[en] New nuclear glass compositions, able to immobilize highly active liquid wastes arising from high burn-up UO₂ fuel reprocessing, are being studied. Investigations are being performed on rare earth rich glasses, known as durable matrices. After a preliminary study, a basic glass composition was selected (Glass A, wt. %): 51.0 SiO₂ - 8.5 B₂O₃ - 12.2 Na₂O - 4.3 Al₂O₃ - 4.8 CaO - 3.2 ZrO₂ - 16.0 Nd₂O₃. The aim of this study is to determine the local environment of the rare earth in this glass and its evolution according to neodymium. To achieve this objective, glasses were prepared from the baseline Glass A with variable neodymium oxide amounts (from 0 to 30 wt. % Nd₂O₃). By coupling characterization methods such as EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy at the neodymium LIII-edge, optical absorption spectroscopy, ¹¹B, ²⁷Al MAS-NMR and Raman spectroscopy, pieces of information the rare earth surroundings in the glass were obtained. (authors)