The transformation of a simulated nuclear waste into nepheline NaAlSiO4 has been studied, using thermogravimetry, mass spectrometry and X-Ray diffraction. Several mixtures have been used, which were elaborated from a simulated waste (containing mainly sodium nitrate), alumina and silica. Considering the various mass losses observed, the phases obtained after each mass loss (identified by X-Ray diffraction) and the gases released, a reaction path for the transformation has been proposed.