Three new layered uranyl phosphates, Ba(3)(UO(2))(2)(HPO(4))(2)(PO(4))(2), Ba(UO(2))F(PO(4)), and Cs(2)(UO(2))(2)(PO(4))(2), were synthesized under mild hydrothermal conditions. These compounds serve as models for uranium alteration phases that might form when spent nuclear fuel is subjected to oxidizing groundwater containing dissolved phosphate. In order to address the possibility of the incorporation of the key fission product (129)I in the form of iodate into uranyl alteration phases, the substitution of IO(3)(-) for the structurally related PO(3)(OH)(2-) or PO(4)(3-) unit was probed. Iodate incorporation into these phases was investigated using LA-ICP-MS, and these data indicate incorporation of iodine with levels as high as 4162 ppm.