Patent Number: 043448720
Section: claims

1. A method of removing fission products from ruthenium-containing nitric acid solutions and thereafter isolating the fission products in a solid mass, the method comprising in combination the steps of: concentrating said solution by evaporation of the nitric acid therefrom to form a fission products concentrate having a solids content in the range of fifteen to twenty-five percent by exposing the solution to a partial vacuum having a pressure below fifty millimeters of mercury and by maintaining the temperature of the solution at a level sufficient to ensure evaporation of the nitric acid at that pressure whereby the evaporated nitric acid has a ruthenium content below one part per million;  condensing the nitric acid vapor having a ruthenium content below one part per million;  separating the nitric acid condensate from the fission products concentrate;  adding vitrifiers and ammonia derivatives capable of nitrous-free nitrate decomposition to the fission products concentrate to form a fission product-vitrifier mixture with a reduced nitrate content, and  heating in an oven the fission product-vitrifier mixture to vitrify same and to thereby isolate the fission products in a solid mass. 2. A method according to claim 1, which includes the steps of diluting the fission products concentrate with water and repeating said vacuum concentration step prior to said adding step. 3. A method according to claim 1, which includes the step of carrying out said concentrating step in a wiping blade evaporator. 4. A method according to claim 1, in which said ammonia derivative is urea and is added in a quantity of about 20 to 300% Mol relative to the nitrate content of said concentrate fission products. 5. A method according to claim 1, which includes the step of drying fission product-vitrifier mixture prior to said heating step. 6. A method according to claim 1, which includes the step of purging the oven with an inert gas during said heating step.