The UO2 in spent nuclear fuel is unstable under moist oxidizing conditions and will be altered to uranyl oxide hydrate phases. The transuranics released during the corrosion of spent fuel may also be incorporated into the structures of secondary U6+ phases. The incorporation of radionuclides into alteration products will affect their mobility. A series of precipitation tests were conducted at either 150 or 90°C for seven days to determine the potential incorporation of Ce4+ and Nd3+ (surrogates for Pu4+ and Am3+, respectively) into uranium phases. lanthinite ([U2
4+(UO2)4O6(OH)4(H2O)4](H2O)5) was produced by dissolying uranium oxyacetate in a solution containing copper acetate monohydrate as a reductant. The leachant used in these tests were doped with either 2.1 ppm cerium or 399 ppm neodymium. Inductively coupled plasmamass spectrometer (ICP-MS) analysis of the solid phase reaction products which were dissolved in a HNO3 solution indicates that about 306 ppm Ce (K
d = 1020) was incorporated into ianthinite, while neodymium contents were much higher, being approximately 24,800 ppm (K
d 115). Solid phase examinations using an analytical transmission electron microscope/electron energy-loss spectrometer (AEM/EELS) indicate a uniform distribution of Nd, while Ce contents were below detection. Becquerelite (Ca[(UO2)6O4(OH)6]·8H2O) was produced by dissolving uranium oxyacetate in a solution containing calcium acetate. The leachant in these tests was doped with either 2.1 ppm cerium or 277 ppm neodymium. ICP-MS results indicate that about 33 ppm Ce (K
d = 17) was incorporated into becquerelite, while neodymium contents were higher, being approximately 1,300 ppm (K
d = 5). Homogeneous distribution of Nd in the solid phase was noted during AEM/EELS examination, and Ce contents were also below detection.