[en] Skull melting is a cold-crucible technique for obtaining high-purity melts of refractory materials, particularly oxides. This technique has been used to synthesize high-purity minerals and to prepare single crystals of uraninite (UO²) and thorianite (ThO²) directly from the melt. A description of the crystal-growing technique is discussed. Los Alamos is also interested in developing the skull-melting technique to zone-refine spent UO² nuclear reactor fuel pins. Since metallic fission products and actinides will behave as solute impurities in a UO² solvent, the success of the zone-refining process will depend on the distribution of the impurities between molten and solid UO². An effective distribution coefficient for Y²O³ segregated between molten and solid UO² was experimentally determined by zone melting. An effective distribution coefficient of k = 0.75 +- 0.05 was obtained, in good agreement with an equilibrium value of k⁰ = 0.6, estimated from the Y²O³-UO² phase diagram