METHOD FOR TREATING HAZARDOUS WASTE

Abstract: Procedure for the treatment of radioactive hazardous waste, in which procedure oxygen is treated with radio-frequency electromagnetic radiation in a manner known in itself so that the oxygen forms a cold plasma, and the waste and the oxygen are fed together.

Description: METHOD FOR TREATING HAZARDOUS WASTE The present invention relates to a procedure for the treatment of hazardous waste. Today, hazardous waste is treated in special hazardous waste disposal plants, where hazardous waste is treated in the first place by burning it in high temperatures and effectively so that the gaseous emis¬ sions produced can be admitted into the atmosphere and solid emissions can be recycled or removed to dumping places. However, treatment of hazardous waste at high temperatures is not always an economic solution, and hazardous waste disposal plants have to use fossil fuels to reach sufficiently high temperatures. Furt- her, there are types of hazardous waste, such as ra¬ dioactive waste, whose disposal by burning is out of the question because of the atmospheric emissions re¬ leased via combustion. Specifications US 5028452, WO 89/10162, DE 4113440, DE 4336768 and DE 4428418 present procedures for the treatment of hazardous waste with a cold plas¬ ma formed by oxygen. Prior-art methods for waste treatment are ge¬ nerally not applicable for the treatment of radioacti- ve hazardous waste. In the treatment of radioactive hazardous waste, it is important that no emissions should be admitted into the atmosphere or waste water. In some way or another, all radioactive waste has to be finally so stored that no emissions are released into the environment. At present, e.g. in connection with the treatment of the waste water of nuclear power stations using ion-exchange resm, low-activity waste is generated which cannot be burned as such expressly because of the radioactive emissions released during combustion. For final storage of the radioactive waste contained in the resin, the resm has been subjected to a bacterial treatment and the bacterial mass obtained has been mixed in concrete mass for final storage. However, there are difficulties and problems in bacterial treatment of resin and final storage of the mass obtained. The object of the present invention is to produce a new method for treating radioactive hazar¬ dous waste in such a way that hazardous waste can also be treated lower temperatures and without releasing harmful emissions into the atmosphere. As for the features characteristic of the in¬ vention, reference is made to the claims. The invention is based on the basic idea, de¬ veloped in the investigations which have been carried out, of converting oxygen into the form of a cold plasma and feeding the oxygen and waste together. Sin¬ ce oxygen in the form of a cold plasma is very reacti¬ ve, hazardous waste can easily be oxidized into a harmless form using such oxygen plasma. Oxygen can be converted mto the form of a cold plasma by subjecting it to radio-frequency electromagnetic radiation, preferably with a frequency of 2 - 14 MHz. If desirable, hazardous waste can also be treated with such electromagnetic radiation. The treatment of waste with oxygen in the form of a plasma is preferably carried out at a tempe¬ rature of 60 - 150 °C. If desired, it is also possible to use temperatures lower or higher than this. The treatment of hazardous waste with oxygen in the form of a plasma can be carried out in a desi¬ red pressure, a negative or a positive pressure. In a preferred embodiment of the invention, the treatment is performed in negative pressure conditions. The invention is also applicable for the tre- atment of radioactive waste, e.g. low-activity waste. Low-activity waste is produced e.g. n the treatment of the cooling water of nuclear power stations with ion-exchange resm, which is used to remove radioacti¬ ve substances from the waste water, i.e. to bind them with the resm. Low-activity ion-exchange resin cannot be burned as such because of the radioactive emissions released durmg combustion. Therefore, the mam appro¬ ach regarding the treatment of such resin has been to place it in final storage. For this purpose, the resm has been fed to bacteria and the bacterial mass obtained has been mixed in concrete mass for final storage. However, the bacterial treatment of resm and final storage of the mass obtained mvolve certain difficulties and problems. When radioactive ion-exchange resin is trea¬ ted by the method of the invention, the structure of the resm is destroyed and it forms waste material that takes up less space than before. Final storage of the waste can be more easily implemented than before, e.g. by concreting or in other ways, e.g. by placing it in containers. The patent specifications referred to in the introductory part of the description relate to the treatment of chemical hazardous waste with cold plasma formed by oxygen. However, these specifications are in no way concerned with plasma treatment of radioactive hazardous waste. Moreover, said specifications do not present the advantages achieved when radioactive ha¬ zardous waste is treated with cold plasma. Thus, ex¬ pressly when applied to radioactive waste, plasma tre¬ atment provides advantages that cannot be achieved m plasma treatment of other types of waste. In the following, the invention is described in detail by the aid of embodiment examples. EXAMPLE 1 A nuclear power station produces annually 20- 40 m of radioactive ion-exchange res , mainly styre¬ ne based and acrylic resin, which is used for the re- moval of partially radioactive impurities and corrosi¬ on products from the primary coolant. Final storage of this waste is expensive. Radioactive resins generally cannot be burned because in normal combustion the high temperature causes the release of a lot of active sub¬ stances mto the flue gases. The treatment of the ga¬ ses generally costs more than the burn-out. An amount of ion-exchange resm is placed in a container made of quartz or glass. Suction is app- lied to the container to create a slight negative pressure m it, and oxygen is supplied mto the con- tamer. Using an antenna and a radio frequency genera¬ tor, an alternating electric field is applied to the container. The electric field ionizes the oxygen so that a low-temperature plasma is formed. This plasma is very reactive, and it oxidizes the mass into carbon dioxide and water. The gases produced are drawn through a filter mto ventilation by means of a vacuum pump. Since the temperature is low, not higher than 150 °C, all radioactivity will remain in the cinders thus produced, so the volume of the waste is signifi¬ cantly reduced. Moreover, the cinders produced are chemically suited for concreting or bitummization, both of which are suitable forms for final storage. EXAMPLE 2 In nuclear power plants, organic cationic and anionic resins are used for the removal of radioactive fission products from the primary circuit cooling wa- ter. For example, n a VVER-440 plant the amount of such resm produced in a year may be 15 m . The resm is extremely radioactive. In the procedure concerned by this patent, this radioactive resm is treated as follows. The used ion-exchange res obtained from the plant contams water. First, the resm is pre-dried in a low temperature. Next, ten litres of pre-dried resin is placed in a 12-litre cylindrical container made of quartz, which is rotated to achieve continuous mixing. Applying a suction with a vacuum pump, gases are con¬ tinuously removed from the container so that the nega¬ tive pressure is about 1 torr. Gaseous oxygen is fed mto the same container in such a way that the negati¬ ve pressure is maintained and the oxygen concentration is as high as possible. Using a suitable antenna, a radio-frequency field with a frequency of e.g. 27.12 MHz and a power of 6 kW is applied to the container. This causes the oxygen in the container to form a plasma, whose temperature may be as low as 60 °C. The oxygen plasma is very reactive. Consequently, it oxi¬ dizes the organic ion-exchange resm in the container mto water and carbon dioxide. These are drawn through a filter into ventilation by the vacuum pump. What re¬ mains m the container are the inorganic constituents of the resin, in the first place metals in the form of oxides. These residual cinders contain all the radio¬ activity. The volume is reduced by a factor of 10-20, depending on the composition of the ion-exchange re¬ sin. The cinders and the radioactivity contamed in them can be solidified either by glazing, concreting or bitummiz g. The solidification product can be sa¬ fely placed n final storage under ground. The embodiment examples are intended to il¬ lustrate the invention without limiting it in any way.

Claims: CLAIMS 1. Procedure for the treatment of radioacti¬ ve hazardous waste, c h a r a c t e r i z e d in that oxygen is treated with electromagnetic radiation in a manner known in itself so that the oxygen forms a cold plasma, and the waste and the oxygen are fed together. 2. Procedure as defined in claim 1, c h a ¬ r a c t e r i z e d in that the oxygen and/or the waste is/are treated with electromagnetic radiation having a frequency of about 2 - 14 MHz. 3. Procedure as defined in claim 1, c h a ¬ r a c t e r i z e d in that the waste is treated at a temperature of 60 - 150 °C. 4. Procedure as defined m any one of claims 1 - 3, c h a r a c t e r i z e d in that the waste is treated in negative pressure conditions. 5. Procedure as defined m any one of claims 1 - 4, c h a r a c t e r i z e d in that the waste is low-activity waste. 6. Procedure as defined in any one of claims 1 - 5, c h a r a c t e r i z e d in that the waste is ra¬ dioactive ion-exchange resm. 7. Procedure as defined in any one of claims 1 - 6, c h a r a c t e r i z e d in that the product obtained is placed in final storage. 8. Procedure as defined in any one of claims 1 - 7, c h a r a c t e r i z e d m that the product obtained is concreted.

Inventors: ROSENBERG ROLF, ROSENBERG, ROLF
Applicants: ROSENBERG ROLF, VALTION TEKNILLINEN, ROSENBERG, ROLF, VALTION TEKNILLINEN TUTKIMUSKESKUS
Application year: 1997
Main classification: G21F9
IPC codes: G21F9, G21G1