Cermet high level waste forms

Abstract

A system and method for stabilizing fission products in a cermet for long term storage. The method includes forming a metal oxide precipitate, combining the metal oxide precipitate with an undissolved solid, and densifying the combined metal oxide precipitate and the undissolved solid to provide a cermet having a ceramic dispersed phase and a metallic matrix phase, wherein the metallic matrix phase includes metallic content from the undissolved solid. The undissolved solid can include fission product metals from the reprocessing of irradiated nuclear fuel. The cermet waste loading can be greater than approximately 30 percent, reducing waste volume by 50 percent or more when compared to baseline glassified articles.

1 . A method for fabricating a cermet comprising:
 forming a metal oxide precipitate;   combining the precipitate with an undissolved solid to form a mixture; and   densifying the mixture to provide a cermet having a ceramic dispersed phase and a metallic matrix phase, wherein the metallic matrix phase includes metallic content from the undissolved solid.   
     
     
         2 . The method of  claim 1  wherein the cermet includes a waste loading greater than approximately 30 percent. 
     
     
         3 . The method of  claim 1  wherein the precipitate is calcined prior to combining and densifying. 
     
     
         4 . The method of  claim 1  further including heating the mixture in a reducing atmosphere to a temperature sufficient to form at least part of the metallic matrix phase. 
     
     
         5 . The method of  claim 1  wherein the undissolved solid includes fission product metals from the reprocessing of nuclear fuel. 
     
     
         6 . The method of  claim 1  wherein the metal oxide precipitate is formed from an aqueous solution containing waste from the reprocessing of nuclear fuel. 
     
     
         7 . The method of  claim 1  wherein the ceramic dispersed phase is chemically tailored to immobilize at least one preselected first radioisotope and the metallic matrix phase is chemically tailored to immobilize at least one preselected second radioisotope. 
     
     
         8 . A cermet for isolating high level waste comprising:
 a ceramic dispersed phase chemically tailored to immobilize at least one preselected first isotope; and   a metallic matrix phase chemically tailored to immobilize at least one preselected second isotope, wherein the metallic matrix phase includes metallic content from an undissolved solid.   
     
     
         9 . The cermet of  claim 8  wherein the cermet waste loading is greater than approximately 30 percent. 
     
     
         10 . The cermet of  claim 8  wherein the cermet is greater than approximately 70 percent ceramic by weight and less than approximately 30 percent metal by weight. 
     
     
         11 . The cermet of  claim 8  wherein the metallic matrix phase is derived primarily from the undissolved solid. 
     
     
         12 . The cermet of  claim 8  wherein the undissolved solid includes fission product metals from the reprocessing of irradiated nuclear fuel. 
     
     
         13 . The cermet of  claim 8  wherein the undissolved solid includes zircaloy alloying metal. 
     
     
         14 . A method of making a cermet comprising:
 providing a slurry comprising ceramic phase particles and metal phase particles;   denitrating the slurry to form a metal oxide precipitate;   combining the metal oxide precipitate with an undissolved fission product; and   densifying the combined metal oxide precipitate and undissolved fission product to provide a cermet having a ceramic dispersed phase and a metallic matrix phase.   
     
     
         15 . The method of  claim 14  wherein the slurry is formed from an aqueous solution containing metal oxides from the reprocessing of irradiated nuclear fuel. 
     
     
         16 . The method of  claim 14  further including calcining the metal oxide precipitate to decompose the metal oxide precipitate into component oxides. 
     
     
         17 . The method of  claim 16  further including heating the combination in a reducing atmosphere to a temperature sufficient to form the metallic matrix phase. 
     
     
         18 . The method of  claim 14  wherein the undissolved fission products include an alloying metal. 
     
     
         19 . The method of  claim 18  wherein the alloying metal includes zircaloy. 
     
     
         20 . The method of  claim 14  wherein the ceramic dispersed phase is chemically tailored to immobilize at least one preselected first radioisotope and the metallic matrix phase is chemically tailored to immobilize at least one preselected second radioisotope.