[en] A new nuclear glass composition, able to immobilize highly radioactive liquid wastes from high burn-up UO₂ fuel, was established and its structure studied. The composition of the selected rare earth-rich glass is (molar %): 61.79 SiO₂ - 8.94 B₂O₃ - 3.05 Al₂O₃ - 14.41 Na₂O - 6.32 CaO - 1.89 ZrO₂ - 3.60 RE₂O₃ (with RE = La, Ce, Pr and Nd). The aim of this study was to determine the local environment of the rare earth in this glass and also to glean information about the effect of glass composition on the rare earth neighbouring (influence of Si, B, Al, Na and Ca contents). To this end, several series of glasses, prepared from the baseline glass, were studied by different characterisation methods such as EXAFS spectroscopy at the neodymium LIII-edge, optical absorption spectroscopy, Raman spectroscopy and ²⁹Si, ²⁷Al and ¹¹B MAS-NMR. By coupling all the results obtained, several hypotheses about the nature of the rare earth neighbouring in the glass were proposed. (author)