Patent Number: 040654001
Section: summary

BACKGROUND OF THE INVENTION The invention relates to continuous solidification of radioactive liquid waste. The invention described herein was made in the course of, or under, a contract with the U.S. Energy Research and Development Administration. Calcination of high level radioactive waste using fluidized bed techniques has been generally investigated. As used herein, "high-level radioactive liquid wastes" refers to those aqueous wastes resulting from the operation of a first cycle solvent extraction system, and the concentrated wastes from subsequent extraction cycles in a facility for reprocessing irradiated nuclear reactor fuels. These wastes may contain virtually all of the nonvolatile fission products, several tenths of one percent of the uranium and plutonium originally in the spent fuels, and all the other actinides formed by transmutation of the uranium and plutonium as normally produced in a nuclear reactor. The processes resulting from previous investigations have been apropos for some specific applications, but had inherent limitations or disadvantages for other applications such as where continuous waste solidification was required. For example, prior art processes for calcining liquid radioactive waste in a fluidized bed reactor may have one or more of the following limitations: A HIGH INVENTORY OF FISSION PRODUCTS IS MAINTAINED IN THE CALCINER BED RESULTING IN DECAY HEAT PROBLEMS; CONTINUOUS OPERATION MAY NOT BE FEASIBLE BECAUSE OF THE REQUIREMENT OF "ART" OR OPERATOR CONTROL STEPS PECULIAR TO THE PROCESS FOR WHICH THERE CANNOT BE AN AUTOMATIC COMPENSATION; PREVIOUS BEDS MAY NOT ACHIEVE EQUILIBRIUM WITHIN SHORT TIME SPANS AND THEREFORE REQUIRE A LONG WAITING PERIOD FOR BED TURNOVER; OPERATION IN SOME PROCESSES WAS LIMITED TO TEMPERATURES BELOW ABOUT 400.degree. C because the bed material had a low melting composition, and the resulting product had a high nitrate and water concentration; PRIOR ART PROCESSES GENERALLY DO NOT PERMIT SUCCESSFUL CALCINATION OF SODIUM BEARING WASTES WITHOUT SIGNIFICANT ADDITION OF FEED ADDITIVES; AND, FINALLY, WHEN PRIOR ART PROCESSES ARE ADJUSTED OR MODIFIED TO ELIMINATE ONE OR ANOTHER OF THE RECITED LIMITATIONS, THE RESULTANT PRODUCTS MAY HAVE INFERIOR OR UNDESIRABLE VITRIFICATION PROPERTIES. SUMMARY OF INVENTION In view of the above recited limitations, it is an object of this invention to provide for continuously solidifying high level radioactive liquid wastes and recovering the calcined solidified product. It is a further object of this invention to provide for solidification of high level liquid wastes wherein a minimum inventory of fission products is maintained in the calciner bed and decay heat problems are minimized. It is a further object of this invention to provide a continuous process for liquid waste solidification wherein the calcined product particle size may be controlled and is readily vitrifiable. It is a further object of this invention to provide a process for solidifying liquid waste employing a fluidized silica bed wherein equilibrium between the inert silica bed and the calcined radioactive waste is rapidly achieved. It is a further object of this invention to provide a process operable at relatively high temperatures, for solidifying liquid waste, to yield a product which has a low nitrate and water concentration. It is a further object of this invention to provide a high temperature process for solidifying liquid waste applicable to the calcination of sodium bearing wastes without the need for extraneous feed additives. Various other objects and advantages will appear from the following description of this invention and the most novel features will be particularly pointed out hereinafter in connection with the appended claims. It will be understood that various changes in the details, materials, and layout of the apparatus and process which are herein described and illustrated in order to explain the nature of the invention may be effected by those skilled in the art without departing from the scope of this invention. The invention comprises, in brief, a method for continuously solidifying high level radioactive liquid waste comprising introducing an inert particulate material into a reaction chamber, heating the particulate material and the chamber to from about 400.degree. to about 1300.degree. C, dispersing a gas beneath the particulate material to agitate same and form a fluidized bed, atomizing the radioactive liquid waste and dispersing the atomized waste into the fluidized bed to effect calcination of the waste, continuing gas dispersal beneath the fluidized bed to effect attrition and elutriation of the calcined products from the bed, and removing attrited and elutriated calcine products from the reaction chamber via fluidizing gas, and removing calcined product and inert bed material from an upper portion of the fluidized bed, and recovering the calcined products.