Patent Number: 042344484
Section: summary

List of Prior Art References (37 CFR 1.56 (a)) The following references are cited to show the state of the art: Japanese Laid-Open Patent Application Specification No. 64699/75 U.S. Pat. No. 3,679,595 This invention relates to a method and apparatus for treating radioactive waste, and more particularly to a method and an apparatus for treating aqueous solutions and suspensions of radioactive waste through a step of drying and pulverizing the aqueous solutions and suspensions, and a successive step of compressing and solidifying the resulting powders of radioactive waste. It is desirable to convert aqueous solutions and suspensions of radioactive waste discharged from atomic power stations into a chemically and physically stable solid state convenient for storage. So far available methods for solidifying the aqueous solutions and suspensions of radioactive waste are based on cement solidification, asphalt solidification, etc. The cement solidification is carried out by mixing the aqueous solutions and suspensions of radioactive waste with cement to solidify the solutions and suspensions into a solid state, but has such a disadvantage as an increase in volume of solidified body, because usually the aqueous solutions and suspensions of radioactive waste are mixed, at a low concentration of the radioactive waste, with the cement. The asphalt solidification includes a step of placing the aqueous solutions and suspensions of radioactive waste into hot asphalt, which offers a danger of fire by the hot asphalt. A method for treating the aqueous solutions and suspensions of radioactive waste by drying and solidification has been proposed to overcome the foregoing disadvantages encountered in the solidification treatment. That is, U.S. Pat. No. 3,679,595 discloses an art of solidification by adding a polyelectrolyte and bone glue to the aqueous solutions and suspensions or radioactive waste, heating and drying the resulting mixture on rollers, and compressing the rolled product. The present invention provides a similar treatment of aqueous solutions and suspensions of radioactive waste by drying and pulverizing the aqueous solutions and suspensions of radioactive waste, and then compressing the resulting powders, thereby making solidified bodies of small volume. A step of drying and pulverization of the aqueous solutions and suspensions of radioactive waste is carried out principally by a centrifugal film drier, and a step of compressing the resulting powders to make solidified bodies is carried out by a pelletizer. The pelletizer usually has two counter-disposed rollers, and powders are put into between the rollers by force, and compressed by revolution of the rollers to make solidified bodies. The rollers have recesses or indents on their surfaces and the solidified bodies are formed in the shapes of such recesses or indents. Usually, solidified bodies in a pellet state usually having sizes of a few centimeters are formed. The solidified bodies in the pellet state are stored in drums, or, if necessary, filled with asphalt, etc., and thrown away into the ocean. The treatment of the aqueous solutions and suspensions of radioactive waste by drying and solidification has a problem in obtaining good solidified bodies. That is, no good solidified bodies are obtained only by compressing the powders to make the solidified bodies, unless the powders having a water content below a definite limit content are employed. The limit content is called "limit water content", which is usually a few percents, but is determined on the basis of strength, etc. required for the solidified bodies. The aqueous solutions and suspensions of radioactive waste are continuously fed to the drier, and powders are formed. The resulting powders have not always a constant water content, depending upon the properties of the aqueous solutions and suspensions of radioactive waste and operating conditions of the drier. Sometimes, powders having a water content for above the limit water content are formed. No good solidified bodies are obtained from such poor powders only by direct compression, and thus a further step is necessary to take the resulting powders having the undesired water content, from the drier. The present invention provides a method and an apparatus which comprises measuring a water content of powders between a step of drying and pulverizing aqueous solutions and suspensions of radioactive waste and a step of compressing and solidifying the resulting powders, and eliminating the powders, when the measured water content of the powders is above a limit water content, from a system of the treatment by washing without passing through the step of compressing and solidifying. An object of the present invention is to form good solidified bodies, that is, solidified bodies of high strength. The present invention further provides a method which comprises eliminating the poor powders having a water content above the limit water content rapidly by washing with hot water at a temperature of not lower than 32.degree. C. as a washing solution, when a main solid component of the radioactive waste is Na.sub.2 SO.sub.4.