Cerium, uranium, and plutonium behavior in glass-bonded sodalite, a ceramic nuclear waste form

Glass-bonded sodalite is being developed as a ceramic waste form (CWF) to i mmobilize radioactive fission products, actinides, and salt residues from e lectrometallurgical treatment of spent nuclear reactor fuel. The CWF consis ts of about 75 mass% sodalite, 25 mass% glass, and small amounts of other p hases. This paper presents some results and interpretation of physical meas urements to characterize the CWF structure, and dissolution tests to measur e the release of matrix components and radionuclides from the waste form. T ests have been carried out with specimens of the CWF that contain rare eart hs at concentrations similar to those expected in the waste form. Parallel tests have been carried out on specimens that have uranium or plutonium as well as the rare earths at concentrations similar to those expected in the waste forms; in these specimens UCl3 forms UO2 and PuCl3 forms PuO2. The no rmalized releases of rare earths in dissolution tests were found to be much lower than those of matrix elements (B, Si, Al, Na). When there is no uran ium in the CWF, the release of cerium is two to ten times lower than the re lease of the other rare earths. The low release of cerium may be due to its tetravalent state in uranium-free CWF. However, when there is uranium in t he CWF, the release of cerium is similar to that of the other rare earths. This trivalent behavior of cerium is attributed to charge transfer or coval ent interactions among cerium, uranium, and oxygen in (U,Ce)O-2. (C) 2000 P ublished by Elsevier Science S.A. All rights reserved.