original assignee: Japan Atomic Energy Research Institute
Current assignee: Japan Atomic Energy Agency
Priority date: 1984-05-16
Filing date: 1985-03-14
Publication date: 1985-11-20
Also published as: GB8506624D0; FR2564633B1; GB2158986B; FR2564633A1; JPS60242399A

Abstract

This invention relates to a method and apparatus for completely burning radioactive organic wastes, comprising thermally decomposing the radioactive organic wastes with an organic solvent, and heating the resulting thermal decomposition product and volatilized product at a controlled oxygen partial pressure while they are in contact with a catalyst.

Description

SPECIFICATION Method and apparatus for burning radioactive organic wastes The present invention provides a useful technique for the treatment or disposal of substances contaminated by radioactivity, particularly radioactive organic wastes.

Nuclear power plants, nuclear fuel processing plants, and fuel retreatment plants produce wastes such as ion-exchange resins contaminated by radioactivity. Conventionally, such resins are first dewatered and dried, and then decomposed by digestion with an acid or incinerated.

The method of digesting the dried waste with an acid requires equipment that is resistant to acid corrosion and is capable of safe disposal of waste acid. Many techniques have been proposed for implementing the incineration method, but because of the high temperatures used in this method, the furnace material is rapidly corroded and radioactive substances are discharged into the atmosphere. Whichever method is used, the ion-exchange resin to be treated must be dried to a considerable degree. The incineration method has a further problem in that incomplete combustion may result from the after-burning of the unburnt substances.

This invention relates to a method of burning radioactive organic waste which comprises thermally decomposing the radioactive organic waste together with an organic solvent, and heating the resulting thermal deomposition product and volatilized product at a controlled oxygen partial pressure while they are in contact with a catalyst.

This invention also relates to an apparatus for burning radioactive organic waste comprising: (a) a unit for mixing the radioactive organic waste and an organic solvent under agitation; (b) a unit for thermally decomposing a suspension of the radioactive organic waste obtained by the mixing under agitation; (c) a furnace wherein the thermal decomposition product and volatilized product formed as a result of the thermal decomposition are subjected to a catalytic reaction; and (d) a means for washing the waste gas resulting from the catalytic reaction.

The objectives and advantages of the present invention will become apparent by reading the following description and the drawing.

The drawing shows the arrangement of an exemplary system for impiementing the method of the present invention.

By means of the method and apparatus of the present invention it is possible to ensure the complete incineration of radioactive organic waste in a manner substantially independent of the water content of the waste without causing damage to the furnace material and without letting radioactive substances be discharged into the atmosphere.

The construction of the present invention is hereunder described in detail by reference to the accompanying drawing, which illustrates the arrangement of an exemplary apparatus for implementing the method of the invention.

in accordance with the present invention, the radioactive organic wastes are stirred in a mixing vessel 1 together with an organic solvent (e.g. alcohol), and the resulting suspension is introduced into a heat decomposing unit 3 through a metered amount supplying unit 2. The heat decomposing unit 3 is made of a sheathed pipe and has a heater within the inner pipe. An oxygen-controlled gas (a mixture of 5-10% 02 and A) is also supplied into the sheathed pipe from the bottom through a line 6. The purpose of introducing this gas is to prevent rapid burning of the organic wastes and the organic solvent. In the sheathed pipe that has been heated internally to 500-600"C, the organic wastes and the organic solvent are thermally decomposed and evaporated.Thereafter, the thermal decomposition product and the evaporation product are introduced into a catalytic reaction furnace 4 by the oxygen-controlled gas. In the reaction furnace, the two products are brought into contact with a catalyst made of copper oxide, iron oxide, cobalt oxide or nickel oxide that has been heated to about 700"C.

Taking copper oxide as a catalyst, the heat decomposition product and the evaporation product can be completely incinerated by the following chemical reactions: lon-exchange decomposition product: CmHn, H2, CO, CO2, H2O, NO,, SO,, Cl2, C (Free Carbon), and Alcohol (C2H5OH) CmHn + xCuO = xCu2O + mCO2 + nH2O m'C + xCuO = CCu2O + m'CO2 n'H2 + xCuO = xCu2O + n'H20 1 C2H5OH + xCuO = xCu2O + 1 CO2 + 1 H20 xCu2O + 02 = xCuO In order to compensate for any shortage of the oxygen that is necessary in the catalytic reaction, air is introduced into the catalyst-filled reaction pipe through an inlet 7.

As a result of the reactions shown above, gas containing SO,, Cl2 and/or other constituents is produced from the ion-exchange resin and is introduced into a waste gas cleaning unit 5, where the waste gas is subjected to a scrubber 8 before collection at a separate unit to absorb said SOx Cl2 and/or other constituents.

Example An ion-exchange resin (500 ml) was mixed with excess ethyl alcohol. The mixture was stirred to form a suspension of the resin, which was continuously pumped to a thermal decomposition furnace that had been heated to 600"C. In order to prevent rapid combustion from occurring in the furnace, the atmosphere in the furnace was controlled to have an oxygen concentration of about 10%. In the atmosphere of about 10% 02 at 600"C, the resin was immediately decomposed thermally and introduced into a catalytic reaction furnace together with the evaporated alcohol. The reaction furnace packed with a copper oxide catalyst had been heated to about 700"C in the presence of an air stream. The thermal decomposition product consisting of hydrocarbons, hydrogen, carbon monoxide and free carbon, formed water and carbon dioxide as a result of contact with the preheated (ca. 700"C) catalyst. Likewise, the evaporated alcohol was converted to the water and carbon dioxide by contact with the catalyst.

In accordance with the present invention, the ion-exchange resin can be completely incinerated without soot formation by heating in the presence of the alcohol and the copper oxide catalyst at a controlled oxygen partial pressure.

Claims

1. A method of burning radioactive organic waste which comprises thermally decomposing the radioactive organic waste together with an organic solvent, and heating the resulting thermal decomposition product and volatilized product at a controlled oxygen partial pressure while they are in contact with a catalyst.

2. A method according to Claim 1 wherein said radioactive organic waste is an ion-exchange resin.

3. A method according to Claim 1 or 2 wherein the thermal decomposition is performed in the temperature range of 500-600"C.

4. A method according to Claim 1, 2 or 3 wherein said catalyst is copper oxide, iron oxide, cobalt oxide or nickel oxide.

5. A method according to Claim 1, 2, 3 or 4 wherein the heating at a controlled oxygen partial pressure is effected at about 700"C.

6. A method of burning radioactive waste substantially as herein described with reference to and as illustrated in the Example.

7. An apparatus for burning radioactive organic waste comprising: (a) a unit for mixing the radioactive organic waste and an organic solvent under agitation; (b) a unit for thermally decomposing a suspension of the radioactive organic waste obtained by the mixing under agitation; (c) a furance wherein the thermal decomposition product and volatilized product formed as a result of the thermal decomposition are subjected to a catalytic reaction; and (d) a means for washing the waste gas resulting from the catalytic reaction.

8. An apparatus according to Claim 7 wherein said unit for thermal decomposition is made of a sheathed pipe having a heating means in its interior.

9. An apparatus according to Claim 8 wherein an inlet for introducing an oxygenconcentration-controlled gas is provided at the bottom of the sheathed pipe.

10. An apparatus according to Claim 7, 8 or 9 wherein said furnace is an annular resistance furnace at each end thereof.

11. An apparatus according to Claim 7, 8, 9 or 10 wherein an air inlet is provided at the furnace.

1 2. Apparatus for burning radioactive waste substantially as herein described with reference to and as illustrated in the accompanying drawing.