Patent Number: 047553324
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of and an apparatus for pelletizing a radioactive waste, and more particularly, to a method of and an apparatus for pelletizing a radioactive waste in which it is possible to shorten the compressing time required when a waste powder is to be compressed or press-molded into a pellet, and to prevent environmental pollution from being caused by the waste powder which may be scattered during the pelletizing operation. 2. Description of the Prior Arts A radioactive waste has been increasingly produced by an atomic power plant concurrently with an increase in the quantity of produced electricity, and therefore, the need for volume-reducing treatment of a radioactive waste has been increased in order to ensure a storage space in a facility. One method of reducing the volume of a radioactive waste has heretofore been proposed in which a concentrated waste liquid (the main component is a soda sulfate) obtained from the concentration of a waste liquid regenerated from ion exchange resins which are produced in large quantities by a boiling water reactor and granular ion exchange resin slurry are dried and milled so as to remove water occupying a large percent of the volume of a radioactive waste, and the thus-treated powder is formed and solidified into a pellet by using a tablet type pelletizer, or alternatively, after inflammable solid wastes have been burnt, the thus-produced ashes are formed and solidified into a pellet by using the tablet type pelletizer. Such method of pelletizing a radioactive waste by the use of the tablet type pelletizer is disclosed in the specifications of Japanese patent unexamined publication No. 100799/1983, Japanese patent unexamined publication No. 100800/1983, and Japanese patent unexamined publication No. 108497/1983. However, these publications only disclose a mixing ratio or a compressive force connected with a radioactive waste powder. According to one of conventional pelletizing methods using the above-mentioned pelletizer, a radioactive waste powder is supplied into a powder receiving cavity formed in a pelletizing section of the pelletizer, and the powder is pelletized within a through bore of a pelletizing die which extends from one end facing the powder receiving cavity to the other end facing the atmosphere, by inserting a first pelletizing rod from the side of the one end of the through bore, through the cavity, into the through bore under condition that a second pelletizing rod is inserted into the through bore by a predetermined length through the other end into the through bore. The waste powder is thus pelletized in a compressed manner within the through bore. However, such prior-art method involves disadvantage in that compressed air is not easily discharged through the through bore and compressing time correspondingly becomes longer. This is because the gap between the first pelletizing rod and the through bore and that between the second pelletizing rod and the through bore constitute minute gaps having substantially the same size or width and the air compressed during the pelletizing or press-molding operation is expelled through the minute gaps out of the through bore. In addition, the above-mentioned method involves a problem in that the compressed air passes through the respective gaps between the through bore and both rods and flows into not only the powder receiving cavity but also the atmosphere, so that part of the waste powder is mixed with the air flowing into the atmosphere, thus raising the problem of environmental pollution. SUMMARY OF THE INVENTION An object of the present invention is to provide method of and an apparatus for pelletizing a radioactive waste powder which is capable of eliminating the above-described disadvantages of the prior art by shortening the compressing time expended during a pelletizing operation and preventing the waste powder from being scattered together with air discharged into the atmosphere. Accordingly, in accordance with one aspect of the present invention, there is provided a method of pelletizing a radioactive waste powder comprising the steps of: supplying the radioactive waste powder in a powder receiving cavity defined in a pelletizing section of a pelletizer; pelletizing the powder within a through bore formed in a pelletizing die by inserting a first pelletizing rod through the receiving cavity into the through bore through one end thereof facing the receiving cavity under condition that a second pelletizing rod is inserted into the through bore by a predetermined length through the other end of said through bore facing the atmosphere, the through bore extending in the pelletizing die from the one end to the other end; and allowing an air compressed in the through bore in the pelletizing step to be discharged into the receiving cavity through the one end without causing the air to leak into the atmosphere through the other end of the through bore. In accordance with another aspect of the present invention, there is provided an apparatus for pelletizing a radioactive waste powder comprising: a pelletizing section; a pelletizing die which has one end facing a cavity defined in the pelletizing section for receiving the radioactive waste powder and the other end exposed to the atmosphere, the pelletizing die being formed therein with a through bore extending from the one end to the other end of the die; a first pelletizing rod arranged to be inserted through the receiving cavity into the through bore from the one end of the die such as to be capable of being drawn out therefrom; a second pelletizing rod arranged to be inserted into the through bore from the other end of the die such as to be capable of being drawn out therefrom; the first and second pelletizing rods being arranged in such a manner that, when the second pelletizing rod is kept stationary in a position inserted in the through bore by a predetermined amount, the first pelletizing rod is inserted though the receiving cavity into the through bore, thereby enabling the pelletizing operation of the powder within the through bore; and an air discharge for allowing air compressed in the through bore to be discharged into the receiving cavity without causing the compressed air to leak into the atmosphere during the pelletizing operation. The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.