Patent Number: 047088222
Section: summary

Background of the Invention The present invention relates to a method of solidifying radioactive waste, and more specifically to a method of solidifying radioactive solid waste having a predetermined shape such as that of a pellet. Radioactive waste has heretofore been solidified by mixing dried and granulated radioactive waste into a solidifying material such as a plastic material or concrete. In this case, the solidifying material such as plastic or concrete admixed with the granulated waste could be regarded as a homogeneous material, and the strength of the solidifying material had to be increased simply to increase the strength of the solidified package. In recent years, a method has been proposed in which the granulated waste is pelletized and is then embedded in the solidifying material (Japanese Patent Laid-Open No. 34,200/1977), in order to increase the ratio of waste material embedded, or to reduce its volume. To increase the strength of the material which is solidified by the above method, however, can not be accomplished simply by increasing the strength of the solidifying material. For example, when the solidified package is disposed at sea and is subjected to high pressures, cracks often develop at the boundaries between the solidifying material and the solidified waste embedded therein. SUMMARY OF THE INVENTION An object of the present invention is to provide a method of solidifying radioactive solid waste which is durable and which maintains a sufficiently large safety factor, i.e., which is not destroyed even under increased pressure conditions. Another object of the present invention is to provide a method of solidifying radioactive solid waste so that it is suitable for sea disposal or ground disposal. The method of solidifying radioactive waste of the present invention was achieved by studying the relationship of the modulus of elasticity of the solidifying material and the waste. According to the present invention, the modulus of elasticity of the solidifying material is adjusted to be equal to, or smaller than, that of the radioactive solid waste, in order to prevent stress concentrations at the boundaries between the solidifying material and the radioactive solid waste, particularly on the solidifying material side thereof. Thus the invention makes it possible to prepare a solidified package with a desired durability and safety factor. If a plastic solidifying material is used, the objects of the invention can be accomplished by using a resin with a large distance between crosslinking points. If cement or any other inorganic solidifying material is used, the objects of the invention can be accomplished by adding a rubber-like binder or the like. According to the present invention, solidified radioactive waste is obtained which does not develop stress concentrations within the solidified package even when high pressures are applied thereto, and which does not develop cracks which would lead to destruction, even under highpressure conditions such as on the seabed.