Patent Number: 047972327
Section: claims

1. A process for the preparation of a borosilicate glass containing nuclear waste, wherein The process comprises the steps of: 1. an inactive borosilicate matrix prepared in an aqueous medium by mixing the following:  2. a silica-based gel precursor,  3. a concentrated aqueous solution of a boron compound, and  4. a concentrated aqueous solution of a vitrification adjuvant,  1. a silica gel precursor for forming silica in the final glass, the precursor being an aqueous suspension of colloidal silica;  2. a boron compound in an aqueous solution for forming boron oxide in the final glass; and 2. the process as claimed in claim 1, wherein the mixture to prepare the inactive matrix is effected with a stirrer which rotates at more than about 500 rpm. 3. The process as claimed in claim 2, wherein the mixing is done at about 65.degree. C. to 70.degree. C. 4. The process as claimed in claim 1, wherein the gel precursor is a sol. 5. The process as claimed in claim 1, wherein the silicon-based gel precursor is an alkaline colloidal silica. 6. The process as claimed in claim 1, wherein the silicon-based gel precursor is an acid colloidal silica. 7. The process as claimed in claim 1, wherein the boron compound is ammonium tetraborate. 8. The process as claimed in claim 1, wherein the boron compound is boric acid. 9. The process as claimed in claim 1, wherein the inactive matrix is dried at between 100.degree. and 200.degree. C., and then calcined at between 300.degree. and 450.degree. C. to provide a calcinate, wherein the said calcinate is dispersed in the aqueous solution of nuclear waste and mixed by stirring, and wherein the resultant mixture is dried, calcined and then melted to form the final glass. 10. The process as claimed in claim 1, wherein the inactive matrix is dried at between about 100.degree.-105.degree. C., wherein the said dried gel is brought into contact with the aqueous solution of waste, with stirring, and wherein the resultant mixture is dried, calcined and then melted to form the final glass. 11. The process as claimed in claim 9, wherein the dried or calcined matrix and the solution of waste are introduced separately into a calciner, and wherein the mixing, drying and calcination are effected in the said calciner. 12. The process as claimed in claim 1, wherein the solution of waste is dried or calcined and the dried waste or calcinate of the waste is introduced separately into a melting furnace to form the final glass. 13. A process for immobilizing nuclear waste in the form of a liquid aqueous solution as a waste material, the process comprising the steps of: 3. an aqueous solution of vitrification adjuvant, the mixing being done at an acid pH and a temperature of about 20.degree. to 80.degree. C. to provide a gel solidified material; 14. A process as defined in claim 13 in which other constitutents of the final glass as a vitrification adjuvant are added in Step A, the adding being simultaneous with the glass forming materials, the other constituents comprising a solution of an aluminum compound that forms Al.sub.2 O.sub.3 in the final glass. 15. A process as defined in claim 14 in which the other constituents comprises solutions of glass-forming compounds that form Na.sub.2 O, ZnO, CaO and ZrO.sub.2 in the final glass. 16. A process as defined in claim 13 in which Step A is performed at about 65.degree. to 70.degree. C. 17. A process as defined in claim 16 in which the aqueous system of Step A has a pH of about 2.5 to 3.5. 18. A process as defined in claim 13 in which the drying Step B is about 100.degree. to 105.degree. C. 19. A process as defined in claim 13 in which Step C is conducted at about 300.degree. to 450.degree. C. 20. A process as defined in claim 13 in which the silica gel precursor is an alkaline colloidal silica that provides a gel to provide the gel solidified mixture of Step A. 21. A process as defined in claim 13 in which the aqueous solution of 1 and 2 in Step A are concentrated in which the solutions are at least about 75% of their saturation concentrations.