Transparent and integral U:CaF2 single crystals with diameters 75 mm were grown by temperature gradient technique. Distribution of uranium in the 0.3 wt% doped CaF2 crystal was determined by inductively coupled plasma-mass spectrometry. For the first time, the segregation coefficient of U in U:CaF2 crystal was calculated, which is equal to 0.53 depending on either the formula, K-0 = C-s/C-1 or the general distribution equation, C-s = K0C0(1-g)(K0-1). The solute-enriched strips parallel to growth direction were observed under optical microscopy. The color of U:CaF2 crystal is almost all red but for 5-mm-thickness periphery which is yellow. From the crystal growth initiating part to the finishing, the shape of absorption spectrum of red crystal does, not change, but the density of all peaks gradually increases with color deepening. The fed crystal mostly contains U3+, while the yellow contains more U2+ ions according to the comparison of optical absorption spectra. (C) 2003 Elsevier B.V. All rights reserved.