Method for noncontaminating solidification of radioactive waste materials

• US 4,202,792 A
• Filed: 12/19/1977
• Issued: 05/13/1980
• Est. Priority Date: 12/17/1976
• Status: Expired due to Term

• Current Assignee: Gesellschaft Fur Kernforschung mbH
• Original Assignee: Gesellschaft FUER Kernforschung
• Inventors: Seiffert, Hartmut, Weisenburger, Siegfried, Koschorke, Herbert, Kaufmann, Friedrich, Sienel, Dieter, Weiss, Karl-Heinz
• Primary Examiner(s): Padgett, Benjamin R.
• Assistant Examiner(s): Kyle, Deborah L.
• Application Number:
  US05/862,048
• Time in Patent Office: 876 Days
• Field of Search: 252/301.1 W, 106/54
• US Class Current: 588/12
• CPC Class Codes: G21F 9/305 Glass or glass like matrix C03B5/005 takes precedence; compositional aspects C03C

Abstract

Method for the solidification, in a manner which protects the environment against contamination, of waste materials obtained during reprocessing of irradiated nuclear fuel and/or breeder materials in a matrix of borosilicate glass. Highly radioactive solutions or slurries containing the waste materials in dissolved or suspended form are evaporated in a vessel in the presence of glass former substances until they are dry, the dry residue is calcinated and the calcinate is melted together with the glass formers while the waste gases are discharged to the environment. The waste liquid is obtained from a reprocessing system without pretreatment, is mixed with glass formers and a reduction agent and then is introduced in a controlled, continuous manner into the center of a borosilicate glass melt disposed in a melting crucible at a temperature in the region of 1000° to 1400° C. to form an island-like drying and calcinating zone on the surface of the melt while avoiding contact of the waste liquid with the walls of the crucible. A reducing atmosphere is formed and the presence of components in the waste gas which would radiologically and/or chemically contaminate the environment are substantially avoided.

Claims

1. Method for the solidification, in a manner which protects the environment against contamination, of waste materials obtained during reprocessing of irradiated nuclear fuel and/or breeder materials in a matrix of borosilicate glass comprising;

introducing, in a controlled and continuous manner, a waste liquid which has been obtained from a reprocessing system without pretreatment and which has been mixed with glass formers and a reduction agent, into the center of a borosilicate glass melt disposed in a melting crucible at a temperature in the region of 1000°

to 1400°

C. to form an island drying and calcinating zone on the surface of the melt while avoiding contact of the waste liquid with the walls of the crucible, to form a reducing atmosphere, and to substantially avoid the presence of components in resulting waste gases which would radiologically and/or chemically contaminate the environment.

2. Process as defined in claim 1, wherein a concentration maximum of the reduction agent is formed in the region of the island zone, with a concentration gradient which decreases with increasing distance from this maximum.

3. Process as defined in claim 1, wherein a positive heat intake is provided which rapidly radially penetrates the melt from the outside toward the center.

4. Process as defined in claim 1, wherein the reduction agent is formic acid.

5. Process as defined in claim 1, wherein the waste liquid which has been mixed with glass former and reduction agent is continuously dispensed in metered quantities into the island zone at a throughput in the range between about 10 liters per hour to about 150 liters per hour.

6. Process as defined in claim 5, wherein an airlift conveying device is used to dispense the waste liquid into the island zone.

7. Method for the solidification, in a manner which protects the environment against contamination, of waste materials obtained during reprocessing of irradiated nuclear fuel and/or breeder materials in a matrix of borosilicate glass, comprising:

(a) mixing a waste liquid which has been obtained from a reprocessing system without pretreatment with glass formers and formic acid to reduce nitric acid and nitrate ions present in said waste liquid, the amount of said formic acid being equal to two to three times the stoichiometrically required amount;

(b) introducing the mixture obtained from step (a) in an amount between 10 1/h to about 150 1/h with the aid of air or another gas, into the center of a borosilicate glass melt disposed in a melting crucible at a temperature in the region of 1000°

to 1400°

C. to form an island drying and calcinating zone extending up to about two-thirds of said melt surface while avoiding contact of the waste liquid with the walls of the crucible, to form a reducing atmosphere, and to substantially avoid the presence of resulting waste gases which would radiologically and/or chemically contaminate the environment.