Patent Number: 041728076
Section: summary

BACKGROUND OF THE INVENTION In present day reprocessing of radioactive waste from nuclear reactors, the high-level waste is obtained in a strong nitric acid solution. The predominant radioactive substances in the waste during the first centuries are strontium-90 and cesium-137. The waste also contains, among other things, minor amounts of uranium, plutonium and transuranic elements which have considerably greater half-lives than strontium-90 and cesium-137. Those skilled in the art are generally of the opinion that it is advantageous, after a suitable period of cooling, to convert the liquid high-level waste into a solid product of good chemical resistance which is stable to leaching out of the contained radioactive substances by water and which is able to withstand heating produced by the fission products and stresses during management and transportation of the product. Materials that have been proposed for use in containing the waste include glasses such as boron silicate glass and phosphate glass, quartz, titanium dioxide, certain zeolites and other minerals existing in nature, particularly those having the ability to retain gases. In a known method of containing high-level waste in glass, the waste is evaporated, calcined and additives are added thereto which, when heated to 1000.degree.-1200.degree. C., result in a glass melt. Calcination of high-level waste may take place at a temperature of the order of magnitude of 300.degree.-500.degree. C. and results in the waste products being transformed into oxides. The melt is poured into tight steel containers which are then transferred to a cooled and supervised storage plant. SUMMARY OF THE INVENTION The present invention is directed to a method of containing high-level waste which allows for an extremely efficient and controllable management of the waste during the process of containment as well as an efficient containment in a resistant material. When the high-level waste has been isolated from the solution, which may, for example, take place in conventional manner by evaporation, possibly followed by calcination, according to the present invention the high-level waste is confined in a capsule at all times during the containment process, and neither gaseous nor liquid products are able to escape from this capsule. This confinement is obtained by sealing the capsule and subjecting the capsule to a hot-isostatic pressing. The isostatic pressure counteracts the formation of volatile constituents in the waste material contained in the capsule during the heating that is required for the contained material to be transformed into a coherent, tight unit, while at the same time achieving the necessary compression of the material. Another important advantage of the method is that it allows enclosing the material in a capsule when the material is at room temperature. A further important advantage of the invention is that it affords great freedom in choosing resistant materials for the containment of the high-level waste material. More particularly, the present invention is directed to a method of anchoring radioactive substances, particulary radioactive substances present in high-level radioactive waste, in a body which is resistant to leaching by water. The method comprises providing a mass containing radioactive substances and either materials which are resistant to leaching by water or materials which, when heated, form materials resistant to leaching by water, enclosing the mass in a capsule, isostatically pressing the capsule at a pressure and a temperature sufficient for the formation of a coherent, tight body of the mass. The capsule is preferably evacuated prior to sealing. Further advantages and features of the invention will become more apparent from a detailed consideration of the particular embodiments as set forth in the following specification in conjunction with the accompanying drawing.